Riding an Ion Drive to the Asteroid Belt

Iron Condor writes "JPL is now close to embarking on another of its trademark, one-of-a-kind missions, this time to the heart of the asteroid belt: The Dawn mission is being prepared for launch this summer from Kennedy Space Center. Dawn will explore Ceres and Vesta, the two largest known asteroids in our solar system, which lie in the vast expanse between Mars and Jupiter. In the process, the mission will make history on several fronts. Besides being the first spacecraft to orbit a main-belt asteroid and the first to ever orbit two targets after leaving Earth, Dawn will be the first science mission powered by electric ion propulsion, the world's most advanced and efficient space propulsion technology."

Comments

"Electric ions"?

[CarpetShark]

Aren't ions charged (or charge-stripped) particles? Do we really need to say "electric ions"? Is there another kind?

Re:"Electric ions"?

[cnettel]

The propulsion is electric, as in the energy source being electricity, although some mass is still needed for the actual thrust, hence the ions.

Re:"Electric ions"?

[Dystopian Rebel]

To the true geek, it's all Impulse Power.

Move along, there's no warping to see here.

Re:"Electric ions"?

[MyLongNickName]

Ummmmm... by definition ions require some type of propellant. There are thoughts on some kind of mass driver that would take advantage of the sparsely populated atoms in space for thrust, but nothing past the drawing boards as far as I know.

That being said, ion drives are many, many times more efficient than traditional chemical propellants. If my memory serves, about 3 orders of magnitude more efficient. This yields a much smaller propellant tank. Especially when you consider that the tanks must also be dragged around.

Re:"Electric ions"?

[Intron]

I use Saturn Ion propulsion.

Re:"Electric ions"?

[Rei]

The Isp (specific impulse) on ion drives varies considerably depending on the type of drive and its operational situation. Chemical rockets are typically 300-450 sec. Ion drives (depending on how broadly you accept the term "ion drive") usually range from 1,000 to 20,000 sec. Of course, Isp isn't the only factor to consider -- you also need to consider thrust, mass (including voltage regulation hardware), and efficiency.

There are some really neat drives on the horizon that combine the best of thermal and ion drives, such as VASIMR. The particles are heated with radio waves to extreme temperatures (like in some fusion apparatuses), but since they're ionized, they're affected by magnetic fields. The fields collaminate them into a spiralling plasma, converting their chaotic energy distribution into a directed flow. A magnetic nozzle then redirects this out the back. Moderate thrust plus high ISP -- a nice combination.

My favorite "long range" design is the dusty fission fragment rocket. Most of the energy of fission reactions is contained in "fission fragments" -- basically, the fission of your fissionable fuel blasts microscopic fragments of the fuel at high speeds. In a normal reactor, these bump into the rest of the fuel or the moderator and are "thermalized"; the heat is then converted into electricity lossily. In a fission fragment reactor, the design is such that the fragments (where are inherently ionized) are allowed to escape the core; they can then be A) decelerated to produce electricity, or B) redirected with a magnetic field and vented out the back to produce a ridiculously high ISP thrust. You can do that with ionized particles. :) The "dusty" part comes from the reactor design. The fuel is nanoscale particles of enriched uranium mixed with graphite. Fission reactions automatically ionize the particles, so to keep them suspended at an even distance from each other, all you have to do is ionize the walls of the reactor. Since the particles are so small, their surface area to volume ratio is incredibly large, making radiative cooling realistic. The radiated heat itself can be turned into extra electricity (and even a bit of extra thrust)

Not the first ion thruster propelled spacecraft

[thue]

From the summary: Dawn will be the first science mission powered by electric ion propulsion

No, a quick Wikipedia check says otherwise: http://en.wikipedia.org/wiki/Ion_thruster#Missions . For example, Deep Space 1 used electric ion thrusters.

Re:Not the first ion thruster propelled spacecraft

[lobotomir]

Japanese and European science/tech validation space missions have also used ion propulsion.

Re:Not the first ion thruster propelled spacecraft

[TheRaven64]

I believe you could make a distinction between science and technology missions. To my knowledge, all previous missions involving ion propulsion have been for the purpose of testing ion drives, while this one is expected to perform scientific exploration and happens to use an ion drive.

We're doomed!

[Timberwolf0122]

Sir, the possibility of successfully navigating an asteroid field is approximately 3,720 to 1.

acceleration with patience

[one_who_uses_unix]

I enjoyed the article - take a look at the FAQ. The author(s) mention that ION drive is "acceleration with patience" - it will take 6 years of accelerate to change the spacecraft's velocity by 10KM/s but will use a fraction of the weight of propellant that conventional chemical propulsion would.

Space exploration and the related technology are still in their infancy, it is really exciting to to see the stuff of decades old sci-fi making into reality. Who can predict what non-conventional propulsion systems will look like in 50 years?

Two targets?

[Atheose]

One thing that surprised me was the fact that it will be the first spacecraft to orbit two seperate targets after launch. For some reason I did not think that this was a difficult thing to do, though now that it has been brought to my attention I can understand why.

Re:Two targets?

[Anonymous Coward]

It's not difficult to do if the two objects are in approximately the same orbital path. So, perhaps, we might soon get a probe looking at Phobos and Deimos.

Of course, most probes orbit the Earth for a while after launch, before injection into their transit path. All the early moon probes orbited both the earth and the moon, and the manned ones then orbited the earth again after return. So you could say that three targets have been orbited before, back in the '60s. This was just the project team looking for a 'first' to impress Americans with.

I suppose the difficulty levels go:

Orbit your base
Orbit your base and your target
Orbit your base, then gravity assist from other object, then orbit your target
Orbit your base, then gravity assist, then swing by one target, then orbit final target (typical multi-planet probe)
Orbit your base, then gravity assist, then orbit one target, then orbit another.

In fact, I was most impressed with the few probes which altered their trajectories in mid-mission to do swing-bys of targets of opportunity. You need flexible fuel provision to do that!

TIE Fighters get smashed

[joekampf]

Yes, look at how those Twin Ion Engine (TIE) Fighters faired in that asteroid belt. Not good.

Correction

[FrostedWheat]

Dawn will explore Ceres and Vesta, the two largest known asteroids in our solar system

Correction: Ceres is now the smallest dwarf planet.

Screw that, we need nuclear propulsion.

[Dr. Manhattan]

This one for liftoff from Earth (exhaust is not radioactive), and in-system work, and this one for deep-space missions. We can move thousands of tons around with these, cheaply and safely. (Note: neither of these is an Orion type, which is another option.)

You are attempting...

[foodnugget]

Dawn is attempting to explore Vesta. Cancel or Allow?