4 ms·

A spacecraft with a 4m diameter spherical living space and 4m of water shielding around it will weigh about 1,000 tons. The propellant tanks needed to move it

A spacecraft with a 4m diameter spherical living space and 4m of water shielding around it will weigh about 1,000 tons. The propellant tanks needed to move it around the solar system will be similarly titanic. How many orders of magnitude were you figuring for your "dramatically cheaper"?

ericd 2mo ago
That's 5 Starship block 4 launches, seems fine? Propellant, presumably for long duration voyages we're not relying entirely on chemical combustion. If we're using cyclers, once they're up to speed, you need barely any fuel for corrections, just to taxi to/from the cycler.
- dessimus 2mo ago
  Maybe when its actually demonstrated that it can actually launch with that payload. The largest payload they'd lifted so far is ~45 tons, and the claims I see on Wikipedia say its estimated 200 tons for LEO, not even for geosynchronous orbit much less a lunar trajectory.
  - ericd 2mo ago
    20 launches would also be doable, though, if there's a reasonable launch cadence? And yeah, I don't expect they'd assemble for a Mars mission or other long range mission where they need a radiation shielded craft in geo or lunar.
vikingerik 2mo ago
And just for comparison on that number, the entire Apollo spacecraft (command+service+lunar modules) was about 50 tons to lunar orbit. And that took a gigantic Saturn V to launch.
- ericd 2mo ago
  SpaceX is planning on launching the significantly more gigantic Starship daily. It's not there yet, but they're steadily grinding toward regular launches, and they supposedly are retiring Falcon 9 from commercial launches within the next couple of years.
  - tharkun__ 2mo ago
    And "From a technology standpoint, Tesla will have a car that can do full autonomy in about three years, maybe a bit sooner.". Uttered by Musk in 2015. So ... yeeeeaaah.
    - ericd 2mo ago
      Have you been following Starship development closely?
      - tharkun__ 2mo ago
        Musk has 10+ years of history we can go by that says: Nobody has to follow anything closely to know that he will just say whatever he wants to say and you should give a rats ass about it timeline wise. Now, do not get me wrong: I got frickin' goose bumps when I saw the first Falcon touchdown. Goose bumps again when they did the first landing out in the open ocean. Of course I still love you! The pincers catching a starship booster were super awesome. Did I mention goose bumps? I am getting them as I write this, thinking back to those moments and now I want to re-watch all of those on youtube after I finish typing this. But believing a single timeline prediction by Musk? No, forget it. EDIT: haha, and yeah I did go re-watch and this is so super awesome when I got reminded of it: https://www.youtube.com/watch?v=bvim4rsNHkQ&t=1s https://www.youtube.com/watch?v=bvim4rsNHkQ&t=1s No this is not meant as a jab btw. I love that they have this up. This is what many of us do in software development. Just we don't blow up actual frickin' spaceships to do it "It's just a rapid unscheduled disassembly!" ;)
    - anon48293 2mo ago
      I mean technologically they can, just not due to safety and legal reasons.
m4rtink 2mo ago
Also you should be able to ISRU[0] water from Moon/Mars/asteroids. [0] https://en.wikipedia.org/wiki/In_situ_resource_utilization https://en.wikipedia.org/wiki/In_situ_resource_utilization
- ericd 2mo ago
  Yeah, I think that’s the longer term solution. But even before we get that infrastructure in place, I don’t think lifting 1000 tons is as absurd as people seem to think. SpaceX’s entire plan is dependent on doing many orders of magnitude more than that on a regular basis to feed their satellite constellations.

ericd 2mo ago

That's 5 Starship block 4 launches, seems fine? Propellant, presumably for long duration voyages we're not relying entirely on chemical combustion. If we're using cyclers, once they're up to speed, you need barely any fuel for corrections, just to taxi to/from the cycler.

dessimus 2mo ago
Maybe when its actually demonstrated that it can actually launch with that payload. The largest payload they'd lifted so far is ~45 tons, and the claims I see on Wikipedia say its estimated 200 tons for LEO, not even for geosynchronous orbit much less a lunar trajectory.
- ericd 2mo ago
  20 launches would also be doable, though, if there's a reasonable launch cadence? And yeah, I don't expect they'd assemble for a Mars mission or other long range mission where they need a radiation shielded craft in geo or lunar.

vikingerik 2mo ago

And just for comparison on that number, the entire Apollo spacecraft (command+service+lunar modules) was about 50 tons to lunar orbit. And that took a gigantic Saturn V to launch.

ericd 2mo ago
SpaceX is planning on launching the significantly more gigantic Starship daily. It's not there yet, but they're steadily grinding toward regular launches, and they supposedly are retiring Falcon 9 from commercial launches within the next couple of years.
- tharkun__ 2mo ago
  And "From a technology standpoint, Tesla will have a car that can do full autonomy in about three years, maybe a bit sooner.". Uttered by Musk in 2015. So ... yeeeeaaah.
  - ericd 2mo ago
    Have you been following Starship development closely?
    - tharkun__ 2mo ago
      Musk has 10+ years of history we can go by that says: Nobody has to follow anything closely to know that he will just say whatever he wants to say and you should give a rats ass about it timeline wise. Now, do not get me wrong: I got frickin' goose bumps when I saw the first Falcon touchdown. Goose bumps again when they did the first landing out in the open ocean. Of course I still love you! The pincers catching a starship booster were super awesome. Did I mention goose bumps? I am getting them as I write this, thinking back to those moments and now I want to re-watch all of those on youtube after I finish typing this. But believing a single timeline prediction by Musk? No, forget it. EDIT: haha, and yeah I did go re-watch and this is so super awesome when I got reminded of it: https://www.youtube.com/watch?v=bvim4rsNHkQ&t=1s https://www.youtube.com/watch?v=bvim4rsNHkQ&t=1s No this is not meant as a jab btw. I love that they have this up. This is what many of us do in software development. Just we don't blow up actual frickin' spaceships to do it "It's just a rapid unscheduled disassembly!" ;)
  - anon48293 2mo ago
    I mean technologically they can, just not due to safety and legal reasons.

m4rtink 2mo ago

Also you should be able to ISRU[0] water from Moon/Mars/asteroids. [0] https://en.wikipedia.org/wiki/In_situ_resource_utilization https://en.wikipedia.org/wiki/In_situ_resource_utilization

ericd 2mo ago
Yeah, I think that’s the longer term solution. But even before we get that infrastructure in place, I don’t think lifting 1000 tons is as absurd as people seem to think. SpaceX’s entire plan is dependent on doing many orders of magnitude more than that on a regular basis to feed their satellite constellations.