Probably the most famous telescope in the world, NASA’s Hubble Space Telescope is back in action after a computer anomaly had suspended the telescope’s observations for more than a month.
Science observations restarted the afternoon of July 17. The telescope’s targets this past weekend included unusual galaxies.
A pleased NASA Administrator Bill Nelson announced: “I’m thrilled to see that Hubble has its eye back on the universe, once again capturing the kind of images that have intrigued and inspired us for decades.
“This is a moment to celebrate the success of a team truly dedicated to the mission. Through their efforts, Hubble will continue its 32nd year of discovery, and we will continue to learn from the observatory’s transformational vision.”
In its first pictures after coming back online, from a program led by Julianne Dalcanton of the University of Washington, Hubble clicked a galaxy with unusual extended spiral arms and the first high-resolution glimpse at an intriguing pair of colliding galaxies. Other initial targets for Hubble included globular star clusters and aurorae on the giant planet Jupiter.
Hubble’s payload computer, which controls and coordinates the observatory’s onboard science instruments, halted suddenly on June 13. When the main computer failed to receive a signal from the payload computer, it automatically placed Hubble’s science instruments into safe mode.
The Hubble team moved quickly to investigate what ailed the observatory, which orbits about 340 miles (547 kilometers) above Earth. Working from mission control at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, as well as remotely due to COVID-19 restrictions, engineers collaborated to figure out the cause of the problem.
The big issue that complicated matters was that Hubble was launched in 1990. To fix a telescope built in the 1980s, the team had to draw on the knowledge of staff from across its lengthy history.
Hubble alumni returned to support the current team in the recovery effort, most of them retired. Other former team members lent a hand by scouring Hubble’s original paperwork, surfacing 30- to 40-year-old documents that would help the team chart a path forward.
“That’s one of the benefits of a programme that’s been running for over 30 years: the incredible amount of experience and expertise,” said Nzinga Tull, Hubble systems anomaly response manager at Goddard. “It’s been humbling and inspiring to engage with both the current team and those who have moved on to other projects.”
At first, the team thought the likeliest problem was a degrading memory module, but switching to backup modules failed to resolve the issue. They then moved on to explore whether other hardware was at fault, including the Command Unit/Science Data Formatter and the Power Control Unit, which is designed to ensure a steady voltage supply to the payload computer’s hardware. However, it would be more complicated to address either of these issues, and riskier for the telescope in general. Switching to these components’ backup units would require switching several other hardware boxes as well.
“The switch required 15 hours of spacecraft commanding from the ground. The main computer had to be turned off, and a backup safe mode computer temporarily took over the spacecraft. Several boxes also had to be powered on that were never turned on before in space, and other hardware needed their interfaces switched,” said Jim Jeletic, Hubble deputy project manager.
“There was no reason to believe that all of this wouldn’t work, but it’s the team’s job to be nervous and think of everything that could go wrong and how we might compensate for it.”
Over the following two weeks, more than 50 people worked to review, update, and vet the procedures to switch to backup hardware, testing them on a high-fidelity simulator and holding a formal review of the proposed plan.
Their findings pointed to the Power Control Unit as the possible cause of the issue. On July 15, they made the planned switch to the backup side of the Science Instrument and Command & Data Handling unit, which contains the backup Power Control Unit.
It was at 11:30 pm local time on July 15 when the team determined the switch was successful. The science instruments were then brought to operational status, and Hubble began taking scientific data once again on July 17.
“Hubble is in good hands. The team has once again shown its resiliency and prowess in addressing the inevitable anomalies that arise from operating the world’s most famous telescope in the harshness of space,” said Kenneth Sembach, director of the Space Telescope Science Institute (STScI) in Baltimore, Maryland, which conducts Hubble science operations.
“I am impressed by the team’s dedication and common purpose over the past month to return Hubble to service. Now that Hubble is once again providing unprecedented views of the universe, I fully expect it will continue to astound us with many more scientific discoveries ahead.”
