NASA engineers are working to reboot the Hubble Space Telescope after an unexpected anomaly.


July 14, 2021: NASA engineers think they've found the root cause of Hubble's troubles in the power control unit, which ensures a steady power supply to the payload computer. They will switch over to a backup payload computer, which contains a backup power control unit, beginning on July 15th. If everything goes to plan, normal science operations will still take a few days to resume. Read more here.

July 12, 2021: NASA completed a review to assess all factors and minimize risks related to Hubble’s possible switch to backup hardware, which may occur later this week. Investigation into the cause of the payload computer issue is ongoing.

June 30, 2021: As NASA continues to investigate the problem Hubble's payload computer experienced, engineers are now also working to turn on backup hardware on the spacecraft. The full process will take a week or so, including testing commands on a simulator on the ground. Read more in NASA's most recent press release.

Discovery shuttle deploys Hubble Space Telescope
Hubble was released from the payload bay on Discovery in 1990.
NASA / Smithsonian Institution / Lockheed Corp.

NASA’s iconic Hubble Space Telescope has hit a spot of trouble, though the end is not yet nigh (we hope). After more than 30 groundbreaking years of discovery, the workhorse telescope ran into difficulties earlier this month when a computer shutdown forced the telescope into safe mode. Now, engineers are sorting through options and possible solutions.

Problems with Hubble

The current spate of troubles began on June 13th, when the telescope’s main payload computer unexpectedly shutdown. The team suspected a degraded memory module as the culprit and planned to switch over to one of three other backup modules. However, several attempts to switch over on June 16th and 17th were not successful, and the telescope remains in safe mode.

As with all space missions, Hubble’s payload computer represents flight-proven and radiation-hardened tech available at the time of launch and repair. Hubble’s original NASA Standard Spacecraft Computer-1 (NSSC-1) and its subsequent replacement are from the late 1980s, complete with four separate 64K Complementary Metal-Oxide Semiconductor (CMOS) memory modules. The system also has a complete backup payload computer for redundancy. The NSSC-1 is located in the Science Instrument Command and Data Handling Unit (SI C&DH), and both were replaced in May 2009 during the final repair mission of the space shuttle era. The original SI C&DH unit failed in 2008. To date, the backup unit has yet to be powered on since initial installation in 2009, though it was thoroughly tested on the ground prior to launch.

"The backup payload computer was thoroughly tested on the ground prior to installation," says Claire Andreoli (NASA-Goddard). "If there is a problem with it, the same process to identify the source of the problem and a potential fix would be initiated."

Workers surround command and data handling unit in the lab.
The replacement SI C&DH unit, seen here in the lab prior to its installation during the final repair mission in 2009.

For now, the team is looking to see if the problem lies in the Standard Interface (STINT) software or the Central Processing Module (CPM) itself. The team is working on procedures for a possible switchover to the backup which, if necessary, will take several days of checkouts to attain operational status.

"The team is currently designing tests that will be run in the next few days to attempt to further isolate the problem and identify a solution," says Andreoli. "If the problem can't be fixed, then the backup payload hardware will be turned on and it will take several days to assess the computer performance and restore normal science operations."

Hubble’s Legacy

Launched on STS-31 space shuttle Discovery and released from the shuttle’s payload bay on April 25, 1990, Hubble has been pushing back the boundaries of our understanding of the universe ever since.

But first, Hubble had to overcome defects in its optics discovered only after it was deployed, problems that were corrected during the first repair mission in December 1993. Since that time, Hubble has been on-hand to witness astronomical events near and far, from the impact of Comet Shoemaker-Levy 9 into Jupiter in 1994, to the discovery of the moons Styx, Nix, Kerberos, and Hydra around Pluto, to finding distant supernovae in other galaxies.

Moons of Pluto, imaged by Hubble
A family portrait of the moons of Pluto.

Astronomers used the telescope to assemble our deepest views of the primordial universe, the Hubble Deep Fields. More recently, its Frontier Fields mosaics of giant galaxy clusters have provided astronomers with their best views of the largest, naturally occurring magnifying lenses.

Abell 370 (Frontier Fields)
The Frontier Fields image of galaxy cluster Abell 370 peered into its central region to look for the distorted shapes of gravitationally lensed background galaxies.
NASA / ESA / J. Lotz / HFF Team (STScI)

Hubble also captured the public’s imagination with some of the most iconic images of our generation, such as the Pillars of Creation nestled in the Eagle Nebula (Messier 16). And although Hubble is best known for its work at visual wavelengths, its capabilities extend into the infrared and ultraviolet as well.

Pillars of Creation Hubb
Hubble’s portrait of the “Pillars of Creation” in the Eagle Nebula, taken with its Wide Field and Planetary Camera 2 back in 1995, is arguably its most famous image ever. In 2014, Hubble revisited these towers of star formation with its Wide Field Camera 3 to capture a wider, more detailed view in both visible (left) and infrared right), revealing stars inside and beyond the nebula’s clouds of gas and dust. This powerful side-by-side demonstration helps visualize why so many astronomers are excited for Hubble to work alongside the upcoming James Webb Space Telescope.
NASA / ESA / Hubble Heritage Team (STSCI / AURA)

The last repair mission in 2009 almost didn’t happen. One of the requirements for shuttle missions after the 2003 Columbia disaster was for orbiters to reach the International Space Station; Hubble is in a different, higher orbit. As a solution, NASA had a second orbiter (Endeavour) on standby during the STS-125 repair mission, should a rescue be needed.

The end of the shuttle program in 2011 also marked the end of on-hand repair capability for Hubble, as NASA no longer has the means to reach and repair the space telescope. Astronauts did, however, install deorbit capability on Hubble during STS-125, for the day when the space telescope’s mission finally comes to an end.

At this point, the team would only consider ending recovery efforts for Hubble "When we have exhausted all of the redundancy options," says Andreoli. "But there are still so many we have not yet tried, and it is extremely likely that one of these will work."

Two Shuttles
A rare sight: two space shuttles on the launch pads (Atlantis and Endeavour) for STS-125.
NASA / Dimitri Gerondidakis

If Hubble gets back up and running, its operational life may overlap with the James Webb Space Telescope, set to launch in November this year. Often touted as the "successor to Hubble," JWST will work at infrared wavelengths. Unlike Hubble, the Webb telescope is headed to the Lagrange (L2) point beyond the orbit of the Moon, putting it out of reach for repair.

If you live between latitudes 30°N and 30°S, you can routinely spot Hubble at dawn or dusk. When we lived in central Florida, Hubble was a familiar sight. Be sure to check Heavens-Above for passes.

With any luck, Hubble will soon be open for business once again.


Image of Andrew James

Andrew James

June 23, 2021 at 8:38 pm

Planned obsolescence or a software lock-out? Whoever in NASA decided to let Hubble last this long ought to be sacked! 🙂

When Hubble does finally meet its end, astronomers should have an official worldwide celebratory wake - based solely on the contribution to our science. Hubble Day?

For me, the loss of new planetary nebulae images will be truly heartbreaking. Sob. 🙁

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