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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)."
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!"Bush's moon and mars plan seem like such a comprehensive change for NASA that they might also have a serious impact on the ESA. With NASA's budget redirected into the new plan, will the ESA pick up the slack with greater involvement in the ISS beyond the ATV? Or will they have a significant involvement in the moon and mars plan - maybe using the ATV to supply a moon base? It would be a shame for them to spend a fortune developing the ATV, only to be told that it was no longer needed because the ISS was no longer maintainable due to a lack of US funds.
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.
An ion drive is still nowhere near effective enough for a manned
interstellar probe.You need a fairly pure fusion drive, or antimatter, or some flavour of beam-rider to get interstellar journey times down to a few years or decades without completely silly mass ratios.