4 ms·

>What makes water mass cheaper to orbit compared to nitrogen mass? Nitrogen needs a high-pressure bottle which is wasted mass, whereas water you can send to or

>What makes water mass cheaper to orbit compared to nitrogen mass? Nitrogen needs a high-pressure bottle which is wasted mass, whereas water you can send to orbit in thin plastic and fabric bags like they do on ISS. Often on ISS they're actually shipping oxygen as water, but still the wasted mass of water being 11% hydrogen plus the wasted mass of the bag is more efficient than a high pressure gas cylinder.

PaulHoule 1y ago
For my baby Bernal sphere it is shipped either as LN2 or NH4. The large airspace needs a lot of it compared to the water inventory. O’Neill’s published designs except for the Stanford torus were much worse. The water inventory of both N2 and H2O on Earth (0.2 cubic km of water per inhabitant) is extravagant. Ceres is roughly 50% water (like the generic outer solar system or interstellar object) and we could use all of it but it adds up to about the mass of our oceans, and that is most of the water inventory the asteroid belt. I’ve looked at various large rotating structures up to the size of the Banks Orbital and concluded you could solve the structural problems if you could make a reliable journal bearing (structural parts don’t need to be spun) that could handle the velocity difference but no matter what you cannot afford tall mountains or deep oceans.
- schiffern 1y ago
  Agreed, liquid is probably the way to go. Very tempting to swap nitrogen for helium, but AIUI the main downsides are that the speed of sound is higher so air will leak out from a breach faster, and there may be negative effects on flammability due to helium's high thermal conductivity and low specific heat.
  - Terr_ 1y ago
    Helium gas also leaks a lot, even when everything is normal.
hotshiitake 1y ago
Probably a naive question but would it possible for us to skim gasses from LEO for use in space stations?
- 05 1y ago
  Putting aside issues with capturing basically vacuum at 8km/s, by doing that you're going to lose impulse that you're going to have to regain, spending more mass in fuel+oxidizer than you gained in gathered gases, unless you use ion propulsion (which ISS doesn't). Also most of what you're going to capture at 400km is going to be atomic oxygen and helium, N2/N share is only a couple percentage points at that altitude.. [0] [0] https://en.wikipedia.org/wiki/Heterosphere https://en.wikipedia.org/wiki/Heterosphere
  - schiffern 1y ago
    Clearly you would not choose similar operational parameters and propulsion as the ISS when designing an atmospheric scooper. Not sure why you would assume so, honestly. There have been proposals to use scoopers with structurally integrated electrodynamic propulsion ("tether without the tether"),[0] which would use zero propellant. [0] https://forum.nasaspaceflight.com/index.php?topic=44542.msg1818140#msg1818140 https://forum.nasaspaceflight.com/index.php?topic=44542.msg1...
wildzzz 1y ago
We already built LOX tanks into rockets. Just send up a tank of LN2. It doesn't need the strength of a bottle, you just need thermally insulating materials which can be very light.

PaulHoule 1y ago

For my baby Bernal sphere it is shipped either as LN2 or NH4. The large airspace needs a lot of it compared to the water inventory. O’Neill’s published designs except for the Stanford torus were much worse. The water inventory of both N2 and H2O on Earth (0.2 cubic km of water per inhabitant) is extravagant. Ceres is roughly 50% water (like the generic outer solar system or interstellar object) and we could use all of it but it adds up to about the mass of our oceans, and that is most of the water inventory the asteroid belt. I’ve looked at various large rotating structures up to the size of the Banks Orbital and concluded you could solve the structural problems if you could make a reliable journal bearing (structural parts don’t need to be spun) that could handle the velocity difference but no matter what you cannot afford tall mountains or deep oceans.

schiffern 1y ago
Agreed, liquid is probably the way to go. Very tempting to swap nitrogen for helium, but AIUI the main downsides are that the speed of sound is higher so air will leak out from a breach faster, and there may be negative effects on flammability due to helium's high thermal conductivity and low specific heat.
- Terr_ 1y ago
  Helium gas also leaks a lot, even when everything is normal.

hotshiitake 1y ago

Probably a naive question but would it possible for us to skim gasses from LEO for use in space stations?

05 1y ago
Putting aside issues with capturing basically vacuum at 8km/s, by doing that you're going to lose impulse that you're going to have to regain, spending more mass in fuel+oxidizer than you gained in gathered gases, unless you use ion propulsion (which ISS doesn't). Also most of what you're going to capture at 400km is going to be atomic oxygen and helium, N2/N share is only a couple percentage points at that altitude.. [0] [0] https://en.wikipedia.org/wiki/Heterosphere https://en.wikipedia.org/wiki/Heterosphere
- schiffern 1y ago
  Clearly you would not choose similar operational parameters and propulsion as the ISS when designing an atmospheric scooper. Not sure why you would assume so, honestly. There have been proposals to use scoopers with structurally integrated electrodynamic propulsion ("tether without the tether"),[0] which would use zero propellant. [0] https://forum.nasaspaceflight.com/index.php?topic=44542.msg1818140#msg1818140 https://forum.nasaspaceflight.com/index.php?topic=44542.msg1...

wildzzz 1y ago

We already built LOX tanks into rockets. Just send up a tank of LN2. It doesn't need the strength of a bottle, you just need thermally insulating materials which can be very light.