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It always surprises me that we let these space stations decay out of orbit instead of glomming them on to something else. I guess the extra delta vee cost of pu

It always surprises me that we let these space stations decay out of orbit instead of glomming them on to something else. I guess the extra delta vee cost of putting new things in orbit is negligible...

jackmott42 3y ago
They are at low orbits which would need constant servicing to stay there, and they big and heavy, so moving them up into a higher permanent orbit would be very expensive. also it reduces space junk to let them decay out.
- Aachen 3y ago
  I agree with purpleflame's sentiment though. Clearly they'd just boost it to a higher orbit if the fuel mass they need to lift for that is smaller than the mass they expect to later salvage from it, so apparently it's not worth it, but it's rather surprising and seems like a waste even if it's, economically, not
  - troutwine 3y ago
    It's also worth mentioning that materials wear out in space in ways we don't always appreciate and certainly did not in the golden era of the Soviet space stations. The Mir, an upgrade over the Salyut program, was pretty trashed by the time it was abandoned. It's absolutely not worth boosting dangerous trash for it to potentially break up. That said, it is sort of a shame we didn't capture Salyut 7 and bring it back down safely, or at least a chunk of it. It would have been interesting to see what uncontrolled heating and cooling does to a body meant for human habitation that big in low orbit.
    - idontwantthis 3y ago
      Would have required using the space shuttle to retrieve a Soviet space station. Impossible, but a very fun idea :) Would the shuttle have landed in the USSR or would Salyut have arrived in the USA?
      - troutwine 3y ago
        Hah! Fun question. While I think if you ripped the solar panels and other instrumentation off you could _just_ fit the Salyut in the Shuttle payload bay it was too heavy for a safe return trip. But, I think the Salyut's orbit would have required a USSR launch? Unless alternate history humanity made a truly humongous specialty retrieval craft and inclination changes meant nothing to it. :)
      - wongarsu 3y ago
        The Buran had about the same payload capacity as the Space Shuttle (slightly more even). It's first (and only) orbital test flight was in '88, 2.5 years before the Salyut deorbit. Had the Soviet Union been just a smidge more solvent and politically stable we might have the whole Salyut 7 sitting in a museum somewhere. All it would have taken was a slightly accelerated Buran program, a Soviet Union that survived maybe 3 years longer, and a decision that bringing back a decommissioned station is a great test mission that boosts national pride. A near miss in history. https://en.wikipedia.org/wiki/Buran_(spacecraft) https://en.wikipedia.org/wiki/Buran_(spacecraft)
Dalewyn 3y ago
Rendezvousing with another orbiting object requires a Hohmann[1] or bi-elliptic[2] transfer maneuver in order to "catch up" to the target object. This requires multiple engine burns, and thus lots of delta-v. If the two objects are in different orbital inclinations, an orbital inclination change[3] maneuver is also required. This requires very long, possibly multiple engine burns, and thus lots of delta-v. In short, "glomming" a station onto another requires quite literally astronomical amounts of delta-v. It's not that launching new stations into orbit is cheap, it's that moving objects in orbit is astronomically expensive as to be downright impractical or even impossible. [1]: https://en.wikipedia.org/wiki/Hohmann_transfer_orbit https://en.wikipedia.org/wiki/Hohmann_transfer_orbit [2]: https://en.wikipedia.org/wiki/Bi-elliptic_transfer https://en.wikipedia.org/wiki/Bi-elliptic_transfer [3]: https://en.wikipedia.org/wiki/Orbital_inclination_change https://en.wikipedia.org/wiki/Orbital_inclination_change
- yellowapple 3y ago
  Hopefully as ion engines and such catch on for these exact sorts of maneuvers we'll see more efforts to glom stations together rather than plunge them back to Earth.
- cornholio 3y ago
  You are perhaps exaggerating the "astronomical" delta-V required. Space stations are generally in a low ~400km prograde circular orbit, at an inclination efficient for an northern hemisphere launch. For example, you could push the last stable Mir into the orbit of the ISS using only a few hundred m/s delta-v, regardless if it was a good idea or not. Of course, you could construct other scenarios where docking is not possible with current available thrust options.
  - Dalewyn 3y ago
    Delta-v is a change in velocity, so "only a few hundred m/s of delta-v" isn't painting the entire picture. The more massive an object is, the more energy (aka fuel) it takes to impart a given amount of velocity change (aka delta-v) upon it. Both a small satellite and a big station module need the same "only a few hundred m/s of delta-v", but the amount of fuel needed to accomplish that maneuver will be astronomically different between them because the station module is so much more massive.
vikingerik 3y ago
At some point, you are better off launching a new station than trying to maintain an old one. They constantly need repairs for things that break and it gets worse over time. They're not gleaming perfection like the Enterprise, it's more like trying to maintain a creaky thirty-year-old RV.
- gregoriol 3y ago
  We always decommission boats, planes, buildings, and space stations are no different. They are even more prone to issues, external or internal, are very difficult to repair or upgrade.
- andyjohnson0 3y ago
  > They're not gleaming perfection like the Enterprise, it's more like trying to maintain a creaky thirty-year-old RV. The ISS has a mould problem due to spores brought in by crew rotations. The crews have to spend significant amounts of time each day just cleaning walls and other surfaces. https://www.cbc.ca/news/science/international-space-station-mould-1.5193970 https://www.cbc.ca/news/science/international-space-station-...
  - euroderf 3y ago
    I had high hopes that the Mir fungus would be mutated by space radiation and then survive re-entry. Awesome basis for a sci-fi/horror film.
    - m000 3y ago
      Not exactly the same concept, but Life (2017) [1] comes close. [1] https://letterboxd.com/film/life-2017/ https://letterboxd.com/film/life-2017/

jackmott42 3y ago

They are at low orbits which would need constant servicing to stay there, and they big and heavy, so moving them up into a higher permanent orbit would be very expensive. also it reduces space junk to let them decay out.

Aachen 3y ago
I agree with purpleflame's sentiment though. Clearly they'd just boost it to a higher orbit if the fuel mass they need to lift for that is smaller than the mass they expect to later salvage from it, so apparently it's not worth it, but it's rather surprising and seems like a waste even if it's, economically, not
- troutwine 3y ago
  It's also worth mentioning that materials wear out in space in ways we don't always appreciate and certainly did not in the golden era of the Soviet space stations. The Mir, an upgrade over the Salyut program, was pretty trashed by the time it was abandoned. It's absolutely not worth boosting dangerous trash for it to potentially break up. That said, it is sort of a shame we didn't capture Salyut 7 and bring it back down safely, or at least a chunk of it. It would have been interesting to see what uncontrolled heating and cooling does to a body meant for human habitation that big in low orbit.
  - idontwantthis 3y ago
    Would have required using the space shuttle to retrieve a Soviet space station. Impossible, but a very fun idea :) Would the shuttle have landed in the USSR or would Salyut have arrived in the USA?
    - troutwine 3y ago
      Hah! Fun question. While I think if you ripped the solar panels and other instrumentation off you could _just_ fit the Salyut in the Shuttle payload bay it was too heavy for a safe return trip. But, I think the Salyut's orbit would have required a USSR launch? Unless alternate history humanity made a truly humongous specialty retrieval craft and inclination changes meant nothing to it. :)
    - wongarsu 3y ago
      The Buran had about the same payload capacity as the Space Shuttle (slightly more even). It's first (and only) orbital test flight was in '88, 2.5 years before the Salyut deorbit. Had the Soviet Union been just a smidge more solvent and politically stable we might have the whole Salyut 7 sitting in a museum somewhere. All it would have taken was a slightly accelerated Buran program, a Soviet Union that survived maybe 3 years longer, and a decision that bringing back a decommissioned station is a great test mission that boosts national pride. A near miss in history. https://en.wikipedia.org/wiki/Buran_(spacecraft) https://en.wikipedia.org/wiki/Buran_(spacecraft)

Dalewyn 3y ago

Rendezvousing with another orbiting object requires a Hohmann[1] or bi-elliptic[2] transfer maneuver in order to "catch up" to the target object. This requires multiple engine burns, and thus lots of delta-v. If the two objects are in different orbital inclinations, an orbital inclination change[3] maneuver is also required. This requires very long, possibly multiple engine burns, and thus lots of delta-v. In short, "glomming" a station onto another requires quite literally astronomical amounts of delta-v. It's not that launching new stations into orbit is cheap, it's that moving objects in orbit is astronomically expensive as to be downright impractical or even impossible. [1]: https://en.wikipedia.org/wiki/Hohmann_transfer_orbit https://en.wikipedia.org/wiki/Hohmann_transfer_orbit [2]: https://en.wikipedia.org/wiki/Bi-elliptic_transfer https://en.wikipedia.org/wiki/Bi-elliptic_transfer [3]: https://en.wikipedia.org/wiki/Orbital_inclination_change https://en.wikipedia.org/wiki/Orbital_inclination_change

yellowapple 3y ago
Hopefully as ion engines and such catch on for these exact sorts of maneuvers we'll see more efforts to glom stations together rather than plunge them back to Earth.
cornholio 3y ago
You are perhaps exaggerating the "astronomical" delta-V required. Space stations are generally in a low ~400km prograde circular orbit, at an inclination efficient for an northern hemisphere launch. For example, you could push the last stable Mir into the orbit of the ISS using only a few hundred m/s delta-v, regardless if it was a good idea or not. Of course, you could construct other scenarios where docking is not possible with current available thrust options.
- Dalewyn 3y ago
  Delta-v is a change in velocity, so "only a few hundred m/s of delta-v" isn't painting the entire picture. The more massive an object is, the more energy (aka fuel) it takes to impart a given amount of velocity change (aka delta-v) upon it. Both a small satellite and a big station module need the same "only a few hundred m/s of delta-v", but the amount of fuel needed to accomplish that maneuver will be astronomically different between them because the station module is so much more massive.

vikingerik 3y ago

At some point, you are better off launching a new station than trying to maintain an old one. They constantly need repairs for things that break and it gets worse over time. They're not gleaming perfection like the Enterprise, it's more like trying to maintain a creaky thirty-year-old RV.

gregoriol 3y ago
We always decommission boats, planes, buildings, and space stations are no different. They are even more prone to issues, external or internal, are very difficult to repair or upgrade.
andyjohnson0 3y ago
> They're not gleaming perfection like the Enterprise, it's more like trying to maintain a creaky thirty-year-old RV. The ISS has a mould problem due to spores brought in by crew rotations. The crews have to spend significant amounts of time each day just cleaning walls and other surfaces. https://www.cbc.ca/news/science/international-space-station-mould-1.5193970 https://www.cbc.ca/news/science/international-space-station-...
- euroderf 3y ago
  I had high hopes that the Mir fungus would be mutated by space radiation and then survive re-entry. Awesome basis for a sci-fi/horror film.
  - m000 3y ago
    Not exactly the same concept, but Life (2017) [1] comes close. [1] https://letterboxd.com/film/life-2017/ https://letterboxd.com/film/life-2017/