Japan's x-ray astronomy program was dealt a new blow last month when a solar geomagnetic storm left an orbiting x-ray telescope spinning out of control. Scientists are dubious about their chances of saving the 7-year-old Advanced Satellite for Cosmology and Astrophysics (ASCA), whose replacement--the ASTRO-E x-ray satellite--was lost shortly after launch in February. "We haven't given up," says Hajime Inoue, head of space astrophysics research at Japan's Institute of Space and Astronautical Science (ISAS) in Sagamihara, outside Tokyo. "But we don't have a great amount of hope."
ISAS scientists believe a solar storm on 14 July expanded Earth's atmosphere to the point that it increased atmospheric drag on the satellite, orbiting at an altitude of about 440 kilometers. The drag disturbed the angular momentum of the satellite, which sent it spinning out of control. The next day it went into a safe mode, spinning in such a way that its solar panels are not facing the sun. Inoue says the best chance for regaining control of the satellite will come in a month or so, when ASCA moves into a better position for generating solar power.
Developed jointly with NASA's Goddard Space Flight Center and several American and Japanese universities, ASCA had been a key component of ISAS's relatively small but carefully targeted space program. Its observations have generated more than 700 papers, Inoue notes proudly. One major finding was the detection of iron in the x-ray emissions from accretion disks, the swirls of gas and dust that orbit black holes. These iron emissions bore telltale evidence of the enormous gravitational pull of the black hole, something expected but never before observed. "ASCA had already been a very big success," Inoue says.
A replacement for ASCA, which was expected to last another a year or so before falling into Earth's atmosphere, is still 4 to 5 years away. In the meantime, Japan's x-ray astronomers are trying to borrow time on other instruments. "There is a big gap in our [observational] program," Inoue says.