in- atmosphere ion engines

I don't know if this is practical or safe, but ion engines in space can run for huge lengths of time, and while they don't provide a large amount of acceleration at one time, they do provide a lot over the entire time they are on. can anyone tell me if it'd be possible to create an atmospheric-capable engine that had a small acceleration rate (.1 G or something like that) but could run for several hours at a time, not necessarily even for an x-prize class vehicle, using some sort of ion engine. No real reason I want to know, just thought that if that's possible, it could provide a cheap, safe, reliable means of getting to space, though obviously slower than a rocket.

In a word, no. The produced thrust is always grossly unproportioned to the needed weight; I've heard about a 28 kgf (that's about 60 lbf) ion engine. It used mercury as propellant and was powered by a nuclear reactor and the total weight was somewhere around 15 tons.

An ion engine producing only .1 G of acceleration would be no use as a launch system because you need at least 1G acceleration to even lift off the ground. Even if you could produce an ion engine that would produce, say, 1.1 G acceleration, the actual acceleration upwards would be only .1 G, the rest serving merely to combat gravity.

This is why acceleration at launch tends to be as high as possible. A shuttle accelerating upwards at 3G is actually under 4G acceleration : 1G being being cancelled out by gravity. In this way, 75% of the rocket's acceleration goes into actual upwards acceleration. An engine producing 1.1G acceleration would be very wasteful since most of the thrust would merely combat gravity leaving very little useful upward acceleration.

true true, that's what i thought, but still an interesting idea. i suppose you might be able to use some xenon ion engine or something for a longer flight like out to the asteroid belt or something if you already had an orbital vehicle, but thats both a long way off and probably won't be relevent by the time we get there anyways i suppose. hopefully it won't be TOO long before we have working fusion . btw, sorry about this being on this forum, thought i was on technology.

The effective specific impulse of a turbojet or fanjet far exceeds that of a rocket engine.

Would it be possible to create a much more powerful ion engine while maintaining the same efficency? If so, that would be the key to cost-effective orbital launches, I've heard before that ion engines have up to ten times the efficency of chemical rockets.

Well yes, but it would need a more powerfull powersource as i understand it.
That could be bigger and more powerfull solar cells or nuclear power..

Ion engine beats the chemical rocket in efficiency by 10:1; providing an Isp between of 5000-6000 seconds. However, a modern turbofan exceeds that figure by twice, while beating the thrust figure in the scale of thousand times.

Given that there is a nuclear reactor light enough to store onboard, it could still be used for propulsion though; instead of accelerating ionized atoms, the ambient air is heated in a turbofan-like engine into several thousand K's.

It seems that JP Aerospace is going to do right that what is proposed in this thread - to use io propulasion within the atmosphere: The ATO will be ion propulsed after leaving the Dark Sky Station for Space and having achieved an altitude where buoyancy no longer is of use.



Dipl.-Volkswirt (bdvb) Augustin (Political Economist)

if you can accelerate the air particles directly through a combination of electric and maganetic fields, yeah.
but not the way it is done in ion engines today, those have a thrust limit.

JP seems to think they will be high enough for drag not to be such a problem. Still...
Maybe that and ion wind both? It kinda looks like a lifter.

At the JP Aerospace homepage I didn't find any detailed informations about the ion drive they have in mind.

So it may be that they will use a quite normal ion drive which is a little bit larger than those of Smart 1, Deep Space 1 etc.

Why not ask jpowell in the General JP Aerospace Forum?

The ATO has extremely large wings - order of magnitude of half a mile or one mile or so.



Dipl.-Volkswirt (bdvb) Augustin (Political Economist)

JP Aerospace can figure using monkeys flying out of their ass as thrust for all that matters. Deep Space 1 Ion engine produces two grams of thrust and if that figure is scaled up to ten thousand times it would still not lift anything off the ground.

Half a mile of wing with few grams of thrust? Please.

The .pdf about the ATO JP Aerospace provide at their homepage makes clear explicitly that their concept no way is lifting something off the ground. So your argument isn't valid regarding JP Aerospace's concept.

They provide an animation too about the ATO: the ATO can't be lifted off the ground because it is already at 42 km altitude when it is going to be launched to go into orbit - it is docked to the Dark Sky Station which is permanently at those altitudes.

From the Dark Sky Station the ATO goes to higher altitudes by buoyancy and then launches horizontally by using an ion engine - no launch "off the ground" no way. The extremely long wings are used to get buoyancy and to not fall down to the earthian surface.

The animation explicitly demonstrates that the ATO will return to the Dark Sky Station horizontally.

Please start a new thread in the General JP Aerospace Forum to ask themselves and to tell them your standpoint.



Dipl.-Volkswirt (bdvb) Augustin (Political Economist)

Ever heard of air resistance?