Testing the water on satellites

It doesn’t quite mark a return to the golden age of steam, but boiling water has made an unlikely reappearance in the design of a satellite propulsion system.

The steam propulsion device, developed by Surrey Satellite Technology (SSTL), was recently demonstrated as an experimental unit on-board the company’s UK-DMC earth observation satellite.

Designed and built in-house at SSTL, the miniature propulsion device is a type of resistoget, which uses a resistor to heat up the propellant. The device weighs 13g and uses just 3W of power to heat the water, emitting steam through a conventional rocket nozzle to generate thrust. The hotter the propellant the higher the specific impulse performance achieved. Specific impulse is a measurement of thrust produced per unit of propellant used. Using just 2.06g of water as a propellant, the spacecraft experienced 3.3 milliNewtons of thrust over a 30-second period.

Dave Gibbon, team leader of SSTL’s propulsion group, said that he envisages the tiny device being used to induce small changes in the orbit of a satellite – typically to increase or decrease the altitude. ‘You’d never get yourself to the moon with it,’ he stressed.

Gibbon added that the system, said to be the first of its kind, has been developed in response to the growing popularity of small, low-cost satellites.

These diminutive spacecraft are increasingly being developed by small research companies and universities that can’t afford expensive rocket fuel and its attendant safety costs. ‘Traditional rocket propellants such as hydrazine are toxic, carcinogenic, flammable, and high-pressure. Water, as well as being free, is non-toxic,’ he explained.

While there are no immediate plans to use the device on any other spacecraft, Gibbon said that the project has generated a great deal of interest and if a commercial opportunity does arise he’s confident of the technology’s benefits and capabilities.

Meanwhile, in another hi-tech spin on industrial-age technology, a team of researchers from Penn State University in the US has developed a new jet fuel derived from coal. Designed for high-performance engines in aircraft such as the F35 joint strike fighter, the coal-based jet fuel remains stable up to 900 degrees F.

This could offer a solution to the problem of fuels decomposing at high temperatures and causing valves, nozzles and other engine parts to become fouled with carbon deposits.

The team has developed two processes for producing the fuel. Both are variants of techniques used in the petroleum industry and could be carried out in existing refineries, said project leader Harold Schobert.