Today I was catching up on the status of the Dawn space probe, which is mere months away from a rendezvous with Vesta, one of the largest asteroids in the Main Asteroid Belt, so much so that the Dawn mission scientists prefer to call it a protoplanet. Dawn is a really cool mission, an ion-powered spacecraft maneuverable enough to rendezvous with Vesta, spend a year in orbit of it, then thrust its way to a rendezvous with Ceres, the full-on dwarf planet member of the Main Belt, in 2015. We’ll finally get detailed images and surveys of these sub-planetary bodies, which are very different from each other: Vesta is dry and rocky and differentiated like a planet, Ceres carbonaceous and probably covered in a thick layer of ice that contains more fresh water than exists on Earth. These are of particular interest to me because of the spec novel I’ve written that’s set in the asteroid belt, and which I’ve alluded to before on this blog.
Anyway, another article I looked at today was this one from the JPL Dawn journal page, and I noted the following paragraph in it:
In December, we saw that by sensing the irregularities in the gravity field, Dawn will reveal the nature of Vesta’s internal structure. Until those detailed measurements have been made and accounted for in the design of the flight plan, however, the subtle effects of the gravity field will cause deviations from the planned trajectory. Therefore, as the spacecraft travels from one science orbit to another, it will thrust for a few days and then stop to allow navigators to get a new fix on its position. As it points its main antenna to Earth, the Doppler shift of its radio signal will reveal its speed, and the time for radio signals (traveling, as all readers know so well, at the universal limit of the speed of light) to make the round trip will yield its distance. Combining those results with other data, mission controllers will update the plan for where to point the thruster at each instant during the next phase of the spiral travel, check it, double check it, and transmit it to the distant explorer which will put it into action. This intensive process will be repeated every few days as Dawn maneuvers between science orbits.
I think that “science orbit” is the most awesome phrase I’ve seen all week. Everything is made cooler by putting “science” in front of it. Can’t you just hear it? ”Helmsman! Prepare to enter… science orbit!“
Dawn will enter science orbit! of Vesta in the science month of Science July, and will surely do much science to it.