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Dawn arrives at the world Ceres

 
 
 
lpetrich

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NASA Spacecraft Becomes First to Orbit a Dwarf Planet | NASA
NASA's Dawn spacecraft has become the first mission to achieve orbit around a dwarf planet. The spacecraft was approximately 38,000 miles (61,000) kilometers from Ceres when it was captured by the dwarf planet’s gravity at about 4:39 a.m. PST (7:39 a.m. EST) Friday.

Mission controllers at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California received a signal from the spacecraft at 5:36 a.m. PST (8:36 a.m. EST) that Dawn was healthy and thrusting with its ion engine, the indicator Dawn had entered orbit as planned.

"Since its discovery in 1801, Ceres was known as a planet, then an asteroid and later a dwarf planet," said Marc Rayman, Dawn chief engineer and mission director at JPL. "Now, after a journey of 3.1 billion miles (4.9 billion kilometers) and 7.5 years, Dawn calls Ceres, home."
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Dawn is now moving away from Ceres, but over the rest of this month, it will slow down and then fall toward the asteroid, and by early next month, it should be in a closer and nearly-circular orbit around the asteroid. Dawn will not be returning many pictures until then, since it will be on Ceres's night side.

Dawn Blog » Dawn Journal | November 28 has more on its odd trajectory for this month.

I got the news from NASA's Dawn Mission (@NASA_Dawn) | Twitter
 
lpetrich said:
NASA Spacecraft Becomes First to Orbit a Dwarf Planet | NASA
NASA's Dawn spacecraft has become the first mission to achieve orbit around a dwarf planet. The spacecraft was approximately 38,000 miles (61,000) kilometers from Ceres when it was captured by the dwarf planet’s gravity at about 4:39 a.m. PST (7:39 a.m. EST) Friday.

Mission controllers at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California received a signal from the spacecraft at 5:36 a.m. PST (8:36 a.m. EST) that Dawn was healthy and thrusting with its ion engine, the indicator Dawn had entered orbit as planned.

"Since its discovery in 1801, Ceres was known as a planet, then an asteroid and later a dwarf planet," said Marc Rayman, Dawn chief engineer and mission director at JPL. "Now, after a journey of 3.1 billion miles (4.9 billion kilometers) and 7.5 years, Dawn calls Ceres, home."
Click to expand...
Dawn is now moving away from Ceres, but over the rest of this month, it will slow down and then fall toward the asteroid, and by early next month, it should be in a closer and nearly-circular orbit around the asteroid. Dawn will not be returning many pictures until then, since it will be on Ceres's night side.

Dawn Blog » Dawn Journal | November 28 has more on its odd trajectory for this month.

I got the news from NASA's Dawn Mission (@NASA_Dawn) | Twitter
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Very cool, though I hate the way it is implied that the gravitational field of Ceres stops at a specific point.

Peez
 
Peez said:
Very cool, though I hate the way it is implied that the gravitational field of Ceres stops at a specific point.
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I hope that it wasn't me implying that about Ceres's gravity.

But there is a point where Ceres's gravity stops being as important as the Sun's gravity, the radius of the  Hill sphere. It's roughly where an unperturbed satellite of Ceres has an orbit period of 1 Ceres year. Ceres's Hill radius is about 220,000 km.

Checking on Dawn Mission: Dawn - Home Page and Dawn Mission: Mission > Where is Dawn Now?, I find, relative to Ceres:

Distance: 61,000 km, 38,000 mi
Speed: 45 m/s, 164 km/h, 102 mph

Well inside Ceres's Hill sphere
 
So, it looks like it will have a circumpolar orbit, is that right?
 
Ceres now has dawn? You mean it was tidally locked and NASA managed to start it spinning??
 
lpetrich said:
Dawn Blog » Dawn Journal | March 6 -- shows some recent pictures turned into a movie showing Ceres rotating. Ceres has some mysterious bright spots on it.
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WOW. That link shows something I haven't seen before. Those bright spots are illuminated after they cross the terminator. This means that they are significantly higher than the rim of the crater they are in (or they are luminous :devil:). Maybe the NASA guess that they are ice volcanoes was a good guess and they are tall ice volcano cones.
 
repoman said:
So, it looks like it will have a circumpolar orbit, is that right?
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Circumpolar?

It will indeed have a polar orbit, one roughly perpendicular to Ceres's orbital motion. That will make it oriented along both the direction to the Sun and Ceres's spin axis.  Standard gravitational parameter contains Ceres's mass in gravitational units, from that asteroid's perturbations of the orbits of other asteroids:
Ceres: 63.1 +- 0.3
Earth: 398600.4418
Sun: 132712440018.
all in km^3/s^2

Additional info from  Ceres (dwarf planet).

From NASA's Dawn Mission (@NASA_Dawn) | Twitter:
Final orbit will be 230 miles above the surface of #Ceres - Carol Raymond

First science orbit will be April 23 with an altitude of 8,400 miles above #Ceres.
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With Ceres's mean radius being 476.2 km, I find

Altitude: 13500 km, 370 km
Orbit radius: 14000 km, 845 km
Orbit velocity: 67 m/s, 273 m/s -- 240 km/h, 980 km/h -- 150 mph, 610 mph
Orbit period: 15 days, 5.4 hours
 
Dawn is getting as slow as it will ever get relative to Ceres without crashing onto the asteroid. The spacecraft is also getting to its maximum overshoot distance.

Distance: 77.34 k km, 48.06 k mi
Speed: 10 m/s, 71 km/h, 44 mph
 
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