8 The Hubble Space Telescope hiccups
EVEN AFTER NEARLY 32 years, the Hubble Space Telescope (HST) remains one of astronomy’s workhorses. But with hard work comes wear and tear. And with the space shuttle retired, there is no way to physically repair the aging space telescope. Instead, NASA relies on remotely diagnosing issues and developing workarounds based on the equipment currently installed on the orbiting observatory, much of which is original hardware built in the 1980s.
Around 4 P.M. EDT on June 13, Hubble’s payload computer, which manages the onboard suite of instruments, stopped working. In response, the telescope’s main computer placed the science instruments into safe mode, halting observations. A June 14 reboot of the payload computer failed to solve the issue, leading to nearly a month of careful testing to determine and resolve the problem that had crippled the observatory.
On June 23 and 24, in an attempt to bypass what engineers believed was a problem due to aging hardware, controllers turned on HST’s backup payload computer, which had never been activated in space. But this failed to solve the issue. So, the team moved on to different solutions, including switching to the telescope’s backup Science Instrument and Command & Data Handling (SI C&DH) unit, a process that required meticulous programming from the ground to turn on several more system backups that had also never before been used in space.
A team of more than 50 people — including HST alumni who had moved on to other projects or retired — worked for two weeks to outline, simulate, and approve this switchover procedure. At the same time, engineers finally determined the real culprit: Hubble’s Power Control Unit (PCU), which regulates energy throughout the telescope, including to the payload computer. Fortunately, HST’s backup SI C&DH unit also houses a backup PCU. The team initiated the switchover on July 15, successfully completing the procedure by 11:30 P.M. EDT that night.
Two days later, NASA announced Hubble had returned to operational status following the successful switch to backup hardware. On July 19, the agency released the first images taken since the shutdown, proving the telescope was back up and running at full capacity.
But the telescope’s instruments again briefly entered safe mode Oct. 25, following two days of error messages indicating issues with HST’s ability to correctly time commands and responses. By Nov. 7, engineers had restored the Advanced Camera for Surveys, while the remaining instruments were kept in safe mode until the error’s origin had been uncovered.
Despite these bumps, HST’s unparalleled capabilities mean mission teams will continue to maintain the prestigious observatory as long as its components — and funding — last.