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Ion Rocket to Map Moon with X-Rays
jralls writes "The Guardian is reporting that a European ion-rocket has taken the last year to reach the moon and is about to enter lunar orbit. Once it slows and gets into a very low orbit, it will probe the surface with x-rays in an effort to solve the long standing puzzle of the moon's origin."
unlike in the 60s and 70s, they are using ion engines for this mission, which can run of solar power.
they give less trust/second, but they can keep burning for allot longer, since the sun gives a constant supply of fuel (in the form of electricity from solar panels).
so you've got a smaller probe, which means easier to get into orbit from where it can fly on it's own power, so even tho it takes longer to get where you want, it will be cheaper to get it into orbit.
btw, they are planning on bigger engines in the future, so hopefully they will go faster someday.
All indicators show that the human race is selectively breeding itself for stupidity.
The ultimate speed of ion propulsion is higher than that of chemical propulsion.
But the mass being expelled at high speeds (the ions) is so low, that accelleration is VERY slow. So it takes a long time to get up to speed, but the maximum speed you can theoretically reach is much greater than that of chemical rockets.
- Spryguy
There are three kinds of people in this world: those that can count and those that can't
Ion rockets can't generate very high accelerations. They can, however, keep going for a long time.
I don't suffer from insanity. I enjoy every minute of it.
The tradeoff is betwen the extra time it takes to get to the destination (due to the low thrust of an ion engine), and the reduced cost created by being able to launch a much smaller amount of mass into space in order to do the mission.
btw, they are planning on bigger engines in the future, so hopefully they will go faster someday.
The issue with ion enginer thrust is not so much size, as it is power. The thrust you get is directly proportional to the amount of power you can generate. If you're using solar arrays, then you're limited to something between 15-20 kW (the Boeing 702 has solar arrays that produce ~15 kW at end-of-life).
The difference is that it will take a chemical rocket much more propellant to get there, because it is far less efficient in its use of propellant mass (i.e. it has a lower specific impulse).
The eart wasn't a solid mass 4 billion years ago. It was molten.
There was no extra weight margins on the launch vehicle to do so. However, if you have a more powerful booster (i.e. lots more money), you can then get higher intial speed.
This mission was to prove to EU that their ion engine worked. So they wanted it to keep running for quit some time. NASA did this be creating deep space one, which ran around picking up steam via its ion engine.
Down the road, you can bet that EU will launch a number of deep space probes based on ion engines with high initial speeds.
In addition, their will be a real push for micro sats with ion engines to control them. Makes a lot of sense to send these to other planets. think of 100 small satillites going though out jupitor or saturn planets. Or better yet, small micro sats around Mars providing surface to space communication, pictures, glp, etc. Send about 100 of these to orbit mars and we would have a very through pic of mars, moon, etc.
I prefer the "u" in honour as it seems to be missing these days.
For anybody who is interested, here's a theory (bottom of the page): "one theory says the moon formed when a big, molten chunk of crust was knocked/blown off from the rest of the planet". And much more info about it.
There was once a theory that the Pacific Ocean was the hole left when the moon was pulled out of the Earth, but...
There is a reason why small objects, like asteroids, are often irregular in shape, while large objects, like planets, tend to be nearly spherical. All parts of an object are attracted to each other by gravity, this tends to pull the object into a spherical shape. Above a certain size (which depends on the materials involved) the object is not strong enough to maintain its shape and collapses into a sphere. Also, even now, the Earth is mostly liquid or softened by the heat, and the collision would have released so much energy that it probably re-melted any part of the Earth that had solidified by then. Add to that the effects of billiions of years of plate tectonics and you would not expect to see the hole.
The earth wasn't a solid mass 4 billion years ago.
It's still not a solid mass now.
That is not so. The sun shines (at one time or another) over the whole surface of the Moon, just like it shines over the whole surface of the Earth.
"I'm not impatient. I just hate waiting." - My Dad
>In space, there is not much that could slow you down.
True. Unless you are somewhat near a large gravity source that the rocket would have to fight against. The Earth for instance.
At each pole, there are such deep caverans that sun never reaches it. That includes X-rays and normal sun light. That is why it is possible for ice to be there. And yes, it is considered part of the surface.
This is an EUROPEAN spacecraft.
SMART-1 has been making bigger and bigger orbits around the earth, because of the smaller thrust explained above. It goes faster and faster, and because the craft gets further from the earth, it becomes easier to get into a bigger orbit. So at first the orbits became larger very slowly, but the last months it has grown faster than ever before.
The last months the orbit was also synchronized with the moon. The highest part of SMART-1's orbit coincided with the lowest point of the moon's orbit. This helps the craft to get an extra boost every month. Take a look at a graph of the orbit here.
Oh, and they do have normal propellant onboard, there's some 70kg left iirc. I think it was installed in case the ion engine failed, but I'm not sure of that. It could also be to correct the initial orbit if the launcher would have placed it in a wrong one. Anyway I *hope* it will be used to attempt a soft landing after the mission is over.
"It's too bad that stupidity isn't painful." - Anton LaVey
> The ultimate speed of ion propulsion is higher than that of
.04 lb of thrust - .64 of an ounce, pushing a spacecraft weighing thousands of pounds on the ground. So the acceleration is very small, meaning takes a long time to get going. The other downside is that the Xenon ions, although chemically pretty neutral, shoot out at such high speeds that anything that gets in the exhaust gets eaten away. This may or may not be an issue depending on there you put it relative to the rest of the spacecraft.
> chemical propulsion.
Depending of course on the fixed mass of the spacecraft, vs it's propellant mass, of course. You get more momentum change from given amount of propellant, but if you only had a teaspoon full of propellant, or the spacecraft was exceptionally massive, you wouldn't get more velocity.
> But the mass being expelled at high speeds (the ions) is so
> low, that accelleration is VERY slow. So it takes a long
> time to get up to speed, but the maximum speed you can
> theoretically reach is much greater than that of chemical
> rockets.
To expand, the measure of efficiency of a rocket engine is the specific impulse or ISP. It's how much momentum change you get per unit of propellant mass, and the usual unit is seconds (lb-sec/lb). The highest actually-achievable ISP from a chemical rocket is somewhere in the 475 seconds. The Saturn 5 first stage was more like about 350, and monopropellant thrusters used for many satellite propulsion systems is more like 150-180! That means that if you want to change the velocity a lot, you need a whole lot of propellant.
I'm not sure which engine this particular program uses, but the ISP of the typical Xenon ion thruster is something like 1800. So you have to carry fantastically less propellant for a given velocity change, meaning it can weight less at liftoff, meaning you can use a weaker/cheaper booster.
The downside is that you don't get something for nothing. It takes, not surprisingly, a whole lot of electrical power to make it go. So you put in 4000-5000 watts of power, and it only generates
Brett
Look up any reasonable book on mechanics and you will find a formula for the final velocity of rockets that have a empty mass M, mass of fuel m, and have an exhaust velocity v. The final velocity of the vehicle is ...
In other words ion rockets will beat chemical rockets because they eject their exhaust at a reasonable fraction of c, whereas chemical rockets have exhaust velocities more like velocities we see on earth (e.g. bullets). So chemical rockets need lots of mass, but that's ok because they throw out lots of mass. Trouble getting to space is expensive ... each kilo of fuel you put in orbit better be wisely used ... so in space ion rockets make sense (apart from the fact you can't use them on Earth anyway ... wouldn't be able to lift off even).
Hope this makes things a bit clearer.
Bitter and proud of it.
I wonder if we are able to observe this interplanetary tortoise from earth? If it passes the bright side in full moon, we should have quite a clear view of it since it's going so slowly.
I'm curious what make you think it will be going slowly? It will be orbiting the moon at exactly the same speed as any other craft at the same altitude would be orbiting the moon. The type of engine or thrust has nothing at all to do with orbital mechanics.
Recent speculation is that the very center has a high ratio of Uranium, enough so that the pressure actually creates a self-sustaining natural nuclear reactor. When it gets too hot it diffuses and shuts down, only to coalesce and restart again (never a big boom). This starting and stopping of the nuclear processes at the Earth's core may be responsible for our planets large magnetic field, and occasional shut downs and reversals of the magnetic field as this nuclear process fluctuates.
You're right that the center would be weightless, but under more pressure than we can possible create in the lab with the best diamond anvils. It only takes a few miles of crust to crush carbon to diamonds, and here we are talking 8,000 miles of rock pressing down. Though the rock (iron) at the center isn't adding any additional pressure, it has thousands of miles of rock above it that is. Quite the hellish place.
BTW, I don't know how I typed Biq in my rirst post when I meant to type Big (no one seems to have noticed)
Letter To Iran
The general idea of a ionization engine is obviously sustained impulse (as previously stated).
Ionizations engines are typically attatched to probes which have initial combustion engines that give them the thrust required to escape the earth's gravity. Once the probes have escaped gravity, the ion engines allow continual thrust that allow (for extremely long range expeditions) extremely high velocity. It is a competing technology with solar sails - which also allows for huge velocities over long distances using continual (though very low) acceleration.
This probe isnt making much use of the ionization engine, as the article says: "Smart was originally designed to test the feasibility of 'ion engines' which operate by shooting out streams of electrically-charged xenon." The duration of the mission isnt long enough to reap the benefits of a continual acceleration device.
Theoretically, ionization engines and such drives are the only currently possible means of probing, say, the other side of the galaxy, within hundreds or thousands of years, instead of taking billions of years with a one-thrust coast - as they have the possibility of reaching fractions of the speed of light.
But this is more about the moon's origins than the ion drive =)