<p>First, to address a common misunderstanding, the gyros that Hubble is having problems with are the small ones used only to detect its rate of rotation, not the large 100 pound flywheels that it uses to generate rotational movement (which we call 'reaction wheels' rather than gyros). It can rotate itself with no problem, but keeping track of how far it has turned is tricky, so accurate steering is a complicated process. Most of the time, during observations, the aim is kept stable by star-tracking optics instead of gyro readings, so once it's locked onto a target, the telescope shouldn't have problems staying there; but getting from one target to the next without getting lost is now quite difficult. There are also difficulties with re-acquiring a target after being interrupted by the Moon or Earth passing between the telescope and its target.</p>
<p>As far as tracking limitations go, according to NASA's article about <a href="https://science.nasa.gov/mission/hubble/observatory/design/hubble-one-gyro-mode/" rel="nofollow noreferrer">operating Hubble in one-gyroscope mode</a>,</p>
<blockquote>
<p>...in one-gyro mode Hubble has some restrictions on the science it can do. For example, Hubble cannot track moving objects that are closer to Earth than the orbit of Mars. Their motion is too fast to track without the full complement of gyros.</p>
</blockquote>
<p>The problem, by the way, isn't how fast the target object is moving compared to the sun, it's how fast Hubble is moving. Hubble is designed for looking at astronomically distant objects, functionally infinitely far away, and for closer objects it needs to rotate to compensate for its orbit around Earth.</p>
<p>For objects that are too close (apparently, Mars being the limit, though that's an amazingly vague description since the distance to Mars varies wildly through the year), the angle changes too fast for the star tracking to stay locked. In the past they've pulled it off, even taking photos of the moon, by essentially spinning the telescope and taking a picture at the right moment without locking on*. But since that technique relies on getting very accurate rotational speed readings, it's not an option anymore.</p>
<p>This does not appear to be a great loss, however. In discussing the situation, the Space Telescope Science Institute's <a href="https://hubblesite.org/contents/news-releases/2024/news-2024-023" rel="nofollow noreferrer">Hubblesite article</a> notes that &quot;these are rare targets for Hubble&quot;. The only things I can think of that Hubble might even want to look at that are closer than Mars would be near-earth asteroids or comets, and while Hubble in its prime may have been able to resolve such objects better than a large ground-based telescope, being limited to &quot;only&quot; using the likes of Keck, SALT, or the Large Binocular Telescope really does not seem like a great loss.</p>
<p>*I believe the kids call this a &quot;360 no-scope&quot;.</p>

CC BY-SA 4.0
2024-06-20T07:12:00.343Z
"... and the rotation it needs it to compensate for its 7 km/s orbit around earth that means the angle to the target is always changing." Can you elaborate on this? Apart from very weak torques due to drag from the tiny amount of atmosphere, photon pressure, and Earth's quadrupole moment, if you point and stabilize Hubble at a certain point on the celestial sphere it will stay pointing at it as it rotates around the Earth. Are you suggesting that for objects closer to Mars, it's their *orbital translation* or the *parallax* due to Hubble's orbit that is the problem? *Thanks!*
uhoh
CC BY-SA 4.0
2024-06-20T12:30:07.867Z
Ooof, that sentence got kind of mangled in editing. I'll try to fix it later. But to answer the question, I'm not sure of the details of tracking under normal infinite-focus mode. Many sources I found mention some variation on using the star trackers to compensate for the telescope's orbital motion, but I haven't had much luck getting clarity on why that would be necessary. You're right, it doesn't seem like the angular difference from one side of the orbit to the other would be large enough to require gross adjustments to the telescope's aim, at least not enough to require gyros to track it.
Darth Pseudonym
CC BY-SA 4.0
2024-07-20T20:31:38.850Z
"360 no-scope" xD
DialFrost
CC BY-SA 4.0
2024-06-20T00:24:52.393Z
2024-06-21T00:01:29.453Z
2024-06-21T00:01:29.453Z
Darth Pseudonym
<p>After 13:49 in Scott Manley's <a href="https://youtu.be/Ra2IpumLMfs?t=829" rel="nofollow noreferrer">How Failed Gyros Are Making Hubble's Life Harder</a>:</p>
<blockquote>
<p>And so with all these systems working together, the telescope can still point at the target and still do top quality science. But it now takes a whole lot longer to move from one orientation to the other because they can't do it as precisely, and they now have to detect the rotation and null out that rotation using star trackers, which weren't really designed to do that.</p>
<p>And so this means there is less time available on Hubble, because it takes longer to go from one observation to the next, <strong>and there's a handful of observations of close fast moving objects that it can't actually track anymore.</strong></p>
</blockquote>
<p><strong>Question:</strong> What is the &quot;handful of observations of close fast moving objects that (Hubble) can't actually track anymore&quot; due to the new one-gyro operation?</p>
<p>Somewhat related:</p>
<ul>
<li><a href="https://astronomy.stackexchange.com/q/32388/7982">Has Hubble ever been used to try to image a near Earth asteroid?</a></li>
<li><a href="https://astronomy.stackexchange.com/q/53064/7982">Did this satellite streak past the Hubble Space Telescope so close that it was out of focus? If so, how close was it?</a></li>
</ul>

CC BY-SA 4.0
2024-06-16T04:13:19.103Z
companion question: [How hard or soft is the Hubbles "science floor" due to atmospheric torque? Do some kinds of observations have lower floors than others?](https://astronomy.stackexchange.com/q/57918/7982)
uhoh
CC BY-SA 4.0
2024-06-18T20:58:14.650Z
I assumed he was talking about comets but I don't actually know.
Darth Pseudonym
CC BY-SA 4.0
2024-06-19T00:24:41.993Z
@DarthPseudonym I'm just curious why comets but not near-earth asteroids? Maybe just NEOs in general? Anything passing near Earth will have a high angular velocity. but perhaps Hubble's UV through IR spectroscopy/photometry and multi-band imaging would be better spent on a comet and it's tails, than on a boring lump of rock. OK.
uhoh
CC BY-SA 4.0
2024-06-19T20:57:16.420Z
That was basically my thought process, yes. I'm hard-pressed to think of much inside the solar system that Hubble would be interested in looking at that it hasn't already observed.
Darth Pseudonym
CC BY-SA 4.0
2024-06-19T23:25:30.463Z
@DarthPseudonym if one can find Hubble's maximum tracking speed now, one could estimate what a handful of fast-moving comets means an write it up as a short and acceptable answer. Unless there's an official list of things that can no longer be seen or some Hubble existing proposals to track them that have been permanently rescinded, I think your comment is basically the answer.
uhoh
<observational-astronomy><space-telescope><hubble-telescope><tracker>
What is the "handful of observations of close fast moving objects that (Hubble) can't actually track anymore" due to the new one-gyro operation?
uhoh
# What is the "handful of observations of close fast moving objects that (Hubble) can't actually track anymore" due to the new one-gyro operation?

(Asked by: username_0 on 2024-06-16)

After 13:49 in Scott Manley's [How Failed Gyros Are Making Hubble's Life Harder](https://youtu.be/Ra2IpumLMfs?t=829):

> And so with all these systems working together, the telescope can still point at the target and still do top quality science. But it now takes a whole lot longer to move from one orientation to the other because they can't do it as precisely, and they now have to detect the rotation and null out that rotation using star trackers, which weren't really designed to do that.
>
> And so this means there is less time available on Hubble, because it takes longer to go from one observation to the next, **and there's a handful of observations of close fast moving objects that it can't actually track anymore.**

**Question:** What is the "handful of observations of close fast moving objects that (Hubble) can't actually track anymore" due to the new one-gyro operation?

Somewhat related:

* [Has Hubble ever been used to try to image a near Earth asteroid?](https://astronomy.stackexchange.com/q/32388/7982)
* [Did this satellite streak past the Hubble Space Telescope so close that it was out of focus? If so, how close was it?](https://astronomy.stackexchange.com/q/53064/7982)

**Tags:** observational-astronomy, space-telescope, hubble-telescope, tracker
> **Comments:**
> **username_0**: companion question: [How hard or soft is the Hubbles "science floor" due to atmospheric torque? Do some kinds of observations have lower floors than others?](https://astronomy.stackexchange.com/q/57918/7982)  
> **username_1**: I assumed he was talking about comets but I don't actually know.  
> **username_0**: @DarthPseudonym I'm just curious why comets but not near-earth asteroids? Maybe just NEOs in general? Anything passing near Earth will have a high angular velocity. but perhaps Hubble's UV through IR spectroscopy/photometry and multi-band imaging would be better spent on a comet and it's tails, than on a boring lump of rock. OK.  
> **username_1**: That was basically my thought process, yes. I'm hard-pressed to think of much inside the solar system that Hubble would be interested in looking at that it hasn't already observed.  
> **username_0**: @DarthPseudonym if one can find Hubble's maximum tracking speed now, one could estimate what a handful of fast-moving comets means an write it up as a short and acceptable answer. Unless there's an official list of things that can no longer be seen or some Hubble existing proposals to track them that have been permanently rescinded, I think your comment is basically the answer.  

---

## 1 answers

### Answer by username_1 on 2024-06-20. Score: 3

First, to address a common misunderstanding, the gyros that Hubble is having problems with are the small ones used only to detect its rate of rotation, not the large 100 pound flywheels that it uses to generate rotational movement (which we call 'reaction wheels' rather than gyros). It can rotate itself with no problem, but keeping track of how far it has turned is tricky, so accurate steering is a complicated process. Most of the time, during observations, the aim is kept stable by star-tracking optics instead of gyro readings, so once it's locked onto a target, the telescope shouldn't have problems staying there; but getting from one target to the next without getting lost is now quite difficult. There are also difficulties with re-acquiring a target after being interrupted by the Moon or Earth passing between the telescope and its target.

As far as tracking limitations go, according to NASA's article about [operating Hubble in one-gyroscope mode](https://science.nasa.gov/mission/hubble/observatory/design/hubble-one-gyro-mode/),

> ...in one-gyro mode Hubble has some restrictions on the science it can do. For example, Hubble cannot track moving objects that are closer to Earth than the orbit of Mars. Their motion is too fast to track without the full complement of gyros.

The problem, by the way, isn't how fast the target object is moving compared to the sun, it's how fast Hubble is moving. Hubble is designed for looking at astronomically distant objects, functionally infinitely far away, and for closer objects it needs to rotate to compensate for its orbit around Earth.

For objects that are too close (apparently, Mars being the limit, though that's an amazingly vague description since the distance to Mars varies wildly through the year), the angle changes too fast for the star tracking to stay locked. In the past they've pulled it off, even taking photos of the moon, by essentially spinning the telescope and taking a picture at the right moment without locking on\*. But since that technique relies on getting very accurate rotational speed readings, it's not an option anymore.

This does not appear to be a great loss, however. In discussing the situation, the Space Telescope Science Institute's [Hubblesite article](https://hubblesite.org/contents/news-releases/2024/news-2024-023) notes that "these are rare targets for Hubble". The only things I can think of that Hubble might even want to look at that are closer than Mars would be near-earth asteroids or comets, and while Hubble in its prime may have been able to resolve such objects better than a large ground-based telescope, being limited to "only" using the likes of Keck, SALT, or the Large Binocular Telescope really does not seem like a great loss.

\*I believe the kids call this a "360 no-scope".

> **Comments:**
> **username_0**: "... and the rotation it needs it to compensate for its 7 km/s orbit around earth that means the angle to the target is always changing." Can you elaborate on this? Apart from very weak torques due to drag from the tiny amount of atmosphere, photon pressure, and Earth's quadrupole moment, if you point and stabilize Hubble at a certain point on the celestial sphere it will stay pointing at it as it rotates around the Earth. Are you suggesting that for objects closer to Mars, it's their *orbital translation* or the *parallax* due to Hubble's orbit that is the problem? *Thanks!*  
> **username_1**: Ooof, that sentence got kind of mangled in editing. I'll try to fix it later. But to answer the question, I'm not sure of the details of tracking under normal infinite-focus mode. Many sources I found mention some variation on using the star trackers to compensate for the telescope's orbital motion, but I haven't had much luck getting clarity on why that would be necessary. You're right, it doesn't seem like the angular difference from one side of the orbit to the other would be large enough to require gross adjustments to the telescope's aim, at least not enough to require gyros to track it.  
> **username_2**: "360 no-scope" xD  

---

