NASA flight to Vesta, Ceres to run on exotic ion power

[Guard Dog]

Excerpts from a long article:

 

NASA scientists hope to celebrate Independence Day a few days late this year, with a spectacular launch of the Dawn mission Saturday -- the world's first flight to the mysterious dwarf planet Ceres and the asteroid Vesta.

 

It is an ambitious enterprise -- the first from Earth to orbit two celestial bodies in succession. The journey is possible only because of Dawn's exotic ion-propulsion engine. Its astonishing efficiency will carry it 3 billion miles on less than 72 gallons of fuel. That has led some to dub the spacecraft "the Prius of space."

 

Getting Dawn from here to there is the job of its solar-electric, ion propulsion engine.

 

With just under 72 gallons of xenon gas for propellant, Dawn will slowly accelerate by about 24,500 mph after leaving Earth orbit. That's far more acceleration than any other spacecraft has managed on its own, said systems engineer Marc D. Rayman of NASA's Jet Propulsion Laboratory in California.

 

Unlike the Galileo mission to Jupiter or the Cassini mission to Saturn, Dawn can't tap the gravity of a giant planet for a big boost in speed. A Mars fly-by in 2009 wouldn't add enough gravitational oomph to do the job, either.

 

Reaching Vesta, orbiting there, then moving on to an orbit around Ceres would have required more chemical fuel than any available rocket could carry.

 

"Without ion propulsion, it really would be impossible to do the mission Dawn is doing," Rayman said.

 

NASA first tested ion propulsion technology in 1998 on its Deep Space 1 mission.

 

Instead of a rearward blast from a chemical rocket, Dawn will press forward in space using a feeble but constant rearward beam of electrically charged atoms of xenon gas. "It's a low-impulse thing, but it can make a lot happen, as long as you're patient," McFadden said.

 

It works like this: Dawn will use solar-generated electric power to knock electrons loose from xenon atoms, giving them a positive electric charge. The charge causes these atoms -- now called ions -- to accelerate toward a negatively charged grid in the back of the engine, then zip out the back at 68,000 mph.

 

The same force that attracts the xenon atoms to the negative grid also draws the grid toward the approaching atoms, and that moves the whole craft forward in space.

 

The push is laughably weak, equal to the weight of a sheet of paper. In fact, it would take Dawn four days to accelerate from zero to 60 mph, and require two pounds of xenon.

 

However, "If you have the time, this is a terrific way to travel," Rayman said. "The job is really too demanding for conventional propulsion systems."

 

Just getting to Vesta would have required 2.5 tons of chemical propellant, he said. But with plenty of time to accelerate and an ion engine, Dawn can get to Vesta, and then Ceres, for less than the 937 pounds of xenon gas on board.

 

NASA officials are eager to launch Dawn on time Saturday. A significant delay would crowd a time-critical August launch window for the Phoenix Mars lander, and the planned Aug. 9 launch of space shuttle Endeavour to the International Space Station.

 

A last-minute delay could postpone Dawn until September, adding as much as $25 million to the mission's expenses.

 

"We're trying to manage Dawn so we're ready to go on the launch window so it's off and on its way by the 23rd," said Todd May, a deputy associate administrator for NASA.

 

Once Dawn does take wing, the eight-year mission will be managed by JPL. Scientists will keep watch on the spacecraft's health and progress, but they won't see data from Vesta until 2011, and their instruments won't reach Ceres until 2015. It's one of the drawbacks of extended space flights, even if the humans involved are waiting safely back on Earth.

 

"It's a long time," McFadden sighed. "I'm eligible for retirement by then."

 

Link! Article

 

The article does go into good detail about the hard science of the mission, and some good details about Ceres and Vesta. But the part I find most interesting is the evolution of the Ion Engine. For those who do not know, it works by applying slow steady acceleration rather that short powerful thrusts. The advantage is that as velocity begins to increase, acceleration is still applied at a constant rate. In a chemical engine, fuel is burned until sufficient speed is reached then the engines shut town to conserve fuel. An ion engine is always accelerating.

 

It's unclear if this will ever be useful for manned spacecrafts but I think is is a big step in the right direction. One of the big hurdles to manned interplanetary travel is that to carry sufficient fuel for the journey increases the mass of the spacecraft (because of the mass of the fuel) to the point that... well, you get the idea.

[Azarkon]

One step closer to science fiction

[Hurlshort]

This is awesome, although it does remind me how much more efficient our personal vehicles could be if Big Oil wasn't constantly standing in the way of progress. Now I sound like a conspiritorial nutcase

[Wistrik]

I remember flying such systems in Microsoft's old Space Simulator. It even had one of those hydrogen scoop things that only functions well at high speeds. Lots of fun. Set course for Mars and go to work. Took awhile but I got there.

[DeathScepter]

yes yes you do, Hurlshot.............and those conspiacies are bad for your brain.......it is a proven fact.

 

 

 

And don't let the green invisible lepercans mess with your head too. For they are the cause for all conspiacies.

Edited July 6, 2007 by DeathScepter

[Aram]

This is awesome, although it does remind me how much more efficient our personal vehicles could be if Big Oil wasn't constantly standing in the way of progress. Now I sound like a conspiritorial nutcase

 

I'm not sure I'd like to drive a car that went from 0-60 in 4 days.

[Walsingham]

Lepercans?

 

"Ye'll never get me pot'o'scabs!"

[Morgoth]

What if Dawn would enter some ominous space-cloud? Wouldn't that brake the acceleration a bit and postpone the mission for 100 years?

[Gorgon]

This is awesome, although it does remind me how much more efficient our personal vehicles could be if Big Oil wasn't constantly standing in the way of progress. Now I sound like a conspiritorial nutcase

 

I'm not sure I'd like to drive a car that went from 0-60 in 4 days.

If you run an engine designed for bio fuel it's every bit as fast as gasoline. If you run bio on an existing diesel it has slightly worse milage but the same performance as diesel. The only reason we are still using gas is that it's cheaper, and engines designed for bio don't sell very well.

Edited July 6, 2007 by Gorgon

[Gfted1]

Being in a constant state of acceleration and having a fixed thrust value would require the craft to start braking about half way there, right?

[Walsingham]

Being in a constant state of acceleration and having a fixed thrust value would require the craft to start braking about half way there, right?

 

I suppose so. Unless you could do something clever with gravity.

[Aram]

This is awesome, although it does remind me how much more efficient our personal vehicles could be if Big Oil wasn't constantly standing in the way of progress. Now I sound like a conspiritorial nutcase

 

I'm not sure I'd like to drive a car that went from 0-60 in 4 days.

If you run an engine designed for bio fuel it's every bit as fast as gasoline. If you run bio on an existing diesel it has slightly worse milage but the same performance as diesel. The only reason we are still using gas is that it's cheaper, and engines designed for bio don't sell very well.

 

Dawn isn't fueled by biodiesel.

[Gorth]

Being in a constant state of acceleration and having a fixed thrust value would require the craft to start braking about half way there, right?

Unless they aim it directly at Vesta and equip the craft with a large coil spring. Then it would make the trip back earth again in no time

[kirottu]

Being in a constant state of acceleration and having a fixed thrust value would require the craft to start braking about half way there, right?

 

I suppose so. Unless you could do something clever with gravity.

 

Like chrashing.

[Humodour]

Cool. Next step is building space craft in space - then you don't need to worry about aerodynamics or escape velocity.

[Guard Dog]

Just heard on the radio, launch now delayed until september so as not to conflict with the shuttle. Grrrrr.