The International Space Station is an extraordinary achievement. It is a unique observatory and laboratory, permanently crewed by at least six astronauts. And it is huge: covering an area the size of a football field and with the volume of a 5 bedroom house. It is also the most expensive object ever built, with a total price tag of a cool $100 billion.
So you’d imagine that it would have enormous scientific potential. After all, it operates in a unique environment offering conditions that are not easy to create on Earth. Scientists ought to be clamouring to get their experiments on board. Right?
Not quite. Operating on the station is hard and today we get a unique insight into just how tough it is thanks to Hiroshi Tsunemi at Osaka University in Japan and several pals, who publish an account of their experience testing an X-ray camera on board the ISS.
X-ray cameras have improved in leaps and bounds in recent years thanks to the development of CCDs that can detect X-rays and so produce digital X-ray images. Many dentists now use X-ray CCDs as a matter of routine.
So putting one in space to look at X-ray sources in the sky is a thoroughly good idea. Many groups have done it on various orbiting observatories and it’s fair to say that these cameras have changed the nature of x-ray astronomy,
So back in the 1990s, the Japan Aerospace and Exploration Agency decided to test the technology by strapping it to the back its laboratory on the ISS. The camera, called MAXI/SSC (Monitor of All-sky X-ray Image/Single Slit Camera), was originally scheduled to fly in 2003 but the Columbia disaster meant it didn’t get up until 2009.
Once up, the engineers discovered that significant flaring occurs in the images when the Sun is close to the field of view. So the camera cannot be used at these times.
Neither can it be used when the station passes through the South Atlantic Anomaly, the area where the Earth’s Van Allen Radiation belt comes closest to the surface.and where radiation levels are so high that the cameras have to be switched off. The ISS passes through this region ten times a day.
The result is that the MAXI/SSC is switched off most of the time.
Then there is the problem of taking dark images, pointing the camera at the night side of the Earth to see how much background noise comes from non-x-ray sources. This is essential for analysing the data but just cannot be done on the ISS.
There are advantages in being on the station, however. When Tsunemi and co discovered a problem with the way the camera downloaded data, they were able to persuade a friendly astronaut to fix it “by adding an extra router”.
Despite these various problems, MAXI/SSC has begun to create an image of the X-ray sky (shown above). The different colours correspond to X-rays sources of different energies and the biggest object is the Vela supernova remnant.
One curious feature is the arcs in the image, particularly in the northern hemisphere. Tsunemi and co say they don’t know where this is coming from. Perhaps more observations will help find the source but without a good measure of background noise, it will be tough to dissect.
Science in space is a difficult business at the best of times. It doesn’t look to be any cheaper, quicker or easier on the ISS.
Ref: arxiv.org/abs/1101.5673: In Orbit Performance Of The MAXI/SSC Onboard The ISS