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Author Topic: Space Thread  (Read 173899 times)

Eric Blank

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Re: Space Thread
« Reply #3075 on: October 26, 2020, 07:58:28 pm »

One day, we will hold ice skating and hockey championships on the moon.
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Cthulhu

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Re: Space Thread
« Reply #3076 on: October 29, 2020, 09:47:27 am »

Quote from: Starlink Terms of Service
For Services provided to, on, or in orbit around the planet Earth or the Moon, these Terms and any disputes between us arising out of or related to these Terms, including disputes regarding arbitrability (“Disputes”) will be governed by and construed in accordance with the laws of the State of California in the United States. For Services provided on Mars, or in transit to Mars via Starship or other colonization spacecraft, the parties recognize Mars as a free planet and that no Earth-based government has authority or sovereignty over Martian activities. Accordingly, Disputes will be settled through self-governing principles, established in good faith, at the time of Martian settlement.

On one hand, this is true.  On the other, do not live on a planet.  Never live on a planet.  If you're in a gravity well you can't escape with compressed air, you've fucked up.
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wierd

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Re: Space Thread
« Reply #3077 on: October 29, 2020, 09:56:56 am »

Arguably, given that Mars' gravity is quite a bit less than on earth...  Items weigh only 1/3 what they do here.

If you could somehow get enough of it, you very well might be able to compress the CO2 atmosphere into dry ice surrounding an electro-resistive heating element, and use that to generate lots of gas on demand, and use it to leave orbit...

Let me get some figures real quick.

--

Mars' escape velocity is approximately 5km/sec.

CO2 has a density of 0.001977 g/mL of volume, at 1ATM, at 0C, in gaseous form. (at earth's gravity.  Since this is Mars, we should take roughly 1/3 of that value for our Delta-V computation)
It has a density of 1.56 g/mL in ice form. (again,  when on earth)

That means it expands ~789.07 times in volume, going from solid to gas, when at 1ATM of ambient pressure.

Mars has an ambient pressure of .088psi (610 pascals). (Earth's pressure at 1ATM is 101325 pascals), which is 1/166th the pressure.
If we keep exhausted gas at 0c, that means the degree of expansion is 166 times that on earth, so 1cm^2 of dry ice will expand to fill a volume of 130,985.62cm^2

--

If somebody else is actually more interested in this, that should get them started.  As I sit here collecting trivia, and looking up online calculators to do the math for me, I am getting more and more sleepy and I have learned the hard way that I make stupid assed errors when in that condition.  Somebody more awake can finish it if they really want to know if a solid fuel CO2 decomposition rocket is sufficient to get the delta-V needed to escape martian orbit.




« Last Edit: October 29, 2020, 10:27:11 am by wierd »
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Cthulhu

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Re: Space Thread
« Reply #3078 on: October 29, 2020, 10:04:56 am »

Yeah but will Tesla-Grumman RaytheonTM's loitering kill vehicles knock you back out of orbit?

Asteroid habitat or bust, get off my space-lawn.
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RedKing

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Re: Space Thread
« Reply #3079 on: October 29, 2020, 10:11:18 am »

Quote from: Starlink Terms of Service
For Services provided to, on, or in orbit around the planet Earth or the Moon, these Terms and any disputes between us arising out of or related to these Terms, including disputes regarding arbitrability (“Disputes”) will be governed by and construed in accordance with the laws of the State of California in the United States. For Services provided on Mars, or in transit to Mars via Starship or other colonization spacecraft, the parties recognize Mars as a free planet and that no Earth-based government has authority or sovereignty over Martian activities. Accordingly, Disputes will be settled through self-governing principles, established in good faith, at the time of Martian settlement.

On one hand, this is true.  On the other, do not live on a planet.  Never live on a planet.  If you're in a gravity well you can't escape with compressed air, you've fucked up.
I forsee a Mars dotted with the estates of uber-wealthy libertarian tech magnates seeking safe harbor from all the Earth governments they've fucked with. John Galt of Mars.
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wierd

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Re: Space Thread
« Reply #3080 on: October 29, 2020, 10:36:12 am »

nwabudike morgan has to start somewhere...


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Bralbaard

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Re: Space Thread
« Reply #3081 on: October 29, 2020, 10:46:20 am »


I forsee a Mars dotted with the estates of uber-wealthy libertarian tech magnates seeking safe harbor from all the Earth governments they've fucked with. John Galt of Mars.

It would be useful for tax evasion as well. So you have to pay taxes for every kg. of stuff you sell/produce/own? Just make sure you are legally based in the asteroid belt where everything weighs 0 kg.
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Cthulhu

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Re: Space Thread
« Reply #3082 on: October 29, 2020, 10:51:07 am »

Obviously the tax laws are going to go by mass, they're not that stupid.

But also I'm on an out-of-plane asteroid so I'm not paying taxes and you can't make me.
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wierd

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Re: Space Thread
« Reply #3083 on: October 29, 2020, 10:51:36 am »

Don't be silly LW.  It will never actually be 0.  Just very very close to 0.  (Since every object with mass, very so gently gravitates to all other objects with mass. This means that your object's attraction to the scale you are using, would depress the scale slightly, thus making it always >0)
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RedKing

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Re: Space Thread
« Reply #3084 on: October 29, 2020, 11:18:55 am »

Obviously the tax laws are going to go by mass, they're not that stupid.

But also I'm on an out-of-plane asteroid so I'm not paying taxes and you can't make me.
That'd be an interesting tax evasion concept. "Sir, the cost in fuel alone to climb above the ecliptic is seven times what he owes."
"What are our options?"
"Well, taking into account estimated fuel costs, required delta-V for intercept, and interest rates, his asteroid will reach a Pareto-optimal intercept point in 221.63 years. Sooner if fuel prices come down or interest rates go up."
"Get the DOE on line 1, and the Federal Reserve on line 2."
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Remember, knowledge is power. The power to make other people feel stupid.
Quote from: Neil DeGrasse Tyson
Science is like an inoculation against charlatans who would have you believe whatever it is they tell you.

wierd

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Re: Space Thread
« Reply #3085 on: October 29, 2020, 11:23:07 am »

"What is the iron content of his asteroid?  It might be possible to nudge it closer a little sooner with well timed deployment schedules of the local itinerant mag-scoops used to scoop up the local ferrous space-gravel. "

"How much sooner?"

"Depends on how efficiently you can manage the mining crews."
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Bralbaard

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Re: Space Thread
« Reply #3086 on: October 29, 2020, 11:26:13 am »

Obviously the tax laws are going to go by mass, they're not that stupid.


I would not be so sure. Current tax laws make it possible for someone with the wealth and income of Trump to pay 0 taxes, I personally do not hold much hope for improvement in the future.

Don't be silly LW.  It will never actually be 0.  Just very very close to 0.  (Since every object with mass, very so gently gravitates to all other objects with mass. This means that your object's attraction to the scale you are using, would depress the scale slightly, thus making it always >0)

Hmm. So if the mass of what you are trying to weigh is actually higher than the weight of the scale it would lift the scale, thereby you would technically have negative weight being registered. You could argue that the tax services need to pay you for all that negative weight.
« Last Edit: October 29, 2020, 11:32:27 am by Bralbaard »
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Starver

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Re: Space Thread
« Reply #3087 on: October 29, 2020, 12:17:23 pm »

Just make sure you are legally based in the asteroid belt where everything weighs 0 kg.
Obviously the tax laws are going to go by mass, they're not that stupid.

*raises hand*

The kilogram is mass. Mass doesn't go away in microgravity/reduce on the surface of smaller bodies, it just has less non-inertial external force acting upon it (and the same inertial force[1]).


Next: Whether a lorry full of canaries can get over a slightly too weak bridge by thumping on the side of the container, and how your helium balloon behaves if you're holding it in a bus swerving round a corner. 

(Was going to do a "The chances of anything coming from Mars..." thing, but I just had to point this out.)



[1] Which is incidentally how they were going to measure OSIRIS-REX’s collected sample of Bennu(/whatever it's called). Close the sampler, extend it back out on its arm and then spin the spacecraft to work out how much mass it has in it. I haven't seen that they've managed to do that, yet, having apparently overfilled their container, with such a good grab of sample, that they couldn't close the capsule properly.
« Last Edit: October 29, 2020, 12:24:32 pm by Starver »
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McTraveller

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Re: Space Thread
« Reply #3088 on: October 29, 2020, 12:33:23 pm »

If you start with compressed CO2 hot enough, you might be able to escape Mars; at 2000K temperature and exhausting to a vacuum you can get an exhaust velocity of about 2340 m/s* (Isp about 239).  For a delta-V of 5km/s in a single stage, you can do it with a full-to-empty ratio of about e^(5000/2340) = 8.5 (about 89% fuel mass).  So it's mathematically possible, but it's probably not feasible with real-world materials.

Spoiler: * (click to show/hide)
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Starver

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Re: Space Thread
« Reply #3089 on: October 29, 2020, 12:44:21 pm »

Double-post rather than re(re)edit. (Or was a DP when I started.)

Plan: Drift slowly onto Bennu, Sample, Drift slowly away, Photo sampler head, Stop drift away, Spin to check mass, if not enough mass (60g) then drift back for another go (maybe at alternate site), if enough then get around to stowing sample in return-capsule, checking, disconnect collector head and stow arm, set off back to Earth.

Actuality: Drift, Sample, Photo, ...cancel away-drift-stop and spin... sample stowed and checked, and the rest.


@McTraveller: It's got to be green gas. Bright green flare (combustion? Copper compound?) drawing a green mist behind it (could be anything, including uncoloured mist still lit by the remains of the flare compounds).
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