Single-stage-to-orbit - AbsoluteAstronomy.com

A single-stage-to-orbit (or SSTO) vehicle reaches orbit

Orbit

In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...

from the surface of a body without jettisoning hardware, expending only propellants and fluids. The term usually, but not exclusively, refers to reusable vehicles

Reusable launch system

A reusable launch system is a launch system which is capable of launching a launch vehicle into space more than once. This contrasts with expendable launch systems, where each launch vehicle is launched once and then discarded.No true orbital reusable launch system is currently in use. The...

.

No Earth-launched SSTO launch vehicles have ever been constructed. Current orbital launches are either performed by multi-stage fully or partially expendable rockets, or by the Space Shuttle

Space Shuttle

The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...

which is multi-stage and partially reusable. Several research spacecraft have been designed and partially or completely constructed, including Skylon, the DC-X

McDonnell Douglas DC-X

The DC-X, short for Delta Clipper or Delta Clipper Experimental, was an unmanned prototype of a reusable single stage to orbit launch vehicle built by McDonnell Douglas in conjunction with the United States Department of Defense's Strategic Defense Initiative Organization from 1991 to 1993...

, the X-33, and the Roton SSTO

Rotary Rocket

Rotary Rocket, Inc, was a rocketry company headquartered in a facility at Mojave Airport that developed the Roton concept in the late 1990s as a fully reusable single-stage-to-orbit manned spacecraft. Roton was intended to reduce costs of launching payloads into low earth orbit by a factor of...

. However, despite showing some promise, none of them has come close to achieving orbit yet due to problems with finding the most efficient propulsion system.

Single-stage-to-orbit has been achieved from the Moon

Moon

The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

by both the Apollo program's Lunar Module

Apollo Lunar Module

The Apollo Lunar Module was the lander portion of the Apollo spacecraft built for the US Apollo program by Grumman to carry a crew of two from lunar orbit to the surface and back...

and several robotic spacecraft of the Soviet Luna programme

Luna programme

The Luna programme , occasionally called Lunik or Lunnik, was a series of robotic spacecraft missions sent to the Moon by the Soviet Union between 1959 and 1976. Fifteen were successful, each designed as either an orbiter or lander, and accomplished many firsts in space exploration...

; the lower lunar gravity and absence of any significant atmosphere makes this much easier than from Earth.

History

Early rocket pioneers believed that single stage to orbit was impossible
In the 1960s people like Philip Bono
Philip Bono
Philip Bono was a Douglas Aircraft Company engineer. He was a pioneer of reusable vertical landing single-stage to orbit launch vehicles....

began to investigate this
From 1965 Robert Salked investigated various single stage to orbit spaceplane concepts
Around 1985 the NASP
NASP
NASP is an acronym that may stand for:In science and academia :* Nuclear autoantigenic sperm protein, a gene in the human genome* National Association of School PsychologistsIn military :...

project was intended to create a scramjet vehicle to reach orbit, but this failed
The HOTOL
HOTOL
HOTOL, for Horizontal Take-Off and Landing, was a British air-breathing space shuttle effort by Rolls Royce and British Aerospace.Designed as a single-stage-to-orbit reusable winged launch vehicle, it was to be fitted with a unique air-breathing engine, the RB545 called the Swallow, to be...

tried to use precooled jet engine technology, but although not entirely unsuccessful, failed to show significant advantages over rocket technology
Around 1992 the Skylon
Skylon
Skylon is a design for an unpiloted spaceplane by the British company Reaction Engines Limited . It uses a combined-cycle, air-breathing rocket engine to reach orbit in a single stage. A fleet of vehicles is envisaged; the design is aiming for re-usability up to 200 times...

spaceplane concept was created

Approaches to SSTO

There have been various approaches to SSTO, including pure rockets that are launched and land vertically, air-breathing scramjet

Scramjet

A scramjet is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow...

-powered vehicles that are launched and land horizontally, nuclear-powered

Project Orion (nuclear propulsion)

Project Orion was a study of a spacecraft intended to be directly propelled by a series of explosions of atomic bombs behind the craft...

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

Propellant

A propellant is a material that produces pressurized gas that:* can be directed through a nozzle, thereby producing thrust ;...

to achieve orbit

Orbit

In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...

, plus a meaningful payload weight. One possibility is to give the rocket an initial speed with a space gun

Space gun

A space gun is a method of launching an object into outer space using a large gun, or cannon. It provides a method of non-rocket spacelaunch‎.In the HARP Project a U.S...

, as planned in the Quicklaunch project.

For air-breathing SSTO, the main challenge is system complexity and associated research and development

Research and development

The phrase research and development , according to the Organization for Economic Co-operation and Development, refers to "creative work undertaken on a systematic basis in order to increase the stock of knowledge, including knowledge of man, culture and society, and the use of this stock of...

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

Supersonic

Supersonic speed is a rate of travel of an object that exceeds the speed of sound . For objects traveling in dry air of a temperature of 20 °C this speed is approximately 343 m/s, 1,125 ft/s, 768 mph or 1,235 km/h. Speeds greater than five times the speed of sound are often...

or hypersonic

Hypersonic

In aerodynamics, a hypersonic speed is one that is highly supersonic. Since the 1970s, the term has generally been assumed to refer to speeds of Mach 5 and above...

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.

Features of SSTO

The goals of fully reusable SSTO vehicles include lower operating costs, improved safety, and better reliability than current launch vehicles. The ultimate goal for an SSTO vehicle would be airliner-like operations.

However, even a non-reusable single-stage vehicle might be worth building, since it would have a much lower part count, and may therefore be cheaper to design and build.

For pure rocket approaches Tsiolkovsky's rocket equation

Tsiolkovsky rocket equation

The Tsiolkovsky rocket equation, or ideal rocket equation is an equation that is useful for considering vehicles that follow the basic principle of a rocket: where a device that can apply acceleration to itself by expelling part of its mass with high speed and moving due to the conservation of...

shows that dead weight will prevent reaching orbit unless the ratio of propellant to structural mass (called mass ratio

Mass ratio

In aerospace engineering, mass ratio is a measure of the efficiency of a rocket. It describes how much more massive the vehicle is with propellant than without; that is, it is the ratio of the rocket's wet mass to its dry mass...

) is very high — between about 10 and 25 (i.e. 24 parts propellant weight to 1 part structural weight; depending on propellant choice).

It is extremely difficult to design a structure which is strong, safe, very light, and economical to build. Designers often liken the task to designing and building an egg shell. The problem originally seemed insuperable, and drove all early designers to multistage rockets.

Multistage rocket

Multistage rocket

A multistage rocket is a rocket that usestwo or more stages, each of which contains its own engines and propellant. A tandem or serial stage is mounted on top of another stage; a parallel stage is attached alongside another stage. The result is effectively two or more rockets stacked on top of or...

s are able to reach orbital velocity because they discard structural weight during boost. Thus a single-stage rocket is at a disadvantage because it must carry its entire vehicle mass to orbit, which in turn reduces payload capacity. On the other hand, a single-stage vehicle does not have to carry a second stage, so the vehicle is easier to make lightweight.

Alternatively, since expendable multistage rockets entail discarding costly structure and engines, if the stages could be reused, this could permit much cheaper operation since the parts costs would be amortized over many flights.

One problem with multistage reusable rockets is the difficulty of reusing even the first stage, and the development cost of such a large device. Analysis shows the optimum staging velocity (the speed at which the first stage is dropped) is very high — possibly 3.65 km/s (12,000 feet per second). This means after separation, the large first stage is at high altitude and headed downrange very fast, which makes it difficult to turn around and get back to the launch point. The stage also must re-enter without damage from a speed as high as Mach 10.

The reusable first stage would be very large, nearly the size of a Saturn V

Saturn V

The Saturn V was an American human-rated expendable rocket used by NASA's Apollo and Skylab programs from 1967 until 1973. A multistage liquid-fueled launch vehicle, NASA launched 13 Saturn Vs from the Kennedy Space Center, Florida with no loss of crew or payload...

to lift an orbiter the size of the current shuttle. Because development cost of aerospace vehicles has historically been related to weight, it is assumed that such a vehicle would be extremely expensive to develop.

Some approaches envisioned parachutes to gently lower a reusable first stage. However, for most US launches the trajectory is over the Atlantic ocean, and complex liquid-fueled stages are easily damaged by a salt water landing.

These problems with the multistage approach drive the design path toward SSTO.

All these complications drove designers to consider a single reusable stage as this:

Avoids discarding expensive engines and structure (vs. expendable).
Avoids difficulty of retrieving the large first stage (vs. reusable multistage).
Avoids increased development cost of two separate vehicles (vs. reusable multistage).

If an SSTO vehicle were combined with reliable systems and lower maintenance design of a more automated nature, it could greatly reduce operational costs. Fully recoverable SSTO craft can be flown on short test missions, and developed incrementally, since no hardware is expended in test flights.

On the other hand, an SSTO vehicle needs to lift its entire structure into orbit. To reach orbit with a useful payload, the rocket requires careful and extensive engineering to save weight. Although an SSTO rocket might theoretically be built, margins would be likely to be very thin: even comparatively minor problems could mean that the craft may fail to achieve the necessary mass-fraction to reach orbit with useful payload.

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

Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

might seem the obvious fuel for SSTO vehicles. When burned with oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

, hydrogen gives the highest specific impulse

Specific impulse

Specific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,...

of any commonly used fuel: around 450 seconds, compared with up to 350 seconds for kerosene

Kerosene

Kerosene, sometimes spelled kerosine in scientific and industrial usage, also known as paraffin or paraffin oil in the United Kingdom, Hong Kong, Ireland and South Africa, is a combustible hydrocarbon liquid. The name is derived from Greek keros...

.

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.

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

Gravity drag

In astrodynamics and rocketry, gravity drag is a measure of the loss in the net performance of a rocket while it is thrusting in a gravitational field...

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 meters per second. While not appearing large, the mass ratio to delta-v

Delta-v

In astrodynamics a Δv or delta-v is a scalar which takes units of speed. It is a measure of the amount of "effort" that is needed to change from one trajectory to another by making an orbital maneuver....

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

Propane

Propane is a three-carbon alkane with the molecular formula , normally a gas, but compressible to a transportable liquid. A by-product of natural gas processing and petroleum refining, it is commonly used as a fuel for engines, oxy-gas torches, barbecues, portable stoves, and residential central...

) 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

Philip Bono

Philip Bono was a Douglas Aircraft Company engineer. He was a pioneer of reusable vertical landing single-stage to orbit launch vehicles....

investigated single stage, VTVL tripropellant rocket

Tripropellant rocket

A tripropellant rocket is a rocket that uses three propellants, as opposed to the more common bipropellant rocket or monopropellant rocket designs, which use two or one fuels, respectively...

s, 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 vehicles use the same engine for all altitudes, which is a problem for traditional engines with a bell-shaped nozzle

Nozzle

A nozzle is a device designed to control the direction or characteristics of a fluid flow as it exits an enclosed chamber or pipe via an orifice....

. 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 not optimized for the height makes the engine less efficient.

One possible solution would be to use an aerospike engine

Aerospike engine

The aerospike engine is a type of rocket engine that maintains its aerodynamic efficiency across a wide range of altitudes through the use of an aerospike nozzle. It is a member of the class of altitude compensating nozzle engines. A vehicle with an aerospike engine uses 25–30% less fuel at low...

, which can be effective in a wide range of ambient pressures. In fact, a linear aerospike engine was used in the X-33 design.

Other solutions involve using multiple engines and other altitude adapting designs

Altitude compensating nozzle

An altitude compensating nozzle is a class of rocket engine nozzles that are designed to operate efficiently across a wide range of altitudes.- Conventional designs :...

such as double-mu bells or extensible bell sections

Expanding nozzle

The expanding nozzle is a type of rocket nozzle that, unlike traditional designs, maintains its efficiency at a wide range of altitudes. It is a member of the class of altitude compensating nozzles, a class that also includes the plug nozzle and aerospike...

.

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 vehicles simply 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

Some designs for SSTO attempt to use airbreathing jet engine

Airbreathing jet engine

An airbreathing jet engine is a jet engine propelled by a jet of hot exhaust gases formed from air that is drawn into the engine via an inlet duct....

s that collect oxidiser 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 scramjet
Scramjet
A scramjet is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow...

s 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.
Oxidiser tanks are very lightweight when empty, approximately 1% of their contents, so the reduction in orbital weight by airbreathing is small, whereas air-breathing engines have a poor thrust/weight ratio which tends to increase the orbital mass.
Very high speeds in the atmosphere necessitate very heavy thermal protection systems, which makes reaching orbit even harder.
While at lower speeds, air-breathing engines are very efficient, the efficiency (Isp
Specific impulse
Specific impulse is a way to describe the efficiency of rocket and jet engines. It represents the derivative of the impulse with respect to amount of propellant used, i.e., the thrust divided by the amount of propellant used per unit time. If the "amount" of propellant is given in terms of mass ,...

) 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 whereas since acceleration is a vector, the effective lift to drag ratios of rocket vehicles at high g is not dissimilar
Gravity drag
In astrodynamics and rocketry, gravity drag is a measure of the loss in the net performance of a rocket while it is thrusting in a gravitational field...

.

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 by the reduction in propellant sufficiently.

On the other hand LACE-like precooled airbreathing designs such as the Skylon spaceplane (and ATREX

ATREX

The ATREX engine developed in Japan is an experimental precooled jet engine that works as a turbojet at low speeds and a ramjet up to mach 6.0....

) 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

Mass fraction

In aerospace engineering, the propellant mass fraction is a measure of a vehicle's performance, determined as the portion of the vehicle's mass which does not reach the destination...

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
Rocket sled launch
A rocket sled launch is a method of launching space vehicles. A rail or maglev track and a rocket or jet booster is used to accelerate a sled holding a vehicle up an eastward facing mountain slope...

(rail, maglev including Bantam, MagLifter
Rocket sled launch
A rocket sled launch is a method of launching space vehicles. A rail or maglev track and a rocket or jet booster is used to accelerate a sled holding a vehicle up an eastward facing mountain slope...

, and StarTram
StarTram
StarTram is a proposal for a maglev space launch system. The initial Generation 1 facility would be cargo only, launching from a mountain peak at 3 km to 7 km altitude with an evacuated tube staying at local surface level, raising ≈150,000 tons to orbit annually...

, etc.)
aircraft tow
Air launch
Air launching is the practice of dropping a parasite aircraft, rocket, or missile from a mothership. The parasite aircraft or missile is usually tucked under the wing of the larger mothership and then "dropped" from underneath the wing while in flight...
in-flight fueling
Lofstrom launch loop/space fountain
Space fountain
A space fountain is a proposed form of space elevator that does not require the structure to be in geostationary orbit, and does not rely on tensile strength for support. In contrast to the original space elevator design , a space fountain is a tremendously tall tower extending up from the ground...

s

And on-orbit resources such as:

hypersonic tethers
Skyhook (structure)
Skyhooks are a theoretical class of cable based techniques intended to lift payloads to high altitudes and speeds. The name skyhook is a reference to an imaginary hook that hangs from the sky....

(single stage to tether)
tugs

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

Project Orion (nuclear propulsion)

Project Orion was a study of a spacecraft intended to be directly propelled by a series of explosions of atomic bombs behind the craft...

and some nuclear thermal

Nuclear thermal rocket

In a nuclear thermal rocket a working fluid, usually liquid hydrogen, is heated to a high temperature in a nuclear reactor, and then expands through a rocket nozzle to create thrust. In this kind of thermal rocket, the nuclear reactor's energy replaces the chemical energy of the propellant's...

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

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 relatively undeveloped, and current technology falls far short of this.

Comparison with the Shuttle

The high cost per launch of the Space Shuttle

Space Shuttle

sparked interest throughout the 1980s in designing a cheaper successor vehicle. Several official design studies were done, but most were basically smaller versions of the existing Shuttle concept.

Most cost analysis studies of the Space Shuttle have shown that workforce is by far the single greatest expense. Early shuttle discussions speculated airliner-type operation, with a two-week turnaround. However, senior NASA planners envisioned no more than 10 to 12 flights per year for the entire shuttle fleet. The absolute maximum flights per year for the entire fleet was limited by external tank manufacturing capacity to 24 per year.

Very efficient (hence complex and sophisticated) main engines

Space Shuttle main engine

The RS-25, otherwise known as the Space Shuttle Main Engine , is a reusable liquid-fuel rocket engine built by Pratt & Whitney Rocketdyne for the Space Shuttle, running on liquid hydrogen and oxygen. Each Space Shuttle was propelled by three SSMEs mated to one powerhead...

were required to fit within the available vehicle space. Likewise the only known suitable lightweight thermal protection

Space shuttle thermal protection system

The Space Shuttle thermal protection system is the barrier that protects the Space Shuttle Orbiter during the searing heat of atmospheric reentry...

was delicate, maintenance-intensive silica tiles. These and other design decisions resulted in a vehicle that requires great maintenance after every mission. The engines are removed and inspected, and prior to the new "block II" main engines, the turbopump

Turbopump

A turbopump is a gas turbine that comprises basically two main components: a rotodynamic pump and a driving turbine, usually both mounted on the same shaft, or sometimes geared together...

s were removed, disassembled and rebuilt. While Space Shuttle Atlantis

Space Shuttle Atlantis

The Space Shuttle Atlantis is a retired Space Shuttle orbiter in the Space Shuttle fleet belonging to the National Aeronautics and Space Administration , the spaceflight and space exploration agency of the United States...

was refurbished and relaunched in 53 days between missions STS-51-J

STS-51-J

STS-51-J was a NASA Space Shuttle mission. It was the first flight of Space Shuttle Atlantis and the 21st shuttle mission overall. It launched from Kennedy Space Center, Florida, on 3 October 1985, carrying a payload for the U.S...

and STS-61-B

STS-61-B

STS-61-B was NASA's 23rd Space Shuttle mission, and its second using Space Shuttle Atlantis. The shuttle was launched from Kennedy Space Center, Florida, on 26 November 1985. During STS-61-B, the shuttle crew deployed three communications satellites, and tested techniques of constructing...

, generally months are required to repair an orbiter for a new mission. Given that there are 25,000 people working on Shuttle operations, the payroll alone is the Shuttle's single biggest operating cost.

Many in the aerospace community concluded that an entirely self-contained, reusable single-stage vehicle could solve these problems. The idea behind such a vehicle is to reduce the processing requirements from those of the Shuttle.

Examples

The early Atlas rocket is an expendable SSTO by some definitions. It is a "stage-and-a-half" rocket, jettisoning two of its three engines during ascent but retaining its fuel tanks and other structural elements. However, by modern standards the engines ran at low pressure

Pressure

Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...

and thus not particularly high specific impulse and were not especially lightweight; using engines operating with a higher specific impulse would have eliminated the need to drop engines in the first place.

The first stage of the Titan II had the mass ratio required for single-stage-to-orbit capability with a small payload. A rocket stage is not a complete launch vehicle, but this demonstrates that an expendable SSTO was probably achievable with 1962 technology.

The Apollo Lunar Module

Apollo Lunar Module

The Apollo Lunar Module was the lander portion of the Apollo spacecraft built for the US Apollo program by Grumman to carry a crew of two from lunar orbit to the surface and back...

was a true SSTO vehicle, albeit on the moon. It achieved lunar orbit using 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 kg of payload, utilizing jet engine

Jet engine

A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...

s for (vertical) landing. While the technical problems seemed to be solvable, the USAF

United States Air Force

The United States Air Force is the aerial warfare service branch of the United States Armed Forces and one of the American uniformed services. Initially part of the United States Army, the USAF was formed as a separate branch of the military on September 18, 1947 under the National Security Act of...

required a winged design (for cross range) that led to the Shuttle as we know it today.

The unmanned DC-X technology demonstrator, originally developed by McDonnell Douglas

McDonnell Douglas

McDonnell Douglas was a major American aerospace manufacturer and defense contractor, producing a number of famous commercial and military aircraft. It formed from a merger of McDonnell Aircraft and Douglas Aircraft in 1967. McDonnell Douglas was based at Lambert-St. Louis International Airport...

for the Strategic Defense Initiative

Strategic Defense Initiative

The Strategic Defense Initiative was proposed by U.S. President Ronald Reagan on March 23, 1983 to use ground and space-based systems to protect the United States from attack by strategic nuclear ballistic missiles. The initiative focused on strategic defense rather than the prior strategic...

(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 tiny crew 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 crashed on the fourth flight after transferring management from the Strategic Defense Initiative Organization to NASA.

The Aquarius Launch Vehicle

Aquarius Launch Vehicle

Space Systems/Loral's Aquarius Launch Vehicle is a low-cost launch vehicle designed to carry small, inexpensive payloads into LEO. The vehicle will be primarily intended to launch into orbit bulk products, like water, fuel, and other consumables, that are inexpensive to replace in the event of a...

was designed to bring bulk materials to orbit as cheaply as possible.

Current Development

Current private SSTO projects include the Japanese Kankoh-maru

Kankoh-maru

The is the name of a proposed vertical takeoff and landing, single-stage to orbit, reusable launch vehicle family of rockets, and the spacecraft tour vehicle designed to be boosted by said rocket.-Details:...

project and the Skylon.

Skylon

The British Government partnered with the ESA in 2010 to promote a single-stage to orbit spaceplane

Spaceplane

A spaceplane is a vehicle that operates as an aircraft in Earth's atmosphere, as well as a spacecraft when it is in space. It combines features of an aircraft and a spacecraft, which can be thought of as an aircraft that can endure and maneuver in the vacuum of space or likewise a spacecraft that...

concept called Skylon

Skylon

Skylon is a design for an unpiloted spaceplane by the British company Reaction Engines Limited . It uses a combined-cycle, air-breathing rocket engine to reach orbit in a single stage. A fleet of vehicles is envisaged; the design is aiming for re-usability up to 200 times...

. This design was pioneered by Reaction Engines Limited

Reaction Engines Limited

Reaction Engines Limited is a British aerospace company based in Oxfordshire, England.- History & personnel :Reaction Engines was founded in 1989 by Alan Bond and Richard Varvill and John Scott-Scott...

, a company founded by Alan Bond

Alan Bond (rocket developer)

Alan Bond is Managing Director of Reaction Engines Ltd and associated with Project Daedalus, Blue Streak missile, HOTOL, Reaction Engines Skylon and the Reaction Engines A2 hypersonic passenger aircraft.- Career :...

after HOTOL

HOTOL

HOTOL, for Horizontal Take-Off and Landing, was a British air-breathing space shuttle effort by Rolls Royce and British Aerospace.Designed as a single-stage-to-orbit reusable winged launch vehicle, it was to be fitted with a unique air-breathing engine, the RB545 called the Swallow, to be...

was canceled. The Skylon spaceplane has been positively received by the British government, and the British Interplanetary Society

British Interplanetary Society

The British Interplanetary Society founded in 1933 by Philip E. Cleator, is the oldest space advocacy organisation in the world whose aim is exclusively to support and promote astronautics and space exploration.-Structure:...

. Pending a successful engine test in June 2011, the company will begin Phase 3 of development with the first orders expected around 2011-2013.

Alternative approaches to cheap spaceflight

Many studies have shown that regardless of selected technology, the most effective cost reduction technique is economies of scale

Economies of scale

Economies of scale, in microeconomics, refers to the cost advantages that an enterprise obtains due to expansion. There are factors that cause a producer’s average cost per unit to fall as the scale of output is increased. "Economies of scale" is a long run concept and refers to reductions in unit...

. Merely launching a large total quantity reduces the manufacturing costs per vehicle, similar to how the mass production

Mass production

Mass production is the production of large amounts of standardized products, including and especially on assembly lines...

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 ’70s, early ’80s in West Germany

West Germany

West Germany is the common English, but not official, name for the Federal Republic of Germany or FRG in the period between its creation in May 1949 to German reunification on 3 October 1990....

with the Democratic Republic of the Congo

Democratic Republic of the Congo

The Democratic Republic of the Congo is a state located in Central Africa. It is the second largest country in Africa by area and the eleventh largest in the world...

-based OTRAG

OTRAG

OTRAG , was a German company based in Stuttgart, which planned in the late 1970s and early 1980s to develop an alternative propulsion system for rockets. OTRAG was the first commercial developer and producer of space launch vehicles...

rocket

OTRAG Rocket

The OTRAG rocket was a modular satellite-delivery rocket developed by the OTRAG company in the 1970s and 80s. The OTRAG rocket was to become a rocket built up from several mass-produced units, intended to carry satellites with a weight of 1-10 tons or more into orbit...

and might have been successful if the project was not killed following political pressure from France

France

The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

, the Soviet Union

Soviet Union

The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

and other parties.

A related idea is to obtain economies of scale from building simple, massive, multi-stage rockets using cheap, off-the-shelf parts. The vehicles would be dumped into the ocean after use. This strategy is known as the "big dumb booster

Big dumb booster

Big Dumb Boosters are a general class of launch vehicle built around the idea that it is cheaper to mass build and operate a large, strong, heavy rocket of simple design than it is to build a few smaller, lighter, more cleverly-designed ones...

" approach.

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 program

China National Space Administration

The China National Space Administration is the national space agency of the People's Republic of China responsible for the national space program. It is responsible for planning and development of space activities...

s still do. These nations' launches are significantly cheaper than their Western counterparts.

External links

A Single-Stage-to-Orbit Thought Experiment
Why are launch costs so high?, an analysis of space launch costs, with a section critiquing SSTO
The Cold Equations Of Spaceflight A critique of SSTO by Jeffrey F. Bell.
Burnout Velocity Vb of a Single 1-Stage Rocket

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

History

Approaches to SSTO

Features of SSTO

Dense versus hydrogen fuels

One engine for all altitudes

Airbreathing SSTO

Launch assists

Nuclear propulsion

Beam-powered propulsion

Comparison with the Shuttle

Examples

Current Development

Skylon

Alternative approaches to cheap spaceflight

See also

External links