Ion-Propulsion Craft Reaches The Moon

Rollie Hawk writes "It ain't warp speed, but it's exciting new technology at work! The European Space Agency put an ion-propelled rocket into lunar orbit today. While not much horsepower is generated, this method of propulsion could be ideal for travel in near-weightless space as it does not require any combustion to occur."

Comments

It REALLY Ain't warp speed

[guitaristx]

Considering that Apollo 8 made it around the moon in less than a week, and this mission took over a year, we're not dealing with lots of speed here.

I'm interested in seeing some comparisons with project cost, energy consumption, etc.

Re:Peak of eternal light

[binarybum]

man, screw your moon base. Perfect place for a five-star resort. This sounds like prime realty. The europeans should stake a claim to it and auction it off as land for when the moon is colonized. The price this would go for would probably fund a colonization project, oh and a moonbase - somewhere else.

Plasma technology is the space enabler

[QuantumG]

Although it's called an "ion engine", it's really just the first step in the progression of plasma propulsion. Next up we have the VASIMR which they've been talking about testing on the space station. It can produce slow thrust like an ion engine, or it can produce hard thrust like a chemical rocket. You can power it with solar panels, or you can power it with a nuclear reactor. Eventually, almost the exact same design will be used in fusion rockets, and possibly even antimatter rockets. Then we're in Startrek country with plasma power distribution and ships which you can actually live and work on.

Re:Is it regular speed?

[centauri]

Could cryogenics and this propulsion technology together land humans on other planets?

No, especially if you're aiming for extrasolar planets. Ion engines are good for a small payload that can take its time getting to where it's going. Humans (even those in some kind of imagined stasis) need something with a higher thrust to get where they're going in a reasonable time (ie, before cosmic radiation carves up their DNA, or a micrometeor holes their lifesupport system).

How is weightlessnes relevant?

[mowler2]

I dont understand why they talk about the probe being (near) weightless in space in the same context as the engine beeing useful in space?

No matter where the probe is, it has got the same mass, and hence the same inertia. Low-thrust engines work good in space because of no friction and often no requirement on quick travel (if it is a non-manned spacecraft). On earth an ion engine would never work for several reasons, one beeing friction against air and ground, but none of them has to do with the weight of the vechile/probe?

Or have I misunderstood something?

Re:I don't get it

[Headw1nd]

Ok.. the reason this is noteworthy, despite it's lethargic speed, has to do with reaction mass. Ion propulsion and rockets are similar in that both require reaction mass for propulsion- the craft goes forward because something goes back. The speed which the craft goes forward is proportional to the speed that something is ejected out back. Ion drives have ejection speeds far above that of conventional rockets, thus are far more efficient in their use of their propellant.

So?

So this is crucial on the long haul. With a reaction drive, when you run out of reaction mass, you're done. The craft becomes inert. The trick here is that the saturn V was out fuel within 15 minutes, wheras this craft is still accelerating a year later. Concievably, it could run for another year, or a dozen. (I don't know how much reaction mass it has) An ion drive craft might be made that could with enough reaction mass for an interstellar voyage, where a chemical rocket could not. (esp. considering the mass needed to decelerate at the ead!)

Re:Is it regular speed?

[bcrowell]

Apollo 11 took 73 hours from the burn that took it out of Earth orbit to the burn that inserted it into lunar orbit. This is actually very close to the time it would take to free-fall to the surface of the Earth from a distance equal to the radius of the moon's orbit. This is pretty much always the case with chemical rockets, which work by doing short burns followed by very long periods of free fall: the time to get there is the time it takes to orbit from here to there. To go to Mars, you can use Kepler's laws, and you find that the time to get to Mars in an elliptical orbit is 0.70 years.

The problem with getting to Mars is fundamentally the radiation. If you send astronauts to Mars on a 0.70-year orbit, without any shielding against penetrating radiation, their radiation dose ends up being on the same order of magnitude as the dose that kills you. This is Not Good :-) There is a variety of ways to get around this:

1. Use electromagnetic shielding. (There was recently a Slashdot article on this. The idea is to use a quadrupole field, which discriminates between high-mass and low-mass particles.)
2. Use really thick material shielding. This requires either a really really really thick layer of rock, steel, ... (very heavy), or a really really thick layer of liquid hydrogen. Either way, it's a lot of mass.
3. Cut the trip time dramatically.

Solar-powered ion drive could make method #2 practical, because it would theoretically allow very large masses to be moved around without having to lift huge amounts of propellant off of the Earth's surface. However, a ship with a nuclear reactor aboard (not just a passive RTG) could accomplish both #2 and #3.

Fundamentally, I don't see the justification for sending humans to Mars in the forseeable future. The really exciting science task would be to find out of there is unicellular life on Mars (with a positive result probably qualifying as the most important scientific result of the last 200 years). This can be accomplished with an uncrewed sample return mission.

Want to send humans to Mars? Great! Please dream up either (a) a valid scientific reason, or (b) a valid commercial reason. I don't think either exists presently, and I don't think either will exist within the next 100 years.