Chandra is a sophisticated instrument that represents a tremendous technological advance in X-ray astronomy. It is the third of NASA's great observatories. The Chandra observatory was first proposed to NASA in 1976 and funding began in 1977 when NASA's Marshall Space Flight Centre started the definition studies of the telescope.
It is designed to allow scientists from around the world to obtain unprecedented X-ray images and spectra of violent, high-temperature events and objects to help foster a better understanding of black holes, quasars, comets and, above all, dark matter. By allowing the users to gaze across vast distances, the telescope should help inform scientists as to the origin of the Universe.
SPACECRAFT
The orbit life of the spacecraft is expected to be less than five years. During this time the perigee of the orbit will be 10,000km, and the apogee will reach 140,000km.
Chandra, which was launched by the Space Shuttle on July 23, 1999, was the largest and heaviest load ever put on a space shuttle. The satellite weighed a total of 12,930lbs at its launch. This consisted of 10lbs pressurant, 2,153lbs propellant and a further 10,560lbs for the "dry" parts. The spacecraft was more than 10m long.
POWER AND COMMUNICATIONS
The rocket uses four engines. These are in action two at a time. The fuel used is Hydrazine and the oxidiser is Nitrogen tetroxide. The satellite is powered by two solar panel arrays, with three panels each. These can generate 2,350W in total. The power is stored in three nickel-hydrogen batteries. The batteries will allow the spacecraft to function when the craft is in an eclipse. For communications, the satellite has two low gain antennas. The command link can handle 2kb/s.
MIRRORS
The centrepiece of the whole device are four sets of nested, grazing incidence paraboloid/hyperboloid mirror pairs. The weight of the mirrors amount to 2,093lbs. Mirrors are 83.3cm long each, constructed of zerodur material and polished to better than 7 angstroms root-mean-square (RMS) micro roughness. The mirrors have a thin coating of iridium of 600 angstroms.
The X-ray telescope has a focal length of 10m and an outer diameter of 1.2m. Because of their high energy, X-ray photons penetrate into a mirror in much the same way that bullets slam into a wall. Likewise, just as bullets ricochet when they hit a wall at a grazing angle, so too will X-rays ricochet off mirrors. The mirrors have to be carefully shaped and aligned nearly parallel to incoming X-rays. Thus they look more like glass barrels than the familiar dish shape of optical telescopes.
OPTICAL INSTRUMENTS
The instruments on board include an AXAF Charged Coupled Imaging Spectrometer (ACIS), a High Resolution Camera (HRC), High Energy Transmission Grating and Low Energy Transmission Grating.
Overall programme cost, including spacecraft and science instrument development, launch on the space shuttle in July 1999, and operations for five years, was about $2.5 billion.
LEAD CONTRACTORS
There were a number of companies involved in the project. The TRW Space and Electronics Group was responsible for the completion and final assembly of the observatory. Optical Coating Laboratories manufactured optical thin film coatings and components used to manage light provided by the lens and mirrors. Eastman Kodak designed, built and integrated the X-ray telescope mirrors.
