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Why would coolant be a consumable? These things are usually cooled with Stirling cryocoolers which are closed systems.

by Sanzig 2y ago

perihelions 2y ago
I did a quick search and it seems there is neither? - "SPHEREx relies on an entirely passive cooling system — no electricity or coolants are used during normal operations" https://www.jpl.nasa.gov/news/6-things-to-know-about-spherex-nasas-newest-space-telescope/ https://www.jpl.nasa.gov/news/6-things-to-know-about-spherex... edit to add: - "The telescope is passively cooled to below 80 K in low-Earth orbit by three nested V-groove radiators. An additional radiator cools the long wavelength focal plane temperature below 60 K to reduce detector dark current." https://arxiv.org/abs/2404.11017v1 https://arxiv.org/abs/2404.11017v1
- dylan604 2y ago
  The Spitzer used passive cooling, but only as a method to reduce the amount of coolant required. It still needed a coolant. "One of the most important advances of this redesign was an Earth-trailing orbit.[1] Cryogenic satellites that require liquid helium (LHe, T ≈ 4 K) temperatures in near-Earth orbit are typically exposed to a large heat load from Earth, and consequently require large amounts of LHe coolant, which then tends to dominate the total payload mass and limits mission life. Placing the satellite in solar orbit far from Earth allowed innovative passive cooling. The sun shield protected the rest of the spacecraft from the Sun's heat, the far side of the spacecraft was painted black to enhance passive radiation of heat, and the spacecraft bus was thermally isolated from the telescope. All of these design choices combined to drastically reduce the total mass of helium needed, resulting in an overall smaller and lighter payload, resulting in major cost savings, but with a mirror the same diameter as originally designed. This orbit also simplified telescope pointing, but did require the NASA Deep Space Network for communications"[0] [0]https://en.wikipedia.org/wiki/Spitzer_Space_Telescope https://en.wikipedia.org/wiki/Spitzer_Space_Telescope
- perihelions 2y ago
  I found an explanation of the "v-groove" radiator geometry, if anyone else was curious about it: (.pdf) https://ttu-ir.tdl.org/server/api/core/bitstreams/71aee1e9-3f65-466f-a804-2737eefd2bed/content https://ttu-ir.tdl.org/server/api/core/bitstreams/71aee1e9-3...
dylan604 2y ago
Every system I'm familiar with that used liquid nitrogen to cool the IR instruments has had a operational lifespan based on the coolant. JWST is one such. "The coolant will slowly vaporize, limiting the lifetime of the instrument from as short as a few months to a few years at most."[0] [0]https://en.wikipedia.org/wiki/James_Webb_Space_Telescope https://en.wikipedia.org/wiki/James_Webb_Space_Telescope
- perihelions 2y ago
  You've misread your source article—what you've quoted is not a description of Webb.
  - deleted 2y ago
    [deleted]
  - dylan604 2y ago
    Does that really change anything?
    - kadoban 2y ago
      Well, it doesn't apply to either JWST or the subject of the article, so kind of feels like it's worth mentioning. It doesn't change your specific, exact point (about previous cooling systems you were aware of), but it makes the conversation a lot less likely to confuse people IMO.
jessriedel 2y ago
As another comment mentions, SPHEREx is passively cooled. But fwiw, plenty of infrared space telescopes use consumable coolant: > Notable infrared missions that carried consumable cryogen include IRAS (1983), ISO (1995–1998), Spitzer (2003–2009 in cryo mode), Herschel (2009–2013), WISE (2009–2011 in cryo mode), and Planck (2009–2013). Each relied on a finite liquid helium (or solid hydrogen) supply to keep detectors cold and reverted to a warmer operating mode or ended once their coolant was depleted.
- perihelions 2y ago
  Notably those were all far-infrared telescopes, which need even lower temperatures (liquid helium) to escape thermal noise.

Why would coolant be a consumable? These things are usually cooled with Stirling cryocoolers which are closed systems.

by Sanzig 2y ago

Why would coolant be a consumable? These things are usually cooled with Stirling cryocoolers which are closed systems.

I did a quick search and it seems there is neither? - "SPHEREx relies on an entirely passive cooling system — no electricity or coolants are used during normal operations" https://www.jpl.nasa.gov/news/6-things-to-know-about-spherex-nasas-newest-space-telescope/ https://www.jpl.nasa.gov/news/6-things-to-know-about-spherex... edit to add: - "The telescope is passively cooled to below 80 K in low-Earth orbit by three nested V-groove radiators. An additional radiator cools the long wavelength focal plane temperature below 60 K to reduce detector dark current." https://arxiv.org/abs/2404.11017v1 https://arxiv.org/abs/2404.11017v1

dylan604 2y ago
The Spitzer used passive cooling, but only as a method to reduce the amount of coolant required. It still needed a coolant. "One of the most important advances of this redesign was an Earth-trailing orbit.[1] Cryogenic satellites that require liquid helium (LHe, T ≈ 4 K) temperatures in near-Earth orbit are typically exposed to a large heat load from Earth, and consequently require large amounts of LHe coolant, which then tends to dominate the total payload mass and limits mission life. Placing the satellite in solar orbit far from Earth allowed innovative passive cooling. The sun shield protected the rest of the spacecraft from the Sun's heat, the far side of the spacecraft was painted black to enhance passive radiation of heat, and the spacecraft bus was thermally isolated from the telescope. All of these design choices combined to drastically reduce the total mass of helium needed, resulting in an overall smaller and lighter payload, resulting in major cost savings, but with a mirror the same diameter as originally designed. This orbit also simplified telescope pointing, but did require the NASA Deep Space Network for communications"[0] [0]https://en.wikipedia.org/wiki/Spitzer_Space_Telescope https://en.wikipedia.org/wiki/Spitzer_Space_Telescope
perihelions 2y ago
I found an explanation of the "v-groove" radiator geometry, if anyone else was curious about it: (.pdf) https://ttu-ir.tdl.org/server/api/core/bitstreams/71aee1e9-3f65-466f-a804-2737eefd2bed/content https://ttu-ir.tdl.org/server/api/core/bitstreams/71aee1e9-3...

dylan604 2y ago

Every system I'm familiar with that used liquid nitrogen to cool the IR instruments has had a operational lifespan based on the coolant. JWST is one such. "The coolant will slowly vaporize, limiting the lifetime of the instrument from as short as a few months to a few years at most."[0] [0]https://en.wikipedia.org/wiki/James_Webb_Space_Telescope https://en.wikipedia.org/wiki/James_Webb_Space_Telescope

perihelions 2y ago
You've misread your source article—what you've quoted is not a description of Webb.
- deleted 2y ago
  [deleted]
- dylan604 2y ago
  Does that really change anything?
  - kadoban 2y ago
    Well, it doesn't apply to either JWST or the subject of the article, so kind of feels like it's worth mentioning. It doesn't change your specific, exact point (about previous cooling systems you were aware of), but it makes the conversation a lot less likely to confuse people IMO.

jessriedel 2y ago

As another comment mentions, SPHEREx is passively cooled. But fwiw, plenty of infrared space telescopes use consumable coolant: > Notable infrared missions that carried consumable cryogen include IRAS (1983), ISO (1995–1998), Spitzer (2003–2009 in cryo mode), Herschel (2009–2013), WISE (2009–2011 in cryo mode), and Planck (2009–2013). Each relied on a finite liquid helium (or solid hydrogen) supply to keep detectors cold and reverted to a warmer operating mode or ended once their coolant was depleted.

perihelions 2y ago
Notably those were all far-infrared telescopes, which need even lower temperatures (liquid helium) to escape thermal noise.