This comment seems to come from ignorance of basic physics and chemistry rather than an acute awareness of it.

The specific energy of the best batteries we have at the moment is only about 2% of that of gasoline. And gasoline isn't that great for a rocket. http://en.wikipedia.org/wiki/Energy_density#Energy_densities...

If you want to talk about taking a jet to mach4, well, now things are starting to get really nuts. Airplanes only work because they can produce lift in excess of their weight. Putting enough batteries on an airplane to make it fly is completely doable; just look at RC airplanes and quadcopters. But getting to mach4 is bonkers at the moment. Drag goes up by speed squared. Doubling your speed quadruples your drag.

Of course, air breathing craft to get above most of the atmosphere are totally viable and so are space elevators (maybe not today but in the future) and the launch loop might be feasible too from a basic physics and material science standpoint.

Once you're in orbit ion drives still aren't awesome at least for human-scale space exploration, but they become viable.

There are manned electric planes quite far into development. For example:

http://www.gizmag.com/e-fan-airbus-electric-plane/31823/

(I'm just pointing out that they are further along than just RC stuff, not trying to argue that it is significant to space flight)

Yeah, sure it's further along. But these kinds of planes fly at 100-200mph.

But mach4 is at least 1000mph or more (depending on altitude). So while the envelope of feasibility might be doable at 100mph or 200mph to go from 100mph->1000mph requires 100x the amount of power. Going from 200mph to 1000mph requires 25x the amount of power.

So here's the rub: not only are your power requirements going up but also your total energy requirements are going up. This is why the Concorde stopped flying. We're too cheap to go fast. Using energy at 100x the rate to go 10x as fast means that your total energy budget has to somehow miraculously go up 10x and 10x more batteries could easily keep a plane from flying.

As battery tech gets better we might find it's possible to do really useful stuff with electric planes. But until really major breakthroughs happen we won't see electric cargo jets or electric-to-launch-orbit. It's not nay-saying that will prevent this but basic physics.

How could I have better put not trying to argue that it is significant to space flight?

The basic thought behind my comment was that people reading your comment might find electric airplanes interesting but not be aware of the progress being made.

You misunderstood. Some aircraft carriers have swapped to electrical propusion systesm vs steam to launch craft. While a rocket sled is no net gain you could launch a rocket to Mach 4+ using rail / coil gun etc which is fairly significant fuel savings. Pushing past that has major issues, but a potential advantage is you can build a air breathing scram jet without needing design your engine for lower speeds.

I agree that: http://eandt.theiet.org/magazine/2014/10/rise-of-electric-ai... is just aboit pointless for rockets.

Building the 32km of track to hit mach 4 at 3g's of acceleration would one of many issues, but my point is simply building another rocket does not really change much. There actually fairly close to the limits of what you can do with a chemical roket.

I think another real problem is that at the end of the 32km of track you need to stop going sideways and start going up. At mach4 (at sea level this is really, really fast) you're going to need either a huge radius or you're going to have incredible g forces. Either way, big engineering problems.

Not 100% clear what you mean by huge g forces. You would not make a round track to do this. You want something close to a straight line with some adjustment for the curved surface of the earth and local gravity.

After launch you’re going to want to rapidly gain altitude as fast as the passengers can tolerate (so ~3g), but even if you lose 30-50% of the input energy your still dramatically reducing your on board fuel needs as in ~30+ seconds of main engine burn.

More importantly you can have an air breathing sage without including a sub sonic air breathing engine which vastly simplifies your design. Further, one proposal was instead of trying to accelerate using an air breathing engine you simply try and maintain velocity as you gain altitude which further expands your useful design space.

Net result, reusable single stage to orbit, with a useful mass fraction, might be possible. Though, I agree trying to hit mach 4 near sea level is going to be a major design issue. But, Mach 2 is defiantly possible and probably a better first goal.

Basically that everything else equal you'd prefer to exit the accelerator straight up rather than horizontally to minimize the time spent in the thick atmosphere slowing down. I agree that a round track is totally nuts.

And you're right, I did misread what you had written earlier. Thanks for engaging rather than downvoting.

Sure, I could see I was not getting my point across.

As to vertical track, you might be able to build a 2 mile near vertical track but you end up adding a lot of energy more cheaply with a horizontal track and for the most part it's energy that's important as you can trade horizontal energy for vertical energy inside the atmosphere. Don't forget for moderate cost you could use balloons to get a few tons to 50+km up where the air is vary thin. But altitude is just not that much of an issue.

If we didn't spend all that time on vacuum tubes then, where would audiophiles be today?

The truth of the matter is that we have a lot of experience with chemical rockets because there is a huge technology overlap with ballistic missiles, from the original German V-2s to modern MRV ICBMs. We haven't yet used those other techs for space launch mostly because they less easily weaponized. So far, national superpowers have been the primary motivators in space development. When they spend money, they like to get some extra power out of the deal.

Air-breathing engines, while useful for initial acceleration of spacecraft, are also useful for moving a missile halfway around the planet. Launch loops, on the other hand, have no practical military uses.

A private space flight industry, with no need to develop dual-purpose tech, would tend to favor lowering the cost of 1 kg to LEO rather than refine the ability to deliver a payload. And that's what makes V.G. and SpaceX so great, even if they are stumbling around like toddlers just out of the playpen right now.