Astronomy - USA (2022-02)

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 observa-

tory, 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 metic-

ulous 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 regu-

lates energy throughout the telescope, including to the payload

computer. Fortunately, HST’s backup SI C&DH unit also

The aging Hubble’s

capabilities will not be replaced,

but rather complemented, by

newer space telescopes,

reinforcing its value. NASA

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light from hydrogen within them com-

bines to create the filamentary glow seen

in the image.

Says Garel, “Our study can be seen as

the first detection of the cosmic web in

typical filamentary environments” —

rather than in the special conditions

under which it’s been spotted before. And

the myriad small, faint galaxies lighting

up the web in the MUSE image had gone

previously undetected. Their presence,

Garel says, “has strong implications for

our understanding of the formation of

galaxies in the universe.” Specifically, he

says, it implies that all the bright, massive

galaxies we easily observe “are just the tip

of the iceberg and that many more much

smaller objects do exist.”

Now, the team plans to use state-of-

the-art cosmological simulations to learn

more about the newly discovered popula-

tion of small galaxies by trying to recreate

the light they produce. Further down the

road, Garel adds, the team hopes to repeat

or even improve on the image, potentially

with a next-generation instrument called

BlueMUSE, which could detect the cosmic

web over an even larger part of the sky.

Astronomers used the MUSE instrument to

stare at a small piece of sky for 140 hours. The

images revealed glowing filaments of hydrogen gas

(blue) in the cosmic web. This gas is lit by numerous

small galaxies, which themselves remain unresolved.

ROLAND BACON, ESO AND NASA

WWW.ASTRONOMY.COM 19

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 brief ly 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.