Airship-based stratospheric launch platform
Stratospheric-launched suborbital shuttle (SLSS)
Upper stage or a spaceplane
Ground facilities in space port and a tug airplane
Stratospheric Launch Platform
Stratospheric-airship-assisted launch platform is based on technologies of high-altitude airship (HAA). It is distinct from conventional HAAs by requiring extremely large payload capacity at high altitude and also the capability to swiftly unload extra buoyancy after launching its cargo, SLSS. However, it doesn't require long endurance. A typical mission lasts for only a couple of hours. In its fast free ascent stage, the platform is more like a balloon. Hydrogen-fueled engines are shut down until the platform reaches a predefined high altitude.
Structurally, the launch platform at least comprises of two types of ballonets, and those respectively are filled with hydrogen(non-recoverable) and helium(recoverable) lifting gas in platform's ascent and cruise stages. As soon as SLSS is launched, hydrogen lifting gas is completely vented from hydrogen ballonet at high altitude. The lifting force for the launch platform's return stage is solely provided by helium.
A service module is hung beneath the platform and equipped with liquid nitrogen (LN2) tank, liquid hydrogen (LH2) tank and pressured helium tank. LN2 is used to cool down liquid oxygen (LOX) in SLSS. Vaporized nitrogen gas is either released to create an inert environment around the service module, or harvested to help removing hydrogen residue in hydrogen ballonet later on. LH2 stored in service module is to compensate the LH2 loss in fuel tanks of SLSS. Vaporized LH2 is harvested to either power launch platform, or inflated into the hydrogen ballonet. Pressured helium provides lifting gas reserve for helium ballonet and also can be used by SLSS and its cargo when necessary.
SLSS structurally is like a fated version of Delta IV's first stage, but integrated with wings, landing gears and a large fairing. Its construction will inherit hardware and technologies of space shuttle and SR 71. Cryogenic engine, preferably RS25, will be used to propel SLSS at the beginning of this project. In scenarios of platform or engine failure, SLSS will dump or burn up all its fuel and glide back to airfield with its payload.
Depends on mission types, SLSS can follow two distinct flight profiles. However, in both flight profiles, SLSS releases its cargo, the assembly of upper stage and payload, above the atmosphere where no fairings are needed, and at a speed lower than orbital speed.
Given its lower speed than space shuttle, SLSS has much lower kinetic energy per unit mass before its reentry. Its mass/(bottom profile area) ratio also can be much lower than space shuttle. Peak temperature on the leading edges of wings and its belly can be substantially lower than those of space shuttle. The complex and heavy heat shielding system on space shuttle thus can be greatly simplified. A combination of titanium alloy and a relatively thin layer of heat isolation would be sufficient to withstand the heat in reentry. Moreover, SLSS as an unmanned vehicle that a higher heat level would be tolerable.
After the reentry, SLSS is recovered by ways of conventional wheel landing, the same as space shuttle.
Stratospheric-Launched Suborbital Shuttle
Facilities at Space Port
The ground facilities at least include a launch pad, a plant where the assembly of upper stage and payload is loaded on SLSS, and a tug plane used to help SLSS gliding back to space port.
In one of the two flight profiles, landing site of SLSS is several hundreds of kilometers away from the space port. Having much lower mass/(bottom profile area) ratio comparing with space shuttle, SLSS glides back to space port with the assistance of a tug plane.