Atlas 5 rocket runs through practice countdown before Mars rover launch

Vapors stream away from a United Launch Alliance Atlas 5 rocket during a fueling test Monday on pad 41 at Cape Canaveral Air Force Station. Credit: United Launch Alliance

The Atlas 5 rocket that will send NASA’s Perseverance rover toward Mars next month aced a countdown rehearsal Monday at Cape Canaveral, helping ensure the United Launch Alliance-built rocket is ready for liftoff during the rover’s 23-day launch window.

Working a few miles away from the Atlas 5 launch pad at the Atlas Spaceflight Operations Center, ULA’s launch team powered up the Atlas 5 rocket and ran the rocket through a practice countdown. During the test — called a “wet dress rehearsal” — ULA loaded super-cold liquid hydrogen and liquid oxygen into the Atlas 5’s Centaur upper stage, and pumped liquid oxygen into the Atlas first stage booster.

The Atlas 5 launch team ended the countdown rehearsal at 1:55 p.m. EDT (1755 GMT) Monday, just before the rocket’s simulated launch time.

ULA kicked off preparations for the wet dress rehearsal Saturday with the rollout of the Atlas 5 rocket — without the Mars Perseverance rover payload on top — from the Vertical Integration Facility to Cape Canaveral’s Complex 41 launch pad about a quarter mile to the north.

Once at the pad, the Atlas 5’s first stage was filled with RP-1 kerosene fuel in preparation for Monday’s countdown test.

With the countdown rehearsal completed Monday, ULA planned to drain the Atlas 5 of its cryogenic hydrogen and oxygen propellants, then allow the rocket’s tanks to warm up to ambient temperatures before rolling the rocket back into the VIF on its mobile launch platform.

The kerosene fuel will remain aboard the Atlas 5’s first stage through launch because it is stored at room temperature, and does not boil off.

The wet dress rehearsal was once a standard part of Atlas 5 launch campaigns. In recent years, ULA has limited the fueling test to Atlas 5 launches carrying NASA payloads with limited interplanetary launch window. A wet dress rehearsal was also conducted before the Atlas 5 launch on the first unpiloted test flight of Boeing’s Starliner crew capsule last year.

ULA plans to hoist NASA’s Perseverance rover atop the Atlas 5 rocket Friday inside the VIF. Already closed up inside its aeroshell for landing on Mars, the spacecraft was expected to be encapsulated inside the Atlas 5’s Swiss-made payload fairing over the past few days.

An update on the status of the encapsulation process, which was to happen inside a clean room at the Kennedy Space Center, was not available Monday.

The Perseverance rover is enclosed within its aeroshell for launch. Credit: NASA/Christian Mangano

With the addition of the Perseverance rover Friday, the Atlas 5 rocket will stand 197 feet (60 meters) tall. ULA and NASA teams will perform electrical interface tests to ensure the Mars-bound payload is properly connected with the launch vehicle.

The final component to be installed on the rover will be its plutonium power source, or Multi-Mission Radioisotope Thermoelectric Generator, in July.

Launch of the Atlas 5 rocket with the Perseverance rover is scheduled for a two-hour window opening at 9:15 a.m. EDT (1315 GMT) July 20. The mission has launch opportunities daily through Aug. 11 — and perhaps until Aug. 15 — to depart Earth on a trajectory to allow a direct seven-month journey to Mars.

Developed with a budget of $2.4 billion, the Perseverance mission is NASA’s first rover to launch toward the Red Planet since the Curiosity rover took off in 2011.

The robotic rover will land on Mars on Feb. 18, 2021, to begin a mission to collect rock core samples for return to Earth by a future mission.

Email the author.

Follow Stephen Clark on Twitter: @StephenClark1.