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Next Goals For The ESA
zeux writes "With all the news we got recently from space I tried to gather some information about the next goals of the ESA (European Space Agency). Along with a space vehicle designed to carry supplies to the ISS between 2004 and 2013, they are working on the new 'Vega' launcher (2006) and still playing with the SMART-1 probe which is slowly heading to the moon testing an ion drive that is ten times more efficient than the usual chemical systems (1500 hours cumulated thrust time so far)."
If you RTFA'd, you would realize that the satelite isn't on a direct moonshot, it's spiralling out from an earth orbit, to a lunar orbit. This would be hella slow compaired to a direct shot, which should get it there in a few days at worst. The thing is traveling at 3850km/h, it's just not doing it with a direct vector to the moon, rather, a spiral.
"Victory means exit strategy, and it's important for the President to explain to us what the exit strategy is." G.W.Bush
The ESA also has a probe named Huygens headed for Titan, the largest moon of Saturn that will land on the surface in 2005 and send back photos. Titan is the only moon in our solar system with a thick atmosphere. It is believed it may be similar to that of Earth's millions of years ago.
What are the technical obstacles to Lagrange point colonies?
Mostly all that vacuum and radiation and fast moving rocks and stuff.
Ya know. The usual.
KFG
SMART-1 is part of the Small Missions for Advanced Research in Technology; these missions are specifically designed to develop new space-based technologies. A sister mission, due for launch in June 2007 is SMART-2 , which will be a testbed for laser ranging. The technology will eventually be put to use by LISA (Laser Interferometry Space Antenna), a proposed ESA mission intended to look for the gravitational waves predicted by Einstein's General Theory of Relativity.
The knowhow obtained from SMART-2 will also prove instrumental in developing ESA's Infra-Red Space Interferometer, known informally as Darwin. Darwin, part of ESA's Horizons 2000 programme, will consist of 6 infra-red telescopes flying in precise formation, with the aim of performing nulling interferometry of nearby solar-type stars. Darwin will be sensitive enough to detect the infra-red absorption-line signatures of water, ozone and carbon dioxide in the atmospheres terrestrial-sized planets orbiting one of these stars; these signatures, if detected together, would amount to strong evidence for extraterrestrial life.
Tubal-Cain smokes the white owl.
But they are economical of fuel. Jettisoning the exhaust at such high speed means you need hardly any fuel; which is good, but the energy source is an issue.
The reason that they are inefficient is that the exhaust velocity is too high. It turns out that the optimum exhaust velocity for minimum energy is about 2/3 the mission delta-v- and the delta-v to get to the moon is about 4.1 km/s whereas an ion drive exhaust velocity is usually around 30km/s... hugely too high from an energetic point of view.
Ok, big deal- it's only energy right? Wrong. The solar panels end up pretty enormous, and pretty heavy, pretty quickly. Nuclear energy? Power/weight ratio is little better.
Still, it works, but it's not even as efficient as chemical rocketry; chemical rockets can hit 80+% energetic efficiency in fact (it's very high because of the high temperatures used in the combustion chamber, rocket engines are actually classed as heat engines).
-WolfWithoutAClause
"Gravity is only a theory, not a fact!"The ATV design strikes me as particularly interesting because it brings up a point that I've been wondering for awhile: Why don't we have more automated exploration and maintenance vehicles in Earth orbit. It seems to me that a spacecraft that could launch, orbit earth, and return to earth (not that the ATV can do that) without humans onboard and built in a mass manufactured way would be extraordinarily effective for Earth orbit science experiments. It might also be useful for maintenance of high value satellites (like HST). Since Earth orbit is almost real-time transmission there is no reason to think that putting a mechanical arm on a spacecraft to do maintenance would be any different that a surgeon doing a remote operation via a mechanical hand. The most complicated part would be the approach of the satellite to be maintained, but since the Space Shuttle obviously had no problem doing this there is no reason to believe that an automated spacecraft (with real-time human backup in a controlling station) couldn't do the same (a little more complicated than the ATV's purpose of docking with the ISS, but I don't think its inanely so).
Suddenly, the hairy finger of a familiar monkey tapped me on the shoulder. It was time.--G. T.
A little flash animation for those confused about ion drives: http://www.esa.int/export/esaSC/SEM3K81P4HD_index_ 0.html . Of course depends on mass, momentum, etc. too....
Probably has to do with the number of available electrons to strip away.
Xenon is pretty plentiful (8 valence electrons), and compared to nitrogen (5 valence electrons), seems to have just a few more electrons available with little increase in mass, while still remaining a noble, inert gas.
IANAC
Support FSF: Stop thinking with your wallet, and think with your imagination. (cc/non-commercial)
You need an element which is easily ionized. you also want the individual ions to be pretty massive. A bonus is if the ionized version of the element is not too reactive. Early drives used mercury or cesium, but they had a habit of sticking to things and clogging them up, and had to be heated before they were ionized.
i'm pretty sure the cost of the xenon is negligible compared to almost any other cost around.
A better better link
You said: "One word: fusion. As soon as fusion comes along, coupled with ion drives, chemical rocketry is history. Period.'
Unlikely.
There are two main designs for a fission rocket.
(1) To couple a semi-conventional PWR or BWR with an ion engine. The big downside to this is that you have to have a large secondary system to use the steam to make electricity. What this means is that you have to have a large heat sink (large radiators) and lots of moving parts. A design like the GT-MHR could simplify this, but not hugely so.
(2) Using a bladder of fuel (hydrogen, or water or whatever), you use this as coolant to a critical reactor that jets the superheated portion directly to space. The downside is that this doesn't make electricity, so you would have to divert some of the coolant (which requires construction of the additional secondary systems) or use solar panels or RTGs to electrically power the spacecraft (there will be additional power requirements due to reactor safety equipment).
There are two main designs for fusion power:
(1) Tokamak: basically shaped like a donut, a low atomic number elemental plasma is magnetically confined and heated (with I^2*R losses or X-rays) to the point where fusion occurs. The means of useful energy transfer is via neutrons emitted which hit a water tank surrounding the fusion reactor. From here its just like the secondary side of a normal fission nuclear reactor (ex 1 above).
(2) A pellet of low atomic number elements is simultaneously hit by energetic radition from all directions compressing it until fusion occurs. Heat transfer like above.
You could argue that either of these fusion reactions could operate like the fission reaction #2 above (with part of coolant directed to make electricity), but an important point is that a significant fraction of the energy released by fusion (if it ever produces more energy than is required to induce it) is required to sustain it. This requires the construction of a very large secondary system compared to that of the fission reactor (a lot more heat being transferred). Since a fission reactor will probably provide way more power than is needed anyways, there is no reason to build a much heavier fusion reactor.
Suddenly, the hairy finger of a familiar monkey tapped me on the shoulder. It was time.--G. T.
Beagle is alive! I just got a message from it in my inbox! Lemme double-click it and see what it says..
Oh.. wait...
They are not ignored by "mainstream" science. Mainstream science has already determined that they don't work.
So mainstream science "ignores" them only in the sense that they also ignore reading chicken entrails to fortell the future.
For starters, this is not a drive without a reaction mass. That's what the ball is.
When the ball hits the spring the spring compresses,i.e. deforms, otherwise it wouldn't be a spring, now would it? But only some of the energy of the ball goes into compressing the spring. Some of that energy goes into driving the entire tube "backwards." When the spring expands, again, some of that energy goes into driving the ball forwards, but some into driving the tube backwards again. In the process, as you note some energy is lost as heat.
When the ball "klunks" it drives the tube forward and the ball backward and some energy is lost as heat.
There is no essential difference between the spring and the klunk with regards to energy transfer other than the difference between the energy losses, as you note, which are very small (the klunk heats the ball more than the spring does).
What you have described is an oscillator that winds down after a relatively few klunks because energy is lost at each exchange. Use your brain. Analyze what "energy is lost" means.
It means the thingy goes back and forth a few times and then stops.
Unless you add energy.
By driving a reaction mass.
i.e. the ball.
And you still need a rocket to get it "up there" 'cause it ain't gonna do squat but fall over if you set it up on end and start it going here on earth. And that rocket has to carry the fuel to get the ball going in the first place, and all the fuel to keep it going, so that it can sit there in space and wobble until the fuel runs out. A quantity of fuel that still has to equal the energy value you intend to get out of the device.
This is nothing more than an obfuscated version of the drop hammer that lifts veeeeeeeeery slowly and thenswings down against a stop suddenly.
When the hammer lifts slowly the machine moves backwards slowly. When it swings down and hits the stop it moves forwards quickly but an equal distance less the heat loss in the impact versus the heat loss in the bearings as it rises and it needs fuel to drive it. Fuel which must be lifted into space and carried by the device. About the same amount of fuel that a conventional rocket uses.
And all it does is wobble.
KFG