NASA Looks At Railgun-Like Rocket Launcher

coondoggie writes "NASA is looking hard at a way to blast spacecraft horizontally down an electrified track or gas-powered sled and into space, hitting speeds of about Mach 10. The craft would then return and land on a runway by the launch site."

Comments

Well, this is not a

[ScrewMaster]

new idea, exactly, but I guess it's good to see NASA looking at other possibilities. There are many. I remember MIT doing work on alternate launch technologies back in the seventies, if not earlier. The mass driver was one (a giant electromagnetic linear accelerator) although the idea was kicked around in science-fiction long before that. My current favorite is a possibly-reusable rocket whose reaction mass is water, using heat energy provided by ground-based lasers. You could launch things into orbit all day long with a setup like that. Probably need a dedicated nuclear power plant to run the thing.

Re:Well, this is not a

[PolygamousRanchKid]

Well, I believe this critter was up and at it in the 70's at Princeton: http://en.wikipedia.org/wiki/Gerard_K._O'Neill

Re:Well, this is not a

[rjstanford]

Ah, Heinlein, may you never cease to spin.

Anyway, the other think to consider (especially for things like laser-based launches) is that the current "spit out a ton of speed really quickly and then coast your way to orbit" approach really sucks. Even a slow nice steady boost will get you to orbit without needing to hit escape velocity.

Re:Well, this is not a

[timeOday]

Oh, it was already imagined in sci-fi novels and childrens' TV programs? Quick, somebody tell NASA before they waste a bunch of money developing a usable capability!

Re:Well, this is not a

[Nyeerrmm]

Who coasts into orbit? Once the engine cuts off in most any launch vehicle you've achieved orbit.

Get going at the right speed from the ground and you'll enter orbit as long as there's not a mountain in the way (you'd probably want to boost your periagee afterwards though). The main reason you go up before accelerating to orbital velocity is that you get above the atmosphere and don't lose as much energy.

Re:Well, this is not a

[ScrewMaster]

Even a slow nice steady boost will get you to orbit without needing to hit escape velocity.

Well, sure, you could do at a walking pace ... if you had the reaction mass.

Re:Well, this is not a

[BlueStrat]

Ah, Heinlein, may you never cease to spin

Yes, Heinlein used this tech as a centerpiece enabling technology for Moon->Earth grain shipments (and as a kinetic weapon used against Earth once the rebellion started..."throwing rice") from a lunar penal colony in his superb science fiction novel "The Moon Is A Harsh Mistress". I highly recommend the story. Heinlein was amazing at predicting tech & science advances far, far ahead of any of his contemporaries.

In the above Heinlein novel, a rail launcher for Earth was proposed for several possible locations. These proposed locations shared certain characteristics, among them was elevation/altitude at the launcher exit point.

NASA could do a lot worse than taking some more inspiration (IIRC he's generally credited with the concept of communications satellites) from such an intellect.

Strat

Re:Well, this is not a

[InfiniteWisdom]

"spit out a ton of speed really quickly and then coast your way to orbit" approach really sucks

A "nice slow steady boost" will burn an enormous amount of fuel.

Let's say your rocket weighs 1,000lb. If you provide = 1000lb of thrust your rocket will just sit there. If you provide 1001lb of thrust it'll start to accelerate every so slowly... if you provide 1002lb of thrust you'll accelerate twice as fast, but only burn ~0.1% more energy.

You'll go faster (for a given thrust) as you burn up fuel and thus shed weight, but at any weight, the higher the thrust, the smaller the percentage of energy you spend just overcoming gravity, and the more you spend accelerating the vehicle.

And don't forget, that if you got above the atmosphere "slow and steady"... if you're under orbit velocity, you're going to fall right down unless you plan on burning fuel forever.

Re:Well, this is not a

[ScrewMaster]

IIRC he's generally credited with the concept of communications satellites

Nope. That was Arthur C. Clarke, another of the grand masters of hard science-fiction.

Re:Well, this is not a

[mdielmann]

There are a number of reasons why rail guns are more attractive than a "steady boost".
First, we don't have anything that gives a steady boost for any reasonable amount of time at a reasonable amount of force. Rockets just don't last very long in the overall scheme of things, and laser-based propulsion systems don't have enough force to launch any appreciable payload (yet).
Second, rail guns don't require you to accelerate fuel in order to keep on accelerating. This puts an effective limit on rockets, and anything the rail gun adds pushes out our capacity based on the fuel limit.
Third, the higher/faster you're going before you start using conventional rockets will reduce fuel requirements, increase payload, or increase orbit. This is somewhat related to the second item, but not entirely. Conventional rockets require you to bring your fuel with you, which reduces payload capacity, and this compounds with the effects of being deeper in the gravity well.

Re:Well, this is not a

[pixelpusher220]

Yeah but going mach 10 at ground level isn't exactly rainbows and ponies either...

Re:Well, this is not a

[Shadow Wrought]

Yeah but going mach 10 at ground level isn't exactly rainbows and ponies either...

True, but you do have the potential to turn ponies into rainbows...

Re:Well, this is not a

[robot256]

That would be a rather unfortunate pony, and a rather monochromatic rainbow. Do these things come with windshield wipers?

Re:Well, this is not a

[robot256]

before gravity takes control.

As the GP said, gravity is a conservative force. It is ALWAYS in control. Right now, gravity from distance stars is pulling us in their direction--the force is infinitestimal but present nonetheless. It is an extreme colloquialism to say that when you throw a ball up in the air gravity "takes control" when it starts to fall down, never mind that gravity caused the slowing of its ascent as well. Same as in orbits.

"Coasting into orbit," in your colloquial usage, simply means cutting the engines at a lower altitude than the final orbital altitude. To pull it off, you have to be going faster than orbital velocity at the lower altitude so that after your engine is cut off, some of your kinetic energy is transferred to potential energy, and you slow down while still going up until you reach the final orbit. This is no doubt used for small portions of most flights. But the GP's point is correct; anyone who understands Newtonian physics will be able to tell whether and what orbit you will reach once you cut your engines, thus no one ever bothers to talk about "coasting".

The only difference with a railgun-only launch system is you reach the maximum velocity at ground level and spend the *entire* trip to orbit "coasting." This is not what NASA is proposing. They will use the railgun only as the first stage, followed by scramjets and an orbital-insertion rocket engine, which is a much more realistic proposal.

Re:Well, this is not a

[u17]

When you cut off your engines, you *are* in orbit. There is no "final" orbit to go to from there. The only question is, does your orbit intersect the Earth or not :-)

Re:Well, this is not a

[dwinks616]

and laser-based propulsion systems don't have enough force to launch any appreciable payload (yet).

And they never will. Lasers will NEVER be able to push anything into orbit, period. E=MC2. If you make E big enough to push a payload into orbit, your E ends up turning into M. Lasers only a bit more powerful than what we have now will end up creating matter in their pumping chambers and halting their output. The top few lasers on the planet are pretty close to the maximum power lasers can attain before spontaneously creating mass from the light they make. What may work, however is using a laser to beam power to the "solar" cells at the bottom of a space elevator and using that power to inch up the elevator cable.

Re:Maybe someone should tell them...

[arkane1234]

Space is not up, it's all over, we're on a sphere.
You can go to your right and ignore gravity completely to reach space.

Re:Maybe someone should tell them...

[ScrewMaster]

That space is up.

Up is relative. Space is away.

NASA still cannot do simple math.

[drcheap]

"...hitting speeds of about Mach 10."

"Starr noted that electric tracks catapult rollercoaster riders daily at theme parks. But those tracks call for speeds of 60 mph -- enough to thrill riders, but not nearly fast enough to launch something into space. The launcher would need to reach at least 10 times that speed over the course of two miles in Starr's proposal."

Mach 10 = 600mph ???

Re:NASA still cannot do simple math.

[vlm]

Once ignited, Mach 10 wouldn't be outrageous for a Scramjet.

Well, that seems a bit optimistic for a device that has been successfully flown, what, twice? Its kind of like planning the Boeing 777 the day after the wright brothers first flight.

The real killer with all these "hybrid" lifter designs is they are all ignorant of the virtually unknown 666 rule.

The 666 rule is that Mach 6 (which is tricky for an air breathing aircraft) at 60000 feet (again, tricky) is a whopping 6% of the way to orbit.

So, if, in your wildest dreams, you can simultaneously achieve mach 6 at 60Kft, which would be quite the noteworthy achievement, you've still got 94% of the way to go.

Alternately, you could take the required second stage, and make the fuel tank at least 6% bigger and skip all this air breathing foolishness.

Re:NASA still cannot do simple math.

[vlm]

im pretty sure mach 25 is orbital velocity. which would make mach 6 a bit over 20% of the speed needed. which is more than 6%.

Ouch, hope your physics teacher doesn't see your post. If E=1/2 * m * v**2, the ratio boils down to (mach6)**2 / (mach25)**2 which works out to 36/625 which works out to 5.76 percent. The energy required to gain altitude does matter, if you're going up a couple hundred miles. If it didn't, elevators wouldn't need motors. You are correct that the velocity is where most of the energy goes, and I didn't bother to verify the math, but its vaguely around the remaining 0.24 percent figure.

My point still stands, an idealized orbital rocket at mach 6 and 60kft has only burned about 6% of its total fuel.

Re:NASA still cannot do simple math.

[vlm]

Yes, you've verified the staging equations, but you're still better off with a traditional, simple, ultra reliable first stage. The absolutely cheapest thing about orbital rocket launchers is the propellants, everything from R+D to launch support costs more. "Saving fuel" is a profoundly false economy for orbital launchers. A great way to spend billions to save millions (or less).

Also first stage is arguably the most phase of flight. A terrible place to "innovate".

Re:NASA still cannot do simple math.

[vlm]

There is great potential for energy savings, which would mean higher payloads and/or less expensive flights.

You want higher payloads, find a rocket that works, and make it bigger.

As for less expense, I take it you believe most of the cost of the space shuttle program is liquid H2? If so, you are horribly misinformed. If, by some utter miracle, the shuttle could be operated on flying unicorns instead of solid boosters and H2/O2, calculate the delta cost in the shuttle program. I think you'll be surprised how many decimal places you'll need to use.

Liquid H2 costs about a buck a pound in the quantities NASA uses. (We'd pay closer to two bucks a pound). The entire shuttle tank holds about a quarter million pounds of liq H2. No math phd required to figure that filling the fuel tank costs about a quarter mil. A similar level of math is required to multiply that by about 130 shuttle flights to get a lifetime program cost of a whopping 30 million or so. Wikipedia claims the total cost of the shuttle program from "I gotta idea" to end of program is about 175 Billion. So, liquid H2 fuel cost works out to 30 / 175000 * 100 = about 0.02 percent of total project cost. "Saving fuel" is simply irrelevant.

So, if we risk the lives of every crewman using a new non-man rated engine and/or delay the vehicle program by decades to develop and deploy the amazing fuel free flying unicorn engine system, we will save a whopping two hundredths of a percent of total program cost. Or rephrased, for the R+D to pay for itself, we need the total cost of R+D and deployment to remain below two hundredths of a percent of program cost.

Two hundredths of a percent of project cost is about what you budget for developing and deploying the HR diversity training, or perhaps company funded picnics. Not a realistic budget factor for a new primary propulsion system.

Re:Maybe someone should tell them...

[AnonymousClown]

That space is up.

You see, they'll fire the spacecraft horizontally and it'll fly really really fast until it falls off the World into orbit.

Re:Maybe someone should tell them...

[Spectre]

Space is not up, it's all over, we're on a sphere.
You can go to your right and ignore gravity completely to reach space.

Damn it, we've been doing this rocketry thing the hard way.
The easy way is just to "ignore gravity"!

(Yes, I know what you mean, but it is more fun this way :)

Let's hope NASA is better at math than TFA

[Just_Say_Duhhh]

According to TFA, the sled will be "hitting speeds of about Mach 10." That's fast, but then the TFA says, "electric tracks catapult rollercoaster riders daily at theme parks. But those tracks call for speeds of 60 mph -- enough to thrill riders, but not nearly fast enough to launch something into space. The launcher would need to reach at least 10 times that speed"

Sorry, but 10x roller coaster speeds isn't close to Mach 10.

NASA is on to something interesting here. It would seem that MagLev is required (no wheels can handle that speed), and it would be interesting to see what kind of acceleration they can get out of LIM's. Rocket propulsion seems a waste in this application. It might help bullet-train technology, and we can get some new spin-off inventions from NASA.

Re:Let's hope NASA is better at math than TFA

[movrev]

Accelerating up to supersonic speeds on a maglev track is quite problematic from a controls/stability perspective. The generated shock waves will bounce off of the ground/track creating some interesting ground effects which will mess up the launch unless properly controlled. I'm sure their proposal is to get the sled up to about Mach 1, at which point they'll be able to take off with a ramjet engine. Once they reach around Mach 5 in the atmosphere, they could transition into a scramjet configuration which can theoretically allow them to reach orbital speeds. This specific problem has been in NASA's mind for a number of years now. I used to work on this precise thing in collaboration with them around 5 years ago.

Re:Let's hope NASA is better at math than TFA

[amh131]

Back of the envelope for 6000 mi/hr (100 x 60 mph rollercoaster) in 2 miles gives something on the order of 114 G.

Re:Let's hope NASA is better at math than TFA

[Athanasius]

This is really just bad wording in his opening paragraph.
Really it's that:

1. 1) The railgun part needs to get things up to 600mph, 10x the rollercoaster speed.
2. 2) Once launched at 600mph off the railgun the scramjet fires up and eventually gets the thing to 'Mach 10'

The Universe Today article is worded a little better: http://www.universetoday.com/73536/nasa-considering-rail-gun-launch-system-to-the-stars/

Re:Maybe someone should tell them...

[butterflysrage]

so basically the trick is to fall down and miss?

Re:Maybe someone should tell them...

[sconeu]

You're being facetious, but that's exactly what would happen.

Finally...

[Prune]

After all the hype that we've been hearing over the years about rail-guns and seeing a few military and hobbyist demos on video sites, this one piece of near-former sci-fi may be finally coming to fruition as a usable approach. It's a great example of the sort of thing that had to wait for technological improvements and refinements, rather than a fundamental scientific or technological breakthrough, and is the convergence of several technologies. I'm encouraged to see more progress on such things which seems to have in recent years been eclipsed by information technology's faster cycles and overhyping in media (and I say this as someone who makes his living as a software engineer).

Re:Finally...

[DerekLyons]

After all the hype that we've been hearing over the years about rail-guns and seeing a few military and hobbyist demos on video sites, this one piece of near-former sci-fi may be finally coming to fruition as a usable approach.

Nope, this piece of "near former sci-fi" is just as far from fruition as it ever was.
 

It's a great example of the sort of thing that had to wait for technological improvements and refinements, rather than a fundamental scientific or technological breakthrough, and is the convergence of several technologies.

It's a great example of people not learning from the past and re-inventing the square wheel because now they have the tech to make carbon fiber square wheels instead of those old fashioned wooden ones.
 
But they're still square wheels.
 
The basic problem with a railgun is that it give only a fraction of the velocity required - and it does so only in one plane. (Orbital velocity has both a horizontal and a vertical component, railguns provide velocity only in the horizontal, cannons only in the vertical.) So you end up still needing a substantial rocket stage in order to provide the missing velocity - but now that rocket stage needs to be reinforced (thus increasing parasitic mass) in order to stand the stresses of being handled (while fueled) horizontally and of having to maneuver while still deep in the atmosphere[1] and insulated against structural heating from friction due to it's high speed low in the atmosphere... You end up not gaining anything over the conventional approach.
 
Railguns don't work because we lack some wonder technology for the gun - they don't work because the structural sums don't add up for the booster. Any materials improvement that you could apply to a railgun boosted launcher, you can also apply to a conventional launcher, which still leaves the railgun launcher trailing in performance and cost.
 
Railguns and a host of other alternative launch schemes look so simple and obvious that people simply cannot convince themselves that they don't work. So, they keep throwing money and tech at the problem convinced that this time it will work, it's so simple it just has to work. So NASA will waste a couple of hundred million dollars dicking around with the new gun - and then they'll discover the problem of booster design (again). And just like the last dozen times they've done this, the project will quietly be dropped.
 
Until the next time someone comes up with a PowerPoint presentation showing how this time it will be different.

[1] If you ever watch a rocket launch, you'll notice it goes more-or-less straight up for a couple of miles before starting to pitch over - there's a reason for that.

One faster

[Anonymous Coward]

Well you could you know, make it one faster, you know go up to Mach eleven. Well, it's one faster, isn't it? It's not ten. You see, the Russians, you know, will be launching at Mach ten. You're on Mach ten here, all the way up, all the way up, all the way up, you're on Mach ten on your magnetic sled. Where can you go from there? Where? Nowhere. Exactly. What we do is, if we need that extra push over the cliff, you know what we do? Mach Eleven. Exactly. One faster.

Put the railgun in orbit

[mangu]

Sorry, but 10x roller coaster speeds isn't close to Mach 10.

And even Mach 10 isn't enough, orbital velocity is close to Mach 25. You cannot run at that speed inside the atmosphere, there's no material that could withstand the heat.

I've seen a much better idea proposed. Put that electric accelerator track in orbit. The energy needed to reach orbital altitude is much less than the energy needed to accelerate to orbital speed.

One could launch the spacecraft vertically to an interception with the accelerator track, then it would catch the track and get the needed horizontal speed while already outside the atmosphere.

Re:Put the railgun in orbit

[X0563511]

... in which case Newton's Laws would adequately describe the reasons why your ultra-expensive orbital mass driver is now an ultra-expensive meteor shower.

Re:Put the railgun in orbit

[dwinks616]

The point of having it evacuated is to avoid air resistance. Every last bit of energy lost to air resistance is energy gained in heat.

Re:Maybe someone should tell them...

[Ethanol-fueled]

Ignoring gravity works when you run off the edge of a canyon or your ACME rocket runs out of propellant. You don't fall until you actually look down and remember gravity.

Re:Maybe someone should tell them...

[GigG]

"Fall down and miss" is orbital dynamics at is most basic.

Why at sea level?

[Anonymous Coward]

Why would they do this at sea level? This should be done somewhere in the American West, at altitude. At 10K feet there is a heck of a lot less air resistance. Could be done on one of the Air Force ranges for sonic boom sake.

Re:Maybe someone should tell them...

[spazdor]

NASA should hire people with surprising bodies and/or opinions to jump out and reveal/explain them, providing a needed distraction at the critical moment.

The Plan is Not Mach 10 on the Track!

[Somegeek]

Everyone is banging their head over trying to hit Mach 10 on the track.

TFS and everyone else is misunderstanding the proposal.

The current idea is for the sled on the track to accelerate a scramjet up to about 600mph, then the scramjet lifts off, flies up to altitude and at about mach 10, releases a rocket which boosts the payload into orbit.

Sled (reusable) on the ground = 1st Stage
Scramjet (reusable) in the atmosphere = 2nd Stage
Booster Rocket in space = 3rd Stage

All extensions of more or less current technology.

Bad Physics

[sjbe]

Anyway, the other think to consider (especially for things like laser-based launches) is that the current "spit out a ton of speed really quickly and then coast your way to orbit" approach really sucks.

Why on earth was this moderated interesting? Is wrong information interesting now? You can't coast to orbit. When the power shuts off you either are in orbit or you aren't. Gravity doesn't take a holiday just because you are out of propellant.

Even a slow nice steady boost will get you to orbit without needing to hit escape velocity.

You can't get into orbit without hitting escape speed (escape velocity is actually a misleading term because it is a scalar). Escape speed doesn't have to be fast (in fact it can be any speed) but again, once the engines shut off you had better be at the escape speed necessary at that altitude or you will fall back to earth.

If a slow steady boost was practical, we'd be doing it. Rocket scientist is a synonym for smart for a reason. We lack the technology to escape earth's gravity well slowly in an economically practical way. I'm not even sure we could do it at all with our current capabilities, but I am sure we can't (yet) do it cheaply.