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Space Travel

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steve_bank

Diabetic retinopathy and poor eyesight. Typos ...
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General issues for space travel.

Energy

Unless you get around Newton's law, Force = m*a and Energy = Force * Distance. Fuel to get back from Mars in a large vehicle with life support may be a problem, let alone leaving the solar system.

Life Support

Does entropy apply? Can O2 and H2O be recycled without loss in a closed system?

Structure

There were pictures of a shuttle window hit by a micrometeorite in orbit. It left a con depression in the window but did not penetrate all the way.

High speed turns and deceleration are a problem. Reaction forces on the structure.

If the structure is rotating it has to be balanced around the spin axis to avoid wobble, and it compounds making maneuvers.


Heat

Unless you get around thermodynamics waste heat is a problem. If the shuttle could not open the bay doors and expose the radiators it could not stay up even with its small electrical load. You can look at the specs for the ISS cooling system,

Equipment

Breaking a system down into redundant modes is routine. There are chips designed to allow 'hot swapping' modules while the system is on. Mechanics can also be made redundant.

But when something breaks you still have to repair or replace it. Medical equipment.

The shuttle had three redundant computers. Each was designed and coded by independent teams.

No matter how much analysis, testing, and simulation is done there is always the 'X factor', the unknown. As in Apollo 13.


Propulsion

Unless the other issues are resolved propulsion is a moot point.
 
:)

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Tigers! said:
We have enough light on earth for the plants to grow. Is there enough on the moon or Mars?
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The Moon gets almost exactly the same power density of solar irradiance as the Earth. At the surface, more, because there's no atmosphere to reflect some of it back into space. It does suffer from nights that last two weeks, though.

Plants are pretty efficient, and would probably grow OK on Mars. The limiting factor on Earth is typically Carbon Dioxide availability, not sunlight.

Solar photovoltaic panels aren't very effective on Mars though. Most Mars probes use radioisotope thermoelectric generators for their power needs.
 
bilby said:

Solar photovoltaic panels aren't very effective on Mars though. Most Mars probes use radioisotope thermoelectric generators for their power needs.
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is that true? I thought RTGs were more for outer solar system (though Juno used large solar panels for Jupiter). One of the issues the Mars rovers have had is dust collecting on their solar panels.
 
Shadowy Man said:
bilby said:

Solar photovoltaic panels aren't very effective on Mars though. Most Mars probes use radioisotope thermoelectric generators for their power needs.
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is that true? I thought RTGs were more for outer solar system (though Juno used large solar panels for Jupiter). One of the issues the Mars rovers have had is dust collecting on their solar panels.
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The dust problem is another reason why RTGs have generally been more successful.

Solar power has been the design choice for Mars landers more often than RTGs; However the most successful, and the largest and best equipped landers were RTG powered, and for solar powered landers, solar panel failure has been a frequent cause for end of mission, in some cases (eg Beagle 2) before the lander even got started with its exploration.

Vikings 1 and 2, Curiosity, and Perseverance were all RTG powered; Sojourner, Spirit, and Opportunity were solar powered. Power failure was anticipated to end the Spirt and Opportunity rovers lives quite quickly, but they were far more successful than the designers anticipated.

The Soviet landers prior to Viking (Mars 2 and 3) were battery powered, as was the 2015 Russian/Italian Schiaparelli lander.

The American Phoenix was powered by both solar panels and batteries, similarly to the design of the failed Mars Polar Lander.

Of American landers that actually sent data from the surface of Mars back to Earth, half were RTG powered, and half solar (or solar + batteries).

Of rovers still operating on Mars, 100% (two out of two ;) ) are RTG powered.

Solar power certainly works on Mars, and even (as you noted) further out in the Solar system.

And it turns out, now I have looked into it a bit more, that my original claim is not true. Fewer Mars probes used RTGs than the number that used solar power, and that remains true even if we only look at the ones that successfully soft landed on the planet*. I stand corrected.







*Though if we include the three fictional Ares missions from Andy Weir's The Martian, the balance goes back towards RTGs. I think. Or did they use both RTGs and solar power? We probably shouldn't count fictional missions, even if they did help my case.
 
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The dust problem is not easily solved for unmanned vehicles.

But I think it would be trivial for crewed missions, wouldn't it? Send someone out with a broom?
 
Jimmy Higgins said:
DBT said:
:)

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Great. We can send plants in sealed jars out into space. :)
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As various experiments have demonstrated, it's quite possible to have a self contained ecosystem like this one, that reaches a stable and self-sustaining equilibrium, but in which that equilibrium isn't able to support human life (or, indeed, any mammalian life, or even animal life).

Indeed, for considerable stretches of its history, the equilibrium composition of our planet's atmosphere has been at the very least unsuitable and uncomfortable for humans. Prior to the Oxygen Catastrophe of the Palaeoproterozoic era (for example), Earth's atmosphere would have been almost instantly deadly to humans, despite the Earth hosting a significant biosphere of photosynthetic organisms.

Building a closed ecosystem in which not just life, but human life, can thrive, is considerably more difficult than just sealing up a big glass container.
 
James Brown said:
The dust problem is not easily solved for unmanned vehicles.

But I think it would be trivial for crewed missions, wouldn't it? Send someone out with a broom?
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Why use a broom? In outer space, surely there's a vacuum. ;)

Seriously though, even without dust buildup, solar panels on Mars generate a lot less power from a given area than such panels do on Earth.

Earth gets about 1.37kW/m2 of power from the Sun; Mars only gets 0.59kW/m2, so ceteris paribus* you need 2.3 times more panels on Mars to get the same power output.











*"This is the bus to the centre of Paris", according to my if-only-it-were-English dictionary
 
I'd say we can solve most of the problems in the OP. That is technology (well, at least getting to a minor fraction of speed of light) development.

The issue becomes entropy in the system over long periods of time. Stuff wears over time, so unless we can make with biohulls like the Vorlon and Shadows have in Babylon 5, entropy ensures things will fall apart over time. That means we need to be able to fix stuff, and do so automatically. That requires technology that might simply be impossible. And on the interior, any process that breaks down can be detrimental.

Then we have psychology, which could be the hardest thing to solve because we are psychotic apes.

And finally, we have the issue of distance. Even at 1/10c, that isn't fast enough. That gets us to the nearest star which does us fuck all good in 40+ years (traveler's time, about the same in Earth time). The distance to Earth would make it impossible to communicate other than status updates. Of course, there wouldn't be much left to communicate after the overpopulation due to the fucking as a result of boredom and then some guy got a Napoleon complex and everyone was now dead.

Regarding Mars, it does seem real stupid. I've loved astronomy my entire life and learning about the geology and the life that existed there at one time would be sweet, but the idea of developing technology to allow people to move to Mars, which is an 8+ month trip, to live on a planet with less gravity that we weren't adapted for and can't breath on the surface is just incredibly dumb and we would be confined to live in confined spaces for the rest of their lives!? That'd be like going on vacation to place that is under a pandemic... but worse... because you can't ever leave as NASA calls no backsies. The only way things work there is a tiny base and dropping real machines on the planet. Just don't get hurt.
 
bilby said:

Solar photovoltaic panels aren't very effective on Mars though. Most Mars probes use radioisotope thermoelectric generators for their power needs.
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We avoid photovoltaic panels on Mars because of dust, not because they don't work. Spacecraft orbiting Mars are still photovoltaic.
 
Jimmy Higgins said:
Regarding Mars, it does seem real stupid. I've loved astronomy my entire life and learning about the geology and the life that existed there at one time would be sweet, but the idea of developing technology to allow people to move to Mars, which is an 8+ month trip, to live on a planet with less gravity that we weren't adapted for and can't breath on the surface is just incredibly dumb and we would be confined to live in confined spaces for the rest of their lives!? That'd be like going on vacation to place that is under a pandemic... but worse... because you can't ever leave as NASA calls no backsies. The only way things work there is a tiny base and dropping real machines on the planet. Just don't get hurt.
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it would seem, though I admit to not running any numbers, cheaper to fully populate the landmasses of Canada and Russia (and perhaps even Antarctica) before moving to Mars.

Earth still has a lot of room far more hospitable to human life than Mars.
 
Shadowy Man said:
it would seem, though I admit to not running any numbers, cheaper to fully populate the landmasses of Canada and Russia (and perhaps even Antarctica) before moving to Mars.

Earth still has a lot of room far more hospitable to human life than Mars.
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Agreed. Add the moon, if there turns out to be sufficient water at the poles.

Jimmy Higgins said:
I'd say we can solve most of the problems in the OP. That is technology (well, at least getting to a minor fraction of speed of light) development.

The issue becomes entropy in the system over long periods of time. Stuff wears over time, so unless we can make with biohulls like the Vorlon and Shadows have in Babylon 5, entropy ensures things will fall apart over time. That means we need to be able to fix stuff, and do so automatically. That requires technology that might simply be impossible. And on the interior, any process that breaks down can be detrimental.

Then we have psychology, which could be the hardest thing to solve because we are psychotic apes.

And finally, we have the issue of distance. Even at 1/10c, that isn't fast enough. That gets us to the nearest star which does us fuck all good in 40+ years (traveler's time, about the same in Earth time). The distance to Earth would make it impossible to communicate other than status updates. Of course, there wouldn't be much left to communicate after the overpopulation due to the fucking as a result of boredom and then some guy got a Napoleon complex and everyone was now dead.

Regarding Mars, it does seem real stupid. I've loved astronomy my entire life and learning about the geology and the life that existed there at one time would be sweet, but the idea of developing technology to allow people to move to Mars, which is an 8+ month trip, to live on a planet with less gravity that we weren't adapted for and can't breath on the surface is just incredibly dumb and we would be confined to live in confined spaces for the rest of their lives!? That'd be like going on vacation to place that is under a pandemic... but worse... because you can't ever leave as NASA calls no backsies. The only way things work there is a tiny base and dropping real machines on the planet. Just don't get hurt.
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That's a great thing about the moon. It's generally possibly to get home. And it's mostly downhill. It's a fine launchpad, observatory, possible fuel production site, recreational tourist destination...
I think ALL of that could be instituted successfully with a fraction of the time and effort of establishing a "Mars base", but it would depend on water.
 
I always womder why they don't put windshield wipers on the Mars rovers solar panels.
 
steve_bank said:
I always womder why they don't put windshield wipers on the Mars rovers solar panels.
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I'm prepared to bet that Martian dust is as abrasive as fuck, and that dragging it across your solar array would do more harm than good.

And of course, wipers and wiper motors weigh something, and use some power to operate, both of which are expensive resources that might be better deployed on other parts of your space probe.

It like the pre-rotation problem for aircraft wheels. The tyres on a jetliner wear out fast, due to hitting the runway at high speed. Many proposals have been made for systems to spin the wheels before landing, so that they aren't skidding along the concrete at touchdown; But all have failed because the cost of lugging around the extra weight of the pre-rotation system outweighs the savings in tyre wear. It's cheaper to just put up with the issue, and replace the tyres more often.

The electricity to power the dust-wipers is likely more than the extra power generated by a panel that has been wiped by them.
 
Why not make the panels covers out of drier sheets. They prevent static cling.

I'm off now to solve other problems.
 
bilby said:
steve_bank said:
I always womder why they don't put windshield wipers on the Mars rovers solar panels.
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I'm prepared to bet that Martian dust is as abrasive as fuck, and that dragging it across your solar array would do more harm than good.
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That's my impression. It's also sticky enough not to wipe off easily.

However, we have seen it can be blown off. I think any effective panel-cleaner will either be based on blowing compressed air or a very high RPM fan (think of Ingenuity's blades.) The accumulation is slow, it need not operate all that often.

However, any solar powered craft on Mars also faces the threat of big dust storms. It doesn't matter how clean your panels are if the sunlight isn't reaching you in the first place. Think of Opportunity.
 
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