Mission managers of NASA's Dawn asteroid probe have a long day ahead of them as they wait for news from the asteroid belt.
At 10 p.m. PT on Friday (1 a.m. ET, Saturday), the ion thruster-propelled spacecraft was due to arrive in orbit around Vesta, one of the largest asteroids living in the asteroid belt between Mars and Jupiter.
However, the probe has been firing its thrusters for several days straight, and until the thrusters switch off, the probe cannot orientate its antenna to communicate with Earth.
BIG PIC: Asteroid Vesta Comes into Focus
Later today, at 11:30 p.m. PT on Saturday (2:30 a.m. ET, Sunday), Dawn will transmit a signal, hopefully confirming that it has been captured by Vesta's gravitational field and that it is now orbiting the large asteroid measuring 330 miles (530 kilometers) across.
But all is not lost if Dawn missed its target.
Using ion thrusters to propel it through interplanetary space, the spacecraft has been sneaking up on Vesta, rather than speeding up and rapidly slowing down. The latter method used by rocket-propeled spacecraft can have catastrophic consequences if the target should be missed. With Dawn's ion drive, if the target is missed, there will be enough fuel to take another shot at entering orbit.
DNEWS VIDEO: DOOMSDAY ASTEROID
"We've always got the ability to catch up," Dawn project manager Robert Mase, of NASA's Jet Propulsion Laboratory in Pasadena, Calif., told SPACE.com .
BIG PIC: 2 Pallas, the Asteroid with Protoplanetary Attitude
Interestingly, the exact mass (and therefore gravity) of Vesta is not known, so small corrections in Dawn's trajectory will likely be needed when in orbit around Vesta.
Vesta is often considered to be a planetary embryo that had its growth stifled early in the history of the solar system. Vesta is one of only three known remnant "protoplanets," the others being Pallas, a main belt asteroid, and Ceres, the only main belt dwarf planet.
Dawn will remain in orbit around Vesta for a year, before gently boosting away to begin the trip to Ceres, the second half of its asteroid belt adventure.