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Overnight to Mars

The idea of using a laser instead of carrying the fuel with you isn't exactly new, and it's a good one. Most of the energy is actually going into accelerating the fuel you carry with you, so that would improve efficiency dramatically, even if your laser isn't perfectly efficient.

The main problems I see are:

1. It ain't gonna be ground based, is it? Because the Earth spins around, and so would your beam. By the time you're anywhere near Mars even at a the lowest distance, we're talking about that beam sweeping at v=rω=55 million km * 2 * PI / 86400s = approx 4000km/s.

Ah, but we'll just angle that laser to follow that craft, right? Weell, to land that beam within +/- 1km of where that craft is by that point, we're talking about an accuracy of arctan(1/55000000)= approx 1.5*10-8 radians, or 0.00009 degrees. And maintaining it on a moving target.


2. Well, bummer, guess then we'll put the laser in orbit. Well, moving the 100 MW laser and whatever fuel you use for powering it into orbit has kinda shaved off most of the savings already.

And that's not even getting into issues like that a 100 MW laser in orbit is an orbital weapon. You'd really have a hard time convincing a lot of countries to sleep easy with that going in circles around the globe. Yeah, guys, rest assured that at no point in the next century, no matter what jingoistic retard the USA may end up electing after the Idiocracy finally comes, no matter how hard China or Russia are gonna flex their muscles, is this going to get flipped around into a James Bond movie kinda doomsday weapon :p

I mean, for comparison, the AN/SEQ-3 is 30kW and it can detonate missiles or fry drones in the air.


3. That's kinda it: it's a bit of a jump from 30kW lasers (and even a lot of those are chemical, so they shoot one pulse and then have to cool down, vent the gases, recharge) to 100 MW lasers capable of staying on for a month or two. It probably will be doable in the future, mind you. I'm optimistic. But... maybe not this year, is all I'm saying.
 
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HansMustermann said:
The idea of using a laser instead of carrying the fuel with you isn't exactly new, and it's a good one. Most of the energy is actually going into accelerating the fuel you carry with you, so that would improve efficiency dramatically, even if your laser isn't perfectly efficient.

The main problems I see are:

1. It ain't gonna be ground based, is it? Because the Earth spins around, and so would your beam. By the time you're anywhere near Mars even at a the lowest distance, we're talking about that beam sweeping at v=rω=55 million km * 2 * PI / 86400s = approx 4000km/s.

Ah, but we'll just angle that laser to follow that craft, right? Weell, to land that beam within +/- 1km of where that craft is by that point, we're talking about an accuracy of arctan(1/55000000)= approx 1.5*10-8 radians, or 0.00009 degrees. And maintaining it on a moving target.


2. Well, bummer, guess then we'll put the laser in orbit. Well, moving the 100 MW laser and whatever fuel you use for powering it into orbit has kinda shaved off most of the savings already.

And that's not even getting into issues like that a 100 MW laser in orbit is an orbital weapon. You'd really have a hard time convincing a lot of countries to sleep easy with that going in circles around the globe. Yeah, guys, rest assured that at no point in the next century, no matter what jingoistic retard the USA may end up electing after the Idiocracy finally comes, no matter how hard China or Russia are gonna flex their muscles, is this going to get flipped around into a James Bond movie kinda doomsday weapon :p

I mean, for comparison, the AN/SEQ-3 is 30kW and it can detonate missiles or fry drones in the air.


3. That's kinda it: it's a bit of a jump from 30kW lasers (and even a lot of those are chemical, so they shoot one pulse and then have to cool down, vent the gases, recharge) to 100 MW lasers capable of staying on for a month or two. It probably will be doable in the future, mind you. I'm optimistic. But... maybe not this year, is all I'm saying.
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tl;dr - Use a ground-based laser to greatly increase the thrust-to-weight ratio of your launch vehicle's first stage, allowing it to put much larger payloads into orbit for the same overall mass. depending on exactly how the math works out, maybe you can replace both first and second stages. This gives you a lot more payload to send to Mars.

Imagine how much more we could have sent to the Moon, if we'd been able to leave half the Saturn V first stage on the launch pad.
 
Well, sure, you can reduce SOME of the energy requirements. Never said you couldn't. But that then saves you an hour to orbit, not get you to mars in 45 days.
 
Dumb question perhaps, but if the laser is so powerful, isn't it going to melt the spaceship that you are trying to accelerate?

Also, what happens to the reflected beam, assuming it doesn't. Doesn't it come right back at the earth?
 
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Puppycow said:
Dumb question perhaps, but if the laser is so powerful, isn't it going to melt the spaceship that you are trying to accelerate?

Also, what happens to the reflected beam, assuming it doesn't. Doesn't it come right back at the earth?
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A reflecting "sail" (a mirror) doubles the efficiency, compared to an absorbing one, in tranferring beam photons momentum to the spaceship and drastically reduces the heat to be dissipated (i.e. only the unwelcomed absorbed energy). The reflected beam points to the source direction only when the normal to the reflecting surface points there too, a very special case (and easily avoidable) for an object orbiting e.g. the earth or the sun since the trajectory is not a straight line from Earth to Mars.
 
That's not what the article proposes.

For this application, lasers are used to deliver power to photovoltaic arrays on a spacecraft, which is converted to electricity to power a Hall-Effect Thruster (ion engine). This idea is similar to a nuclear-electric propulsion (NEP) system, where a laser array takes the place of a nuclear reactor.​

Which makes Puppycow's question actually quite smart and justified. Solar panels are nowhere NEAR 100% efficiency. In fact, the current best ones are just under 23% efficiency. That means that out of 100 MW, only about 23 MW would actually be usable for the engine. And while some of the rest would be reflected, you're still left with some tens of MW worth of heat to somehow dissipate.

Essentially take a look at all those huge cooling panels on the ISS, and that's to dissipate 14kW or so into space if I'm not mistaken. (Which I may well be.) That's needed because unlike Earth, you're not really transferring the extra heat to a medium like air (or water in the case of warships), so Stefan–Boltzmann is your only way to get rid of it. Now picture literally anywhere between 1000 and 4000 times that area, if we're talking MW instead of kW.

That does indeed sound like a real problem I hadn't thought about.
 
Also this means we can't quite use it instead of the first stage to get to orbit either. To get to orbit you need high thrust. Ion engines are more like high specific impulse, low thrust engines to get you to Mars after you've already cleared that hurdle. Essentially the former is the kind where you want a lot of acceleration in a burst, while the latter is something that will give you a modest acceleration very efficiently, but can keep at it for months. The big delta-V is just the effect of multiplying that small acceleration by a very large time. But they can't really work as a substitute for the former, when you need a lot of delta-V fast to get out of Earth's gravity well.

Edit: unless we're going TWIN Ion Engine, I guess. Those fighters seemed to have plenty of thrust ;)
 
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Puppycow said:
Dumb question perhaps, but if the laser is so powerful, isn't it going to melt the spaceship that you are trying to accelerate?
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Yep! And that can be a feature: Put the fuel at the ass end of the spaceship, so it will be the first thing to go when the laser hits. Does a rocket melt when the fuel ignites and blows out the base of the rocket? Same principle here. The advantage of the laser in this scenario is that otherwise the rocket has to carry more fuel with it. By having the ground-based laser provide some of the energy, the rocket gets to carry less energy on board, and more payload.

Also, what happens to the reflected beam, assuming it doesn't. Doesn't it come right back at the earth?
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The beam mostly gets absorbed, so that's okay.
 
theprestige said:
Yep! And that can be a feature: Put the fuel at the ass end of the spaceship, so it will be the first thing to go when the laser hits. Does a rocket melt when the fuel ignites and blows out the base of the rocket?
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Uh... yes? Why do you think they have the whole tubes around to heat the fuel instead? If you just lit a fire at that end and didn't use active cooling, yes, it would even melt tungsten quite soon.

And unfortunately that doesn't work when we're talking about a ion engine. It doesn't use a ton of cryogenically cooled fuel to take that heat out. In fact, the whole point of that laser is to replace carrying such fuel.
 
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I just got around to reading the Bone Loss paper (So Little Time. So many Scientific Papers!) at https://www.nature.com/articles/s41598-022-13461-1 and see it actually says:

Our findings indicate that microgravity induces irreversible damage to bone strength, density, and trabecular bone microarchitecture. While bone partially recovers after spaceflight, sustained losses represent at least a decade of normal age-related bone loss, potentially advancing onset of osteoporosis. Inter-individual differences in bone’s response to microgravity and recovery after return to Earth are largely explained by mission duration. Unless countermeasures improve, incomplete recovery of bone structure and strength may worsen as missions get even longer. Future work is needed to clarify the temporality of bone loss in space and to optimize countermeasures for mitigating bone loss on long-duration flights. Until then, elevated biomarkers of bone turnover appear to identify astronauts at greatest risk of irreversible bone loss; thus, these individuals may benefit most from enhanced preventative measures.
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(Highlighting mine.)
 
HansMustermann said:
Which makes Puppycow's question actually quite smart and justified. Solar panels are nowhere NEAR 100% efficiency. In fact, the current best ones are just under 23% efficiency.
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Solar panel efficiency is limited by the ability to collect energy from a broad spectrum of sunlight filtered through the atmosphere. The best efficiency achieved so far (with triple-junction devices) is 46%.

But laser illuminated photocells aren't operating as solar panels. They only have to work at the single frequency of the laser, so their efficiency can be much higher. The attached graph shows measured efficiencies for a selection of photocells designed for laser power transfer. Quantum efficiencies close to 100% are achieved at many popular semiconductor laser wavelengths.

Photovoltaic Cells for Laser Light: Optical Power Transmission for Sensor Electronics
 

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Which changes my point a little, but doesn't completely eliminate it. Even if you achieved 99% efficiency for the whole system, from the photovoltaic panels to the coils of the ion engine to everything, that would still leave you with about 1MW to dissipate into space. That's some pretty bloody huge radiators, is all I'm saying.
 
HansMustermann said:
Which changes my point a little, but doesn't completely eliminate it. Even if you achieved 99% efficiency for the whole system, from the photovoltaic panels to the coils of the ion engine to everything, that would still leave you with about 1MW to dissipate into space. That's some pretty bloody huge radiators, is all I'm saying.
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I'm not sure what your point is. The proposed method that Puppycow questioned doesn't involve photovoltaic panels, but instead directly heats the propellant in a heating chamber similar to a rocket's combustion chamber. The article even mentions the need for high temperature materials to handle the heat.

If PV panels were used then they would have a large surface area that could easily dissipate the waste heat. The electricity generated would power an ion engine. This might only be 80% efficient, but again would presumably be large enough to dissipate the heat (just like current ion engines are). The ion engine and PV panels might be combined into a single unit forming the bulk of the spaceship, which would be very large but extremely lightweight to get a good thrust/weight ratio.

But again, this was not the method proposed in the article. What method (if any) actually gets used will depend more on another measure of efficiency - cost. 100MW space lasers don't come cheap. I doubt anyone will be willing to pay for a much faster than normal trip, especially since there's a good chance they won't make it back. Why be in a hurry to die?
 
I'm not totally sure if this is the same proposal from the OP, but Fraser Cain talks about a rocket that could theoretically get to Mars in 45 days in his most recent video:



(As well as other space news)
 
Roger Ramjets said:
I'm not sure what your point is. The proposed method that Puppycow questioned doesn't involve photovoltaic panels, but instead directly heats the propellant in a heating chamber similar to a rocket's combustion chamber. The article even mentions the need for high temperature materials to handle the heat.

If PV panels were used then they would have a large surface area that could easily dissipate the waste heat. The electricity generated would power an ion engine. This might only be 80% efficient, but again would presumably be large enough to dissipate the heat (just like current ion engines are). The ion engine and PV panels might be combined into a single unit forming the bulk of the spaceship, which would be very large but extremely lightweight to get a good thrust/weight ratio.

But again, this was not the method proposed in the article. What method (if any) actually gets used will depend more on another measure of efficiency - cost. 100MW space lasers don't come cheap. I doubt anyone will be willing to pay for a much faster than normal trip, especially since there's a good chance they won't make it back. Why be in a hurry to die?
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I'm not clear on how the panels can be oriented so as to absorb the maximum possible solar energy, and also radiate waste heat.
 
More Bad News!

Researchers investigate impacts of space travel on eye health

However, their recently published study found that lower body negative pressure (LBNP), while successful in shifting fluid towards the lower body, did not effectively reduce OPP. If elevated OPP is indeed linked to SANS, it suggests that LBNP may not be an effective countermeasure for this syndrome. The team underscores the need for future research to better understand the relationship between OPP and SANS, as well as the impact of LBNP on these ocular responses, for the development of effective countermeasures.
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Umm.
 
Here we go again!

oilprice.com

New Propulsion Technology Could Send Spaceships to Mars in a Month | OilPrice.com

Russia's Rosatom is developing a plasma electric rocket engine that could drastically reduce travel time to Mars, potentially making the journey in 30 to 60 days.
oilprice.com oilprice.com

Maybe?

"While new space propulsion systems show great promise, most innovative technologies are still in the testing phase, meaning it will likely take several years before we see the results. However, greater research and development in the sector make it more likely that we will see vast improvements in efficiency and safety in space travel in the coming decades. "

That's more like it.
 
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