To update: Hubble took its first picture since entering Safe Mode on June 13th! More information here.
On Sunday June 13th, the Hubble Space Telescope terrified the astronomical community when its payload computer suddenly stopped working. This caused the main computer to put the telescope and its scientific instruments into safe mode. What followed were many tense weeks as the HST surgical team tried to pinpoint the source of the problem and devise a strategy to turn Hubble back on.
On Friday, July 17th, after more than a month of checking, re-checking, and attempting reboots, the Hubble operations team identified the source of the problem and restored power to the telescope’s hardware and all of its instruments. Scientific operations can now be resumed, and the groundbreaking space telescope that brought us over thirty years of dedicated astronomy, cosmology and astrophysics still has some life in it!
The problems began when an unspecified problem caused Hubble’s payload computer, a NASA Standard Spacecraft Computer-1 (NSSC-1) system, to stop working. As part of the telescope’s Science Instrument Command and Data Handling (SI C&DH) module, this computer is responsible for controlling and coordinating the scientific instruments on board the spacecraft.
Hubble image of the Ring Nebula (also known as Messier 57). Photo credit: NASA / ESA / Hubble Heritage (STScI / AURA) – ESA / Hubble Collaboration
As a result, the main computer no longer received the “keep-alive” signal from the payload computer and automatically put all Hubble scientific instruments into a safe mode. A day later, the Hubble operations team restarted the payload computer, but it stopped again. At this point, the operations team began investigating various SI C&DH components and trying to switch to backup modules.
These included the possibility of a degraded memory core, a problem with the Standard Interface (STINT) hardware, the Central Processing Module (CPM), the Command Unit / Science Data Formatter (CU / SDF) and a controller in the Power Control Unit (PCU) ). At the same time, the team made several attempts to restart and reconfigure the computer and the backup computer, but to no avail.
However, on July 14, the operations team announced that these tests allowed them to gather vital information that suggested that the cause of the problem lay in the PCU. This unit ensures a constant voltage supply for the payload computer and its memory. It also includes a power regulator that maintains a constant supply of five volts and a secondary protection circuit that warns the payload computer if the voltage exceeds or falls below that level.
This will trip the secondary protection circuit, which will then instruct the payload computer to stop operating. The team’s analysis found that either the secondary circuit tripped or it got stuck in this lockout condition over time due to deterioration. On July 15, the team then began to switch to the backup of the SI C&DH units, which also contains the backup PCU.
The pillars of creation of the Eagle Nebula, taken in 1995 (right) and 2015. The new image was taken with the Wide Field Camera 3, which was installed by astronauts in 2009. Photo credit: Left: NASA, ESA / Hubble / HHT / STScI / J. Hester and P. Scowen (ASU)
The team also switched other hardware parts to their alternative interfaces in order to establish a connection to the backup SI C&DH. Once this was done, the backup payload computer was turned on, loaded with the flight software, and put into normal operating mode. On July 17th, Hubble’s scientific instruments were restored to working order and NASA announced that scientific data collection will now resume.
This news is a welcome relief to NASA and the countless millions who value the Hubble Space Telescope so highly. As NASA Administrator Bill Nelson recently said in a NASA press release:
“Hubble is an icon who gives us incredible insights into the cosmos of the last three decades. I’m proud of the Hubble team, from current members to Hubble alumni who stepped in to provide their support and expertise. Thanks to their dedication and thoughtful work, Hubble will continue to build on its 31-year legacy and expand our horizons with his view of the universe. “
This process is similar to what happened in 2008 when Hubble’s previous CU / SDF module (another part of the SI C&DH) failed and the surgical team switched to the backup module to keep scientific operations going. The last maintenance mission (STS-125) followed in May 2009, during which the crew of the Space Shuttle Atlantis met with Hubble in orbit and replaced the defective SI-C & DH unit with the one currently in use.
With his feet firmly anchored on the shuttle’s robotic arm, astronaut Mike Good maneuvers to retrieve the tool caddy needed to repair the Space Telescope Imaging Spectrograph during the final Hubble maintenance mission in May 2009. state-of-the-art instruments that allow astronomers ever better insights into the cosmos. Credits: NASA
For those whose founding years coincided with the 1990s, the name Hubble is synonymous with astronomy and scientific discovery. In the 31 years of operation, Hubble has made over 1.5 million observations of the universe, published over 18,000 scientific papers using its data, and it has contributed to some of the most significant discoveries in our universe.
This includes observations that proved that the universe is expanding at an accelerated rate, which led to the theory of dark energy. His observation campaigns, such as the Deep Field and the Ultra Deep Field, provided new insights into the evolution of galaxies and clues to the role of dark matter. His observations of exoplanets also led to the first atmospheric studies of planets outside the solar system.
It’s good to know that after 31 years and so many scientific breakthroughs, Hubble, the workhorse and pioneer of space telescopes, still has some life in it. Nancy Grace Roman would be proud of her child!
Further reading: NASA