After reading the thread Expandable vs. Reusable I kept on wondering why expandable space vehicles are so much cheaper then reusable ones even if they were frequently used. The wings of the Space Shuttle design gave us the key to reusability, but not the cost-savings that should go along with it. Many comments were made about wings that they are dead weight in a space launch. They are actually right if the vehicle goes straight up at once. Wings are not the most efficient way to achieve reusability in a vertical takeoff (certainly if the wings of the RLV are large compared with its VT (Vertical Takeoff) launch system like the Space Shuttle). The main advantage of an expandable (or partly reusable) rocket with a vertical takeoff is the loss of weight by shedding a component during each stage of launch. In this case any kind of extra weight is a disadvantage. Wings might give reusability to a space vehicle, but if those wings are too big (compared with the VT launch system) that advantage might not compensate the extra costs of R&D, special materials, weight and maintenance. Especially if those wings do not add anything extra but dead weight to the take off.
It might even be that full reusability in a vertical launch system might not even be desirable from a production/cost perspective and technological point of view. First the components will have to re-enter the atmosphere at Mach 10 and they will also have to withstand sea-water. Then the components will have to be recovered and transported. After undergoing that amount of stress a significant amount of detailed inspection is required. Finally the repairs and testing of components doesn’t help lowering the costs either. Any kinds of reusability in a vertical take-off doesn’t only add up in R&D and maintenance costs, but also in dead weight, while it lowers the possible amount of pay-load at the same time. Too often we associate reusability and SSTO with rockets that are launched vertical. If we shift from the idea from a reusable Single-STO with a vertical takeoff to a reusable 3- or 2-STO with a HTHL (horizontal take-off & landing) we might be able to avoid most of those problems.
A reusable 3-STO vehicle could be completely reusable, cost effective and easy to develop at the same time if all vehicles of the three different stages have wings and take off horizontally in comparison to a Vertical Takeoff SSTO
• Each stage vehicle can be designed (and shaped) to perform at their optimum according to their specific flight conditions (from subsonic to hypersonic speed) with common technology, which makes the R&D of a reusable 3STO relatively easy and cheap compared with a reusable SSTO:
1. First Stage of launch could be a fuel efficient lightweight conventional airplane (whether subsonic or supersonic), which is able to carry the 2nd & 3rd stage vehicles to a height of 50000 feet or more.
2. Second stage of launch could be a rocket with wings (like the wings of the *Pegasus (rocket)
http://en.wikipedia.org/wiki/Pegasus_(rocket) ) and should also be able to land like an airplane.
3. Only the spaceplane in the third stage of launch would need full ablative protection. This means less complexity and weight for the first and second stage vehicles.
• The airlift provided by all the wings in a horizontal take-off could compensate the extra weight by the wings in the first stage of launch with less (wing-)weight at each stage of launch. It will also avoid rocket flight in the densest part of the atmosphere where more rocket fuel, and thus a larger launch vehicle, would be needed to overcome air friction.
• The 3STO vehicle can take off horizontally combined and each stage vehicle could land separately like an airplane, which makes all the 3 stages fully reusable and avoids most of the problems of a reusable vertical landing (see above).
• Other advantages are: less subject to launch-constraining weather, reduced national range scheduling constraints, minimum launch site requirements, and reduced range, safety concerns, and equatorial launch from the US
In this case I would prefer the 3M2-5 Myasishchev design (
http://www.ussr-airspace.com/index.php? ... cts_id=637). I think this Russian designs has the potential to become a fully reusable HTHL 3-STO if the 2nd stage rocket also would have wings (like the *Pegasus (rocket)
http://en.wikipedia.org/wiki/Pegasus_(rocket)) and an autopilot for unmanned landings. By putting the 2nd and 3rd stage vehicles on the back of the carrier airplane there’s enough space for eventual wings of the 2nd & 3rd stage vehicles, which also could provide an extra air-lift. The (winged) rocket & spaceplane could be then launched like a military projectile from a conventional subsonic or supersonic airplane.
(*Manufacturer of the Pegasus rocket: Orbital Sciences Corporation. Most of the Pegasus was designed by a team led by Dr. Antonio Elias and the wing was designed by Burt Rutan! Check out the mission results!)
A reusable HTHL SSTO would require a lot of funding, fundamental research in new (lighter, stronger and heat-resistant) materials and rocket engine technology. The question is then where to start, how to do it and who are willing and able to do it. It is not unrealistic to design a reusable SSTO, but it simply would take too many hurdles, unknown factors and time to do that in one straight line. I think funding and R&D of a SSTO or any kind of new technology can give uncertain outcome. That is why multiple back-up plans are always needed. I think it would be a safe bet and good foundation to develop an air-launch to orbit system for medium cargo first and then to design a reusable HTHL 3-STO for commercial manned launch. In a later stadium the carrier airplane & rocket could be replaced a suborbital spaceplane (See Youtube: Peregrine Mission Animation by deanfilip
http://www.youtube.com/watch?v=wHPck9PFzZc). If there are new developments in materials, launch assists (Maglev, etc…) and rocket technology (SABRE, LACE, etc…), then we could see a possible transition from a reusable muliple-STO into a reusable SSTO with HTHL. Even if it turns out at the end of route that a new RLV (for example the Skylon or the X-33) would not be capable to launch itself into orbit on their own there would still be a carrier airplane or suborbital spaceplane available (from former programs) to give them piggy back ride into LEO (or the new RLV like Skylon and/or X33 could become suborbital carrier spaceplanes themselves). By the way even Elon Musk from SpaceX has expressed his interest in air launch to orbit systems to lower costs further and to achieve full reusability at the same time. At the moment he will ofcourse stick with the common approach of vertical launch&landing, because this is the safest bet and fastest approach of manned launch into LEO and to the moon. On the long term however if he wants more "normal" folk on board then a more affordable and comfortable approach is needed. Cooperation in reusable air launch to orbit systems for cargo and humans between SpaceX, Virgin Galactic/Scaled Composites and Orbital Sciences Corporation in the near future would not be a bad idea as a first start of designing a reusable HTHL 3-STO and with a reusable HTHL SSTO as the finish line. Travelling into space might never be as cheap and easy as air travel, but it is all about making it affordable and doable for most people even if it is going to be an event that happens once or twice in anyone’s life-time for the coming decades. If we really want affordable and mass transportation to multiple BA inflatable spacestations in LEO or even to the moon, then I think this would be a doable path to take.
) so much as you will have either moved on to a new job maybe in a new country or field or something like that.
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