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Absent from that link but important context: The reason why they are actively shutting it down, is that they are running low on fuel, and want to ensure that t

Absent from that link but important context: The reason why they are actively shutting it down, is that they are running low on fuel, and want to ensure that the spacecraft does not litter important orbital locations. Gaia has spent its life at Earth's L2 Lagrange point, which is a valuable and limited area of space; they do not want to have to plan around dead spacecraft in future missions. Thus, before the spacecraft runs out of fuel, they have moved it away from L2 into its final graveyard orbit. It is not capable of performing the science for which it was designed in its graveyard orbit.

8bitsrule 2y ago
Thanks. That page also helped me find one that sums up the mission so far, and explains what's to come in 2026 & 2023. https://www.esa.int/Science_Exploration/Space_Science/Gaia/Last_starlight_for_ground-breaking_Gaia https://www.esa.int/Science_Exploration/Space_Science/Gaia/L...
- normie3000 2y ago
  > what's to come in 2026 & 2023 Weird, I checked the link but there's no mention of time travel.
  - pinkmuffinere 2y ago
    The time travel discussion is on the 2028 page, but intentionally absent from the 2025 page to minimize risks of contamination.
  - 8bitsrule 2y ago
    I guess you didn't read to the line where it says > two massive data releases are tabled for around 2026 and the end of this decade, respectively.
alfiedotwtf 2y ago
Oh?! I was always under the impression that Lagrange points were convenient calculation spots where everything sums out, but from what you’re saying, it’s a deep gravity well? Mind blown! Edit: don’t mind me, I was completely off… thanks ChatGPT!
- dmoy 2y ago
  L4 and L5 are more stable. L2 isn't super stable, hence the need for fuel for station keeping. More polite to vacate on purpose rather than just erratically bounce around a nearby orbit after fuel runs out. Idk if I'd describe any of them as "deep gravity well"
- margalabargala 2y ago
  It's not a deep gravity well, it's a fairly weak gravity well, but with fuel one can orbit L2 reliably. Without fuel, one can orbit L2 erratically. People with the ability to send satellites places, don't like sending expensive satellites to places with large bodies in erratic orbits.
  - JumpCrisscross 2y ago
    > Without fuel, one can orbit L2 erratically It takes an infintessimal amount of energy to detatch something from L2.
    - margalabargala 2y ago
      Sure, you won't be at L2, but you may remain near L2 for some time.
- numpad0 2y ago
  Where everything sums out is a completely flat spot on a table, it won't hold a freely moving object. Lagrange points are more like shallow dents that tend to attract rolling marbles.
perihelions 2y ago
- "Earth's L2 Lagrange point, which is a valuable and limited area of space" That's a strong exaggeration; it's millions of km across in three dimensions. Gaia's orbit alone is - "263 000 x 707 000 x 370 000 km, 180 day-long orbit around L2" https://www.esa.int/Science_Exploration/Space_Science/Gaia/Gaia_enters_its_operational_orbit https://www.esa.int/Science_Exploration/Space_Science/Gaia/G...
- echoangle 2y ago
  L2 is also said to be unstable, but I don't know how long it would take for Gaia to move far away enough that the collision risk would be negligible.
  - perihelions 2y ago
    The issue with that is things that naturally escape from Lagrange points often crash into the Earth, which is one of the risks they're trying to mitigate.
    - happyopossum 2y ago
      If by “crash into earth” you mean “burn up harmlessly in the upper atmosphere” then ok - but it kinda sounds like that’s not what you’re claiming…
      - perihelions 2y ago
        Pieces of spacecraft often survive atmospheric reentry.
tgsovlerkhgsel 2y ago
I understood why they are shooting it into a graveyard orbit, but not why they're actively turning it off rather than trying to get whatever science they can out of it. (I'm sure that if I have a basic idea like this, the people at ESA also had it, but I haven't seen the reasoning explained anywhere.) I think this part of the Wikipedia article answers it: > In order to maintain the fine pointing to focus on stars many light years away, the only moving parts are actuators to align the mirrors and the valves to fire the thrusters. It has no reaction wheels or gyroscopes. So without "fuel" (reaction mass/gas) for the cold gas thrusters, it likely couldn't hold a stable attitude, and a tumbling spacecraft is likely quite useless because you can't even properly communicate with it, let alone use instruments. I wonder what considerations went into not attempting to use it as a low-value probe sending out telemetry using a low bandwidth omnidirectional antenna (which I would expect the spacecraft to have for recovery in case something goes wrong). Maybe we already have all the science that would be interesting from other probes, maybe management/budget decisions, maybe it wouldn't work, but it would be interesting to see the decision making.
- Facemelters 2y ago
  Costs money to support the mission
- tekla 2y ago
  The DSN is already strained
randoomed 2y ago
ESA is actively trying to reduce the amount of debris in orbit. To this end all missions have to actively clean them self's up at end of life. See https://www.esa.int/Space_Safety/Clean_Space/ESA_s_Zero_Debris_approach https://www.esa.int/Space_Safety/Clean_Space/ESA_s_Zero_Debr... and https://www.esa.int/Space_Safety/Space_Debris/Mitigating_space_debris_generation https://www.esa.int/Space_Safety/Space_Debris/Mitigating_spa...

8bitsrule 2y ago

Thanks. That page also helped me find one that sums up the mission so far, and explains what's to come in 2026 & 2023. https://www.esa.int/Science_Exploration/Space_Science/Gaia/Last_starlight_for_ground-breaking_Gaia https://www.esa.int/Science_Exploration/Space_Science/Gaia/L...

normie3000 2y ago
> what's to come in 2026 & 2023 Weird, I checked the link but there's no mention of time travel.
- pinkmuffinere 2y ago
  The time travel discussion is on the 2028 page, but intentionally absent from the 2025 page to minimize risks of contamination.
- 8bitsrule 2y ago
  I guess you didn't read to the line where it says > two massive data releases are tabled for around 2026 and the end of this decade, respectively.

alfiedotwtf 2y ago

Oh?! I was always under the impression that Lagrange points were convenient calculation spots where everything sums out, but from what you’re saying, it’s a deep gravity well? Mind blown! Edit: don’t mind me, I was completely off… thanks ChatGPT!

dmoy 2y ago
L4 and L5 are more stable. L2 isn't super stable, hence the need for fuel for station keeping. More polite to vacate on purpose rather than just erratically bounce around a nearby orbit after fuel runs out. Idk if I'd describe any of them as "deep gravity well"
margalabargala 2y ago
It's not a deep gravity well, it's a fairly weak gravity well, but with fuel one can orbit L2 reliably. Without fuel, one can orbit L2 erratically. People with the ability to send satellites places, don't like sending expensive satellites to places with large bodies in erratic orbits.
- JumpCrisscross 2y ago
  > Without fuel, one can orbit L2 erratically It takes an infintessimal amount of energy to detatch something from L2.
  - margalabargala 2y ago
    Sure, you won't be at L2, but you may remain near L2 for some time.
numpad0 2y ago
Where everything sums out is a completely flat spot on a table, it won't hold a freely moving object. Lagrange points are more like shallow dents that tend to attract rolling marbles.

perihelions 2y ago

- "Earth's L2 Lagrange point, which is a valuable and limited area of space" That's a strong exaggeration; it's millions of km across in three dimensions. Gaia's orbit alone is - "263 000 x 707 000 x 370 000 km, 180 day-long orbit around L2" https://www.esa.int/Science_Exploration/Space_Science/Gaia/Gaia_enters_its_operational_orbit https://www.esa.int/Science_Exploration/Space_Science/Gaia/G...

echoangle 2y ago
L2 is also said to be unstable, but I don't know how long it would take for Gaia to move far away enough that the collision risk would be negligible.
- perihelions 2y ago
  The issue with that is things that naturally escape from Lagrange points often crash into the Earth, which is one of the risks they're trying to mitigate.
  - happyopossum 2y ago
    If by “crash into earth” you mean “burn up harmlessly in the upper atmosphere” then ok - but it kinda sounds like that’s not what you’re claiming…
    - perihelions 2y ago
      Pieces of spacecraft often survive atmospheric reentry.

tgsovlerkhgsel 2y ago

I understood why they are shooting it into a graveyard orbit, but not why they're actively turning it off rather than trying to get whatever science they can out of it. (I'm sure that if I have a basic idea like this, the people at ESA also had it, but I haven't seen the reasoning explained anywhere.) I think this part of the Wikipedia article answers it: > In order to maintain the fine pointing to focus on stars many light years away, the only moving parts are actuators to align the mirrors and the valves to fire the thrusters. It has no reaction wheels or gyroscopes. So without "fuel" (reaction mass/gas) for the cold gas thrusters, it likely couldn't hold a stable attitude, and a tumbling spacecraft is likely quite useless because you can't even properly communicate with it, let alone use instruments. I wonder what considerations went into not attempting to use it as a low-value probe sending out telemetry using a low bandwidth omnidirectional antenna (which I would expect the spacecraft to have for recovery in case something goes wrong). Maybe we already have all the science that would be interesting from other probes, maybe management/budget decisions, maybe it wouldn't work, but it would be interesting to see the decision making.

Facemelters 2y ago
Costs money to support the mission
tekla 2y ago
The DSN is already strained

randoomed 2y ago

ESA is actively trying to reduce the amount of debris in orbit. To this end all missions have to actively clean them self's up at end of life. See https://www.esa.int/Space_Safety/Clean_Space/ESA_s_Zero_Debris_approach https://www.esa.int/Space_Safety/Clean_Space/ESA_s_Zero_Debr... and https://www.esa.int/Space_Safety/Space_Debris/Mitigating_space_debris_generation https://www.esa.int/Space_Safety/Space_Debris/Mitigating_spa...