Dawn's approach to Vesta (orbit planned for August)

[Martin]

I am intrigued by the Dawn mission to Vesta and Ceres---the two largest in the asteroid belt. Ceres is now rated "dwarf planet", diameter ~1000 km, estimated large amount of underground water.

 

Dawn uses solar-powered Xenon ion drive.

 

Dawn and Vesta are now both roughly the same distance from the sun (about 2 AU) and "running neck and neck" at roughly the same speed around 20 km/second.

Vesta is slowly overtaking and Dawn is thrusting to speed up, so that it can exactly match speeds. It is now about 0.1 AU from Vesta.

 

Ion propulsion is very gradual. It will take 9 to 10 months before Dawn is in orbit around Vesta.

 

The first "science orbit" will be August 2011. Dawn will stay in useful orbit around Vesta for 9 or 10 months (in the general vicinity for roughly one year but not all that time in "science orbit").

In May 2012 the plan is for it to turn on thrust, spiral out from Vesta and go spend some time studying Ceres. If all goes well it will be orbit Ceres for about 5 months (February-July 2015.)

 

Here's a map of the Dawn journey:

http://neo.jpl.nasa.gov/orbits/fulltraj.jpg

 

Simulated view of Sun, Earth, and Venus as seen from the spacecraft's perspective

http://neo.jpl.nasa.gov/orbits/fullview3.jpg

 

General overview:

http://dawn.jpl.nasa.gov/mission/dawn_fact_sheet.pdf

 

Current status report:

http://dawn.jpl.nasa.gov/mission/status.asp

 

More simulated views, if anyone is interested:

http://dawn.jpl.nasa.gov/mission/live_shots.asp

 

http://en.wikipedia.org/wiki/Ceres_(dwarf_planet) ~1000 km diameter

http://en.wikipedia.org/wiki/4_Vesta (average diameter ~530 km)

Edited October 23, 2010 by Martin

[Moontanman]

I have been very excited by this space craft and it's mission from the beginning. I look forward to seeing the surface of Vesta but Ceres is the biggie for me. I think Ceres will turn out to be the most interesting object in the inner solar system.

Edited October 23, 2010 by Moontanman

[Martin]

I have been very excited by this space craft and it's mission from the beginning. I look forward to seeing the surface of Vesta but Ceres is the biggie for me. I think Ceres will turn out to be the most interesting object in the inner solar system.

 

Yes, you are quite possibly right.

 

I don't know enough to guess as to the scientific interest---it will say a lot about the chemical composition of the very early solar system. Surely one of the most interesting things inside the orbit of Jupiter (as you say, the inner solar system.)

 

I keep returning to the thought that it might also turn out to be the most USEFUL new object in the inner system. It's water is at a HIGHER GRAVITATIONAL POTENTIAL than elsewhere. It is easier to get stuff off the surface of Ceres, than, for example off the surface of the Moon or Mars.

 

Stuff incoming at Mars can use atmospheric breaking (parachutes have been used.) So to ship an unmanned package from Ceres to Mars should be comparatively cheap.

 

Water is scarce in the inner SS and Ceres has a lot of it. Ceres may also have abundant carbon and nitrogen too---I have no way of estimating the odds. But ammonia and methane are common enough in the outer SS and Ceres is more like outer bodies. It's composition could be more like the moons of Jupiter.

 

Its a very longterm proposition, but one can speculate about a chemical industry on Ceres.

 

Industry might have to be largely robotic, I'm not optimistic about humans adapting to radiation and low gravity. But those who do get to go there should find Ceres great fun.

Do you happen to know its surface gravity? It's escape velocity?

 

Hmm, I see that the surface gravity is 3% of earth. Imagine weighing only 4-6 pounds, only 3% of what you weigh on earth. I suppose one would tunnel down, perhaps down to a water table or ice layer. One might live in ice caves, with pressurized atmosphere.

 

I see the escape velocity is 1/2 a kilometer per second. Divide by the sqrt(2) to get the circular orbit velocity at surface. Not terribly fast.

 

Around 360 meters per second, and the speed of sound at the earth's surface is about 340 meters per second. So you could shoot something horizontally at Ceres surface, at 360 m/s, and it would orbit at ground level all the way around assuming it didn't hit surface irregularities.

 

Maybe you can tell me more about Ceres. You may be more educated about solar system stuff than I am.

Edited October 28, 2010 by Martin