Sample Return from Shackleton Crater with the Deep Space Tether Pathfinder (DSTP) (original) (raw)

Scientific Return of a Lunar Elevator

The concept of a space elevator dates back to Tsilokovsky, but they are not commonly considered in near-term plans for space exploration, perhaps because a terrestrial elevator would not be possible without considerable improvements in tether material. A Lunar Space Elevator (LSE), however, can be built with current technology using commercially available tether polymers. This paper considers missions leading to infrastructure capable of shortening the time, lowering the cost and enhancing the capabilities of robotic and human explorers. These missions use planetary scale tethers, strings many thousands of kilometers long stabilized either by rotation or by gravitational gradients. These systems promise major reduction in transport costs versus chemical rockets, in a rapid timeframe, for a modest investment. Science will thus benefit as well as commercial activities.

THE RETRIEVE MICROSATELLITE TETHER DEORBIT EXPERIMENT

We have designed and built prototype hardware for a very small electrodynamic tether device for deorbiting a micro-satellite at the end of its mission. This experiment is intended to fly as a secondary payload on a microsatellite mission. It is designed to present no risk to the spacecraftÕs primary payloads, remaining completely dormant until the spacecraft has completed its mission. At the end of the spacecraftÕs mission, the tether device will deploy a 2 km long interconnected -multiline conducting tether upwards from the microsatellite, and will use passive electrodynamic drag to lower the orbit of the microsatellite. To minimize the mass of the device, we developed a new tether deployment mechanism in which the tether deployer ejects itself away from the spacecraft and becomes the tether endmass ballast. Laboratory testing of this deployment mechanism indicates that it can successfully deploy a multiline tether at tensions low enough for successful deployment. We evaluated several plasma contactor technologies for this experiment, and selected a thermionic device based upon a COTS dispenser cathode for its minimal mass and technology maturity. With this tether hardware, a ÒbarebonesÓ experiment to deorbit a 100 kg microsatellite can be implemented with a total mass of less than 2.5 kg., which is less than the propellant required to fully deorbit such a microspacecraft using thrusters. A more capable experiment, with active control of tether dynamics and diagnostics on tether performance and dynamics, can be implemented with a total mass of 3.5 kg.

Results of the Young Engineers' Satellite Tether Programme

The emptiness of space and the near-weightlessness there make it possible to deploy very long and thin tethers. Tethers exploit basic principles of physics to provide propellantless propulsion and enable unique applications such as the provision of comfortable artificial gravity or the removal of space debris. Nevertheless there are still no tether applications in use today - there appears to be a "gap of skepticism". A safe tether and deployer system has therefore been designed and verified with the help of simulation and innovative ground testing equipment. Through a hands-on educational approach, the YES and YES2 low-cost space tether experiments have been launched into orbit. In September 2007, all 32 km of the YES2 tether are deployed in orbit. With the help of this tether, a student-built re-entry capsule is deorbited over Kazakhstan.

Data Analysis of a Tethered SpaceMail Experiment

The Second Young Engineers’ Satellite is a 36 kg student-built experiment that piggybacked on the Foton-M3 microgravity platform in September 2007. Its mission was tethered SpaceMail: a propellantless sample return from an orbital platform. The experiment included a two-stage tether deployment, leading to a swing of the tether toward the local vertical, in which finally a capsule was released from the bottom of the tethered system into a reentry trajectory. The first deployment stage of 3.4km was completed within about 20maccuracy. The second stage started on time and the end mass initially accelerated nominally. Then, due to an electrical problem, the tether was deployed to its full length of 31.7 km, rather than to the target length of 30 km. It was nevertheless released at the proper time and at a near-nominal in-plane angle. Data analysis shows that the Second Young Engineers’ Satellite scientific objectives were achieved. The two-stage deployment trajectory could be reconstructed and the capsule trajectory could be estimated. The proper performance of the deployer hardware and controller was demonstrated, and tether physical properties were also determined. Finally, simulation and test results could be matched to flight data, providing both confidence and recommendations for preparation of future tether missions.