Energy on the Moon

[swansont]

The gravity on the Moon is so low, that a space elevator would be taking a sledgehammer to crack a nut.

The amount of rocket power needed to lift off from the Moon is tiny. You only have to compare what the astronauts lifted off in on their return journey, to the gigantic rockets needed to lift men off from the Earth. It was tiny, and most of it was living space. The rockets were negligible.

 

It's actually possible to build a gun, that would shoot materials off the surface of the Moon into orbit, just using normal shell propellant.

The lack of atmosphere makes the job easier.

Or you could build electrically driven railguns, that don't need propellant at all, just electrical power.

 

Mars would be a totally different problem though. Lifting off from Mars would need big rockets, with lots of fuel, due to it's much higher gravity than the Moon.

 

 

The rockets lifting off from earth were carrying the entire mission payload. The ones leaving the moon were carrying the men and moon rocks. The command module and fuel for the return trip stayed in orbit. The difference is not just about the gravity

 

We're talking about people, so the acceleration of a railgun needs to be compatible with surviving the launch. Plus you have the aforementioned dust issue.

[mistermack]

 

 

The rockets lifting off from earth were carrying the entire mission payload. The ones leaving the moon were carrying the men and moon rocks. The command module and fuel for the return trip stayed in orbit. The difference is not just about the gravity

 

We're talking about people, so the acceleration of a railgun needs to be compatible with surviving the launch. Plus you have the aforementioned dust issue.

Yes, but even going by your own post, it's obvious that the problem is a small one.

 

You can use a railgun to get MATERIALS into orbit, just leaving people and very delicate objects to be lifted off with very small rockets.

 

Given the improvement in rockets and lightweight materials, since 1969, that's really not going to be a problem.

 

Or, you could probably use a combination of the rail-gun at lower power, with rockets taking over at the end, to put people into orbit with very little rocket power needed.

[swansont]

Yes, but even going by your own post, it's obvious that the problem is a small one.

 

You can use a railgun to get MATERIALS into orbit, just leaving people and very delicate objects to be lifted off with very small rockets.

 

 

 

My response was to a question/comment about getting people into orbit on a daily basis.

[mistermack]

 

 

My response was to a question/comment about getting people into orbit on a daily basis.

I think the same applies. As they are just going from the Moons surface to an orbiting space station, they would need the minimum vehicle necessary for that, just a pared down shuttle vehicle. It would be smaller and lighter than the original lunar module, so would require a lot less in the way of rocket power.

 

It could be a lot more dangerous though, in the case of a rocket failure. There would be no chance of using a parachute.

The ascent would need to be pretty much 100% reliable. But I guess that's the same with most rockets, really.

[swansont]

I think the same applies. As they are just going from the Moons surface to an orbiting space station, they would need the minimum vehicle necessary for that, just a pared down shuttle vehicle. It would be smaller and lighter than the original lunar module, so would require a lot less in the way of rocket power.

 

It could be a lot more dangerous though, in the case of a rocket failure. There would be no chance of using a parachute.

The ascent would need to be pretty much 100% reliable. But I guess that's the same with most rockets, really.

 

 

I am pointing out that a railgun is outside the scope of what I was talking about.

 

But I disagree that you would use less than the lunar lander. That was a pretty minimalistic vehicle. And you'd be doing things in reverse — the launch vehicle would need to be outfitted so it could return to the surface, unlike the lander. So the fuel for return landing has to be aboard, which of course requires even more fuel to lift it up. And you might have to shuttle supplies up to the station, since you are fabricating things on the surface.

[Endy0816]

You should be able to modify a graviton ride for simulating gravity. Mainly nobody knows how big an issue low G is going to be. If it is survivable without huge amount of atrophy before changing G's may not be worth expending resources on.

 

With propellants you have to mine and process. Hydrogen used as fuel would also lead to rapid depletion. There are other options that might work though. Silicates are plentiful.

 

RL they did look at adding a rotating sleeping module for the ISS at one point. Something like that could work well for a Mars trip or further out.

 

Nautilus X if anyone is interested.

[mistermack]

The thing with artificial gravity is that the station has to be more than 200m across, to avoid sickness due to the rotation of the balance canals in our ears. Preferably a good bit more than 200m.

That would be easier to set up in zero gravity, maybe initially just two pods connected by a cable and rotating round each other.

 

It might be an expensive thing to arrange, I agree, but still far cheaper than a return trip to Earth, to spend time in 1g.

Something like a railgun might be essential to the whole enterprise. You could shoot fuel containers into orbit, eliminating the need to carry up the fuel for the descent.

What would be ideal would be to divert a comet into lunar orbit. Or blast off a huge chunk of one, and send it into orbit around the Moon. You could make all the fuel you would ever need from one of those.

[Janus]

How about a space elevator?

 

With low gravity, better technology, and an endless supply of water-ice to create hydrogen fuel, maybe launching modest payloads of astronauts from the surface of the moon or Mars into orbit could be a daily routine?

A space elevator is not a feasible option for the Moon. The space elevator works by extending past the geostationary orbital distance (or in the case of the Moon a lunar-stationary orbit.) There are no stable lunar-stationary orbits for the Moon. Because of its slow rotation rate, such orbits would be outside the Moon's Hill sphere.

The closest you come are the L1 and L2 points and, due to the Moon's librations, even they don't remain fixed relative to the Moon's surface.

We're talking about people, so the acceleration of a railgun needs to be compatible with surviving the launch. Plus you have the aforementioned dust issue.

Some numbers to go with that comment. Assume that we want to keep the acceleration to about that experienced by astronauts during launches from the Earth, which is ~2g.

A rail gun capable of delivering a capsule to an orbit 200 km above the Moon's surface would need to get this capsule up to ~1.73 km/sec. (If it wants to maintain orbit at that altitude it will need to have a rocket and enough fuel to add ~90 m/s to its velocity)

At 2g, this will take ~88 sec or just under 1.5 min. The rail gun would have to be over 76 km long.

Edited April 7, 2017 by Janus

[fiveworlds]

What about making use of the fact that the moon has a limited magnetosphere is there anything that we could use to capture electricity from the solar wind/radiation etc? There was a 2008 article using carbon nanotubes packed with gold surrounded by lithium hydride being used to directly convert radiation into electricty. Supposedly radiation exposure on the moon is about the same as working in a uranium mine so would it generate enough electricity?

 

https://www.newscientist.com/article/dn13545-nanomaterial-turns-radiation-directly-into-electricity/

Edited April 7, 2017 by fiveworlds

[mistermack]

Maybe, by the time we have rotating space stations with artificial gravity, we won't need people on the Moon.

The machinery will be so advanced, you will be able to run it remotely from a desk on the space station, removing the need for shuttling people back and forth almost altogether.

They might just have remotely operated mining machines, that are constantly digging out what we need, and sending the raw materials into orbit via the rail gun.

It might take a couple of hundred years, but it will be happening in some form. If we don't all kill each other off in the meantime.

[Argent]

 

Yeah, I think we'll need to look at simulating gravity on the surface or find medical solutions.

 

Not talking anything too unrealistic in managing muscle mass and bone loss. We do need more research on gestation in space though.

I am not aware what conclusions have been reached about the long term impact on physiology of low gravity, as on the moon, versus micro-gravity (erroneously called zero-g by some). Perhaps we shall get lucky and find lunar gravity, in combination with reasonable exercise, will be sufficient to maintain long term condition. Does anyone know of any research that has explored this issue?

[imatfaal]

I am not aware what conclusions have been reached about the long term impact on physiology of low gravity, as on the moon, versus micro-gravity (erroneously called zero-g by some). Perhaps we shall get lucky and find lunar gravity, in combination with reasonable exercise, will be sufficient to maintain long term condition. Does anyone know of any research that has explored this issue?

 

Just to be clear - zero-g is probably just as good a name as micro-gravity; Gravity in the circumstances referred to is neither zero nor even much diminished - it is the reactive force from the ground which is missing. Those in orbit are in a state of free-fall - which is to say that gravity is the only force acting upon them. This is highly analogous to true zero-g or micro-gravity (ie hugely away from any mass) because their environment is in an exactly similar state of freefall so they appear weightless

[mistermack]

Maybe it would be possible to design an installation on the moon that replicated 1g of gravity, but it would be a huge undertaking.

It's the minimum diameter of 200m that's the problem. Making machines that big on the Moon is probably a thousand years away.

 

One advantage of the cold on the Moon might be the ability to use superconductors as bearings, I only have a vague notion of how that stuff works without looking it up. But I know that they generally work much better in cold temperatures.

 

So maybe some sort of huge 250m plus rotating station could be made and run without much maintenance or energy input.

[imatfaal]

Maybe it would be possible to design an installation on the moon that replicated 1g of gravity, but it would be a huge undertaking.

It's the minimum diameter of 200m that's the problem. Making machines that big on the Moon is probably a thousand years away.

 

One advantage of the cold on the Moon might be the ability to use superconductors as bearings, I only have a vague notion of how that stuff works without looking it up. But I know that they generally work much better in cold temperatures.

 

So maybe some sort of huge 250m plus rotating station could be made and run without much maintenance or energy input.

 

Did you not see the post about the negative issues regarding the regolith and associated charged dust particles? Also in the sun things heat up a lot - whilst there is no warming atmosphere so it may seem colder there is no atmosphere to allow heat dissipation in the ways this would happen on earth (ie warm up the air around you which gets replaced by colder air from further away). Engineering on the moon is fraught with difficulty

[mistermack]

 

Did you not see the post about the negative issues regarding the regolith and associated charged dust particles? Also in the sun things heat up a lot - whilst there is no warming atmosphere so it may seem colder there is no atmosphere to allow heat dissipation in the ways this would happen on earth (ie warm up the air around you which gets replaced by colder air from further away). Engineering on the moon is fraught with difficulty

I don't think high temperatures would be such a problem. The lack of atmosphere also means that the temperature in the shade is very cold, so if you don't want things to get hot, you can just shade them with a thin reflective material.

The dust would be a problem, but not insurmountable. I started a thread the other day about new filters being made from graphene oxide, that are so precise, they can filter out salt ions from seawater. They are also looking good for all sorts of ultra-fine filtration, including separating gases by filtering out the bigger molecules. So ultra-fine dust would be manageable with modern filtration methods.

 

But I'm sure that there will be loads of other unforeseen problems lurking.

 

Wikipedia now has a page on colonisation of the Moon.

They say that the Russians and Japanese are planning to have Moon bases by 2030, and the US is talking about something similar.

I doubt that any of it is realistic, but it will come eventually.

https://en.wikipedia.org/wiki/Colonization_of_the_Moon

[swansont]

I don't think high temperatures would be such a problem. The lack of atmosphere also means that the temperature in the shade is very cold, so if you don't want things to get hot, you can just shade them with a thin reflective material.

 

 

 

That only delays the problem. Nothing is 100% reflective. Eventually it heats up, and radiates according to its temperature.

[Danijel Gorupec]

 

 

That only delays the problem. Nothing is 100% reflective. Eventually it heats up, and radiates according to its temperature.

Multi-layer insulation is used on spacecrafts.

[Janus]

Multi-layer insulation is used on spacecrafts.

Which doesn't solve the problem, as it works both ways. It also prevents you from shedding excess waste heat. The space shuttle had panels on the inside of it cargo bay doors that were designed to radiate away the waste heat generated by the shuttle itself. This is why the shuttle kept those doors open while in orbit. a reflective surface plus a vacuum is essentially the principle behind the Dewar flask( more commonly known as a thermos bottle.), and while they are good at keeping cool things cool, they also keep hot things hot, and if what is in them is generating it own heat, what is inside will just get hotter and hotter.

[mistermack]

It's not all bad news for engineering on the Moon though.

Firstly, if you want to shade something, you can use incredibly thin and light materials, because of the lack of weather, and the low gravity.

So long as your shade was erected a short distance from what it's shading, overheating would be no problem at all.

The daytime temperatures max at about 125 c on the Moon. That's for a surface that's not very reflective at all.

A highly reflective material should stay reasonably cool. I don't remember the US flag melting on the stick.

 

Also, the Sun moves very slowly in the Sky on the Moon, so you wouldn't have to be constantly moving any shades that you erect.

[mistermack]

Horizon is on BBC at the moment, about telescopes. The James Webb space telescope has a plastic shade, to effectively block out the Sun's rays.

It's thin plastic sheeting, about the thickness of a human hair. About the size of a tennis court, and several layers, with a gap between each layer of a few inches. This is designed to keep the temperature of the telescope steady at minus 220c. so that it can pick up infra-red from the universe without swamping it with it's own infra-red.

 

Going by that, preventing things from overheating on the Moon would be pretty easy.

Edited April 24, 2017 by mistermack

[imatfaal]

Horizon is on BBC at the moment, about telescopes. The James Webb space telescope has a plastic shade, to effectively block out the Sun's rays.

It's thin plastic sheeting, about the thickness of a human hair. About the size of a tennis court, and several layers, with a gap between each layer of a few inches. This is designed to keep the temperature of the telescope steady at minus 220c. so that it can pick up infra-red from the universe without swamping it with it's own infra-red.

 

Going by that, preventing things from overheating on the Moon would be pretty easy.

 

Not a huge number of moving parts generating their own heat through friction, nor engines operating inefficiently, and the rest of the telescope (ie everything that may generate heat) is cooled to much lower by active systems so no bleed through from the rest. Any machinery on moon would be generating heat and that can only be radiated away or actively cooled by refrigerants

[mistermack]

 

Not a huge number of moving parts generating their own heat through friction, nor engines operating inefficiently, and the rest of the telescope (ie everything that may generate heat) is cooled to much lower by active systems so no bleed through from the rest. Any machinery on moon would be generating heat and that can only be radiated away or actively cooled by refrigerants

That's true, but machinery would all be electrical, not generating huge amounts of heat. They coped with the problem 45 years ago, so it shouldn't be too much of a problem now. Astronauts produce heat, but the suits coped with that, and the direct sunlight.

Cooling by radiation will be much faster with no clouds or atmosphere. Even at mid Lunar Day, a radiant surface that is shaded would shed heat very fast.

[imatfaal]

That's true, but machinery would all be electrical, not generating huge amounts of heat. They coped with the problem 45 years ago, so it shouldn't be too much of a problem now. Astronauts produce heat, but the suits coped with that, and the direct sunlight.

Cooling by radiation will be much faster with no clouds or atmosphere. Even at mid Lunar Day, a radiant surface that is shaded would shed heat very fast.

 

Hmm.

 

[latex]\frac{q}{A}=\sigma \cdot T^4 [/latex]

 

where q is the Watts given off , A is the Area (so LHS is Power per area, ie the Joules per second per Square metre), Sigma is the Stefan-Boltzman Constant,and T is the absolute Temperature. If you want to be keeping stuff at superconductor temperature then lets say that your ratdiators are at 200K

 

[latex]\frac{q}{A}=\sigma \cdot T^4 = 5.67*10^{-8} \cdot 200^4 = 5.67*16 = 91 Watts/m^2[/latex]

 

That's pretty damn poor. And that is basis a perfect blackbody radiator at abs zero. Your surface will be a grey body and will not be at abs zero

 

[latex]\frac{q}{A}= \epsilon \cdot \sigma \cdot (T_{radiator}^4 - T_{surroundings}^4)[/latex]

 

T_surroundings will be greater than zero so will reduce your emission and epsilon will be less than 1 so will further reduce them

[mistermack]

I seem to remember reading recently that superconductors have advanced hugely recently, and no longer need the extremes of cold that they originally required.

There is even serious talk of achieving superconduction at temperatures in the region of room temperature.

I can't give a link for that, but it was very recently.

 

Just checked on Wikipedia, and they have a whole page on high temperature superconductors.

"HTS have been observed with transition temperatures as high as 138 K (−135 °C), and can be cooled to superconductivity using liquid nitrogen.^[2] Until 2008, only certain compounds of copper and oxygen (so-called "cuprates") were believed to have HTS properties, and the term high-temperature superconductor was used interchangeably with cuprate superconductor for compounds such as bismuth strontium calcium copper oxide (BSCCO) and yttrium barium copper oxide (YBCO). Several iron-based compounds (the iron pnictides) are now known to be superconducting at high temperatures.^[5][6][7]";

The latest discovery is high pressure H2S, which can operate at about 200K.

https://en.wikipedia.org/wiki/High-temperature_superconductivity

 

So there is a real prospect of superconductors being usable on the Moon with just an effective sun shade.

Especially, given the length of time that will have passed, by the time serious use is being made of the Moon.

It would be surprising if no more progress had been made by then in the HTS field.