The Space Sortie Vehicle

Transcription

1 The Space Sortie Vehicle Until now, apart from the NASA space shuttle, almost every national space program has been based around vertically launched expendable rockets. These are not only very expensive but they also are very difficult to operate, in most circumstances a long preparation period of days, even months is needed for a successful launch. It is a widely spread belief that the ideal vehicle would be a system that could take off like a conventional airliner, reach high altitude, place its cargo into orbit and later land as a conventional airliner. Such a system would combine the operational agility of common aircraft with a very low operating cost because it would be totally reusable. However all previous concepts (single stage to orbit - SSTO) would require a huge amount of thrust potential from the engines and so it would be quite a leap from the available technology for the time being. The following concept is for a more easily realized two stage to orbit (TSTO) vehicle that would consist of a carrier aircraft and a smaller orbital vehicle. In 1982, the US Air Force studied the concept of an air-launched spaceplane called the Space Sortie Vehicle (SSV). The various designs were mostly smaller variations of other space shuttle concepts (e.g., the NASA Shuttle or the Star Clipper). This SSV would be small enough to be launched from a Boeing 747, possibly the same Shuttle Carrier Aircraft that is used to ferry the existing NASA Space Shuttles, albeit with a modified V-tail. The standard Star Clipper design would use eleven main engines when it launched from the Kennedy Space Center. The air-launched version of the Star Clipper would use only three of the Star Clippers main engines. All three would be used for the initial ascent but only the center one would remain operating once the main eternal tanks (ETs) had been separated. One design for an SSV, a mini-star Clipper, could be used for passenger flights to orbit. The artist has used artistic license to depict the SSV with all three engines operating after the ETs have separated.

2 A mini-nasa shuttle design for an SSV from the USAF studies of the 1980s. This scaled-down mini-shuttle (with a payload capacity of 2,000 pounds or 8 crew) could be used for military missions (tactical reconnaissance), crew transfer to the ISS and even the first-phase of orbital space tourism (with an excessive ticket price of course). By launching from an aircraft, the SSV would not be constrained to wait for orbital launch windows where the rotation of the earth has to be synchronised with the orbital trajectory of the destination - which is precisely what happens when the NASA Shuttle has to launch on a mission to the ISS. An SSV could be prepared, launched and rendezvous with the ISS within as little as 24 hours the carrier aircraft would merely takeoff and fly to the nearest convenient global location with a launch window. The concept was so promising that the Soviet government realized that it would be prudent to develop their own version of the SSV to counter the potential military threat of the US SSV. The Soviet SSV project commenced in 1988 and was thoroughly researched but ultimately canceled in 1991 due to the collapse of the Russian economy and the breakup of the Soviet Union. This Russian spaceplane was called MAKS (Multipurpose Aerospace System). The orbiter was supposed to reduce the cost of transporting materials to Earth orbit by a factor of ten. The reusable orbiter and its external non-reusable fuel tank would be launched by an Antonov AN-225 airplane. Had it been built, the system would have weighed 275 tons, and would have been capable of carrying a 7 ton payload. Three variants of the MAKS system were conceived, the standard configuration, one with upgraded payload capability, and a future version that included its fuel tank within the envelope of the orbiter, becoming fully reusable. Research on the project was so advanced at the time of its cancellation that an aerodynamic flight-test vehicle, comprising an orbiter and an external tank was built. The wings of the MAKS spaceplane would fold/tilt upward to reduce atmospheric heating on re-entry. Also, if the air-launch technique proved technically unfeasible, a variation (called the OK-M2 version) could have been launched from a conventional booster rocket.

3 The three variations of the MAKS. The MAKS system would consist of two stages: 1. Antonov AN-225 carrier plane, which is currently the world s largest aircraft. It would take-off from suitable airports around the world and transport the second stage for launch on any staging point above the Earth. The An-225 would use in-flight refueling for equatorial launches. 2. Space Stage would be carried on top of the An-225. Three different Space Stages were envisaged: MAKS-OS (Reusable Spaceplane) with an external tank. It would be used to carry from 2 up to 6 crew. MAKS-T would use an expendable unmanned stage instead of the MAKS Spaceplane to launch payloads up to 19,500kg to low earth orbit or 5000kg to GEO. MAKS-M will be the ultimate version of MAKS. It would be a fully reusable spaceplane. This would become the Holy Grail of space transportation, enabling commercial, passenger-paying space flight to commence from any major airport around the world. It is clear to any casual observer that the MAKS was an almost direct copy of the USAF SSV concept, in particular the mini-nasa Shuttle, which would have been launched from the Shuttle Carrier Aircraft. However, the Russian design would utilize the far larger AN-225 which would effectively solve the complex technical problem of designing such a small spaceplane. If the USAF had gone ahead and built their SSV, the American orbiter vehicle would have had a maximum landing mass of ten tons (including payload) whereas the Russian MAKS would have a landed mass of 20 tons (including payload). Clearly, the AN- 225 would be a superior ferry/launch aircraft.

4 In the late 1980s and early 90s, expensive mock-ups were constructed to allow Russian engineers to test the integrity of the vehicle s structure. Static vibration tests were done to ensure that the vehicle would hold together during the ascent and the punishing turbulence of re-entry. Also, ergonomics tests were performed - not only for the astronauts and passengers but also for the ground personnel who would have to gain access to any critical systems and perform the maintenance at the conclusion of every mission.

5 The key to the [future] success of the MAKS would be the propulsion system. The MAKS would utilize a unique tri-propellant engine that would start the ascent using liquid oxygen and kerosene, but then later switch (in mid-flight) to using liquid oxygen and liquid hydrogen. This would allow for greater thrust during the start of the flight but also enable greater efficiency at higher altitudes. The above illustration shows the internal structure of the ET and how it connects to MAKS.

6 The external tank (ET) would have three chambers: one for liquid hydrogen (at the front), one for liquid oxygen (in the middle), and one for kerosene (at the rear closest to the MAKS spaceplane). A full mock-up of the ET was constructed at the same time as the MAKS test vehicle. This was done not only to allow for structural/vibration testing, but also to determine the efficiency of the Russian manufacturing techniques - and thus lower the cost and time inbetween flights of the vehicle. The above diagram shows the payload bay for the MAKS. Although tiny in comparison to the NASA Shuttles, the compact design would allow for logistics flights to a space station, as well as passenger transport, satellite repair and recovery, and possibly even space warfare missions (tactical reconnaissance or anti-satellite operations).

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8 The above diagram shows the separation angle of the MAKS from the AN-225. Scale diagram, showing the angle of the vehicle in relation to the ground and the ET.