Peanuts for space

    Most moonshots have cost taxpayers billions. Not so with the European SMART-1 moon probe. SMART-1, currently on its way to the Moon, cost ESA (= the European Space Agency) only 50 million € (= Euro), mere peanuts in the lavishly exorbitant space business.

    SMART-1 (= Small Missions for Advanced Research and Technology 1), looking like an average washing machine and weighing about 350 kg, was shot into Earth orbit on September 27, 2003, riding piggyback on an Ariane-5 rocket (together with three other satellites, to save launching costs). It has been gathering momentum ever since, circling the Earth at steadily increasing speeds and ever wider orbits, thanks to the continuous thrust of its rather unusual propulsion engine. On November 15, after a total of some 400 increasingly faster orbital rotations, it is scheduled to reach the required velocity for leaving its Earthbound orbit and head for the Moon. Estimated arrival date: January 13, 2005.

Small is beautiful for a long time

    The secret of thrift lies in combining a small (= cheap) engine with lots of time to spend. SMART-1’s engine is extremely weak, with a thrust equivalent to the earthly gravitational pull on 6 grams, the weight of an ordinary postcard. But there is no air resistance in space, so even this minute thrust steadily accelerates the vehicle. To compensate for the measly thrust, you have to take your time, in the case of SMART-1 about 14 months of relentless speed-gathering.

Electric rocket

    What about rocket fuel? There isn’t any. The SMART-1 is equipped with an ion engine, which runs entirely on electricity from its solar panels. The ion engine works on the same principle as a pea-shooter. For every pea that you shoot out, you receive a recoil force in the opposite direction. If you replace the peas with heavier lead balls, then your recoil thrust increases. Just as important for the recoil is the velocity of the peas.

    Instead of peas, ion engines shoot out ions of the heavy noble gas xenon. Xenon gas is first ionised and then accelerated in an electric field to very high velocities (15 km/s), before the ions are shot out, in the opposite direction to the vehicle’s travelling path.

Don’t forget your xenon

    There is no need for fuel for the solar-powered ion engine, but you have to take along a sufficient supply of ”peas”, of course. However, because the velocity of the expelled xenon ions is 10 times higher than that of the exhaust gases from ordinary rocket engines, a supply of 80 kg xenon is sufficient to travel to the moon and put SMART-1 into moon orbit. With combustion-powered rocket engines the vehicle would have needed 800 kg of fuel to accomplish the same task.

    The ion engine is originally a Russian idea from 1959. The SMART-1 moon expedition is the second time that an ion engine has been used as the sole source of propulsion in a spacecraft. The first time was in 1998, when NASA launched a spacecraft called Deep Space 1, which flew by an asteroid and went on to intercept a comet. Well, in fact Deep Space 1 cheated a little, because it didn't entirely depend on its ion engine. Its launch rocket gave it enough initial velocity to get into deep space without 14 months of accelerating in circles around Earth. So SMART-1 can actually be regarded as THE first ion-engine-powered spacecraft.

Looking for lunar water and Midnight Sun

    The main purpose of the new European moonshot is to gain more extensive experience of the ion engine for possible use in future missions into deep space. There are some scientific tasks for SMART-1 as well, among them to find out whether there might be some water on the south pole of the Moon. There could also be mountain ridges in the vicinity, where the sun always shines, day and night. If SMART-1 localizes such a place, then in future it could be used as a site for a lunar solar-powered power station.

A model for NASA, costwise

    The prime contractor for designing and building SMART-1 has been the Swedish space company Rymdbolaget (Swedish Space Corporation, SSC), who has used 15 subcontractors from six European countries. The main design principle has been to use available technology as much as possible in order to save costs.

    The amazingly small budget for this European moon mission has also attracted American interest. In April 2004 a US Congressional committee conducted an inquiry, asking representatives from the Swedish company how it was possible for a small company in a small country to accomplish their task so quickly (4 years) and at such a low cost, apparently hoping to teach NASA to cut costs.

Dagens Nyheter, 2004-11-07

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