Dawn Spacecraft Shuts Down Ion Engines
Written by Nancy Atkinson
Dawn mission banner. Credit: NASA/JPL
The Dawn spacecraft's three ion engines have done their work for now, and mission engineers shut down the frugal but powerful ion propulsion system on Thursday as scheduled. The spacecraft is now gliding toward a Mars flyby/gravity assist in February 2009. "Dawn has completed the thrusting it needs to use Mars for a gravity assist to help get us to Vesta," said Marc Rayman, Dawn's chief engineer from JPL "Dawn will now coast in its orbit around the sun for the next half a year before we again fire up the ion propulsion system to continue our journey to the asteroid belt." The unique propulsion system will allow Dawn to travel to the asteroid Vesta in 2011, enter orbit around the asteroid, and then leave that orbit to head to orbit another asteroid, Ceres in 2015. This has never been accomplished before, and the ion engines make it all possible.
Dawn's ion engines are vital to the success of the misson's 8-year, 4.9-billion-kilometer (3-billion-mile) journey to asteroid Vesta and dwarf planet Ceres. Just one of these extremely frugal powerhouses can generate more than 24 hours of thrusting while consuming about .26 kilograms (about 9 ounces) of the spacecraft's xenon fuel supply — less than the contents of a can of soda. Over their lifetime, Dawn's three ion propulsion engines will fire cumulatively for about 50,000 hours (over five years) — a record for spacecraft.
Artists concept of Dawn. Credit: NASA/JPL
Dawn's ion engines may get a short workout next January to provide any final orbital adjustments prior to its encounter with the Red Planet. Ions are also scheduled to fly out of the propulsion system during some systems testing in spring. But mostly, Dawn's three ion engines will remain silent until June, when they will again speed Dawn toward its first appointment, with Vesta.
Vesta is the most geologically diverse of the large asteroids and the only known one with distinctive light and dark areas — much like the face of our Moon. Ceres is the largest body in the asteroid belt. By utilizing the same set of instruments at two separate destinations, scientists can more accurately formulate comparisons and contrasts. Dawn's science instrument suite will measure shape, surface topography, tectonic history, elemental and mineral composition, and will seek out water-bearing minerals. In addition, the Dawn spacecraft itself and how it orbits both Vesta and Ceres will be used to measure the celestial bodies' masses and gravity fields.
Source: NASA
Filed under: Missions, Space Flight
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November 21st, 2008 at 12:14 pm
Dawn's supply of liquid xenon is about 425 kg from what I've been able to find and would take up about 142 litres of space. According to one website liquid xenon costs about US$10 per litre so the cost to fill up Dawn's gas tank is about US$1420 and this will get it about 6.3 billion kilometres of mileage. That works out to 2.3 L / 100-million km. The 0.24 kg used in 24 hours (as Nancy suggested above) works out to be about 0.087 L (87 ml), our about 1/4 of a pop can.
My Toyota Matrix can go about 600 km on a 50 L tank of gasoline (or about 8.3 L/ 100 km) at a current price of about CA$1/L. So for me to drive for 24 hours (about 2000 km) I would use about 165 L of gasoline.
So for me to drive to Ceres it would cost me about CA$525-billion (or about US$420-billion) and would take me about 8630 years and use 525-billion litres of gasoline.
So I would say that NASA is getting their time and money out of Dawn!
November 21st, 2008 at 12:16 pm
oops. I did mean to write 0.26 kg in 24 hours! The 87 ml figure is based on 0.26 kg!
November 21st, 2008 at 1:44 pm
SOOOO why aren't we integrating this tech into commercial cars ?
November 21st, 2008 at 2:34 pm
Unfortunately, if you used ion propulsion tech in cars they'd have 0-60 acceleration measured in years rather than seconds, and I for one don't want to wait that long to get home from work. To get high efficiency, Dawn's engines sacrifice specific impulse (the 0-60 part).
November 21st, 2008 at 4:02 pm
"To get high efficiency, Dawn's engines sacrifice specific impulse (the 0-60 part)."
Actually the specific impulse is quite high. The ion engines however lack thrust, making them unsuitable for automobile use.
November 22nd, 2008 at 8:55 am
formulaterp,
You're absolutely right, it's the high specific impulse that make's ion power so cool. I just slipped a groove for a moment…
November 22nd, 2008 at 12:58 pm
Actually the thrust of the ion engine is so low, that it could not move a car on the surface of the Earth at all, due to static frictional forces.
However, it would cause the car to lean forward a bit, but you'd need some pretty fancy equipment to detect that – assuming we had equipment sufficiently sensitive!
-Nivag
November 22nd, 2008 at 3:11 pm
"Aye, Captain! Ion drive… we could learn a thing or two from that one"
March 24th, 2009 at 5:21 pm
Seversky Ionocraft, patented in the 1960s, was rated more energy efficient than small aircraft such as Cessna or helicopters. Today, with improved materials and manufacturing tech, including carbon fiber fuselage and parts, we could have not only working aircraft with "no moving parts" in the propulsion system, but also could use this same technology to power small energy efficient cars, especially if we use BlackLightPower.com high power density energy source for electric power generator onboard. (Carbon fiber manufacturing efficiency has been maximized by Dr. Amory Lovins and associates.) Just as the Woody Norris counterrotating helicopter blades are being ignored in general application, apparently, so too the Seversky Ionocraft is being totally ignored by "the big boys."