Solar wind

From Wikipedia, the free encyclopedia

Ulysses observations of solar wind speed as a function of helio latitude during solar minimum. Slow wind (~400 km/s) is confined to the equatorial regions, while fast wind (~750 km/s) is seen over the poles.^[1] Red/blue colours show inward/outward polarities of the heliospheric magnetic field.

The solar wind is a stream of charged particles released from the upper atmosphere of the Sun. This plasma consists of mostly electrons, protons and alpha particles with thermal energies between 1.5 and 10 keV. Embedded within the solar-wind plasma is the interplanetary magnetic field.^[2] The solar wind varies in density, temperature and speed over time and over solar latitude and longitude. Its particles can escape the Sun's gravity because of their high energy resulting from the high temperature of the corona, which in turn is a result of the coronal magnetic field.

At a distance of more than a few solar radii from the sun, the solar wind is supersonic and reaches speeds of 250 to 750 kilometers per second.^[3] The flow of the solar wind is no longer supersonic at the termination shock. The Voyager 2 spacecraft crossed the shock more than five times between 30 August and 10 December 2007.^[4] Voyager 2 crossed the shock about a billion kilometers closer to the Sun than the 13.5 billion kilometer distance where Voyager 1 came upon the termination shock.^[5][6] The spacecraft moved outward through the termination shock into the heliosheath and onward toward the interstellar medium. Other related phenomena include the aurora (northern and southern lights), the plasma tails of comets that always point away from the Sun, and geomagnetic storms that can change the direction of magnetic field lines.

History

The existence of particles flowing outward from the Sun to the Earth was first suggested by British astronomer Richard C. Carrington. In 1859, Carrington and Richard Hodgson independently made the first observation of what would later be called a solar flare. This is a sudden, localised increase in brightness on the solar disc, which is now known^[7] to often occur in conjunction with an episodic ejection of material and magnetic flux from the Sun's atmosphere, known as a coronal mass ejection. On the following day, a geomagnetic storm was observed, and Carrington suspected that there might be a connection, which is now attributed to the arrival of the coronal mass ejection in near-Earth space and its subsequent interaction with the Earth's magnetosphere. George FitzGerald later suggested that matter was being regularly accelerated away from the Sun and was reaching the Earth after several days.^[8]

Laboratory simulation of the magnetosphere's influence on the Solar Wind; these auroral-like Birkeland currents were created in a terrella, a magnetised anode globe in an evacuated chamber.

In 1910 British astrophysicist Arthur Eddington essentially suggested the existence of the solar wind, without naming it, in a footnote to an article on Comet Morehouse.^[9] The idea never fully caught on even though Eddington had also made a similar suggestion at a Royal Institution address the previous year. In the latter case, he postulated that the ejected material consisted of electrons while in his study of Comet Morehouse he supposed them to be ions.^[9]

The first person to suggest that the ejected material consisted of both ions and electrons was Kristian 
Birkeland. His geomagnetic surveys showed that auroral activity was nearly uninterrupted. As these displays and other geomagnetic activity were being produced by particles from the Sun, he concluded that the Earth was being continually bombarded by "rays of electric corpuscles emitted by the Sun".^[8] In 1916, Birkeland proposed that, "From a physical point of view it is most probable that solar rays are neither exclusively negative nor positive rays, but of both kinds". In other words, the solar wind consists of both negative electrons and positive ions.^[10] Three years later in 1919, Frederick Lindemann also suggested that particles of both polarities, protons as well as electrons, come from the Sun.^[11]

Around the 1930s, scientists had determined that the temperature of the solar corona must be a million degrees Celsius because of the way it stood out into space (as seen during total eclipses). Later spectroscopic work confirmed this extraordinary temperature. In the mid-1950s Sydney Chapman calculated the properties of a gas at such a temperature and determined it was such a superb conductor of heat that it must extend way out into space, beyond the orbit of Earth. Also in the 1950s, Ludwig Biermann became interested in the fact that no matter whether a comet is headed towards or away from the Sun, its tail always points away from the Sun. Biermann postulated that this happens because the Sun emits a steady stream of particles that pushes the comet's tail away.^[12] Wilfried Schröder claimed that Paul Ahnert was the first to relate solar wind to comet tail direction based on observations of the comet Whipple-Fedke (1942g).^[13]

Eugene Parker realised that the heat flowing from the Sun in Chapman's model and the comet tail blowing away from the Sun in Biermann's hypothesis had to be the result of the same phenomenon, which he termed the "solar wind".^[14][15] Parker showed in 1958 that even though the Sun's corona is strongly attracted by solar gravity, it is such a good heat conductor that it is still very hot at large distances. Since gravity weakens as distance from the Sun increases, the outer coronal atmosphere escapes supersonically into interstellar space. Furthermore, Parker was the first person to notice that the weakening effect of the gravity has the same effect on hydrodynamic flow as a de Laval nozzle: it incites a transition from subsonic to supersonic flow.^[16]

Opposition to Parker's hypothesis on the solar wind was strong. The paper he submitted to the Astrophysical Journal in 1958 was rejected by two reviewers. It was saved by the editor Subrahmanyan Chandrasekhar (who later received the 1983 Nobel Prize in physics).

In January 1959, the Soviet satellite Luna 1 first directly observed the solar wind and measured its strength.^[17][18][19] They were detected by hemispherical ion traps. The discovery, made by Konstantin Gringauz, was verified by Luna 2, Luna 3 and by the more distant measurements of Venera 1. Three years later its measurement was performed by Neugebauer and collaborators using the Mariner 2 spacecraft.^[20]

In the late 1990s the Ultraviolet Coronal Spectrometer (UVCS) instrument on board the SOHO spacecraft observed the acceleration region of the fast solar wind emanating from the poles of the Sun and found that the wind accelerates much faster than can be accounted for by thermodynamic expansion alone. Parker's model predicted that the wind should make the transition to supersonic flow at an altitude of about 4 solar radii from the photosphere (surface); but the transition (or "sonic point") now appears to be much lower, perhaps only 1 solar radius above the photosphere, suggesting that some additional mechanism accelerates the solar wind away from the Sun. The acceleration of the fast wind is still not understood and cannot be fully explained by Parker's theory. The gravitational and electromagnetic explanation for this acceleration is, however, detailed in an earlier paper by 1970 Nobel laureate for Physics, Hannes Alfvén.^[21][22]

The first numerical simulation of the solar wind in the solar corona including closed and open field lines was performed by Pneuman and Kopp in 1971. The magnetohydrodynamics equations in steady state were solved iteratively starting with an initial dipolar configuration.^[23]

In 1990, the Ulysses probe was launched to study the solar wind from high solar latitudes. All prior observations had been made at or near the Solar System's ecliptic plane.^[24]

Acceleration

While early models of the solar wind relied primarily on thermal energy to accelerate the material, by the 1960s it was clear that thermal acceleration alone cannot account for the high speed of solar wind. An additional unknown acceleration mechanism is required and likely relates to magnetic fields in the solar atmosphere.

The Sun's corona, or extended outer layer, is a region of plasma that is heated to over a million kelvin. As a result of thermal collisions, the particles within the inner corona have a range and distribution of speeds described by a Maxwellian distribution. The mean velocity of these particles is about 145 km/s, which is well below the solar escape velocity of 618 km/s. However, a few of the particles achieve energies sufficient to reach the terminal velocity of 400 km/s, which allows them to feed the solar wind. At the same temperature, electrons, due to their much smaller mass, reach escape velocity and build up an electric field that further accelerates ions away from the Sun.^[25]

The total number of particles carried away from the Sun by the solar wind is about 1.3×10³⁶ per second.^[26] Thus, the total mass loss each year is about (2–3)×10⁻¹⁴ solar masses,^[27] or about one billion kilograms per second. This is equivalent to losing a mass equal to the Earth every 150 million years.^[28] However, only about 0.01% of the Sun's total mass has been lost through the solar wind.^[29] Other stars have much stronger stellar winds that result in significantly higher mass loss rates.

Properties and structure

Fast and slow solar wind

The solar wind is observed to exist in two fundamental states, termed the slow solar wind and the fast solar wind, though their differences extend well beyond their speeds. In near-Earth space, the slow solar wind is observed to have a velocity of 300–500 km/s, a temperature of 1.4–1.6×10⁶ K and a composition that is a close match to the corona. By contrast, the fast solar wind has a typical velocity of 750 km/s, a temperature of 8×10⁵ K and it nearly matches the composition of the Sun's photosphere.^[30] The slow solar wind is twice as dense and more variable in nature than the fast solar wind.^[26][31]

The slow solar wind appears to originate from a region around the Sun's equatorial belt that is known as the "streamer belt", where coronal streamers are produced by magnetic flux open to the heliosphere draping over closed magnetic loops. The exact coronal structures involved in slow solar wind formation and the method by which the material is released is still under debate.^[32][33][34] Observations of the Sun between 1996 and 2001 showed that emission of the slow solar wind occurred at latitudes up to 30–35° during the solar minimum (the period of lowest solar activity), then expanded toward the poles as the solar cycle approached maximum. At solar maximum, the poles were also emitting a slow solar wind.^[1]

The fast solar wind originates from coronal holes,^[35] which are funnel-like regions of open field lines in the Sun's magnetic field.^[36] Such open lines are particularly prevalent around the Sun's magnetic poles. The plasma source is small magnetic fields created by convection cells in the solar atmosphere. These fields confine the plasma and transport it into the narrow necks of the coronal funnels, which are located only 20,000 kilometers above the photosphere. The plasma is released into the funnel when these magnetic field lines reconnect.^[37]

Pressure

The wind exerts a pressure at 1 AU typically in the range of 1–6 nPa (1–6×10⁻⁹ N/m²), although it can readily vary outside that range.

The dynamic pressure is a function of wind speed and density. The formula is
P = 1.6726×10⁻⁶ * n * V²
where pressure P is in nPa (nanopascals), n is the density in particles/cm³ and V is the speed in km/s of the solar wind.^[38]

Coronal mass ejection

Both the fast and slow solar wind can be interrupted by large, fast-moving bursts of plasma called interplanetary coronal mass ejections, or ICMEs. ICMEs are the interplanetary manifestation of solar coronal mass ejections, which are caused by release of magnetic energy at the Sun. CMEs are often called "solar storms" or "space storms" in the popular media. They are sometimes, but not always, associated with solar flares, which are another manifestation of magnetic energy release at the Sun. ICMEs cause shock waves in the thin plasma of the heliosphere, launching electromagnetic waves and accelerating particles (mostly protons and electrons) to form showers of ionizing radiation that precede the CME.
When a CME impacts the Earth's magnetosphere, it temporarily deforms the Earth's magnetic field, changing the direction of compass needles and inducing large electrical ground currents in Earth itself; this is called a geomagnetic storm and it is a global phenomenon. CME impacts can induce magnetic reconnection in Earth's magnetotail (the midnight side of the magnetosphere); this launches protons and electrons downward toward Earth's atmosphere, where they form the aurora.

ICMEs are not the only cause of space weather. Different patches on the Sun are known to give rise to slightly different speeds and densities of wind depending on local conditions. In isolation, each of these different wind streams would form a spiral with a slightly different angle, with fast-moving streams moving out more directly and slow-moving streams wrapping more around the Sun. Fast moving streams tend to overtake slower streams that originate westward of them on the Sun, forming turbulent co-rotating interaction regions that give rise to wave motions and accelerated particles, and that affect Earth's magnetosphere in the same way as, but more gently than, CMEs.

Solar System effects

The heliospheric current sheet results from the influence of the Sun's rotating magnetic field on the plasma in the solar wind.

Over the Sun's lifetime, the interaction of its surface layers with the escaping solar wind has significantly decreased its surface rotation rate.^[39] The wind is considered responsible for comets' tails, along with the Sun's radiation.^[40] The solar wind contributes to fluctuations in celestial radio waves observed on the Earth, through an effect called interplanetary scintillation.^[41]

Magnetospheres

Schematic of Earth's magnetosphere. The solar wind flows from left to right.

Where the solar wind intersects with a planet that has a well-developed magnetic field (such as Earth, Jupiter and Saturn), the particles are deflected by the Lorentz force. This region, known as the magnetosphere, causes the particles to travel around the planet rather than bombarding the atmosphere or surface. The magnetosphere is roughly shaped like a hemisphere on the side facing the Sun, then is drawn out in a long wake on the opposite side. The boundary of this region is called the magnetopause, and some of the particles are able to penetrate the magnetosphere through this region by partial reconnection of the magnetic field lines.^[25]

Noon meridian section of magnetosphere.

The solar wind is responsible for the overall shape of Earth's magnetosphere. Fluctuations in its speed, density, direction, and entrained magnetic field strongly affect Earth's local space environment. For example, the levels of ionizing radiation and radio interference can vary by factors of hundreds to thousands; and the shape and location of the magnetopause and bow shock wave upstream of it can change by several Earth radii, exposing geosynchronous satellites to the direct solar wind. These phenomena are collectively called space weather.

From the European Space Agency’s Cluster mission, a new study has taken place that proposes that it is easier for the solar wind to infiltrate the magnetosphere than previously believed. A group of scientists directly observed the existence of certain waves in the solar wind that were not expected. A recent study shows that these waves enable incoming charged particles of solar wind to breach the magnetopause. This suggests that the magnetic bubble forms more as a filter than a continuous barrier. This latest discovery occurred through the distinctive arrangement of the four identical Cluster spacecraft, which fly in a controlled configuration through near-Earth space. As they sweep from the magnetosphere into interplanetary space and back again, the fleet provides exceptional three-dimensional insights on the phenomena that connect the sun to Earth.

The research characterized variances in formation of the interplanetary magnetic field (IMF) largely influenced by Kelvin-Helmholtz waves (which occur at the interface of two fluids) as a result of differences in thickness and numerous other characteristics of the boundary layer. Experts believe that this was the first occasion that the appearance of Kelvin-Helmholtz waves at the magnetopause had been displayed at high latitude dawnward orientation of the IMF. These waves are being seen in unforeseen places under solar wind conditions that were formerly believed to be undesired for their generation. These discoveries show how Earth’s magnetosphere can be penetrated by solar particles under specific IMF circumstances. The findings are also relevant to studies of magnetospheric progressions around other planetary bodies. This study suggests that Kelvin-Helmholtz waves can be a somewhat common, and possibly constant, instrument for the entrance of solar wind into terrestrial magnetospheres under various IMF orientations.^[42]

Atmospheres

The solar wind affects other incoming cosmic rays interacting with planetary atmospheres. Moreover, planets with a weak or non-existent magnetosphere are subject to atmospheric stripping by the solar wind.

Venus, the nearest and most similar planet to Earth, has 100 times denser atmosphere, with little or no geo-magnetic field. Space probes discovered a comet-like tail that extends to Earth's orbit.^[43]

Earth itself is largely protected from the solar wind by its magnetic field, which deflects most of the charged particles; however some of the charged particles are trapped in the Van Allen radiation belt. A smaller number of particles from the solar wind manage to travel, as though on an electromagnetic energy transmission line, to the Earth's upper atmosphere and ionosphere in the auroral zones. The only time the solar wind is observable on the Earth is when it is strong enough to produce phenomena such as the aurora and geomagnetic storms. Bright auroras strongly heat the ionosphere, causing its plasma to expand into the magnetosphere, increasing the size of the plasma geosphere and injecting atmospheric matter into the solar wind. Geomagnetic storms result when the pressure of plasmas contained inside the magnetosphere is sufficiently large to inflate and thereby distort the geomagnetic field.

Although Mars is larger than Mercury and four times farther from the Sun, it is thought that the solar wind has stripped away up to a third of its original atmosphere, leaving a layer 1/100th as dense as the Earth's. It is believed the mechanism for this atmospheric stripping is gas caught in bubbles of magnetic field, which are ripped off by solar winds.^[44] In 2015 the NASA Mars Atmosphere and Volatile Evolution (MAVEN) mission measured the rate of atmospheric stripping caused by the magnetic field carried by the solar wind as it flows past Mars, which generates an electric field, much as a turbine on Earth can be used to generate electricity. This electric field accelerates electrically charged gas atoms, called ions, in Mars’ upper atmosphere and shoots them into space.^[45] The MAVEN mission measured the rate of atmospheric stripping at about 100 grams (~1/4 lb) per second.^[46]

Moons and planetary surfaces

Apollo's SWC experiment

Mercury, the nearest planet to the Sun, bears the full brunt of the solar wind, and since its atmosphere is vestigial and transient, its surface is bathed in radiation.

Mercury has an intrinsic magnetic field, so under normal solar wind conditions, the solar wind cannot penetrate its magnetosphere and particles only reach the surface in the cusp regions. During coronal mass ejections, however, the magnetopause may get pressed into the surface of the planet, and under these conditions, the solar wind may interact freely with the planetary surface.

The Earth's Moon has no atmosphere or intrinsic magnetic field, and consequently its surface is bombarded with the full solar wind. The Project Apollo missions deployed passive aluminum collectors in an attempt to sample the solar wind, and lunar soil returned for study confirmed that the lunar regolith is enriched in atomic nuclei deposited from the solar wind. These elements may prove useful resources for lunar colonies.^[47]

Outer limits

The solar wind "blows a bubble" in the interstellar medium (the rarefied hydrogen and helium gas that permeates the galaxy). The point where the solar wind's strength is no longer great enough to push back the interstellar medium is known as the heliopause and is often considered to be the outer border of the Solar System. The distance to the heliopause is not precisely known and probably depends on the current velocity of the solar wind and the local density of the interstellar medium, but it is far outside Pluto's orbit. Scientists hope to gain perspective on the heliopause from data acquired through the Interstellar Boundary Explorer (IBEX) mission, launched in October 2008.

Notable events

• From May 10 to May 12, 1999, NASA's Advanced Composition Explorer (ACE) and WIND spacecraft observed a 98% decrease of solar wind density. This allowed energetic electrons from the Sun to flow to Earth in narrow beams known as "strahl", which caused a highly unusual "polar rain" event, in which a visible aurora appeared over the North Pole. In addition, Earth's magnetosphere increased to between 5 and 6 times its normal size.^[48]
• On 13 December 2010, Voyager 1 determined that the velocity of the solar wind, at its location 10.8 billion miles from Earth had slowed to zero. "We have gotten to the point where the wind from the Sun, which until now has always had an outward motion, is no longer moving outward; it is only moving sideways so that it can end up going down the tail of the heliosphere, which is a comet-shaped-like object," said Voyager project scientist Edward Stone.^[49][50]

Mars Direct

From Wikipedia, the free encyclopedia

Mars Direct is a proposal for a human mission to Mars which purports to be both cost-effective and possible with current technology. It was originally detailed in a research paper by Martin Marietta engineers Robert Zubrin and David Baker in 1990, and later expanded upon in Zubrin's 1996 book The Case for Mars. It now serves as a staple of Zubrin's speaking engagements and general advocacy as head of the Mars Society, an organization devoted to the colonization of Mars.^[1]

The Habitat Unit and the Earth Return Vehicle on Mars.

History

Space Exploration Initiative

On July 20, 1989, George H. W. Bush – then President of the United States – announced plans for what came to be known as the Space Exploration Initiative (SEI). In a speech on the steps of the National Air and Space Museum he described long-term plans which would culminate in a manned mission to the surface of Mars.^[2]

By December 1990, a study to estimate the project's cost determined that long-term expenditure would total approximately 450 billion dollars spread over 20 to 30 years.^[3] The "90 Day Study" as it came to be known, evoked a hostile Congressional reaction towards SEI given that it would have required the largest single government expenditure since World War II.^[4] Within a year, all funding requests for SEI had been denied.

Dan Goldin became NASA Administrator on April 1, 1992, officially abandoning plans for near-term human exploration beyond Earth orbit with the shift towards a "faster, better, cheaper" strategy for robotic exploration.^[5]

Development

While working at Martin Marietta designing interplanetary mission architectures, Robert Zubrin perceived a fundamental flaw in the SEI program. Zubrin came to understand that if NASA's plan was to fully utilize as many technologies as possible in support of sending the mission to Mars, it would become politically untenable. In his own words:

The exact opposite of the correct way to do engineering.^[4]

Zubrin's alternative to this "Battlestar Galactica" mission strategy (dubbed so by its detractors for the large, nuclear powered spaceships that supposedly resembled the science-fiction spaceship of the same name) involved a longer surface stay, a faster flight-path in the form of a conjunction class mission, in-situ resource utilization and craft launched directly from the surface of Earth to Mars as opposed to be being assembled in orbit or by a space-based drydock.^[6] After receiving approval from management at Marietta, a 12-man team within the company began to work out the details of the mission. While they focused primarily on more traditional mission architectures, Zubrin began to collaborate with colleague David Baker's^[7] extremely simple, stripped-down and robust strategy. Their goal to "use local resources, travel light, and live off the land" became the hallmark of Mars Direct.^[4]

Mission scenario

First launch

The first flight of the Ares rocket (not to be confused with the similarly named rocket of the now defunct Constellation program) would take an unmanned Earth Return Vehicle to Mars after a 6-month cruise phase, with a supply of hydrogen, a chemical plant and a small nuclear reactor. Once there, a series of chemical reactions (the Sabatier reaction coupled with electrolysis) would be used to combine a small amount of hydrogen (8 tons) carried by the Earth Return Vehicle with the carbon dioxide of the Martian atmosphere to create up to 112 tonnes of methane and oxygen. This relatively simple chemical-engineering procedure was used regularly in the 19th and 20th centuries,^[8] and would ensure that only 7% of the return propellant would need to be carried to the surface of Mars.
96 tonnes of methane and oxygen would be needed to send the Earth Return Vehicle on a trajectory back home at the conclusion of the surface stay; the rest would be available for Mars rovers. The process of generating fuel is expected to require approximately ten months to complete.

Second launch

Some 26 months after the Earth Return Vehicle is originally launched from Earth, a second vehicle, the Mars Habitat Unit, would be launched on a 6-month long low-energy transfer trajectory to Mars, and would carry a crew of four astronauts (the minimum number required so that the team can be split in two without leaving anyone alone). The Habitat Unit would not be launched until the automated factory aboard the ERV had signaled the successful production of chemicals required for operation on the planet and the return trip to Earth. During the trip, artificial gravity would be generated by tethering the Habitat Unit to the spent upper stage of the booster, and setting them rotating about a common axis. This rotation would produce a comfortable 1 g working environment for the astronauts, freeing them of the debilitating effects of long-term exposure to weightlessness.^[4]

Landing and surface operations

Upon reaching Mars, the upper stage would be jettisoned, with the Habitat Unit aerobraking into Mars orbit before soft-landing in proximity to the Earth Return Vehicle. Precise landing would be supported by a radar beacon started by the first lander. Once on Mars, the crew would spend 18 months on the surface, carrying out a range of scientific research, aided by a small rover vehicle carried aboard their Mars Habitat Unit, and powered by the methane produced by the Earth Return Vehicle.

Return and follow-up missions

To return, the crew would use the Earth Return Vehicle, leaving the Mars Habitat Unit for the possible use of subsequent explorers. On the return trip to Earth, the propulsion stage of the Earth Return Vehicle would be used as a counterweight to generate artificial gravity for the trip back.
Follow-up missions would be dispatched at 2 year intervals to Mars to ensure that a redundant ERV would be on the surface at all times, waiting to be used by the next crewed mission or the current crew in an emergency. In such an emergency scenario, the crew would trek hundreds of kilometers to the other ERV in their long-range vehicle.

Components

The Mars Direct proposal includes a component for a Launch Vehicle "Ares", an Earth Return Vehicle (ERV) and a Mars Habitat Unit (MHU).

Launch Vehicle

The plan involves several launches making use of heavy-lift boosters of similar size to the Saturn V used for the Apollo missions, which would potentially be derived from Space Shuttle components. This proposed rocket is dubbed "Ares", which would use space shuttle Advanced Solid Rocket Boosters, a modified shuttle external tank, and a new Lox/LH2 third stage for the trans-Mars injection of the payload. Ares would put 121 tonnes into a 300 km circular orbit, and boost 47 tonnes toward Mars.^[9]

Earth Return Vehicle

The Earth Return Vehicle is a two-stage vehicle. The upper stage comprises the living accommodation for the crew during their six-month return trip to Earth from Mars. The lower stage contains the vehicle's rocket engines and a small chemical production plant.

Mars Habitat Unit

The Mars Habitat Unit is a 2- or 3-deck vehicle providing a comprehensive living and working environment for a Mars crew. In addition to individual sleeping quarters which provide a degree of privacy for each of the crew and a place for personal effects, the Mars Habitat Unit includes a communal living area, a small galley, exercise area, and hygiene facilities with closed-cycle water purification. The lower deck of the Mars Habitat Unit provides the primary working space for the crew: small laboratory areas for carrying out geology and life science research; storage space for samples, airlocks for reaching the surface of Mars, and a suiting-up area where crew members prepare for surface operations. Protection from harmful radiation while in space and on the surface of Mars (e.g. from solar flares) would be provided by a dedicated "storm shelter" in the core of the vehicle.

The Mars Habitat Unit would also include a small pressurized rover that is stored in the lower deck area and assembled on the surface of Mars. Powered by a methane engine, it is designed to extend the range over which astronauts can explore the surface of Mars out to 320 km.

Since it was first proposed as a part of Mars Direct, the Mars Habitat Unit has been adopted by NASA as a part of their Mars Design Reference Mission, which uses two Mars Habitat Units – one of which flies to Mars unmanned, providing a dedicated laboratory facility on Mars, together with the capacity to carry a larger rover vehicle. The second Mars Habitat Unit flies to Mars with the crew, its interior given over completely to living and storage space.

To prove the viability of the Mars Habitat Unit, the Mars Society has implemented the Mars Analogue Research Station Program (MARS), which has established a number of prototype Mars Habitat Units around the world.

Reception

Baker pitched Mars Direct at the Marshall Spaceflight Center in April 1990,^[10] where reception was very positive. The engineers flew around the country to present their plan, which generated significant interest. When their tour culminated in a demonstration at the National Space Society they received a standing ovation.^[4] The plan gained rapid media attention shortly afterwards.

Resistance to the plan came from teams within NASA working on the Space Station and advanced propulsion concepts^{[citation needed]}. The NASA administration rejected Mars Direct. Zubrin remained committed to the strategy, and after parting with David Baker attempted to convince the new NASA administration of Mars Direct's merits in 1992.^[4]

After being granted a small research fund at Martin Marietta, Zubrin and his colleagues successfully demonstrated an in-situ propellant generator which achieved an efficiency of 94%.^[4] No chemical engineers partook in the development of the demonstration hardware.^[4] After showing the positive results to the Johnson Space Center, the NASA administration still held several reservations about the plan.^[4]

In November 2003, Zubrin was invited to speak to the U.S. Senate committee on the future of space exploration.^[4] Two months later the Bush administration announced the creation of the Constellation program, a manned spaceflight initiative with the goal of sending humans to the Moon by 2020. While a Mars mission was not specifically detailed, a plan to reach Mars based on utilizing the Orion spacecraft was tentatively developed for implementation in the 2030s. The program's funding was denied in 2011 by the Obama administration^{[citation needed]} and the Constellation program ended.

There are a variety of psychological and sociological issues affecting long-duration expeditionary space missions. Early human spaceflight missions to Mars are expected to have significant psycho-social problems to overcome, as well as provide considerable data for refining mission design, mission planning, and crew selection for future missions.^[11]

Revisions

Since Mars Direct was initially conceived, it has undergone regular review and development by Zubrin himself, the Mars Society, NASA, Stanford University and others.

Mars Semi-Direct

Artist's rendering of Mars Semi-Direct/DRA 1.0: The Manned Habitat Unit is "docked" alongside a pre placed habitat that was sent ahead of the Earth Return Vehicle.

Zubrin and Weaver developed a modified version of Mars Direct, called Mars Semi-Direct, in response to some specific criticisms.^[12] This mission consists of three spacecraft and includes a "Mars Ascent Vehicle" (MAV). The ERV remains in Mars orbit for the return journey, while the unmanned MAV lands and manufactures propellants for the ascent back up to Mars orbit. The Mars Semi-Direct architecture has been used as the basis of a number of studies, including the NASA Design Reference Missions.

When subjected to the same cost-analysis as the 90-day report, Mars Semi-Direct was predicted to cost 55 billion dollars over 10 years, capable of fitting into the existing NASA budget.

Mars Semi-Direct became the basis of the Design Reference Mission 1.0 of NASA, replacing the 90-day report.

Design Reference Mission

The NASA model, referred to as the Design Reference Mission, on version 5.0 as of September 1, 2012, calls for a significant upgrade in hardware (at least three launches per mission, rather than two), and sends the ERV to Mars fully fueled, parking it in orbit above the planet for subsequent rendezvous with the MAV.

Mars Direct and SpaceX

With the potentially imminent advent of low-cost heavy lift capability, Zubrin has posited a dramatically lower cost manned Mars mission using hardware developed by space transport company SpaceX. In this simpler plan, a crew of two would be sent to Mars by a single Falcon Heavy launch, the Dragon spacecraft acting as their interplanetary cruise habitat. Additional living space for the journey would be enabled through the use of inflatable add-on modules if required. The problems associated with long-term weightlessness would be addressed in the same manner as the baseline Mars Direct plan, a tether between the Dragon habitat and the TMI (Trans-Mars Injection) stage acting to allow rotation of the craft.

The Dragon's heatshield characteristics could allow for a safe descent if landing rockets of sufficient power were made available. Research at NASA's Ames Research Center has demonstrated that a robotic Dragon would be capable of a fully propulsive landing on the Martian surface.^{[citation needed]} On the surface, the crew would have at their disposal two Dragon spacecraft with inflatable modules as habitats, two ERVs, two Mars ascent vehicles and 8 tonnes of cargo.

Other Studies

The Mars Society and Stanford studies retain the original two-vehicle mission profile of Mars Direct, but increase the crew size to six.

Mars Society Australia developed their own four-person Mars Oz reference mission, based on Mars Semi-Direct. This study uses horizontally landing, bent biconic shaped modules, and relies on solar power and chemical propulsion throughout,^[13] where Mars Direct and the DRMs used nuclear reactors for surface power and, in the case of the DRMs for propulsion as well. The Mars Oz reference mission also differs in assuming, based on space station experience, that spin gravity will not be required.

Mars Analogue Research Stations

The Mars Society has argued the viability of the Mars Habitat Unit concept through their Mars Analogue Research Station program. These are two or three decked vertical cylinders ~8 m in diameter and 8 m high. Mars Society Australia plans to build its own station based on the Mars Oz design.^[14] The Mars Oz design features a horizontal cylinder 4.7 m in diameter and 18 m long, with a tapered nose. A second similar module will function as a garage and power and logistics module.
Mars Direct was featured on a Discovery Channel programs Mars: The Next Frontier in which issues were discussed surrounding NASA funding of the project, and on Mars Underground, where the plan is discussed more in-depth.

Alternatives

"Mars to Stay" proposals involve not returning the first immigrant/explorers immediately, or ever. It has been suggested the cost of sending a four or six person team could be one fifth to one tenth the cost of returning that same four or six person team. Depending on the precise approach taken, a quite complete lab could be sent and landed for less than the cost of sending back even 50 kilos of Martian rocks. Twenty or more persons could be sent for the cost of returning four.^[15]

In fiction

• Mars Direct is the mission mode used in Gregory Benford's novel The Martian Race, Geoffrey A. Landis's novel Mars Crossing, Larry Niven's novel Rainbow Mars, Robert M. Blevins' novel The 13th Day of Christmas, as well as Zubrin's own novel, First Landing.
• Mars Direct forms the basis for the 2000 film Mission to Mars.
• In the Futurama episode "The Luck of the Fryrish", a short clip shows the first man on Mars with a spacecraft that resembles the Mars Habitat Unit.
• In the West Wing episode "The Warfare of Genghis Khan", a NASA staffer describes Mars Direct to the skeptical White House Deputy Chief of Staff Josh Lyman and is able to convince him of its merit.
• Both Mars Direct and Mars for Less concepts figure prominently in Brian Enke's 2004 novel, Shadows of Medusa.
• The Martian, a novel by Andy Weir, describes the Ares missions, a series of manned missions to Mars, using Mars Semi-Direct.

SpaceX

From Wikipedia, the free encyclopedia

SpaceX

SpaceX hangar at Kennedy Space Center Launch Complex 39 next to Launch Pad 39A, June 2015
Type	Private
Industry	Aerospace
Founded	May 6, 2002; 14 years ago[1]
Founder	Elon Musk
Headquarters	Hawthorne, California, U.S. 33.9207°N 118.3278°WCoordinates: 33.9207°N 118.3278°W
Key people	Elon Musk (CEO and CTO) Gwynne Shotwell (President and COO) Tom Mueller (CTO of Propulsion)
Products	Falcon launch vehicles Dragon capsules
Services	Orbital rocket launch
Owner	Elon Musk Trust (54% equity; 78% voting control)[2]
Number of employees	Nearly 5,000[3][4] (February 2016)
Website	www.spacex.com
Footnotes / references [5][6][7][8]

Space Exploration Technologies Corporation, better known as SpaceX, is an American aerospace manufacturer and space transport services company headquartered in Hawthorne, California. It was founded in 2002 by entrepreneur Elon Musk, with the goal of reducing space transportation costs and enabling the colonization of Mars.^[9] SpaceX has developed the Falcon launch vehicle family and the Dragon spacecraft family, which deliver payloads into Earth orbit.

SpaceX's achievements include the first privately-funded, liquid-propellant rocket to reach orbit (Falcon 1 in 2008);^[10] the first privately-funded company to successfully launch, orbit, and recover a spacecraft (Dragon in 2010); and the first private company to send a spacecraft to the International Space Station (Dragon in 2012).^[11] As of March 2017, SpaceX has since flown ten missions to the International Space Station (ISS) under a cargo resupply contract.^[12] NASA also awarded SpaceX a further development contract in 2011 to develop and demonstrate a human-rated Dragon, which would be used to transport astronauts to the ISS and return them safely to Earth.^[13]

SpaceX announced in 2011 they were beginning a privately-funded reusable launch system technology development program. In December 2015, a first stage was flown back to a landing pad near the launch site, where it successfully accomplished a propulsive vertical landing. This was the first such achievement by a rocket for orbital spaceflight.^[14] In April 2016, with the launch of CRS-8, SpaceX successfully vertically landed a first stage on an ocean drone-ship landing platform.^[15] In May 2016, in another first, SpaceX again landed a first stage, but during a significantly more energetic geostationary transfer orbit mission.^[16] In March 2017, SpaceX became the first to successfully re-launch and land the first stage of an orbital rocket. ^[17]

In September 2016, CEO Elon Musk unveiled the mission architecture of the Interplanetary Transport System program, an ambitious privately-funded initiative to develop spaceflight technology for use in manned interplanetary spaceflight, and which, if demand emerges, could lead to sustainable human settlements on Mars over the long term.^[18][19] In February 2017, Elon Musk announced that the company had been contracted by two private individuals to send them in a Dragon spacecraft on a free return trajectory around the Moon.^[20][21][22] Provisionally launching in 2018, this may well become the first instance of lunar tourism.

History

SpaceX employees with the Dragon capsule at SpaceX HQ in Hawthorne, California, February 2015.

In 2001, Elon Musk conceptualized Mars Oasis, a project to land a miniature experimental greenhouse and grow plants on Mars, "so this would be the furthest that life’s ever traveled"^[23] in an attempt to regain public interest in space exploration and increase the budget of NASA.^[24][25][26] Musk tried to buy cheap rockets from Russia, but returned empty-handed after failing to find rockets for an affordable price.^[27][28]

Falcon 9 carrying CRS-7 Dragon on SLC-40 pad.

On the flight home, Musk realized that he could start a company that could build the affordable rockets he needed.^[28] According to early Tesla and SpaceX investor Steve Jurvetson,^[29] Musk calculated that the raw materials for building a rocket actually were only 3 percent of the sales price of a rocket at the time. By applying vertical integration,^[27] producing around 85% of launch hardware in-house,^[30][31] and the modular approach from software engineering, SpaceX could cut launch price by a factor of ten and still enjoy a 70 percent gross margin.^[32] SpaceX started with the smallest useful orbital rocket, instead of building a more complex and riskier launch vehicle, which could have failed and bankrupted the company.^[33]

Launch of Falcon 9 carrying ORBCOMM OG2-M1.

In early 2002, Musk was seeking staff for his new space company, soon to be named SpaceX. Musk approached renowned rocket engineer Tom Mueller (now SpaceX's CTO of Propulsion) and Mueller agreed to work for Musk, and thus SpaceX was born.^[34] SpaceX was first headquartered in a warehouse in El Segundo, California. The company has grown rapidly since it was founded in 2002, growing from 160 employees in 2005 to "nearly 5,000" in late 2015^[3] and February 2016.^[4]

Falcon 9 rocket's first stage on the landing pad after the first successful vertical landing of an orbital rocket stage, OG2 Mission.

At year-end 2012, SpaceX had over 40 launches on its manifest representing about $4 billion in contract revenue, with many of those contracts already making progress payments to SpaceX. The contracts included both commercial and government (NASA/DOD) customers.^[35] As of December 2013, SpaceX had a total of 50 future launches under contract, two-thirds of them were for commercial customers.^[36][37] In late 2013, space industry media began to comment on the phenomenon that SpaceX prices are undercutting the major competitors in the commercial comsat launch market—the Ariane 5 and Proton-M^[38]—at which time SpaceX had at least 10 further geostationary orbit flights on its books.^[37]

Falcon 9 first stage on an ASDS barge after the first successful landing at sea, CRS-8 Mission.

Goals

Musk has stated that one of his goals is to improve the cost and reliability of access to space, ultimately by a factor of ten.^[39] The company plans in 2004 called for "development of a heavy lift product and even a super-heavy, if there is customer demand" with each size increase resulting in a significant decrease in cost per pound to orbit. CEO Elon Musk said: "I believe $500 per pound ($1,100/kg) or less is very achievable."^[40]

Conceptual rendering of Falcon Heavy at Pad 39A, Cape Canaveral.

A major goal of SpaceX has been to develop a rapidly reusable launch system. As of March 2013, the publicly announced aspects of this technology development effort include an active test campaign of the low-altitude, low-speed Grasshopper vertical takeoff, vertical landing (VTVL) technology demonstrator rocket,^[41][42][43] and a high-altitude, high-speed Falcon 9 post-mission booster return test campaign where—beginning in mid-2013, with the sixth overall flight of Falcon 9—every first stage will be instrumented and equipped as a controlled descent test vehicle to accomplish propulsive-return over-water tests.^[44] SpaceX COO Gwynne Shotwell said at the Singapore Satellite Industry Forum in summer 2013 "If we get this [reusable technology] right, and we’re trying very hard to get this right, we’re looking at launches to be in the US$5 to 7 million range, which would really change things dramatically."^[45]

Musk stated in a 2011 interview that he hopes to send humans to Mars' surface within 10–20 years.^[46] In 2010, Musk's calculations convinced him that the colonization of Mars was possible.^[47] In June 2013, Musk used the descriptor "Mars Colonial Transporter" (only later changed to "Interplanetary Transport System"; see below) to refer to the privately funded development project to design and build a spaceflight system of rocket engines, launch vehicles and space capsules to transport humans to Mars and return to Earth.^[48] In March 2014, COO Gwynne Shotwell said that once the Falcon Heavy and Dragon 2 crew version are flying, the focus for the company engineering team will be on developing the technology to support the transport infrastructure necessary for Mars missions.^[49]

Achievements

Landmark achievements of SpaceX include:^[50]

• The first privately funded liquid-fueled rocket to reach orbit (Falcon 1 Flight 4 — September 28, 2008)
• The first privately funded company to successfully launch, orbit, and recover a spacecraft (Falcon 9 Flight 2 — December 9, 2010)
• The first private company to send a spacecraft to the International Space Station (Falcon 9 Flight 3 — May 25, 2012)
• The first private company to send a satellite into geosynchronous orbit (Falcon 9 Flight 7 — December 3, 2013)
• The first landing of an orbital rocket's first stage on land (Falcon 9 Flight 20 — December 22, 2015)
• The first landing of an orbital rocket's first stage on an ocean platform (Falcon 9 Flight 23 — April 8, 2016)
• The first relaunch and landing of a used orbital rocket (Falcon 9 Flight 32 — March 30, 2017)^[51]

In December 2015, SpaceX launched an upgraded Falcon 9 rocket from Cape Canaveral Air Force Station into Low Earth orbit, on a mission designated Flight 20. After completing its primary burn, the first stage of the multistage rocket detached from the second stage as usual. The first stage then fired three of its engines to send it back to Cape Canaveral, where it achieved the world's first successful landing of a rocket that was used for an orbital launch.^[52]

Setbacks

In March 2013, a Dragon spacecraft in orbit developed issues with its thrusters. Due to blocked fuel valves, the craft was unable to properly control itself. SpaceX engineers were able to remotely clear the blockages. Because of this issue, the craft arrived at and docked with the International Space Station one day later than expected.

In June 2015, CRS-7 launched a Dragon capsule atop a Falcon 9 to resupply the International Space Station. All telemetry readings were nominal until 2 minutes and 19 seconds into the flight, when a loss of helium pressure was detected and a cloud of vapor appeared outside the second stage. A few seconds after this, the second stage exploded. The first stage continued to fly for a few seconds before disintegrating due to aerodynamic forces. The capsule was thrown off and survived the explosion, transmitting data until it was destroyed on impact.^[53] Later it was revealed that the capsule could have landed intact if it had software to deploy its parachutes in case of a launch mishap.^[54] The problem was discovered to be a failed 2-foot-long steel strut purchased from a supplier to hold a helium pressure vessel that broke free due to the force of acceleration.^[55] This caused a breach and allowed high-pressure helium to escape into the low-pressure propellant tank, causing the failure.The Dragon software issue was also fixed in addition to an analysis of the entire program in order to ensure proper abort mechanisms are in place for future rockets and their payload.^[56]

In September 2016, a Falcon 9 exploded during a propellant fill operation for a standard pre-launch static fire test.^[57][58] The payload, the Spacecom Amos-6 communications satellite valued at $200 million, was destroyed.^[59] Musk described the event as the "most difficult and complex failure" ever in SpaceX's history; SpaceX reviewed nearly 3,000 channels of telemetry and video data covering a period of 35–55 milliseconds for the postmortem.^[60] Musk reported the explosion was caused by the liquid oxygen that is used as propellant turning so cold that it solidified and it ignited with carbon composite helium vessels.^[61] The rocket explosion sent the company into a four-month launch hiatus while it worked out what went wrong, and SpaceX finally returned to flight in January 2017.^[62]

Ownership and valuation

SpaceX launches by year.

In August 2008, SpaceX accepted a $20 million investment from Founders Fund.^[63] In early 2012, approximately two-thirds of the company were owned by its founder^[64] and his 70 million shares were then estimated to be worth $875 million on private markets,^[65] which roughly valued SpaceX at $1.3 billion as of February 2012.^[66] After the COTS 2+ flight in May 2012, the company private equity valuation nearly doubled to $2.4 billion.^[67][68] In January 2015, SpaceX raised $1 billion in funding from Google and Fidelity, in exchange for 8.333% of the company, establishing the company valuation at approximately $12 billion. Google and Fidelity joined the then current investorship group of Draper Fisher Jurvetson, Founders Fund, Valor Equity Partners and Capricorn.^[69][70]

As of May 2012, SpaceX had operated on total funding of approximately $1 billion in its first ten years of operation. Of this, private equity provided about $200M, with Musk investing approximately $100M and other investors having put in about $100M (Founders Fund, Draper Fisher Jurvetson, …).^{[71][dead link]} The remainder has come from progress payments on long-term launch contracts and development contracts. As of April 2012, NASA had put in about $400–500M of this amount, with most of that as progress payments on launch contracts.^[66] By May 2012, SpaceX had contracts for 40 launch missions, and each of those contracts provide down payments at contract signing, plus many are paying progress payments as launch vehicle components are built in advance of mission launch, driven in part by US accounting rules for recognizing long-term revenue.^[66]

In 2012, an initial public offering (IPO) was perceived as possible by the end of 2013,^[65] but then Musk stated in June 2013 that he planned to hold off any potential IPO until after the "Mars Colonial Transporter is flying regularly,"^[48] and this was reiterated in 2015 indicating that it would be many years before SpaceX would become a publicly traded company,^[72][73] where Musk stated that "I just don’t want [SpaceX] to be controlled by some private equity firm that would milk it for near-term revenue"^[74]

Spacecraft and flight hardware

SpaceX's Falcon 9 rocket carrying the Dragon spacecraft, lifts off during the COTS Demo Flight 1 in December 2010.

SpaceX currently manufactures two broad classes of rocket engine in-house: the kerosene fueled Merlin engine and the hypergolic fueled Draco/SuperDraco vernier thrusters. The Merlin powers their two main space launch vehicles: the large Falcon 9,^[75] which flew successfully into orbit on its maiden launch in June 2010^[76] and the super-heavy class Falcon Heavy, which is scheduled to make its first flight in 2017. SpaceX also manufactures the Dragon, a pressurized orbital spacecraft that is launched on top of a Falcon 9 booster to carry cargo to low-Earth orbit, and the follow-on Dragon 2 spacecraft, currently in the process of being human-rated through a variety of design reviews and flight tests that began in 2014.^[77][78]

Rocket engines

Since the founding of SpaceX in 2002, the company has developed three families of rocket engines — Merlin and Kestrel for launch vehicle propulsion, and the Draco control thrusters. SpaceX is currently developing two further rocket engines: SuperDraco and Raptor.
Merlin is a family of rocket engines developed by SpaceX for use on its Falcon rocket family of launch vehicles. Merlin engines use LOX and RP-1 as propellants in a gas-generator power cycle. The Merlin engine was originally designed for sea recovery and reuse. The injector at the heart of Merlin is of the pintle type that was first used in the Apollo Program for the lunar module landing engine. Propellants are fed via a single shaft, dual impeller turbo-pump.

Kestrel is a LOX/RP-1 pressure-fed rocket engine, and was used as the Falcon 1 rocket's second stage main engine. It is built around the same pintle architecture as SpaceX's Merlin engine but does not have a turbo-pump, and is fed only by tank pressure. Its nozzle is ablatively cooled in the chamber and throat, is also radiatively cooled, and is fabricated from a high strength niobium alloy.

Draco are hypergolic liquid-propellant rocket engines that utilize a mixture of monomethyl hydrazine fuel and nitrogen tetroxide oxidizer. Each Draco thruster generates 400 newtons (90 lbf) of thrust.^[79] They are used as reaction control system (RCS) thrusters on the Dragon spacecraft.^[80] SuperDraco are a much more powerful version of the Draco thrusters, which will be initially used as landing and launch escape system engines on the version 2 Dragon spacecraft, Dragon 2.

Raptor is a new family of methane-fueled full flow staged combustion cycle engines to be used in its future Interplanetary Transport System. Development versions have been test fired.

Falcon launch vehicles

The Falcon 1 prototype at SpaceX's assembly facilities.

Since 2010, SpaceX has flown all its missions on the Falcon 9. They are also actively developing the Falcon Heavy, and previously developed and flew the Falcon 1 pathfinder vehicle.

From left to right, Falcon 1, Falcon 9 v1.0, three versions of Falcon 9 v1.1, three versions of Falcon 9 v1.2 (Full Thrust), and Falcon Heavy.

Falcon 1 was a small rocket capable of placing several hundred kilograms into low earth orbit.^[76] It functioned as an early test-bed for developing concepts and components for the larger Falcon 9.^[76] Falcon 1 attempted five flights between 2006 and 2009. On September 28, 2008, on its fourth attempt, the Falcon 1 successfully reached orbit, becoming the first privately funded, liquid-fueled rocket to do so.^[81]

Falcon 9 is an EELV-class medium-lift vehicle capable of delivering up to 22,800 kilograms (50,265lb) to orbit, and is intended to compete with the Delta IV and the Atlas V rockets, as well as other launch providers around the world. It has nine Merlin engines in its first stage.^[82] The Falcon 9 v1.0 rocket successfully reached orbit on its first attempt on June 4, 2010. Its third flight, COTS Demo Flight 2, launched on May 22, 2012, and was the first commercial spacecraft to reach and dock with the International Space Station.^[83] The vehicle was upgraded to Falcon 9 v1.1 in 2013 and again in 2015 to the current Falcon 9 Full Thrust version. As of February 2017, Falcon 9 vehicles have flown 28 successful missions with two failures.

Falcon Heavy began development as a heavy-lift configuration using a cluster of three Falcon 9 first stage cores with a total 27 Merlin 1D engines and propellant crossfeed in 2011.^[84][85][86] SpaceX is aiming for the first demonstration flight of the Falcon Heavy in the summer of 2017.^[87]

Dragon capsules

The Dragon spacecraft approaching the ISS.

In 2005, SpaceX announced plans to pursue a human-rated commercial space program through the end of the decade.^[88] The Dragon is a conventional blunt-cone ballistic capsule which is capable of carrying cargo or up to seven astronauts into orbit and beyond.^{[89] [89]}

In 2006, NASA announced that the company was one of two selected to provide crew and cargo resupply demonstration contracts to the ISS under the COTS program.^[90] SpaceX demonstrated cargo resupply and eventually crew transportation services using the Dragon.^[83] The first flight of a Dragon structural test article took place in June 2010, from Launch Complex 40 at Cape Canaveral Air Force Station during the maiden flight of the Falcon 9 launch vehicle; the mock-up Dragon lacked avionics, heat shield, and other key elements normally required of a fully operational spacecraft but contained all the necessary characteristics to validate the flight performance of the launch vehicle.^[91] An operational Dragon spacecraft was launched in December 2010 aboard COTS Demo Flight 1, the Falcon 9's second flight, and safely returned to Earth after two orbits, completing all its mission objectives.^[77] In 2012, Dragon became the first commercial spacecraft to deliver cargo to the International Space Station,^[83] and has since been conducting regular resupply services to the ISS.^[92]

The interior of the COTS 2 Dragon.

In 2009 and 2010, Musk suggested on several occasions that plans for a human-rated variant of Dragon were proceeding and had a 2- to 3-year time line to completion.^[93][94] In April 2011, NASA issued a $75 million contract, as part of its second-round commercial crew development (CCDev) program, for SpaceX to develop an integrated launch escape system for Dragon in preparation for human-rating it as a crew transport vehicle to the ISS.^[95] This Space Act Agreement runs from April 2011 until May 2012, when the next round of contracts are to be awarded.^[95] NASA approved the technical plans for the system in October 2011, and SpaceX began building prototype hardware.^[96]

SpaceX plans to launch its Dragon 2 spacecraft on an unmanned test flight to the ISS in November 2017, and later in 2018, a crewed Dragon will send US astronauts to the ISS for the first time since the retirement of the Space Shuttle. In February 2017 SpaceX announced that two would-be space tourists had put down "significant deposits" for a mission which would see the two private astronauts fly on board a Dragon capsule to the moon and back again. At the press conference announcing the mission Elon Musk said that the cost of the mission would be "comparable" to that of sending an astronaut to the International Space Station; about $70 million US dollars per astronaut in 2017.^[20] The mission is slated for late 2018.^[97]

Research and development

First test firing of a scale Raptor development engine in September 2016 in McGregor, Texas.

SpaceX are actively pursuing several different research and development programs. Most notable are the programs intended to develop reusable launch vehicles, an interplanetary transport system, and a global telecommunications network.

SpaceX has on occasion developed new engineering development technologies to enable it to pursue its various goals. For example, at the 2015 GPU Technology Conference, SpaceX revealed their own computational fluid dynamics (CFD) software to improve the simulation capability of evaluating rocket engine combustion design.^[98][99]

Reusable launch system

Just Read the Instructions in position prior to Falcon 9 Flight 17 carrying CRS-6.

SpaceX's reusable launcher program was publicly announced in 2011 and the design phase was completed in February 2012. The system returns the first stage of a Falcon 9 rocket to its launchpad using only its own propulsion systems.^[100]

SpaceX's active test program began in late 2012 with testing low-altitude, low-speed aspects of the landing technology. Grasshopper and the Falcon 9 Reusable Development Vehicles (F9R Dev) were experimental technology-demonstrator reusable rockets that performed vertical takeoffs and landings. DragonFly is a test vehicle to develop propulsive and propulsive-assist landing technologies in a series of low-altitude flight tests planned to be conducted in 2015–2016.^[101]

High-velocity, high-altitude aspects of the booster atmospheric return technology began testing in late 2013 and have continued through 2016. SpaceX has been improving the autonomous landing and recovery of the first stage of the Falcon 9 launch vehicle, with steadily increasing success. As a result of Elon Musk's goal of crafting more cost-effective launch vehicles, SpaceX conceived a method to reuse the first stage of their primary rocket, the Falcon 9,^[102] by attempting propulsive vertical landings on solid surfaces. Once the company determined that soft landings were feasible by touching down over the Atlantic and Pacific Ocean, they began landing attempts on a solid platform. SpaceX leased and modified several barges to sit out at sea as a target for the returning first stage, converting them to autonomous spaceport drone ships (ASDS). SpaceX first achieved a successful landing and recovery of a first stage in December 2015,^[103] and in April 2016, the first stage booster first successfully landed on the ASDS Of Course I Still Love You.^[104][105]

SpaceX continues to carry out first stage landings on every orbital launch that fuel margins allow. By October 2016, following the successful landings, SpaceX indicated they were offering their customers a ten percent price discount if they choose to fly their payload on a reused Falcon 9 first stage.^[106] On March 30, 2017, SpaceX launched a "flight-proven" Falcon 9 for the SES-10 mission. This was the first time a re-launch of a payload-carrying orbital rocket went back to space.^[107][51] The first stage was recovered and landed on the ASDS Of Course I Still Love You in the Atlantic Ocean, also making it the first landing of a reused orbital class rocket. Elon Musk called the achievement an "incredible milestone in the history of space."^[108][109]

Interplanetary Transport System

Artist's impression of the Interplanetary Spaceship on the Jovian moon Europa.

SpaceX is developing a super-heavy lift launch vehicle—the ITS launch vehicle—a fully reusable booster stage and integrated second-stage/spacecraft—Interplanetary Spaceship and ITS tanker—to support flights to interplanetary space.^[110] Development of the Interplanetary Transport System and its super-heavy launch vehicle will be the major focus of SpaceX once Falcon Heavy and DragonCrew are flying regularly.^[111]

SpaceX has signaled on multiple occasions that it is interested in developing much larger engines than it has done to date. A conceptual plan for the Raptor project was first unveiled in a June 2009 AIAA presentation.^[112] In November 2012, Musk announced a new direction for propulsion side of the company: developing LOX/methane rocket engines for launch vehicle main and upper stages.^[113] The Raptor LOX/methane engine will use the more efficient staged combustion cycle,^[114] a departure from the open cycle gas generator cycle system and LOX/RP-1 propellants that the current Merlin 1 engine series uses."^[114] The rocket would be more powerful than previously released publicly, with over 1,000,000 lbf (4,400 kN) of thrust.^[115] Raptor engine component-level testing will begin in 2014.^[116] The Raptor engine will likely be the first in a family of methane-based engines SpaceX intends to build.^[116]

Musk's long term vision for the company is the development of technology and resources suitable for human colonization on Mars. He has expressed his interest in someday traveling to the planet, stating "I'd like to die on Mars, just not on impact."^[117] A rocket every two years or so could provide a base for the people arriving in 2025 after a launch in 2024.^[118][119] According to Steve Jurvetson, Musk believes that by 2035 at the latest, there will be thousands of rockets flying a million people to Mars, in order to enable a self-sustaining human colony.

In addition to SpaceX's privately funded plans for an eventual Mars mission, NASA Ames Research Center had developed a concept called Red Dragon: a low-cost Mars mission that would use Falcon Heavy as the launch vehicle and trans-Martian injection vehicle, and the Dragon capsule to enter the Martian atmosphere. The concept was originally envisioned for launch in 2018 as a NASA Discovery mission, then alternatively for 2022, but as of September 2015 it has not been yet formally submitted for funding within NASA.^[120] The objectives of the mission would be return the samples from Mars to Earth at a fraction of the cost of the NASA own return-sample mission now projected at 6 billion dollars.^[120] In April 2016, SpaceX announced its plan to launch a modified Dragon lander to Mars by 2018. This project is part of a public-private partnership contract between NASA and SpaceX.^[121]

Other projects

In January 2015, SpaceX CEO Elon Musk announced the development of a new satellite constellation to provide global broadband internet service. In June 2015 the company asked the federal government for permission to begin testing for a project that aims to build a constellation of 4,000 satellites capable of beaming the Internet to the entire globe, including remote regions which currently do not have internet access.^[122][123] The internet service will use a constellation of 4,000 cross-linked communications satellites in 1,100 km orbits. Owned and operated by SpaceX, the goal of the business is to increase profitability and cashflow, to allow SpaceX to build its Mars colony.^[72] Development began in 2015, initial prototype test-flight satellites are expected to be flown in 2017, and initial operation of the constellation could begin as early as 2020. As of March 2017, SpaceX filed with the US regulatory authorities plans to field a constellation of an additional 7,518 "V-band satellites in non-geosynchronous orbits to provide communications services" in an electromagnetic spectrum that had not been previously been "heavily employed for commercial communications services." Called the "V-band low-Earth orbit (VLEO) constellation," it would consist of "7,518 satellites to follow the [earlier] proposed 4,425 satellites that would function in Ka- and Ku-band.^[124]
In June 2015, SpaceX announced that they would sponsor a Hyperloop competition, and would build a 1-mile-long (1.6 km) subscale test track near SpaceX's headquarters for the competitive events, which could be held as early as June 2016.^[125][126] The plan was later delayed to January 2017, as there were many requests from teams for more time designing and building their pods.^[127]

Infrastructure

The company's headquarters, located in Hawthorne, California.

SpaceX is headquartered in California, which also serves as their primary manufacturing plant. They own a test site in Texas, and operate three current launch sites, with another under development. SpaceX also run regional offices in Texas, Virginia, and Washington, D.C.^[35] and a satellite development facility in Seattle.^[128]

Headquarters and manufacturing plant

Falcon 9 v1.1 rocket cores under construction at the SpaceX Hawthorne facility, November 2014.

SpaceX Headquarters is located in the Los Angeles suburb of Hawthorne, California. The large three-story facility, originally built by Northrop Corporation to build Boeing 747 fuselages,^[129] houses SpaceX's office space, mission control, and vehicle factory. The area has one of the largest concentrations of aerospace headquarters, facilities, and/or subsidiaries in the U.S., including Boeing/McDonnell Douglas main satellite building campuses, Raytheon, NASA's Jet Propulsion Laboratory, Lockheed Martin, BAE Systems, Northrop Grumman, and AECOM, etc., with a large pool of aerospace engineers and recent college engineering graduates.^[129]

SpaceX utilizes a high degree of vertical integration in the production of its rockets and rocket engines.^[27] SpaceX builds its rocket engines, rocket stages, spacecraft, principal avionics and all software in-house in their Hawthorne facility, which is unusual for the aerospace industry. Nevertheless, SpaceX still has over 3,000 suppliers with some 1,100 of those delivering to SpaceX nearly weekly.^[130]

Development and test facility

SpaceX McGregor engine test bunker, September 2012.

SpaceX operates their Rocket Development and Test Facility in McGregor, Texas. All SpaceX rocket engines are tested on rocket test stands, and low-altitude VTVL flight testing of the Falcon 9 Grasshopper v1.0 and F9R Dev1 test vehicles were carried out at McGregor.

The company purchased the McGregor facilities from Beal Aerospace, where it refitted the largest test stand for Falcon 9 engine testing. SpaceX has made a number of improvements to the facility since purchase, and has also extended the acreage by purchasing several pieces of adjacent farmland. In 2011, the company announced plans to upgrade the facility for launch testing a VTVL rocket,^[41] and then constructed a half-acre concrete launch facility in 2012 to support the Grasshopper test flight program.^[42] As of October 2012, the McGregor facility has seven test stands that are operated "18 hours a day, six days a week"^[131] and is building more test stands because production is ramping up and the company has a large manifest in the next several years.

In addition to routine testing, Dragon capsules (following recovery after an orbital mission), are shipped to McGregor for de-fueling, cleanup, and refurbishment for reuse in future missions.

Launch facilities

SpaceX west coast launch facility at Vandenberg Air Force Base, during the launch of CASSIOPE, September 2013.

SpaceX currently operates three orbital launch sites, at Cape Canaveral, Vandenberg Air Force Base, and Kennedy Space Center, and have announced plans for a fourth in Brownsville, Texas. SpaceX has indicated that they see a niche for each of the four orbital facilities and that they have sufficient launch business to fill each pad.^[132] Before it was retired, all Falcon 1 launches took place at the Ronald Reagan Ballistic Missile Defense Test Site on Omelek Island.

Cape Canaveral Air Force Station Space Launch Complex 40 (SLC-40) is used for Falcon 9 launches to low-earth and geostationary orbits. SLC-40 is not capable of supporting Falcon Heavy launches, or polar launches. As part of SpaceX's booster reusability program, the former Launch Complex 13 at Cape Canaveral, now renamed Landing Zone 1, has been designated for use for Falcon 9 first-stage booster landings.

Falcon 9 Flight 20 landing on Landing Zone 1 in December 2015.

Vandenberg Air Force Base Space Launch Complex 4 East (SLC-4E) is used for payloads to polar orbits. The Vandenberg site can launch both Falcon 9 and Falcon Heavy,^[133] but cannot launch to low inclination orbits. Post-launch landings will take place at the neighboring SLC-4W.

Kennedy Space Center Launch Complex 39A (LC39A) has been under development by SpaceX since December 2013, when NASA announced that they had selected SpaceX as the new commercial tenant.^[134] SpaceX signed the lease agreement in April 2014.^[135] They have been given a twenty-year exclusive lease of Pad 39A.^[136] SpaceX plans to launch their Falcon 9 and Falcon Heavy from the pad and build a new hangar near it.^{[136][135][137]} Elon Musk, has stated that he wants to shift most of SpaceX's NASA launches to LC39A, including Commercial Cargo and Crew missions to the ISS.^[134][138]

In August 2014, SpaceX announced they would be building a new commercial-only launch facility at Brownsville, Texas.^[139][140] The Federal Aviation Administration released a draft Environmental Impact Statement for the proposed Texas facility in April 2013, and "found that 'no impacts would occur' that would force the Federal Aviation Administration to deny SpaceX a permit for rocket operations,"^[141][141] and issued the permit in July 2014.^[142] SpaceX started construction on the new launch facility in 2014 with production ramping up in the latter half of 2015,^[143] with the first launches from the facility no earlier than 2016.^{[144][needs update]} Real estate packages at the location have been named by SpaceX with names based on the theme "Mars Crossing".^[145][146]

Satellite prototyping facility

In January 2015, SpaceX announced it would be entering the satellite production business and global satellite internet business. The satellite factory would be located in Seattle, Washington. The office will initially have approximately 60 engineers, with the potential to grow to 1,000 over several years. In July 2016, SpaceX acquired an additional 740 square meters (8,000 sq ft) creative space in Irvine, California (Orange County) to focus on satellite communications.^[147]

Launch contracts

SpaceX has been contracted by NASA to initially develop the technology and subsequently carry out the task of resupplying the International Space Station (ISS). SpaceX is also certified for US military launches of Evolved Expendable Launch Vehicle-class (EELV) payloads. In addition to this, SpaceX has (as of January 2013) a purely commercial launch manifest of "23 missions scheduled over the next 4 years, exclusive of US government flights," of a total of 40 flights scheduled through 2017."^[148] In September 2015, SpaceX stated that they had over 60 missions on manifest representing over $7B under contract.^[149]

NASA contracts

COTS

The COTS 2 Dragon is berthed to the ISS by Canadarm2.

In 2006, NASA announced that SpaceX had won a NASA Commercial Orbital Transportation Services (COTS) contract to demonstrate cargo delivery to the ISS, with a possible option for crew transport.^[150] This contract, designed by NASA to provide "seed money" for developing new boosters, paid SpaceX $278 million to develop the Falcon 9.^[151] In December 2010, the launch of the COTS Demo Flight 1 mission, SpaceX became the first privately funded company to successfully launch, orbit and recover a spacecraft.^[152] Dragon was successfully deployed into orbit, circled the Earth twice, and then made a controlled re-entry burn for a splashdown in the Pacific Ocean.^[153] With Dragon's safe recovery, SpaceX become the first private company to launch, orbit, and recover a spacecraft; prior to this mission, only government agencies had been able to recover orbital spacecraft.^[153] COTS Demo Flight 2 launched in May 2012, in which Dragon successfully berthed with the ISS, marking the first time that a private spacecraft had accomplished this feat.^[154][155]

Commercial cargo

Commercial Resupply Services (CRS) are a series of contracts awarded by NASA from 2008–2016 for delivery of cargo and supplies to the ISS on commercially operated spacecraft. The first CRS contracts were signed in 2008 and awarded $1.6 billion to SpaceX for 12 cargo transport missions, covering deliveries to 2016.^[156] SpaceX CRS-1, the first of the 12 planned resupply missions, launched in October 2012, achieved orbit, berthed and remained on station for 20 days, before re-entering the atmosphere and splashing down in the Pacific Ocean.^[157] CRS missions have flown approximately twice a year to the ISS since then. In 2015, NASA extended the Phase 1 contracts by ordering an additional three resupply flights from SpaceX.^[158][159] After further extensions late in 2015, SpaceX is currently scheduled to fly a total of 20 missions.^[160] A second phase of contracts (known as CRS2) were solicited and proposed in 2014. They were awarded in January 2016, for cargo transport flights beginning in 2019 and expected to last through 2024.

Commercial crew

Crew Dragon undergoing testing prior to flight.

The Commercial Crew Development (CCDev) program intends to develop commercially operated spacecraft that are capable of delivering astronauts to the ISS. SpaceX did not win a Space Act Agreement in the first round (CCDev 1), but during the second round (CCDev 2), NASA awarded SpaceX with a contract worth $75 million to further develop their launch escape system, test a crew accommodations mock-up, and to further progress their Falcon/Dragon crew transportation design.^{[96][161][162]} The CCDev program later became Commercial Crew Integrated Capability (CCiCap), and in August 2012, NASA announced that SpaceX had been awarded $440 million to continue development and testing of its Dragon 2 spacecraft.^[163][164]

In September 2014, NASA chose SpaceX and Boeing as the two companies that will be funded to develop systems to transport U.S. crews to and from the ISS. SpaceX won $2.6 billion to complete and certify Dragon 2 by 2017. The contracts include at least one crewed flight test with at least one NASA astronaut aboard. Once Crew Dragon achieves NASA certification, the contract requires SpaceX to conduct at least two, and as many as six, crewed missions to the space station.^[165]

Defense contracts

In 2005, SpaceX announced that it had been awarded an Indefinite Delivery/Indefinite Quantity (IDIQ) contract for Responsive Small Spacelift (RSS) launch services by the United States Air Force, which could allow the Air Force to purchase up to $100 million worth of launches from the company.^[166] In April 2008, NASA announced that it had awarded an IDIQ Launch Services contract to SpaceX for up to $1 billion, depending on the number of missions awarded. The contract covers launch services ordered by June 2010, for launches through December 2012.^[167] Musk stated in the same 2008 announcement that SpaceX has sold 14 contracts for flights on the various Falcon vehicles.^[167] In December 2012, SpaceX announced its first two launch contracts with the United States Department of Defense. The United States Air Force Space and Missile Systems Center awarded SpaceX two EELV-class missions: Deep Space Climate Observatory (DSCOVR) and Space Test Program 2 (STP-2). DSCOVR was launched on a Falcon 9 launch vehicle in 2015, while STP-2 will be launched on a Falcon Heavy in 2017.^[168]

In May 2015, the United States Air Force announced that the Falcon 9 v1.1 was certified for launching "national security space missions," which allows SpaceX to contract launch services to the Air Force for any payloads classified under national security.^[169] In April 2016, the U.S. Air Force awarded the first such national security launch, an $82.7 million contract to SpaceX to launch a GPS satellite in May 2018; this estimated cost was approximately 40% less than the estimated cost for similar previous missions.^[170][171] In April 2016, the Pentagon announced that SpaceX has been awarded an $82.7 million contract from the U.S. Air Force to launch a next-generation GPS satellite aboard its Falcon 9 rocket in May 2018.^[172] Prior to this, United Launch Alliance was the only provider certified to launch national security payloads.^{[173][173][174]}

Commercial contracts

The Falcon 9 carrying the SES-8 communications satellite into orbit.

SpaceX announced in March 2010, that it had been contracted to launch SES-8, a telecommunications satellite for SES S.A.; it was successfully launched in December 2013.^[175] SES-8 was SpaceX's first launch of a geostationary comsat, signalling its entrance into the lucrative commercial launch market.^{[37][37][175]} In June 2010, SpaceX was awarded the largest-ever commercial launch contract, worth $492 million, to launch Iridium satellites using Falcon 9 rockets.^[176] As of December 2013, SpaceX has a total of 50 future launches under contract; two-thirds of them are for commercial customers.^[36]

Launch market competition and pricing pressure

SpaceX's low launch prices, especially for communication satellites flying to geostationary (GTO) orbit, have resulted in market pressure on its competitors to lower their own prices.^[27] Prior to 2013, the openly competed comsat launch market had been dominated by Arianespace (flying Ariane 5) and International Launch Services (flying Proton).^[177] With a published price of US$56.5 million per launch to low Earth orbit, "Falcon 9 rockets [were] already the cheapest in the industry. Reusable Falcon 9s could drop the price by an order of magnitude, sparking more space-based enterprise, which in turn would drop the cost of access to space still further through economies of scale."^[178] SpaceX has publicly indicated that if they are successful with developing the reusable technology, launch prices in the US$5 to 7 million range for the reusable Falcon 9 are possible.^[45]

In 2014, SpaceX had won nine contracts out of 20 that were openly competed worldwide in 2014 at commercial launch service providers.^[179] Space media reported that SpaceX had "already begun to take market share" from Arianespace.^[180] Arianespace has requested that European governments provide additional subsidies to face the competition from SpaceX.^[181][182] European satellite operators are pushing the ESA to reduce Ariane 5 and the future Ariane 6 rocket launch prices as a result of competition from SpaceX. According to one Arianespace managing director in 2015, it was clear that "a very significant challenge [was] coming from SpaceX ... Therefore things have to change ... and the whole European industry is being restructured, consolidated, rationalised and streamlined."^[183] Jean Botti, Director of innovation for Airbus (which makes the Ariane 5) warned that "those who don't take Elon Musk seriously will have a lot to worry about."^[184] In 2014, no commercial launches were booked to fly on the Proton.^[179]

Also in 2014, SpaceX capabilities and pricing had also begun to affect the market for launch of US military payloads. For nearly a decade the large US launch provider United Launch Alliance (ULA) had faced no competition for military launches.^[185] Anticipating a slump in domestic military and spy launches, ULA stated that it would go out of business unless it won commercial satellite launch orders.^[186] To that end, ULA announced a major restructuring of processes and workforce in order to decrease launch costs by half.^[187][188]