ESA spacecraft tracks target asteroid

PARIS, Aug. 4 (UPI) -- The European Space Agency says its Rosetta spacecraft has started visually tracking its first target asteroid to determine its orbit with more accuracy.

The ESA said Rosetta started the optical navigation process Monday at a distance of about 15 million miles from the target asteroid called Steins. The optical tracking is to continue until Sept. 4, when the spacecraft will be approximately 590,000 miles from the asteroid.

"The orbit of Steins, with which Rosetta will rendezvous on Sept. 5, closing to a distance of 800 kilometers (500 miles), is only known thanks to ground observations, but not yet with the accuracy we would like for the close fly-by," said Gerhard Schwehm, ESA's Rosetta mission manager. "We will be able to use the first data set for the trajectory correction maneuver planned for mid-August."

Schwehm said that for the first three weeks of the tracking, Rosetta will image Steins twice a week and then, starting Aug. 25, it will take images daily until Sept. 4.

The ESA said the optical navigation follows a series of active check-outs of Rosetta's scientific instrumentation, which began July 5 and ended Sunday.