ADVANCED SPACEPLANES


Hybrid rocket/scramjet spaceplanes jettisoning their extra fuel pods while boosting their way to orbit. Art copyright Richard Bartrop. Visit the artists's website at http://bartrop.purrsia.com/ .

Antipodal Bomber
Tech Level: 9
X-38 Crew Return Vehicle
Tech Level: 10
Advanced Rocket Spaceplanes
Tech Level: 11
X-33 Venturestar
Tech Level: 12
Scramjet Spaceplanes
Tech Level: 13
Advanced Propulsion Spaceplanes
Tech Level: 14

A spaceplane is a spacecraft that is also designed for controlled flight within Earth’s atmosphere. This means that it take the general shape of an aircraft, with wings, stabilizers, and aerodynamic lifting and control surfaces.

In the real world, a number of spaceplanes have already taken flight above the atmosphere. The US Space Shuttle is the most famous example, but others include the X-15 rocket planes, the USSR’s Buran Space Shuttle, Virgin Galactic’s Spaceships One and Two, and the USAF’s X-37B. These craft have either been suborbital or fully capable of orbital flight.

Spaceplanes are also very prevalent in science fiction, ranging from small suborbital transports to full fledged FTL starships. Their most famous role, however, is as one-man fighters capable of handling both air and space flight equally well. Examples include such vehicles as the Viper fighters from Battlestar Galactica and the X-303s from the various Stargate series, among many others.

All spaceplanes are designed for reusability, making them more attractive economically than throwaway one-use space capsules. At least in theory. While this did seem the case with vehicles like the latter X-series spaceplanes, the Space Shuttle proved much more expensive per flight than capsules, most likely due to its much greater size and complexity. Future, more modestly sized spaceplanes such as Spaceship Two may fulfill their promise of more affordable spaceflight.

Spaceplanes tend to have smaller, more angular wings and lifting surfaces than normal aircraft for two main reasons. One, during reentry, they have to handle hypersonic airflow and need airframes that can handle those kinds of extreme conditions. Such airframes tend to be sleek and angular with smaller wings, much like transonic aircraft have today.

They also have to minimize aerodynamic instability during vertical lift-offs. Very large wings could cause irregularities of airflow in the lower atmosphere and make the spacecraft veer off course or even crash. This danger is minimized with high-altitude launches, like those used by Spaecships Two, and with horizontal runway take-offs, like those theorized may be used by future spaceplanes.

All real-life spaceplanes have so far been multiple-stage vehicles, either needing a booster rocket or a mothership aircraft for the initial lift off the ground. The ideal is to eventually develop SSTO (Single Stage To Orbit) spaceplanes, where they can either take off and land on a runway or utilize VTOL technology without the need for an extra stage. If this becomes feasible, spaceplanes could be launched from existing commercial airports with the proper facilities in place.


ANTIPODAL BOMBER
Tech Level: 9

An antipodal bomber is a suborbital spaceplane designed to use a technique called skip-glide to reach almost anywhere in the world to deliver its payload. For a skip-glide maneuver, the vehicle would control its angle of descent and use its flat-bottomed shape to ‘skip’ off the outer edges of the atmosphere, much like a stone skipping off the surface of a pond. It could do this repeatedly, using skip-glide hops of hundreds or even thousands of kilometers long to reach anywhere on the globe. Of course, the passengers may be in for a rough ride, as each ‘skip’ would bring quite a bit of potential turbulence and put considerable thermal stress on the aircraft (it is, after all, a type of aborted re-entry.)

Antipodal bombers were first envisioned in Germany in the early 1930s, and the Nazi regime in its latter days had tentative plans to research the technology, but nothing except some preliminary designs were created.

The idea was revived in the late 1950s with the X-20 project, nicknamed "Dyna-Soar" (short for Dynamic Soarer.) Unfortunately, budgetary constraints in the mid-1960s prematurely ended the project before it could even begin test flights. A decade later, however, much of the design work and testing for the X-20 concept was later revived for the Space Shuttle.

Both iterations called for an advanced, delta-winged, rocket-powered bomber to be boosted to the edge of space on top of a conventional vertical launch vehicle. The size and power of the launch rocket would determine the initial velocity and altitude of the bomber-glider.

Because of the powerful boosters available to it, including the Titan and Saturn rockets, the X-20 version could also have theoretically achieved orbit instead of just being limited to suborbital flight. In this case it may have used a more advanced "boost-glide" technique to reach its target. It would initiate a de-orbit burn, still using its shape and the proper angle to ‘skip’ off the outer atmosphere. At its lowest point, it would deploy its payload, in most cases intended to be nuclear bombs. After the skip, it would use its rocket motors to push itself back into orbit. This was thought to be a rather brutal maneuver for the pilot, as he would be pulling a very uncomfortable number of G’s both de-orbiting and accelerating up to altitude again.

To aid in a boost-glide mission, the X-20 was often depicted as having an attached rocket booster on its aft end, to give it the extra fuel and thrust needed to make repeated burns both into and out of the edge of the atmosphere. This booster would be jettisoned prior to final descent.

Many consider the antipodal bomber, and especially the X-20 program, one of the great ‘what-if’ scenarios of modern manned space flight. If the project had gone ahead, it would have given the US a reusable winged spacecraft fifteen years before the Space Shuttle, and would have been a potential game changer for space flight for decades afterward.

However, it was intended mostly for military reconnaissance and long-range nuclear strike missions, which have since proven much cheaper to accomplish with automated satellites and ICBMs, respectively. So even if the X-20 project had gone forward, it would have had a hard time finding the proper niche in which to justify its continued great expense.

Still, the technology for the antipodal bomber is long since proven, and it would be interesting to see if any of the emerging fledgling space powers will ever resurrect the technology for other applications.



X-38 CREW RETURN VEHICLE
Tech Level: 10
CRV with engine module attached. Image courtesy NASA.

This project was a small vessel designed to let personnel safely evacuate space facilities in low orbit during an emergency. A prototype, the X-38 Crew Return Vehicle (CRV), was being pioneered by NASA primarily for use as a lifeboat on the International Space Station until budget concerns killed it in April 2002. The project at the time was 80% complete and had undergone extensive flight-testing, proving the viability of the concept.

The CRV uses a aerodynamically optimized lifting body borrowed from the X-24A project of the 1970s. It was also equipped with a rear engine rocket module, with which it uses for a de-orbit burn. When this is exhausted, the engine module is jettsoned and the CRV glides back to Earth unpowered like the Space Shuttle. It uses a steerable parafoil parachute for its final descent phase. Its life-support system was designed to support six passengers for up to nine hours, though de-orbit would take two hours at the most.

Though the project is dead at NASA, the European Space Agency (ESA) has expressed interest in using the design as a Crew Transport Vehicle (CTV), basically an updated space capsule, if and when that organization ever begins to accommodate manned missions.


ADVANCED ROCKET SPACEPLANES
Tech Level: 11

The next generation of spaceplanes would most likely try to realize the ideal of an SSTO winged vehicle. These spaceplanes would use conventional jet engines to take off and ascend as high as possible, then switch to a rocket motor to carry it the rest of the way into space. They would then glide back to Earth in a manner similar to the Space Shuttle. Small suborbital models would likely come first, followed by larger, more robust spaceplanes designed for full orbital flight.

A good example of this was Bristol Spaceplane Limited’s Ascender project. The two-passenger craft would use standard jet engines to carry it up to an altitude of 8 kilometers, and to assist it in landing in the very last stage of its descent. At 8000 meters, the craft would disengage its jet engines and fire its twin rocket engines in a steep vertical climb. At 64 kilometers height, the engines would cut and the craft would coast up to a final altitude of 100 kilometers in a ballistic trajectory. It would then fall back into the atmosphere and undergo re-entry, gliding most of the way to a landing and using its jet engines for maneuvering if needed. Total flight time would be about 30 minutes.

The Ascender had been an Ansari X-Prize contender founded on an earlier study conducted in the 1990s. Unfortunately, lack of funding never allowed the spacecraft to get out of the design phase, despite the apparent solidity of the concept and the intended use of off-the-shelf technology.

If the Ascender test vehicle had proven viable, it would have led to the development a larger "SpaceCab" vehicle, which would have pretty much have been the same concept scaled up to an airliner-sized vehicle. The SpaceCab would have been able of achieving orbit with up to to six passengers anoard.

Advanced rocket spaceplanes from science fiction would include the ‘super space shuttles’ seen in the movie Armageddon. A commercial fleet of them were also featured in the novel Moonfall by Jack McDevitt.


X-33 VENTURESTAR
Tech Level: 12
Image courtesy NASA.

The X-33 project was intended to develop a Space Shuttle replacement, a 1/3 scale functional test model. The Venturestar would have been the name of the full-scale vehicle. If this project had reached fruition, it would have represented a radical leap forward in spaceplane technology and manned spaceflight in general.

The X-33 combined a number of cutting edge technologies, such as an aerodynamic lifting body, metallic thermal protection systems, composite cryogenic fuel tanks, and perhaps most significantly, aerospike rocket engines. Through the use of advanced materials, its lifting body design, and more efficient areospike engines, designers hoped to prove the concept of an SSTO spaceplane lightweight and powerful enough that could perform just as well as the Space Shuttle in hauling cargo into space.

The Venturestar would have been able to take off vertically and land on commercial runways of sufficient size, and was intended to be operated by the private sector in the same way that NASA today is farming out manned spacecraft operations today. Besides space missions, it was also intended for possible intercontinental suborbital flights. It would have been able to perform almost any task the Space Shuttle had, but was intended to be easier to maintain and safer to operate, as well as having a quicker turnaround time.

Whether it could have fulfilled such promises is unknown, as the project was scuttled due to budgetary and engineering concerns in 2001. Both the Air Force and the project’s main contractor, Lockheed Martin, have expressed interest in reviving the project in the years since, but have so far been unsuccessful in obtaining funding. In the future, technology developed for the project may find its way into other ventures, and a space power outside the US government may decide to use the design or elements of it in the future.


SCRAMJET SPACEPLANES
Tech Level: 13

A more detailed description of scramjet technology is linked to at the bottom of this page. Basically, scramjets allow supersonic airflow through their engines, which in turn allows them to achieve astonishing hypersonic speeds.

The extreme upper speed limits of a scramjet engine is undetermined, but is thought to be in the range of Mach 20 to 25, fast enough to acquire orbital velocity wiuth a inimal use of rocket boosters. Whether the rest of the craft could be built to withstand the structural stress of such in-atmosphere velocities remains to be seen, however. In practical use, it more likely scramjet vehicles will operate in the speed range of Machs 2 (their minimal operating speed) to about 10 (the maximum velocity modern airframes are expected to be able to withstand in the lower atmosphere.)

Besides being much faster, scramjet engines also have a much higher operational ceiling than their lower-tech jet cousins. Advanced turbojets have an extreme operational ceiling of about 40 km, while ramjets have a ceiling of about 55 km. Scramjets can operate up to 75 km high without fear of stalling.

If scramjets could achieve their theoretical extreme speed limit of Mach 20 to 25, it would be possible for a vehicle equipped with them to scream up to 75 km altitude, building up all the velocity they could, and then just "coast" up into orbit.

However, it is far more likely that we’ll see scramjet/rocket hybrid spaceplanes. The liquid fuel rocket engine would be used for takeoff, subsonic, and low hypersonic flight. Once past the lower scramjet velocity threshold of about Mach 2-3, the scramjets takes over, further accelerating the vehicle to its maximum velocity of Mach 10 or so. The rocket engines then re-ignite to supplement the scramjet engine. Past Mach 18 the rocket engine takes over completely, propelling the vehicle into orbit and allowing it to maneuver in space. Alternately, the vehicle could also be towed or carried up to scramjet speed by a first-stage aircraft, which could also carry it up over the thicker layers of the atmosphere where drag could impede its acceleration.

There has also been talk of a rocket/ramjet/scramjet combined cycle engine, so the vehicle can take full advantage of optimized engine efficiency at each speed stage (rocket up to Mach 2-3, ramjet from Mach 3 to Mach 6, scramjet from Mach 6 to Mach 12, scramjet/rocket to Mach 18, and rocket only beyond Mach 18.) Also, the vehicle may have a turbojet/ramjet/scramjet combined cycle engine for take-off through Mach 12, then use separate rocket engines, either integrated onto the vehicle or attached as modular add-on boosters, to allow the acceleration to space and to de-orbit. However, combining all these engines, either in separate sections of the craft or using the same exhaust housing, would be a major engineering feat in and of itself.

NASA and a number of other interests are actively pursuing research into scramjet engines, and several successful, if brief, flight tests of the engines have proven the viability of the concept.


ADVANCED PROPULSION SPACEPLANES
Tech Level: 14

In many science fiction sources featuring futuristic spaceplanes, particularly space operas, the vehicles will often use engines much more advanced than conventional jets or chemical rockets. The more sophisticated means of propulsion could include things like ion engines, plasma rockets, fusion rockets, or even gravitic repulsors, FTL drives, and the like on very advanced versions. Some options like plasma rockets could be used exclusively, where the rocket engines can just be amped up or down for whatever speed is needed, while others may be combined with high-end in-atmosphere engines like scramjets. The latter may be necessary for propulsion such as fusion rockets, whose radioactive exhaust could result in a number of unfortunate effects if they were used inside an atmosphere.

In a world where suborbital and orbital travel is routine, investment in these faster, more efficient, and more powerful types of advanced propulsion spaceplanes would be a smart investment, to provide better services and to get a leg up on the competition.

Advanced spaceplanes in fiction would include the generic Shuttle subcraft from the Traveller tabletop RPG, the Imperial Shuttle from Star Wars, and the Quninjet from Marvel’s Avengers comic. Many one or two-man fighters seen in science fiction would also fall into this category, and will be detailed in a separate article.


FURTHER INFORMATION

http://orbitalvector.com/Orbital%20Travel/Suborbital%20Travel/SUBORBITAL%20PASSENGER%20TRAVEL.htm

http://orbitalvector.com/Orbital%20Travel/Dropships/Dropships.htm

http://en.wikipedia.org/wiki/Spaceplane

http://www.howstuffworks.com/space-plane.htm

http://www.aerospaceguide.net/spaceplanes/index.html

Ascender Project

http://www.bristolspaceplanes.com/projects/ascender.shtml

X-33 Venturestar

http://en.wikipedia.org/wiki/Lockheed_Martin_X-33

http://www.nasaspaceflight.com/2006/01/x-33venturestar-what-really-happened/

http://orbitalvector.com/Orbital%20Travel/Aerospike%20Rockets/Aerospike%20Rockets.htm

Scramjets

http://orbitalvector.com/Orbital%20Travel/Scramjets/Scramjets.htm


Article added 23 May 2011

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