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Design of a rapid transit to Mars mission using laser-thermal propulsion

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Re: Design of a rapid transit to Mars mission using laser-thermal propulsion

#21

Post by jmyeet »

bbojan wrote: post #5
jmyeet wrote: post #2

Sure let's continue unmanned exploration of Mars but manned exploration let alone colonization makes absolutely zero sense. mars is nothing more than a further, more annoying version of the Moon. Similar gravity, less sunlight (ie further from the Sun), communication latency (~10 minutes vs 1.5 seconds), no magnetosphere (just like the Moon so you'll probably need to live underground) and just enough atmosphere to pr…

The Moon has very little hydrogen, carbon and nitrogen, which Mars has in abundance. These are very important elements both for biology and chemistry. E.g. if you want to have a self-sufficient colony outside Earth, you could do it on Mars but not on the Moon. Mars could be terraformed (in theory); the Moon never could.

> The Moon has very little hydrogen,

That's not quite true. The Moon definitely has polar ice but it also likely has more water than that [1][2]. Nitrogen seems only to be present in trace quantities [3].

> Mars could be terraformed (in theory); the Moon never could.

Yes and no (on both). People who make this claim often don't understand the magnitude of what they're claiming. Here's just one perspective: molecular velocities in the atmosphere are (of course) a Boltzmann distribution. As such a small percentage of those particles achieve escape velocity and fly off into space (called the Jeans escape energy) in exactly the same way that liquid water cools by evaporation. That amounts to around one million tonnes per year.

Mars has a lower gravity so the loss would be greater at Earth atmospheric pressure and that's just the loss you need to account for and gas that you need to manufacture or produce. Earth's atmosphere has a mass of ~5x10^18 kg. The scale of producing this just in terms of energy consumption is insanely massive.

So when you're talking about this level of energy expenditure it doesn't really matter all that much if you do it on the Moon or Mars.

But what's more, terraforming would necessarily be extremely violent. Do it too fast and you cook the planet. The likely way of getting what you need there is by impacting large bodies from space into the Moon. You probably don't want to live there while doing that. The timescales are likely to be in the thousands of years.

[1]: https://www.nasa.gov/press-release/nasa-s-sofia-discovers-wa...

[2]: https://www.planetary.org/articles/water-on-the-moon-guide

[3]: https://en.wikipedia.org/wiki/Geology_of_the_Moon#Elemental_...

Re: Design of a rapid transit to Mars mission using laser-thermal propulsion

#22

Post by gambiting »

ben_w wrote: post #17
gambiting wrote: post #14

Earlier quoted context omitted.

If that really is your goal then build a colony at the bottom of the ocean or deep under ground here on Earth - at sufficient depth there is literally nothing that could endanger such colony, it's functionally equivalent to being on mars without the idiotic travel cost.

Plausible, but I remember when I did my degree, one of the examples given about the importance of choosing a good site for “off site backups” was a company whose main site was one of the WTO twin towers, whose off site was the the other tower on the grounds that they couldn’t conceive of anything that would affect both without also destroying civilisation as a whole.

Well sure, but that's always a question of what are you trying to defend yourself against(what kind of scenario is the backup helping with). Twin towers are probably good enough for any kind of fire/electrical failure/theft/vandalism, but not for a meteor strike, war or as we've seen - terrorism. It's not that people in your example were stupid and didn't see it - just that most likely they didn't consider those dangers as important to have a backup for(if a war breaks out or a meteor strikes New York you probably have bigger problems).

It's the same here - most of the "human extinction"-scale events really don't touch a base that's 10km under water or under ground. Nuclear war or meteor strike? nope. Earthquakes? There are places safe from that. Solar flares? Nope. Deadly virus? Quarantine everyone arriving like you would with the journey to Mars.

Terrorism remains the main risk, but it would have been the same risk on Mars too.

And most importantly - it teaches us how to run an independent colony deep underground, which is important because despite all the Sci-Fi films showing us otherwise, the base on Mars would really have to be underground because of radiation risk.

So yeah, sure, run an underground base for a few decades then you can just transplant the technology to Mars - don't start with Mars first.

Re: Design of a rapid transit to Mars mission using laser-thermal propulsion

#23

Post by jmyeet »

kilroy123 wrote: post #20
jmyeet wrote: post #2

Sure let's continue unmanned exploration of Mars but manned exploration let alone colonization makes absolutely zero sense. mars is nothing more than a further, more annoying version of the Moon. Similar gravity, less sunlight (ie further from the Sun), communication latency (~10 minutes vs 1.5 seconds), no magnetosphere (just like the Moon so you'll probably need to live underground) and just enough atmosphere to pr…

I strongly disagree and I dare say this is an incredibly short sighted view. Pushing forward to living on Mars will unlock tons of technological and scientific advances that will only help us better live here on Earth, and Mars. The mother of invention will always been necessity. We simply don't need a lot of the tech that will be created, until we try to live off-world. So much technology and scientific know-how, ca…

Let's accept this premise (which amounts to essentially "we don't know what we don't know") and I'll ask a natural follow up question: what is the difference between colonizing the Moon and colonizing Mars in terms of problems we'd need to solve and thus technology we'd likely gain?

Re: Design of a rapid transit to Mars mission using laser-thermal propulsion

#24

Post by merpnderp »

gambiting wrote: post #14
ben_w wrote: post #11

Earlier quoted context omitted.

Disaster recovery, the penultimate in off-site backups of humanity itself.

If that really is your goal then build a colony at the bottom of the ocean or deep under ground here on Earth - at sufficient depth there is literally nothing that could endanger such colony, it's functionally equivalent to being on mars without the idiotic travel cost.

Except 8 billion starving desperate people trying to get it.

For instance if people were starving or hiding from fallout, those doomsday shelters the rich are building for themselves would likely be overran by the locals who helped build them or heard all about them from town gossip.

Re: Design of a rapid transit to Mars mission using laser-thermal propulsion

#25

Post by jmyeet »

ben_w wrote: post #8
Gravityloss wrote: post #4

Earlier quoted context omitted.

Well stated! Humans can be surprisingly useful still, even if we are very costly to maintain. https://en.wikipedia.org/wiki/Moravec%27s_paradox I'm hopeful about artificial magnetic fields - modern superconducting magnets could do wonders in orbit with solar power. Or here's sending ions from Phobos to do it: https://arxiv.org/abs/2111.06887

Even without superconductors. If I was in change of a lunar colonisation plan, first thing I’d do is send up a rover with some limited ability to process lunar regolith — at a minimum into aluminium, preferably also PV. This rover would slowly crawl around the moon (doesn’t need to be the equator, but at least 5.14+6.68° from the poles to avoid being in darkness at the wrong time of year), leaving a fat conductor beh…

I don't disagree with your assessment of building aluminium conductors but my argument is that this isn't even really necessary. Living underground just makes so much more sense and is much, much easier. There is strong evidence of extinct lava tubes on the Moon. Sealing one of those up and pressurizing it is just so much easier, practical and incrementally scalable.

Re: Design of a rapid transit to Mars mission using laser-thermal propulsion

#26

Post by politician »

shoulderfake wrote: post #7
jmyeet wrote: post #2

Sure let's continue unmanned exploration of Mars but manned exploration let alone colonization makes absolutely zero sense. mars is nothing more than a further, more annoying version of the Moon. Similar gravity, less sunlight (ie further from the Sun), communication latency (~10 minutes vs 1.5 seconds), no magnetosphere (just like the Moon so you'll probably need to live underground) and just enough atmosphere to pr…

Quoted post unavailable.

Thankfully Elon doesn’t need funding from this crowd.

Re: Design of a rapid transit to Mars mission using laser-thermal propulsion

#27

Post by mchusma »

jmyeet wrote: post #2

Sure let's continue unmanned exploration of Mars but manned exploration let alone colonization makes absolutely zero sense. mars is nothing more than a further, more annoying version of the Moon. Similar gravity, less sunlight (ie further from the Sun), communication latency (~10 minutes vs 1.5 seconds), no magnetosphere (just like the Moon so you'll probably need to live underground) and just enough atmosphere to pr…

I also think Dyson swarms are the future. But I think the Mars effort is helpful towards getting there.

Elon's public motivation for Mars is basically a human backup plan. And for that, it probably may be the best shot of the next 100 years. It seems like a million people living and working on Mars is more likely to survive a worst case scenario that a million people in rotating space habitats.

Re: Design of a rapid transit to Mars mission using laser-thermal propulsion

#28

Post by rthomas6 »

gambiting wrote: post #14
ben_w wrote: post #11

Earlier quoted context omitted.

Disaster recovery, the penultimate in off-site backups of humanity itself.

If that really is your goal then build a colony at the bottom of the ocean or deep under ground here on Earth - at sufficient depth there is literally nothing that could endanger such colony, it's functionally equivalent to being on mars without the idiotic travel cost.

I can think of some things that would require them to stay there, unable to surface, for thousands of years. Having the ability to mine asteroids and create additional colonies and space stations seems better to me.

Re: Design of a rapid transit to Mars mission using laser-thermal propulsion

#29

Post by ericmay »

0_____0 wrote: post #10
ericmay wrote: post #3

Earlier quoted context omitted.

Mars has water and more “acceptable” temperatures, I believe. This doesn’t have to be a mutually exclusive endeavor. We can put a base on Luna and colonize Mars. Maybe the Moon is the stepping stone to Mars?

This doesn't answer the question of why you'd want to put people on Mars in the first place.

Why do anything?

Re: Design of a rapid transit to Mars mission using laser-thermal propulsion

#30

Post by politician »

0_____0 wrote: post #12
slothtrop wrote: post #9

Earlier quoted context omitted.

If terraforming is in the cards, stands to reason it would be first tried in our own backyard. Mars is the best contender for it. Actually it might be useful in other respects than being livable. The vision is far less romantic if you consider it a distant future project.

At least Venus has a magnetosphere. How are you going to terraform a planet that can't retain more than 6.5 millibars worth of atmosphere? Build a big-ass bubble around the planet to deflect solar wind? Nuke the core of the planet to re-melt it and get a magnetic field back?

Watch any of the videos on terraforming Venus by Isaac Arthur on YouTube.
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