Inflatable space structures - large structures made in space by inflation.

Project Persephone proposes that, in the long run, projectile space launch should help make exovivaria much cheaper to build and maintain. Inflatables should help keep costs down as well. Inflation is a way to create large structures from small packages, without resorting to complex on-orbit assembly procedures, and without paying the weight penalty of ruggedizing a finished structure to survive stresses it will never undergo again after launch.

OV1-8 Gridsphere

Launching inflatables to orbit using projectile space launch is probably feasible and might be the cheapest way to put a large structure in orbit. During Project HARP, experiments with aluminized parachutes and meteorological balloons demonstrated that they could survive accelerations in excess of 40,000 Gs.1

Long before any projectile launch is available, however, Project Persephone could probably benefit by past and present R&D on inflatable space structures.


Echo inflation test

There is nothing new about the idea of inflatable space structures. Among the first communications satellites launched by the U.S. in the early 60s were the inflatables of the Echo series. They were designed to reflect radio signals. Each was little more than a mylar bag. Inflating one in orbit resulted in a 41-meter balloon, just barely visible from Earth. The launched payload, including balloon, was small: about 65Kg. Much of the mass of this payload was instrumentation, solar cells, and other equipment. Because orbit features near-perfect vacuum, not much gas was needed to inflate an Echo. Inflating it after orbit was clearly cheaper. Inflating an Echo before orbit would have entailed launching it in enormous payload fairing, weighing much more than the satellite itself -- if indeed such a launch would even be possible.

Space station model

In the early 60s, NASA explored the possibility of a small space station made from an inflatable torus, to be rotated for artificial gravity. One model, with a possible population of one or two astronauts, made it into production,2 though it was never used -- the project was cancelled after the decision to go directly to the Moon for the Apollo program.

Contemporary work

National space agencies and some private companies are engaged in R&D on inflatables for a variety of space applications. In the late 80s, an inflatable radiator for spacecraft heat rejection was proposed.3 Bigelow Aerospace has been developing human-habitable inflatable modules to help reduce the cost of launching and constructing space stations.4 ILC Dover LP has been developing inflatable structure technology for trusses, sunshades, booms, solar panels and antennas.5

Bigelow Aerospace

To help reduce orbital debris, several researchers have proposed using a balloon to increase drag in order to de-orbit nanosatellites within a few years of end-of-life or after operational failures.6. Conceivably, the first tests of exovivarium deployment might be to bring a short-mission-duration nanosatellite down from orbit.

A nanosat for testing solar sailing has been deployed from a microsat.7,8

Inflatables within an inflatable habitat

Laser-tag maze

Even inside exovivaria, inflatability might be useful. If telebots have wheels, something like rubber tires might be used, as suggested for Mars rovers.9 Mazes might be constructed for games, using modular inflatables as on Earth, but with the possibility of multiple levels: Under low gravity, inflatable structures, even though "gossamer" in construction, should be able to bear the weight of animals, plants and telebots.

Blimp in a stadium

With low artificial gravity and high enough air density, lighter-than-air UAVs should be possible.10 In the event an internal inflatable is punctured11 repair might be possible using ecosystem-derived adhesives, fabrics and dyes.

Reentry vehicles

Although exovivaria are not likely to be exporting very much to Earth, inflatables might be useful for return capsules. At this point, it's hard to know whether there would be demand for artifacts and creatures made or born on orbit, but they might eventually gain such collector value that the Project could, through auctions of such items, raise enough money to launch special missions to send them back to Earth, while also replenishing the exovivarium on the same trip. If exovivaria are used for biological experiments requiring live-species return (as with the Mars Gravity Biosatellite), some kind of heat-shielded return capsule will be required. An ordinary ablatively shielded return capsule wouldn't be a good candidate for projectile space launch, but an inflatable designed for reentry might be. NASA is at work on inflatable reentry shields.12

Inflatable Re-entry Vehicle Experiment (IRVE), Langely Research Center

1 CH Murphy, GV Bull, "A review of Project HARP, Ballistics Research Laboratories, Aberdeen Proving Ground, 1966; also Annals of the New York Academy of Sciences, v.140, Planetology and Space Mission Planning, pp.337357, Dec 1966. DOI:10.1111/j.1749-6632.1966.tb50970.x

2 "Inflatable Station Concept", Great Images in NASA, updated May 13, 2010.

3 Jonathan Beard, Balloon in Space Takes the Heat Off Spacecraft", New Scientist, October 1989

4 Video: Inflatable Space Structures, New Scientist, March 7, 2010

5 Inflatable Gossamer Space Structure Technologies

6 see e.g., "Simple and Small De-orbiting Package for Nano-Satellites Using an Inflatable Balloon", Nakasuka, Shinichi; Senda, Kei; Watanabe, Akihito; Yajima, Takashi; Sahara, Hironori, Transactions of Space Technology Japan, Volume 7, Issue ists26, pp. Tf_31-Tf_36 (2009). DOI 10.2322/tstj.7.Tf_31

7 NASA's First Solar Sail NanoSail-D Deploys in Low-Earth Orbit Inflatable Gossamer Space Structure Technologies

8 "NanoSail-D", NASA?, 2009

9 "Experimental Characterization of a Robotic Inflatable Wheel", Dimitrios Apostolopoulos, Michael D. Wagner, Chris Leger, and Jack Jones. 8th International Symposium on Artificial Intelligence, Robotics and Automation in Space, September, 2005

10 This might require electrolyzing water for hydrogen, posing some combustion risk, but there is commercial technology for such aircraft, e.g., the Plantraco Microblimp

11 Perhaps by orbital debris strikes and spallation from them, or by animals or telebots accidentally tearing them.

12 "NASA to Test Inflatable Heat Shield", Parabolic Arc, May 23, 2012

Spartan 207/Inflatable Antenna Experiment (IAE), in orbit, clouds in background

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