ULA's Atlas V Ready to Launch MUOS-5 – UPDATE

UPDATE, June 24, 2016:  The launch was successfully conducted at 10:30 am ET today.

ORIGINAL STORY, June 22, 2016: The United Launch Alliance (ULA) is getting ready to launch an Atlas V rocket on Friday, the first since an anomaly occurred on a March 22 launch that placed the Orbital ATK OA-6 Cygnus cargo spacecraft into orbit.  Friday’s launch of a military communications satellite, MUOS-5, originally was planned for May 5, but was delayed while ULA and its suppliers diagnosed and fixed the problem.

During the March 22 launch, the Atlas V first stage engine shut down 6 seconds early.  Fortunately, the Centaur second stage was able to compensate for the under-performance of the first stage.  It fired 60 seconds longer than planned, placing the OA-6 Cygnus spacecraft into the proper orbit and allowing it to successfully dock with the International Space Station (ISS) and deliver supplies.  Cygnus just completed its mission today and reentered Earth’s atmosphere.  It is not designed to survive reentry.  (Cygnus departed from the ISS on June 14 and then was used for the SAFFIRE-1 experiment where a fire was intentionally started inside the capsule to study how fire evolves in microgravity.  Later, several small “cubesats” were ejected into orbit before Cygnus itself made its final maneuver into a destructive reentry.)

Atlas V is powered by Russia’s usually highly reliable RD-180 engine.  ULA quickly traced the problem to the RD-180’s fuel system and in late April specified that it was the RD-180’s Mixture Ratio Control Valve.  In a June 15 statement, ULA went further in explaining what happened:  “at approximately T+222 seconds, an unexpected shift in fuel pressure differential across the RD-180 Mixture Ratio Control Valve (MRCV) and a reduction in fuel flow to the combustion chamber caused an oxidizer-rich mixture of propellants and a reduction in first stage performance. The imbalanced propellant consumption rate resulted in depletion of the first stage oxidizer with significant fuel remaining at booster engine shutdown. The engine supplier has implemented a minor change to the MRCV assembly to ensure the anomaly does not occur on future flights.”

ULA’s Atlas V is used for a broad range of military and civilian space launches and the company insists that it will launch all of its 2016 scheduled missions by the end of the year.  That includes NASA’s asteroid sample return mission OSIRIS-REx, scheduled for September.  Use of the RD-180 engine for national security launches is currently the topic of intense congressional debate and the U.S. goal is to build a U.S. alternative to it.

Friday’s launch of the Navy’s fifth Multiple User Objective System (MUOS-5) communications satellite from Cape Canaveral, FL is scheduled for 10:30 am EDT.  The window is open until 11:15 am EDT.  The weather forecast is 80 percent favorable.  ULA typically webcasts its launches.