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Confronting the Credibility Gap for Crewed Exploration of Mars

caseyexaustralia.blogspot.com

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Re: Confronting the Credibility Gap for Crewed Exploration of Mars

#71

Post by Symmetry »

mannykannot wrote: post #7
XorNot wrote: post #6

Earlier quoted context omitted.

It violates conservation of momentum (i.e. why solar sails work). This is a pretty big problem with any evidence purporting that it does work because it requires a massive reinterpretation of our understanding of existing physical laws: i.e. it's mechanism of operation has to simplify to existing theory in such a way as to also explain why the effect is undetectable at the staggeringly high resolutions of measurement…

As far as I can tell, the quote given by fapjacks is saying that the reactionless drive is impossible. Note that it is in a paragraph that begins "The other major kind of shonky coverage covers mythical propulsion..." (I had to look up 'shonky', but it is consistent with the above reading.)

That, and that the amount of energy you put in to produce a unit of impulse with a theoretical EM drive is 10 times larger than the amount of energy required to produce that same impulse with a Hall effect thruster. For the journey to Mars that means the EM drive would tend to be much slower in practice even if it worked.

Re: Confronting the Credibility Gap for Crewed Exploration of Mars

#72

Post by nonbel »

XorNot wrote: post #20
techdragon wrote: post #8

Earlier quoted context omitted.

There is a big difference between "does violate" and "appears to violate". The orbital motion of Mercury "violates" Newtonian gravity. There are other examples but I'm not trying to make a history lesson. I just want to point out, that science moves forward by impartial investigation of EVERYTHING. It's misguided to assume we know all and that there cannot be some thing we don't understand. I'm as sceptical as anyone…

The Relativity of Wrong [ http://chem.tufts.edu/answersinscience/relativityofwrong.htm ] Mercury's motion does violate Newtonian gravity. General Relativity however simplifies to Newtonian gravity for various low-dimension applications though (i.e. an Apple falling from a tree, the orbit of the moon for most astronomical guidance purposes over that distance etc.) In much the same way we don't account for the curvatur…

>"General Relativity however simplifies to Newtonian gravity"

I still don't see how this is possible. In GR gravity travels at the speed of light, in Newtonian mechanics it is instantaneous. I have been unable to find an acceptable explanation for how these two very different universes can be compatible.

Re: Confronting the Credibility Gap for Crewed Exploration of Mars

#73

Post by woah »

brilliantcode wrote: post #69

Why Mars though? Why not build a lunar base on the moon? Maybe even a hotel on the moon, I'm sure people will enjoy watching earth from the moon. I just fail to see this obsession with Mars. We don't even have manned landing on Mars and we are already having questionable stuff like "Mars One" And finally (one for the conspiracists): nearly 50 years ago we landed on the moon without any of the technology we have today…

I think part of it is that mars has an atmosphere

Re: Confronting the Credibility Gap for Crewed Exploration of Mars

#74

Post by nine_k »

chandmer wrote: post #63
nine_k wrote: post #58

Earlier quoted context omitted.

A floating station (eventually a city?) in the atmosphere of Venus would also be fine. On certain height, the temperature and the pressure are close to Earth's surface, and sun shines brightly enough for plants to generate oxygen. There's plenty of carbon dioxide in the atmosphere to feed the plants. No roaming over the surface, though.

No access to generic raw materials and huge lifting gas overhead, even huger delta-V requirements to do anything. I don't get Venus cloud tops. I've never seen anyone explain how to transport, fuel and launch a Saturn V rocket from a zeppelin.

The access to solids is definitely a problem. One approach might be digging them from the surface and lifting up using balloons. High temperatures don't help, but without the need to stay on the surface for very long periods, the digging robots may probably accumulate enough cold while high in the atmosphere, and then dive down for a short while, managing the temperature e.g. by melting and boiling the coolant, then go up again.

The lifting gas can be initially transported in a highly pressurized form (e.g. liquid helium). It would be enough to support a small initial platform. That platform can generate lighter gases right from the atmosphere, using solar energy. CO2 is pretty heavy, so even oxygen and nitrogen would be lifting gases. Hydrogen is also somehow available for extraction from the atmosphere. These gases could be used to support more and more incoming structures as they arrive from orbit. (Yes, easier said than done.)

The bigger problem would probably be compounds like sulfuric acid, hydrogen chloride and fluoride, etc, that would readily react with many construction materials, especially metals.

Given the atmosphere composition, it's probably even possible to synthesize both fuel and oxidizer for a rocket, e.g. hydrocarbons and O2 or HNO3. Launching a large rocket from a zeppelin is tricky. Launching a rocket from a plane has been shown to work on Earth, so it's possibly also doable from Venusian cloud tops. Again, easier said than done.

But still possible!

Re: Confronting the Credibility Gap for Crewed Exploration of Mars

#75

Post by dTal »

woah wrote: post #73
brilliantcode wrote: post #69

Why Mars though? Why not build a lunar base on the moon? Maybe even a hotel on the moon, I'm sure people will enjoy watching earth from the moon. I just fail to see this obsession with Mars. We don't even have manned landing on Mars and we are already having questionable stuff like "Mars One" And finally (one for the conspiracists): nearly 50 years ago we landed on the moon without any of the technology we have today…

I think part of it is that mars has an atmosphere

An atmosphere that provides none of the benefits of appropriate pressure, temperature and gas mix but all of the challenges of weather and airborne dust.

Re: Confronting the Credibility Gap for Crewed Exploration of Mars

#76

Post by dTal »

jcoffland wrote: post #37
Animats wrote: post #26

Landing is really hard. Not enough atmosphere for aerobraking, and too far from home to have enough fuel for a powered landing. It's a fuel problem. There's the expensive approach. Send multiple unmanned tanker ships into Mars orbit and have them rendezvous into an orbital supply depot. Send landing tanker ship to rendezvous with them and refuel with enough fuel for a powered landing. Landing ship descends. Repeat to…

How about we harpoon Mars and pull down one end of a space elevator?

Interesting proposal.

You still need a lot of delta vee to get a harpoon+cable from orbit to the surface. You can't just fire it straight down, you have to cancel most of your orbital velocity (which would have to be way out at geostationary). Dunno what the strength requirements of the cable would be either, but I imagine the answer is "not small".

Doing the same trick to Earth probably wouldn't be that much harder than Mars. So maybe, once you've solved the hard problems, you wouldn't have to worry so much about mass-to-orbit anyway.

Re: Confronting the Credibility Gap for Crewed Exploration of Mars

#77

Post by dTal »

pilom wrote: post #51
jcoffland wrote: post #37

Earlier quoted context omitted.

How about we harpoon Mars and pull down one end of a space elevator?

The biggest problem with a space elevator on Mars is that the orbit of one of its moons is closer than the minimum height of a space elevator to be stable. Eventually the elevator cable will get hit.

Hang the cable from the moon and let the end trail?

Re: Confronting the Credibility Gap for Crewed Exploration of Mars

#78

Post by namlem »

Animats wrote: post #26

Landing is really hard. Not enough atmosphere for aerobraking, and too far from home to have enough fuel for a powered landing. It's a fuel problem. There's the expensive approach. Send multiple unmanned tanker ships into Mars orbit and have them rendezvous into an orbital supply depot. Send landing tanker ship to rendezvous with them and refuel with enough fuel for a powered landing. Landing ship descends. Repeat to…

Alternatively, send a probe that generates LOX and liquid methane from water ice and CO2 on Mars using solar power to create the fuel needed for ascent.

Re: Confronting the Credibility Gap for Crewed Exploration of Mars

#79

Post by namlem »

dTal wrote: post #75
woah wrote: post #73

Earlier quoted context omitted.

I think part of it is that mars has an atmosphere

An atmosphere that provides none of the benefits of appropriate pressure, temperature and gas mix but all of the challenges of weather and airborne dust.

The martian atmosphere does have the benefit of having created much less abrasive dust over the years. Moon dust causes much more wear to moving parts. Mars also has accessible carbon, which the moon does not. The martian atmosphere can supply plants with the CO2 they need, enabling agriculture.

Re: Confronting the Credibility Gap for Crewed Exploration of Mars

#80

Post by namlem »

semi-extrinsic wrote: post #45
coldtea wrote: post #43

Earlier quoted context omitted.

> Human psychology is another, perhaps even bigger problem, also independent of destination. We've had various experiments with prolonged isolation, but none where the subjects know that they're never coming back to Earth. Who said they're never coming back to Earth? > no perfectly rational, mentally healthy human would volunteer for such a mission That's an easy problem to solve, as there are no "perfectly rational"…

How are they going to come back? All realistic plans I've seen are for one-way trips. The thought of dying isn't the inherently problematic part, but rather the extreme isolation. People who go to war are there for only some months and have plans for going home, back to friends and family. People who dive and explore the oceans are isolated for a few days at worst; perhaps months in a nuclear sub, but there you have…

What are you talking about? Both NASA's and Musk's plans involve return trips.
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