Author Topic: Luna Lithobraking strip :)  (Read 13977 times)

Offline KelvinZero

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Luna Lithobraking strip :)
« on: 11/20/2008 08:14 am »
(  Tom Ligon mentioned something possibly exactly the same here: http://forum.nasaspaceflight.com/index.php?topic=14070.0 )

At some point in history after the VSE but before any complex manufacture is possible on the moon we may wish to land large scale payloads more cheaply.

The proposal is saving the cost of the landing stage by skidding to a halt along a specially prepared strip of fine regolith. I imagine this strip will have to be hundreds of kilometers long so it is fairly far in the future. However it only involves some snow plow/ snow-blower like contraption rather than complex manufacturing. These machines might not need to be dedicated to this task so that might offset the cost somewhat.

Lets say we have our strip, as wide as an air strip, consisting of super fine absolutely level dust and perhaps bounded by all the larger dust and rocks we have raked aside. What about the craft?

Unlike an airplane, there is no air so the only force 'throwing' the craft into the runway is the moon's gravity, which would grow smoothly from 0 to 1/6g as you slowed.

I imagine something fairly front heavy with a long lightweight tail to give maximum leverage to some fairly low power steering thrusters at the back. Their main purpose is to stop the tail rising due to the friction at the front.

Im not sure what we would use at the front for friction but it might not involve any direct contact. What I think you are more likely to get is an aircushion-like effect of dust particles bouncing between the contact surface and the ground, explosively stirring up more particles. Perhaps a fine spray of water could be used to hit the ground ahead of the craft to adjust the density of this cushion. Even water would explode like rocket fuel on contact due to the velocity difference between the craft and the ground. With careful design most of the energy could be disappated in dust hitting dust rather than in grinding away the hull of your craft.
« Last Edit: 11/20/2008 08:27 am by KelvinZero »

Offline Vacuum.Head

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Re: Luna Lithobraking strip :)
« Reply #1 on: 11/20/2008 09:39 pm »
Sorry if this is OT for the thread but if you are going to have a landing strip why not an arrestor cable system. Could be an interesting material science problem!
http://en.wikipedia.org/wiki/Arrestor_cable
I also remember reading somewhere, probably in the halcyon daze of O'Neillan Space Colonisation, of an inverse Lunar Catapult using electromagnetic breaking for dumb (and high g) tolerant payloads. But the idea was to get the mass into orbit and process it there!
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Offline KelvinZero

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Re: Luna Lithobraking strip :)
« Reply #2 on: 11/21/2008 06:24 am »
Sorry if this is OT for the thread but if you are going to have a landing strip why not an arrestor cable system. Could be an interesting material science problem!
http://en.wikipedia.org/wiki/Arrestor_cable
I also remember reading somewhere, probably in the halcyon daze of O'Neillan Space Colonisation, of an inverse Lunar Catapult using electromagnetic breaking for dumb (and high g) tolerant payloads. But the idea was to get the mass into orbit and process it there!

The arrestor cable sounds like it is to solve a shortage of landing strip? As far as I know there isnt any shortage of flat areas on the moon, given a willingness to fill some potholes. What we want is to avoid stopping too quickly.

If I got my maths right, if you can decelerate at 3g, starting from 2.4k/s then it would take 80 seconds and about 100km of landing strip. (2.4km/s might be overstating it a bit since you would probably already be in orbit.)


Offline tnphysics

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Re: Luna Lithobraking strip :)
« Reply #3 on: 12/06/2008 02:17 am »
Plus, the energy can be captured (for a wheeled system) by onboard generators and beamed to a base or ascent vehicle.

Such a system could also be used for launch from the Moon.

Offline KelvinZero

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Re: Luna Lithobraking strip :)
« Reply #4 on: 12/06/2008 05:54 am »
Plus, the energy can be captured (for a wheeled system) by onboard generators and beamed to a base or ascent vehicle.

Such a system could also be used for launch from the Moon.

Im guessing that when you start talking about capturing energy and relaunching, you really want some sort of mass driver. That has been a dream since the seventies. I would love to see not just mass drivers but maglev tracks that circle the moons equator, so you could accelerate or decelerate as gently as you like. (and also share power from the day side to the night side)

When we have an industry on the moon that supports a few hundred thousand people such things will come. But how to get there from here?

On the issue of wheels, I expect a typical design would rip itself apart if it tried to rotate at about 2.3km/s on its rim.

I did wonder if instead of a wheel you could have a spinning centre that extruded tiny hairs, tens of meters long, like the spokes of a bicycle wheel. At the speeds we are talking about the hairs would be very rigid at the rim and possibly enough to support a craft against lunar gravity as the hairs rapidly wore down.


Offline kkattula

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Re: Luna Lithobraking strip :)
« Reply #5 on: 12/06/2008 08:56 am »
Some sort of mag-lev so the vehicle never touches the strip until it's slowed down?

Of course that's a little harder to build than a regolith strip.

Offline KelvinZero

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Re: Luna Lithobraking strip :)
« Reply #6 on: 12/06/2008 11:44 am »
Yes way way harder. Great for some moderately distant future. We cant build maglev tracks on the moon until we actually have a heavy industry there.

My thought was that the luna landing strip might be a cheaper way of landing the initial industry than rockets. It would be no good for initial exploration and made redundant once we have something like the maglev scheme.

Offline HarryM

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Re: Luna Lithobraking strip :)
« Reply #7 on: 12/06/2008 03:41 pm »
Seems at the very high speeds some sort of sphere would be better than a sled. Spin it up very fast so there is less of an instant rotational speed change when it hits the landing zone.

Offline gospacex

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Re: Luna Lithobraking strip :)
« Reply #8 on: 12/06/2008 04:15 pm »
Lets say we have our strip, as wide as an air strip, consisting of super fine absolutely level dust and perhaps bounded by all the larger dust and rocks we have raked aside.

It already exists, but it is on Mimas, covered by very fine snow, and needs to be able to accept 100-150 m/s fast objects only, due to small size and density of Mimas.

Ultimate skiing experience.

Offline KelvinZero

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Re: Luna Lithobraking strip :)
« Reply #9 on: 12/07/2008 01:30 am »
If the sphere does not come apart it might roll too well. You need it to decelerate at something like 3g to stop within a hundred km.

By 'sled' I was actually thinking more along the lines of a ground-effect machine. The dust particles bouncing between the ground and the 'sled' could form a sort of aircushion-like effect.

Offline KelvinZero

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Re: Luna Lithobraking strip :)
« Reply #10 on: 12/07/2008 01:37 am »
It already exists, but it is on Mimas, covered by very fine snow, and needs to be able to accept 100-150 m/s fast objects only, due to small size and density of Mimas.

Ultimate skiing experience.

As a ski resort, I wish Mimas were a little closer. I guess it keeps the riff-raff out.

Offline kkattula

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Re: Luna Lithobraking strip :)
« Reply #11 on: 12/07/2008 01:58 am »
Here's a thought, the rim of a wheel toucing the ground is not moving horizontally relative to the ground, unless it's skidding. So if you spin the wheel up to the correct speed before touchdown, (about 14,000 rpm for 1 m radius wheels at orbital velocity), the main friction should be on the axle bearing. Which could be magnetic.

Offline KelvinZero

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Re: Luna Lithobraking strip :)
« Reply #12 on: 12/07/2008 05:52 am »
Here's a thought, the rim of a wheel toucing the ground is not moving horizontally relative to the ground, unless it's skidding. So if you spin the wheel up to the correct speed before touchdown, (about 14,000 rpm for 1 m radius wheels at orbital velocity), the main friction should be on the axle bearing. Which could be magnetic.


using a=v^2/r (with v = 2.4*1000 m/s and r = 1m)
I calculate the inwards-acceleration at the rim to be about 5.8 million m/s^2, which equates to about about half a million gravities.

I dont know if any material could stand that. but there is another problem:

If you intend to do your breaking using the axel bearing then you still have to transfer your momentum though the wheel to the ground. This implies a very good grip. But if you have anything like a tire tread then you have the ridges of these treads pounding into the ground at orbital velocities.

Finally you would have to do something with the huge energies you are collecting: the entire orbital velocity of the craft converted to electricity within about 80 seconds if we are going with my 3g decelleration/100km track statistics. In the case of a mass driver or maglev you have the tracks themselves which could connect to some arbitrarily large storage.
« Last Edit: 12/07/2008 05:58 am by KelvinZero »

Offline Robotbeat

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Re: Luna Lithobraking strip :)
« Reply #13 on: 12/07/2008 06:58 am »
If you're using a wheel with a magnetic bearing, then couldn't you do the exact same thing BUT IN REVERSE??? (in other words, accelerate with wheels to--or near to--lunar orbit) It seems to me that if the wheel idea could work, it would work it the opposite direction as well, except you would probably use over-head power lines to power the craft.

BTW, a wheel approach could possibly work since the fastest land speed record is 341 m/s, and I'm sure the limit is not the wheels. This surely needs some advanced materials, but seems within reach of material science.
« Last Edit: 12/07/2008 07:00 am by Robotbeat »
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Offline KelvinZero

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Re: Luna Lithobraking strip :)
« Reply #14 on: 12/07/2008 09:10 am »
there is quite a big difference between 2400 m/s and 340 m/s.

In terms of velocity it is 'only' a factor of 7. But in terms of kinetic energy it is a factor of 7 squared, ie almost 50 times more energy/kg.

In principle these things might work in reverse, but instead of wheels and powerlines I think we are definitly in the realm of mass-drivers and maglevs here. These devices are entirely reasonable.. eventually.

Offline William Barton

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Re: Luna Lithobraking strip :)
« Reply #15 on: 12/07/2008 09:51 am »
If you're using a wheel with a magnetic bearing, then couldn't you do the exact same thing BUT IN REVERSE??? (in other words, accelerate with wheels to--or near to--lunar orbit) It seems to me that if the wheel idea could work, it would work it the opposite direction as well, except you would probably use over-head power lines to power the craft.

BTW, a wheel approach could possibly work since the fastest land speed record is 341 m/s, and I'm sure the limit is not the wheels. This surely needs some advanced materials, but seems within reach of material science.

You could call this thing, "The Moon Trolley." Definitely a 19th Century Lunar Mass Driver! Somewhere in France, Jules Verne is sitting up in his grave, clapping a hand to his forehead, and crying out, "D'oh!"

Offline hop

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Re: Luna Lithobraking strip :)
« Reply #16 on: 12/07/2008 09:54 am »
BTW, a wheel approach could possibly work since the fastest land speed record is 341 m/s, and I'm sure the limit is not the wheels. This surely needs some advanced materials, but seems within reach of material science.
Wheels used in top end land speed vehicles actually present significant engineer challenges. ThrustSSC pushed the limit of very carefully manufactured solid aluminum wheels. The next generation car will use titanium. See http://www.bloodhoundssc.com/car/wheels.cfm

The whole concept of a lunar landing strip, wheels or not, strikes me as a completely nuts. Even if it could work in theory, by the time we have the capability to land the hundreds of tons of equipment needed to completely smooth 100km of lunar regolith, we will by definition have solved that problem pretty well. The dV needed to get on and off the moon is well within the reach of conventional rockets.

Offline Robotbeat

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Re: Luna Lithobraking strip :)
« Reply #17 on: 12/07/2008 03:29 pm »
(Monocrystalline silicon ingot, I've seen prices of around $350/kg, still well over an order of magnitude less than getting the same mass into orbit)

Well, solid aluminum is all well and good, but mono-crystalline silicon has about 20 times the tensile strength. It would be very difficult, indeed. (There are also flywheels that operate at supersonic speeds, so this seems possible, especially in the Moon's lowered gravity.) Also, by tapering the thickness of the material, you can get away with lower tensile strength than otherwise (much like a space elevator).

It seems to me that there's no way to have a coefficient of static friction of 18 (3G of de/acceleration and the Moon's gravity of about 1/6 G; it's static friction in the case of a wheel). Basically, we have to have a monorail system, where you can clamp a wheel on each side of a rail in order to provide unlimited acceleration--unlimited in terms of coefficient of friction, since you can just squeeze the rail tighter (probably also want a third wheel on top). Of course, you are even further pushing material properties to the limits in this case.

The question is: Is it easier to build a 50 km (for 6-Gs instead of only 3) monorail with really high-speed wheels or just go the whole way and build a 50-km maglev system, which wouldn't put the materials as far to their limit? Either one would probably be easier for launching stuff than landing stuff, but a monorail seems to me much easier to make using lunar regolith.

It also seems to me that you should just go to the limits of physiology and go with 9 or 10 G's so that you can build the shortest monorail/maglev possible. It'd still be ~30 km, though.

Another possibility is to only launch a craft high and fast enough that a lower-thrust but much higher ISP engine could be used to actually achieve orbit, perhaps some sort of advanced ion engine. This could limit the length of track required even more, perhaps to a reasonable length of under 1 km. Also, since your speeds would be greatly reduced, your material properties can be much further from the limits

Quote
The whole concept of a lunar landing strip, wheels or not, strikes me as a completely nuts.
I agree! But it's still fun to speculate. ;)
« Last Edit: 12/07/2008 04:44 pm by Robotbeat »
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Offline A_M_Swallow

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Re: Luna Lithobraking strip :)
« Reply #18 on: 12/07/2008 06:44 pm »
Using delta_E = 0.5 * m * (v02 - v12)

A 3g landing strip for an object moving at 2.4 km/s would have to absorb up to 70 kJ per second for every kilogram that lands.  The 70 kJ would be over 2.4 km.  At the start of the landing a 50 mT lander would supply 1.46 MJ per metre, decreasing as it goes along.

A possible way of cooling the landing strip is to radiate the heat away over say the next hour.

The launcher and the landing strip can be separate machine.

A maglev launcher could rotate around the rim of a crater.  Constant acceleration launches may be nearly impossible but by taking several hours to get to escape velocity a constant energy system is possible.  (This is covered in other threads.)

Offline hop

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Re: Luna Lithobraking strip :)
« Reply #19 on: 12/07/2008 10:51 pm »

Well, solid aluminum is all well and good, but mono-crystalline silicon has about 20 times the tensile strength. It would be very difficult, indeed. (There are also flywheels that operate at supersonic speeds, so this seems possible, especially in the Moon's lowered gravity.) Also, by tapering the thickness of the material, you can get away with lower tensile strength than otherwise (much like a space elevator).
Tensile strength is all well and good, but what happens when it hits a tiny imperfection in the surface, or a dust grain ?

Very slight damage / erosion of the wheel would fatally compromise balance.


Offline kkattula

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Re: Luna Lithobraking strip :)
« Reply #20 on: 12/08/2008 03:03 am »
Trying to land at > escape velocity (2.4 km/s) is 'just silly' (TM).

Orbital velocity makes 'more' sense since the vehicle will follow the curvature of the moon, using friction to slow it down. 100 km may be a bit short.

Really big wheels?

Offline A_M_Swallow

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Re: Luna Lithobraking strip :)
« Reply #21 on: 12/08/2008 03:17 am »
You land at what ever speed you have when you arrive.  The spacecraft may have to be below orbital speed to be horizontal relative to the landing strip.

I suspect there will have to be a magnetic linkage between the strip and the spacecraft to prevent them from touching at high speed.

Offline usn_skwerl

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Re: Luna Lithobraking strip :)
« Reply #22 on: 12/08/2008 06:14 am »
If engineered right, what about a sort of tapered chute or track for semi-rigid outrigger type protrusions. The outrigger devices would resemble something similar to crumple frames like on a car. Easy, inexpensive and reliable for safe deceleration in <20 miles.


Another idea could be something like runaway truck ramps have, but made of a type of foam or other energy absorber. visualize something like using cardboard boxes to slow/stop a vehicle in a car jump stunt.
« Last Edit: 12/08/2008 06:15 am by usn_skwerl »
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Offline KelvinZero

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Re: Luna Lithobraking strip :)
« Reply #23 on: 12/08/2008 07:07 am »
In the original idea, all that was required was a 100km long landing strip composed of dust selected for fineness.

This would require some fairly robust sort of snowblower like device, but still far less effort than the industry to construct the components for either a high performance mass driver of 100km that could slow large objects at 3g, or a lower performance maglev that extended much further than 100km, to allow slower deceleration.

It would not require perfect smoothness because the lander does not need to come into direct contact with the ground. The intention was to develop a sort of ground effect/ air cushion, where the superfine dust used to form the strip acts almost like an atmosphere trapped between the craft and the landing strip. Because these particles are caused to bounce forwards to raise up more particles infront of the craft, the entire front surface would be armored against this, a thick metal heatshield of some type. So the decelerating force is spread over a fairly wide area, just as when you enter an atmosphere.

The initial dust could be raised by spraying something ahead of the craft as it came in for landing, so at no time (until it slowed) would the craft need to actually contact the surface. Perhaps the initial range would be a few feet.

The strip would be repaired by the snowblower as needed.

Offline hop

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Re: Luna Lithobraking strip :)
« Reply #24 on: 12/09/2008 06:06 am »
This would require some fairly robust sort of snowblower like device, but still far less effort than the industry to construct the components for either a high performance mass driver of 100km that could slow large objects at 3g, or a lower performance maglev that extended much further than 100km, to allow slower deceleration.
You would need a lot more than a snowblower. You would inevitably have to fill craters and rilles, knock down local hills, move or blast through boulders and so on. So you need earth-moving (err moon-moving) equipment at least similar to what would be required to build a 100km stretch of freeway on earth. This alone will run into hundreds or thousands of tons with conventional equipment. Then you need the equipment and facilities to maintain it. Given how nasty and abrasive regolith is, wear is going to be major factor. It's not soft and fluffy like snow... try running a hundred km of fresh granite dust through your snowblower ;)

All of the above on the highly dubious assumption that the dust cushion idea is workable.

Offline usn_skwerl

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Re: Luna Lithobraking strip :)
« Reply #25 on: 12/09/2008 06:23 am »
my examples were just simple, safe, reliable concepts. brainstorming, if you will.
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Offline KelvinZero

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Re: Luna Lithobraking strip :)
« Reply #26 on: 12/09/2008 08:03 am »
You would need a lot more than a snowblower. You would inevitably have to fill craters and rilles, knock down local hills, move or blast through boulders and so on. So you need earth-moving (err moon-moving) equipment at least similar to what would be required to build a 100km stretch of freeway on earth. This alone will run into hundreds or thousands of tons with conventional equipment. Then you need the equipment and facilities to maintain it. Given how nasty and abrasive regolith is, wear is going to be major factor. It's not soft and fluffy like snow... try running a hundred km of fresh granite dust through your snowblower ;)

All of the above on the highly dubious assumption that the dust cushion idea is workable.

It works or it doesnt. Name calling has nothing to do with it. Its not like you have to build the thing to test the idea.

You are right that regolith is very different from snow. The term was mainly intended to explain the intent, not the mechanism. There may well be a static charge mechanism for picking up the finest dust, solving your filtering and you wear problems at once, for example.

In terms of comparing to a 100km highway, about the only similarity is '100km'. The moon is has large flat areas, covered everywhere in regolith, you dont need to connect two specific cities so it is ok to avoid those mountains. The gravity is six times less. You do not need to seal it. The materials you need lie right at hand.

The gain? Suppose your decent stage and fuel are 2/3 the mass of your craft. You can omit this fairly expensive component and launch from earth using a rocket a third the size.

Offline hop

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Re: Luna Lithobraking strip :)
« Reply #27 on: 12/10/2008 03:06 am »
I didn't take snow blower to mean an actual snow blower, the point is that anything with moving parts is going to suffer.
In terms of comparing to a 100km highway, about the only similarity is '100km'. The moon is has large flat areas, covered everywhere in regolith, you dont need to connect two specific cities so it is ok to avoid those mountains.
Relatively flat. What looks like a gentle rolling on foot could be a major problem at 1000 m/s. There are also craters of pretty much every scale. It's unlikely you can draw a 100km line without crossing some significant ones.

Nor is regolith just fine dust. There's chunks of rocks of pretty much every size.

In other words, you need the equivalent of bulldozers, loaders and so on.

The Apollo 12 landing site likes nice and smooth from orbital imagery. Now try zooming in... http://www.google.com/moon/#lat=-2.960227&lon=-23.408131&zoom=15&apollo=


edit:
It's worth noting that the really flat places on earth are (almost?) all associated with liquid water: Bonneville, Black Rock, Salar de Uyuni

I'm having trouble thinking of processes on the moon that would have a similar result, but I'm not a planetary geologist by any stretch.
« Last Edit: 12/10/2008 03:24 am by hop »

Offline khallow

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Re: Luna Lithobraking strip :)
« Reply #28 on: 12/10/2008 06:50 pm »

I'm having trouble thinking of processes on the moon that would have a similar result, but I'm not a planetary geologist by any stretch.

The Mares were formed by lava flooding. Should be relatively flat.
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Offline hop

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Re: Luna Lithobraking strip :)
« Reply #29 on: 12/11/2008 05:38 am »
Quote from: khallow link=topic=15034.msg342987#msg342987
The Mares were formed by lava flooding. Should be relatively flat.
Relatively flat ? No question, they are. But they aren't anything close to the places I mentioned.

Even assuming they started as flat as the dry lake beds (not likely), a couple billion years of impacts and aging has taken care of that. I suppose I should have said "geologically recent processes"

Point being that if you'll have trouble finding anywhere that doesn't have elevation changes in the 10s of meters over fairly short distances. For any of the landing strip scenarios, you'll have to smooth that out, which over 100km adds up to a lot of regolith to move.

Offline Robotbeat

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Re: Luna Lithobraking strip :)
« Reply #30 on: 12/11/2008 02:06 pm »
Hmmm... So, you can't build a landing strip, huh? Well, what about a MONORAIL! Monorail, Monorail!

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Offline A_M_Swallow

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Re: Luna Lithobraking strip :)
« Reply #31 on: 12/11/2008 02:38 pm »
Hmmm... So, you can't build a landing strip, huh? Well, what about a MONORAIL! Monorail, Monorail!

A long monorail would be Ok for take-off, since we can control things at 1 mph.  Unfortunately we do not yet have the guidance technology to align items with an error of less than one inch, that have a speed difference of thousands of miles an hour, on the first only attempt.  So something else would have to be used for landings.
« Last Edit: 12/11/2008 02:39 pm by A_M_Swallow »

Offline KelvinZero

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Re: Luna Lithobraking strip :)
« Reply #32 on: 12/12/2008 07:07 am »
This is off topic, but I always imagined that as the easy part compared to building the thing.. almost like docking in freefall except you are maneuvering up to a rail instead of a point, so it is even easier. The difference in velocity would not be apparent unless you touched the rail. If you abort before making contact then you still have all your velocity and could either expend a little fuel to circularise your orbit or simply make another attempt after a full orbit.

I expect that even now it would be possible to build something to massive precision if you can build it at all, even putting a slight warp in the rail to exactly compensate for any mascons.

Offline meiza

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Re: Luna Lithobraking strip :)
« Reply #33 on: 12/13/2008 02:55 am »
Could magnetic braking work with regolith even if it contains only small amounts of conducting materials and iron etc? If you put very powerful superconducting magnets on the craft (a few Teslas), it could perhaps induce eddy currents in the ground. That's how some train brakes work afaik.

It also makes the craft stick the ground if theres some ferromagnetic material. This could be advantageous in the later part when the velocity is not great enough for magnetic braking and wheels are used.

The velocity can be so great and the magnetic field can be so strong that nonnegligible forces could be created.

Ie a magnetic braking "kinda-maglev" without the track.

Some real physicist could probably pop out an order of magnitude estimate out in no time.

Offline Robotbeat

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Re: Luna Lithobraking strip :)
« Reply #34 on: 12/13/2008 05:08 am »
If it was just magnetic lunar soil, it would fly everywhere when you tried to land with the magnetic braking you're talking about. Seems to me it'd be easier if it was in a singular rail of some sort. ;-)
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Offline KelvinZero

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Re: Luna Lithobraking strip :)
« Reply #35 on: 12/13/2008 09:41 am »
I was wondering how effective a maglev made of (probably inferior) luna materials could be for just braking.

Electrodynamic suspension sounds interesting. Perhaps since you have so much initial velocity and you only need to counteract the moon's gravity, the track could be made of quite inefficient coils?

http://en.wikipedia.org/wiki/Maglev_train#Electrodynamic_suspension

Maglev would be a great way to connect all the colonies on the moon as well.

Offline A_M_Swallow

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Re: Luna Lithobraking strip :)
« Reply #36 on: 12/13/2008 05:12 pm »
There is plenty of iron on the moon to make a wide landing strip from.

Offline KelvinZero

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Re: Luna Lithobraking strip :)
« Reply #37 on: 12/13/2008 11:16 pm »
There is plenty of iron on the moon to make a wide landing strip from.

Not sure I get you. Are you saying luna materials are not inferior because there is iron?



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Re: Luna Lithobraking strip :)
« Reply #38 on: 12/14/2008 12:20 am »
There is plenty of iron on the moon to make a wide landing strip from.

Not sure I get you. Are you saying luna materials are not inferior because there is iron?

Iron is a magnetic material.  It is easier to make a high quality magnetic strip out of pure iron than moon rocks chosen without quality control.  The iron can be extracted from the lunar soil.

Offline KelvinZero

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Re: Luna Lithobraking strip :)
« Reply #39 on: 12/14/2008 06:40 am »
Oh ok.

I think meiza was wondering if you can exploit magnetic properties for braking specifically before we have the infrastructure to build something a 100km long (or similar) from smelted materials.

I was wondering if some sort of track, perhaps of iron for magnetisim or aluminium for conductive coils, would be suitable for braking a craft even if it is not efficient enough to launch it.

I imagine that the first materials we produce will be quite inferior to whatever we can produce on earth.

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Re: Luna Lithobraking strip :)
« Reply #40 on: 12/14/2008 12:04 pm »
A track for take off can be much thinner than a track for landing.  A ring round a crater will do for take off.

Offline KelvinZero

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Re: Luna Lithobraking strip :)
« Reply #41 on: 12/15/2008 05:42 am »
Interesting point, but I was referring to the quality of the materials.

Wikipedia claims most designs assume superconducting coils for example. Dunno if this is true, but I suspect there isnt even much copper on the moon.

Luna materials might be suitable for a large scale project requiring only low quality conductors and magnets before we achieve the quality necessary to build launchers from them.

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Re: Luna Lithobraking strip :)
« Reply #42 on: 01/30/2009 11:27 pm »
KelvinZero
Great minds think alike. Just found this and thought you might be interested.

http://altairvi.blogspot.com/2007/11/lunar-slide-lander-1979.html

"Geolunar Industrial Transportation for Low Propellant Expenditure with New Energy Management Concepts for Lunar Access," IAF-79-F-120, K. A. Ehricke; paper presented at the 30th Congress of the International Astronautical Federation, Munich, Federal Republic of Germany, September 17-22, 1979.

Description of Ehricke's "Slide Landing Mode" by David S. F. Portree

But I still think moving all that material to get a level landing field is harder engineering than a electromagnetic capture loop/arrestor/whatever...
For your original 100 km strip:
Now this is a 'gut' feeling but I think we are in skip and escape scenario with the existing lunar curvature.
From the Interweb (http://www.islandone.org/MMSG/aasm/AASM5B.html):

The general horizon distance formula is X = (h^2 + 2hR)^0.5, where X is the distance to the horizon, R is lunar radius, and h is height of the observer/transmitter above ground.

So solving for h with a 100 km landing strip we get a end 'height' of the 'flat' runway of  2.8745 km!
BOTE + online quadratic equation solution.
Am i wrong? Or is that a lot of Moondust!

(Reverse) Lunatrons (from "Man and the Planets" Duncan Lunan 1983)
150g 1km
100g 3.3km
20g 14.4km
1.7g 160km

Still like the idea of a tailhook tho.
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Offline KelvinZero

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Re: Luna Lithobraking strip :)
« Reply #43 on: 01/31/2009 10:43 pm »
Probably more a case of infinite monkeys on typewriters eventually bashing out Shakespear :)

This was always just a zany idea. I just like ideas that at least can be disected with known physics.

As to skipping off I guess it depends on how close your orbit can be to circular at the moment you begin lithobraking. I guess you could not use it like aerobraking in order to slow yourself enough to be captured by luna gravity. You would already have to be captured and just use it to remove your orbital velocity. At least all the maneuvering beforehand could be done with something more efficient than a chemical rocket.


Offline Axel

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Re: Luna Lithobraking strip :)
« Reply #44 on: 05/09/2009 12:30 am »
KelvinZero
Great minds think alike. Just found this and thought you might be interested.

http://altairvi.blogspot.com/2007/11/lunar-slide-lander-1979.html

"Geolunar Industrial Transportation for Low Propellant Expenditure with New Energy Management Concepts for Lunar Access," IAF-79-F-120, K. A. Ehricke; paper presented at the 30th Congress of the International Astronautical Federation, Munich, Federal Republic of Germany, September 17-22, 1979.


A slightly more detailed description is in http://www.lpi.usra.edu/publications/books/lunar_bases/LSBchapter12.pdf

Also quite interesting is the following section about "ThePartiallyEnclosed LaunchTrack".

What I hear Ehricke was known to be a high class engineer. It would be interesting to learn more about the "multitude of other aspects" he did examine.

So solving for h with a 100 km landing strip we get a end 'height' of the 'flat' runway of  2.8745 km!
BOTE + online quadratic equation solution.
Am i wrong? Or is that a lot of Moondust!

(Reverse) Lunatrons (from "Man and the Planets" Duncan Lunan 1983)
150g 1km
100g 3.3km
20g 14.4km
1.7g 160km

Still like the idea of a tailhook tho.

There is really no need to keep the landing strip that straight vertically. All that has to be avoided is local bumps.

I don't think a tail hook would work at this speed. Remember the kinetic energy grows squared with speed. Hard to imagine, but it makes much of a difference.

With careful design most of the energy could be disappated in dust hitting dust rather than in grinding away the hull of your craft.

Wouldn't this dust behave like something in between of micro meteorites and sand blasting? My guess is that the shielding needed for this is much more heavy than what is needed for aerobraking. And I wonder how much erosion Ehricke calculated for this braking (and how).

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