NASA's EPOXI Closes on Hartley 2 Comet

NASA's EPOXI mission continues to close in on its target, comet Hartley 2, at a rate of 12.5 kilometers (7.8 miles) per second. On Nov. 4 at about 10:01 a.m. EDT (7:01 a.m. PDT) the spacecraft will make its closest approach to the comet at a distance of about 700 kilometers (434 miles). It will be the fifth time that a comet has been imaged close-up and the first time in history that two comets have been imaged with the same instruments and same spatial resolution.

The mission's encounter phase begins the evening of Nov. 3, when the spacecraft is about 18 hours from the time of closest approach to the comet's nucleus. At that time the spacecraft will stop transmitting through its large high-gain antenna and reorient itself so its two visible-light and one infrared imager maintain lock on the comet for the next 24 hours-plus.

The hours surrounding comet encounter will be especially challenging for the mission team as they are commanding a recycled spacecraft that was not designed for this comet flyby. The spacecraft was designed and employed successfully for NASA's Deep Impact encounter of comet Tempel 1 back on July 4, 2005. By recycling Deep Impact's already built, tested and in-flight spacecraft, the EPOXI mission provided savings on the order of 90% that of a hypothetical mission with similar goals, starting from the ground up.