NASA Looks At Railgun-Like Rocket Launcher 231
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."
Re:Well, this is not a (Score:4, Informative)
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 [wikipedia.org]
Let's hope NASA is better at math than TFA (Score:4, Informative)
Sorry, but 10x roller coaster speeds isn't close to Mach 10.
NASA is on to something interesting here. It would seem that MagLev [wikipedia.org] 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 [wikipedia.org]. 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:Maybe someone should tell them... (Score:5, Informative)
You're being facetious, but that's exactly what would happen.
Re:Well, this is not a (Score:3, Informative)
Re:Maybe someone should tell them... (Score:2, Informative)
Re:NASA still cannot do simple math. (Score:5, Informative)
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:Well, this is not a (Score:3, Informative)
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 (Score:3, Informative)
"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 (Score:4, Informative)
IIRC he's generally credited with the concept of communications satellites
Nope. That was Arthur C. Clarke [lakdiva.org], another of the grand masters of hard science-fiction.
Re:Let's hope NASA is better at math than TFA (Score:2, Informative)
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 (Score:2, Informative)
This is really just bad wording in his opening paragraph.
Really it's that:
The Universe Today article is worded a little better: http://www.universetoday.com/73536/nasa-considering-rail-gun-launch-system-to-the-stars/ [universetoday.com]
Re:The Plan is Not Mach 10 on the Track! (Score:1, Informative)
Here is the the link [popsci.com].
Bad Physics (Score:3, Informative)
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.
Re:Well, this is not a (Score:4, Informative)
before gravity takes control.
As the GP said, gravity is a conservative force. [wikipedia.org] 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 (Score:3, Informative)