After four weeks of head scratching and trial and error, NASA engineers have finished a workaround on the electronics onboard the Hubble Space Telescope that should enable the science satellite to resume observing the universe.

The space agency posted a statement yesterday saying that the Hubble's crippled control and communications backup unit finally responded properly to instructions sent to it by ground controllers. This clears the way for handlers at the Goddard Space Flight Center in Greenbelt, Md., to initiate the first of the Hubble's science instruments tomorrow.

The orbiting platform went dark on 27 September when a component known as the Science Instrument Control and Data Handling system failed after 18 years in service in the cold of space. That left NASA with the problem of starting up a parallel version of the control system for the first time by sending a complex series of commands from the ground. It took the agency's engineers a couple of weeks to figure out how to get everything working fully (please see NASA Ready to Reboot Hubble Telescope), but they seem to have now overcome some initial setbacks.

The proof will come when the Goddard team instructs the platform's Wide Field Planetary Camera to begin aiming at a distant object and transmitting images on Saturday. If that goes well, the second test will come next week when they attempt to restart the Advanced Camera for Surveys for solar observations.

A committee quickly assembled to study the Hubble failure reported its preliminary findings to the space agency yesterday, as well. The review group, headed by the chief of NASA's Wallops Flight Facility, John Campbell, issued the following analysis:

Regarding the sudden halt of the spacecraft computer, the team concluded that three separate events occurring with near-simultaneity were responses to a single triggering event. The triggering event was most likely caused by a self-clearing short-circuit, or a transient open-circuit, in the Science Instrument Control and Data Handling system. One or more such events would not be highly improbable in hardware inactive since 1990, and will not harm the telescope, although it could cause another interruption of science operations.

If all goes well over the next week, the Hubble should be able to resume a portion of its historic observations of the cosmos. NASA, which had been planning to send astronauts to the telescope this month to upgrade its equipment, will then proceed with a shuttle mission early next year to replace the compromised control system along with new parts for other aging components.

Wish them luck.