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.
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.
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!
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"
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.
They also overwrote the EEPROM of the satellite computer before shutting it, because apparently they were concerned that the satellite would reawake, because it has multiple autonomous recovery modes.
> As part of its decommissioning, the names of around 1500 team members who contributed to its mission were used to overwrite some of the back-up software stored in Gaia’s onboard memory. Personal farewell messages were also written into the spacecraft’s memory, ensuring that Gaia will forever carry a piece of its team with it as it drifts through space.
I find it wild that we’ve been using triangular reckoning (parallax) for over a millennium, all the way back to early mariners. Measure two angles, draw a triangle, know where you are. That same method now maps galaxies. We’re still navigating the unknown with geometry.
"Gaia is measuring their positions to an accuracy of 24 microarcseconds. This is comparable to measuring the diameter of a human hair at a distance of 1000 km."
Thank you to everyone involved in the Gaia mission and to everyone whose contributions (including taxpayers) who made it possible. Gaia's data will shape our understanding of the universe for generations to come.
You’d need 320+ m/s of delta-V to knock something from Sun-Earth L2 to Earth [1]. Not impossible. But akin to the energy required to go from Earth transfer to Mars or Venus transfer [2]. Less likely to fall to Earth than become an orbital pest.
It's actually much less than 320 m/s—that's a figure for a fast transfer. If you have time for it, three-body dynamics let you get arbitrarily cheap transfers in the regions of the Sun/Earth/Moon Lagrange points,
To make it less abstract than the argument that it costs "delta v": it's a bit like asking, what if this rock I placed on the floor impacts a nuclear plant one day? It requires energy to move there. This change in velocity, making something drop from orbit by itself, happens across months~years for only the lowest orbits around the earth, caused by stray particles from our atmosphere impacting the spacecraft/satellites there, but at L2 that's afaik not a factor
Generally getting things out of space also requires effort/fuel. A graveyard orbit is specifically easier to get to but uninteresting from a "hitting other things" perspective.
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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.
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.
https://www.esa.int/Science_Exploration/Space_Science/Gaia/L...
Weird, I checked the link but there's no mention of time travel.
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/G...
Edit: don’t mind me, I was completely off… thanks ChatGPT!
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.
Idk if I'd describe any of them as "deep gravity well"
> As part of its decommissioning, the names of around 1500 team members who contributed to its mission were used to overwrite some of the back-up software stored in Gaia’s onboard memory. Personal farewell messages were also written into the spacecraft’s memory, ensuring that Gaia will forever carry a piece of its team with it as it drifts through space.
[0]: https://www.esa.int/Enabling_Support/Operations/Farewell_Gai...
https://www.esa.int/Science_Exploration/Space_Science/Gaia
https://zah.uni-heidelberg.de/gaia/outreach/gaiasky
Don't anthropomorphize machines. They hate it when you do that.
Deleted Comment
"Gaia is measuring their positions to an accuracy of 24 microarcseconds. This is comparable to measuring the diameter of a human hair at a distance of 1000 km."
https://www.esa.int/Science_Exploration/Space_Science/Gaia/G...
If for any reason it fell from orbit, later, it could impact an important surface (city, nuclear plant), and definitely a larger area.
You’d need 320+ m/s of delta-V to knock something from Sun-Earth L2 to Earth [1]. Not impossible. But akin to the energy required to go from Earth transfer to Mars or Venus transfer [2]. Less likely to fall to Earth than become an orbital pest.
(It's a good question.)
[1] https://www.researchgate.net/figure/Duration-and-delta-v-req...
[2] https://en.m.wikipedia.org/wiki/File:Solar_system_delta_v_ma...
https://nebula.esa.int/sites/default/files/neb_study/1167/C4...
(Table 1 disposal options: 88.56 m/s to crash Gaia into the Earth—or even just 6.18 m/s to crash Euclid, another SEL-2 dweller).
It’s not really intuitive when most personal experience is how hard it is to keep things from not falling.