Problem during fueling preps forces Atlas 5 launch delay

EDITOR’S NOTE: Updated with details about temperature sensor.

The payload shroud of ULA’s Atlas 5 rocket, containing the SBIRS GEO 5 missile warning satellite. Credit: Stephen Clark/Spaceflight Now

United Launch Alliance called off a launch attempt Monday after hitting a snag during preparations to fill an Atlas 5 rocket with cryogenic propellants at Cape Canaveral, delaying the liftoff of a new U.S. Space Force infrared surveillance satellite until no earlier than Tuesday.

ULA had a 40-minute window beginning at 1:35 p.m. EDT (1735 GMT) Monday to get the mission off the ground. The Atlas 5 launch team pushed back the target launch time by seven minutes earlier in the countdown, a brief delay designed to ensure the rocket would not get fly close to an object already in orbit.

Then preparations to fill the Atlas 5 with cryogenic liquid oxygen, used as an oxidizer on the rocket’s engines, encountered trouble during the pre-loading chilldown procedure, which is design to thermally condition supply lines with small amounts of the super-cold fluid.

The Atlas first stage and Centaur upper stage both consume liquid oxygen — in combination with kerosene and liquid hydrogen fuels, respectively — and ULA reported the issue during Monday’s countdown was with the liquid oxygen supply to the Centaur upper stage.

The launch team dispatched a crew back to the Atlas 5 pad to troubleshoot some valves associated with the liquid oxygen ground systems, but ULA could not resolve the issue in time to resume the countdown and launch before the end of Monday’s 40-minute window.

Tory Bruno, ULA’s CEO, said late Monday that the launch team could not confirm the progress of the chilldown process due to a   “faulty temperature” sensor in the liquid oxygen ground system.

“Bad sensor prevented us from confirming the chill,” Bruno tweeted. “Was actually fine. Ran out of time before we sufficiently understood it.”

ULA plans to try again to launch the billion-dollar mission Tuesday during a 40-minute window opening at 1:31 p.m. EDT (1731 GMT).

There is an 80% chance of favorable weather for launch during Tuesday’s window, according to the U.S. Space Force weather team at Cape Canaveral. The primary weather concern is a slight chance of cumulus clouds violating safety criteria for launch.

One of the two solar array wings on the SBIRS GEO 5 spacecraft is deployed during ground testing. Credit: Lockheed Martin

The payload enshrouded on top of the 194-foot-tall (59-meter) Atlas 5 rocket is the Space Force’s fifth Space Based Infrared System, or SBIRS, satellite.

After deployment from the Atlas 5 rocket’s Centaur upper stage in an elongated transfer orbit, the SBIRS GEO 5 satellite will use its own propulsion system to reach a circular geosynchronous orbit more than 22,000 miles (nearly 36,000 kilometers) over the equator.

The SBIRS GEO 5 spacecraft, built by Lockheed Martin, weighs about 10,700 pounds (4,850 kilograms) fully fueled for launch, a company officials said. It carries sophisticated infrared scanning and staring sensors to detect hot exhaust plumes from missile launches, allowing the military to track missiles that might threaten U.S. and allied forces.

The SBIRS satellite fleet provides global early warning coverage. Four previous SBIRS satellites have launched since 2011 to operate in equatorial geosynchronous orbits, and four SBIRS instruments have launched into high-altitude elliptical orbits to detect missile launches in polar regions.

Each SBIRS satellite costs about $1 billion, according to the Space Force.

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Follow Stephen Clark on Twitter: @StephenClark1.