Smart-1 suffering blackouts due to radiation particles

Brussels, 30 Jan 2004

European Space Agency (ESA) engineers are hoping to solve an engine problem on Smart-1 that, if they fail, could leave the Moon probe adrift in space.

The cause of the problem is high energy particles from the Sun and the radiation belts surrounding the Earth. When such particles strike electronic circuits, they can cause harmful electrical surges. As with most spacecraft, capacitors were built into Smart-1's circuits to absorb such surges, but soon after it was launched in September 2003, ESA mission control realised there was a problem.

The engineers that built Smart-1 realised that they had failed to equip certain vital circuits with capacitors. As a result, every time a high energy particle strikes a particular optical sensor, the resulting surge in voltage causes the probe's ion engine to be switched off, known as a 'flameout'.

Smart-1 has suffered 18 such flameouts since it began its 15 month trip to the Moon. Whilst it is a simple process for ground control to reboot the engine when they next make contact with the craft, the unusual route that Smart-1 is taking to the Moon means that the fault could jeopardise the entire mission.

Instead of flying directly to the moon, Smart-1 is using its novel ion engine to gradually increase the size of its orbit around the Earth, until it is captured by the gravity of the Moon. In order for this to work, the team has to control the probe's highly elliptical orbits so that when it is at its farthest point from the Earth, it simultaneously makes its closest approach to the Moon.

But as Luca Stagnaro, the mission's software specialist, told New Scientist: 'There are three or four crucial points in the mission when, if the engine flames out, the spacecraft will not achieve [the necessary orbit, and] we will not have enough fuel to make it to the Moon.'

To try and solve the problem, Mr Stagnaro has developed a software programme that will enable Smart-1 to switch its engine back on automatically following a flameout. The team tried a similar fix in December, but the programme overloaded the probe's computer, so a streamlined version has been developed.
For further information, please consult the following web address:
http://www.esa.int/export/esaMI/SMART-1/

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