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                 Electric Engines Keep Many Satellites in Orbit

   by George Putic

   Among the challenges of deep-space travel is the amount of fuel needed
   for long flights. One of the solutions could be the electrical engine,
   powered by electricity from solar panels. Such engines already are in
   use aboard many satellites.

   Physicists consider gravity a weak force. After all, we overcome its
   pull each morning when we get out of bed!

   However, launching a satellite requires more effort: a large rocket and
   a lot of chemical fuel, which is quickly burned as it powers upward.
   Once the payload reaches about 160 kilometers above the earth, the
   effect of gravity has weakened enough for it to stay in orbit.

   A one-way mission into deep space would require even more fuel,
   according to [1]NASA senior technologist for space propulsion, Michael
   Patterson.

   "For any mission application, particularly in deep space, the energy
   required to do the mission is huge, so the propellant fraction is
   typically quite large," he said.

   Patterson said in the 1950s, the space agency started experimenting
   with so-called electric propulsion, or EP - - a jet of electrically
   charged particles that does not require too much power. Once in space,
   an EP-craft would keep gradually accelerating toward its destination,
   moving faster and faster the longer it travels. After four years, for
   example, it could be travelling at 10 kilometers a second.

   Ion jets

   That makes it ideal for long-range missions. But while NASA was testing
   EP for deep-space voyaging, engineers found another application for ion
   jets closer to our home planet.

   The gravity of the sun, moon and earth constantly pull on
   geosynchronous commercial satellites, which stay in the same position
   relative to earth. Electric propulsion proved to be very useful for
   making sure that they stay in their required position.

   Patterson says out of approximately 250 geosynchronous satellites in
   orbit today, about 43 percent have some form of EP on board.

   Applications for deep space missions had to wait for another decade.

   "It wasn't until the 1990s where electric propulsion actually started
   being used by NASA for a NASA mission and that was with the advent if
   the ion thruster technology that was flown on the Deep Space One
   mission."

   Efficient propulsion

   Scientists continue to experiment with other forms of propulsion that
   require even less energy. While NASA is developing the next generation
   ion propulsion system called NEXT, others are experimenting with more
   radical concepts, such as Q-Thruster, that uses radio-frequency
   microwaves instead of charged particle jets.

   Critics call it "the impossible engine," saying that the concept
   violates the basic principles of physics, while proponents say they
   have proof that it has actually generated thrust.

   Patterson points out that EP is not appropriate for crewed missions in
   earth's orbital environment or for travel to the moon, because it would
   take too long.

   "Crossover point is in the kind of, Mars kind of destination, or
   beyond, meaning, if you have enough power on board it starts to
   possibly may make sense to use electrical propulsion for a crewed
   mission," said Patterson.

   He said for now, however, it would be reasonable to use EP for big
   unmanned vehicles taking cargo to Mars orbit, to support human
   infrastructure on the ground.




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   [2]http://www.voanews.com/content/electric-engines-keep-many-satellites
   -in-orbit/2415418.html

References

   1. http://www.nasa.gov/
   2. http://www.voanews.com/content/electric-engines-keep-many-satellites-in-orbit/2415418.html