Orbital ATK announced today that the return to flight of its Antares rocket is being postponed again. Scheduled for August 22, it now will take place in the second half of September. The exact date has not been set. It will be the first flight of Antares since an October 2014 failure.

Antares was developed under NASA’s Commercial Orbital Transportation Services (COTS) program to launch cargo missions to the International Space Station (ISS) using the Cygnus spacecraft. Antares/Cygnus competes with SpaceX’s Falcon 9/Dragon and, more recently, with Sierra Nevada Corporation’s Atlas V/Dream Chaser system for NASA Commercial Resupply Services (CRS) contracts.

It was originally designed to use Russian NK-33 engines built four decades ago, refurbished by Aerojet Rocketdyne and designated AJ26. Two test flights, one of which took cargo to the ISS as a demonstration mission, and two operational missions to ISS were successfully conducted in 2013 and 2014. At the time, the company was Orbital Sciences Corporation and the two operational missions were designated Orb-1 and Orb-2.

The launch of Orb-3 on October 28, 2014 ended in failure 15 seconds after liftoff. Orbital Sciences, which merged with ATK in February 2015 to become Orbital ATK, decided to replace the NK-33/AJ26 engines with new Russian RD-181s. The process is taking longer than expected. The return to flight of the re-engined Antares was supposed to take place this past spring, but the date has slipped several times since then.

The delay announced today was due to “a variety of interrelated factors,” the company said. They include Orbital ATK’s continued processing, inspection and testing of the Antares rocket and NASA’s scheduling of activities aboard the ISS. Cygnus is one of four cargo vehicles that resupply the ISS. Russia’s Progress, SpaceX’s Dragon, and Japan’s HTV are the others; Japan just announced its own delay of the next HTV launch that was scheduled for October because of a spacecraft problem. The ISS crew also is preparing for spacewalks in August and September, and a Soyuz crew rotation flight is coming up in September as well. All of these activities must be coordinated.

While waiting for Antares to resume flights, Orbital ATK purchased two launches for its Cygnus spacecraft on United Launch Alliance (ULA) Atlas V rockets to ensure that it could meet its contractual requirements to deliver cargo for NASA. Those launches took place in December 2015 and March 2016 and were designated Orbital ATK-4 (OA-4) and OA-6. The Antares flight will launch OA-5 which, as its designation indicates, was supposed to take place in between the two ULA launches.

Orbital ATK made the announcement this morning at the same time as its preliminary second quarter (2Q) 2016 financial results. The company revealed that it was delaying filing its official 2Q results and would be restating financial results going back several quarters because of recently discovered financial misstatements associated with an Army ammunition contract signed in 2012. The issue is unrelated to Orbital ATK’s space business, but the company’s stock fell on the news.