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This new topic is offered to provide a focus for a subset of the many launch loop ideas already discussed in the NewMars archive.
The default example of a launch loop concept is the Lofstrom design, first published (from my personal collection) in the L5 News.
The Lofstrom design was intended for use from Earth, and featured kinetic lofting of components of the loop from Earth, to sustain the loop.
This topic is offered for collection of less ambitious designs which might find practical application on the Moon, or on asteroids.
The attraction of the design which employs a loop to accelerate payloads is that no mass is lost in the process.
A swing arm concept has been proposed to give payloads a rotational velocity, after which they are released for travel to a destination, much as a baseball leaves the hand of a pitcher on Earth.
The proposal intended for discussion in this topic is a continuous belt to which a payload will be attached. The belt would be accelerated with electric motors or similar devices, and the payload would be released at the end of the belt at the needed velocity, headed in the desired direction.
An example of an electricity powered payload acceleration method is the magnetic accelerator invented and demonstrated by the O'Neill team at Princeton in the 1980's. That system could be put into service on the Moon, with sufficient investment. The principles of operation have been proven.
This topic is intended to focus on a much simpler concept.
Conveyor belts are in use all over the Earth in 2020. The ones I know about generally run at a fixed rate, and move physical objects from one place to another in an efficient manner.
The belt I have in mind here would launch material from the Moon or asteroids by accelerating the belt (with the payload attached) until the payload reaches the velocity needed to escape the body, at which point the payload would be released and the belt would slow back down to a stop.
If someone would be interested in doing the math to further describe this system, I'd be happy to see the results.
(th)
Last edited by tahanson43206 (2020-02-18 09:21:05)
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Google Question: maximum practical rpm for electric motors
forums.tesla.com/forum/forums/max-motor-rpm
@Vall
According to their specs, max power is around 6000 rpm, and the torque starts to decline a few hundred RPM before that.According to their specs, max power is around 6000 rpm, and the torque starts to decline a few hundred RPM before that. Actually max power is gained at 6000RPM but it stays more or less constant quite a lot higher, according to options-page 6000-9500RPM for standard 85kWh and 6000-8600 RPM.
Taking 6000 rpm as a reasonable number, far below what is possible, and then taking as the escape velocity from the Moon of a “reasonable” figure of 2376 meters per second, then the velocity of the payload as it approaches the end of a belt would be about 2400 meters per second.
A point on the circumference of a pulley driving the belt would need to be moving at 2400 meters per second. The size of the pulley should be knowable, given the rpm of the shaft and the rotation rate of the circumference.
Because the velocity is given in meters per second, we will convert the chosen rotation rate from minutes to seconds, giving 100 rotations per second.
The circumference of the pulley can be computed as 100th of 2400 meters, or 24 meters.
From this preliminary computation, I would deduce that a payload on the Moon could be accelerated along a belt to a velocity of 2400 meters per second, if the motors driving the belt accelerate in coordination to 6000 rpm, and if the drive pulleys are 24 meters in circumference, or (per Google) 7.64~ meters.
The ideal length of the acceleration belt remains to be computed.
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The original mass driver concept was a coil gun, accelerating a magnetic bucket through the middle of multiple solenoid coils which activate ahead of the bucket and deactivate as the bucket passes through them. Fly wheels might be a good way of storing energy to accelerate the package, as they can discharge very quickly. The mass driver would be a very cheap way of delivering bulk materials into high Earth orbit to support space manufacturing.
Let us suppose that we can install a 100MW power source on the moon to support a mass driver and the device itself is 50% efficient. With a launch speed of 2400m/s the mass driver could launch 274,000 tonnes of bulk minerals into space each year. Even if it cost several billions to set up a driver of this size, it could still launch bulk materials for a few dollars a kilo. This is the only practical option if are really serious about building the infrastructure needed to colonise space.
The required length of the mass driver will depend upon the achievable acceleration. If the buckets and payloads can tolerate 1000g, then the mass driver would need to be 288m long. A shorter section would be needed at the end of the driver to decelerate the empty buckets and return them to be loaded with more ore.
Last edited by Calliban (2020-02-18 17:03:21)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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https://history.nasa.gov/SP-4029/Apollo … _Phase.htm
https://en.wikipedia.org/wiki/Lunar_orbit
Starting with what you know is we want to not expend fuels to get payloads from the moons surface back into orbital status. Going for 100% reduction just does not sound possible but some value over 50% would be still a reduction in fuel needs.
Seems that low lunar obit could be as low as 50km to 100km depending on how long we would want to stay there with the parkibg orbit just a bit higher of just 20km higher for 120km.
https://www.shodor.org/succeedhi/succee … ntent.html
https://physics.stackexchange.com/quest … ular-orbit
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For Calliban re #3
Your mention of the 'original' mass driver brought back a flood of memories.
ssi.org is a major repository of history of the Space Studies Institute created by Dr. O'Neill, their many symposium, and their many projects.
The article at the link below is about Mass Driver I. It gives a useful hint of the version I saw in operation at Princeton, during one of the Space Manufacturing Conferences. I ** think ** the version I saw was Mass Driver III.
https://ssi.org/reading/ssi-newsletter- … mmer-1980/
"Folk lore" has it that Dr. O'Neill designed the Mass Driver prototype using an Apple II computer.
If you are interested in picking up up the ball from the Princeton team, I'm pretty sure most of them are still alive and they might be interested in helping.
***
For SpaceNut ... this is a detail that arises from the work done in the 1970's, and reported in 1977 ... The purpose of the original mass driver design was to ship material from the surface of the Moon to a location well away from the Moon, and most definitely NOT in lunar orbit. The details of that plan are available in the book "Colonies in Space" by TA Heppenheimer. The purpose of the shipments was to provide material for construction, but at this point I can't remember if the construction was to build a solar powered satellite or a habitat.
I'll try to find previous references to that book in the NewMars archive.
***
I asked FluxBB to search for posts with one or more references to Heppenheimer.
The results were mostly from the asteroid topic Calliban created, but I found a post by member "karov" which quoted a long article by Paul Birch.
The article covers a lot of ground, and includes a comprehensive bibliography. If a forum member (or visitor) has a bit of time, the Birch quotation may prove interesting.
http://newmars.com/forums/viewtopic.php?id=9110
http://newmars.com/forums/viewtopic.php … 94#p159394
http://newmars.com/forums/search.php?se … =701984257
http://newmars.com/forums/viewtopic.php … 82#p159382
http://newmars.com/forums/viewtopic.php … 61#p159361
http://newmars.com/forums/viewtopic.php … 86#p121186 karov >> Paul Birch
(th)
Last edited by tahanson43206 (2020-02-18 19:17:52)
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The momentum will allow for the mass to keep moving until another force pulls it from its outward trajectory...
Its like watch one of the ww bombing films where the artilery is peppering the sky...any incoming crew would be in the line of fire and then some.
Linear electromagnetic accelerators
Extremely lightweight on orbit mass driver
Moonbase and Mass drivers etc etc
Presentation Of New Launch Method
Mass Drivers on Mars - "Space gun" to shoot stuff to Earth???
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In 1977, when TA Heppenheimer wrote "Colonies in Space", the current thinking was limited by the technology available at the time.
While the idea of sending packages of Lunar regolith to a processing facility conveniently located with respect to the Earth-Moon system seems as valid to me now as it did when I first read it, the idea of building a huge "catcher's mitt" for the tossed packets from the Moon seems antiquated.
Calliban has reminded us of the potential of the electromagnetic mass driver invented decades ago and demonstrated at Princeton in the early 1980's. Having seen the demo, and talked to the graduate students who worked on it, I am less optimistic than some may be that the system will be put into service on any meaningful scale any time soon.
It's not that the technology can't be relearned by a fresh set of young people. I'm sure that it can. What I suspect is that the elder community is out of gas in the United States.
It is going to take arrival of an inspirational leader, and perhaps an incentive of some kind, to give all those talented young people who live on Earth a chance to focus their energies on the complex problem of simultaneously building:
1) A reason to ship Lunar mass to a location between Earth and Moon
2) The transportation system to deliver equipment to the Moon
3) The transportation system to deliver equipment to the preferred location for a space enterprise, wherever that turns out to be
4) The equipment for the moon, including the throwing equipment as well as the extraction/gathering equipment
5) The equipment for the manufacturing location
***
For Calliban re a distance over which 1000 g acceleration would take place ... Thanks for a concrete example to think about.
I suspect the 1000 g system is NOT the one you'll see on the first try. My impression (from seeing the demo) is that you'll discover, if you decide to build the machine, that you'll be earning your salary << grin >>.
That said, by all means, give it a try! A good start would be to duplicate the demo, using locally available resources.
The documentation of the design and specifics of the test articles should be publicly available.
Edit#1: The point I had set out to make got lost in the digression about the project planning ...
What I logged on to suggest was to use intelligent capsules to convey the shipped material to the manufacturing facility. These would have the ability to adjust course using solar sail techniques and ion drive if absolutely necessary, so none of the payloads should get lost in transit. Transit itself can take as long as natural forces dictate. There's no hurry. The train of material, once started, should flow regularly, at whatever rate is designed into the tossing system, whatever it may turn out to be.
The intelligent capsules can be returned to the Moon in large numbers, using a single freighter designed for a Lunar landing.
(th)
Last edited by tahanson43206 (2020-03-04 09:36:03)
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The simplest idea I can imagine is just a simple tower, a cable with the middle point over the tower, two identical loads in each end of the cable, and just make it rotate. The cable could be rolled up in each side, so the high of the could don't need to be too high, and with enough rotation, the cables will be near parallel to the surface.
The cables extends more and more, making the radius bigger and bigger. Naturally, when the radius extends, they will rotate slower, but the tower will push in the center more speed.
When the cables reach enough lenght, the speed of each end side could be enough high to reach orbital speed (just in opposite directions... and if it's parallel to Moon's rotation, one will be slower than the other... but could be enough to reach orbital speed in any case).
So... A not so high tower. A strong piece over the tower to push the cables as strong as needed, big cables, and probably the cables, the roller system could be a different part of the loads. It simply detach them.
In fact... with this system, because the radius is dynamic, it could be calibrate to work at a constant 1g equivalent acceleration on each side (just the radius grows until the tangential speed is reached).
I think its a very easy to build system.
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If you have cables that won't break under such strain.
It would seem to be far easier to just build a Lunar space elevator... the stress is far lower. It could be built of basalt.
Use what is abundant and build to last
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If you have cables that won't break under such strain.
It would seem to be far easier to just build a Lunar space elevator... the stress is far lower. It could be built of basalt.
That's not a bad idea. Or at least an orbital tether that can pick up payloads from a hill top, say. If the ground speed of the tether tip is no more than about 100m/s, inert payloads could be lifted by means of a hook. The lower portion of the cable could carry a long spring or be made from elastomer, to limit the stresses on the cable as the payload is picked up and rapidly accelerated to 100m/s and then reeled in.
If acceleration can be limited to ~10g, then fragile payloads and people could be lifted from the surface in this way. At a tip speed of 100m/s, the elastic portion of the tether would need to stretch some 50m in order to keep acceleration to <10g.
Probably worthy of a separate topic.
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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If you have cables that won't break under such strain.
It would seem to be far easier to just build a Lunar space elevator... the stress is far lower. It could be built of basalt.
I guess you didn't understand my idea, because the tensions are far lower than a space elevator.
I checked the numbers. Use 1g means too big tower, but 3g make a very reasonable idea.
I will explain again.
First, the principle is just like a gigant carousel, like a double sling , with seats attached to the top. Use two opposite launchs are just arbitrary to make it a central point of gravity. Another configurations are possible.
Using a gravity spin calculator
https://www.artificial-gravity.com/sw/SpinCalc/
I will use 1400 m/s as tangentian velocity as a orbital speed reference.
3g of "gravity" - because greater accelerations means less cable and lower tower (and the tower is high in any case)
It gets ~66,6215 km of radius.
This is for zero gravity.
Ok... This will be built on the Moon, so on the parallel plane, the launch objects needs to separate that 66.62 km from the tower to reach the 1400 m/s of tangential speed.
Because we are on the Moon, the cables won't be parallel to the surface. In fact, it will be in a triangle represented by the two perpendicular vectors. Pseudoacceleration (3g) and Moon gravity (~0,166g)
So... 66,62115*0,166/3~=3,6864 ...
The cable will be a total length of: sqrt(66,62115^2 + 3,6864^2) ~= 66.73 km
A tower 4km high could work.
It's very high. Higher that any tower in Earth (0.8298 today) but it would be just a structure AND Moon low gravity helps a lot.
So, we just attach opposite cargos to the both cables, we make it spin faster and faster while the cables extends up to 66.73 km (it will never touch the surface because at that speed, only will be at 4-3,6864 distance), with a increasing perception of acceleration (centripetal acceleration) and, just release.
1400 m/s. Enough to put in a orbital position. Although it would be better to have some propulsion and use the first orbit to raise the perihelium. It would be very, very low and a collision is possible in the next encounter with the lower altitude.
The weigth that the cables must endure are just the weight of cargo at 3g plus the weight of the cable.
Less than 70 km cable. Not too much.
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On Earth, rocket sleds travelling on steel rails have achieved velocities of up to 10,325 km/h. That is 20% faster than lunar escape velocity and almost twice the speed of a 100km lunar orbit. So launching something from the lunar surface via rocket sled is feasible, if an adequate means of propulsion could be found.
https://en.wikipedia.org/wiki/Rocket_sled
What could provide propulsion? If we pass a current through the sled through sliding contacts on the rails, the sled will accelerate in a perpendicular magnetic field. So you would mount electromagnets either side of the track and the vehicle will accelerate as the magnetic field exerts a force on the current carrying conductor passing through the vehicle. This is how a rail gun works.
https://en.wikipedia.org/wiki/Railgun
Rail guns have achieved muzzle velocity up to 3km/s on Earth. To launch payloads from the moon, we need muzzle velocity 50-80% of this value. Which is beneath the speed record for a rocket sled here on Earth. So the concept appears to be achievable, especially if we are launching inert payloads that can tolerate high acceleration. To launch people, we would need a track at least 10km long.
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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For Spaniard, Terraformer, Calliban ....
Thanks for adding so much value to this topic!
I agree with Calliban that this idea deserves its own topic.
Spaniard, you can do that if you are willing. Just go to the Index, find Interplanetary transportation, and create a topic with the name that is best for your idea.
Then, other forum members, and hopefully non-registered forum readers who are inspired to contribute will register to do so.
For Calliban ... the sled idea seems a LOT more practical than the mass driver, impressive as that system is.
The pure simplicity of the sled is appealing, and as mentioned a few posts ago in this or in another topic, the payload need not travel in a dumb lump as was imagined in 1977, in the early days of space colonization thinking.
The sled need not stop and return, and indeed, it can become an intelligent carrier for the payload, capable of navigating (within limits of course) on its own to its intended destination. The great number of gravitational influences that exist in the solar system, and the variety of solar particle 'winds' that exist are inevitably going to push and pull the payload carrier away from the desired flight path. Modest trajectory maintenance capability would insure safe arrival of the payload.
There is another distinct advantage to your concept ... the size of the payload package is not limited as it would be for the original mass driver design.
And finally, your mention of human passengers is helpful, because your concept here is not limited by the length of the track.
For all those reasons, I'd like to try to encourage you to join Spaniard in creating a dedicated topic for a launch sled.
The original idea for which this topic was created is looking less and less attractive to me at this point, but I am delighted it has spawned such creative alternatives. Best wishes to each of you for success with (what I hope) will be vibrant new topics.
(th)
Last edited by tahanson43206 (2020-02-19 08:33:24)
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Which posts need removal to a new title?
Any item that has a rotary motion in any form means we are not just talking about the radius, diameter, RPM, speed ect as we are talking about the power called torque as its the force to move the item. Whether its a wheel or a cable on a drum we are still looking at this factor.
https://kurz.com/understanding-relation … pm-torque/
How is it calculated
http://www.epi-eng.com/piston_engine_te … torque.htm
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SpaceNut,
Jack Kane (EPI Engineering) is a "smarter than your average bear" kind of guy when it comes to piston aircraft engine design, amongst other things. I spoke with him about the torsional vibration damping issue with my own homebuilt aircraft project. His website provides a working knowledge base for that topic and whether or not an automotive engine conversion makes sense for a small aircraft (not so much, in most cases, as it turns out). There are also discussions on this topic over on the Homebuilt Airplanes website. The engineering consensus is that such problems are solvable, but most of the solutions are far from simple or easy to implement.
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For Calliban ...
By any chance have you been following kbd512's discussion of an electromagnetic launch system for the Earth.
The technology that kbd512 described is (apparently) in service on (at least one) US Navy carrier today. The engineering feature that I find interesting is the (reported) use of rotating mass energy storage devices to dump massive amounts of current into the magnets of the electromagnetic aircraft launch system.
The techology kbd512 described seems (as I read it) to be almost perfectly transferable to the Moon, with the distinct advantage of no atmosphere to impose drag on the delivery packages.
(th)
On Earth, rocket sleds travelling on steel rails have achieved velocities of up to 10,325 km/h. That is 20% faster than lunar escape velocity and almost twice the speed of a 100km lunar orbit. So launching something from the lunar surface via rocket sled is feasible, if an adequate means of propulsion could be found.
https://en.wikipedia.org/wiki/Rocket_sledWhat could provide propulsion? If we pass a current through the sled through sliding contacts on the rails, the sled will accelerate in a perpendicular magnetic field. So you would mount electromagnets either side of the track and the vehicle will accelerate as the magnetic field exerts a force on the current carrying conductor passing through the vehicle. This is how a rail gun works.
https://en.wikipedia.org/wiki/RailgunRail guns have achieved muzzle velocity up to 3km/s on Earth. To launch payloads from the moon, we need muzzle velocity 50-80% of this value. Which is beneath the speed record for a rocket sled here on Earth. So the concept appears to be achievable, especially if we are launching inert payloads that can tolerate high acceleration. To launch people, we would need a track at least 10km long.
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For the moon the reason for such a launch system is to not waste the water resources that we might find on refueling and launching of ships from its surface.
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This is for Calliban primarily. Hopefully other forum members may appreciate the reminder of earlier work in the archive.
Calliban, while searching for something else today, I found this earlier discussion of rail guns on the Moon, which you brought up earlier in this topic.
I thought the reply to questions from 2005 was well written and helpful to someone who is unfamiliar with the physics and orbital mechanics of the situation.
http://newmars.com/forums/viewtopic.php … 581#p84581
Discussion from 2005 about rail guns on the Moon. Helpful reply to questions.
(th)
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Thanks for the reminder to these older topics as they are spot on. The ISA member was just one of several which did do work early in the forums years before the crash.
It meantioned sending the payload to a stable orbit where it could be towed to the final destination. That still has the matching of orbital speed to the capture ship without getting in the launch path, using fuels that we do not have on the moon and cost much to transport from earth for those same fuels to tow it to where we need it.
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Lunartrak: Lunar Rail Systems for High-Mass General Transport, Dust Mitigation, and Power Conveyance
https://arc.aiaa.org/doi/10.2514/6.2023-4686
Project HARP, short for High Altitude Research Project, was a joint venture of the United States Department of Defense and Canada's Department of National Defence created with the goal of studying ballistics of re-entry vehicles and collecting upper atmospheric data for research
https://en.wikipedia.org/wiki/Project_HARP
Chinese navy testing world's most powerful coil gun
Report
https://www.wionews.com/world/chinese-n … ort-629517
2016 article
'Moonbase by 2022 For $10 Billion, Says NASA'
https://www.universetoday.com/128011/mo … says-nasa/
and $4.1 billion SLS rocket
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