So, if it is generated in a thermal process, the temperature must be of the order 1000 times greater that that in places where light is produced. Thus a search for cosmic x-rays is a search for material at temperatures of millions of degrees. Unfortunately, the earth's atmosphere absorbs these high energy rays, hindering astronomers attempts to learn their secrets. Therefore rockets are required to lift X-ray dectectors above earth's atmosphere. It is not a trivial matter to build instruments that are large enough to be sensitive, yet small enough to fit within a rocket.
Instruments have to withstand the rigors of launch but also operate in a vacuum.
This was a surprising discovery as these first sources had not been predicted by astronomers. Until 1962, very few astronomers believed that the universe contained objects capable of generating detectable amounts of high energy radiation and little was expected from the first observations. This source consequently became known as Sco X-1, the first discovered source in the constalation Scorpius. The diffuse X-ray background was also not anticipated before discovery. It was initially recognised in data from the 1962 rocket flight which first detected Sco X-1.