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Water Found Deep Inside the Moon

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Re: Water Found Deep Inside the Moon

#191

Post by danblick »

Robotbeat wrote: post #172
tambourine_man wrote: post #7

I've always been more excited about a Moon colony than a Mars one. I mean, compared to Mars, the Moon is ridiculously close. Many of the same benefits Musk seeks (backup for Civilization, excitement) for a fraction of the cost. Low gravity and atmosphere on a dome would be more complicated, but again, compared to Mars, it's right there . It would be a more humble and realistic first step, IMO.

It's questionable that it's really much lower cost. The Moon, as a vacuum body, doesn't give the option of aerobraking or atmospheric entry, which dramatically reduces delta-V. You can get a payload to Mars' surface with less propellant than getting it to the Moon's surface. And because atmosphere is everywhere (which includes oxygen in the form of CO2 and also water vapor), propellant is way easier to make, so it's…

Are you assuming travel is one-way?

That seems okay for probes and maybe problematic for people.

Although the poor slob plan comes to mind:

https://books.google.com/books?id=7ejGJaFjLccC&lpg=PA154&ots...

Re: Water Found Deep Inside the Moon

#192

Post by kbenson »

ribosometronome wrote: post #163
kbenson wrote: post #92

Earlier quoted context omitted.

It's important for the exact same reason you're able to ask that question. Without humanity, who asks why? Humanity is, to the best of our knowledge, the best and possibly only chance of increasing understanding of the universe. I care about that, as well as about our species generally in what is likely an evolved and chemically reinforced way. At some point that may be less true, and I would care less (but would sti…

It sounds like you value the persistence of understanding in a way that just isn't particularly important to me. The survival of my loved ones -- and that's a category that can go across species -- is absolutely important to me. The survival of evil space Nazis? Eh. That said, I also don't really think I see being an evolutionary dead end as too huge of a concern. Many of us appreciate things that aren't truly keen f…

> The survival of my loved ones -- and that's a category that can go across species -- is absolutely important to me. The survival of evil space Nazis? Eh.

The idea is that if it's between all people dead, or all people except evil space Nazis, I'll take evil space Nazis. Just because they are evil space Nazis now doesn't mean they will be hundreds of years from now, but they'll never get that chance if all humans are gone.

Human history is largely a story about bigoted, insular racist violent psychopaths becoming slightly less of each of those things over time. I don't see why that trend won't continue in general even if we hit a local maxima of fascist oppression from time to time (as this would be).

Because I love people, I can understand the concept of loving people in general, and want other people to be able to experience that. Human extinction means that nobody might ever experience that again, and I think that's a shame, and will do what I can to prevent that type of outcome.

> Many of us appreciate things that aren't truly keen from an evolutionary perspective.

There isn't appreciation of that type without people to do the appreciating. Your ability to appreciate it is provided by our current circumstances. I think keeping those circumstances active is worthwhile. Otherwise you are taking more than you are giving to the species as a whole, which is unsustainable if too many people do so. Even if you don't care about how sustainable it is, you would be riding on the hard work the rest of the species is putting into the system to propagate. Don't be taker.

Re: Water Found Deep Inside the Moon

#194

Post by keenerd »

simonh wrote: post #167
keenerd wrote: post #75

Earlier quoted context omitted.

The Martian atmosphere is next to worthless for aerobraking human-scale infrastructure. One of the most significant points in the Moon's favor is the (relative) ease with which a space elevator could be built. It doesn't need unobtainium, current structural materials are strong enough.

SpaceX have run the simulations and while Red Dragon is possible, there's no way they can adapt Dragon to land on the Moon without adding an extra stage. That difference is entirely down to Aerobraking. Even the thin atmosphere of Mars makes a huge difference. Anyone who plays KSP can confirm this for you, especially using the Real Solar System mod, though the same lessson is apparent even in the stock game.

We can also look at delta-V charts. Earth to the Moon is like 16.4km/s, Earth to Mars is like 14.3km/s using every available aerobraking opportunity (6.4km/s saved) and assuming 500m/s for the final powered landing. (The Red Dragon plan called for aerobraking from 6km/s to 540m/s and then switching to thrusters.)

Is that 2.1km/s really a whole extra stage? Or can it be met by reducing cargo capacity somewhat?

Two interesting points about Red Dragon - it wasn't feasible to put parachutes on it so its aerobraking would have been greatly limited. It wouldn't have much surface to use for deceleration in that case. I'm curious just how long it would have spent aerobraking, SpaceX's docs don't seem to mention that. And it was cancelled a few months ago with the intent of designing a "vastly" heavier lander, for which aerobraking will be that much less practical.

edit: But I can do a back of the envelope calculation. Decelerating 6500kg from 6km/s to 540m/s is 116G joules. The diameter is 3.6 meters so a molecule of air in from of the Dragon would be displaced (on average) 0.53 meters. Let's assume the atmosphere is a constant density (0.020 kg/m^3). Assume a drag coefficient of 0.05 (and ignoring the lifting body effect) that is around 200kN of force, tapering down to 1.5kN. That is like 3000 km of aerobraking at maximum atmospheric density and should take around 2300 seconds. But that depends a lot on the deorbit profile. I'm going to need a bigger simulation...

Re: Water Found Deep Inside the Moon

#195

Post by jshelly »

tambourine_man wrote: post #7

I've always been more excited about a Moon colony than a Mars one. I mean, compared to Mars, the Moon is ridiculously close. Many of the same benefits Musk seeks (backup for Civilization, excitement) for a fraction of the cost. Low gravity and atmosphere on a dome would be more complicated, but again, compared to Mars, it's right there . It would be a more humble and realistic first step, IMO.

I wonder if launching a trip to Mars would also be easier from the moon?

Re: Water Found Deep Inside the Moon

#196

Post by Mtinie »

Fej wrote: post #188
Robotbeat wrote: post #172

Earlier quoted context omitted.

It's questionable that it's really much lower cost. The Moon, as a vacuum body, doesn't give the option of aerobraking or atmospheric entry, which dramatically reduces delta-V. You can get a payload to Mars' surface with less propellant than getting it to the Moon's surface. And because atmosphere is everywhere (which includes oxygen in the form of CO2 and also water vapor), propellant is way easier to make, so it's…

Mars has the radiation problem while in-transit, which is still unsolved. We have already gone to the Moon. Given that the travel time is relatively short, radiation is far less of a concern. This is why the Moon is attractive. We know how to get there already and it's not too difficult, all things considered. The problem of how to get there and back with humans aboard has already been solved. It's never been done to…

Without a magnetosphere isn't solar radiation a problem, long-term on the Moon?

Re: Water Found Deep Inside the Moon

#197

Post by [deleted] »

Robotbeat wrote: post #172
tambourine_man wrote: post #7

I've always been more excited about a Moon colony than a Mars one. I mean, compared to Mars, the Moon is ridiculously close. Many of the same benefits Musk seeks (backup for Civilization, excitement) for a fraction of the cost. Low gravity and atmosphere on a dome would be more complicated, but again, compared to Mars, it's right there . It would be a more humble and realistic first step, IMO.

It's questionable that it's really much lower cost. The Moon, as a vacuum body, doesn't give the option of aerobraking or atmospheric entry, which dramatically reduces delta-V. You can get a payload to Mars' surface with less propellant than getting it to the Moon's surface. And because atmosphere is everywhere (which includes oxygen in the form of CO2 and also water vapor), propellant is way easier to make, so it's…

[deleted]

Re: Water Found Deep Inside the Moon

#198

Post by njarboe »

tambourine_man wrote: post #7

I've always been more excited about a Moon colony than a Mars one. I mean, compared to Mars, the Moon is ridiculously close. Many of the same benefits Musk seeks (backup for Civilization, excitement) for a fraction of the cost. Low gravity and atmosphere on a dome would be more complicated, but again, compared to Mars, it's right there . It would be a more humble and realistic first step, IMO.

No reason that 7 billion humans can't work towards both at the same time. Many technologies (like cheap, reusable heavy-lift rockets) will be useful for both. Bezos seems interested in the Moon and Musk in Mars, but I don't think you would hear either of them saying one place must have a colony before starting to work towards the other. Let a thousand flowers bloom.

Re: Water Found Deep Inside the Moon

#199

Post by Zancarius »

vl wrote: post #81
Zancarius wrote: post #33

Earlier quoted context omitted.

> Moreover, only half of the Moon sees the light of the Sun. What do you mean by this? The moon is tidally locked to the Earth, but the entire surface sees sunlight over the course of ~a month with the exception of a handful of polar craters where small portions are perpetually in shadow.

Factually this is correct: only half of any planet in the solar system sees light of the Sun at any given moment. :)

Only with a literalist interpretation of said fact. :)

Re: Water Found Deep Inside the Moon

#200

Post by [deleted] »

Mtinie wrote: post #196
Fej wrote: post #188

Earlier quoted context omitted.

Mars has the radiation problem while in-transit, which is still unsolved. We have already gone to the Moon. Given that the travel time is relatively short, radiation is far less of a concern. This is why the Moon is attractive. We know how to get there already and it's not too difficult, all things considered. The problem of how to get there and back with humans aboard has already been solved. It's never been done to…

Without a magnetosphere isn't solar radiation a problem, long-term on the Moon?

[deleted]
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