<p>The potential duplicates don't quite cover your scenario, but the issues to consider are similar - whether you really gain any precision, and the telemetry and power requirements.</p>
<p>From what I understand, you are thinking of two position measurement instruments, one of which you keep near the Earth (maybe at L2) and the other you send away to orbit Jupiter. You then combine the position measurements from these two telescopes in some way to determine parallaxes.</p>
<p>Obviously there is also a cost issue in sending things to Jupiter, which I'll ignore. There is also a possible radiation damage issue when sending anything to orbit Jupiter.</p>
<p>The telemetry issue is very serious. Gaia, which is stationed at L2, is telemetry-limited. It has to pick and choose which stars, and which areas on its detectors it can send data back for. Jupiter is of order 300 times further away than L2. Assuming a similar beam width on your antenna then you will likely have to have 90000 times the signal power to achieve something similar. That power is certainly not going to come from the Sun. Gaia is powered by solar panels, but the power per unit area received in Jupiter orbit would be 25 times smaller.</p>
<p>There is then the point that the gain in precision is probably not as big as you had hoped (at least within any reasonable mission lifetime). Whilst you are sending your spacecraft to Jupiter (5 years?) you can do an awful lot of parallax measurements from a single spacecraft close to the Earth. Once it has got there, then assuming there is no systematic noise floor level (which there might be) that stops you achieving the increase in precision suggested by the baseline, full-precision parallax measurements could only be achieved for stars at right angles to the line between the Earth and Jupiter - a rather limited portion of the sky. To get whole-sky coverage you would need to wait for Jupiter to complete half an orbit around the Sun (another 6 years) and I think to properly separate the parallax wobble of a star from its pseudo-linear proper motion across the sky, you would probably need another half orbit (another 6 years).</p>
<p>All the while you are waiting for these data, a competing spacecraft at L2 like Gaia could be busily taking multiple measurements and beating down the uncertainties on the parallax (essentially, in <span class="math-container">$N$</span> Earth orbits you reduce the error in a single parallax estimate by <span class="math-container">$\sqrt{N}$</span>) . This averaging process means that you gain much less (for a mission aimed at getting parallaxes across the whole sky) than the simple increase in baseline would suggest.</p>
<p>For all these reasons I think, unless there is some compelling reason to measure the parallax to some individual object very accurately (which would not require a lot of telemetry or power), a specific mission to measure parallax in this way is unlikely.</p>

CC BY-SA 4.0
2024-12-05T10:44:16.493Z
> you are thinking of two position measurement instruments, one of which you keep near the Earth (maybe at L2) and the other you send away to orbit Jupiter.  == No, we're not doing interferometry, I figure we'll do a parallax measurement on one side of Jupiter's orbit and then five years later, we get another parallax measurement. == A third measurement five years later, will detect and cancel  the star's proper motion, revealing just the parallax == I made it  Jupiter's orbit because the outer planets take too long to orbit. == In 10 years, will have extremely accurate parallax data.
Miss Understands
CC BY-SA 4.0
2024-12-05T11:19:32.867Z
@MissUnderstands in which case it is a duplicate of https://astronomy.stackexchange.com/questions/34076/why-is-gaia-operating-around-earth-orbit-why-not-send-it-to-neptunes-orbit?noredirect=1&lq=1 , all the arguments are the same. IYou need more than 1 orbit to distinguish proper motion from parallax because the proper motion can be in the same direction as the parallax.
ProfRob
CC BY-SA 4.0
2024-12-05T11:38:26.607Z
Hi, Professor rob! ==  If the proper motion is in the direction of parallax, then you've got the classical epicycles. Why would it take more than one orbit to parameterize that? == If you had infinite accuracy, you could watch the way the proper motion changes, and infer the curve from just a few seconds observation. Right? == Or am I, once again, WAY off?
Miss Understands
CC BY-SA 4.0
2024-12-05T11:46:49.373Z
@MissUnderstands yes, perhaps so. Like trying to estimate the amplitude of a sine wave by sampling a small fraction of a cycle against the background of a nearly constant drift.
ProfRob
CC BY-SA 4.0
2024-12-05T16:22:27.260Z
If you have the difference in angle to a star from Jupiter and from the Earth simultaneously, then you have the parallax in that direction.  To get accuracy in the perpendicular direction better than Gaia the separation in that direction needs to reach 2 AU.  Proper motion is irrelevant for simultaneous measurements.
eshaya
CC BY-SA 4.0
2024-12-05T20:59:35.783Z
@eshaya yes, I think that is the case for the 2 spacecraft situation. I do need to revise this answer, but it turns out to be a duplicate in any case.
ProfRob
CC BY-SA 4.0
2024-12-05T10:27:11.817Z
2024-12-05T11:51:51.543Z
2024-12-05T11:51:51.543Z
ProfRob
<p>I'm thinking a nuclear powered astrometry  telescope in a Jupiter-distance orbit. Every five years, you could look at the same object with a parallax baseline of a billion miles. Push it out to Saturn for a baseline of 2 billion miles. That's 10X better than what we have now.</p>
<p>An astronautry satellite wouldn't have to be large; it only has to be large enough to see the furthest stars that show parallax.</p>
<p>Would establishing extremely accurate distance measurements for close stars, and the first parallax measurements for distant stars be particularly useful, Or are our numbers close enough?</p>
<p>Would it be worth the cost?</p>

CC BY-SA 4.0
2024-12-04T22:22:38.813Z
It depends to what extent the measurement accuracy has a systematic noise floor.
ProfRob
CC BY-SA 4.0
2024-12-04T23:33:44.960Z
Better yet, three telescopes headed out of the solar system along three perpendicular axes.
eshaya
CC BY-SA 4.0
2024-12-05T07:01:41.503Z
Related, and maybe a duplicate, [question](https://astronomy.stackexchange.com/q/34076/44977)
matteol
CC BY-SA 4.0
2024-12-05T09:31:45.593Z
See also https://astronomy.stackexchange.com/questions/34083/why-not-send-a-gaia-like-mission-to-mars?noredirect=1&lq=1
ProfRob
CC BY-SA 4.0
2024-12-05T11:25:48.297Z
This question is similar to: [Why is Gaia operating around Earth orbit? Why not send it to Neptune's orbit?](https://astronomy.stackexchange.com/questions/34076/why-is-gaia-operating-around-earth-orbit-why-not-send-it-to-neptunes-orbit). If you believe it’s different, please [edit] the question, make it clear how it’s different and/or how the answers on that question are not helpful for your problem.
ProfRob
<space-telescope><parallax>
Will there be any utility in stationing a space telescope a billion miles away to get very accurate parallax measurements?
Miss Understands
# Will there be any utility in stationing a space telescope a billion miles away to get very accurate parallax measurements?

(Asked by: username_0 on 2024-12-04)

I'm thinking a nuclear powered astrometry telescope in a Jupiter-distance orbit. Every five years, you could look at the same object with a parallax baseline of a billion miles. Push it out to Saturn for a baseline of 2 billion miles. That's 10X better than what we have now.

An astronautry satellite wouldn't have to be large; it only has to be large enough to see the furthest stars that show parallax.

Would establishing extremely accurate distance measurements for close stars, and the first parallax measurements for distant stars be particularly useful, Or are our numbers close enough?

Would it be worth the cost?

**Tags:** space-telescope, parallax

> **Comments:**
> **username_1**: It depends to what extent the measurement accuracy has a systematic noise floor.  
> **username_2**: Better yet, three telescopes headed out of the solar system along three perpendicular axes.  
> **username_3**: Related, and maybe a duplicate, [question](https://astronomy.stackexchange.com/q/34076/44977)  
> **username_1**: See also https://astronomy.stackexchange.com/questions/34083/why-not-send-a-gaia-like-mission-to-mars?noredirect=1&lq=1  
> **username_1**: This question is similar to: [Why is Gaia operating around Earth orbit? Why not send it to Neptune's orbit?](https://astronomy.stackexchange.com/questions/34076/why-is-gaia-operating-around-earth-orbit-why-not-send-it-to-neptunes-orbit). If you believe it’s different, please [edit] the question, make it clear how it’s different and/or how the answers on that question are not helpful for your problem.  

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## 1 answers

### Answer by username_1 on 2024-12-05. Score: 1 | Accepted answer

The potential duplicates don't quite cover your scenario, but the issues to consider are similar - whether you really gain any precision, and the telemetry and power requirements.

From what I understand, you are thinking of two position measurement instruments, one of which you keep near the Earth (maybe at L2) and the other you send away to orbit Jupiter. You then combine the position measurements from these two telescopes in some way to determine parallaxes.

Obviously there is also a cost issue in sending things to Jupiter, which I'll ignore. There is also a possible radiation damage issue when sending anything to orbit Jupiter.

The telemetry issue is very serious. Gaia, which is stationed at L2, is telemetry-limited. It has to pick and choose which stars, and which areas on its detectors it can send data back for. Jupiter is of order 300 times further away than L2. Assuming a similar beam width on your antenna then you will likely have to have 90000 times the signal power to achieve something similar. That power is certainly not going to come from the Sun. Gaia is powered by solar panels, but the power per unit area received in Jupiter orbit would be 25 times smaller.

There is then the point that the gain in precision is probably not as big as you had hoped (at least within any reasonable mission lifetime). Whilst you are sending your spacecraft to Jupiter (5 years?) you can do an awful lot of parallax measurements from a single spacecraft close to the Earth. Once it has got there, then assuming there is no systematic noise floor level (which there might be) that stops you achieving the increase in precision suggested by the baseline, full-precision parallax measurements could only be achieved for stars at right angles to the line between the Earth and Jupiter - a rather limited portion of the sky. To get whole-sky coverage you would need to wait for Jupiter to complete half an orbit around the Sun (another 6 years) and I think to properly separate the parallax wobble of a star from its pseudo-linear proper motion across the sky, you would probably need another half orbit (another 6 years).

All the while you are waiting for these data, a competing spacecraft at L2 like Gaia could be busily taking multiple measurements and beating down the uncertainties on the parallax (essentially, in $N$ Earth orbits you reduce the error in a single parallax estimate by $\sqrt{N}$) . This averaging process means that you gain much less (for a mission aimed at getting parallaxes across the whole sky) than the simple increase in baseline would suggest.

For all these reasons I think, unless there is some compelling reason to measure the parallax to some individual object very accurately (which would not require a lot of telemetry or power), a specific mission to measure parallax in this way is unlikely.

> **Comments:**
> **username_0**: > you are thinking of two position measurement instruments, one of which you keep near the Earth (maybe at L2) and the other you send away to orbit Jupiter.  == No, we're not doing interferometry, I figure we'll do a parallax measurement on one side of Jupiter's orbit and then five years later, we get another parallax measurement. == A third measurement five years later, will detect and cancel  the star's proper motion, revealing just the parallax == I made it  Jupiter's orbit because the outer planets take too long to orbit. == In 10 years, will have extremely accurate parallax data.  
> **username_1**: @MissUnderstands in which case it is a duplicate of https://astronomy.stackexchange.com/questions/34076/why-is-gaia-operating-around-earth-orbit-why-not-send-it-to-neptunes-orbit?noredirect=1&lq=1 , all the arguments are the same. IYou need more than 1 orbit to distinguish proper motion from parallax because the proper motion can be in the same direction as the parallax.  
> **username_0**: Hi, Professor rob! ==  If the proper motion is in the direction of parallax, then you've got the classical epicycles. Why would it take more than one orbit to parameterize that? == If you had infinite accuracy, you could watch the way the proper motion changes, and infer the curve from just a few seconds observation. Right? == Or am I, once again, WAY off?  
> **username_1**: @MissUnderstands yes, perhaps so. Like trying to estimate the amplitude of a sine wave by sampling a small fraction of a cycle against the background of a nearly constant drift.  
> **username_2**: If you have the difference in angle to a star from Jupiter and from the Earth simultaneously, then you have the parallax in that direction.  To get accuracy in the perpendicular direction better than Gaia the separation in that direction needs to reach 2 AU.  Proper motion is irrelevant for simultaneous measurements.  
> **username_1**: @username_2 yes, I think that is the case for the 2 spacecraft situation. I do need to revise this answer, but it turns out to be a duplicate in any case.  

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