The orbital airship, or "space blimp," is a proposed means of moving cargo from the ground to low earth orbit without the use of conventional rocketry. The design of an orbital airship consists of three stages, designed to move payloads from earth to space in about a week. Although there are several organizations working toward creating such a ship, the concept is best known part of a program called Airship to Orbit (ATO), envisioned by JP Aerospace, a California-based volunteer organization that sees itself as a private competitor to NASA. Despite JP Aerospace's enthusiasm about their proposed design, a number of experts doing independent analyses have argued that certain details are physically unworkable.
The first stage of ATO is a conventional airship filled with helium. V-shaped for the purpose of being aerodynamic, it is labeled the Ascender. The orbital airship ascends to about 25 miles (40 km), then docks with stage two, a permanent, crewed platform called Dark Sky Station (DSS).
Like the Ascender, the Dark Sky Station is an inflated structure without a rigid shell. The first stage is prevented from ascending beyond 25 miles (40 km) because any orbital airship capable of surviving atmospheric winds would unfortunately be too heavy to make the trip into space. Several prototypes of both the Ascender and the Dark Sky Station have already been created.
The third stage of ATO is the Orbital Ascender, a 6,000 foot (1.8 km) long air/spaceship designed to make the trip from the DSS to 93 miles (150 km), or low Earth orbit. Although helium is still lighter than air at 25 miles (40 km), this effect diminishes and eventually halts, making the craft heavier than its surroundings. At 93 miles (150 km) the density of air is only three billionths of what it is at sea level.
JP Aerospace has proposed covering this massive Ascender in solar panels and using ion engines to accelerate the craft to approximately 5 miles per second (8,000 meters per second), the required speed for any object to reach orbit. It has been claimed that this process would take around five days.
Unfortunately, some simple calculations show that ion engines coupled with solar panels would not provide sufficient thrust to propel the massive envelope of gas to the speed required for atmospheric exit. Possibly by combusting on-board hydrogen, creating a blimp design that folds during ascent to become more aerodynamic, or by beaming power in microwave form from the Dark Sky Station to the Orbital Ascender, this scheme could become practical. Alternatively, the Dark Sky Station might simply be used as a platform for the launch of chemical rockets.
Many details still need to be worked out to make the orbital airship viable. No lighter-than-air craft has yet flown at hypersonic speeds, leading many experts to be skeptical at proposals of an orbital airship.
