First, however, it is worth recalling that this is not Dawn’s primary responsibility, which is to continue to measure cosmic rays in order to improve scientists’ ability to establish the atomic species down to about a yard (meter) underground. Sensing the space radiation requires the spacecraft to stay more than 4,500 miles (7,200 kilometers) above the dwarf planet that is its gravitational master. The gamma ray and neutron detector will be operated continuously as Dawn changes its orbit and then performs the new observations. The ongoing high-priority radiation measurements will not be affected by the new plans.

The principal objective of the orbital maneuvers is to swivel Dawn’s orbit around Ceres. Imagine looking down on Ceres’ north pole, with the sun far to the left. (To help your imagination, you might refer to this figure from last month. As we will explain in May, Dawn’s orbital plane is slowly rotating clockwise, according to plan, and it is now even closer to vertical than depicted in January. That does not affect the following discussion.) From your perspective, looking edge-on at Dawn’s orbit, its elliptical path looks like a line, just as does a coin seen from the edge. In its current orbit (labeled 6 in that figure), Dawn moves from the bottom to the top over the north pole. When it is over the south pole, on the other side of the orbit, it flies from the top of the figure back to the bottom. The purpose of the current maneuvering is to make Dawn travel instead from the left to the right over the north pole (and from the right to the left over the south pole). This is equivalent to rotating the plane of the orbit around the axis that extends through Ceres’ poles and up to Dawn’s altitude. From the sun’s perspective, Dawn starts by revolving counterclockwise and the orbit is face-on. We want to turn it so it is edge-on to the sun.

That may not sound very difficult. After all, it amounts mostly to turning right at the north pole or left at the south pole. Spaceships in science fiction do that all the time (although sometimes they turn right at the south pole). However, it turns out to be extremely difficult in reality, not to mention lacking the cool sounds. When going over the south pole, from the top of the figure to the bottom, the spacecraft has momentum in that direction. To turn, it needs to cancel that out and then develop momentum to the left. That requires a great deal of work. It is energetically expensive. Fortunately, the ever-resourceful flight team has an affordable way.

As we discuss this more, we will present three diagrams of the trajectory. It may be challenging to follow Dawn’s three-dimensional motion on two-dimensional figures, especially if you are not accustomed to reading such depictions. Don’t worry! The team has it all under control, and it works. But consider that however complicated the figures seem, designing and flying the maneuvers is somewhat more complicated. Nevertheless, if you want to try, it might help to try to reproduce Dawn’s movements with your finger as you read the text and study the illustrations. (And if the figures are not helpful for understanding the trajectory, they may at least serve as fun optical illusions, as they did for one member of the test audience.)