4 ms·

Is there not a way to control moisture during assembly? If there is, and they did. What amount of moisture are we talking about to cause this issue?

SiempreViernes 3y ago
Well, the deposition is estimated as just a few nanometres thick so were talking about something like a grain sand crushed to a fine powder, and then a few grains of that...
- chongli 3y ago
  Still, I would've thought they'd do a very long vacuum bake-out stage before sealing up the satellite inside the launch rocket.
  - Sharlin 3y ago
    It's not going to be in a vacuum inside the payload shroud. There's air, and that air contains some amount of moisture. And Florida isn't known for its dry air (it was launched from Cape on a Falcon 9 – but French Guiana would hardly have been better in that respect). > It was always expected that water could gradually build up and contaminate Euclid’s vision, as it is very difficult to build and launch a spacecraft from Earth without some of the water in our planet’s atmosphere creeping into it.
    - nick238 3y ago
      Satellites are transported in very specialized containers that will often be purged with dry nitrogen. Then after encapsulation in the faring, conditioned air of whatever sort is pumped into the faring from rollout to launch. [Example air conditioning duct attached to a Thor-Agena](https://space.stackexchange.com/questions/39440/why-use-an-air-conditioning-blanket-instead-of-supplying-air-into-the-fairing https://space.stackexchange.com/questions/39440/why-use-an-a...)
    - 0cf8612b2e1e 3y ago
      Can ice sublimate at these temperatures?
  - SiempreViernes 3y ago
    They did: > This icing issue is not uncommon, and, as a result, part of the telescope’s commissioning phase included an “outgassing campaign.” This process involved Euclid turning to face the Sun for a total of 96 hours. This process was implemented specifically to reduce the risk of ice build-up after the agency’s Gaia mission faced a similar issue. Apparently, it wasn't as effective as they hoped.
    - BobbyTables2 3y ago
      They should have put one of those silica “do not eat” desiccant packets in there
seszett 3y ago
They say Approximately 10 kg of MLI covers Euclid's two science instruments, but this material can absorb 1% of its own weight in water so at most 100 grams of water. Assuming they were careful, maybe a tenth of that remains, so around 10 grams of water, a small fraction of which sublimates and eventually meets a mirror and deposits there. They say it's "several layers of molecules". I suppose they could have used another type of insulation, but since they also have very precise temperature requirements, maybe it was a trade off they had to make.

SiempreViernes 3y ago

Well, the deposition is estimated as just a few nanometres thick so were talking about something like a grain sand crushed to a fine powder, and then a few grains of that...

chongli 3y ago
Still, I would've thought they'd do a very long vacuum bake-out stage before sealing up the satellite inside the launch rocket.
- Sharlin 3y ago
  It's not going to be in a vacuum inside the payload shroud. There's air, and that air contains some amount of moisture. And Florida isn't known for its dry air (it was launched from Cape on a Falcon 9 – but French Guiana would hardly have been better in that respect). > It was always expected that water could gradually build up and contaminate Euclid’s vision, as it is very difficult to build and launch a spacecraft from Earth without some of the water in our planet’s atmosphere creeping into it.
  - nick238 3y ago
    Satellites are transported in very specialized containers that will often be purged with dry nitrogen. Then after encapsulation in the faring, conditioned air of whatever sort is pumped into the faring from rollout to launch. [Example air conditioning duct attached to a Thor-Agena](https://space.stackexchange.com/questions/39440/why-use-an-air-conditioning-blanket-instead-of-supplying-air-into-the-fairing https://space.stackexchange.com/questions/39440/why-use-an-a...)
  - 0cf8612b2e1e 3y ago
    Can ice sublimate at these temperatures?
- SiempreViernes 3y ago
  They did: > This icing issue is not uncommon, and, as a result, part of the telescope’s commissioning phase included an “outgassing campaign.” This process involved Euclid turning to face the Sun for a total of 96 hours. This process was implemented specifically to reduce the risk of ice build-up after the agency’s Gaia mission faced a similar issue. Apparently, it wasn't as effective as they hoped.
  - BobbyTables2 3y ago
    They should have put one of those silica “do not eat” desiccant packets in there

seszett 3y ago

They say Approximately 10 kg of MLI covers Euclid's two science instruments, but this material can absorb 1% of its own weight in water so at most 100 grams of water. Assuming they were careful, maybe a tenth of that remains, so around 10 grams of water, a small fraction of which sublimates and eventually meets a mirror and deposits there. They say it's "several layers of molecules". I suppose they could have used another type of insulation, but since they also have very precise temperature requirements, maybe it was a trade off they had to make.