[LINK] On the Dawn probe and its Vesta visit

[rfmcdonald]

Over at the Planetary Society's blog, Dawn space probe engineer Mark Rayman goes into wonderful detail about the ion-drive probe's July 2011 encounter with Vesta.

From [high altitude mapping orbit], at an altitude of about 660 kilometers (410 miles), Dawn will have an excellent view of Vesta, close enough to see plenty of fascinating details and yet far enough to allow its science camera to cover most of the surface of this uncharted world during the month of mapping. In addition to using the camera to develop the global maps, the visible and infrared mapping spectrometer (VIR) will be trained on many regions, providing even better resolution on the minerals that compose the surface than it could achieve from the higher survey orbit. When its work in HAMO is complete, the craft will fly in for an even closer look.

[. . .]

Dawn's target after HAMO will be an altitude of around 180 kilometers (110 miles), closer to the surface beneath it than most satellites are that orbit Earth. It may take six to eight weeks to follow the winding path from HAMO to this low altitude mapping orbit (LAMO) under the delicate push of the ion thrust. While that may seem like a long time, a mission to Vesta that relied on conventional chemical propulsion would be quite unaffordable within NASA's Discovery Program, and a mission to both Vesta and Ceres would essentially be impossible. In a real sense then, the time to travel from one orbit to another is about as fast as possible given humankind's present selection of tools for probing the cosmos.

Irregularities in Dawn's orbit will let the spacecraft map the world's mass distribution in fine detail.

As I noted in my previous Vesta post, this asteroid is important because in many ways it's quite like a terrestrial planet.

There is good reason to believe Vesta has a complex internal structure, as do the other large rocky residents of the inner solar system, one of which is immediately beneath your correspondent as he writes this and some of you as you read it. In addition to Earth and Vesta, Mercury, Venus, the moon, and Mars all are thought to have grown very hot as they were forming, and that caused the minerals within them to separate into layers of different composition. In this process, known to planetary geologists as differentiation, the denser materials tend to sink while the lighter materials rise to the top, and when the body cools, the layers are frozen in place. Other processes during the history of the planet may create pockets of higher or lower density rock as well.

Vesta may be the smallest relic from the solar system's formation to have experienced planetary differentiation, and the information scientists glean from studying the interior structure (in concert with all of Dawn's other measurements) will contribute to understanding the process by which planets formed. Even though it is Lilliputian compared to the planets, Vesta is Brobdingnagian compared to most asteroids. In the context of planetary formation mechanisms, its closer brethren are the rocky worlds named above.

I can't wait!