Orbital airship
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The orbital airship, also called the space blimp, is a proposed space transportation system that carries payloads to and from low Earth orbit.
In the Airship To Orbit (ATO) design envisioned by JP Aerospace, there are three components. A conventional airship (Ascender) lifts payloads up to 30 to 40 kilometers above the ground - roughly the maximum altitude a conventional airship can achieve. At this altitude the second component, a docking station (Dark Sky Station), acts as a resupply station for the third stage. The third stage is an "orbital airship" (Orbital Ascender), which takes payloads to low earth orbit in three to nine days (i.e., it accelerates itself horizontally to orbital velocity and gains sufficient altitude). Their estimated marginal costs are one dollar per ton per mile of altitude, and their development costs thus far have been under one million dollars.
Two stages are needed because any airship made strong enough to survive the atmosphere would be too heavy to lift payloads to space. An orbital airship would need to be built larger to improve the volume/surface area ratio, with thinner walls, and designed to operate at notably lower pressure. Even in the outer fringes of the atmosphere, helium is still lighter than air. Consequently, airships can continue lifting payloads, but the same airship cannot make the entire trip.
Both the atmospheric and orbital airships will be V-shaped for aerodynamics. However, the orbital airship will be angled upwards to help generate lift. As the airship gains altitude, drag will reduce. According to JP Aerospace, there is a wide margin between the thrust that engines can provide the airship and the amount of drag the airship would experience in the outer fringes of the atmosphere. Early stages of the station and the airships will be powered by fuel cells. In the long term, the surface of these objects can be sprayed with a thin-film solar cell, which, while inefficient in energy conversion, would benefit from light weight, simplicity, and the large surface area.
Several potential problems exist in the design, the largest of which is the threat of micrometeorites. As these will frequently impact the airship, it must have an effective self-healing mechanism, without gaining much weight. Still, additional helium will need to be continually added to the airship to help keep it buoyant. It also faces some of the other risks that face a space elevator, such as elemental oxygen and space debris.
JP Aerospace believes the problems can be solved, and has already begun tests of the Ascender. They hope to test a 30 meter wide prototype station at 9 kilometers altitude by the end of 2005, and have been funding their operations thus far with contracts for development of military communication and spy airships designed to hover over battlefields at altitudes too high for conventional anti-aircraft systems. They also point out that, unlike getting to space on a rocket, if something goes wrong on an airship, nothing bad will happen to you or your payload.
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[edit] Skepticism
Nobody outside JP Aerospace seems to know how the problems of high drag and low lift/drag ratios that are very typically found at hypersonic speeds might be overcome in such a vehicle; and a large degree of skepticism exists.[1]
