Atlas 5 rocket rehearses countdown for upcoming launch to Asteroid Bennu

The venting Atlas 5 during today's WDR. Credit: NASA-KSC/Kim Shiflett
The venting Atlas 5 during today’s WDR. Credit: NASA-KSC/Kim Shiflett

CAPE CANAVERAL — Running through a practice countdown to check systems before launching a NASA sample-return probe to Asteroid Bennu in exactly two weeks, an Atlas 5 successfully completed its Wet Dress Rehearsal today.

The United Launch Alliance rocket will propel the OSIRIS-REx spacecraft on a trajectory to intercept the asteroid for a daring “touch-and-go” maneuver to grab a specimen that the satellite will bring back to Earth.

The 7-year, round trip adventure launches Sept. 8 at 7:05 p.m. EDT (2305 GMT).

In preparation for departing Earth, the Atlas 5 was moved from its assembly building to the pad at Complex 41 yesterday and took on 25,000 gallons of RP-1, a highly refined kerosene fuel for the first stage.

During today’s seven-hour countdown, the Atlas-Centaur was filled with 65,000 gallons of cryogenic liquid hydrogen and liquid oxygen under a realistic sequence.

It was all part of NASA’s desire to simulate launch day for the Atlas 5 to uncover any technical bugs in the launch pad equipment or flight hardware before the planned liftoff date.

“If buys down risk early. If we find something during Wet Dress Rehearsal, it beats finding it on the day of launch. If it’s something that can be changed out — like a valve — or an irregularity with cryogenic tanking, it’s worth it for us,” said OSIRIS-REx Launch Director Tim Dunn.

WDRs have become a rarity for Atlas 5 missions on the East Coast in recent years as United Launch Alliance phased them out to reduce the time it takes to prepare a rocket for flight.

“As part of ULA’s initiatives over the last several years, they informed us four years ago that they wanted to eliminate WDRs from the sequence. We said we could get comfortable with that, except for our planetary missions,” Dunn said.

The OSIRIS-REx mission has a tight window, extending only to Oct. 12, in which to launch due to Earth’s alignment with the asteroid. That factor alone drove NASA to request a WDR for this Atlas 5 rocket as insurance the spacecraft will fly.

After draining the cryos from the Atlas-Centaur this afternoon, the rocket will be allowed to warm up before it is rolled back to the Vertical Integration Facility tomorrow. The OSIRIS-REx payload, which was encapsulated in the nose cone yesterday at the Payload Hazardous Servicing Facility, will mounted atop the vehicle on Monday.

On Sept. 8, the Atlas 5 will have 25 launch opportunities, one every five minutes, during a two-hour period extending from 7:05 to 9:05 p.m. EDT (2305-0105 GMT).

It will take nearly an hour for the rocket to accelerate OSIRIS-REx to the proper velocity and release the probe to begin a two-year outbound journey to reach Bennu.

The launch will mark the 65th for the Atlas 5 program.

The rocket’s most recent flight July 28 eclipsed the Atlas 2 program’s stellar record of 100 percent reliability in 63 straight successes between 1991 and 2004 for every Atlas 2, 2A and 2AS rocket ever launched. But now Atlas 5 has one-upped Atlas 2 with a history that stands at 64 successes since 2002 and counting.

See earlier OSIRIS-REx coverage.

Our Atlas archive.