Mass Drivers on Mars - "Space gun" to shoot stuff to Earth???

Byron · 2002-06-13 07:15:02

I was wondering, since the biggest impediment to Mars being economically viable is the high cost of getting things produced/mined/extracted on Mars to Earth. Even with Mars' lower gravity, it'll still be costly to lift large amounts of cargo into space from the Martian surface, let alone achieve the delta-v needed to get it to Earth.

To get around this problem, what do you think of the possibility of constructing a mass driver on the slopes of one of the Tharsis volcanoes to shoot containers of cargo straight out into space and towards Earth? Would shooting objects at speeds of 10-15 k/s up through the atmosphere (thin as it is) present a problem?

If the idea of a "space gun" is doable, it'd be a whole lot easier to build than the space elevators everybody seems to be fixated on...

B

Josh Cryer · 2002-06-13 12:48:17

I haven't really thought about the feasiblity of such a thing. Mars' escape velocity is about 5 km/s, or about 11250 mph. So the numbers are less than you think.

The idea is totally doable, I think. And it wouldcertainly be easier than building a space elevator. But I'm not sure we want to mine on Mars when asteroids, with much smaller gravity wells, aren't too far away at that point.

Phobos · 2002-06-13 16:10:17

I wonder if a human occupant would be able to survive being shot out of a Martian space gun. I know on Earth you'd be squashed like a bug since payloads have to accelerate to very high speeds quickly, but would the same be true on Mars? If you constructed the gun long enough perhaps you could reduce the acceleration rate to a point that a person could survive. It would beat having fleets of spacecraft with complicated engines that are prone to failure.

Shaun Barrett · 2002-06-14 19:10:25

If your rail is long enough, then you can keep the acceleration within tolerable limits for humans. But how long is long enough? That depends ... !
If you need to send people to Earth from the surface of Mars, you need a final velocity of 5000m/s (Martian escape velocity). Let's assume that an average human can tolerate a 5g acceleration for a limited time. At 5g acceleration, it's going to take 100 seconds to reach 5kms/s. So far, so good.
But, to accelerate at 5g for 100 seconds, your rail needs to be a whopping 250kms long!
Even if you only want to transport people from the surface to LMO (low Mars orbit), you will need a final velocity of about 4000m/s. At 5g acceleration (this time for 80 seconds), your rail still needs to be 160kms long!
And I'm not sure how many people could cope with 5g acceleration for 80 seconds. Is this tolerable for most humans?
My biggest concern is atmospheric drag and heating. Even up on the higher slopes of Olympus Mons, I believe the atmospheric pressure is still 1 or 2 millibars. This doesn't sound like much but, at a velocity of 4 or 5 kilometres per second, I think it would produce significant problems.
Atmospheric drag will probably be the show-stopper for any kind of rail-gun launching system on Mars, even for LMO-bound cargo which can be accelerated at 50g (which, incidentally, would still require a rail 16kms long! ).
The Moon is the ideal place for a rail-gun system with its low escape velocity and negligible atmosphere. But for Mars, unless the Podkletnov gravity-modifying device gives us a new way of overcoming gravity wells, I'm still a space elevator fan!!

Byron · 2002-06-15 06:36:16

If your rail is long enough, then you can keep the acceleration within tolerable limits for humans. But how long is long enough? That depends ... !
If you need to send people to Earth from the surface of Mars, you need a final velocity of 5000m/s (Martian escape velocity). Let's assume that an average human can tolerate a 5g acceleration for a limited time. At 5g acceleration, it's going to take 100 seconds to reach 5kms/s. So far, so good.
But, to accelerate at 5g for 100 seconds, your rail needs to be a whopping 250kms long!
Even if you only want to transport people from the surface to LMO (low Mars orbit), you will need a final velocity of about 4000m/s. At 5g acceleration (this time for 80 seconds), your rail still needs to be 160kms long!
And I'm not sure how many people could cope with 5g acceleration for 80 seconds. Is this tolerable for most humans?
My biggest concern is atmospheric drag and heating. Even up on the higher slopes of Olympus Mons, I believe the atmospheric pressure is still 1 or 2 millibars. This doesn't sound like much but, at a velocity of 4 or 5 kilometres per second, I think it would produce significant problems.
Atmospheric drag will probably be the show-stopper for any kind of rail-gun launching system on Mars, even for LMO-bound cargo which can be accelerated at 50g (which, incidentally, would still require a rail 16kms long! ).
The Moon is the ideal place for a rail-gun system with its low escape velocity and negligible atmosphere. But for Mars, unless the Podkletnov gravity-modifying device gives us a new way of overcoming gravity wells, I'm still a space elevator fan!!

For the most part, I agree with Shaun, in that using a rail gun would not be be practical for human use, due to the high accelerations involved (although, if proper chairs and g-suits are used, people can stand up to 8 gees, although anything over a minute would be pushing it..lol.)

I was envisioning using the mass driver just for cargo containers that could withstand super-high accelerations, so the rail would only have to be 20-30 km long, 50 at the most. The thing about atmospheric drag bothers me too, but I was hoping a way could be found to overcome that, perhaps by plasma shielding of some sort to enable the container to "slip" through the upper atmosphere with a minimum of drag. I can't imagine that a mere 1 mb of pressure would be a show-stopper for the rail gun concept, but I guess you would have to build in a bit of extra speed to overcome the drag (20-40% more??)

Also, is a delta-v of 5 km/s is all you need to get all the way from Mars to Earth? I was thinking it was something on the order of 11 km/s, but perhaps I stand to be corrected.

B

Michael Bloxham · 2002-06-20 19:57:49

Perhaps an uncrewed spacecraft could be sent to orbit via a short, 100g rail gun, while the crew would be sent up to rendezvous with their craft via conventional means, i.e space shuttles. Once in orbit, they might blast off to the moon with a short supply of fuel, strap into a second, much longer rail gun located on the lunar surface, and shoot to mars. This scenario could be repeated on mars, although a single rail gun on Olympus Mons will probably work just as well.

Shaun Barrett · 2002-06-25 03:48:37

I hate to rain on parades but the prospect of launching anything from Earth on a rail-gun is a forlorn hope.
I think the power required to accelerate tons of stuff at 100g would be very large, even in a vacuum. In Earth's atmosphere, the drag would make it much harder to do.
The velocity you need for LEO is 7.88 kms/s. To reach that velocity at an acceleration of 100g takes just over 8 seconds. But, in 8 seconds, your payload will have covered 31.6 kms!! So you'll need a rail that long!
Even if you enclose the rail in an evacuated tube to eliminate friction with the air during acceleration, the payload must hit the atmosphere when it emerges. This will be like hitting a wall and will probably destroy the capsule. Even if it doesn't, massive drag will dramatically slow the capsule and heat it to incandescence! Far from achieving orbit, it will describe a fiery arc in the sky as it plummets to the ground.
Sorry. But we'll have to forget about rail-guns on this planet. I love the idea but it just ain't gonna work!!

Palomar · 2002-06-25 16:18:05

I wonder if a human occupant would be able to survive being shot out of a Martian space gun.

*Don't know.

What I do know is that I wouldn't volunteer to try it.

--Cindy

Phobos · 2002-06-25 18:21:23

*Don't know.
What I do know is that I wouldn't volunteer to try it.

Ah C'mon, it'll be fun.

Aetius · 2002-06-25 20:27:59

Where do I sign up? Sounds like a rush...

Byron · 2002-06-27 15:07:10

Actually, you can get a taste of what riding a mass driver would be like by hopping on the "Superman" ride at Six Flags Magic Mountain near L.A. That thing shoots a car along a magnetic track (just like a mass driver would), and it accelerates from 0 to 100 mph in less than 6 seconds, flies up the curved track into the sky for 40 stories, and falls back down the same track, again reaching 100 mph before braking to a stop. Big fun..LOL...

B

Phobos · 2002-06-27 23:15:07

Oh yeah, I've ridden the Super Man ride at Six Flags. It's my favorite ride, I love that acceleration.

C.COMMARMOND (FR) · 2002-08-27 07:43:38

Hello every body,

You will find on this site the calculations to use a superconducting Maglev to send freight and spacecraft on LEO (they talk of 200 Metric tons).

http://www.newworlds.com/startram.html and http://www.newworlds.com/reports/PUR-19.PDF

I made some checks on it and it seems OK, even if in fact, it is may be not possible to build it easily. The first problem is the 1000 Km tunnel, but if you build it in africa, exactly on the equator (or very close to), it's not impossible the second problem (the biggest) is the 200 km pipe to climb to 20 km altitude(...). But their document seems to address all the problems aith solutions. After the infrastructure built, the price to LEO should be some $.

CC

turbo · 2002-08-27 09:15:31

Hi everybody!
I just spent the last year building a mass driver. The biggest problem with the things is they take a LOT of current to generate the magnetic fields. University of Texas has an 18-footer that can throw a 2 kg ball at 6 Km/sec, but it takes 6 MILLION Amperes to do it, so a two story power station was built just for the rail gun.

Second big problem...the rails and mountings must be VERY sturdy. Mass drivers have no recoil like cannon, but the same force acting to push the projectile along is trying to do everything to push the rails apart because the fields have the same polarity.

How do poor college students make power for a rail gun? Tesla Coil! Now the embarrassing part: 80% of the time we hauled the coil out to tune it, nature provided lightning of her own, so we had to put the coil away. So, presentation last night with a Senior Project that hadn't fired because the power system never reached full output.

After so many weekends working on this thing, my friend and I decided to continue with the project until we get the whole thing working. We also decided to actually spend two weeks without dealing with it, so stay tuned and I'll let you know how well ours works.

OH yes, by the way, a railgun's projectile provides the connection between the rails for the massive power, so it not only gets zapped with high current, it gets subjected to a powerful electromagnetic pulse.

Okay, I'm supposed to be finishing my term paper. Railgun 101 can be continued later.

turbo, your favorite electronics student

Phobos · 2002-08-27 22:08:39

How do poor college students make power for a rail gun? Tesla Coil! Now the embarrassing part: 80% of the time we hauled the coil out to tune it, nature provided lightning of her own, so we had to put the coil away. So, presentation last night with a Senior Project that hadn't fired because the power system never reached full output.

Turbo, after you test your mass driver would it be possible for you to film it and put it in .mpg or .mov format? I have absolutely no idea how to turn films into those computer formats but it'd be cool to see it.

turbo · 2002-08-28 12:29:46

Hi Phobos!
I'm not sure I can get an mpg through to the forum, maybe a few jpg's? There will definately be video tape on the launchings as we promised some of our instructors.

Our small rails are mounted and have a feed mechanism attached. The large rails need more cross braces and then aligned. The Tesla coil itself is the obstacle, but we'll get that thing going. If our scheme to tap the power works the way we want it to, I'll post that under power systems if you like.

turbo, favorite electronics student whose classes are now done and just waiting on Graduation night

Phobos · 2002-08-28 20:54:21

I was thinking that it might be possible for you to set up a website on geocities or somewhere similiar and put the movie up there. But I won't complain at some jpg's. Try to get a cool shot of the projectile flying out of the barrel or whatever it's flying out of.

Shaun Barrett · 2002-08-29 20:35:10

Turbo, I think it's fantastic that you've built such a device!
I did some mathematics on the figures (simple mathematics ... I'm no rocket scientist, I hasten to add! ) and found that achieving 6kms per second over a distance of 18 feet, takes an acceleration of approximately 334,000g !!
Is there any problem with the projectile deforming under such acceleration? Or does the field act on every part of the projectile simultaneously, thus causing no internal stress at all?
Do you get your professor to catch the projectile for you?!

turbo · 2002-08-30 09:56:15

HI Shaun!
Our research has shown the projectile develops a field as well, perpendicular to the fields on the rails. We also found that projectiles tend to be either spheres or a dart/sabot combination. The darts are titanium while the sabots are made from aluminum billets. The big concern seems to be air resistance.

I have yet to see anything on internal stresses, only that without massive supports, the rails will fly apart. MIT built one that is about two meters long and weighs in at about 160 kilograms.

The larger rail guns are always fired at steel plates, so deformation is likely. My partner and I are looking for range, so I'll let you know how far we get with a horizontal launch.
We agreed on a two week hiatus, so no work this weekend.

turbo, who loves the conversion button on a scientific calculator

turbo · 2002-09-01 09:40:37

Mass Drivers on Mars?!?! You guys aren't even on Mars yet and already you want to start a war with Earth?!? Crazy Marzies!

Mass drivers are for sending things back to earth, or to moonbases, or to the outer solar system. I think earth is more than capable of having wars without any help from mars.

Tyr · 2002-10-17 14:57:50

Perhaps a mass driver atop one of the great volcanoes in the really thin "air" of high martian altitude might be able to launch cargos without to much drag/friction/heat. Only problem is launch windows to Earth only come every 2.13 years. Better to launch stuff to Mars orbit or a martian Lagrange point, then use a rocket for flight back to Earth-Moon space to sell things for $$$$. If the mass driver doesn't work, it is still possible to use SSTO vehicles to orbit things mined on Mars, since Mars orbital V is so low, and it will be possible to mine the moonlets Deimos and Phobos which have negligible gravity wells.

Number04 · 2002-10-22 10:04:25

What about using a mass driver instead of initial booster rockets? put a shuttle on a few hundred meters of rail to give it an extra boots?

And if we could lay down a 10 or 20 Km of rail on mars, it could do allot of the work, and cut down on allot of the fuel needs or rockets and what not.

RobS · 2002-10-22 15:24:15

Regarding the problem of air friction on Mars, somewhere I read that the tops of the big volcanoes are so high, you can't use parachutes for Viking-style landers there. The Earth's atmosphere has a mass of ten tonnes per square meter, so if you launch something at sea level that is five meters in diameter (with a circular area of 20 square meters) it has to punch through 200 tonnes of air to get to space. naturally, that creates a lot of drag. But Olympus Mons has a pressure of something like 1 millibar, a thousandth that at the Earth's surface, and that is produced by a mass that has 38% as much weight on Earth; therefore the mass you are dealing with is a thousandth divided by 0.38 = 0.0026 X 200 tonnes = 0.5 tonnes of air between the space vehicle (5 meters in diameter) and space. It seems to me the vehicle could deal with 500 kilograms of air, and at 5 km/sec it would pass through that air in about 30 seconds (to get to 150 km, which is about the top of the atmosphere). Most of that air will be in the way in the first few seconds.

I have not verified the air pressure on top of the volcanoes is 1 mb; I just used it from the previous posting. But I think it's about right. If it is 2 mb, we are dealing with 1 tonne of air instead.

As for velocities, according to http://222.pma.caltech.edu/~chirata/deltav.html, low orbit around Mars (from the surface in all these cases) takes 4.1 km/ sec; Phobos transfer orbit, 5 km/sec; Deimos transfer orbit, 5.3 km/sec; Mars escape, 5.5 km/sec; flight to Earth (Hohmann trajectory), 6.4 km/sec.

-- RobS

Shaun Barrett · 2002-10-22 20:01:21

It seems this whole thread lives or dies by the effect 1 or 2 millibars of Martian air will have on a projectile hitting it at 4 or 5 kilometres per second.
We can assume all sorts of things but we really need a definitive answer in terms of numbers to determine the magnitude of the shock and the heat produced.

I've always doubted that a rail gun would work on Mars, even at such high altitudes, but Rob S has got me wondering now! Maybe I've been too pessimistic.

PS. I assume the tube would have to be evacuated to improve
efficiency by reducing drag during acceleration?

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#1 2002-06-13 07:15:02

Re: Mass Drivers on Mars - "Space gun" to shoot stuff to Earth???

#2 2002-06-13 12:48:17

Re: Mass Drivers on Mars - "Space gun" to shoot stuff to Earth???

#3 2002-06-13 16:10:17

Re: Mass Drivers on Mars - "Space gun" to shoot stuff to Earth???

#4 2002-06-14 19:10:25

Re: Mass Drivers on Mars - "Space gun" to shoot stuff to Earth???

#5 2002-06-15 06:36:16

Re: Mass Drivers on Mars - "Space gun" to shoot stuff to Earth???

#6 2002-06-20 19:57:49

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#7 2002-06-25 03:48:37

Re: Mass Drivers on Mars - "Space gun" to shoot stuff to Earth???

#8 2002-06-25 16:18:05

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#9 2002-06-25 18:21:23

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#10 2002-06-25 20:27:59

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#11 2002-06-27 15:07:10

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#12 2002-06-27 23:15:07

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#13 2002-08-27 07:43:38

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#14 2002-08-27 09:15:31

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#15 2002-08-27 22:08:39

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#16 2002-08-28 12:29:46

Re: Mass Drivers on Mars - "Space gun" to shoot stuff to Earth???

#17 2002-08-28 20:54:21

Re: Mass Drivers on Mars - "Space gun" to shoot stuff to Earth???

#18 2002-08-29 20:35:10

Re: Mass Drivers on Mars - "Space gun" to shoot stuff to Earth???

#19 2002-08-30 09:56:15

Re: Mass Drivers on Mars - "Space gun" to shoot stuff to Earth???

#20 2002-09-01 09:40:37

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#21 2002-10-17 14:57:50

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