Colonization Discussion Thread (split from SpaceX)

[Spaceception]

1 hour ago, sh1pman said:

There’s no free return from Mars. You’d need to wait 3-4 months for the return window, otherwise you’ll get stranded in solar orbit forever. In case something bad happens, the crew will have to fix it.

I thought there was if you did a Hohmann transfer. That's why some people spoke against getting there faster - and instead using advanced propulsion for more cargo, because there would be no free return. Or is my memory crapping out?

[HebaruSan]

3 minutes ago, Spaceception said:

I thought there was if you did a Hohmann transfer. That's why some people spoke against getting there faster - and instead using advanced propulsion for more cargo, because there would be no free return. Or is my memory crapping out?

The confusion may be regarding whether the return leg is also a Hohmann.

https://en.wikipedia.org/wiki/Free-return_trajectory#Earth–Mars

Quote

The Hohmann transfer orbit can be made free-return. It takes 250 days (0.68 years) in the transit to Mars, and in the case of a free-return style abort without the use of propulsion at Mars, 1.5 years to get back to Earth, at a total delta-v requirement of 3.34 km/s.

So unlike a relatively symmetrical lunar free return, this return would swing you out somewhere non-optimal to compensate for the non-alignment of the planets, taking more than twice as long as the outgoing segment.

[sh1pman]

Just now, Spaceception said:

I thought there was if you did a Hohmann transfer. That's why some people spoke against getting there faster - and instead using advanced propulsion for more cargo, because there would be no free return. Or is my memory crapping out?

No, by the time you get to Mars, the planets won’t be aligned correctly for a return trajectory to intercept Earth. Hohmann transfer to Mars takes 8.5 months. 8.5 more months for a return trip. 17 months total. When you reach Earth’s orbit, the Earth itself will be on the opposite side of the Sun from you. That’s why you have to wait several months before departing from Mars.

[Rakaydos]

7 minutes ago, sh1pman said:

No, by the time you get to Mars, the planets won’t be aligned correctly for a return trajectory to intercept Earth. Hohmann transfer to Mars takes 8.5 months. 8.5 more months for a return trip. 17 months total. When you reach Earth’s orbit, the Earth itself will be on the opposite side of the Sun from you. That’s why you have to wait several months before departing from Mars.

There's a free return double flyby trajectory earth/Mars/Venus/earth.

[sh1pman]

5 minutes ago, Rakaydos said:

There's a free return double flyby trajectory earth/Mars/Venus/earth.

I need to test this in KSP...

12 minutes ago, HebaruSan said:

So unlike a relatively symmetrical lunar free return, this return would swing you out somewhere non-optimal to compensate for the non-alignment of the planets, taking more than twice as long as the outgoing segment.

..How is it called free-return if it requires 3.3km/s dv?.. never mind, got it. So it’s a Hohmann transfer that uses a gravity assist from Mars to fling you into a longer orbit that intercepts Earth, right?

Edited September 5, 2018 by sh1pman

[HebaruSan]

21 minutes ago, sh1pman said:

So it’s a Hohmann transfer that uses a gravity assist from Mars to fling you into a longer orbit that intercepts Earth, right?

I haven't found a diagram of it yet, but yes, I agree with that interpretation.

[CatastrophicFailure]

1 hour ago, sh1pman said:

 Hmm, would I explode or freeze first?

You would asphyxiate after maybe 30 seconds of useful consciousness. Most of the really unpleasant stuff would only happen to you after you were dead. 

 

40 minutes ago, sh1pman said:

I need to test this in KSP...

The Soviets actually had a plan to do this. Unfortunately, their rocket kept failing to get to space today. 

[sh1pman]

Just now, CatastrophicFailure said:

You would asphyxiate after maybe 30 seconds of useful consciousness. Most of the really unpleasant stuff would only happen to you after you were dead. 

 

Ok, not so bad. 

But what will eventually happen to the body? I guess water and fluids will evaporate into space, leaving a mummified corpse. Complex organics will eventually photo-dissociate into simple molecules and ions, and escape as well. And after a while, there will only be a bleached space skeleton. 

[Rakaydos]

2 hours ago, HebaruSan said:

I haven't found a diagram of it yet, but yes, I agree with that interpretation.

A quick google for "Mars venus free return"

https://arc.aiaa.org/doi/abs/10.2514/6.2000-4139

[cubinator]

6 hours ago, Spaceception said:

The second thing is what SpaceX should do in the event of it being too dangerous to live there (And some of you can probably already guess), but I think, using the BFR's capability, they should establish mining bases on the Moon (Maybe Mars), to set up orbital colonies instead. Get our eggs out of one basket, but getting around the problem of living on a planet with weak gravity. People could still live short term on the Moon and Mars, but only for less than a year at a time. Most of the time, they would live in space.

If Mars is uninhabitable, then open space is even more uninhabitable-er in almost all respects. We can put ring stations on the ground, too. Just angle them so that the spinning and the gravity add up to 1 g in the vector perpendicular to the floor. I don't think BFR is big enough to assemble a proper orbital colony anywhere near what Mars can sustain by building structures from local materials.

[HebaruSan]

2 hours ago, Rakaydos said:

A quick google for "Mars venus free return"

https://arc.aiaa.org/doi/abs/10.2514/6.2000-4139

Looks like that's paywalled. (I assume you don't mean the pair of Hohmann transfers on the first page.)

[Bill Phil]

2 hours ago, cubinator said:

If Mars is uninhabitable, then open space is even more uninhabitable-er in almost all respects. We can put ring stations on the ground, too. Just angle them so that the spinning and the gravity add up to 1 g in the vector perpendicular to the floor. I don't think BFR is big enough to assemble a proper orbital colony anywhere near what Mars can sustain by building structures from local materials.

Yeah, but if the bearings fail on the ground... well, I wouldn't want to be there. Not to mention Mars offers way less potential for expansion than some of the large asteroids would on their own. Nor does it offer the wonders of requiring very little energy to get to free fall, or the ability to take advantage of the space environment to manufacture many things that would be far more difficult to manufacture on a planet.

In Equatorial LEO below 500 km, radiation is low enough that almost no shielding is necessary. This puts orbital habitats much closer in terms of distance, time, energy, and capability. Only 500 km up, not millions. Only hours away, not days, months, or years. Less energy between here and LEO than here and Mars. The biggest thing we put on Mars is 1 tonne. Biggest thing in LEO is 400 tonnes. 

[Rakaydos]

1 hour ago, HebaruSan said:

Looks like that's paywalled. (I assume you don't mean the pair of Hohmann transfers on the first page.)

Found one.

 

[MinimumSky5]

3 hours ago, Bill Phil said:

In Equatorial LEO below 500 km, radiation is low enough that almost no shielding is necessary. This puts orbital habitats much closer in terms of distance, time, energy, and capability. Only 500 km up, not millions. Only hours away, not days, months, or years. Less energy between here and LEO than here and Mars. The biggest thing we put on Mars is 1 tonne. Biggest thing in LEO is 400 tonnes. 

True, but you wouldn't build up in orbit until it becomes cheaper to build new land in the habitats, than simply building down here on earth. 

[Green Baron]

5 hours ago, Rakaydos said:

Found one.

Clear case for Kerbal Alarm Clock !

[tater]

Not sure what a free return buys you for BFR (this bit was split from SpaceX, so that was the assumption). It requires failure after TMI for the abort mode (free return), but then what? If it's engines, you're toast anyway, you can't land back on Earth. If the failure is not with propulsion that forces abort, then you might be better to land on Mars, anyway (assuming prepositioned supplies).

What are possible mission failure modes (very broadly)?

1. Propulsion system.

2. Life support.

In the case of 1 (again, BFS is the assumption here, not a cycler), you're either dead on a shorter transit, or on a free return, another vehicle(s) needs to rendezvous and save everyone in X hundred days. Doing this would be non-trivial, but I suppose possible. That said, is a propulsion system failure likely after a TMI burn? During, that burn, you are likely not yet on free return, and the next restart is either to exit free return in advance of Mars to set up the EDL. Failure there is either a restart fail (still on free return), or during that burn, in which case you're neither free return anymore, nor capable of landing (dead). Alternately, the small dv to set up entry is an RCS issue, in which case failure is on EDL (dead).

Strikes me that a shorter transit is preferable since there are not many likely situations where free return helps.

[kerbiloid]

That's the reason why emergency escape systems should use another (even if redundant) set of equipment.

If a spaceship with a docked Orion capsule returns back without engines, the crew could move into the capsule and return.

(And probably a double set of life support is required. Just remember how many times an ISS toilet was out of order.)

Edited September 5, 2018 by kerbiloid

[sh1pman]

1 hour ago, tater said:

Failure there is either a restart fail (still on free return), or during that burn, in which case you're neither free return anymore, nor capable of landing (dead). Alternately, the small dv to set up entry is an RCS issue, in which case failure is on EDL (dead).

Maybe the solution is to send BFS to and from Mars in groups of two. If one suffers a mission-ending failure in space, another can dock to it (requires nose docking port) and save the crew. Obviously, it can't be done during EDL, but if the problem is discovered earlier, there will be a way to save the people. 

[Bill Phil]

6 hours ago, MinimumSky5 said:

True, but you wouldn't build up in orbit until it becomes cheaper to build new land in the habitats, than simply building down here on earth. 

Yeah.

But, provided space hotels become a thing at all, it may be more cost-effective, not to mention comfortable, to provide artificial gravity by rotation in the hotel. It would also likely be cost effective to make the hotel as closed loop as possible to reduce the number of launches needed to resupply it. So the necessary technology may well be developed regardless. Eventually, space hotel size may grow to the point where it becomes a settlement in its own right.

Of course, that hinges on space hotels happening.

54 minutes ago, sh1pman said:

Maybe the solution is to send BFS to and from Mars in groups of two. If one suffers a mission-ending failure in space, another can dock to it (requires nose docking port) and save the crew. Obviously, it can't be done during EDL, but if the problem is discovered earlier, there will be a way to save the people. 

Sounds like classic von Braun style missions to me.

[ment18]

54 minutes ago, sh1pman said:

Maybe the solution is to send BFS to and from Mars in groups of two. If one suffers a mission-ending failure in space, another can dock to it (requires nose docking port) and save the crew. Obviously, it can't be done during EDL, but if the problem is discovered earlier, there will be a way to save the people. 

I think SpaceX is already planning on this.  Their first Mars crew flight has 2 manned  bfs

[tater]

58 minutes ago, sh1pman said:

Maybe the solution is to send BFS to and from Mars in groups of two. If one suffers a mission-ending failure in space, another can dock to it (requires nose docking port) and save the crew. Obviously, it can't be done during EDL, but if the problem is discovered earlier, there will be a way to save the people. 

Yeah, this is the way to go. This split thread is about "colonization," something I'm not really concerned about (since I see no reason to colonize Mars). Even so, such a mission architecture requires that either craft can hold all the crew for EDL, and of course it requires surface redundancy, so it's not a matter of saving XX people in space, just to have them starve to death (along with everyone else) on Mars, for lack of enough supplies for landed craft + XX people without supplies.

[sh1pman]

39 minutes ago, tater said:

Even so, such a mission architecture requires that either craft can hold all the crew for EDL, and of course it requires surface redundancy, so it's not a matter of saving XX people in space, just to have them starve to death (along with everyone else) on Mars, for lack of enough supplies for landed craft + XX people without supplies.

Or it would result in a shorter mission time. Like making them stay on Mars for 4 months instead of 2 years. Alternatively, it may require sending an additional supply BFS during the next transfer window (if there’s enough supplies to survive until it arrives).

[tater]

1 minute ago, sh1pman said:

Or it would result in a shorter mission time. Like making them stay on Mars for 4 months instead of 2 years. Alternatively, it may require sending an additional supply BFS during the next transfer window (if there’s enough supplies to survive until it arrives).

Assuming they could refill and leave in that timeframe.

[sh1pman]

1 minute ago, tater said:

Assuming they could refill and leave in that timeframe.

Yep.

TBH, these scenarios need to be understood and prepared for before the first manned BFR sets off to Mars.

[tater]

25 minutes ago, sh1pman said:

Yep.

TBH, these scenarios need to be understood and prepared for before the first manned BFR sets off to Mars.

I have always assumed any first crew missions will be minimal crew, round trip.