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A combination launch system is a launch system that consists of multiple launch technologies that work together to boost a payload into orbit for a small fraction of the cost of current launch vehicles. It works by reducing the amount of velocity that the rocket-powered components of the launch system need to achieve. This reduces the propellant fraction and increasing the payload fraction of the launch vehicle to such a degree that airliner like operations to orbit with a fully reusable launch system becomes possible.[1][2][3]

The components

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An inclined track ground accelerator.
Subsonic air-assisted launch.
Supersonic air-assisted launch.

The first component of a combination launch system consists of either a ground-assisted launch or an air-assisted launch. A ground-assisted launch can be performed using a horizontal track ground accelerator, an inclined track ground accelerator, a vertically oriented ground accelerator, or a trackless winch-launch system similar to the ones used to launch sailplanes. An air-assisted launch can be performed using a subsonic carrier aircraft as was done with the X-15 rocket plane, the Pegasus (rocket), and both SpaceShipOne and SpaceShipTwo. The Stratolaunch carrier aircraft is another example of subsonic air-assisted launch. Another type of subsonic air-assisted launch is the Towed Glider Air-Launch System. An air-assisted launch can also be performed at supersonic speeds as was done with the D-21 drone when it was launched from the back of the SR-71, and as was proposed for a follow-on X-15 program that would have used the XB-70 as a supersonic carrier aircraft.

The second component of a combination launch system is to make the launch vehicle reusable. This can be a reusable first stage with expendable upper stage launch vehicle, a fully reusable two-stage launch vehicle, or a fully reusable single stage launch vehicle. The launch vehicles can be vertical landers like the Falcon 9, or horizontal landers like the X-15 and the Space Shuttle. Fully reusable two stage to orbit and single stage to orbit launch vehicles have not been possible in the past due to the increase in empty weight that comes with making them reusable. This increase in empty weight reduces the amount of useful payload they can carry to zero when they go to orbit on their own. Using either of these two types of launch vehicles as part of a combination launch system reduces their propellant fraction enough that they can now carry a worthwhile payload.

The third component of a combination launch system is to include some sort of combination air-breathing and rocket motor propulsion system with the reusable launch vehicle. This can consist of separate ramjets mounted on the sides of a launch vehicle that also has conventional rocket motors mounted at the rear of the vehicle. It can also consist of a combination flow path rocket-ramjet or a combination flow path rocket-ramjet-scramjet. All of these reduce the amount of oxidizer the launch vehicle needs to carry which allows it to carry a larger payload.

Non-rotating skyhook.

The fourth component of a combination launch system is a non-rotating skyhook. The non-rotating skyhook works by reducing the velocity the launch vehicle needs to achieve to reach orbit as the lower end of the Skyhook is moving at less than orbital velocity for its altitude. Like air-assisted launch, ground-assisted launch, and combination air-breathing and rocket motor propulsion systems, this reduction in velocity reduces the propellant fraction and increases the payload fraction of the launch vehicle which reduces the cost to orbit. Some proposals for combination launch systems that include a non-rotating skyhook start out with a skyhook that has an initial overall length of approximately 200-kilometers. This helps to keep the size of the initial investment down when the flight rate is low which also helps to keep the cost to orbit down. As demand for flights to the skyhook increases it is possible to Increase the length of the skyhook which also increases the amount of velocity reduction to the launch vehicle. This allows for an even lower propellant fraction and an additional increase in payload fraction on the launch vehicle which further reduces the cost of getting to orbit. Proponents of combination launch systems have claimed that a fully mature system has the potential of reducing the cost to orbit to $100 per pound or less.

The idea of using a non-rotating skyhook as part of a space transportation system for Earth where sub-orbital reusable launch vehicles would fly to the bottom end of the tether, and spacecraft bound for higher orbit, or returning from higher orbit, would use the upper end of the tether, was first proposed by E. Sarmont in 1990,[4] and later expanded on in a number of follow-on works.[5][6][7][8][9] Other scientists and engineers, as well as NASA, Lockheed Martin, former astronaut Bruce McCandless II, and Dr. Robert Zubrin, have also investigated, validated, and added to this concept.[10][11][12][13][14][15][16][17][18][19][20]

History

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The idea of a combining multiple launch methods has been around for a long time. The earliest occurred in 904 A.D. when the Chinese attached small gunpowder rocket motors to arrows as a way of extending the range of the arrows. In this case, the bow was the ground accelerator that gave the arrow its initial speed and direction, and the rocket was used to add to the speed of the arrow and thereby increase its range. They were called fire arrows. Aircraft catapults/ground accelerators have also been used to accelerate aircraft up to flight speed as well as for launching the V-1 flying bomb in WW2. Other examples of combination launch systems were the air-launched reusable rocket planes of the 1940's, 1950's, and 1960's. The most well-known of these being the B-52 launched X-15 rocket plane.

Combination launch systems in literature and film

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  • Robert A. Heinlein used a mountain slope ground accelerator to launch a reusable rocket in his 1949 novel The Man Who Sold the Moon.
  • When Worlds Collide (1951 film) used a mountain slope ground accelerator to launch the Ark, but the book did not.
  • Fireball XL5, a 1960s children's television show, used a horizontal ground accelerator to launch a reusable rocket called the Fireball XL5.
  • Dean Ing used a mountain slope ground accelerator with a reusable launch vehicle in his 1988 novel "The Big Lifters".
  • Opening the High Frontier is a book about combination launch systems and how they can be used to build a spacefaring civilization.

See also

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References

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  1. ^ Combination Launch Systems, high-frontier.org, October 2016
  2. ^ Combination Launch Systems, part 2, high-frontier.org, November 2016
  3. ^ Combination Launch System, wordpress.com, June 2017
  4. ^ Sarmont, E. (26 May 1990). An Orbiting Skyhook: Affordable Access to Space. International Space Development Conference. Anaheim California.
  5. ^ Sarmont, E. (October 1994). "How an Earth Orbiting Tether Makes Possible an Affordable Earth-Moon Space Transportation System". SAE 942120. SAE Technical Paper Series. 1. doi:10.4271/942120.
  6. ^ Sarmont, E. (July 2014). "Affordable Access to Space: Basic Non-Rotating Skyhook with Falcon 9 & Dragon" (PDF). {{cite journal}}: Cite journal requires |journal= (help)
  7. ^ Sarmont, E. (August 2016). Opening the High Frontier: Our Future in Space. ISBN 978-0692760024.
  8. ^ Sarmont, E. (October 2016). "Opening the High Frontier". high-frontier.org.
  9. ^ Sarmont, E. (August 2017). "Combination Launch Systems" (PDF). Starship Congress 2017.
  10. ^ Wilson, N. (August 1998). "Space Elevators, Space Hotels and Space Tourism". SpaceFuture.com.
  11. ^ Smitherman, D.V. "Space Elevators, An Advanced Earth-Space Infrastructure for the New Millennium". NASA/CP-2000-210429. {{cite web}}: Check |archiveurl= value (help)CS1 maint: url-status (link)
  12. ^ Mottinger, T; Marshall, L (2000). "The Bridge to Space – A space access architecture". doi:10.2514/6.2000-5138. AIAA 2000-5138. {{cite journal}}: Cite journal requires |journal= (help)
  13. ^ Mottinger, T; Marshall, L (2001). "The Bridge to Space Launch System". Space Technology and Applications International Forum. CP552.
  14. ^ Marshall, L; Ladner, D; McCandless, B (2002). "The Bridge to Space: Elevator Sizing & Performance Analysis". Space Technology and Applications International Forum. CP608.
  15. ^ Stasko, S; Flandro, G (2004). "The Feasibility of an Earth Orbiting Tether Propulsion System". 40th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit. doi:10.2514/6.2004-3901. ISBN 978-1-62410-037-6. AIAA 2004-3901.
  16. ^ Zubrin, R (September 1993). "The Hypersonic Skyhook". Analog Science Fiction / Science Fact. 113 (11): 60–70.
  17. ^ Zubrin, R (March 1995). "The Hypersonic Skyhook". Journal of the British Interplanetary Society. 48 (3): 123–128. Bibcode:1995JBIS...48..123Z.
  18. ^ Andrews, D. (3 September 2009). "Advanced ETO Space Transportation". NASA Langley Advanced Space Transportation Workshop. Archived from the original on 2014-07-13.
  19. ^ Andrews, D. "Space Colonization: A Study of Supply and Demand" (PDF). Archived (PDF) from the original on 2012-03-11.
  20. ^ Sarmont, E. "Affordable to the Individual Spaceflight". {{cite web}}: Check |archiveurl= value (help)CS1 maint: url-status (link)
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