What this video doesnt really convey effectively is why ion propulsion was chosen for the Dawn mission as versus some other form of propulsion. The reason for it is fuel efficiency - ion engines can get more thrust from less fuel than almost any other kind of propulsion. This efficiency is measured in what is called specific impulse or Isp. Really efficient chemical engines like the Space Shuttle main engines can get an Isp of about 450 in a vacuum (higher number = better efficiency). The nuclear thermal rocket engines that were developed and tested back in the Fifties and Sixties could get about twice that, 800 Isp. How does the ion propulsion on the Dawn spacecraft compare? Well it can get as high as 3000 Isp, but there are ion engines under development by the ESA that could get as much as 20,000 Isp. The downside? The ion thrusters on Dawn only generate about the same thrust as the weight of a piece of copy paper pressing down on your hand on Earth. However, since these thrusters can operate continuously for weeks, months or even years, they can build up to tremendous velocities. The upshot of this is that you can have a space probe flying around the asteroid belt for years visiting multiple locations and not have huge fuel tanks to carry around (which would require more thrust to move and more fuel to get into space to begin with.) Thats why they are used on Dawn, and on other missions for which getting far fast and making a lot of maneuvers with low launch weight is important. https://youtube/watch?v=DLcZDHx0vJg
Posted on: Wed, 14 Jan 2015 01:03:05 +0000
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