Andy Pasztor of The Wall Street Journal has an update on Sierra Nevada Corporation’s appeal of NASA’s Commercial Crew Program award to Boeing. The Government Accountability Office is set to decide on the appeal by the first week in January.

In recent weeks, details have emerged that some of the arguments at the heart of the proceeding revolve around Sierra Nevada’s claims that a high-ranking agency official opted to rank Boeing’s proposal higher than a previous panel of agency procurement experts.

According to people familiar with the details, Sierra Nevada has alleged that Boeing won unfairly, because the choice was partly based on agency projections that the Chicago-based aerospace giant was more likely than its rival to complete the work on time. Sierra Nevada’s filings, however, contend that the National Aeronautics and Space Administration’s formal bidding criteria put a premium on price combined with technical issues, without indicating that scheduling considerations would be major factors in ranking rival proposals, one of these people said.

Sierra Nevada’s bid was about $900 million lower than the one Boeing submitted, but NASA’s final decision memo noted that Sierra Nevada’s plans entailed “considerably more schedule risk.”

Sierra Nevada has challenged Boeing’s award on various grounds. One of the main assertions, according to one person familiar with the details, is that William Gerstenmaier, the agency’s top human exploration official and the one who made the final decision, overstepped his authority by unilaterally changing the scoring criteria.