3 ms·

"Because it will use a low-density fuel, liquid hydrogen, a great volume is needed to contain enough energy to reach orbit. The propellant is intended to be kep

"Because it will use a low-density fuel, liquid hydrogen, a great volume is needed to contain enough energy to reach orbit. The propellant is intended to be kept at low pressure to minimise stress; a vehicle that is both large and light has an advantage during atmospheric reentry compared to other vehicles due to a low ballistic coefficient.[44] Because of the low ballistic coefficient, Skylon would be slowed at higher altitudes where the air is thinner. As a result, the skin of the vehicle would only reach 1,100 Kelvin (K).[45] In contrast, the smaller Space Shuttle was heated to 2,000 K on its leading edge, and so employed an extremely heat-resistant but fragile silica thermal protection system. The Skylon design does not require such a system, instead opting for using a far thinner yet durable reinforced ceramic skin.[2] However, due to turbulent flow around the wings during re-entry, some parts of Skylon would need to be actively cooled.[42]" -- Wikipedia http://en.wikipedia.org/wiki/Skylon_(spacecraft)#Fuselage_and_structure http://en.wikipedia.org/wiki/Skylon_(spacecraft)#Fuselage_an...

cstross 12y ago
Point of note: some of the design constraints of the Shuttle were imposed by the USAF, whose proposed mission for it was to retrieve KH-11 class spysats from polar orbit for refurbishing/relaunch. (This mission was never actually carried out, but probably seemed like a Good Idea circa 1968-74. NASA needed USAF lobbying support to get funding for the STS program past Congress, so they deliberately tailored the shuttle design to suit speculative Air Force requirements.) A corollary of the Shuttle being designed to transport classified payloads during re-entry was that at no stage during re-entry must the shuttle overfly "hostile" (Soviet or Chinese) territory, lest a disintegration result in classified payload fragments falling into the wrong hands. Consequently the shuttle was designed with that outsized (spysat-friendly) payload bay which seldom got used to maximum effect, and with a short, fast, hot re-entry profile (so that it could commence and complete re-entry after leaving hostile airspace). Hence the need for an exotic, high-specification thermal protection system. (This mission requirement probably contributed to the loss of the Columbia as well.)
- 001sky 12y ago
  Random Question: What is the altitude of "enemy airspace"? Is there some cutoff or threshold recognized by the UN or some other int'l protocol? (Presumably one isn't infringing on enemy airspace in actual earth orbit.)
  - throwaway_yy2Di 12y ago
    This guy wrote an entire thesis about that: "There is no international agreement on the vertical limit of State sovereignty, the boundary between territorial airspace and outer space. The need for defining this boundary has been debated for over 50 years." http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA436627 http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA436627
    - 001sky 12y ago
      Thanks! As a datapoint, the order of magnitude [10km -100km] range seems like the focus of his recommendation: More and more States are developing their own domestic space launch capability. Few of these new space powers will be able to freely access space, or utilize the most efficient launch azimuths, if neighboring States can claim sovereignty up to even 62 miles (100 km). They will have even more difficulty returning objects to Earth if the boundary is set at that altitude. Even the U.S. and Russia are facing limitations on their ability to freely access space. Setting a low vertical limit on State sovereignty will ensure all States have equal access to space. (p81).

cstross 12y ago

Point of note: some of the design constraints of the Shuttle were imposed by the USAF, whose proposed mission for it was to retrieve KH-11 class spysats from polar orbit for refurbishing/relaunch. (This mission was never actually carried out, but probably seemed like a Good Idea circa 1968-74. NASA needed USAF lobbying support to get funding for the STS program past Congress, so they deliberately tailored the shuttle design to suit speculative Air Force requirements.) A corollary of the Shuttle being designed to transport classified payloads during re-entry was that at no stage during re-entry must the shuttle overfly "hostile" (Soviet or Chinese) territory, lest a disintegration result in classified payload fragments falling into the wrong hands. Consequently the shuttle was designed with that outsized (spysat-friendly) payload bay which seldom got used to maximum effect, and with a short, fast, hot re-entry profile (so that it could commence and complete re-entry after leaving hostile airspace). Hence the need for an exotic, high-specification thermal protection system. (This mission requirement probably contributed to the loss of the Columbia as well.)

001sky 12y ago
Random Question: What is the altitude of "enemy airspace"? Is there some cutoff or threshold recognized by the UN or some other int'l protocol? (Presumably one isn't infringing on enemy airspace in actual earth orbit.)
- throwaway_yy2Di 12y ago
  This guy wrote an entire thesis about that: "There is no international agreement on the vertical limit of State sovereignty, the boundary between territorial airspace and outer space. The need for defining this boundary has been debated for over 50 years." http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA436627 http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA436627
  - 001sky 12y ago
    Thanks! As a datapoint, the order of magnitude [10km -100km] range seems like the focus of his recommendation: More and more States are developing their own domestic space launch capability. Few of these new space powers will be able to freely access space, or utilize the most efficient launch azimuths, if neighboring States can claim sovereignty up to even 62 miles (100 km). They will have even more difficulty returning objects to Earth if the boundary is set at that altitude. Even the U.S. and Russia are facing limitations on their ability to freely access space. Setting a low vertical limit on State sovereignty will ensure all States have equal access to space. (p81).