Sounding rockets are sub-orbital rockets that carry a payload above the Earth's atmosphere for period of up to 15 minutes, but which do not place the payload into orbit around the Earth. The field of X-ray astronomy began with a sounding rocket flight in 1962 carrying a Geiger counter that discovered the first X-rays from an astronomical object outside the Solar System. The Sun was known to be a bright X-ray source, but because it is so much closer than other stars, no other stars were expected to be detectable in X-rays. The purpose of the 1962 rocket flight was to investigate X-rays from the Moon. Instead, this flight discovered both Sco X-1, the brightest X-ray source in the sky, and a completely unexpected diffuse glow of X-rays known as the cosmic X-ray background.

X-ray observations of astronomical sources are possible only from rockets or satellites because X-rays from space are absorbed in the Earth's atmosphere and do not reach the ground. While sounding rockets were the primary means of observing X-rays from space in the 1960s and 1970s, most work in X-ray astronomy today is done from satellites (current X-ray satellites include the German/US/UK ROSAT satellite, the Japanese/US ASCA satellite, and the US XTE satellite). Today, sounding rockets continue to play an important role in instrumentation development and graduate student training. We feel that the latter role is particularly important, because sounding rockets are the only NASA program that can provide training in all aspects of a typical flight program, from instrument definition through launch and data analysis, within the typical graduate student tenure of five to six years.

Penn State has maintained an active program of X-ray astronomy payloads launched on NASA sounding rockets since 1981. Over the past decade this work has focussed on applications of photon-counting CCD instruments. The first photon-counting CCD X-ray camera ever flown was launched by our group twice from Woomera, Australia, to observe Supernova 1987A. In March, 1990, the payload flew again with a Lincoln Labs CCID-7 chip to take spectrally resolved images of the Puppis-A supernova remnant. The picture at right shows the CCD camera from this flight. The CCD is the rectangular chip at the top with the gold border; the active area is the gray rectangular area in the center of the CCD package. The circular electronics board below the CCD contains a preamplifier and a temperature control circuit. This entire package is enclosed in a cylindrical vacuum chamber for testing and launch.

Over the past several years the payload was modified to operate with an EEV CCD similar to those being flown in our CUBIC satellite instrument. The first flight with the new detector occurred on May 22, 1995 from White Sands, New Mexico. This intended target for this flight was the North Polar Spur, a large region of the sky that is very bright at about 3/4 keV, and is believed to be produced by the hot boundary of an old supernova remnant located about 450 light years from the Sun in the general direction of the galactic center. Unfortunately, an error in the pointing commands for this flight resulted instead in pointing towards a region in the constellation Draco, one of the faintest parts of the sky at these energies. While these data appear to provide an interesting background spectrum, they did not achieve our scientific objectives, and we have now repeated this flight on May 2, 1997. Meanwhile, we travelled to Woomera, Australia again in October 1995 to launch the payload for an observation of a (possibly) related object south of the galactic plane in the constellation Corona Australis. This launch was successfully carried out on October 25, 1995, and the data are being analyzed now for publication in the Astrophysical Journal. (Preliminary results are given in Mendenhall et al. 1996.)

Our most recent rocket launch occurred on August 14, 1998 from White Sands, New Mexico. This was a reflight of the same payload used in the last three launches with the same CCD detector used for the last flight (May 1997). The target was Sco X-1, the brightest X-ray source in the sky. Details of the experiment are given in our Experimenter's Data Package.

In addition to these launch successes the program has lead to publications on the proper statistical treatment of data in the Poisson noise regime, projected radiation damage effects on CCDs, and detection of extremely low energy X-rays with CCDs. Six graduate students have received degrees in the past six years based on work stemming from the rocket program.

Our future plans include developing a rocket payload based on STJs (Superconducting Tunneling Junctions) with even higher spectral and spatial resolution than the current CCD technology (click here for an explanation of similar work being done at the European Space Agency), and exploring low cost alternatives for X-ray telescope technology.

Be sure to see our Sounding Rocket Photo Gallery and our list of rocket launches.

For more information about our rocket program or about our graduate degree program, contact Dr. David Burrows ( burrows@astro.psu.edu ).

Web page maintained by Scott Koch (tsk@astro.psu.edu)
Last update: December 2, 1998