Airship to Orbit
Airship To Orbit (ATO) is a launch scheme proposed by JP Aerospace. It is a means of employing fuel efficient electric rocket propulsion, rather than conventional rocket propulsion, through use of an airship-derived launch vehicle instead of a missile-derived launch vehicle.
JP Aerospace's Airship to Orbit architecture for orbital launches consists of three steps, each performed by a different vehicle: an airship, an aerostatic platform, and an airship-derived spacecraft.
This is a photograph of JP Aerospace's Ascender 175 prototype during a float test.
In the first step of the ascent, an Ascender airship carries a payload to mesospheric altitudes, where it docks with an aerostatic platform called a Dark Sky Station (DSS).
The Dark Sky Station
This is a CAD drawing of a full-sized Dark Sky Station large enough to support Airship to Orbit operations.
The DSS acts as a transfer point between the Ascender airship and Orbital Ascender, as well as a dock for the OAV. The Ascender cannot be built sufficiently lightweight for an ascent to orbit, and the Orbital Ascender must be too lightly built to survive a descent through the lower atmosphere. Thus, they need to either dock directly or have a service station to meet their needs. JP Aerospace, developing the system incrementally, has opted to create a DSS as a service station for the two, as the DSS can be employed for other purposes before an Orbital Ascender is built. Also, the DSS can serve as a testbed for components and techniques used to build the Orbital Ascender, and is arguably the most convenient place for final assembly of an Orbital Ascender.
The planned final version of the DSS is expected to be on the order of two kilometers across. This is large enough to enable it to carry a massive payload, such as a manned platform, a factory, and/or an entire unassembled Orbital Ascender. The large size of the DSS (greater than the largest balloons launched to date) can be achieved by using a multiple-cell construction and conducting final assembly at altitude. It is possible because of the non-turbulent behavior of upper level winds.
The Orbital Ascender
This is a CAD drawing of a sub-orbital prototype of the Orbital Ascender.
The Orbital Ascender completes the final step of the orbital launch. It is an airship-derived spacecraft. It flies horizontally like an airship, powered by a low thrust reaction drive such as an electric rocket engine. It will employ bouyancy and aerodynamic lift at the beginning of its flight rather than the high vertical thrust of conventional missile-derived launch vehicles. Taking advantage of the rapid variation in atmospheric properties at mesospheric and thermospheric altitudes, it will be able to maintain sufficient horizontal velocity to provide aerodynamic lift all the way up to orbit.
Because of its low density, the Orbital Ascender is capable of relatively smooth re-entry as well, enabling it to act as a re-usable vehicle.
Criticism and Potential Theoretical Limitations
There are several legitimate criticisms of the Airship to Orbit scheme which have not yet been satisfactorily answered by JP Aerospace. For example:
The thin air at the Orbital AscenderÃ¢ÂÂs altitude provides little damping of lateral motions, and may make that vehicle subject to damaging chaotic dynamic effects. The vehicles themselves may yet prove impractical to build and operate, being too light to withstand the stresses involved.
Operation of a vehicle which is constructed mainly of plastics promises to be problematic at hypersonic speeds (where aerodynamic energy begins to be transferred into ionizing the incident gases Ã¢ÂÂ and vaporizing plastic). The Orbital AscenderÃ¢ÂÂs heat transfer characteristics will be daunting, if they can be dealt with at all. There may be the possiblity of depositing a thin layer of metal on the skin of the craft, to reduce this, but the metal could ablate as well.
And the low buoyancy available at its intended launch altitude suggests that the Orbital AscenderÃ¢ÂÂs allowed launch weight will be substantially less than that of the proposed DSS. Even if it works, itÃ¢ÂÂs payload to orbit may be too small to make it a profitable system.
All of these issues must be dealt with in order to yield a practical ATO design. However, taken individually, none of them is physically impossible to resolve. The ATO system is still at an early stage of development, and its design is clearly still in a state of flux. Later changes to deal with these issues are highly probable.
JP Aerospace regards their Airship To Orbit designs as trade secrets, and have deliberately tried to obfuscate aspects which they regard as proprietary. This has allowed unsubstantiated claims about their designs to flourish. Elementary engineering errors have been alleged by some critics, and JP Aerospace has not definitively refuted any of these claims beyond simple denial.
Some alleged design errors which JP Aerospace has refused to address even by denial are quite telling, to the point where it is reasonable to speculate that the organizationÃ¢ÂÂs silence on these issues is deliberate. Given the organizationÃ¢ÂÂs otherwise eager attempts at promoting their project, they may have one of two motives. Either the alleged oversights are real, or the answers to the allegations would provide unwanted insight into the nature of their proposed system.
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