Reusable launch system
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A reusable launch system (or RLV: reusable launch vehicle) is a launch vehicle which is capable of launching into space more than once. This is in opposition to an expendable launch system, where each launch vehicle is launched once and then discarded.
No true orbital reusable launch system is in use as of June, 2005. The closest example is the grounded Space Shuttle. The Orbiter, which includes the main engines and the two solid rocket boosters, is reused after several months of refitting work for each launch. The external fuel drop tank is discarded.
Orbital RLVs are thought to provide the possibility of low cost and highly reliable access to space. However, given the lack of experience with these vehicles, the actual costs and reliability are yet to be seen.
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History
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As usual, fiction preceded actual science work in this area. In the early 1950s popular science fiction often depicted space launch vehicles as either single-stage reusable rocketships which could launch and land vertically (SSTO VTVL), or single-stage reusable rocketplanes which could launch and land horizontally (SSTO HTHL).
The realities of early engine technology with low specific impulse or insuficient thrust-to-weight ratio to escape our gravity well, compounded by construction materials without adequate performance (strength, stiffness, heat resistance) and low weight seemingly rendered that original single-stage reusable vehicle vision impossible.
However some thought the problems could be surpassed.
Before VTVL SSTO designs came the partially reusable multi-stage NEXUS launcher by Krafft Ehricke. The pioneer in the field of VTVL SSTO, Philip Bono, worked at Douglas. Bonno proposed several launch vehicles including: ROOST (http://www.astronautix.com/lvs/roost.htm), ROMBUS (http://www.astronautix.com/lvs/rombus.htm), Ithacus (http://www.astronautix.com/lvs/ithacus.htm), Pegasus (http://www.astronautix.com/lvs/pegvtovl.htm) and SASSTO (http://www.astronautix.com/lvs/sassto.htm). Most of his vehicles combined similar innovations to achieve SSTO capability. Bonno proposed:
- Plug nozzle engines to retain high specific impulse at all altitudes.
- Base first reentry which allowed the reuse of the engine as a heat shield, lowering required heat shield mass.
- Use of spherical tanks and stubby shape to reduce vehicle structural mass further.
- Use of drop tanks to increase range.
- Use of in-orbit refueling to increase range.
Bonno also proposed the use of his vehicles for space launch, rapid intercontinental military transport (Ithacus), rapid intercontinental civilian transport (Pegasus), even Moon and Mars missions (Project Selena (http://www.abo.fi/~mlindroo/SpaceLVs/Slides/sld009.htm), Project Deimos (http://www.abo.fi/~mlindroo/SpaceLVs/Slides/sld010.htm)).
In Europe, Dietrich Koelle, inspired by Bono's SASSTO design, proposed his own VTVL vehicle named BETA (http://www.spacefuture.com/archive/beta_a_single_stage_reusable_ballistic_space_shuttle_concept.shtml).
Before HTHL SSTO designs came Eugen Sδnger and his Silbervogel ("Silverbird") suborbital skip bomber. HTHL vehicles which can reach orbital velocity are harder to design than VTVL due to their higher vehicle structural weight. This led to several multi-stage prototypes such as an suborbital X-15. Aerospaceplane being one of the first HTHL SSTO concepts. Proposals have been made to make such a vehicle more viable including:
- Rail boost.
- Use of lifting body designs to reduce vehicle structural mass.
- Use of in-flight refueling.
Other launch system configuration designs are possible such as horizontal launch with vertical landing (HTVL) and vertical launch with horizontal landing (VTHL). One of the few HTVL designs made is Hyperion (http://www.astronautix.com/lvs/hypnssto.htm) by Philip Bono. X-20 Dyna-Soar is one example of an early VTHL design.
The late 1960s saw the start of the Space Shuttle design process. From an initial multitude of ideas a two-stage reusable VTHL design was pushed forward. That eventually ended up as a reusable orbiter with an expendable drop tank and reusable solid rocket boosters to reduce design expenses.
During the 1970s further VTVL and HTHL SSTO designs were proposed for solar power satellite and military applications. There was a VTVL SSTO study (http://www.abo.fi/~mlindroo/SpaceLVs/Slides/sld043.htm) by Boeing. HTHL SSTO designs included the Rockwell Star-Raker (http://www.abo.fi/~mlindroo/SpaceLVs/Slides/sld047.htm) and the Boeing HTHL SSTO study (http://www.abo.fi/~mlindroo/SpaceLVs/Slides/sld041.htm). However the focus of all space launch funding in the United States on the Shuttle killed off these prospects. The Soviet Union followed suit with Buran. Others preferred expendables for their lower design risk, and lower design cost.
Eventually the Shuttle was found to be expensive to maintain, even more expensive than an expendable launch system would have been. The cancelation of a Shuttle-Centaur rocket after the loss of Challenger also caused an hiatus that would make it necessary for the United States military to scramble back towards expendables to launch their payloads. Many commercial satellite customers had switched to expendables even before that, due to unresponsiveness to customer concerns by the Shuttle launch system.
Then the Soviet Union imploded and the cost of Buran became untenable. Russia has only used pure expendables for space launch since then.
The 1990s saw interest in developing new reusable vehicles. The military Strategic Defense Initiative ("Star Wars") program "Brilliant Pebbles" required low cost, rapid turnaround space launch. From this requirement came the McDonnell Douglas Delta Clipper VTVL SSTO proposal. The DC-X prototype for Delta Clipper demonstrated rapid turnaround time and that automatic computer control of such a vehicle was possible. It also demonstrated it was possible to make a reusable space launch vehicle which did not require a large standing army to maintain like Shuttle. From the commercial side, large satellite constellations such as Iridium were proposed which also had low cost space access demands. This fueled a private launch industry, including partially reusable vehicle players, such as Kistler, and reusable vehicle players such as Rotary Rocket.
The end of that decade saw the implosion of the satellite constellation market with the bankruptcy of Iridium. In turn the nascent private launch industry collapsed. The fall of the Soviet Union eventually had political ripples which led to a scaling down of ballistic missile defense, including the demise of the "Brilliant Pebbles" program. The military decided to replace their ageing expendable launcher workhorses, evolved from ballistic missile technology, with the EELV program. NASA proposed riskier SSTO concepts to replace Shuttle, to be demonstrated under the X-33 and X-34 programs.
The 21st century saw rising costs and teething problems lead to the cancelation of both X-33 and X-34. Then the Space Shuttle Columbia disaster and another grounding of the fleet. The Shuttle design was now over 20 years old and in need of replacement. Meanwhile the military EELV program churned out a new generation of better expendables. The commercial satellite market is depressed due to a glut of cheap expendable rockets and there is a dearth of satellite payloads.
Against this dire backdrop came the Ansari X Prize contest, inspired by the aviation contests made in the early 20th century. Many private competitors disputed the Ansari X Prize, the winner being Scaled Composites with their reusable HTHL SpaceShipOne. It won the ten million dollars, by reaching 100 kilometers in altitude twice in a two week period with the equivalent of three people on board, with no more than ten percent of the non-fuel weight of the spacecraft replaced between flights. While SpaceShipOne is suborbital like the X-15, some hope the private sector can eventually develop reusable orbital vehicles given enough incentive. SpaceX is a recent player in the private launch market which has partially reusable vehicles.
Orbital reusable launchers
Currently in use
- Space Shuttle (partially reusable)
Planned
- SpaceX Falcon I (partially reusable; maiden flight May, 2005)
- SpaceX Falcon V (partially reusable; maiden flight 2nd quarter, 2006)
- Kistler Aerospace K-1 (maiden flight schedule not yet announced)
- Kliper (Russian-European partially reuseable spacecraft to be launched around 2011 for the first time)
Historical
- Soviet Union Buran (partially reusable)
Suborbital reusable launchers
Currently in use
Planned
- Armadillo Aerospace Black Armadillo
- Canadian Arrow
- Pablo de Leon & Associates Gauchito
- TGV Rockets MICHELLE-B
- Aeronautics and Cosmonautics Romanian Association (ARCA) Orizont
- Starchaser Industries Starchaser V - Thunderstar
- The da Vinci Project Wild Fire MK VI
- XCOR Aerospace Xerus
Historical
External links
- History of the Phoenix VTOL SSTO and Recent Developments in Single-Stage Launch Systems (http://www.spacefuture.com/archive/history_of_the_phoenix_vtol_ssto_and_recent_developments_in_single_stage_launch_systems.shtml)fr:Navette spatiale
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