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"?

[Bromskloss]

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

Exactly, human language needs more of parentheses, like in mathematics, so it's "electric (ion propulsion)" rathern than "(electric ion) propulsion". :-)

Re:"Electric ions"?

[ArieKremen]

The European Space Agency (ESA) has recently sent a satellite to the moon using ion propulsion. (http://www.esa.int/SPECIALS/SMART-1/SEMLZ36LARE_0 .html)

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)

Re:"Electric ions"?

[beckerist]

It's all about momentum:
p = m * v
p = momentum, v = velocity, m = mass

Yeah, an ion drive is just spitting out...well...ions. As there's negligible gravity the further your distance from any large body, you don't have (noticeable) friction / angular acceleration to slow you down. Spitting out a single ion might not get you moving much faster, and it might not give you a lot more momentum, but it is still a measurable effect.

Now spit out trillions upon trillions of ions... It's moved from being a measurable effect to cheap (not monetarily, I'm referring to energy expenditure) and effective means of moving in space.

Re:"Electric ions"?

[Rei]

Specific impulse (Isp) is a very real, very important term in rocketry. The standard unit is "seconds" (sec), and is the velocity of the exhaust divided by the acceleration of gravity at the surface of the Earth (9.81m/s^2). Isp and thrust are the two most cited stats for rocket engine performance.

Of course, the velocity of the exhaust itself is more useful in calculations (who needs Earth's gravity factored in?), but that's just how things go. :)

Re:"Electric ions"?

[ozeki]

Actually having worked for the company http://www.spectrumastro.com/ that built Deep Space 1 http://nmp.nasa.gov/ds1/tech/sep.html. It has been in use as a main propuslion system since 98. There was a 'gas' tank that held xenon that was the source of the propulsion.

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

[kickedfortrolling]

Perhaps its the first science mission

we all know deep space 1 was just a NASA trip to get more doritos that got a bit out of hand

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.

Re:Not the first ion thruster propelled spacecraft

[morgan_greywolf]

Gosh, I hadn't realized Doritos were so popular worldwide!

Re:Not the first ion thruster propelled spacecraft

[Brett Buck]

>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.

      Not even that; The Russians have been using them for decades for various spacecraft, and at least some current US comsats use them as well. I am working on another one right now, a comsat that uses it for orbit raising and on-orbit stationkeeping/repositioning.

      I read TFA and it's mostly a load. I don't see why JPL has to jump on the same "we did it first" (except for all the other people who did it before us) bandwagon. I expect that sort of nonsense from ESA but JPL shouldn't have to pump themselves up, since they actually did do a lot of legitimate "firsts".

          Brett

            Brett

Not the first to use ION Propulsion

[jmoo]

Nasa's Deep Space 1 first used ION Propulsion several years ago. http://nmp.nasa.gov/ds1/tech/sep.html

We're doomed!

[Timberwolf0122]

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

Re:We're doomed!

[SQLGuru]

Never tell me the odds.

Layne

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?

Re:acceleration with patience

[morgan_greywolf]

I'll take a stab.

Propulsion systems will likely be driven by some sort of nuclear energy. The theory of operation of these systems will probably revolve around some set of quantum effects, maybe even superposition. These will be early systems based on this technology and, as such, may be prone to various difficulties imposed by the limits of an unrefined technology. They will be capable of traveling at unprecedented speeds using amazingly small amounts of fuel.

While there will definitely be privately-funded space travel, systems based on these new technologies will be very costly, and thus will only be in use by government space agencies around the world. The key to developing these new technologies will be international colloboration, most likely between Japan, Europe, the United States, Canada and possibly India and China.

How's that?

Re:acceleration with patience

[JudgeSlash]

I'm voting for VASIMR (variable specific impulse magnetoplasma rocket). They are meant to be able to "change gears" from high thrust, low specific impulse to low thrust, high specific impulse and vice-versa. In theory you could use the same engine to climb out of Earth's gravity well, coast on the flat space-time bits inbetween, and then come wail on those pesky martians from the top of their gravity well. Suckers.

http://en.wikipedia.org/wiki/Variable_specific_imp ulse_magnetoplasma_rocket

Re:acceleration with patience

[Rei]

The complaints are either obsolete or misguided.

Misguided: they assume Orion launching from the surface, not in space beyond effective EMP range. Most modern proposals call for a space launch.
Obsolete: We now do have the technology to initiate fusion chain reactions on even a miniscule amount of fusion fuel (antimatter-initialized microfusion, AIM)

Of course, Orion itself is an obsolete design, having been replaced by Medusa. Every part of the design (system mass, ability to scale down, specific impulse, radiation exposure, etc) works better than in the classical Orion design.

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!

Re:Two targets?

[Anonymous Coward]

A small correction: The Apollo spacecrafts came straight in from the moon with no orbiting the Earth. See the movie Apollo 13.

Re:Two targets?

[TheThiefMaster]

You're citing a Hollywood movie as an authoritative source?

Because those are so good with facts...

Re:Two targets?

[RendonWI]

"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!" So this thing runs on E85?

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?

American exaggeration...?

[Anonymous Coward]

Reading below, this is NOT the:

First to visit an asteroid
First to orbit two targets
or First to use an Ion Drive

and, in fact, space probes are now becoming sufficiently common for the launches to be a yawn in the press. The Europeans are dropping probes on Titan, for christsake!

What is it with us? This kind of trumpeting makes the rest of the world assume we're so insecure that we need to keep pretending that we're the best...... Oh wait, maybe that's true??

Re:American exaggeration...?

[swanchr]

So... you might want to check your facts. The Americans (Cassini spacecraft) dropped the European Probe (Huygens) on Titan. The press release is somewhat U.S. centric but the first to orbit two separate Planetary bodies is probably a valid claim.

Stairway to heaven

[Nefarious Wheel]

Propulsion systems will likely be driven by some sort of nuclear energy

Every once in a while I drift back to Doc Smith on the bookshelf. Although his space suits were made of Bakelite, some of his thoughts were rather far-seeing (thinking for example of the replicated logic units of his Skylark electronic brain) considering he wrote in the 30's, where Einstein's mass-energy equation hadn't yet been popularised. Pre-atomic era. He thought that with enough energy you could turn energy directly into matter and use that for reaction mass. Sturgeon's Law holds with his ideas, for sure, but still it really makes me wonder...

About time

[huckamania]

It's nice to see well thought out and efficient science experiments like this one. The asteroids in our solar system are probably more valuable to us in the short term than any of the planets or moons, with the exception of our own moon. I remember an estimate of how much iron is in the asteroid belt once and its enough to cover the earth several times over.

As scary or foolish as it may seem, our only future is to get off this rock and learn to live in space. Mars is El Dorado, worthless except in the minds of poets and dreamers. There may be hope for purchase on some of the moons, but to get to them or Mars we'll have to have already adapted to space.

I don't think it will work with out fusion, but if they find gold or oil in one of those rocks, who knows what could happen.

Re:About time

[Loke the Dog]

As unromantic as it might sound, water will probably be the first stuff mined from asteroids, and the only stuff for a long time.

The thing is that bringing asteroids to the surface of the earth isnt easy, and even gold isnt really THAT expensive on earth. You have to launch mining equipment, mine the asteroid, bring the stuff to earth and then land it on earth. Add those things up, and it might not be worth it. Lastly, finding gold on an asteroid is unlikely.

Water on the other hand has many advantages. It can be found in very pure forms on asteroids, it is very easy to mine, requires no processing and it doesnt need to be transported safely to the surface of the earth, but can be sold directly in earth orbit.

After that, we might see metals mined that are useful in space and require very simple processing. I think the space industry will have to build around tourism and exploration for another 100 years before stuff can actually be imported to earth.

Actually, there's a subtle distinction

[iamlucky13]

There's several different types of ion engies. The Dawn mission is using electrostatic ion thrusters of the same design from the Deep Space 1 mission. The Smart-1 mission, and I'm pretty sure the Hayabusa mission as well, used Hall effect ion thrusters. The differences are small and each has a few advantages and disadvantages. So the submitter would have technically been more correct if they said "electrostatic" instead of "electric." The parent's link also has links to descriptions of each type.

Additionally:

Deep Space 1 was primarily a technology demonstrator mission. It carried a few instruments, but these were also prototypes.

Smart-1 was a combined technology demonstrator / science mission.

Hayabusa has both an ion thruster and hypergolic chemical rockets.

Re:American exaggeration... (not really, no)

[ausoleil]

No space launch is ever "routine." While the world (especially the Russians and the US) are roughly fifty years past the days of rockets usually exploding rather than flying, there is still a great deal of risk involved whether the payload is a satellite for cable tv, a manned mission to orbit the Earth or even a robotic mission to another celestial body.

People seem to forget the number of failures exploring Mars. The Americans lost the Observer, the Climate Orbiter, Deep Space 2, and the Polar Lander since 1990. The Russians lost Mars 96. The Euros lost Beagle 2 -- all of which offset the spectacular successes of the Pathfinder, Spirit and Opportunity, and the Mars Reconnaisance Observer. So yeah, it's "routine" all right to travel the vast distance from Earth and explore the nearest planetary body.

Space is, in fact, far from routinely explored.

Firsts-O-Matic

[Tablizer]

I believe you could make a distinction between science and technology missions.

But they are slicing thin to create new "firsts" in general. Being the first to orbit asteroids in the *main belt* is also kind of a yawner because Eros, outside the belt, was also orbited IIRC. Being inside the belt is almost like saying, "Pioneer X is the first probe to pass Jupiter while Earth was between a 30 and 50 degrees angle relative to the Sun". It is easy to make up records and firsts if you combine enough factors. Sports announcers do similar stuff: "Dribbley Dunkor was the first point-guard over 6-foot-4-inches to score more than 25 points with a broken big toe before the all-star break!"