Spaceflight Insider

ULA: Issue with Atlas V’s MRCV responsible for March 22 in-flight anomaly

Atlas V 401 rocket lifts the GPS IIF-11 satellite to orbit. ULA Photo posted on SpaceFlight Insider

Photo Credit: United Launch Alliance

Colorado-based United Launch Alliance (ULA) announced today that engineers with the company have determined that an anomaly with the RD-180 Mixture Ratio Control Valve (MRCV) assembly caused a reduction in fuel flow during the March 22, 2016, flight of an Atlas V 401 rocket carrying the OA-6 Cygnus to the International Space Station. This led to the boost phase being approximately 5.5 seconds shorter than had been planned. 

With an understanding as to why the in-flight anomaly occurred in hand, the firm is now carrying out an inspection of its supply of RD-180 rocket engines.

So far, the anomaly has only impacted the launch of the fifth, and final, Mobile User Objective System satellite (MUOS-5). 

On Friday, April 22, the Atlas V 551 rocket that has been tasked with launching the MUOS-5 spacecraft completed the Launch Vehicle on Stand (LVOS) operation. During this launch milestone, the Atlas V launch vehicle is erected at the Vertical Integration Facility (VIF) located at Cape Canaveral Air Force Station in Florida in preparation for its eventual flight.

That rocket’s RD-180 engine will now be inspected to ensure that it is ready for launch. A launch date has not yet been issued, with the mission still being listed as “indefinite” on the Eastern Range, although ULA hopes to get the mission underway sometime in early summer.

While ULA has stated previously that the March 22 event and the subsequent investigation had only impacted the MUOS-5 mission, today’s statement adjusted that by saying: The impact to the remainder of the Atlas V manifest is in review with new launch dates being coordinated with our customers. 

United Launch Alliance is still working toward completing the remaining Atlas V launches slated to take place in 2016 by the close of the year. Of all the missions impacted by the March 22 in-flight anomaly, the most vulnerable is, perhaps, NASA’s Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx). That mission is still set to launch in September of this year (2016) so as to be able to maintain its critical science window.

Despite having the core stage’s engine cut off early, the Atlas V 401’s Centaur second stage, powered by its lone Aerojet Rocketdyne RL10C-1 engine, was able to burn for about a minute longer than was initially planned. This allowed the Orbital ATK S.S. Rick Husband Cygnus cargo vessel to be placed on the appropriate orbit to set it on the path toward the International Space Station.



Jason Rhian spent several years honing his skills with internships at NASA, the National Space Society and other organizations. He has provided content for outlets such as: Aviation Week & Space Technology,, The Mars Society and Universe Today.

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