Emmet Fletcher

When satellite imaging is mentioned, we usually think of satellites taking pictures of the weather, floods or downtown New York. This is one of the primary uses of satellites and one which has brought great benefits to many people. Within space surveillance, satellite imaging refers to taking pictures of satellites on orbit. But why would we want to do that?

One reason is when things don’t go as planned. Satellite operators cannot always see what is happening on the satellite directly, but rely on specific sensors to tell them if something has – or hasn’t – worked. This could be a signal to say that the solar panels have been set correctly. If this signal hasn’t been received, it could mean one of two things. Either the solar panel hasn’t been set correctly or the sensor has malfunctioned. But which one of the two is it? Sometimes this specific situation can be verified because there is no power being generated by the solar panel or the satellite’s attitude moves in such a way that indicates the solar panel is not sticking out of the side of the satellite body. In either case, an independant way to verify this would be useful.

Another reason is during re-entry. The way a space object is oriented can effect large changes in the re-entry profile. It can determine if the satellite will break up high in the atmosphere and these small pieces vapourise without touching the Earth’s surface or if the orientation will cause some drag or lift as it comes through the atmopshere and hence change the impact point. Being able to image an object as it comes close to re-entry and begins to be affected by the atmosphere can really help reduce the uncertainty in both these areas.

A final reason why satellite imaging is important is – as can be guessed – military. Having intelligence regarding the capabilities of satellites in orbit is very useful to military commanders. Using satellite imaging could be a good way to do this.

Of course any specific military requirments are out of the scope of the ESA SSA programme. It can be predicted that the resolution required to perform the first two functions of anomaly resolution and re-entry prediction is much less than that required for the third one.