Interstellar travel

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A Bussard ramjet, one of many possible methods that could serve as propulsion of a starship.

Interstellar travel is the term used for hypothetical crewed or uncrewed travel between stars or planetary systems. Interstellar travel will be much more difficult than interplanetary spaceflight; the distances between the planets in the Solar System are less than 30 astronomical units (AU)—whereas the distances between stars are typically hundreds of thousands of AU, and usually expressed in light-years. Because of the vastness of those distances, interstellar travel would require a high percentage of the speed of light; huge travel time, lasting from decades to millennia or longer; or a combination of both.

The speeds required for interstellar travel in a human lifetime far exceed what current methods of spacecraft propulsion can provide. Even with a hypothetically perfectly efficient propulsion system, the kinetic energy corresponding to those speeds is enormous by today's standards of energy production. Moreover, collisions by the spacecraft with cosmic dust and gas can produce very dangerous effects both to passengers and the spacecraft itself.

A number of strategies have been proposed to deal with these problems, ranging from giant arks that would carry entire societies and ecosystems, to microscopic space probes. Many different spacecraft propulsion systems have been proposed to give spacecraft the required speeds, including nuclear propulsion, beam-powered propulsion, and methods based on speculative physics.^[1]

For both crewed and uncrewed interstellar travel, considerable technological and economic challenges need to be met. Even the most optimistic views about interstellar travel see it as only being feasible decades from now—the more common view is that it is a century or more away. However, in spite of the challenges, when interstellar travel will be realized, a wide range of scientific benefits is expected.^[2]

Most interstellar travel concepts require a developed space logistics system capable of moving millions of tons to a construction / operating location, and most would require gigawatt-scale power for construction or power (such as Star Wisp or Light Sail type concepts). Such a system could grow organically if space-based solar power became a significant component of Earth's energy mix. Consumer demand for a multi-terawatt system would automatically create the necessary multi-million ton/year logistical system.^[3]

Challenges

Interstellar distances

Distances between the planets in the Solar System are often measured in astronomical units (AU), defined as the average distance between the Sun and Earth, some 1.5×10⁸ kilometers (93 million miles). Venus, the closest other planet to Earth is (at closest approach) 0.28 AU away. Neptune, the farthest planet from the Sun, is 29.8 AU away. As of January 2018, Voyager 1, the farthest man-made object from Earth, is 141.5 AU away.^[4]

The closest known star, Proxima Centauri, is approximately 268,332 AU away, or over 9,000 times farther away than Neptune.

Object	A.U.	light time
Moon	0.0026	1.3 seconds
Sun	1	8 minutes
Venus (nearest planet)	0.28	2.41 minutes
Neptune (farthest planet)	29.8	4.1 hours
Voyager 1	141.5	19.61 hours
Proxima Centauri	268,332	4.24 years

Because of this, distances between stars are usually expressed in light-years, defined as the distance that a light photon travels in a year. Light in a vacuum travels around 300,000 kilometres (186,000 mi) per second, so this is some 9.461×10¹² kilometers (5.879 trillion miles) or 1 light-year (63,241 AU) in a year. Proxima Centauri is 4.243 light-years away.

Another way of understanding the vastness of interstellar distances is by scaling: One of the closest stars to the Sun, Alpha Centauri A (a Sun-like star), can be pictured by scaling down the Earth–Sun distance to one meter (3.28 ft). On this scale, the distance to Alpha Centauri A would be 276 kilometers (171 miles).

The fastest outward-bound spacecraft yet sent, Voyager 1, has covered 1/600 of a light-year in 30 years and is currently moving at 1/18,000 the speed of light. At this rate, a journey to Proxima Centauri would take 80,000 years.^[5]

Required energy

A significant factor contributing to the difficulty is the energy that must be supplied to obtain a reasonable travel time. A lower bound for the required energy is the kinetic energy ${\displaystyle K={\tfrac {1}{2}}mv^{2}}$ where ${\displaystyle m}$ is the final mass. If deceleration on arrival is desired and cannot be achieved by any means other than the engines of the ship, then the lower bound for the required energy is doubled to ${\displaystyle mv^{2}}$.^[6]

The velocity for a manned round trip of a few decades to even the nearest star is several thousand times greater than those of present space vehicles. This means that due to the ${\displaystyle v^{2}}$ term in the kinetic energy formula, millions of times as much energy is required. Accelerating one ton to one-tenth of the speed of light requires at least 450 petajoules or 4.50×10¹⁷ joules or 125 terawatt-hours^[7] (world energy consumption 2008 was 143,851 terawatt-hours),^{[citation needed]} without factoring in efficiency of the propulsion mechanism. This energy has to be generated onboard from stored fuel, harvested from the interstellar medium, or projected over immense distances.

Interstellar medium

A knowledge of the properties of the interstellar gas and dust through which the vehicle must pass is essential for the design of any interstellar space mission.^[8] A major issue with traveling at extremely high speeds is that interstellar dust may cause considerable damage to the craft, due to the high relative speeds and large kinetic energies involved. Various shielding methods to mitigate this problem have been proposed.^[9] Larger objects (such as macroscopic dust grains) are far less common, but would be much more destructive. The risks of impacting such objects, and methods of mitigating these risks, have been discussed in the literature, but many unknowns remain^[10] and, owing to the inhomogeneous distribution of interstellar matter around the Sun, will depend on direction travelled.^[8] Although a high density interstellar medium may cause difficulties for many interstellar travel concepts, interstellar ramjets, and some proposed concepts for decelerating interstellar spacecraft, would actually benefit from a denser interstellar medium.^[8]

Hazards

The crew of an interstellar ship would face several significant hazards, including the psychological effects of long-term isolation, the effects of exposure to ionizing radiation, and the physiological effects of weightlessness to the muscles, joints, bones, immune system, and eyes. There also exists the risk of impact by micrometeoroids and other space debris. These risks represent challenges that have yet to be overcome.^[11]

Wait calculation

It has been argued that an interstellar mission that cannot be completed within 50 years should not be started at all. Instead, assuming that a civilization is still on an increasing curve of propulsion system velocity and not yet having reached the limit, the resources should be invested in designing a better propulsion system. This is because a slow spacecraft would probably be passed by another mission sent later with more advanced propulsion (the incessant obsolescence postulate).^[12] On the other hand, Andrew Kennedy has shown that if one calculates the journey time to a given destination as the rate of travel speed derived from growth (even exponential growth) increases, there is a clear minimum in the total time to that destination from now.^[13] Voyages undertaken before the minimum will be overtaken by those that leave at the minimum, whereas voyages that leave after the minimum will never overtake those that left at the minimum.

Prime targets for interstellar travel

There are 59 known stellar systems within 40 light years of the Sun, containing 81 visible stars. The following could be considered prime targets for interstellar missions:^[12]

System	Distance (ly)	Remarks
Alpha Centauri	4.3	Closest system. Three stars (G2, K1, M5). Component A is similar to the Sun (a G2 star). On August 24, 2016, the discovery of an Earth-size exoplanet (Proxima Centauri b) orbiting in the habitable zone of Proxima Centauri was announced.
Barnard's Star	6	Small, low-luminosity M5 red dwarf. Second closest to Solar System.
Sirius	8.7	Large, very bright A1 star with a white dwarf companion.
Epsilon Eridani	10.8	Single K2 star slightly smaller and colder than the Sun. It has two asteroid belts, might have a giant and one much smaller planet,[14] and may possess a Solar-System-type planetary system.
Tau Ceti	11.8	Single G8 star similar to the Sun. High probability of possessing a Solar-System-type planetary system: current evidence shows 5 planets with potentially two in the habitable zone.
Wolf 1061	~14	Wolf 1061 c is 4.3 times the size of Earth; it may have rocky terrain. It also sits within the ‘Goldilocks’ zone where it might be possible for liquid water to exist.[15]
Gliese 581 planetary system	20.3	Multiple planet system. The unconfirmed exoplanet Gliese 581g and the confirmed exoplanet Gliese 581d are in the star's habitable zone.
Gliese 667C	22	A system with at least six planets. A record-breaking three of these planets are super-Earths lying in the zone around the star where liquid water could exist, making them possible candidates for the presence of life.[16]
Vega	25	A very young system possibly in the process of planetary formation.[17]
TRAPPIST-1	39	A recently discovered system which boasts 7 Earth-like planets, some of which may have liquid water. The discovery is a major advancement in finding a habitable planet and in finding a planet that could support life.

Existing and near-term astronomical technology is capable of finding planetary systems around these objects, increasing their potential for exploration

Proposed methods

Slow, uncrewed probes

Slow interstellar missions based on current and near-future propulsion technologies are associated with trip times starting from about one hundred years to thousands of years. These missions consist of sending a robotic probe to a nearby star for exploration, similar to interplanetary probes such as used in the Voyager program.^[18] By taking along no crew, the cost and complexity of the mission is significantly reduced although technology lifetime is still a significant issue next to obtaining a reasonable speed of travel. Proposed concepts include Project Daedalus, Project Icarus, Project Dragonfly, Project Longshot,^[19] and more recently Breakthrough Starshot.

Nanoprobes

Near-lightspeed nano spacecraft might be possible within the near future built on existing microchip technology with a newly developed nanoscale thruster. Researchers at the University of Michigan are developing thrusters that use nanoparticles as propellant. Their technology is called "nanoparticle field extraction thruster", or nanoFET. These devices act like small particle accelerators shooting conductive nanoparticles out into space.^[21]

Michio Kaku, a theoretical physicist, has suggested that clouds of "smart dust" be sent to the stars, which may become possible with advances in nanotechnology. Kaku also notes that a large number of nanoprobes would need to be sent due to the vulnerability of very small probes to be easily deflected by magnetic fields, micrometeorites and other dangers to ensure the chances that at least one nanoprobe will survive the journey and reach the destination.^[22]

Given the light weight of these probes, it would take much less energy to accelerate them. With onboard solar cells, they could continually accelerate using solar power. One can envision a day when a fleet of millions or even billions of these particles swarm to distant stars at nearly the speed of light and relay signals back to Earth through a vast interstellar communication network.

As a near-term solution, small, laser-propelled interstellar probes, based on current CubeSat technology were proposed in the context of Project Dragonfly.^[19]

Slow, manned missions

In crewed missions, the duration of a slow interstellar journey presents a major obstacle and existing concepts deal with this problem in different ways.^[23] They can be distinguished by the "state" in which humans are transported on-board of the spacecraft.

Generation ships

A generation ship (or world ship) is a type of interstellar ark in which the crew that arrives at the destination is descended from those who started the journey. Generation ships are not currently feasible because of the difficulty of constructing a ship of the enormous required scale and the great biological and sociological problems that life aboard such a ship raises.

Suspended animation

Scientists and writers have postulated various techniques for suspended animation. These include human hibernation and cryonic preservation. Although neither is currently practical, they offer the possibility of sleeper ships in which the passengers lie inert for the long duration of the voyage.^[28]

Frozen embryos

A robotic interstellar mission carrying some number of frozen early stage human embryos is another theoretical possibility. This method of space colonization requires, among other things, the development of an artificial uterus, the prior detection of a habitable terrestrial planet, and advances in the field of fully autonomous mobile robots and educational robots that would replace human parents.^[29]

Island hopping through interstellar space

Interstellar space is not completely empty; it contains trillions of icy bodies ranging from small asteroids (Oort cloud) to possible rogue planets. There may be ways to take advantage of these resources for a good part of an interstellar trip, slowly hopping from body to body or setting up waystations along the way.^[30]

Fast missions

If a spaceship could average 10 percent of light speed (and decelerate at the destination, for manned missions), this would be enough to reach Proxima Centauri in forty years. Several propulsion concepts have been proposed ^[31] that might be eventually developed to accomplish this (see also the section below on propulsion methods), but none of them are ready for near-term (few decades) developments at acceptable cost.

Time dilation

Assuming faster-than-light travel is impossible, one might conclude that a human can never make a round-trip farther from Earth than 20 light years if the traveler is active between the ages of 20 and 60. A traveler would never be able to reach more than the very few star systems that exist within the limit of 20 light years from Earth. This, however, fails to take into account relativistic time dilation.^[32] Clocks aboard an interstellar ship would run slower than Earth clocks, so if a ship's engines were capable of continuously generating around 1 g of acceleration (which is comfortable for humans), the ship could reach almost anywhere in the galaxy and return to Earth within 40 years ship-time (see diagram). Upon return, there would be a difference between the time elapsed on the astronaut's ship and the time elapsed on Earth.

For example, a spaceship could travel to a star 32 light-years away, initially accelerating at a constant 1.03g (i.e. 10.1 m/s²) for 1.32 years (ship time), then stopping its engines and coasting for the next 17.3 years (ship time) at a constant speed, then decelerating again for 1.32 ship-years, and coming to a stop at the destination. After a short visit, the astronaut could return to Earth the same way. After the full round-trip, the clocks on board the ship show that 40 years have passed, but according to those on Earth, the ship comes back 76 years after launch.

From the viewpoint of the astronaut, onboard clocks seem to be running normally. The star ahead seems to be approaching at a speed of 0.87 light years per ship-year. The universe would appear contracted along the direction of travel to half the size it had when the ship was at rest; the distance between that star and the Sun would seem to be 16 light years as measured by the astronaut.

At higher speeds, the time on board will run even slower, so the astronaut could travel to the center of the Milky Way (30,000 light years from Earth) and back in 40 years ship-time. But the speed according to Earth clocks will always be less than 1 light year per Earth year, so, when back home, the astronaut will find that more than 60 thousand years will have passed on Earth.

Constant acceleration

This plot shows a ship capable of 1-g (10 m/s² or about 1.0 ly/y²) "felt" or proper-acceleration^[33] can go far, except for the problem of accelerating on-board propellant.

Regardless of how it is achieved, a propulsion system that could produce acceleration continuously from departure to arrival would be the fastest method of travel. A constant acceleration journey is one where the propulsion system accelerates the ship at a constant rate for the first half of the journey, and then decelerates for the second half, so that it arrives at the destination stationary relative to where it began. If this were performed with an acceleration similar to that experienced at the Earth's surface, it would have the added advantage of producing artificial "gravity" for the crew. Supplying the energy required, however, would be prohibitively expensive with current technology.^[34]

From the perspective of a planetary observer, the ship will appear to accelerate steadily at first, but then more gradually as it approaches the speed of light (which it cannot exceed). It will undergo hyperbolic motion.^[35] The ship will be close to the speed of light after about a year of accelerating and remain at that speed until it brakes for the end of the journey.

From the perspective of an onboard observer, the crew will feel a gravitational field opposite the engine's acceleration, and the universe ahead will appear to fall in that field, undergoing hyperbolic motion. As part of this, distances between objects in the direction of the ship's motion will gradually contract until the ship begins to decelerate, at which time an onboard observer's experience of the gravitational field will be reversed.

When the ship reaches its destination, if it were to exchange a message with its origin planet, it would find that less time had elapsed on board than had elapsed for the planetary observer, due to time dilation and length contraction.

The result is an impressively fast journey for the crew.

Propulsion

Rocket concepts

All rocket concepts are limited by the rocket equation, which sets the characteristic velocity available as a function of exhaust velocity and mass ratio, the ratio of initial (M₀, including fuel) to final (M₁, fuel depleted) mass.

Very high specific power, the ratio of thrust to total vehicle mass, is required to reach interstellar targets within sub-century time-frames.^[36] Some heat transfer is inevitable and a tremendous heating load must be adequately handled.

Thus, for interstellar rocket concepts of all technologies, a key engineering problem (seldom explicitly discussed) is limiting the heat transfer from the exhaust stream back into the vehicle.^[37]

Ion engine

A type of electric propulsion, spacecraft such as Dawn use an ion engine. In an ion engine, electric power is used to create charged particles of the propellant, usually the gas xenon, and accelerate them to extremely high velocities. The exhaust velocity of conventional rockets is limited by the chemical energy stored in the fuel’s molecular bonds, which limits the thrust to about 5 km/s. This gives them high power^{[clarification needed]} (for lift-off from Earth, for example) but limits the top speed. By contrast, ion engines have low force, but the top speed in principle is limited only by the electrical power available on the spacecraft and on the gas ions being accelerated. The exhaust speed of the charged particles range from 15 km/s to 35 km/s.^[38]

Nuclear fission powered

Fission-electric

Nuclear-electric or plasma engines, operating for long periods at low thrust and powered by fission reactors, have the potential to reach speeds much greater than chemically powered vehicles or nuclear-thermal rockets. Such vehicles probably have the potential to power Solar System exploration with reasonable trip times within the current century. Because of their low-thrust propulsion, they would be limited to off-planet, deep-space operation. Electrically powered spacecraft propulsion powered by a portable power-source, say a nuclear reactor, producing only small accelerations, would take centuries to reach for example 15% of the velocity of light, thus unsuitable for interstellar flight during a single human lifetime.^[39]

Fission-fragment

Fission-fragment rockets use nuclear fission to create high-speed jets of fission fragments, which are ejected at speeds of up to 12,000 km/s (7,500 mi/s). With fission, the energy output is approximately 0.1% of the total mass-energy of the reactor fuel and limits the effective exhaust velocity to about 5% of the velocity of light. For maximum velocity, the reaction mass should optimally consist of fission products, the "ash" of the primary energy source, so no extra reaction mass need be bookkept in the mass ratio.

Nuclear pulse

Modern Pulsed Fission Propulsion Concept.

Based on work in the late 1950s to the early 1960s, it has been technically possible to build spaceships with nuclear pulse propulsion engines, i.e. driven by a series of nuclear explosions. This propulsion system contains the prospect of very high specific impulse (space travel's equivalent of fuel economy) and high specific power.^[40]

Project Orion team member Freeman Dyson proposed in 1968 an interstellar spacecraft using nuclear pulse propulsion that used pure deuterium fusion detonations with a very high fuel-burnup fraction. He computed an exhaust velocity of 15,000 km/s and a 100,000-tonne space vehicle able to achieve a 20,000 km/s delta-v allowing a flight-time to Alpha Centauri of 130 years.^[41] Later studies indicate that the top cruise velocity that can theoretically be achieved by a Teller-Ulam thermonuclear unit powered Orion starship, assuming no fuel is saved for slowing back down, is about 8% to 10% of the speed of light (0.08-0.1c).^[42] An atomic (fission) Orion can achieve perhaps 3%-5% of the speed of light. A nuclear pulse drive starship powered by fusion-antimatter catalyzed nuclear pulse propulsion units would be similarly in the 10% range and pure matter-antimatter annihilation rockets would be theoretically capable of obtaining a velocity between 50% to 80% of the speed of light. In each case saving fuel for slowing down halves the maximum speed. The concept of using a magnetic sail to decelerate the spacecraft as it approaches its destination has been discussed as an alternative to using propellant, this would allow the ship to travel near the maximum theoretical velocity.^[43] Alternative designs utilizing similar principles include Project Longshot, Project Daedalus, and Mini-Mag Orion. The principle of external nuclear pulse propulsion to maximize survivable power has remained common among serious concepts for interstellar flight without external power beaming and for very high-performance interplanetary flight.

In the 1970s the Nuclear Pulse Propulsion concept further was refined by Project Daedalus by use of externally triggered inertial confinement fusion, in this case producing fusion explosions via compressing fusion fuel pellets with high-powered electron beams. Since then, lasers, ion beams, neutral particle beams and hyper-kinetic projectiles have been suggested to produce nuclear pulses for propulsion purposes.^[44]

A current impediment to the development of any nuclear-explosion-powered spacecraft is the 1963 Partial Test Ban Treaty, which includes a prohibition on the detonation of any nuclear devices (even non-weapon based) in outer space. This treaty would, therefore, need to be renegotiated, although a project on the scale of an interstellar mission using currently foreseeable technology would probably require international cooperation on at least the scale of the International Space Station.

Nuclear fusion rockets

Fusion rocket starships, powered by nuclear fusion reactions, should conceivably be able to reach speeds of the order of 10% of that of light, based on energy considerations alone. In theory, a large number of stages could push a vehicle arbitrarily close to the speed of light. These would burn such light element fuels as deuterium, tritium, ³He, ¹¹B, and ⁷Li. Because fusion yields about 0.3–0.9% of the mass of the nuclear fuel as released energy, it is energetically more favorable than fission, which releases <0 .1="" 0="" 4="" a="" achievable="" although="" and="" are="" as="" available="" be="" best="" c.="" centuries.="" concepts="" correspondingly="" decades="" difficulties="" easily="" energetically="" energy="" engineering="" exhaust="" fission="" for="" fraction="" fuel="" fusion="" high-energy="" higher="" however="" human="" intractable="" involve="" large="" lifetime="" long="" loss.="" mass-energy.="" massive="" maximum="" may="" most="" nbsp="" nearest-term="" nearest="" neutrons="" of="" offer="" or="" out="" p="" potentially="" prospects="" reactions="" release="" s="" seem="" significant="" source="" stars="" still="" technological="" than="" the="" their="" these="" they="" thus="" to="" travel="" turn="" typically="" velocities="" which="" within="">
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Daedalus interstellar vehicle.

Early studies include Project Daedalus, performed by the British Interplanetary Society in 1973–1978, and Project Longshot, a student project sponsored by NASA and the US Naval Academy, completed in 1988. Another fairly detailed vehicle system, "Discovery II", designed and optimized for crewed Solar System exploration, based on the D³He reaction but using hydrogen as reaction mass, has been described by a team from NASA's Glenn Research Center. It achieves characteristic velocities greater than 300 km/s with an acceleration of ~1.7•10⁻³ g, with a ship initial mass of ~1700 metric tons, and payload fraction above 10%. Although these are still far short of the requirements for interstellar travel on human timescales, the study seems to represent a reasonable benchmark towards what may be approachable within several decades, which is not impossibly beyond the current state-of-the-art. Based on the concept's 2.2% burnup fraction it could achieve a pure fusion product exhaust velocity of ~3,000 km/s.

Antimatter rockets

An antimatter rocket would have a far higher energy density and specific impulse than any other proposed class of rocket.^[31] If energy resources and efficient production methods are found to make antimatter in the quantities required and store^[47][48] it safely, it would be theoretically possible to reach speeds of several tens of percent that of light.^[31] Whether antimatter propulsion could lead to the higher speeds (>90% that of light) at which relativistic time dilation would become more noticeable, thus making time pass at a slower rate for the travelers as perceived by an outside observer, is doubtful owing to the large quantity of antimatter that would be required.^[31]

Speculating that production and storage of antimatter should become feasible, two further issues need to be considered. First, in the annihilation of antimatter, much of the energy is lost as high-energy gamma radiation, and especially also as neutrinos, so that only about 40% of mc² would actually be available if the antimatter were simply allowed to annihilate into radiations thermally.^[31] Even so, the energy available for propulsion would be substantially higher than the ~1% of mc² yield of nuclear fusion, the next-best rival candidate.

Second, heat transfer from the exhaust to the vehicle seems likely to transfer enormous wasted energy into the ship (e.g. for 0.1g ship acceleration, approaching 0.3 trillion watts per ton of ship mass), considering the large fraction of the energy that goes into penetrating gamma rays. Even assuming shielding was provided to protect the payload (and passengers on a crewed vehicle), some of the energy would inevitably heat the vehicle, and may thereby prove a limiting factor if useful accelerations are to be achieved.

More recently, Friedwardt Winterberg proposed that a matter-antimatter GeV gamma ray laser photon rocket is possible by a relativistic proton-antiproton pinch discharge, where the recoil from the laser beam is transmitted by the Mössbauer effect to the spacecraft.^[49]

Rockets with an external energy source

Rockets deriving their power from external sources, such as a laser, could replace their internal energy source with an energy collector, potentially reducing the mass of the ship greatly and allowing much higher travel speeds. Geoffrey A. Landis has proposed for an interstellar probe, with energy supplied by an external laser from a base station powering an Ion thruster.^[50]

Non-rocket concepts

A problem with all traditional rocket propulsion methods is that the spacecraft would need to carry its fuel with it, thus making it very massive, in accordance with the rocket equation. Several concepts attempt to escape from this problem:^[31][51]

Interstellar ramjets

In 1960, Robert W. Bussard proposed the Bussard ramjet, a fusion rocket in which a huge scoop would collect the diffuse hydrogen in interstellar space, "burn" it on the fly using a proton–proton chain reaction, and expel it out of the back. Later calculations with more accurate estimates suggest that the thrust generated would be less than the drag caused by any conceivable scoop design. Yet the idea is attractive because the fuel would be collected en route (commensurate with the concept of energy harvesting), so the craft could theoretically accelerate to near the speed of light. The limitation is due to the fact that the reaction can only accelerate the propellant to 0.12c. Thus the drag of catching interstellar dust and the thrust of accelerating that same dust to 0.12c would be the same when the speed is 0.12c, preventing further acceleration.

Beamed propulsion

This diagram illustrates Robert L. Forward's scheme for slowing down an interstellar light-sail at the star system destination.

A light sail or magnetic sail powered by a massive laser or particle accelerator in the home star system could potentially reach even greater speeds than rocket- or pulse propulsion methods, because it would not need to carry its own reaction mass and therefore would only need to accelerate the craft's payload. Robert L. Forward proposed a means for decelerating an interstellar light sail in the destination star system without requiring a laser array to be present in that system. In this scheme, a smaller secondary sail is deployed to the rear of the spacecraft, whereas the large primary sail is detached from the craft to keep moving forward on its own. Light is reflected from the large primary sail to the secondary sail, which is used to decelerate the secondary sail and the spacecraft payload.^[52] In 2002, Geoffrey A. Landis of NASA's Glen Research center also proposed a laser-powered, propulsion, sail ship that would host a diamond sail (of a few nanometers thick) powered with the use of solar energy.^[53] With this proposal, this interstellar ship would, theoretically, be able to reach 10 percent the speed of light.

A magnetic sail could also decelerate at its destination without depending on carried fuel or a driving beam in the destination system, by interacting with the plasma found in the solar wind of the destination star and the interstellar medium.^[54][55]

The following table lists some example concepts using beamed laser propulsion as proposed by the physicist Robert L. Forward:^[56]

Mission	Laser Power	Vehicle Mass	Acceleration	Sail Diameter	Maximum Velocity (% of c)
1. Flyby – Alpha Centauri, 40 years
outbound stage	65 GW	1 t	0.036 g	3.6 km	11% @ 0.17 ly
2. Rendezvous – Alpha Centauri, 41 years
outbound stage	7,200 GW	785 t	0.005 g	100 km	21% @ 4.29 ly
deceleration stage	26,000 GW	71 t	0.2 g	30 km	21% @ 4.29 ly
3. Manned – Epsilon Eridani, 51 years (including 5 years exploring star system)
outbound stage	75,000,000 GW	78,500 t	0.3 g	1000 km	50% @ 0.4 ly
deceleration stage	21,500,000 GW	7,850 t	0.3 g	320 km	50% @ 10.4 ly
return stage	710,000 GW	785 t	0.3 g	100 km	50% @ 10.4 ly
deceleration stage	60,000 GW	785 t	0.3 g	100 km	50% @ 0.4 ly

Interstellar travel catalog to use photogravitational assists for a full stop

The following table is based on work by Heller, Hippke and Kervella.
 

Name	Travel time (yr)	Distance (ly)	Luminosity (L☉)
Sirius A	68.90	8.58	24.20
α Centauri A	101.25	4.36	1.52
α Centauri B	147.58	4.36	0.50
Procyon A	154.06	11.44	6.94
Vega	167.39	25.02	50.05
Altair	176.67	16.69	10.70
Fomalhaut A	221.33	25.13	16.67
Denebola	325.56	35.78	14.66
Castor A	341.35	50.98	49.85
Epsilon Eridiani	363.35	10.50	0.50

• Successive assists at α Cen A and B could allow travel times to 75 yr to both stars.
• Lightsail has a nominal mass-to-surface ratio (σ_nom) of 8.6×10⁻⁴ gram m⁻² for a nominal graphene-class sail.
• Area of the Lightsail, about 10⁵ m² = (316 m)²
• Velocity up to 37,300 km s⁻¹ (12.5% c)

Pre-accelerated fuel

Achieving start-stop interstellar trip times of less than a human lifetime require mass-ratios of between 1,000 and 1,000,000, even for the nearer stars. This could be achieved by multi-staged vehicles on a vast scale.^[45] Alternatively large linear accelerators could propel fuel to fission propelled space-vehicles, avoiding the limitations of the Rocket equation.

Theoretical concepts

Faster-than-light travel

Artist's depiction of a hypothetical Wormhole Induction Propelled Spacecraft, based loosely on the 1994 "warp drive" paper of Miguel Alcubierre. Credit: NASA CD-98-76634 by Les Bossinas.

Scientists and authors have postulated a number of ways by which it might be possible to surpass the speed of light, but even the most serious-minded of these are highly speculative.^[59]

It is also debatable whether faster-than-light travel is physically possible, in part because of causality concerns: travel faster than light may, under certain conditions, permit travel backwards in time within the context of special relativity.^[60] Proposed mechanisms for faster-than-light travel within the theory of general relativity require the existence of exotic matter^[59] and it is not known if this could be produced in sufficient quantity.

Alcubierre drive

In physics, the Alcubierre drive is based on an argument, within the framework of general relativity and without the introduction of wormholes, that it is possible to modify a spacetime in a way that allows a spaceship to travel with an arbitrarily large speed by a local expansion of spacetime behind the spaceship and an opposite contraction in front of it.^[61] Nevertheless, this concept would require the spaceship to incorporate a region of exotic matter, or hypothetical concept of negative mass.^[61]

Artificial black hole

A theoretical idea for enabling interstellar travel is by propelling a starship by creating an artificial black hole and using a parabolic reflector to reflect its Hawking radiation. Although beyond current technological capabilities, a black hole starship offers some advantages compared to other possible methods. Getting the black hole to act as a power source and engine also requires a way to convert the Hawking radiation into energy and thrust. One potential method involves placing the hole at the focal point of a parabolic reflector attached to the ship, creating forward thrust. A slightly easier, but less efficient method would involve simply absorbing all the gamma radiation heading towards the fore of the ship to push it onwards, and let the rest shoot out the back.

Wormholes

Wormholes are conjectural distortions in spacetime that theorists postulate could connect two arbitrary points in the universe, across an Einstein–Rosen Bridge. It is not known whether wormholes are possible in practice. Although there are solutions to the Einstein equation of general relativity that allow for wormholes, all of the currently known solutions involve some assumption, for example the existence of negative mass, which may be unphysical.^[65] However, Cramer et al. argue that such wormholes might have been created in the early universe, stabilized by cosmic string.^[66] The general theory of wormholes is discussed by Visser in the book Lorentzian Wormholes.^[67]

Designs and studies

Enzmann starship

The Enzmann starship, as detailed by G. Harry Stine in the October 1973 issue of Analog, was a design for a future starship, based on the ideas of Robert Duncan-Enzmann. The spacecraft itself as proposed used a 12,000,000 ton ball of frozen deuterium to power 12–24 thermonuclear pulse propulsion units. Twice as long as the Empire State Building and assembled in-orbit, the spacecraft was part of a larger project preceded by interstellar probes and telescopic observation of target star systems.^[68]

Project Hyperion

Project Hyperion, one of the projects of Icarus Interstellar.^[69]

NASA research

NASA has been researching interstellar travel since its formation, translating important foreign language papers and conducting early studies on applying fusion propulsion, in the 1960s, and laser propulsion, in the 1970s, to interstellar travel.

The NASA Breakthrough Propulsion Physics Program (terminated in FY 2003 after a 6-year, $1.2-million study, because "No breakthroughs appear imminent.")^[70] identified some breakthroughs that are needed for interstellar travel to be possible.^[71]

Geoffrey A. Landis of NASA's Glenn Research Center states that a laser-powered interstellar sail ship could possibly be launched within 50 years, using new methods of space travel. "I think that ultimately we're going to do it, it's just a question of when and who," Landis said in an interview. Rockets are too slow to send humans on interstellar missions. Instead, he envisions interstellar craft with extensive sails, propelled by laser light to about one-tenth the speed of light. It would take such a ship about 43 years to reach Alpha Centauri if it passed through the system. Slowing down to stop at Alpha Centauri could increase the trip to 100 years,^[72] whereas a journey without slowing down raises the issue of making sufficiently accurate and useful observations and measurements during a fly-by.

100 Year Starship study

The 100 Year Starship (100YSS) is the name of the overall effort that will, over the next century, work toward achieving interstellar travel. The effort will also go by the moniker 100YSS. The 100 Year Starship study is the name of a one-year project to assess the attributes of and lay the groundwork for an organization that can carry forward the 100 Year Starship vision.

Harold ("Sonny") White^[73] from NASA's Johnson Space Center is a member of Icarus Interstellar,^[74] the nonprofit foundation whose mission is to realize interstellar flight before the year 2100. At the 2012 meeting of 100YSS, he reported using a laser to try to warp spacetime by 1 part in 10 million with the aim of helping to make interstellar travel possible.^[75]

Other designs

• Project Orion, manned interstellar ship (1958–1968).
• Project Daedalus, unmanned interstellar probe (1973–1978).
• Starwisp, unmanned interstellar probe (1985).^[76]
• Project Longshot, unmanned interstellar probe (1987–1988).
• Starseed/launcher, fleet of unmanned interstellar probes (1996)
• Project Valkyrie, manned interstellar ship (2009)
• Project Icarus, unmanned interstellar probe (2009–2014).
• Sun-diver, unmanned interstellar probe^[77]
• Breakthrough Starshot, fleet of unmanned interstellar probes, announced in April 12, 2016.

Non-profit organizations

A few organisations dedicated to interstellar propulsion research and advocacy for the case exist worldwide. These are still in their infancy, but are already backed up by a membership of a wide variety of scientists, students and professionals.

• 100 Year Starship ^[81]
• Icarus Interstellar ^[74]
• Tau Zero Foundation (USA) ^[82]
• Initiative for Interstellar Studies (UK) ^[83]
• Fourth Millennium Foundation (Belgium) ^[84]
• Space Development Cooperative (Canada) ^[85]

Feasibility

The energy requirements make interstellar travel very difficult. It has been reported that at the 2008 Joint Propulsion Conference, multiple experts opined that it was improbable that humans would ever explore beyond the Solar System.^[86] Brice N. Cassenti, an associate professor with the Department of Engineering and Science at Rensselaer Polytechnic Institute, stated that at least 100 times the total energy output of the entire world [in a given year] would be required to send a probe to the nearest star.^[86]

Astrophysicist Sten Odenwald stated that the basic problem is that through intensive studies of thousands of detected exoplanets, most of the closest destinations within 50 light years do not yield Earth-like planets in the star's habitable zones.^[87] Given the multi-trillion-dollar expense of some of the proposed technologies, travelers will have to spend up to 200 years traveling at 20% the speed of light to reach the best known destinations. Moreover, once the travelers arrive at their destination (by any means), they will not be able to travel down to the surface of the target world and set up a colony unless the atmosphere is non-lethal. The prospect of making such a journey, only to spend the rest of the colony's life inside a sealed habitat and venturing outside in a spacesuit, may eliminate many prospective targets from the list.

Moving at a speed close to the speed of light and encountering even a tiny stationary object like a grain of sand will have fatal consequences. For example, a gram of matter moving at 90% of the speed of light contains a kinetic energy corresponding to a small nuclear bomb (around 30kt TNT).

Interstellar missions not for human benefit

Explorative high-speed missions to Alpha Centauri, as planned for by the Breakthrough Starshot initiative, are projected to be realizable within the 21st century.^[88] It is alternatively possible to plan for unmanned slow-cruising missions taking millennia to arrive. These probes would not be for human benefit in the sense that one can not foresee whether there would be anybody around on earth interested in then back-transmitted science data. An example would be the Genesis mission,^[89] which aims to bring unicellular life, in the spirit of directed panspermia, to habitable but otherwise barren planets.^[90] Comparatively slow cruising Genesis probes, with a typical speed of ${\displaystyle c/300}$, corresponding to about ${\displaystyle 1000\,{\mbox{km/s}}}$, can be decelerated using a magnetic sail. Unmanned missions not for human benefit would hence be feasible ^[91]

Discovery of Earth-Like planets

In February 2017, NASA has announced the discovery of 7 Earth-like planets in the TRAPPIST-1 system orbiting an ultra-cool dwarf star 40 light-years away from our solar system.^[92] NASA's Spitzer Space Telescope has revealed the first known system of seven Earth-size planets around a single star. Three of these planets are firmly located in the habitable zone, the area around the parent star where a rocky planet is most likely to have liquid water. The discovery sets a new record for greatest number of habitable-zone planets found around a single star outside our solar system. All of these seven planets could have liquid water – the key to life as we know it – under the right atmospheric conditions, but the chances are highest with the three in the habitable zone.

Robots in the bloodstream: the promise of nanomedicine

February 26, 2002 by Robert A. Freitas Jr.
Original link:  http://www.kurzweilai.net/robots-in-the-bloodstream-the-promise-of-nanomedicine

In just a few decades physicians could be sending tiny machines into our bodies to diagnose and cure disease. These nanodevices will be able to repair tissues, clean blood vessels and airways, transform our physiological capabilities, and even potentially counteract the aging process.

It is the year 2031, and the age of advanced nanomedicine has arrived. A young man arrives at his physician’s office with a mild fever, nasal congestion, discomfort and a cough. The physician pulls from her pocket a lightweight, handheld device resembling a pocket calculator. She unsnaps from it a cordless, self-sterilizing, pencil-sized probe and inserts it into the patient’s mouth as if it were a tongue depressor. On the tip of the probe are billions of molecular assay receptors, mounted on hundreds of self-guiding retractile stalks. Each receptor is sensitive to the chemical signature of a specific kind of bacterium or virus. “Ahhh,” says the patient, and a few seconds later a three-dimensional, color-coded map of his throat appears on the display panel of the device. Beneath the map scroll columns of data, revealing the unique molecular signature of a known and unwelcome bacterial pathogen.

With the diagnosis complete, the infectious microorganism can be exterminated. No need for antihistamines, cough drops and a week-long course of antibiotics. The physician keeps several generic classes of nanorobots in her office for just such a circumstance. Using a desktop appliance in her office, she programs billions of nanorobots to find, recognize and destroy the particular microbial strain. The nanomachines are suspended in a carrier fluid that the patient inhales into his lungs, after which the mobile devices march down the patient’s throat, propelled on tiny legs. Following a search pattern, the nanorobots ingest and destroy the harmful bacteria they encounter using mechanical and chemical phagocytosis. The patient feels nothing: nanorobots are the size of bacteria, which constantly crawl on and inside the body without ever being noticed. After several minutes, the physician activates an acoustic homing beacon to guide the nanorobots back into the patient’s mouth, where she retrieves them through a collection port on the tip of the homing device. A further survey with the original diagnostic probe reveals no evidence of the pathogen.

This is a wonderful vision of medicine in the future, but how do we get there from here? Nanotechnology (“nano” from the Greek word for dwarf) involves engineering and manufacturing at the molecular, or nanometer, level. One nanometer is one billionth of a meter, about the width of six bonded carbon atoms. How does one build at this scale?

Scientists at New York University have adopted the self-assembly approach, and have succeeded in producing complementary strands of DNA that can zip themselves into complex structures. They have built cubes, octahedra and other solids made of just a few thousand nucleotides each, by the billions per batch. Meanwhile at Cornell University, researchers have genetically engineered a natural biomotor normally found in the enzyme ATPase to allow it to incorporate nonbiological parts such as a silicon nitride bar 100 nanometers in length, making the first artificial hybrid nanomotor (see ‘In Pictures’ side panel, 1). In a microscopic video presentation, dozens of bars attached to artificial molecular motors in a large precise array could be seen spinning at 200 revolutions per minute, like a field of tiny propellers.

Another way to build at the molecular level is by positional assembly – picking and placing molecular parts exactly where you want them. A device capable of positional assembly would work much like the robot arms that manufacture cars on automobile assembly lines, or like the ribosome that assembles amino acids one by one into proteins in our cells. The US engineering firm Zyvex Corp. [for whom the author works as a research scientist] is aiming to be the first to create an artificial molecular assembler using positional assembly to manufacture atomically precise structures.

Elsewhere, researchers at Harvard University have constructed the first general-purpose “nanotweezers,” using a pair of electrically controlled carbon nanotubes (side panel, 2). These have successfully grasped 300-nanometer clusters of polystyrene spheres and extracted a single semiconductor wire 20 nanometers wide from a mass of entangled wires. The scientists hope eventually to produce nanotweezers small enough to grab individual large molecules.

Such nanoresearch will eventually lead to applications affecting almost every aspect of modern life, including the home, transport, computers, energy and the environment. Some of the most important and life-changing applications, however, are likely to be seen in medicine. We may see the first nanomedical materials and devices in use within the next few years. Scientists at the University of Michigan’s Center for Biologic Nanotechnology are currently pursuing the use of dendrimers as a safer and more effective genetic therapy agent. Dendrimers (side panel, 3) are branching synthetic molecules that can be grown nanometer by nanometer to reach the desired size. They take on a spherical shape, and have sufficiently large openings and cavities to carry small molecules – dendrimers could therefore be used to sneak DNA into cells without triggering an immune response. At the same center, researchers have reported using dendrimer “nanodecoys” to trap and deactivate influenza virus particles.

Relatively simple nanodevices could soon offer cures for major conditions such as diabetes. Researchers at Ohio State University and the University of Illinois have managed to construct silicon-based microcapsules highly perforated with “nanopores,” each as small as 20 nanometers in diameter. These pores are large enough to allow small molecules such as oxygen, glucose and insulin to pass through, but are small enough to impede the passage of much larger immune system molecules such as immunoglobulins. Microcapsules containing islet cells could be implanted beneath the skin of some diabetes patients, temporarily restoring the body’s delicate glucose control feedback loop without the need for powerful immuno-suppressants that can leave the patient at serious risk for infection. The same method of encapsulation could be used to treat other enzyme- or hormone-deficiency diseases. Encapsulated neurons could also be implanted in the brain and then electrically stimulated to release neurotransmitters, possibly as part of a future treatment for Alzheimer’s or Parkinson’s disease.

Artificial “biobots” could be in our bodies within five to 10 years. Advances in genetic engineering are likely to allow us to construct an artificial microbe – a basic cellular chassis – to perform certain functions. These biobots could be designed to produce vitamins, hormones, enzymes or cytokines in which the host body was deficient, or they could be programmed to selectively absorb and break down poisons and toxins. A new company called engeneOS, Inc., founded in late 2000, has already announced plans to develop artificial Engineered Genomic Operating Systems using the techniques of molecular biology. These systems will comprise a library of component device modules and proprietary modular components. This will allow the engineering and construction of programmable biobots with novel form and function.

The greatest power of nanomedicine will emerge in the longer term, perhaps 10-20 years from now, when we learn how to design and construct complete artificial nanorobots using strong diamond-like materials, nanometer-scale parts, and onboard subsystems including sensors, motors, manipulators, power plants, and molecular computers.

One example is an artificial mechanical cell called a respirocyte, which could be used to keep a patient’s tissues safely oxygenated for up to about four hours (at maximum dosage) if their heart has stopped beating. These cells (side panel, 4) could also enable a healthy person to sprint at top speed for at least 15 minutes without breathing, or to sit underwater at the bottom of a swimming pool for hours. Still entirely theoretical, the respirocyte is a micron-wide spherical nanorobot made of 18 billion atoms precisely arranged in a diamondoid structure to form a tiny 1,000-atmosphere pressure tank. Several billion molecules of oxygen and carbon dioxide can be absorbed into, or released from, this tank using computer-controlled molecular pumps powered by serum glucose and oxygen. External gas concentration sensors would allow respirocytes to mimic the action of the natural hemoglobin-filled red blood cells, with oxygen released and carbon dioxide absorbed in the tissues, and vice versa in the lungs. Each respirocyte would be able to hold 200 times more gas per unit volume than a natural red cell, so a few cubic centimeters injected into the human bloodstream would exactly replace the gas carrying capacity of the patient’s entire 5.4 liters of blood.

Other proposed medical nanorobots offer equally astonishing performance improvements over nature. For instance, micron-size artificial mechanical platelets could allow complete hemostasis (control of bleeding by clot formation) in just one second, even for moderately large wounds, a response time 100-1,000 times faster than the natural system. This would be achieved by rapidly unfurling a compactly stowed onboard biodegradable mesh under the control of an onboard computer. These “clottocytes” would be about 10,000 times more effective as clotting agents than an equal volume of natural platelets.

Nanorobotic phagocytes called microbivores could patrol the bloodstream, seeking out and digesting unwanted pathogens including bacteria, viruses or fungi. Each nanorobot could completely destroy one pathogen in just 30 seconds – about 100 times faster than natural leukocytes or macrophages – releasing a harmless effluent of amino acids, mononucleotides, fatty acids and sugars. No matter that a bacterium has acquired multiple drug resistance to antibiotics or to any other traditional treatment. The microbivore will eat it anyway, achieving complete clearance of even the most severe septicemic infections in minutes to hours, as compared to weeks or even months for antibiotic-assisted natural phagocytic defenses, without increasing the risk of sepsis or septic shock. Related nanorobots could be programmed to recognize and digest cancer cells, or to clear circulatory obstructions within minutes in order to rescue stroke patients from ischemic damage.

More sophisticated medical nanorobots will be able to intervene at the cellular level, performing surgery within cells. Physician-controlled nanorobots could extract existing chromosomes from a diseased cell and insert newly manufactured ones in their place, a process called chromosome replacement therapy. This would allow a permanent cure of any pre-existing genetic disease, and permit cancerous cells to be reprogrammed to a healthy state.

In recent years, many gerontologists have begun to think of aging as a genetic disease that might be cured. New evidence from the Human Genome Project suggests that just a few hundred genes at most may be directly involved in aging. If we can completely understand these few genes and how they work, we may be able to alter them to eliminate this unwanted syndrome. Using cytosurgical nanorobots, corrected genes could be installed in every one of the 10 trillion tissue cells in our bodies. We would then no longer naturally age, and our bodies would again repair themselves as well as they did when we were children.

Although nanotechnology is in its infancy, researchers are steadily making major breakthroughs. If we can learn to harness and precisely control the ability to manipulate molecules, then many aspects of our lives will change forever. In particular, the ability to carry out medical procedures at the molecular level will revolutionize medical practice. The next few decades will be very interesting indeed.

Copyright 2001, Pathways, The Novartis Journal. Reprinted with permission.
www.novartis.com/pathways

SpaceX to attempt five recoveries in less than two weeks as fleet activity ramps up

written by Michael Baylor July 19, 2018

Original link:  https://www.nasaspaceflight.com/2018/07/spacex-five-recoveries-less-two-weeks-fleet-activity/

 

Begining July 22nd, SpaceX is currently scheduled to perform three Falcon 9 droneship recoveries, a fairing recovery, and a Dragon recovery in less than two weeks. A total of five recoveries in short succession paves the way for an unprecedented amount of activity from SpaceX’s fleet of recovery vessels.


The fleet operates out of the Port of LA in California to support Vandenberg launches and Port Canaveral in Florida to support Cape launches. Dragon recoveries are also executed out of the Port of LA.

In total, the current fleet consists of one Fast Supply Vessel (FSV), four smaller crew boats, and two Autonomous Spaceport Droneships (ASDS or droneship). Additionally, a tugboat is also required to tow each ASDS.

The SpaceX fleet of vessels in Port Canaveral.

Credit: Julia Bergeron

The boats are owned and operated by other companies for SpaceX – a common practice in the maritime industry.

First Stage Recoveries:

When a Falcon 9 or Falcon Heavy core is unable to return to land due to the mission’s requirements, SpaceX will often position an ASDS downrange to allow for a first stage recovery. While the ASDS is the landing platform, it is not the only ship required to enable a recovery.

First of all, the droneships do not make the journey out to sea by themselves. They only operate autonomously when holding their position ahead of a landing attempt. As a result, the droneships are towed by a tug when being transported to and from the landing location.

Over the past year, the tugboat Hawk has been supporting nearly all of the Cape based missions which utilized the droneship Of Course I Still Love You (OCISLY). The only exception to this were the two most recent OCISLY recoveries.

The tug Rachel arrives in Port Canaveral towing OCISLY. The

booster on the droneship is B1046 – the first Block 5 core.

Credit: Julia Bergeron

During the TESS and Bangabandhu missions, Hawk was in Tampa Bay for maintenance. Therefore, the tug Rachel was utilized. Hawk has since finished her maintenance and is towing OCISLY for the upcoming landing attempt during the Telstar 19V mission. The launch is currently scheduled for no earlier than July 22nd.

As far as the west coast goes, the tugboat which pulls the droneship Just Read the Instructions (JRTI) has never been consistent. Furthermore, there has not been a JRTI landing since October 2017. Therefore, it is a complete mystery as to which tug will be used for the landing during the Iridium-7 mission on July 25th.

Apart from the tugboats, a crew boat is also needed to support the droneship recoveries. These vessels house the crew needed to secure the rocket post-landing. The boats also gather telemetry from the booster. The ship NRC Quest is used to support JRTI and GO Quest supports OCISLY.

For a typical mission, the droneship will leave port 3-4 days in advance of the landing attempt. The tugboat typically pulls the ASDS at approximately 6-8 knots. The crew boat is capable of traveling at a faster 8-10 knots, and thus sometimes leaves port a few hours after the droneship.

A tug tows JRTI back to port with NRC Quest accompanying

after the Iridium-3 mission. Credit: Sam Sun for NSF L2

When returning from a successful landing, the crew boat will accompany the droneship back to port so that the crew can assist the booster.

The crew boats may also be used when no landing is attempted, as SpaceX will often elect to perform experimental recovery tests during expendable missions. Therefore, the vessel will be deployed to collect telemetry from the later portions of the test when the Falcon 9 is out of range from the ground-based tracking stations.

As for the droneships themselves, while OCISLY has been regularly used over the past several months, JRTI has been out of action. This has been due to SpaceX’s regular use of flight-proven boosters for Vandenberg based missions. SpaceX has elected not to refly Block 3 and Block 4 cores more than once. Consequently, the boosters have been expended on their second flight.

The Iridium-7 launch will see JRTI return to action after approximately eight months on the sidelines. The mission will feature B1048 – a new Block 5 core.

On the east coast, fleet watchers have been eagerly awaiting the arrival of A Shortfall of Gravitas (ASoG). SpaceX CEO Elon Musk announced on Twitter earlier this year that a new droneship was under construction to support Falcon Heavy missions where both side boosters require a droneship.

OCISLY in Port Canaveral.

Credit: Brady Kenniston for NSF L2

Additionally, having two east coast droneships would enable a faster launch cadence. Afterall, it can take over a week for OCISLY to support a single recovery attempt. Therefore, if SpaceX wants to perform two missions requiring an ASDS landing in a short period of time, another droneship would be required.

However, it is now understood that the construction of ASoG has been temporarily paused.
The pause makes sense when considering SpaceX’s 2019 manifest. Earlier this year, the company’s president Gwynne Shotwell told CNBC that next year will see a decrease in the company’s launch cadence. The slip is due to a decline in the number of large geostationary communications satellites needing a launch.

Missions to a geostationary transfer orbit make up the majority of launches requiring a droneship recovery. Therefore, it is unlikely that two east coast droneships will be needed to support Falcon 9 over the next year or two.

Furthermore, there are also no known Falcon Heavy missions which would require the side boosters to land on droneships. With this in mind, there does not appear to be a short-term need for ASoG.

That being said, it is understood that ASoG remains part of SpaceX’s long-term plans.

Dragon Recoveries:

Currently, SpaceX’s Dragon cargo capsules return to Earth via parachute and splash down in the Pacific Ocean. They are then hoisted aboard NRC Quest – the same crew boat used to support JRTI.

The CRS-4 Dragon prepares for splashdown in the Pacific

Ocean. Credit: SpaceX

Next, after being unloaded at the Port of LA, Dragon is sent to SpaceX’s test facility in McGregor Texas. From there, Dragon returns to the Cape for its next mission.

To simplify the process, for the upcoming Dragon 2 missions, SpaceX will look to return the Dragon capsules off the east coast of Florida. This will allow Port Canaveral based GO Searcher to return the capsule, crew, and cargo to a location closer to the launch site.

At Cape Canaveral, SpaceX is currently constructing a new Dragon processing facility near the company’s landing zones. The new facility will eliminate the need to transport the capsule across the country after each mission.

Satellite imagery of the SpaceX landing zones and Dragon

processing facility construction via Planet Labs.

However, while the preferred landing location will off the east coast of Florida, SpaceX will still have the option of returning the capsules to the Pacific Ocean in the event that weather is not acceptable in the Atlantic.

Additionally, SpaceX is also looking into the option of landing the capsules in the Gulf of Mexico for additional flexibility. Earlier this year, the company filed for an FAA Reentry license to enable this possibility.

To support the important Crew Dragon missions, GO Searcher has been undergoing modifications. It recently returned to Port Canaveral with a large dome on its bridge – likely a new tool to aid the recovery process.

GO Searcher with her new modifications.

Credit: Marek Cyzio for NSF

On top of that, a few new structures have been built on GO Searcher’s deck which may potentially be used to house Dragon’s crew post-landing.

GO Searcher has been working with NASA to refine the recovery process for crewed missions. Several training sessions with a mock Crew Dragon capsule have been held off the coast of Florida. These sessions will help ensure that GO Searcher is prepared for the first east coast Dragon landing.

Currently, the first Dragon mission to land on the east coast is not confirmed. However, the most likely candidate is the first Dragon 2 flight designated Demonstration Mission-1 (DM-1). The mission is an uncrewed test flight for NASA’s Commercial Crew program and scheduled to launch later this year.

Fairing Recoveries:

In 2018, SpaceX has significantly ramped up their efforts to recover the fairing which protects the payload during launch. To do so, SpaceX plans to capture the fairing halves in a large net attached to a vessel.

Half of a payload fairing returns to Earth via parachute.

Credit: Elon Musk

For Florida launches, GO Pursuit has been deployed to support every launch featuring a fairing. However, the vessel is not equipped with a net, and therefore a full recovery is not possible. That being said, GO Pursuit can still monitor the fairing halves as they descend and lift them aboard after a soft splashdown in the Atlantic Ocean.

On the west coast, SpaceX has their first ship which is designed for the full recovery. The boat – named Mr. Steven – features a large net designed to catch the fairing halves. Musk describes the vessel as a “catcher’s mitt in boat form.”

Starting with the PAZ mission from Vandenberg last February, Mr. Steven has made an attempt at a catch on each west coast mission. To date, three full fairing recovery attempts have been made – all of them unsuccessful.

However, while Mr. Steven is yet to catch a fairing, SpaceX is making progress.

In recent launches, SpaceX has made noticeable improvements in the parafoil system which controls the fairing halves as they descend through the atmosphere. GO Pursuit and Mr. Steven are now regularly returning intact fairing halves to port albeit wet.

Mr. Steven at Berth 240 in the Port of LA.

Credit: Jack Beyer for NSF L2

To increase the odds of success in the future, Mr. Steven has been undergoing modifications at the Port of LA to allow for a net four times as large as the previous version. The construction has been taking place at Berth 240 – the same Berth which SpaceX has recently leased to build the next generation BFR rocket (Big Falcon Rocket).

So far, the modifications have progressed at a rapid pace with four new arms and a net all being assembled in a matter of days. Therefore, the new hardware is ready in time for the next Vandenberg launch on July 25th, when a Falcon 9 will launch the Iridium-7 mission.

In the meantime, Mr. Steven’s crew have been performing practice recovery operations. Data available on MarineTraffic.com showed that Mr. Steven performed what appeared to be a test run on June 28th, 2018.

Interestingly, a NOTAM was filed with the FAA for the location of Mr. Steven, potentially signaling that a fairing half may have been dropped from a helicopter as part of the test. Musk had previously stated on Twitter that fairing drop tests were going to be performed, but did not specify if Mr. Steven would be involved. However, it is known that the net construction was not completed at the time. Therefore, Mr. Steven’s crew would have had to let the fairing hit the water before collecting it.

NRC Quest was also in the vicinity of the apparent test – potentially to help monitor the results.

While Mr. Steven has performed numerous test runs in the past, this was the first to appear to have a corresponding NOTAM and the first to have NRC Quest accompanying Mr. Steven.

More recently, Mr. Steven has been conducting practice sessions with the addition of the new net. MarineTraffic data has shown Mr. Steven executing numerous tight turns and dramatic changes of speed. Additionally, a drone video has also been captured which shows Mr. Steven operating in reverse.

Brian Herbert, a Senior Dynamic Positioning Officer (SDPO) on a Well Intervention Vessel has had personal interactions with Mr. Steven and its crew before SpaceX leased the ship. NASASpaceflight.com interviewed him last February to learn more about Mr. Steven’s capabilities. He stated that “the vessel’s maneuverability, large deck size, and high rate of speed would be her best assets in a fairing recovery operation.”

Herbert also explained that Mr. Steven has three modes of control. The first mode is manual controls which can be used with “main propulsion to travel at a high rate of speed and steer like a ship.” Next, Dynamic Position (DP) mode is where “a computer system operates the thrusters and propulsion system to hold a location or make maneuvers.”

“The third method is Joystick mode, where the vessel operator (Captain or mate) uses a joystick to operate the thrusters and propulsion systems in unison – giving the vessel commands along 3 axes using the joystick controller.” It is this mode that Herbert believes is the best suited for a fairing recovery operation.

Once SpaceX has refined the fairing recovery process using Mr. Steven, the next step will be to enable recoveries on the east coast. The amount of ships needed is not yet known, as it has not been confirmed if Mr. Steven is capable of recovering both fairing halves in on mission or if two ships are needed for a full recovery.

However, it is highly unlikely that GO Pursuit is capable of being converted into a fairing recovery ship. This is due to the vessels slower top speed and smaller size relative to Mr. Steven.

If only one ship is needed for a recovery, then SpaceX would simply need to add one more ship to their fleet. If two ships are needed, SpaceX will have to add three new boats to their fleet – one on the west coast and two on the east coast.

Five recoveries in two weeks:

Between July 22nd and August 3rd, SpaceX is currently scheduled to perform five recoveries (three Falcon 9 first stages, one Dragon, and one fairing) and two fairing collection tests in less than two weeks.

Hawk prepares to depart Port Canaveral with OCISLY ahead

of the Telstar 19V mission. Credit: Julia Bergeron

Wednesday morning, Hawk towed OCISLY out of Port Canaveral and began the journey down range to support the first stage landing during the Telstar 19V mission on July 22nd. GO Quest and GO Pursuit also left port a few hours later.

As usual, GO Quest will be supporting OCISLY during the first stage landing. GO Pursuit will perform additional fairing recovery testing by attempting to collect the fairing halves after they splashdown in the Atlantic Ocean. As GO Pursuit is not capable of catching a fairing half like Mr. Steven, this event is not counted as a full recovery attempt.

Following the Telstar 19V mission, Hawk, OCISLY, GO Pursuit, and GO Quest will race back to port to unload the rocket hardware and prepare for their next recovery operation during the Telkom-4 (Merah Putih) mission. Telkom-4 is scheduled to launch on August 2nd, and the east coast recovery fleet will perform a nearly identical operation to the Telstar 19V mission. If the schedule holds, less than eleven days will separate Telstar 19V and Telkom-4 – making this SpaceX’s fastest turnaround of a droneship.

Mr. Steven will attempt the first fairing recovery with an

enlarged net during the Iridium-7 mission.

Credit: Jack Beyer for NSF L2

In the meantime, SpaceX’s west coast fleet will be supporting the Iridium-7 recoveries on July 25th. During this mission, the first stage will attempt to land on JRTI which will be assisted by the crew boat NRC Quest. Additionally, Mr. Steven will attempt to recover a fairing half. This fairing recovery attempt will be the first with Mr. Steven’s larger net and the first to be executed in darkness.

Furthermore, the Iridium-7 launch will also be the first to feature both first stage and fairing recovery attempts.

Finally, following the Iridium-7 mission, NRC Quest will race back to port to prepare for the final recovery of the two week period. The Dragon capsule from the CRS-15 resupply mission will splashdown in the Pacific Ocean on August 3rd. Following the splashdown, NRC Quest will lift Dragon onto her deck before returning the spacecraft to the Port of LA.