Engineershave elected to replace a vital control unit inside the steering system of anOrbital Sciences Minotaur rocket, delaying Friday's launch of the vehicle andits Air Force spacecraft cargo by several weeks.
The booster will fly fromVandenberg Air Force Base in California to deliver the Experimental SatelliteSystem-11 (XSS-11) craft into orbit for demonstrations of autonomous operationsand close maneuvering with other space objects.
But concerns overreliability of some capacitors within a box called the Thrust Vector Controller(TVC) led to the postponement, the Air Force said Tuesday. These boxes controlthe steering of the Minotaur's engine nozzles during ascent.
"The capacitors in theTVC come from two different vendors. It was determined in testing and physicalexamination after the tests that one vendor's capacitors are significantly morerobust than another's," according to officials at the Air Force Space andMissile Systems Center.
"Concerns overcapacitors have existed for some months, and all TVCs received additionalbox-level testing as a result. The intent of the additional testing was toscreen out questionable capacitors or workmanship.
"Testing over the lastseveral days of individual capacitors revealed that box-level testing might notcatch all potential defects, and that one vendor's capacitor was more robust.It was therefore decided to take a conservative approach and change to the morerobust capacitor."
The controllers used onMinotaur rockets are the same carried aboard Orbital Sciences' air-launchedPegasus vehicles. A circuit card or possibly an entire TVC featuring the bettercapacitors will be removed from the Pegasus earmarked to launch the Air Force'sC/NOFS satellite later this year for installation on this Minotaur.
Plans are still beingdeveloped for the replacement work. But the Air Force says initial estimatessuggest the Minotaur could be ready for the $80 million launch in late April.
This will be the thirdMinotaur flight, following two successful missions in 2000. The rocketincorporates decommissioned first and second stages from a Minuteman 2 ICBMmissile and solid-fuel motors from Pegasus for third and fourth stages. Thevehicle is designed to provide the U.S. government with reliable access tospace for small satellites.
The 319-pound XSS-11spacecraft was built by Lockheed Martin at its facilities near Denver for theAir Force Research Laboratory.
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