Included in the space technology experiments Prisma will test there is even a new scientific instrument. This is PRIMA, PRIsma Mass Analyzer, a collaboration between the Swedish Institute of Space Physics, IRF, and Chalmers. PRIMA uses revolutionary micromechanics in order to measure particle mass in space.


Space imposes very specific demands on instrumentation, both in terms of performance and in terms of weight and size. Prisma will test a completely new type of instrument for measuring particle mass in space. The instrument is called PRIMA. The Swedish Institute of Space Physics has the primary responsibility for PRIMA, while Chalmers has fabricated one of the key components.
 
“PRIMA will examine the plasma in the space surrounding Prisma and identify which types of charged particles there are there by measuring their mass,” says Martin Wieser at IRF, lead scientist for PRIMA.
 
Measuring the mass of particles in the vicinity of the Earth and in other parts of the solar system is important in order to understand how the sun interacts with the planets and moons and how the Earth and other planets evolved. 
 
Previous shutters have been too large
PRIMA is based on a method called time-of-flight measurements, a specific method that measures the time it takes for a particle to travel a certain distance in order to measure its velocity. Traditional time-of-flight measurements have often been based on the particles crashing through a thin foil thereby releasing electrons, which gives rise to a measurable current. The current pulse indicates when the particle has passed the foil. It is also possible to instead reflect the particle against a surface. By then measuring the time it takes for the particle to reach the detector of the instrument as well as the energy of the particle it is relatively easy to calculate its mass.
 
There has been in existence for a long time a further technique for measuring flight times, and that is by using a shutter, similar to the shutter in an analogue camera. By knowing exactly when the shutter is open it is also possible to know exactly when a particle can pass through it. The problem with using this technique on a satellite is that a shutter is a relatively large moving part that moves very rapidly.
 
The shutters previously tested were composed of spinning wheels with slots in. The size, the energy consumption, and not least the torque the spinning wheel imposed on the satellite made the shutter technique impossible to use in practice in space. Now technology development has delivered a solution, and Swedish micromechanics appear to be the first to demonstrate that the shutter technology is now ready for space.
 
“I only know of one other group working with micromechanic shutters for time-of-flight measurements. PRIMA is really on the cutting edge,” says Martin Wieser.
 
MEMS gives new possibilities
The Institute for Microtechnology and Nanoscience, MC2, at Chalmers in Gothenburg is responsible for the micromechanics. The technology is called MEMS – Micro-Electro-Mechanical Systems. By using MEMS it is possible to open the shutter more rapidly which increases the sensitivity of the instrument, reduces the energy consumption, allows it to take up less room and be significantly lighter.
 
MEMS-based mass spectrometers would therefore be a very welcome addition to the toolbox of space research. But, as for other space technology systems, even scientific instruments have a substantial threshold to overcome.
 
“It is a chicken-and-egg problem,” says Martin Wieser. “It is of enormous importance to demonstrate that the technology is functional in space; that the instrument gets to fly. Prisma is a unique opportunity as it is a platform for testing new technologies.”

 
If everything goes as it should PRIMA will be the first nanotechnology-based microshutter instrument that analyses particles in space.
 
High-technology with ordinary components
PRIMA will also test electronic components and new methods for surface treatment.
 
“These can be tested in the lab, but eventually must also be flight-tested,” states Martin Wieser.
 
The instrument should demonstrate that it is possible to build high-performance scientific instruments with commercially available components, and not specially fabricated ones.
 
“Commercial components are not as tolerant to radiation and are more sensitive for extreme temperatures. But they are much cheaper,” says Martin Wieser. “It is a challenge to build an instrument from such components, but there is much to be gained, both in terms of costs and availability. It is a current trend to more and more try to use commercially available components.”
 
PRIMA was delivered at the beginning of the autumn to the Swedish Space Corporation in Solna to be mounted on Prisma, and the planned launch is now less than a year away.

Kim Bergström
November 2008