Talk:Mass driver

Do you need a paramagnetic material in order to induce eddy currents in it.? I have not heard of this one before!--Light current 21:59, 19 September 2005 (UTC)

The article says "build a mass driver on Earth that can launch radioactive waste into space... to dispose of [nuclear] waste safely and permanently". Could someone who knows more about this clarify where in space the destination would be? Is the proposal to send the waste into the Sun, or into an orbit that may intersect the future position of Earth or a spacecraft? --Chauncey27 16:29, 28 December 2005 (UTC)

Similarly, the article says "the mass driver ... has the potential to send solid reaction mass travelling at dangerously high relative speeds into useful orbits and traffic lanes. To overcome this problem, most schemes plan to throw finely-divided dust, or liquids." Could someone please clarify how a collision with dust or liquid moving at "dangerously high relative speeds" would be any better? --Chauncey27 16:32, 28 December 2005 (UTC)

It wouldn't. But dust or some liquids if fired in interplanetary space would get carried away over time by the solar wind and light pressure and would leave the solar system at awesome speeds. Large solid objects have much higher ballistic coefficient, and so are much less affected by solar wind and light; so there's a significant chance of a collision because it tends to hang around in orbit.

The other advantage of dust is that you actually can shield against it; since the impacts are quite small. Similarly with tiny crystals of a liquid once it has solidified in a vacuum.WolfKeeper 17:01, 28 December 2005 (UTC)

This article is missing the most important information---how a mass driver works, so I think there is little to gain from this article for anyone (such as myself) who is not already familiar with the idea. If anyone here knows how it works, can you add an explanation at the beginning of the article? Folding Chair 00:48, 3 April 2006 (UTC)

The sentences added are a good step an clear up a lot. I'm not going to remove the expand tag yet though, because I think it would be really good to have perhaps a whole section devoted to explaining technically and in detail how a mass driver works. (If someone else thinks this is good enough and wants to remove the expand tag, I won't object) Folding Chair 01:49, 4 April 2006 (UTC)

Of course, you could always find out how it works elsewhere, add to the article and then remove the tag...?WolfKeeper 02:01, 4 April 2006 (UTC)

"Now the fact remains that it shares the same fundamental limits that conventional rocket engines do,"

I removed this, because it's wrong. Conventional rocket engines; presumably chemical rocket engines have an exhaust velocity that is limited by the energy in the propellant. Mass drivers are externally powered, and hence have no theoretical limit. Atleast one experimental magnetic propulsion system in a storage ring on earth has given speeds as high as 20km/s (2000 seconds).WolfKeeper 21:56, 26 June 2006 (UTC)

"Propelling the reaction mass to solar escape velocity would be another way to ensure that it will not remain a hazard."

Considering that the escape velocity of the sun is 617.5 km/s, I think this statement warrants a citation. I marked it as citation needed and added the actual solar escape velocity so the reader can judge whether that's really a possibility or not.

213.41.244.122 (talk) 01:12, 26 January 2009 (UTC)

LOL. That's the escape velocity at the surface of the Sun to Solar escape. The escape velocity at Earth's orbit to solar escape is only 42km/s. I don't think that mass drivers would work all that well at the surface of the Sun, and you would have much bigger problems than working out what happened to your exhaust!- (User) Wolfkeeper (Talk) 11:55, 26 January 2009 (UTC)

Something to think about

Every time we walk or drive a car, we apply a force to the earth. We effectively steal some momemtum from the earth.

Is it possible that, over time, with enough large masses being launched at high velocities in the same direction, that the rotation of the earth could be significantly (0.001%??) increased or decreased? How could such a change effect the orbital mechanics of the earth, or the atmosphere, or ocean currents, or time. Could be an interesting paragraph to discuss in the article, backed up by some reputable calculations of how much it would change the period of rotation of the earth. 130.179.33.44 17:31, 9 August 2006 (UTC)

Do not be silly! Relative masses are too disparate. When you do the calculation use scientific notation and compare to Avogadro's number or time/energy to reach .001% with the age of the universe. Try using launch mass of current annual U.S. or world steel production. Further, if launch momentum rose to a level of legitimate concern then one would simply install the mass drivers in pairs and launch pairs of payloads in opposing directions to leave Earth in a pristine momentum state except for the torque generated by pair launch. Upon losing court case mass drivers could then be installed in pairs of pairs designed to neutralize torque. Except the trucks moving payloads to the mass driver also impart momemtum and Earth is not flat. So now we have to work with the Chinese or other continents and learn enough math, instrumentation and control theory to use the mass drivers to counterbalance the effect the various continental Interstate and Highway Systems are having on radioactive decay rates under Yucca Mountain.

How long a time did you (130.179.33.44) have in mind? Earth already has these changes from other causes. Thus, the occasional leap second is applied. The effect from a mass driver wouldn't be noticeable, because it would be a lot smaller than the tidal effect the moon has on the length of the day. Also, there can be tiny effects from changes in the shape of the Earth due to quakes (such as the one that caused the Dec. 2004 Tsunami), and the occasional passing asteroid or comet. 206.53.196.246 (talk) 00:26, 19 April 2009 (UTC)

This is quite funny. Hate to point it out but the earth weighs some 6x10^24 kilograms, since momentum transfer is m₁ x v₁ verses m₂ x v₂ I don't think we need to worry. Take a pretty much worst case scenario - accelerate a billion tons to the speed of light, thats 1x10^12 kg x 3x10^8 m/s, that will only change the earths momentum by 5x10^-5 m/s - a tenth the width of a human hair every second. 10^24 really is quite big :) Lucien86 (talk) 01:08, 31 August 2009 (UTC)

Revenge Of The Sith

"In Star Wars Episode III: Revenge of the Sith, massdrivers are used by the Invisible Hand against a Venator class Star Destroyer during a broadside attack that eventually results in the Invisible Hand plummeting toward Coruscant's surface."

I thought The Invisible Hand was using Tubo Lasers with removable power packs.

Dudtz 8/17/06 7:40 PM EST

Why aren't mass drivers used by someone?

It takes a tremndous amount of fuel to get into orbit, why aren't they used to get non-human payload up to several miles per second, and save on the huge fuel requirements to get into orbit, or beyond? With all the countries currently launching into space I'd think one of them would us it as a first stage. —Preceding unsigned comment added by SmallIsSmart (talk • contribs)

Part of it may be the difficulty and expense of designing the rest of the rocket to survive the immense acceleration a mass driver would impose on it during launch. Another part may be that even if the per-launch cost is reduced the mass driver itself would still be rather expensive to build, so it may not be as good an economic tradeoff if you've only got a limited number of launches. And finally, it's an unproven technology as yet. Hard to get investors to gamble billions on something like that. Those would be my guesses. Bryan 18:36, 26 August 2006 (UTC)

On Earth air friction is a major consideration. The SR71 is probably speed limited (mach 3+) by the temperature of the leading aerodynamic edges and points. LEO is about Mach 25. Consider the shuttle's problems with heat and it starts at Mach 25 and slows down to zero at landing. The launch projectile of a mass driver must start high enough that it is at Mach 25 in LEO after passing through the atmosphere. Schemes have been proposed for 100 mile high altitude mass drivers but air friction and novelty are still big engineering problems.

Confusing paragraph

"While linear motors can, with current technology, convert up to about 50% of the electrical energy into kinetic energy of the projectile, the energy of interest is the kinetic energy of the vehicle, and as the muzzle velocity increases, this is a smaller and smaller percentage of the generated power."

This makes no sense. The thrust acquired by the vehicle is equal and opposite the momentum add to the projectile.

Correct. But irrelevant. The thrust is not the same as the energy.WolfKeeper 05:54, 24 October 2006 (UTC)

Thus within the range of the current technology up to 50% of the electrical energy is converted to useful momentum for the vehicle.

Wrong. The easiest way to see this is if the exhaust velocity is much, much higher than the vehicle speed. In this case the exhaust ends up going backwards at considerable speed, and nearly all the energy ends up in the exhaust. The optimum is when the exhaust recedes from the vehicle at the vehicles instantaneous speed; then it has no kinetic energy at all (it turns out that that uses rather a lot of fuel, but it is highly energy efficient- in this case 50% efficient, the rest ends up as heat.) Anyway, if that sounds completely nuts, then you're probably starting to work it out. Find the article on energy from the rocket equation, also the spacecraft propulsion has stuff on it.WolfKeeper 05:54, 24 October 2006 (UTC)

This should be reworded or deleted as extraneous. Alternately a graph could be shown with the fall off in efficiency as the projectile emission speeds rise.

There you go, find the equation, draw. Project for you.WolfKeeper 05:54, 24 October 2006 (UTC)

The high energy demands are one of the major reasons why no full-scale mass driver installations exist today. The other being the high initial cost.

Not the energy cost is the problem, but the difficulties to control its release as precisely as needed for a launch. It is quite difficult to control and direct the energy amounts needed by a large mass driver capable of full surface-to-orbit launch. Semiconductors (silicon etc.) is highly accurate but cannot handle high voltage and current. More conventional switching systems are probably not accurate enough on the timing.

Say one wants to lift a one-tonne projectile (1000kg = 2200 pounds) to LEO (8km/s). That's m = 1000, and v²/2 = 32 million. One would have to convert 32 gigajoules, or roughly 9000 kWh, into kinetic energy. On top of that all energy which is turned into waste heat or atmospheric friction. Even if the rails are as long as 320km (200 miles), a projectile wouldn't take more than 80 seconds (average velocity 4km/s) to travel that far.

BTW, the two "citation needed" in that paragraph should probably be dropped, since the spacecraft propulsion article goes into more detail, and comes with an efficiency graph.

Comments appreciated.

217.254.162.120 (talk) 14:38, 28 October 2010 (UTC)

When a spacecraft needs a certain delta-v to accomplish its mission, I'm starting to understand the tradeoff between either lots of energy or tons of mass or some compromise between them.

However, the article makes two statements that still seem obviously wrong to me. Perhaps they are non-obvious truths, or perhaps they are a bit ambiguous and need to be clarified.

The article currently claims heavier projectile masses give lower specific impulse but proportionately higher thrust. Is that so?

This seems to be saying that if I spit out a ton of propellant, I get 10 times as much useful thrust on my spacecraft if I spit out a ton of 10 gram projectiles rather than a ton of 1 gram projectiles. But as Galileo Galilei pointed out, it is a logical contradiction to assume that ten one-gram projectiles moving at the same speed have a different effect depending on whether they are connected by a thin thread (making them a single 10 gram projectile) or whether the thread is cut.

The article also claims that in a design one must choose a tradeoff between energy consumption and consumption of reaction mass. Is that so?

This is certainly true for chemical rockets -- after a chemical rocket has been fueled, "energy consumption" is directly proportional to "consumption of reaction mass". Various tradeoffs are possible, but only at design time before the vehicle has been fueled. But this article is talking about mass drivers, and a mass driver design does *not* need to choose a tradeoff at design time. Instead, a mass driver can be designed to handle a range of exhaust speeds, to allow mission planners to choose, long after the vehicle has been launched, choose whether any given delta-v maneuver is accomplished with a high-exhaust-velocity, high-energy, low-mass maneuver, or a low-exhaust-velocity, low-energy, high-mass maneuver, or some tradeoff compromise.

How can we fix this article so it no longer seems "obviously wrong"? --68.0.124.33 (talk) 07:37, 9 December 2010 (UTC)

The last sentence of the 2nd alinea in the section "Spacecraft-based mass drivers" says simply: "Exhaust velocity is best neither too low nor too high." without first stating what the best propulsion would be, or what the trade-off's are. As stated above, there are trade-off's to consider regarding energy expenditure and specific impulse, but these are only explained later. I suggest (re)moving this sentence to avoid confusion. Besides, in current (2016) spacecraft, the specific impulse of a propulsion system is of far greater concern than the thrust, except for launch systems and other situations where high thrust-weight ratios are required. Mass driver propulsion with an 'intermediate' exhaust velocity can not simply be stated to be 'better' than one with exhaust velocities in the hundreds of km/s. The energy-momentum trade-off is not unique to mass-drivers anyway, it will always be present in reaction mass based engines. LuxArdens (talk) 12:20, 18 April 2016 (UTC)

Need more differentiation

"All existing and contemplated mass drivers use coils of wire energized by electricity to make electromagnets"

This is not true. Mass drivers could be railguns, gauss cannon, or coilguns. The three types use fundamentally different principles to operate - only gauss cannon use electromagnets. Railguns use an electric current to provide a repulsive force, and a magnetic field is generated merely as a byproduct. Any electrically conductive payload will work, it does not need to be ferromagnetic. Coilguns are different yet, using an attractive force to draw a magnetic projectile or magnetic sabot down the barrel.

A good summary can be found at http://everything2.com/index.pl?node=Electrical%20weapon

Acehunter 19:58, 31 January 2007 (UTC)

Final Fantasy 8

Didn't they use one of those in Final Fantasy VIII to transport the protagonists to the space station, I think this was on disc 3.

I found it odd that this was not mentioned in the "Mass driver in science fiction" section, so I thought I may of misread the article, can someone confirm that there are similarities.

They both sound like shoving someone in a tube and shooting them out of a cannon into space to me. --Wafflemou 07:37, 21 August 2007 (UTC)

Mass Driver is not a railgun!!

The article says "A mass driver is essentially a coil gun" and Railgun says "It [a railgun] is not to be confused with a coilgun (Gauss gun)." Yet in "Mass drivers in science fiction" some of the references are of railguns! --70.179.72.172 (talk) 22:52, 7 December 2007 (UTC)

Mass drivers are any driver that throws mass.

Is this perhaps an english localization issue? In science fiction the word mass driver has always been used to generically imply anything which throws mass no matter what manner it choses to do so. The only real distinction between a mass driver and a rocket is that a majority of the kinetic energy is imparted by an outside mechanism on the mass.

Looking at dictionaries though it seems some of them are also using the word to mean magnetic catapults. I'm certain plenty of references can be found to show that even modern day weapons are mass drivers though. Anyways I felt the issue should be brought up at least. —Preceding unsigned comment added by 64.126.82.205 (talk) 06:32, 17 December 2007 (UTC)

Yes, mass driver is a generic term, strictly speaking, for anything that moves anything else (eg, changes the momentum of anything that has mass-energy). In the context of space habitation and development, the term has been established in the community for over thirty years to mean something that uses electromagnetic means to shoot material off at a fairly high speed, to one of two purposes: (a) to deliver the material from a planet or moon to a destination in space, or (b) to use material nominally available as junk (such as asteroidal dirt) as reaction mass so that the momentum given it provides a reaction force on a vehicle or smallish asteroid: ie, as a rocket that runs on electric energy and junk.

I think a rail gun would qualify as a mass driver if it is used to deliver payload or provide thrust (but not as a weapon or device to destroy a target), yet there are mass drivers which are not rail guns. By convention no one would call an ion drive a mass driver, but English usage is not perfectly logical.

I don't think it would, or at least, I've never seen it defined that way. If nothing else, a railgun's rails are subject to ablation, whereas a coilgun-type design has no wear. If some magical new technology appeared that obviated that restriction then I could see the definition changing, but right now, the coilgun type design is the only game in town. Or at leasts, that's what I believe is the NPOV position, but I'll certainly accept a good reference to the contrary, and then we can add it to the article, I'm not sure that science fiction counts though.- (User) WolfKeeper (Talk) 01:26, 20 December 2007 (UTC)

For the space launch application, "a fairly high speed" would need to be comparable to the escape (or orbital) velocity of the body being launched from, eg, about 2.5 km/sec (orbital, ~1.5 km/s) for The Moon, as in an Arthur C. Clarke short story describing a lunar electromagnetic launcher. This is difficult to achieve for Earth because of the atmosphere, which is harsh if you are traveling 11.2 km/s (~8 km/s) near sea level. Since the payload is to be used off-site, it would typically need to be contained in a package for collection, not just dissipated.

For the thrust or rocket motor application, the exhaust velocity needs to be of the order of the "mission velocity" (or total velocity you want to achieve), in order to get a good balance between the need for low mass usage and reasonable energy efficiency (this is a general issue for all kinds of rockets). The reaction mass can be carried in "buckets" or something similar, so that the buckets are slowed and recycled (with their energy recovered, one hopes) and reused, while the reaction mass is simply released.

Wwheaton (talk) 00:05, 20 December 2007 (UTC)

Science fiction?

"A spacecraft could carry a mass driver as its primary engine. With a suitable source of electrical power (probably a nuclear reactor) the spaceship could then use the mass driver to accelerate pieces of matter of almost any sort, boosting itself in the opposite direction."

Is this theory truly important enough to be relevant to science? I know there is science behind it, but this sort of factual presentation seems undeserved as of yet. —Preceding unsigned comment added by 66.57.177.5 (talk) 04:37, 21 February 2008 (UTC)

This is a hypothetical rocket engine a spacecraft could carry, and sounds like pretty much at the same state as Nuclear Thermal Rocket, Ion propulsion and etc. Still in testing state with model built, yet still long from being used in practical. MythSearcher^talk 05:57, 21 February 2008 (UTC)

Not sci fi at all, this is the principle behind Ad Astra Rocket Company's VASIMR propulsion. It can accelerate any ionized particles. Successful vacuum chamber tests were performed this year, and a version of the engine is scheduled for installation on the ISS. -- 99.233.186.4 (talk) 17:46, 14 November 2009 (UTC)

Moved science fiction to specific article

Articles are supposed to be on a single topic. The article scope is clearly real mass drivers, so the fiction is offtopic. So I've moved it out and linked the other article.- (User) WolfKeeper (Talk) 00:41, 5 July 2008 (UTC)

Lacking decent references

The two references this article cites are pretty questionable (a blog and a news site). Additionally they do not provide a great deal of detail which is included in the article. Tagging refimprove. 86.133.229.194 (talk) 11:32, 23 September 2008 (UTC)

New Diagram

Hello, I'm new to wikapedia editing, but I have some 3D experience, and this article is listed as needing a diagram. I would like to make that diagram and I just thought I'd ask for suggestions for the best and most useful way to depict a mass driver. What I had in mind was a simple luner maglev track, a circular loop followed by a ramp, launching a spherical payload. Advice for level of detail, technical accuracy, final resolution, format(GIF?), animation length, filesize etc. is greatly appreciated, as this would be my first submission to wikapedia.
Here is a sample of my work:
Perpetual Motion Machine[1]
Dashrendaer (talk) 23:32, 26 August 2009 (UTC)

disposable buckets

given large costs of lifting to orbit in the first place, why dispose of any mass, ever? 100% of payload mass should be re-used. worst case: it could be broken down and re-used as reaction mass for propulsion. -- 99.233.186.4 (talk) 17:52, 14 November 2009 (UTC)

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With humans on board, a mass driver's track would need to be how long?

I've replaced the text "several hundreds of kilometers" with "almost 1000 kilometres"

Accelerating at 30m/s^2 (more than 3g) for 250 seconds would accelerate the spacecraft to 7,500 m/s in a distance of 937,500m or nearly 1000km. There was NO reference given for the claim of "several hundreds" other than the equations of motion and any fool can do their own calculation to show that "several hundreds" of Km just isn't long enough.

It looks like whomsoever added "several hundreds" added his (wrong) original research and by correcting that mistake, I've arguably added my own "original research" which of course violates policy too. So what is to be done? Start a discussion. Peter Dow (talk) 12:46, 15 April 2021 (UTC)