The Engines of Dawn and The Dwarf Planet Ceres
Using its revolutionary engine, the Dawn Spacecraft is readying itself for the closest approach ever to a Dwarf planet. As an appetizer, she offers us the best picture ever of Ceres.
NASA’s Dawn spacecraft is on an epic journey. Launched in 2007, its first mission in the asteroid belt was to orbit Vesta which is variously described as an asteroid, dwarf-planet, and a proto-planet. Dawn’s final planned mission is to orbit and study Ceres which it will do this March, beating the New Horizon Probe’s close approach to Pluto by a few months.
The latest image from Dawn shows the enigmatic white spot first seen by Hubble. It also shows the first hints of cratering, owing to a 30% increase in resolution over the best image that the bigger but more distant Hubble Space Telescope could attain.
Hopefully we’ll find many new surprises as well as answers to Ceres’ current mysteries when Dawn gets real close this March.
You may have noticed that Dawn’s mission wasn’t merely to do a flyby of these two planetary bodies but to orbit both, one after the other. This is no trivial footnote to the mission however. This is actually the first time ever that anything like that has ever happened and it’s all because of Dawn’s three revolutionary Ion Engines.
Conventional rocket engines carry a tremendous amount of expensive fuel to flit around the solar system. Well, actually they don’t permit that much flitting because almost every significant maneuver a spacecraft makes requires a tremendous amount of extra fuel to pull off. So much so that NASA has never launched a spacecraft capable of orbiting two different bodies in our solar system, until now.
Ion engines however do not have this limitation. They are ten times as efficient as rocket engines and require about a tenth of fuel. This is achieved in this new class of engine by bombarding on-board xenon atoms with electrons to turn them into ions. Using charged metal plates, these ions are accelerated out the back of the engine at a staggering 90,000 miles per hour. This backward action causes a forward re-action pushing the spacecraft towards its destination. This push is tiny however. Go put a piece of paper on your hand. That weight you feel is equivalent to the feeble force generated by the engine. This force builds up however. Such a tiny push can accelerate the 65 foot 2,700 pound craft from 0 to 60 mph in four days. Not impressed? Well the engine can literally do this for years, attaining long before that its maximum velocity of 25,000 mph.
This uses so little fuel that Dawn could use what’s left to not only slow down and orbit Vesta but later break orbit, accelerate all the way to Ceres, and then do the same thing all over again (and still have 1/10th of its original fuel left over). This capability of Ion Propulsion will permit NASA to perform very long and distant missions that would otherwise either obliterate their budget or prove to be impossible with conventional engines.
These engines however are not well-suited to missions carrying humans (you knew there was a big drawback right?) They are just too slow for people who want (and need) to get to their destinations as quickly as possible.
Ion engines are all about patience.
Image Credits: NASA, JPL, Wikipedia