WASHINGTON – NASA will not repair a defective electronic unit on the recently completed Orion spacecraft for the Artemis 1 mission after concluding that there was sufficient redundancy in the overall system.
In a December 17 statement, NASA said it had decided to “use as is” one of the eight power and data units (PDUs) on the Orion spacecraft, which provide communications between the ship’s computers and other components. One of the two redundant channels in one of the two communication boards in that PDU does not work.
NASA announced the problem with the PDU on November 30, saying only that it “solves the problem”. The problem was first reported by The Verge, who said that the presentations of the first contractor Lockheed Martin warned that it could take up to a year to replace the PDU, because it is in an adapter between the crew module and the service module that it is now inaccessible that two modules are paired with each other.
This time estimate assumed that the crew module would be removed from the service module, the repaired PDU and the two modules combined again and tested. An alternative option could complete the repairs in just four months, but would require removing the adapter panels to reach the PDU, which is not what the hardware was designed for.
NASA, in its statement on the decision not to replace the PDU, did not go into detail about the repair options, but said that the risks of damage to the spacecraft during the repair of the PDU are greater than any data loss if which the unit does not work completely.
The engineers, the agency said, “determined that due to the limited accessibility of this box, the degree of intrusion of global spacecraft systems and other factors, the risk of collateral damage outweighed the risk associated with losing a redundancy leg in an extremely redundant system. “
“NASA is confident in the health of the entire power and data system, which has gone through thousands of hours of power operations and tests,” the agency added, noting that the PDU in question was still “fully operational.”
Even before the statement, NASA officials were reducing the possibility of carrying out an extensive spacecraft repair to replace the PDU. “You will receive a first report, and the first report will show all the most unfavorable possibilities,” Ken Bowersox, deputy associate director of NASA’s Exploration and Human Operations Mission, said in a December 7 media briefing on a report on the science planned for the Artemis 3 monthly landing mission. “At best, we can see it’s something we can live with.”
At the time of this briefing, Bowersox said that NASA was still studying the issue, but was optimistic that it would not have a major effect on the Artemis 1 mission. “As we look at it, we do not believe it will have a major impact on the final program.” , he said.
With the decision not to replace the PDU, NASA is moving forward with the final closures of the spacecraft. In mid-January, it will move from the Kennedy Space Center facility where it was assembled to the Multiple Task Processing Facility there, where it will be powered and prepared to be installed on the space launch system.
The critical path for the launch of Artemis 1, still scheduled for November 2021, remains the basic stage of SLS, which is undergoing a series of tests called Green Run at Stennis Space Center. NASA said on December 17 that it had resumed preparations for a power test called wet rehearsal after canceling a first attempt at that test in early December because liquid oxygen was flowing in the central stage at slightly higher temperatures than desired.