Moonbase

[Exarch]

i'm fascinated by space exploration, and especially moon colonisation.
so what does it mean when ppl say things like 'whoever controls the moon, determines who gets on and gets off the earth?"
and isnt the moon supposed to be military free? (outer space treaty)

and how would several moonbases affect the tides on earth? plus i reckon the moon would not look as pristine as it does now if some installations are built on the side facign us...

[CtrlAltDe1337]

I can see it now, Moon War I

[christof139]

Moonbases wouldn't affect the tides on earth to ANY MEASURABLE DEGREE, just as the earth's cities and huge mountain ranges don't affect the spin of the earth to any great degree.

Chris

[Tiwaz]

i'm fascinated by space exploration, and especially moon colonisation.
so what does it mean when ppl say things like 'whoever controls the moon, determines who gets on and gets off the earth?"

Well, Moon circles us out there. If someone were to put, for example, some railguns into the Moon... Anything coming to Earth would have to come past orbit of Moon. This being space, it means they could be shot at way before they get to orbit. Moon has no air and low escape velocity so it would not be all that difficult. And out in the space, there simply wouldn't be anything to slow down those pellets so they could start rather early on.

Of course you could try to evade pellets fired by railguns, but considering that they could be small enough to make radar useless... You would have to evade blindly. Notice that it means you would be wasting lots of energy doing so as well.

Bigger problem if anyone had moonbase, railgun/accelerator and bad attitude is detail that they sit at the edge of Earth gravity well. If they toss big packets into our direction, they will come down. Hard. Big enough pile of moonrock and it will turn into meteorite and hit something on Earth.

[Juvenal]

These issues are all rather nicely explored in Robert Heinlein's novel The Moon is a Harsh Mistress (1966).

Heinlein managed to include an incredible number of ideas in this re-telling of the American Revolution. If you find some of them unsurprising, then try to remember he was writing this in 1965 when no one had yet landed on the Moon, mixed-marriages were almost unheard of, computers were the size of large rooms and dumb-terminals were state-of-the-art.

• Lunar ice
• Hydroponics
• Rail-guns
• Emergent A.I.
• Virtual reality
• Orbital mechanics
• Sociology of penal colonies
• Alternative forms of marriage
• Anarcho-capitalism as a viable government model
• Advantages of being at the top of a gravity-well

It is definitely my favourite Heinlein story and I would recommend it to anyone.

[Simetrical]

Well, Moon circles us out there. If someone were to put, for example, some railguns into the Moon... Anything coming to Earth would have to come past orbit of Moon.

Not if you stick to the opposite side of the Earth.

Bigger problem if anyone had moonbase, railgun/accelerator and bad attitude is detail that they sit at the edge of Earth gravity well. If they toss big packets into our direction, they will come down. Hard. Big enough pile of moonrock and it will turn into meteorite and hit something on Earth.

Not quite so easy. If you just drop something, it will begin orbiting the Earth. You have to reduce its angular momentum enough for it to fall into the atmosphere, which requires a considerable amount of energy for a large object. Once it hits the atmosphere it will fall, losing the rest of its angular momentum to air friction. But that will also burn away a large part of the projectile.

So maybe doable, but not exactly simple. Maybe not even simpler than launching rockets, I don't know.

[Tiwaz]

Not if you stick to the opposite side of the Earth.

Which, due to Moon orbiting Earth, equals to running insanely large spiral in an attempt to keep Earth as cover. And hoping they do not toss junk in the way of your approach.

Not quite so easy. If you just drop something, it will begin orbiting the Earth. You have to reduce its angular momentum enough for it to fall into the atmosphere, which requires a considerable amount of energy for a large object. Once it hits the atmosphere it will fall, losing the rest of its angular momentum to air friction. But that will also burn away a large part of the projectile.

So maybe doable, but not exactly simple. Maybe not even simpler than launching rockets, I don't know.

It's all math. Once huge piece of rock is on certain trajectory, it will remain on it. This being space after all.

Route rock takes is possible to calculate with computers. Energy on the other hand is not problem on the Moon, where you have lots of space (for solar panels for example) and suitable helium for fusion.

Stones would be rather effective weapons, biggest problem being of course possibility of attempted missile interception. And yeah, they will lose a lot of mass... But it's not like there isn't a lot of junk out there to use.

With Moon as staging point, if you can use helium available etc, you could use spacecraft far more efficiently to fetch more material further out without need to fight Earth gravity.

It's one of more realistic uses for Moon... Refuelling point before rest of solar system.

[Simetrical]

Well, Moon circles us out there. If someone were to put, for example, some railguns into the Moon... Anything coming to Earth would have to come past orbit of Moon.

Not if you stick to the opposite side of the Earth.

Bigger problem if anyone had moonbase, railgun/accelerator and bad attitude is detail that they sit at the edge of Earth gravity well. If they toss big packets into our direction, they will come down. Hard. Big enough pile of moonrock and it will turn into meteorite and hit something on Earth.

Not quite so easy. If you just drop something, it will begin orbiting the Earth. You have to reduce its angular momentum enough for it to fall into the atmosphere, which requires a considerable amount of energy for a large object. Once it hits the atmosphere it will fall, losing the rest of its angular momentum to air friction. But that will also burn away a large part of the projectile.

[Juvenal]

...Not quite so easy. If you just drop something, it will begin orbiting the Earth. You have to reduce its angular momentum enough for it to fall into the atmosphere, which requires a considerable amount of energy for a large object. Once it hits the atmosphere it will fall, losing the rest of its angular momentum to air friction. But that will also burn away a large part of the projectile.

Heinlein explained all of this quite well. Earth launches require 8 km/sec just to achieve orbit, and more than 11 km/sec for escape velocity. But the Moon's orbital velocity is only 1.03 km/sec. So I assume this is all you need to achieve relative to the Moon to launch an object to intersect the Earth.

Launching an object from the Moon with a rail-gun is straighforward because there is no air-resistance and the rail-gun can be almost horizontal. The object could be a large rock wrapped in a metal jacket or mesh for the rail-gun to act upon (Heinlein, writing in 1965, was actually describing a Gauss-gun consisting of stator rings activated in sequence rather than a rail-gun).

The rail-gun would be pointing back along the Moon's orbit, and could select any target on Earth just by changing the launch time and velocity.

Air-resistance is only significant for small objects. If you are launching a large rock (i.e. tons rather than ounces) then there will only be time for the surface layer to ablate off before it hits your target. Time in atmosphere is actually going to be quite short.

I believe that meteorites are often found to be cold to the touch even just after landing, because the heat generated by air friction has vapourised the surface layer in flight but didn't have time to conduct far into the body of the meteorite.

Intercepting a large rock is going to be quite hard. Interceptors are designed to deal with other missiles, they only have small explosive power to destroy the guidence and detonation mechanisms of the target. Big rocks don't have any mechanisms, so most interceptors are going to have negligible effect on them.

[Simetrical]

Which, due to Moon orbiting Earth, equals to running insanely large spiral in an attempt to keep Earth as cover. And hoping they do not toss junk in the way of your approach.

The Moon orbits the Earth with a period on the order of thirty days (depending on how you count). That's far longer than it would take to get out of the effective range of a reasonable weapon. Moreover, there's no way you can achieve any accuracy with a projectile weapon against a small target moving at thousands of miles an hour from thousands of miles away. The target only has to shift its course by a fraction of a degree every few minutes for your projectile to miss by miles.

It's all math. Once huge piece of rock is on certain trajectory, it will remain on it. This being space after all.

Unless deflected. A rock large enough to cause serious damage would be extremely easy to detect and intercept. A sufficient quantity of explosives would cause it to fragment into pieces small enough to break up in the atmosphere.

Stones would be rather effective weapons, biggest problem being of course possibility of attempted missile interception. And yeah, they will lose a lot of mass... But it's not like there isn't a lot of junk out there to use.

Every pound of mass means that much more energy and impulse needed to accelerate: that many more engines to fabricate, or that much more damage to your rail gun, or that much more fuel to load up, etc. It might well prove to be more feasible to fabricate a small quantity of high explosives than to expend the resources to move a much greater mass of rock.

With Moon as staging point, if you can use helium available etc, you could use spacecraft far more efficiently to fetch more material further out without need to fight Earth gravity.

It's one of more realistic uses for Moon... Refuelling point before rest of solar system.

No more useful, really, than an orbiting space station. Indeed, a space station in high Earth orbit has less of a gravity well to contend with than the Moon does. It does also have less ready access to raw resources, of course.

Heinlein explained all of this quite well. Earth launches require 8 km/sec just to achieve orbit, and more than 11 km/sec for escape velocity. But the Moon's orbital velocity is only 1.03 km/sec. So I assume this is all you need to achieve relative to the Moon to launch an object to intersect the Earth.

Less than that, really, yes. You can do it, but you do need some kind of sophisticated propulsion system. 1 km/s is nothing to sneeze at; the Voyager probes aren't moving at more than 20 km/s, and they've had decades to accelerate.

Launching an object from the Moon with a rail-gun is straighforward because there is no air-resistance and the rail-gun can be almost horizontal. The object could be a large rock wrapped in a metal jacket or mesh for the rail-gun to act upon (Heinlein, writing in 1965, was actually describing a Gauss-gun consisting of stator rings activated in sequence rather than a rail-gun).

The rail-gun would be pointing back along the Moon's orbit, and could select any target on Earth just by changing the launch time and velocity.

If you had a rail gun miles long, perhaps you could achieve the needed velocities without damaging it, yes. On the other hand, you could do the same from the Earth. You would need to vacuum-seal the rail gun, which is doable, and then just make sure everything gets out of the way of the projectile. If it's large enough to survive going down through the atmosphere, it should be large enough to survive going down, too.

I still don't think that rocks would make the best projectiles. They're just too massive for their effect. It would be cheaper and easier to simply launch a thermonuclear missile, whether from the Moon to Earth or vice versa. It would have about the same effect as a large enough rock, but it would be much cheaper to launch, harder to intercept, and faster (given the same amount of propulsion). It would also be easier to build, presumably, given that currently we can build thermonuclear missiles but not effective rail guns.

Intercepting a large rock is going to be quite hard. Interceptors are designed to deal with other missiles, they only have small explosive power to destroy the guidence and detonation mechanisms of the target. Big rocks don't have any mechanisms, so most interceptors are going to have negligible effect on them.

But big rocks are much larger targets, hence easier to hit. The interceptor missiles merely need to be made more powerful. They could use tactical nukes if necessary. Alternatively, Earth could respond by launching a smaller rock to knock the larger one off course. As I outlined above, it would be about as feasible to build a big Earth rail gun as a big Moon rail gun, although doubtless the former would be more expensive for the same payload.

[Tiwaz]

The Moon orbits the Earth with a period on the order of thirty days (depending on how you count). That's far longer than it would take to get out of the effective range of a reasonable weapon. Moreover, there's no way you can achieve any accuracy with a projectile weapon against a small target moving at thousands of miles an hour from thousands of miles away. The target only has to shift its course by a fraction of a degree every few minutes for your projectile to miss by miles.

You forget that in space there is not necessarily effective range. Given enough velocity, small projectiles have ability to be rather lethal. And are cheap and cheerful to toss around. Thus, lots of shifts in course to avoid all incoming fire.

Again, there is also the problem of missiles. Moon launched missile has greater range due to reduced gravitational pull to fight against.

Unless deflected. A rock large enough to cause serious damage would be extremely easy to detect and intercept. A sufficient quantity of explosives would cause it to fragment into pieces small enough to break up in the atmosphere.

And again you have to use resources to deflect it. Rocks are cheap unlike missiles so to say. Nothing says you have to put single rock on collision course.

Every pound of mass means that much more energy and impulse needed to accelerate: that many more engines to fabricate, or that much more damage to your rail gun, or that much more fuel to load up, etc. It might well prove to be more feasible to fabricate a small quantity of high explosives than to expend the resources to move a much greater mass of rock.

As said, question of energy is rather moot in Moon. Solar energy is plentiful thanks to permanent tilt of the Moon.

No more useful, really, than an orbiting space station. Indeed, a space station in high Earth orbit has less of a gravity well to contend with than the Moon does. It does also have less ready access to raw resources, of course.

You have to take into account also space. Everything for space station has to be brought from elsewhere and expanding means building more with imported resources. Along with vulnerability.

If you dig your base into Moon, you can put several meters of rock, dust etc between you and vacuum. Hell, even dozens of meters if you want to go mole. And expansion is question of digging more. Space station is limited to it's hull.

[Juvenal]

Every pound of mass means that much more energy and impulse needed to accelerate: that many more engines to fabricate, or that much more damage to your rail gun, or that much more fuel to load up, etc. It might well prove to be more feasible to fabricate a small quantity of high explosives than to expend the resources to move a much greater mass of rock....

...If you had a rail gun miles long, perhaps you could achieve the needed velocities without damaging it, yes...

Gauss Gun
I think we are debating at cross-purposes here. Heinlein's magnetic catapult (Gauss Gun), or something like it, seems a sensible idea and worth building if we are going to have a substantial Lunar base.

In the story it was a Moon-based launch system for sending produce back to Earth. Although he didn't mention it, I would imagine it was nuclear powered. It was indeed miles long and consisted of a series of stator rings (i.e. electro-magnets) which were switched on and off in succession to pull the payload along a straight track.

The rebels of the story took control of the catapult and used it to demonstrate that dropping rocks from the moon was equivalent to having an unlimited nuclear missile arsenal (that is until the catapult gets bombed).
I don't see why such a system operating on metal objects in a vacuum shouldn't be able to accelerate large masses to 1 km/sec.

It is much less attractive as an Earth-based system because it would been to be much longer and more powerful, and because your payload would need to be massive and rugged enough able to cope with moving at escape velocity in the lower atmosphere.

Unless deflected. A rock large enough to cause serious damage would be extremely easy to detect and intercept. A sufficient quantity of explosives would cause it to fragment into pieces small enough to break up in the atmosphere.

I still don't think that rocks would make the best projectiles. They're just too massive for their effect. It would be cheaper and easier to simply launch a thermonuclear missile, whether from the Moon to Earth or vice versa. It would have about the same effect as a large enough rock, but it would be much cheaper to launch, harder to intercept, and faster (given the same amount of propulsion). It would also be easier to build, presumably, given that currently we can build thermonuclear missiles but not effective rail guns.

But big rocks are much larger targets, hence easier to hit. The interceptor missiles merely need to be made more powerful. They could use tactical nukes if necessary. Alternatively, Earth could respond by launching a smaller rock to knock the larger one off course. As I outlined above, it would be about as feasible to build a big Earth rail gun as a big Moon rail gun, although doubtless the former would be more expensive for the same payload.

Utility of big rocks
A large rock intersecting the Earth at several km per second is going to have vast kinetic energy. A normal (non-nuclear) interceptor will have no effect. A nuclear interceptor may split the rock, but it will still retain its kinetic energy and still hit just as hard. It therefore doesn't matter that the rock is a big target and easy to hit since it can't actually be stopped. Vapourising a big rock requires really big bombs.

It is not cheap and easy to launch thermonuclear missiles, one missile will buy you thousands of big rocks in mesh jackets. Admittedly building a multi-kilometre Gauss Gun on the Moon would be very expensive, but once it is in place, individual launches would be very cheap.

[volpesmagnus]

a base on the moon would help a great deal with refueling space craft before returning to their journey. the lack of the atmosphere would save a lot of fuel during take-off.

[Simetrical]

"Enourmous Rail Guns" are an anachronism today, as Sim said, with the themonuclear and intercontinental ballistic missiles being able to to do the same or more damage without the need for a huge tube.

Well, I wouldn't go that far. Rail guns launching massive rocks at Earth are pointless, as I say. Rail guns used for other purposes might be very useful, ultimately perhaps as a replacement for conventional firearms.

[chris_uk_83]

But surely, if they've got a moonbase with railguns on it and you want to leave the Earth you simply wait until your bit of the Earth is pointing away from the moon!

[Redem]

But surely, if they've got a moonbase with railguns on it and you want to leave the Earth you simply wait until your bit of the Earth is pointing away from the moon!

It's a fair distance, you would have to time it so that the part you want to hit was turned towards you just as the projectile hits the surface.

And as long as you don't care too much about what you hit. Railguns fire unguided projectiles, so you can't correct course at the last minute, and again with such a huge distance, hitting something specific will be near impossible.


Other problems are that you are outside the magnetosphere of the earth most off the time, so your railgun will be subject to solar winds, which will decimate the electronic of it.

[Exarch]

what other strategic reasons would one want to colonise the moon?

[Syron]

what other strategic reasons would one want to colonise the moon?

Quite a few, from it being the perfect staging point for further exploration or asteroid mining to the potential mining of Helium-3 which is a much more viable fuel for Nuclear Fusion than D/T.


Of course this would be complex given the Outer Space Treaty.

[Exarch]

Quite a few, from it being the perfect staging point for further exploration or asteroid mining to the potential mining of Helium-3 which is a much more viable fuel for Nuclear Fusion than D/T.


Of course this would be complex given the Outer Space Treaty.

i think we're currently witnessing the tearing up of the outer space treaty
http://www.globalissues.org/Geopolit...trol/Space.asp

[Syron]

I'm pretty sure that as China increases it's capabilities in space the US will be forced into a compromise on Space Weaponisation. Simply put China will eventualy be in a much stronger position and a pro-weaponisation American policy would backfire and give China even more influence.