The Hubble Space Telescope Still Works Great — Except When It Doesn't

Sep 7, 2020
Originally published on September 8, 2020 12:39 pm

Mike Brown has been using the Hubble Space Telescope pretty consistently for most of the past three decades since it launched in 1990. But recently he had an experience with Hubble that he never had before.

Brown, an astronomer at the California Institute of Technology, got permission to use Hubble to do a detailed study of Jupiter's four largest moons. These moons are called the Galilean moons after Galileo Galilei, who spotted them in 1610.

They include: Ganymede, which is bigger than the planet Mercury and has a mysterious magnetic field; Io, which is the most volcanically active place in the solar system; Europa, which has more liquid water than Earth; and Callisto, which is kind of a simple ol' cratered moon.

After Hubble was supposed to have checked out Ganymede, the data got beamed down, processed and sent to Brown by email. He eagerly opened it up. There was nothing there.

He immediately thought to himself, "What did I screw up this time?" which is, as he puts it, "Pretty much what you always do as a scientist, when you see something that didn't work."

He checked and rechecked the instructions he sent to Hubble. They were fine.

Nonetheless, it turns out that Hubble had been pointing at the wrong patch of sky. Brown says this kind of error quickly happened two more times as he tried to survey Jupiter's moons.

"I don't know if three times in a week is unusual or not, but it seems pretty unusual to me," Brown says.

The Hubble Space Telescope floats in space after its release from the space shuttle's robotic arm following a servicing mission in March 2002.
NASA

Tom Brown, head of the Hubble mission office at the Space Telescope Science Institute in Baltimore — and no relation to Mike Brown — says that Hubble does indeed just sometimes aim in the wrong direction.

"It used to happen on the order of about 1% of the time," he says. "These days, it happens more like 5% of the time."

This is an aging telescope after all. Back in 2018, when a gyroscope on Hubble failed, researchers activated one of its on-board spares — the so-called gyroscope 3. It's been glitchy from the get-go.

"It tells you the telescope is moving around even when it's not," Brown says.

Telescope operators compensate for this error, but sometimes it gets out of whack before they're able to adjust things.

Disappointed researchers can submit a request to have a do-over, and they'll generally get their data eventually — assuming they weren't trying to see some once-in-a-million years brief cosmic event.

No one really knows why gyroscope 3 is such a pain, Brown says, and conceivably, it could get so bad that they might have to turn that one off.

"The biggest downside then is, instead of having the entire sky available at any one time, we would have half the sky available at any one time," he says.

Still, Hubble remains enormously popular. Hundreds of teams get to use the telescope every year. They are the lucky ones, because there is so much demand that the majority of proposed observations have to be rejected.

Hubble is being used for fields that didn't even exist when it was launched, such as studying planets that orbit distant stars.

An image captured by the Hubble Space Telescope as three of Jupiter's largest moons parade in front of the gas giant on Feb. 5, 2015. On the left is the moon Callisto and on the right, Io. The shadows from Europa, which cannot be seen in the image, Callisto and Io are strung out from left to right.
NASA, ESA, Hubble Heritage Team

"Hubble really is a very unique resource for humanity. And once it's gone — I mean, a lot of people are already dreading that day — but I think when it's gone, it's going to hit people ... hard," Brown says.

Engineers estimate that Hubble could keep going for at least another five years and probably longer.

NASA has another big space telescope called the James Webb in the works, but it's not exactly like Hubble has experienced multiple delays and huge cost overruns. It won't launch before late next year.

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AILSA CHANG, HOST:

The Hubble Space Telescope is whizzing around our planet at 17,000 miles per hour. This is the telescope that's shown us things like super-detailed images of Saturn and gorgeous stellar nurseries where thousands of stars are born. Scientists who use Hubble eagerly await the images that are beamed down. But as NPR's Nell Greenfieldboyce reports, they sometimes get a surprise.

NELL GREENFIELDBOYCE, BYLINE: The Hubble Space Telescope launched back in 1990, when Mike Brown was just getting started as a professional astronomer.

MIKE BROWN: I've been using it pretty consistently for most of the last 30 years.

GREENFIELDBOYCE: Brown works at Caltech, and recently, he had an experienced with Hubble that he's never had before. He got permission to use Hubble to do a detailed study of Jupiter's four largest moons. These moons are called the Galilean moons since Galileo spotted them in the year 1610. Ganymede is the largest. It's actually the most massive moon in the solar system. It's bigger than the planet Mercury, and Brown says Ganymede has a huge magnetic field.

M BROWN: It is bizarre that it has that huge magnetic field. No other moons have magnetic fields that are measurable. We really don't have any idea why it would have such a strong magnetic field, why it would have a magnetic field at all.

GREENFIELDBOYCE: And then there's the three other moons of Jupiter that he wanted Hubble to peer at - Io, Europa, Callisto.

M BROWN: Io's got the volcanoes. Like, who doesn't love volcanoes? It's the most volcanically active place in the solar system. Europa has more liquid water than the Earth does. And Callisto - well, there's Callisto.

GREENFIELDBOYCE: Callisto is just a boring cratered moon. But still, Hubble was going to look at them all. After Hubble was supposed to have checked out Ganymede, the data got beamed down, processed and sent to Brown by email. He eagerly opened it up. There was nothing there.

M BROWN: Pretty much what you always do as a scientist - when you see something that didn't work, you're like, what did I screw up this time?

GREENFIELDBOYCE: He checked and rechecked the instructions he sent to Hubble. They were fine. So was Ganymede just inexplicably gone? Did a Death Star obliterate it? It might seem like anything is possible. This is, after all, the year 2020. But the reality is mundane. Hubble was just pointing at the wrong patch of sky. Brown says this kind of error quickly happened two more times.

M BROWN: I don't know if three times in a week is unusual or not, but it seems pretty unusual to me.

GREENFIELDBOYCE: I called up the head of the Hubble mission at the Space Telescope Science Institute in Baltimore. Tom Brown - no relation to Mike Brown - told me that, yes, Hubble does sometimes just aim in the wrong direction.

TOM BROWN: So it used to happen on the order of about 1% of the time, and these days, it happens more like 5% of the time.

GREENFIELDBOYCE: This is an aging telescope, after all. A couple years ago, when a gyroscope on Hubble failed, researchers activated one of its onboard spares, so-called gyroscope 3. It's been glitchy from the get-go.

T BROWN: It tells you the telescope is moving around even when it's not.

GREENFIELDBOYCE: Telescope operators compensate for this error, but sometimes it gets out of whack before they're able to adjust things. A disappointed researcher can submit a request to have a do-over, so they'll get their data eventually, assuming they weren't trying to see some once-in-a-million-years, brief cosmic event. Brown says no one really knows why gyroscope 3 is such a pain, and conceivably, it could get so bad, they might have to turn that one off.

T BROWN: The biggest downside then is, instead of having the entire sky available at any one time, we would have half the sky available at any one time.

GREENFIELDBOYCE: Still, Hubble would remain enormously popular. Hundreds of teams get to use the telescope every year. They are the lucky ones. There is so much demand, the majority of proposed observations have to be rejected. Hubble is being used for fields that didn't even exist when it was launched, like studying planets that orbit distant stars.

T BROWN: Hubble really is a very unique resource for humanity. And once it's gone, I mean, a lot of people are not - you know, are already dreading that day. But I think when it's gone, it's going to hit people even more hard.

GREENFIELDBOYCE: He says Hubble could keep going for at least another five years. NASA has another big space telescope called the James Webb in the works, but it's not exactly like Hubble and won't launch before late next year.

Nell Greenfieldboyce, NPR News. Transcript provided by NPR, Copyright NPR.