Engage Impulse Engines, Mr Sulu


Tests on a prototype called the Dual-Stage 4-Grid (DS4G) thruster, at ESA’s Electric Propulsion Laboratory in the Netherlands showed that DS4G’s two-step process produces an ion exhaust plume that travelled at 210 kilometres per second – more than 10 times faster than possible with the engine in SMART-1, and four times faster than the latest prototype ion engine designs.

Super-powerful new ion engine revealed

DS4G thruster firing during tests in the ESTEC Electric Propulsion facility's CORONA vacuum chamber (Image: ESA)

A new design for an ion engine promises up to 10 times the fuel-efficiency of existing electric propulsion engines, according to tests by the European Space Agency. The new thruster could be used to propel craft into interstellar space, or to power a crewed mission to Mars, ESA says.
Ion engines work by using an electric field to accelerate a beam of positively charged particles – ions – away from the spacecraft, thereby providing propulsion. Existing models, such as the engine used in ESA’s Moon mission, SMART-1, extract the ions from a reservoir and expel them in a single process.
Tests on a prototype called the Dual-Stage 4-Grid (DS4G) thruster, at ESA’s Electric Propulsion Laboratory in the Netherlands showed that DS4G’s two-step process produces an ion exhaust plume that travelled at 210 kilometres per second – more than 10 times faster than possible with the engine in SMART-1, and four times faster than the latest prototype ion engine designs. This would mean a spacecraft could carry much more weight for a given amount of fuel, or it could go further, faster.
“Crewed or heavyweight robotic missions to Mars become a distinct possibility. And there’s even talk of interstellar missions,” says Orson Sutherland of the Australian National University in Canberra, who led the team that built the engine.
Collision erosion
The conventional ion engine contains three grids perforated with thousands of millimetre-wide holes. These grids are attached to a chamber containing the charged particles.
The first grid operates at thousands of volts, while the second is kept at a low voltage. This voltage difference creates an electric field, which extracts the ions from the fuel reservoir and accelerates them out into space in one step. The third grid acts to stop electrons flying back into the ion beam.
Ideally, the voltage difference between the first two grids should be as high as possible, to maximise the speed at which the ions are expelled, and also the fuel efficiency of the engine. But when the difference approaches 5000 volts, ions collide with the second grid, and start to erode it.
The new design incorporates four grids. First, the ions are extracted from the reservoir using two closely spaced grids that both operate at a very high voltage, with a voltage difference (of 3000 v to 5000 v) between them.
Acceleration comes in the second stage, when the extracted ions are channelled into two more grids, which operate at low voltages.
Mars and back
This system allows voltage differences of up to 30,000 v between the two grid sets, producing much faster ion exhaust plumes than previously possible, and without damage to the engine.
Given sufficient electrical power, a cluster of DS4G engines could take a crew to Mars and back, says ESA. Alternatively, the design could be used to slash the time of longer missions to Pluto, or the Kuiper belt.
But given the extensive testing required of a new ion engine design, it could be a decade before DS4G engines make their debut in a space mission, Sutherland says.

Posted: Wed - January 18, 2006 at 10:35 PM          

©