Working through the smoothest post-Challenger countdown to date, engineers Thursday primed the shuttle Atlantis for launch Friday to send a robot spacecraft to Venus in the first U.S. interplanetary mission in 11 years.

NASA's mission management team, established in the shadow of the Challenger accident, reviewed launch processing Wednesday and found nothing that would stand in the way of an on-time liftoff at 12:24 p.m. MDT Friday."It's been a real good count to date," NASA test director Ronald Phelps told reporters early Thursday during a planned 15-hour, 34-minute "hold" in the countdown. "We've been ahead of schedule, or on schedule, on all of our timelines. It's been a real smooth count."

The weather outlook for launch time Friday remained good with scattered clouds expected and acceptable high-altitude winds. Phelps said the only concern was the possibility of high crosswinds at the shuttle's emergency landing strip but otherwise, "we're go as far as the weather is concerned."

Atlantis commander David Walker, 44, co-pilot Ronald Grabe, 43, Mary Cleave, 42, Mark Lee, 36, and Norman Thagard, 45, faced a light schedule Thursday that included a final round of briefings and free time to spend with family members.

While the crew slept overnight, Vice President Dan Quayle, visiting a NASA tracking station near Canberra, Australia, called the crew quarters at the Kennedy Space Center to chat with veteran shuttle flier Charles Bolden about Atlantis's mission to launch the Magellan Venus radar mapping probe.

"You tell Captain Walker and the whole crew that I wish them godspeed," said Quayle, chairman of the National Space Council.