Orbital Sciences's Cygnus Rendezvous With ISS Delayed by Troubled Data Exchange

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NASA's Mission Control early Sunday called for a delay of at least 48 hours in the docking of Orbital Science Corp's Cygnus re-supply craft with the International Space Station.

A patch to fix discrepancies in navigation software of the two spacecraft discovered at 1:30 a.m.,EDT, is under way, according to statements from both NASA and Orbital Sciences. The new patch will be tested Sunday in a Cygnus ground-based simulator, and then transmitted to the orbiting freighter, which was otherwise operating as expected. In orbit testing of the software patch is planned Sunday night and early Monday.

With a successful verification, a rendezvous and final approach demonstration would resume late Monday and early Tuesday, Orbital said.

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Artist's illustration of Cygnus rendezvous. Image credit: Orbital Sciences

The unpiloted capsule was scheduled to rendezvous with the space station on Sunday, maneuvering close enough to be grappled by European Space Agency astronaut Luca Parmitano and NASA astronaut Karen Nyberg at 7:25 a.m., EDT, and subsequently berthed to the ISS U.S. segment.  The capsule and a cargo that includes 1,543 pounds of non-critical crew provisions was launched Wednesday from the Mid-Atlantic Regional Spaceport in Virginia to initiate a 30-day demonstration mission under NASA's Commercial Orbital Transportation System (COTS) program.

Sunday's difficulties surfaced  as the Cygnus established a direct communications link with the ISS for the final stages of the rendezvous. Cygnus found discrepancies in the data exchange that prompted an interruption in the dynamic rendezvous sequence supervised by Orbital's control team at Dulles, Va., and NASA's Mission Control in Houston.

"The minimum turnaround time to resume the approach to the ISS following an interruption such as this is approximately 48 hours due to orbital mechanics of the approach trajectory," NASA said.

It was unclear if Cygnus operations might be affected by Russia's plans to launch three new crew members to the ISS on Wednesday. Cosmonauts Oleg Kotov and Sergei Ryanzanskiy and NASA astronaut Mike Hopkins are preparing to lift off at 4:58 p.m., EDT, atop the Soyuz TMA-10M from the Baikonur Cosmodrome in Kazakhstan. Their four-orbit trajectory would place the capsule and the three newcomers at the station's Russian segment docking port at 10:48 p.m., EDT.

If necessary, the Cygnus freighter could loiter in orbit for at least a week and perhaps for up to two to three months, Frank Culbertson, Orbital's executive vice president and Cygnus mission manager, told a pre-launch news briefing.

"We can loiter on orbit waiting for the rendezvous activity for a week, or even up to two to three months, if necessary,” Culbertson said.

The Antares/Cygnus launch was postponed 24 hours to replace a damaged ground systems data cable without a change in the planned Sunday rendezvous date.

The Cygnus mission is to mark the end of Orbital's participation in NASA's COTS program, a  5 1/2 year partnership in which the space agency is providing the company with $288 million to develop a second commercial ISS re-supply capability in the aftermath of the shuttle program's 2011 retirement.

Orbital had successfully achieved three of 10 COTS mission milestones when Sunday's interruption occurred.

Orbital's COTS wind down clears the company to execute an eight flight, $1.9 billion Commercial Resupply Services agreement with NASA's ISS program. Orbital's inaugural CRS flight is tentatively planned for December

SpaceX, of Hawthorne, Calif., fulfilled a COTS partnership agreement in May 2012 with a similar demonstration flight. SpaceX has completed two if its 12 missions under a $1.6 billion CRS contract, also awarded in December 2008.

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