Mission of Orbital ATL Cygnus cargo spacecraft (OA-7), which was scheduled for March 10, was postponed due the problems with the launch vehicle - United launch Alliance Atlas V rocket. New launch date was set to 21st March 2017 with "not earlier than" status.
Mission was planned as commercial resupply flight, with Cygnus S.S. John Glenn robotic cargo spacecraft delivered under the fairing of Atlas V (401) rocket. Due the decision of NASA, Cygnus was prepared to this mission in extended configuration with 3500 kg of payload instead of 3200 kg in regular variant. It determined choice of launch vehicle for this mission. It was necessary to launch Cygnus on the top of the Atlas V not, as it was planned originally on the top of modified Antares rocket in 230 variant.
Decision that flight should be postponed was made after spotting problems which appeared during tests performed at SLC-41 at Cape Canaveral on March 10. United LAunch Alliance specialists spotted malfunction of hydraulic system of the booster (first core stage) during prelaunch testing. Due the necessity of replacing broken element and further tests, it was necessary to postpone launch for at least ten days to March 21st. Payload and spacecraft remain secured under fairing as rocket still stands on its launch position.