The ion engine

[Shinova]

I've been hanging around JPL's website recently, and I think, from what I read on that site, that they've more or less cleaned out the bugs regarding the ion engine.

They also have this thing they call a plasma thruster, and another propulsion drive called pulsed thruster, or something like that.

Anyway, ion engines are slated to become the main propulsion drive for spacecraft in future missions, including the one that's slated to head for Ceres and one another asteroid.

[Admiral Valdemar]

They'll need to be nuclear powered, ion engines have jack shit for thrust, go near any reasonable mass and the gravity is going to drag you down with a bump.

[Cap'n Hector]

They'll need to be nuclear powered, ion engines have jack shit for thrust, go near any reasonable mass and the gravity is going to drag you down with a bump.

In free space or with gravity slingshots you can use 'em pretty well. It just takes more work.

[Admiral Valdemar]

They'll need to be nuclear powered, ion engines have jack shit for thrust, go near any reasonable mass and the gravity is going to drag you down with a bump.

In free space or with gravity slingshots you can use 'em pretty well. It just takes more work.

But taking off an landing is what I meant, you could use a deodrant can for propulsion if you wanted, but try landing using it.

[Cap'n Hector]

They'll need to be nuclear powered, ion engines have jack shit for thrust, go near any reasonable mass and the gravity is going to drag you down with a bump.

In free space or with gravity slingshots you can use 'em pretty well. It just takes more work.

But taking off an landing is what I meant, you could use a deodrant can for propulsion if you wanted, but try landing using it.

Then use ion drives for deep space and carry fuel for landing. Ion drives mean less fuel while in flight, thus it's easier to launch and so forth.

EDIT: Stupid spelling error.

[Enlightenment]

They'll need to be nuclear powered, ion engines have jack shit for thrust, go near any reasonable mass and the gravity is going to drag you down with a bump.

Spacecraft don't need propulsive power to go near masses: maintaining an orbit requires no power. A spacecraft with an ion drive can get as close to a large mass as any craft with any other reasonable propulsion system: the common no-go area for all craft is below the top of the atmosphere.

Then use ion drives for deep space and carry fuel for landing. Ion drives mean less fuel while in flight, thus it's easier to launch and so forth.

Landing an interplanetary spacecraft would be rather like putting wheels on a container ship with the objective of delivering its cargo to the end user by driving the entire ship on city streets. It's an utterly bizzare concept with dubious practical merit.

Carry dedicated landers on the interplanetary craft instead. It's much cheaper in terms of both mass and cost.

[SyntaxVorlon]

If it's a cargo hauler it just needs a superconductor mass accel ring to launch cargo to another ring on the target, planet, asteroid(probably more dangerous), or large station. If the cargo is traded completely they can recoup all their power used. They wouldn't have to get that close to the planet at all. Extremely high orbit would work fine. Though if the planet has a heavy atmosphere then the cargo ring would be on an orbital.

[SWPIGWANG]

ITS TIME FOR NUCLEAR ELECTRIC ENGINES MUHAHAHAHAHAHAHAHAHA

what, you think using \/\/U$$ solar panels are going to feed my ION ENGINE OF DOOM!!!!!11111 with enough poWar?

[HemlockGrey]

I have a very basic question.

In space, there are no natural brakes, ne? So, once you're free of any sort of gravity, wouldn't you only need to fire the thrusters once to get you up to speed, and then only fire them when you need to alter direction, instead of a continous burn?

[SyntaxVorlon]

In very low grav, deep space, situations Ion engines would be useful, in high grav fusion engines. Why not use fusion engines for inter sys? Fuel.

The acceleration you get from an equivalent mass of ion fuel to nuke fuel is far different. Nuke fuel burns at nova levels and goes out the back pretty fast, but you end up having fuel problems far faster. With Ion propulsion you are using far less fuel but getting higher net thrust.
At least I think that's how it works out. In the end you can end up going further on ion drives than on fusion drives.

[Shaka[Zulu]]

actually, if we were able to build a true fusion drive, its' fuel consumption would be quite competitive with ion engines (both types would be expelling propellant at high velocities), yet it would also be capable of much more usable thrust levels.

[Howedar]

I have a very basic question.

In space, there are no natural brakes, ne? So, once you're free of any sort of gravity, wouldn't you only need to fire the thrusters once to get you up to speed, and then only fire them when you need to alter direction, instead of a continous burn?

Correct. However, if your fuel consumption is low enough (as with ion engines), you can do a continuous burn all the way to the halfway point, then turn 180 degrees and do a continuous decel burn.

[Beowulf]

VASIMR drives are also pretty good...

[SyntaxVorlon]

I have a very basic question.

In space, there are no natural brakes, ne? So, once you're free of any sort of gravity, wouldn't you only need to fire the thrusters once to get you up to speed, and then only fire them when you need to alter direction, instead of a continous burn?

Correct. However, if your fuel consumption is low enough (as with ion engines), you can do a continuous burn all the way to the halfway point, then turn 180 degrees and do a continuous decel burn.

Or do accel to a certain point near the target then blast like hell with the fusion engines and you'll get there much faster, though one mistake will put you spinning out and away like Frank Poole.

[Enlightenment]

So, once you're free of any sort of gravity, wouldn't you only need to fire the thrusters once to get you up to speed, and then only fire them when you need to alter direction, instead of a continous burn?

You're under a misconception here. In space you're never free of gravity. Objects in orbit feel no gravity (they are in perpetual freefall) but the force of gravity is still there. Indeed, orbits only work because of gravity.

Escaping gravity is not possible: in theory, the gravitational influence of every body in the universe extends to the edge of the universe. In practice gravitational influence will fall off to insignificantly low levels well before reaching the edge of the universe but the distances involved are still far greater than the average spacecraft will travel.

For more information, take a look at NASA JPL's Basics of Spaceflight pages, particularly sections 3 through 5.

To answer your specific question, you are generally correct that it's not necessary to run a propulsion system continously to get from A to B.

Imagine a probe on a simple mission to orbit mars. The launch vehicle used to lift the probe off the ground will deliver the probe into a low-altitude transfer orbit. From this point, all propulsion will be up to the probe itself. Three burns are required to complete the mission: one to break Earth orbit and enter a Hohmann transfer orbit to Mars, a Martian injection burn to enter Martian orbit, and finally a circularization burn to alter the shape of its martian orbit from an elipse to a circle. In practice more burns will be needed for course corrections and to keep the spacecraft in the proper orientation, but in general, during most of the rest of the flight the probe can--and generally will--coast.

Getting around in space is not simply a matter of pointing in the right direction, applying a slight push, and waiting. Major position changes such as travelling from Earth to Mars--or altering an orbital plane--involve very significant velocity changes. Chemical rockets are simply not fuel efficient enough to impart major velocity changes with anything resembling a substantial payload. This is where the ion drive comes in.

Ion drives are far more fuel efficient than chemical rockets. They can accelerate much more substantial payloads to the velocities needed for interplanetary transit using far less fuel than a chemical rocket would require for the same velocity change (delta v).

This efficiency comes at a price, however. Ion drives have pathetic accelerations (low thrust, poor thrust-to-weight in some cases e.g. when nuclear-powered). Pathetic accelerations mean very long burn times to impart the necessary delta v to travel any significant distance. Given that an ion drive must be run for a long period of time to impart sufficient delta v for a mission, there's no real drawback to running them continously--earning as a result considerably more delta v and shorter trip times.

Continous burns aren't mandated or ruled out by orbital mechanics; in the case of ion drives they are simply convinent and efficient.

[SyntaxVorlon]

I have a very basic question.

In space, there are no natural brakes, ne? So, once you're free of any sort of gravity, wouldn't you only need to fire the thrusters once to get you up to speed, and then only fire them when you need to alter direction, instead of a continous burn?

Correct. However, if your fuel consumption is low enough (as with ion engines), you can do a continuous burn all the way to the halfway point, then turn 180 degrees and do a continuous decel burn.

Or do accel to a certain point near the target then blast like hell with the fusion engines and you'll get there much faster, though one mistake will put you spinning out and away like Frank Poole.

Also when we say free of gravity then we say that we can measure the force exerted on us to be in the centinewtons or millinewtons. Deep space.

[Enlightenment]

The acceleration you get from an equivalent mass of ion fuel to nuke fuel is far different. Nuke fuel burns at nova levels and goes out the back pretty fast, but you end up having fuel problems far faster. With Ion propulsion you are using far less fuel but getting higher net thrust.
At least I think that's how it works out. In the end you can end up going further on ion drives than on fusion drives.

No, you've got it backwards.

Specific impulse is the key measure of rocket efficiency. Ion drives have between 2,000 and 10,000 seconds of specific impulse. Fusion torches weigh in at around 100,000s; pulsed fusion drives (ICF, pure fusion Orion) pack a whopping 2,000,000 seconds. Fusion drives are far more fuel efficient than even ion drives and have much higher thrusts to boot. The only thing that beats pulse fusion drives are antimatter drives.

See http://snork.home.texas.net/jason/tep/rockets.html for a comparison of various propulsion concepts.

The only reason NASA hasn't used fusion drives yet is that we don't know how to build them. There would also be political problems associated with most of the low-hanging pulsed fusion drives on account of the fact that the fuel source is basically a large number of decent-sized nuclear weapons.

Note: none of these things are suitable for launching payloads from the surface. Fusion torches don't have good enough thrust to weight ratios to make orbit and the fallout from pulse fusion drives would kill a substatial number of people. Like ion drives, fusion drives are for deep space use only.

[Captain tycho]

In free space or with gravity slingshots you can use 'em pretty well. It just takes more work.

But taking off an landing is what I meant, you could use a deodrant can for propulsion if you wanted, but try landing using it.

Then use ion drives for deep space and carry fuel for landing. Ion drives mean less fuel while in flight, thus it's easier to launch and so forth.

EDIT: Stupid spelling error.

First of all, ion drives were never meant for liftoff and landing, only for deep space.

[Howedar]

This is correct, however upon launch by chemical rockets, if the spacecraft is maneuverd with an ion engine, that ion engine takes less fuel, and therefore the payload weighs less. A savings in weight at the top saves weight everywhere.

[GrandMasterTerwynn]

I've been hanging around JPL's website recently, and I think, from what I read on that site, that they've more or less cleaned out the bugs regarding the ion engine.

They also have this thing they call a plasma thruster, and another propulsion drive called pulsed thruster, or something like that.

Anyway, ion engines are slated to become the main propulsion drive for spacecraft in future missions, including the one that's slated to head for Ceres and one another asteroid.

This reminds me of an idea I read in New Scientist, put forward by some NASA engineer. Using a nuclear/electric ion engine to start, you take deuterium and tritium slush and turn it into ions. And then, as it's moving down the line, you hit it with microwaves to heat the plasma up by millions of degrees. This causes the tritium and deuterium to fuse into high energy helium nuclei, which can then be directed out the back of the engine in streams. So really it would be a hybrid ion/fusion engine, but it would actually be feasible, since we wouldn't be as concerned about containment (we want the helium ash to go out the back of the rocket, that's what would provide the propulsion.)