New Glenn

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https://en.wikipedia.org/wiki/New_Glenn

 

 

New Glenn
rocket developed by Blue Origin
Illustration of New Glenn
Use	Partially reusable orbital launcher
Manufacturer	Blue Origin
Country of origin	United States
Size
Height	98 m (322 ft)
Diameter	7 m (23 ft)
Stages	2
Payload to low Earth orbit (LEO)
Mass	45,000 kg (99,000 lb)
Payload to geostationary transfer orbit (GTO)
Mass	13,600 kg (30,000 lb)
Launch history
Status	In development
Launch sites	Cape Canaveral, LC-36 Vandenberg Air Force Base
First flight	Late 2022 (planned)
First stage
Height	57.5 m (189 ft)
Diameter	7 m (23 ft)
Powered by	7 × BE-4
Maximum thrust	17.1 MN (3,850,000 lbf)
Propellant	CH4 / LOX
Second stage
Height	16.1 m (53 ft) tank section, 23.4 m (77 ft) including the two high expansion ratio nozzle BE-3Us
Diameter	7 m (23 ft)
Powered by	2 × BE-3U
Maximum thrust	1,400 kN (320,000 lbf)
Propellant	LH2 / LOX

New Glenn, named after NASA astronaut John Glenn, is a heavy-lift orbital launch vehicle in development by Blue Origin. Design work on the vehicle began in 2012. Illustrations of the vehicle, and the high-level specifications, were initially publicly unveiled in September 2016. New Glenn is described as a two-stage rocket with a diameter of 7 m (23 ft). Its first stage will be powered by seven BE-4 engines that are also being designed and manufactured by Blue Origin.

Like the New Shepard suborbital launch vehicle that preceded it, the New Glenn's first stage has been designed to be reusable since inception in 2016. In 2021, the company initiated conceptual design work on approaches to potentially make the second stage reusable as well, with the project codenamed Project Jarvis.

Originally aiming for first launch in 2020, by 2018, Blue Origin expected to launch New Glenn in 2021. In February 2021, Blue Origin delayed the target date for the first launch to no earlier than the fourth quarter of 2022.

History

After initiating the development of an orbital rocket system prior to 2012, and stating in 2013 on their website that the first stage would do a powered vertical landing and be reusable, Blue Origin publicly announced their orbital launch vehicle intentions in September 2015. In January 2016, Blue Origin indicated that the new rocket would be many times larger than New Shepard even though it would be the smallest of the family of Blue Origin orbital vehicles. Blue Origin publicly released the high-level design of the vehicle and announced the name New Glenn — with both two-stage and three-stage variants planned — in September 2016.

Early development work on orbital subsystems

Blue Origin began developing systems for orbital human spacecraft prior to 2012. A reusable first-stage booster was projected to fly a suborbital trajectory, taking off vertically like the booster stage of a conventional multistage launch vehicle. Following stage separation, the upper stage would continue to propel astronauts to orbit while the first-stage booster would descend to perform a powered vertical landing similar to its New Shepard suborbital vehicle. The first-stage booster was to be refueled and relaunched to reduce costs of access for humans to space.

The booster launch vehicle was projected to lift Blue Origin's biconic Space Vehicle capsule to orbit, carrying astronauts and supplies. After completing its mission in orbit, the Space Vehicle was designed to reenter Earth's atmosphere and land under parachutes on land, to be reused on future missions.

Engine testing for the (then named) Reusable Booster System (RBS) launch vehicle began in 2012. A full-power test of the thrust chamber for Blue Origin BE-3 liquid oxygen/liquid hydrogen upper-stage rocket engine (BE-3U) was conducted at a John C. Stennis Space Center (NASA test facility) in October 2012. The chamber successfully achieved full thrust of 100,000 lbf (about 440 kN). By early 2018, it was announced that the BE-3U hydrolox engine would power the second stage of the New Glenn.

Orbital launch vehicle

Design work on the vehicle began in 2012, with the beginning of BE-4 engine development. Further plans for an orbital launch vehicle were made public in 2015. By March 2016, the launch vehicle was referred to by the placeholder name of "Very Big Brother". It was stated to be a two-stage-to-orbit liquid-propellant rocket, with the launcher intended to be reusable. In early 2016, Blue Origin indicated that the first orbital launch was expected no earlier than 2020 from the Florida launch facility, and in September 2017 continued to forecast a 2020 debut. In a February 2016 interview, Blue Origin president Rob Meyerson referred to engine development and orbital launch vehicle milestones.

The vehicle itself, and the high-level specifications, were initially publicly unveiled in September 2016. New Glenn was described as a 7 m (23 ft) in diameter, two- or three-stage rocket, with the first and second stages being liquid methane/liquid oxygen (methalox) designs using Blue Origin engines. The first stage is planned to be reusable and will land vertically, just like the New Shepard suborbital launch vehicle that has been flying suborbitally since the early 2010s. Although these plans would subsequently change, the 2016 plans called for the first stage to be powered by seven of Blue Origin's BE-4 single-shaft oxygen-rich staged combustion liquid methane/liquid oxygen rocket engines, the second-stage to be powered by a single vacuum-variant of the BE-4 (BE-4U) and the third stage to use a single BE-3 hydrolox engine. In 2016, the first stage was planned to be designed to be reused for up to 100 flights. Blue Origin announced that they intended to launch the rocket from Launch Complex 36 (LC-36), and manufacture the launch vehicles at a new facility to be built on nearby land in Exploration Park. Acceptance testing of the BE-4 engines was also announced to be planned for Florida.

Blue explained in the 12 September 2016 announcement that the rocket would be named New Glenn in honor of the first American astronaut to orbit the Earth, John Glenn. Three weeks of wind tunnel testing of a scale model New Glenn were completed in September 2016 in order to validate the CFD design models of transonic and supersonic flight.

In March 2017, Jeff Bezos showed graphics of the New Glenn which had two large strakes at the bottom of the booster. In the September 2017 announcement, Blue announced a much larger payload fairing for New Glenn, this one 7 m (23 ft) in diameter, up from 5.4 m (18 ft) in the originally announced design.

By March 2018, the launch vehicle design had changed. It was announced that the New Glenn second stage will now be powered by two vacuum versions of the flight proven BE-3 liquid hydrogen/liquid oxygen rocket engine (BE-3U) with a single BE-3U engine for the third stage deep space option. The three stage booster variant was subsequently cancelled completely in January 2019. By mid-2018, the low-level design was not yet complete and the likelihood of achieving an initial launch by 2020 was being called into question by company engineers, customers, industry experts, and journalists. In October 2018, the Air Force announced Blue Origin was awarded US$500 million for development of New Glenn as a potential competitor in future contracts, including Evolved Expendable Launch Vehicle (EELV) Phase 2. The October 2018 award was terminated in December 2020 after receiving US$255.5 million of the US$500 million.

By February 2019, several launches for New Glenn had been contracted: five for OneWeb, an unspecified amount of Telesat, one each for Eutelsat, mu Space Corp and SKY Perfect JSAT.^] In February 2019, Blue Origin indicated that no plans to build a reusable second stage were on the company's roadmap. In the event, by July 2021, Blue was evaluating options for getting to a reusable second-stage design: Project Jarvis.

In August 2020 the Air Force announced that New Glenn was not selected for the National Security Space Launch Phase 2 launch procurement. Due to this, in February 2021 Blue Origin announced that the first flight would now be targeted for late 2022.

By December 2020, Blue Origin indicated that the BE-4 engine delivery to ULA would slip to summer 2021, and ULA disclosed that the first launch of the New Glenn competitor ULA Vulcan Centaur would now be no earlier than 4Q 2021. Blue announced a further schedule slip for the first launch of New Glenn in March 2021 when the company said New Glenn "would not launch until the fourth quarter of 2022, at the earliest."

By 2021, Blue had reduced the published reuse specification for New Glenn to a minimum of 25 flights, from previously stating in 2016 that they were planning the design to support up to 100 flights.

Project Jarvis

See also: Blue Origin § Project Jarvis

Information became public in July 2021 that Blue Origin had begun a "project to develop a fully reusable upper stage for New Glenn," Project Jarvis. A principal goal of the project is to reduce the overall launch cost of New Glenn by gaining an operational capacity to reuse second stages, just as SpaceX is aiming to do with their Starship second stage by building a fully-reusable orbital launch vehicle. If Blue is able to realize such a second stage design, and bring it into operational use, it would substantially bring down the cost of launches of the New Glenn system.

Beyond the technical changes indicated, Bezos has created a new management structure for the new efforts, walling off "parts of the second-stage development program from the rest of Blue Origin [telling] its leaders to innovate in an environment unfettered by rigorous management and paperwork processes." No budget has been publicly released.

One part of the effort is focusing on developing a stainless steel propellant tank and main structure for the second stage rocket, and evaluating it as a part of a solution for a complete second stage system. By 24 August, Blue had rolled a stainless steel test tank to their Launch Complex 36 facility, on which ground pressure testing with cyrogenic propellants could begin as early as September.

In addition to the Jarvis team working on a new second stage tank design, Blue Origin has set up another team to focus on design approaches that might be used to make a New Glenn second stage reusable, something that was not a design objective for the original second stage for New Glenn prior to 2021. As of August 2021, three approaches are being explored: adding wings to allow the stage to operate as a spaceplane on reentry; using an aerospike engine on the second stage that could double as a heat shield on reentry; and an approach similar to SpaceX's Starship concept using high-drag flaps in combination with propulsive deceleration. A decision on which approach to take into full development is slated for later in 2021.

Description and technical specifications

The first hotfire-tested Blue Origin BE-4 rocket engine, serial number 103, at the 34th Space Symposium in Colorado Springs, Colorado, April 2018, showing the liquid methane inlet side of the engine.

The New Glenn is a 7 m (23 ft) in diameter two-stage orbital launch vehicle with a reusable first stage  and an expendable second stage. An optional third stage was envisaged with a single BE-3U engine, and was planned as of October 2018.

The first stage is designed to be reusable for a minimum of 25 flights, and will land vertically, a technology previously developed by Blue Origin and tested in 2015–2016 on its New Shepard suborbital launch vehicle. The second stage will share the same diameter as the first and use two BE-3U vacuum optimized engines. It will use hydrogen/oxygen as propellant and will be expendable. This engine is manufactured by Blue Origin. The company has revealed the planned full operational payload capacity of the two-stage version of New Glenn as 13,000 kg (29,000 lb) to GTO and 45,000 kg (99,000 lb) to a 51.6° inclined LEO, though the initial operating capability may be somewhat lower. Dual-satellite launches will be offered after the first five flights.

Both stages will use orthogrid aluminum tanks with welded aluminum domes and common bulkheads. Both stages will also use autogenous pressurization. The first stage will be powered by seven BE-4 methane/oxygen engines — designed and manufactured by Blue Origin — producing 17,000 kN (3,800,000 lb_f) of liftoff thrust. The second stage will be powered by two BE-3U engines, also designed and manufactured by Blue Origin. BE-3Us are an expander cycle variant of the BE-3 engine, which are explicitly designed for use in upper stages. Preliminary design numbers from 2015 projected the BE-3U to have a vacuum thrust of 670 kN (150,000 lb_f).

Launches of the New Glenn are planned to be made from Launch Complex 36 (LC-36), which was leased to Blue Origin in 2015. A launch site at Vandenberg Space Force Base is also planned. New Glenn will also be available for space tourism flights, with priority given to customers of New Shepard. The first stage boosters of New Glenn are intended to be reusable, and will be recovered downrange on the Atlantic Ocean via their landing platform ship Jacklyn, which will be acting as a floating movable landing platform. The hydrodynamically-stabilized ship increases the likelihood of successful recovery in rough seas.

Manufacturing

The main assembly of the New Glenn launch vehicle will occur in the Blue Origin rocket manufacturing facility in Florida, near Launch Complex 36 (LC-36) which the company leased from Spaceport Florida. Launch Complex 36 (LC-36) has hosted more than 100 launches, formerly launching the Atlas II and Atlas III.

Tooling and equipment for the factory began to be ordered and built in 2015. In July 2018, the build of the largest device, a 16 m (52 ft) tall × 41 m (135 ft) long × 13 m (43 ft) wide Ingersoll "Mongoose" cryogenic-tank and fairing fabrication machine, was completed after a three-year design/build process. It will be installed in the Florida facility in Exploration Park later in 2018. As of September 2018, Blue Origin had invested over US$1 billion in its Florida manufacturing facility and launch site, and intends to spend much more going forward.

Launch services

Blue will offer both single-payload dedicated flights and, after the fifth launch, dual-manifesting of large communications satellites to be transported to geostationary transfer orbit (GTO). All contracted launches from the start will feature a reusable first-stage, so just like the practice in commercial aircraft transport, landing conditions can affect the timing and flight parameters of a launch.

Launch service customers

By 2018, Blue Origin had contracts in place with four customers for New Glenn flights. Eutelsat, Thailand startup mu Space Corp and SKY Perfect JSAT have geosynchronous orbit communications satellite launches planned after 2020, while internet satellite constellation fleet operator OneWeb has an agreement for five launches.

In January 2019, Telesat signed a multi-launch contract "to launch satellites for its future low-Earth-orbit broadband constellation on multiple New Glenn missions" and thus is Blue's fifth customer.

Schedule-oriented launch cadence

Blue intends to contract for launch services a bit differently than contract options that have been traditionally offered in the commercial launch market. The company has stated they will contract to aim to have a regular launch cadence of up to eight times a year. If one of the payload providers for a multi-payload launch is not ready on time, Blue will hold to the launch timeframe, and fly the remaining payloads on time at no increase in price. This is different from how dual-launch manifested contracts have been traditionally handled by Arianespace (Ariane 5 and Ariane 6) and Mitsubishi Heavy Industries (H-IIA and H3). SpaceX and International Launch Services can offer dual-launch contracts, but prefer dedicated missions.

Funding

The development and manufacture of the New Glenn is being funded by Jeff Bezos, founder of Amazon.com, and the Department of the Air Force. Initially funded entirely by Bezos, after 2019 New Glenn will also receive US$500 million in funding under the United States Space Force National Security Space Launch (NSSL) program. By September 2017, Bezos had invested US$2.5 billion into New Glenn.

Single-stage-to-orbit

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Single-stage-to-orbit 

 

The VentureStar was a proposed SSTO spaceplane.

A single-stage-to-orbit (or SSTO) vehicle reaches orbit from the surface of a body using only propellants and fluids and without expending tanks, engines, or other major hardware. The term usually, but not exclusively, refers to reusable vehicles. To date, no Earth-launched SSTO launch vehicles have ever been flown; orbital launches from Earth have been performed by either fully or partially expendable multi-stage rockets.

The main projected advantage of the SSTO concept is elimination of the hardware replacement inherent in expendable launch systems. However, the non-recurring costs associated with design, development, research and engineering (DDR&E) of reusable SSTO systems are much higher than expendable systems due to the substantial technical challenges of SSTO, assuming that those technical issues can in fact be solved. SSTO vehicles may also require a significantly higher degree of regular maintenance.

It is considered to be marginally possible to launch a single-stage-to-orbit chemically-fueled spacecraft from Earth. The principal complicating factors for SSTO from Earth are: high orbital velocity of over 7,400 metres per second (27,000 km/h; 17,000 mph); the need to overcome Earth's gravity, especially in the early stages of flight; and flight within Earth's atmosphere, which limits speed in the early stages of flight and influences engine performance.

Advances in rocketry in the 21st century have resulted in a substantial fall in the cost to launch a kilogram of payload to either low Earth orbit or the International Space Station, reducing the main projected advantage of the SSTO concept.

Notable single stage to orbit concepts include Skylon, which used the hybrid-cycle SABRE engine that can use oxygen from the atmosphere when it is in low altitude, and then using onboard liquid oxygen after switching to the closed cycle rocket engine in high altitude, the McDonnell Douglas DC-X, the Lockheed Martin X-33 and VentureStar which was intended to replace the Space Shuttle, and the Roton SSTO, which is a helicopter that can get to orbit. However, despite showing some promise, none of them has come close to achieving orbit yet due to problems with finding a sufficiently efficient propulsion system and discontinued development.

Single-stage-to-orbit is much easier to achieve on extraterrestrial bodies that have weaker gravitational fields and lower atmospheric pressure than Earth, such as the Moon and Mars, and has been achieved from the Moon by the Apollo program's Lunar Module, by several robotic spacecraft of the Soviet Luna program, and by China's Chang'e 5.

History

Early concepts

ROMBUS concept art

Before the second half of the twentieth century, very little research was conducted into space travel. During the 1960s, some of the first concept designs for this kind of craft began to emerge.

One of the earliest SSTO concepts was the expendable One stage Orbital Space Truck (OOST) proposed by Philip Bono, an engineer for Douglas Aircraft Company. A reusable version named ROOST was also proposed.

Another early SSTO concept was a reusable launch vehicle named NEXUS which was proposed by Krafft Arnold Ehricke in the early 1960s. It was one of the largest spacecraft ever conceptualized with a diameter of over 50 metres and the capability to lift up to 2000 short tons into Earth orbit, intended for missions to further out locations in the solar system such as Mars.

The North American Air Augmented VTOVL from 1963 was a similarly large craft which would have used ramjets to decrease the liftoff mass of the vehicle by removing the need for large amounts of liquid oxygen while traveling through the atmosphere.

From 1965, Robert Salkeld investigated various single stage to orbit winged spaceplane concepts. He proposed a vehicle which would burn hydrocarbon fuel while in the atmosphere and then switch to hydrogen fuel for increasing efficiency once in space.

Further examples of Bono's early concepts (prior to the 1990s) which were never constructed include:

• ROMBUS (Reusable Orbital Module, Booster, and Utility Shuttle), another design from Philip Bono. This was not technically single stage since it dropped some of its initial hydrogen tanks, but it came very close.
• Ithacus, an adapted ROMBUS concept which was designed to carry soldiers and military equipment to other continents via a sub-orbital trajectory.
• Pegasus, another adapted ROMBUS concept designed to carry passengers and payloads long distances in short amounts of time via space.
• Douglas SASSTO, a 1967 launch vehicle concept.
• Hyperion, yet another Philip Bono concept which used a sled to build up speed before liftoff to save on the amount of fuel which had to be lifted into the air.

Star-raker: In 1979 Rockwell International unveiled a concept for a 100 ton payload heavy-lift multicycle airbreather ramjet/cryogenic rocket engine, horizontal takeoff/horizontal landing single-stage-to-orbit spaceplane named Star-Raker, designed to launch heavy Space-based solar power satellites into a 300 nautical mile Earth orbit. Star-raker would have had 3 x LOX/LH2 rocket engines (based on the SSME) + 10 x turboramjets.

Around 1985 the NASP project was intended to launch a scramjet vehicle into orbit, but funding was stopped and the project cancelled. At around the same time, the HOTOL tried to use precooled jet engine technology, but failed to show significant advantages over rocket technology.

DC-X technology

Main article: McDonnell Douglas DC-X

The maiden flight of the DC-X

The DC-X, short for Delta Clipper Experimental, was an uncrewed one-third scale vertical takeoff and landing demonstrator for a proposed SSTO. It is one of only a few prototype SSTO vehicles ever built. Several other prototypes were intended, including the DC-X2 (a half-scale prototype) and the DC-Y, a full-scale vehicle which would be capable of single stage insertion into orbit. Neither of these were built, but the project was taken over by NASA in 1995, and they built the DC-XA, an upgraded one-third scale prototype. This vehicle was lost when it landed with only three of its four landing pads deployed, which caused it to tip over on its side and explode. The project has not been continued since.

Roton

Main article: Rotary Rocket

From 1999 to 2001 Rotary Rocket attempted to build a SSTO vehicle called the Roton. It received a large amount of media attention and a working sub-scale prototype was completed, but the design was largely impractical.

Approaches

There have been various approaches to SSTO, including pure rockets that are launched and land vertically, air-breathing scramjet-powered vehicles that are launched and land horizontally, nuclear-powered vehicles, and even jet-engine-powered vehicles that can fly into orbit and return landing like an airliner, completely intact.

For rocket-powered SSTO, the main challenge is achieving a high enough mass-ratio to carry sufficient propellant to achieve orbit, plus a meaningful payload weight. One possibility is to give the rocket an initial speed with a space gun, as planned in the Quicklaunch project.

For air-breathing SSTO, the main challenge is system complexity and associated research and development costs, material science, and construction techniques necessary for surviving sustained high-speed flight within the atmosphere, and achieving a high enough mass-ratio to carry sufficient propellant to achieve orbit, plus a meaningful payload weight. Air-breathing designs typically fly at supersonic or hypersonic speeds, and usually include a rocket engine for the final burn for orbit.

Whether rocket-powered or air-breathing, a reusable vehicle must be rugged enough to survive multiple round trips into space without adding excessive weight or maintenance. In addition a reusable vehicle must be able to reenter without damage, and land safely.

While single-stage rockets were once thought to be beyond reach, advances in materials technology and construction techniques have shown them to be possible. For example, calculations show that the Titan II first stage, launched on its own, would have a 25-to-1 ratio of fuel to vehicle hardware. It has a sufficiently efficient engine to achieve orbit, but without carrying much payload.

Dense versus hydrogen fuels

Hydrogen fuel might seem the obvious fuel for SSTO vehicles. When burned with oxygen, hydrogen gives the highest specific impulse of any commonly used fuel: around 450 seconds, compared with up to 350 seconds for kerosene.

Hydrogen has the following advantages:

• Hydrogen has nearly 30% higher specific impulse (about 450 seconds vs. 350 seconds) than most dense fuels.
• Hydrogen is an excellent coolant.
• The gross mass of hydrogen stages is lower than dense-fuelled stages for the same payload.
• Hydrogen is environmentally friendly.

However, hydrogen also has these disadvantages:

• Very low density (about 1⁄7 of the density of kerosene) – requiring a very large tank
• Deeply cryogenic – must be stored at very low temperatures and thus needs heavy insulation
• Escapes very easily from the smallest gap
• Wide combustible range – easily ignited and burns with a dangerously invisible flame
• Tends to condense oxygen which can cause flammability problems
• Has a large coefficient of expansion for even small heat leaks.

These issues can be dealt with, but at extra cost.

While kerosene tanks can be 1% of the weight of their contents, hydrogen tanks often must weigh 10% of their contents. This is because of both the low density and the additional insulation required to minimize boiloff (a problem which does not occur with kerosene and many other fuels). The low density of hydrogen further affects the design of the rest of the vehicle: pumps and pipework need to be much larger in order to pump the fuel to the engine. The end result is the thrust/weight ratio of hydrogen-fueled engines is 30–50% lower than comparable engines using denser fuels.

This inefficiency indirectly affects gravity losses as well; the vehicle has to hold itself up on rocket power until it reaches orbit. The lower excess thrust of the hydrogen engines due to the lower thrust/weight ratio means that the vehicle must ascend more steeply, and so less thrust acts horizontally. Less horizontal thrust results in taking longer to reach orbit, and gravity losses are increased by at least 300 metres per second (1,100 km/h; 670 mph). While not appearing large, the mass ratio to delta-v curve is very steep to reach orbit in a single stage, and this makes a 10% difference to the mass ratio on top of the tankage and pump savings.

The overall effect is that there is surprisingly little difference in overall performance between SSTOs that use hydrogen and those that use denser fuels, except that hydrogen vehicles may be rather more expensive to develop and buy. Careful studies have shown that some dense fuels (for example liquid propane) exceed the performance of hydrogen fuel when used in an SSTO launch vehicle by 10% for the same dry weight.

In the 1960s Philip Bono investigated single-stage, VTVL tripropellant rockets, and showed that it could improve payload size by around 30%.

Operational experience with the DC-X experimental rocket has caused a number of SSTO advocates to reconsider hydrogen as a satisfactory fuel. The late Max Hunter, while employing hydrogen fuel in the DC-X, often said that he thought the first successful orbital SSTO would more likely be fueled by propane.

One engine for all altitudes

Some SSTO concepts use the same engine for all altitudes, which is a problem for traditional engines with a bell-shaped nozzle. Depending on the atmospheric pressure, different bell shapes are optimal. Engines operating in the lower atmosphere have shorter bells than those designed to work in vacuum. Having a bell that is only optimal at a single altitude lowers the overall engine efficiency.

One possible solution would be to use an aerospike engine, which can be effective in a wide range of ambient pressures. In fact, a linear aerospike engine was to be used in the X-33 design.

Other solutions involve using multiple engines and other altitude adapting designs such as double-mu bells or extensible bell sections.

Still, at very high altitudes, the extremely large engine bells tend to expand the exhaust gases down to near vacuum pressures. As a result, these engine bells are counterproductive due to their excess weight. Some SSTO concepts use very high pressure engines which permit high ratios to be used from ground level. This gives good performance, negating the need for more complex solutions.

Airbreathing SSTO

Skylon spaceplane

Some designs for SSTO attempt to use airbreathing jet engines that collect oxidizer and reaction mass from the atmosphere to reduce the take-off weight of the vehicle.

Some of the issues with this approach are:

• No known air breathing engine is capable of operating at orbital speed within the atmosphere (for example hydrogen fueled scramjets seem to have a top speed of about Mach 17). This means that rockets must be used for the final orbital insertion.
• Rocket thrust needs the orbital mass to be as small as possible to minimize propellant weight.
• The thrust-to-weight ratio of rockets that rely on on-board oxygen increases dramatically as fuel is expended, because the oxidizer fuel tank has about 1% of the mass as the oxidizer it carries, whereas air-breathing engines traditionally have a poor thrust/weight ratio which is relatively fixed during the air-breathing ascent.
• Very high speeds in the atmosphere necessitate very heavy thermal protection systems, which makes reaching orbit even harder.
• At lower speeds, air-breathing engines are very efficient, but the efficiency (Isp) and thrust levels of air-breathing jet engines drop considerably at high speed (above Mach 5–10 depending on the engine) and begin to approach that of rocket engines or worse.
• Lift to drag ratios of vehicles at hypersonic speeds are poor, however the effective lift to drag ratios of rocket vehicles at high g is not dissimilar.

Thus with for example scramjet designs (e.g. X-43) the mass budgets do not seem to close for orbital launch.

Similar issues occur with single-stage vehicles attempting to carry conventional jet engines to orbit—the weight of the jet engines is not compensated sufficiently by the reduction in propellant.

On the other hand, LACE-like precooled airbreathing designs such as the Skylon spaceplane (and ATREX) which transition to rocket thrust at rather lower speeds (Mach 5.5) do seem to give, on paper at least, an improved orbital mass fraction over pure rockets (even multistage rockets) sufficiently to hold out the possibility of full reusability with better payload fraction.

It is important to note that mass fraction is an important concept in the engineering of a rocket. However, mass fraction may have little to do with the costs of a rocket, as the costs of fuel are very small when compared to the costs of the engineering program as a whole. As a result, a cheap rocket with a poor mass fraction may be able to deliver more payload to orbit with a given amount of money than a more complicated, more efficient rocket.

Launch assists

Many vehicles are only narrowly suborbital, so practically anything that gives a relatively small delta-v increase can be helpful, and outside assistance for a vehicle is therefore desirable.

Proposed launch assists include:

• sled launch (rail, maglev including Bantam, MagLifter, and StarTram, etc.)
• air launch or aircraft tow
• in-flight fueling
• Lofstrom launch loop/space fountains

And on-orbit resources such as:

• Space tether
• tugs

Nuclear propulsion

Main article: Nuclear propulsion

Due to weight issues such as shielding, many nuclear propulsion systems are unable to lift their own weight, and hence are unsuitable for launching to orbit. However, some designs such as the Orion project and some nuclear thermal designs do have a thrust to weight ratio in excess of 1, enabling them to lift off. Clearly, one of the main issues with nuclear propulsion would be safety, both during a launch for the passengers, but also in case of a failure during launch. No current program is attempting nuclear propulsion from Earth's surface.

Beam-powered propulsion

Main article: Beam-powered propulsion

Because they can be more energetic than the potential energy that chemical fuel allows for, some laser or microwave powered rocket concepts have the potential to launch vehicles into orbit, single stage. In practice, this area is not possible with current technology.

Design challenges inherent in SSTO

The design space constraints of SSTO vehicles were described by rocket design engineer Robert Truax:

Using similar technologies (i.e., the same propellants and structural fraction), a two-stage-to-orbit vehicle will always have a better payload-to-weight ratio than a single stage designed for the same mission, in most cases, a very much better [payload-to-weight ratio]. Only when the structural factor approaches zero [very little vehicle structure weight] does the payload/weight ratio of a single-stage rocket approach that of a two-stage. A slight miscalculation and the single-stage rocket winds up with no payload. To get any at all, technology needs to be stretched to the limit. Squeezing out the last drop of specific impulse, and shaving off the last pound, costs money and/or reduces reliability.

The Tsiolkovsky rocket equation expresses the maximum change in velocity any single rocket stage can achieve:

${\displaystyle \Delta v=I_{\text{sp}}\cdot g_{0}\ln(MR)}$

where:

${\displaystyle \Delta v}$ (delta-v) is the maximum change of velocity of the vehicle,

${\displaystyle I_{\text{sp}}}$ is the propellant specific impulse,

${\displaystyle g_{0}}$ is the standard gravity,

${\displaystyle MR}$ is the vehicle mass ratio,

${\displaystyle \ln }$ refers to the natural logarithm function.

The mass ratio of a vehicle is defined as a ratio the initial vehicle mass when fully loaded with propellants ${\displaystyle \left(m_{i}\right)}$ to the final vehicle mass ${\displaystyle \left(m_{f}\right)}$ after the burn:

${\displaystyle MR={\frac {m_{i}}{m_{f}}}={\frac {m_{p}+m_{s}+m_{\text{pl}}}{m_{s}+m_{\text{pl}}}}}$

where:

${\displaystyle m_{i}}$ is the initial vehicle mass or the gross liftoff weight ${\displaystyle \left(GLOW\right)}$,

${\displaystyle m_{f}}$ is the final vehicle mass after the burn,

${\displaystyle m_{s}}$ is the structural mass of vehicle,

${\displaystyle m_{p}}$ is the propellant mass,

${\displaystyle m_{\text{pl}}}$ is the payload mass.

The propellant mass fraction (${\displaystyle \zeta }$) of a vehicle can be expressed solely as a function of the mass ratio:

${\displaystyle \zeta ={\frac {m_{p}}{m_{i}}}={\frac {m_{i}-m_{f}}{m_{i}}}=1-{\frac {m_{f}}{m_{i}}}=1-{\frac {1}{MR}}={\frac {MR-1}{MR}}}$

The structural coefficient (${\displaystyle \lambda }$) is a critical parameter in SSTO vehicle design. Structural efficiency of a vehicle is maximized as the structural coefficient approaches zero. The structural coefficient is defined as:

Comparison of growth factor sensitivity for Single-Stage-to-Orbit (SSTO) and restricted stage Two-Stage-to-Orbit (TSTO) vehicles. Based on a LEO mission of Delta v = 9.1 km/s and payload mass = 4500 kg for range of propellant Isp.

${\displaystyle \lambda ={\frac {m_{s}}{m_{p}+m_{s}}}={\frac {m_{s}}{m_{i}-m_{\text{pl}}}}={\frac {\frac {m_{s}}{m_{i}}}{1-{\frac {m_{\text{pl}}}{m_{i}}}}}}$

The overall structural mass fraction ${\displaystyle \left({\frac {m_{s}}{m_{i}}}\right)}$ can be expressed in terms of the structural coefficient:

${\displaystyle {\frac {m_{s}}{m_{i}}}=\lambda \left(1-{\frac {m_{\text{pl}}}{m_{i}}}\right)}$

An additional expression for the overall structural mass fraction can be found by noting that the payload mass fraction ${\displaystyle \left({\frac {m_{\text{pl}}}{m_{i}}}\right)}$, propellant mass fraction and structural mass fraction sum to one:

${\displaystyle 1={\frac {m_{\text{pl}}}{m_{i}}}+{\frac {m_{p}}{m_{i}}}+{\frac {m_{s}}{m_{i}}}={\frac {m_{\text{pl}}}{m_{i}}}+\zeta +{\frac {m_{s}}{m_{i}}}}$

${\displaystyle {\frac {m_{s}}{m_{i}}}=1-\zeta -{\frac {m_{\text{pl}}}{m_{i}}}}$

Equating the expressions for structural mass fraction and solving for the initial vehicle mass yields:

${\displaystyle m_{i}=GLOW={\frac {m_{\text{pl}}}{1-\left({\frac {\zeta }{1-\lambda }}\right)}}}$

This expression shows how the size of a SSTO vehicle is dependent on its structural efficiency. Given a mission profile ${\displaystyle \left(\Delta v,m_{\text{pl}}\right)}$ and propellant type ${\displaystyle \left(I_{\text{sp}}\right)}$, the size of a vehicle increases with an increasing structural coefficient. This growth factor sensitivity is shown parametrically for both SSTO and two-stage-to-orbit (TSTO) vehicles for a standard LEO mission. The curves vertically asymptote at the maximum structural coefficient limit where mission criteria can no longer be met:

${\displaystyle \lambda _{\text{max}}=1-\zeta ={\frac {1}{MR}}}$

In comparison to a non-optimized TSTO vehicle using restricted staging, a SSTO rocket launching an identical payload mass and using the same propellants will always require a substantially smaller structural coefficient to achieve the same delta-v. Given that current materials technology places a lower limit of approximately 0.1 on the smallest structural coefficients attainable, reusable SSTO vehicles are typically an impractical choice even when using the highest performance propellants available.

Examples

It is easier to achieve SSTO from a body with lower gravitational pull than Earth, such as the Moon or Mars. The Apollo Lunar Module ascended from the lunar surface to lunar orbit in a single stage.

A detailed study into SSTO vehicles was prepared by Chrysler Corporation's Space Division in 1970–1971 under NASA contract NAS8-26341. Their proposal (Shuttle SERV) was an enormous vehicle with more than 50,000 kilograms (110,000 lb) of payload, utilizing jet engines for (vertical) landing. While the technical problems seemed to be solvable, the USAF required a winged design that led to the Shuttle as we know it today.

The uncrewed DC-X technology demonstrator, originally developed by McDonnell Douglas for the Strategic Defense Initiative (SDI) program office, was an attempt to build a vehicle that could lead to an SSTO vehicle. The one-third-size test craft was operated and maintained by a small team of three people based out of a trailer, and the craft was once relaunched less than 24 hours after landing. Although the test program was not without mishap (including a minor explosion), the DC-X demonstrated that the maintenance aspects of the concept were sound. That project was cancelled when it landed with three of four legs deployed, tipped over, and exploded on the fourth flight after transferring management from the Strategic Defense Initiative Organization to NASA.

The Aquarius Launch Vehicle was designed to bring bulk materials to orbit as cheaply as possible.

Current development

Current and previous SSTO projects include the Japanese Kankoh-maru project, ARCA Haas 2C, and the Indian Avatar spaceplane.

Skylon

Main article: Reaction Engines Skylon

The British Government partnered with the ESA in 2010 to promote a single-stage to orbit spaceplane concept called Skylon. This design was pioneered by Reaction Engines Limited (REL), a company founded by Alan Bond after HOTOL was canceled. The Skylon spaceplane has been positively received by the British government, and the British Interplanetary Society. Following a successful propulsion system test that was audited by ESA's propulsion division in mid-2012, REL announced that it would begin a three-and-a-half-year project to develop and build a test jig of the Sabre engine to prove the engines performance across its air-breathing and rocket modes. In November 2012, it was announced that a key test of the engine precooler had been successfully completed, and that ESA had verified the precooler's design. The project's development is now allowed to advance to its next phase, which involves the construction and testing of a full-scale prototype engine.

Alternative approaches to inexpensive spaceflight

Many studies have shown that regardless of selected technology, the most effective cost reduction technique is economies of scale. Merely launching a large total number reduces the manufacturing costs per vehicle, similar to how the mass production of automobiles brought about great increases in affordability.

Using this concept, some aerospace analysts believe the way to lower launch costs is the exact opposite of SSTO. Whereas reusable SSTOs would reduce per launch costs by making a reusable high-tech vehicle that launches frequently with low maintenance, the "mass production" approach views the technical advances as a source of the cost problem in the first place. By simply building and launching large quantities of rockets, and hence launching a large volume of payload, costs can be brought down. This approach was attempted in the late 1970s, early 1980s in West Germany with the Democratic Republic of the Congo-based OTRAG rocket.

This is somewhat similar to the approach some previous systems have taken, using simple engine systems with "low-tech" fuels, as the Russian and Chinese space programs still do.

An alternative to scale is to make the discarded stages practically reusable: this is the goal of the SpaceX reusable launch system development program and their Falcon 9, Falcon Heavy, and Starship. A similar approach is being pursued by Blue Origin, using New Glenn.