Japanese Tether Experiment Slated To Launch with GPM Core Observatory


The upcoming launch of a U.S.-Japanese rainfall measuring satellite aboard Japan’s H-2A rocket also will deploy a small space tether experiment that could demonstrate a low-cost means of orbital debris removal.

The Space Tethered Autonomous Robotic Satellite (STARS) 2 electrodynamic tether experiment will fly as a secondary payload on a mission whose main objective is to deploy the Global Precipitation Measurement (GPM) Core Observatory, a joint project of NASA and the Japan Aerospace Exploration Agency. Launch is scheduled for Feb. 28 from the Tanegashima Space Center in southern Japan.

STARS 2 features two cube-shaped spacecraft — mother and daughter — joined by a special wire tether that will measure 300 meters long when fully outstretched. The spacecraft, measuring 16 centimeters on a side and weighing 9 kilograms apiece, were developed for JAXA by the Kagawa University.

As they cross Earth’s magnetic field while in orbit, electrodynamic tethers can build up an electrical charge along their length. This voltage in turn interacts with the magnetic field to generate drag on the tether’s host spacecraft or, alternatively, forward propulsion. Some technologists believe electrodynamic tethers hold promise as a means of deorbiting space debris or for powerless propulsion for spacecraft.

The STARS 2 experiment follows up on the STARS 1 experiment, which was deployed in January 2009 by an H-2A rocket whose primary payload was JAXA’s Gosat environmental monitoring satellite. STARS 1, also consisting of a mother and daughter satellite, was supposed to deploy a 5-meter tether. Due to a problem with the tether reel mechanism, the tether deployed only to a length of a few centimeters, but the basic functionality of the reel and other mechanisms was confirmed, according to information posted online by the Kagawa University.

For STARS 2, the electrodynamic tether is expected to deploy, initially by a spring mechanism, to a length of 300 meters between the mother and daughter satellite, with the daughter satellite positioned between the mother satellite and Earth. The system will be stabilized in this orientation by Earth’s gravity. Once deployed, the tether is expected to begin carrying an electrical current.

The tether is composed of several metal filaments of less than 0.1 millimeter in diameter that are woven together to create a primary strand that is as tough as it is thin. The primary strands are wrapped in a net-like material for added structural redundancy.  

Photographs taken by the spacecraft during the experiment will be transmitted to the ground using amateur radio frequencies, the university said.