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Overnight to Mars

Everything I know about peoplekind living for extended time in low gravity I learned from A Specter Is Haunting TexasWP. So don't listen to me. ;)
 
That's a funny name with a funny (apparent) origin and especially so since Texas is still haunted by the specter of communism.
 
It's always useful to go to the source. The original article is quite upfront:

An Earth-based laser array of unprecedented size (10 m diameter) and power (100 MW) is assumed to be enabled by ongoing developments in photonic laser technology
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That is, as the saying goes, a mouthful. That's a 10-meter optical system which remains diffraction-limited while dissipating something like 100 MW (assuming 50% emitter efficiency). It also assumes a 45-day trip duration.

But we're talking here about overnight, or 1/2 day. So the velocity impulse will need to be 90 times greater. However, if we assume the same optical performance of the array, then the boost acceleration will need to be about 100 times greater in order to keep the boost phase complete within the range of the laser array. The paper assumes a 58-minute boost duration to produce a 14 km/sec delta-v. That is an acceleration of 4 meters/sec^2, or 0.4 g. The new flight profile will need an acceleration of 40 g s. The structural demands on the receiving optical array which concentrates the beam onto a thermal receiver (which must be extremely light - the paper assumes a 1 tonne vehicle with 70% going for fuel and a 6% payload) would seem a very appropriate use for unobtainium. The receiver doesn't have to be diffraction-limited, but it does need to keep its shape, and do it under a 40 g acceleration.

Meanwhile, the emitter array has jumped from 100 MW to 10 GW in a 10 m^2 area. Assuming a 99% efficient emitter, that's still waste heat on the order of 1 MW/m^2. And optical power densities of nearly 100 MW/m^2.

This also assumes that the Isp of the fuel will remain constant with an increase of exhaust velocity of a factor of 100.

"Unprecedented" does seem like a pretty fair description.
 
Just for the record, despite the whimsical title of the thread the limited discussion seems to have been mostly about the 45 day plan. Also, not really seeing that a receiver holding it's shape against 40g necessitates unobtanium, not even close. Plenty of materials can do that. The force could even be used in tension to help the receiver maintain it's shape.
 
RecoveringYuppy said:
Just for the record, despite the whimsical title of the thread the limited discussion seems to have been mostly about the 45 day plan. Also, not really seeing that a receiver holding it's shape against 40g necessitates unobtanium, not even close. Plenty of materials can do that. The force could even be used in tension to help the receiver maintain it's shape.
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Sorry about the whimsy. It was just me playing homage to Boney M and their Night Flight to Venus.

The article WhatRoughBeast quoted above does say in its conclusion:

The preliminary design of critical subsystems necessary for such a spacecraft has not found fundamental technological roadblocks to realize this propulsion system.
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So, just engineering! :duck:
 
W.D.Clinger said:
A few engineers figured out how to build a few bridges that haven't fallen down yet.
Building a bridge to Mars is more difficult, I think, but it might not need to hold up for quite so many centuries.
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Gord's point was disingenuous. No need to belabor the rebuttal just because it's mine.
 
RecoveringYuppy said:
Interesting choice. Why?
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Because the way I see it, the whole point of a crewed mission to Mars hinges on being able to bring the crew home again.

That would be a problem I think we do understand well enough now.
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I'm sure "we" understand the problem just fine. What I'm looking forward to is the solution. It's not like we have any experience at all with launching man-rated vehicles from the Martian surface, requiring no more ground support than the crew of the vehicle itself. The Moon, with its zero atmosphere and much lower gravity, doesn't seem to teach us a lot of lessons for this kind of thing.

I expect one or two sample return missions will happen before we send people.
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It make sense to combine the test of a self-contained surface-return system with a sample return mission. It's exactly the design and development of that system that I'm looking forward to.

I also see a way to mitigate risk by sending the ascent components to Mars on an earlier mission.
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That might be a way to mitigate risk, depending on the details of the design and the overall trade-offs. There's also risk inherent in requiring the crew to assemble, integrate, and check out their return vehicle, on the Martian surface, in environment suits rather than shirt-sleeves. Unless the design includes sending a Vehicle Assembly Building where they can work in a more Earthlike environment.

I'm not saying it can't be done (something I don't believe). I'm not saying it shouldn't be done (though I am actually a fan of not doing crewed missions to Mars).

I'm saying that getting the crew back to Earth at the end of their mission is in my opinion the most important part of the mission profile, and that therefore I'm very interested to see what they end up doing to make it happen.

Why do you think this is an "interesting" choice? Do you think I should be more interested in some other aspect of the mission profile, than getting the crew back alive?
 
I agree with all that. I just wouldn't have chosen to describe that as interesting. It's obviously important and I might have used that word instead.
 
RecoveringYuppy said:
I agree with all that. I just wouldn't have chosen to describe that as interesting. It's obviously important and I might have used that word instead.
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I didn't describe it as "interesting". You did. I said that I was really interested in seeing the solution to the most important problem of the mission profile.

Is it really that notable to you, that I would be most interested in the solution to the most important problem?
 
RecoveringYuppy said:
FFS. You said you were interested in it. And your current post is just pointless contrarianism.
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Of course I'm interested in it! It's only the most important problem facing this mission proposal! We wouldn't even be having this conversation if you hadn't been so quick to dismiss my interest, for reasons which still escape me. Instead of complaining about my contrarianism, help me understand yours.
 
Roboramma said:
(It's also quite possible to include artificial gravity on the spacecraft that we send to Mars if this really is an issue, but it's probably not necessary.)
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From a physics point of view it is possible. But from an engineering point of view it is completely untested. Mars trips are going to be seriously mass constrained. Any method of artificial gravity is going to require more mass than you'd take otherwise. That will be a hard sell.

I agree that the lack of gravity for the duration is likely not the main constraint on such a journey.
 
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An update to "Bones in Space".

Six months in space leads to a decade’s worth of long-term bone loss

https://www.sciencenews.org/article/space-bone-loss-density-astronaut-recovery-gravity

During space missions lasting six months or longer, astronauts can experience bone loss equivalent to two decades of aging. A year of recovery in Earth’s gravity rebuilds about half of that lost bone strength, researchers report June 30 in Scientific Reports.
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and, further:

Astronauts in space for less than six months were able to regain their preflight bone strength after a year back in Earth’s gravity. But those in space longer had permanent bone loss in their shinbones, or tibias, equivalent to a decade of aging. Their lower-arm bones, or radii, showed almost no loss, likely because these aren’t weight-bearing bones, says Gabel.
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Thank God that Mars has lower gravity. We'll be hobbling around in orthopedic space shoes. :(
 
Gord_in_Toronto said:
... Doctors can't even cure the common cold. :teacher:
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That's a myth. There are ~200 agents that result in "common cold" symptoms. Many are curable and/or preventable. There is no reason to track down every single virus that causes mild cold symptoms but if we did we could probably develop treatment or vaccines for them.

So they have or they can in most cases. :pedant :fg:
 
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Skeptic Ginger said:
That's a myth. There are ~200 agents that result in "common cold" symptoms. Many are curable and/or preventable. There is no reason to track down every single virus that causes mild cold symptoms but if we did we could probably develop treatment or vaccines for them.

So they have or they can in most cases. :pedant :fg:
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"If you do everything known to medical science, you can cure the common cold in 7 days. If you do nothing, it goes away in a week." Anon.

Everything I know about the CC I learnt from the research done at the UK Government's Common Cold UnitWP. I figure if they spent a billion pounds they must have discovered something.
 
RecoveringYuppy said:
Interesting choice. Why? That would be a problem I think we do understand well enough now. I expect one or two sample return missions will happen before we send people. I also see a way to mitigate risk by sending the ascent components to Mars on an earlier mission.
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I dunno how well we understand the problem. What I'm interested in seeing is a complete understanding of the solution

As for why? That should be obvious. Without a viable manned launch solution from the Martian surface, it's a suicide mission.
 
An update of the bones problem. Apparently the problem can be mitigated by jumping up and down.

Astronauts may need to jump in space to fight bone loss

https://www.space.com/astronaut-bone-loss-jumping-exercise-study

The authors thus propose adding "jumping resistance-based exercise that provides high-impact dynamic loads on the legs" to astronauts' existing exercise routines to prevent bone loss and promote bone growth while on spaceflight missions.
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So this becomes "just an engineering issue". ;)

Of course, any new jumping regimen would require specialized equipment, and space is always limited aboard any spaceflight. "Successful implementation of high-load jump-training on-orbit will require an exercise device that mitigates forces transferred to the vehicle, along with an exercise regimen that accounts for astronaut deconditioning," the researchers wrote in the new study.
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