WASHINGTON — Orbital Sciences Corp. is scrambling to keep the maiden launch of its Antares cargo rocket on track for April 17 after a malfunctioning engine valve forced the company to scrub a planned wet dress rehearsal test April 13.

In a short note posted on its website after the test was aborted with just 16 seconds left in the countdown, the Dulles, Va.-based company said it planned to replace the valve in time to keep Antares’ launch on track for April 17. Antares is launching from the Mid-Atlantic Regional Spaceport located at NASA’s Wallops Island Flight Facility in Virginia.

Antares is the rocket Orbital is developing to fly eight cargo delivery missions for NASA under a $1.8 billion contract it got in 2008. For the maiden flight, Antares will be sent to orbit without its companion cargo spacecraft, Cygnus.

The flight scheduled for this week is the first of two demonstration spaceflights Orbital has to complete before it can begin paid cargo runs to the international space station. 

Orbital’s Antares Wet Dress Rehearsal Test Identifies Engine Valve That Needs To Be Replaced

April 2013

On Saturday (April 13), Orbital conducted the wet dress rehearsal for the Antares rocket in preparation its Test Flight scheduled for later this week on April 17. Late in the countdown, at about T-16 minutes, the test was halted because the launch team had detected a technical anomaly in the process. Orbital has determined that a secondary pyro valve aboard one of the two first-stage engines used in the propellant chilldown process was not functioning properly. A replacement unit will be installed within 24 hours with the goal of maintaining the April 17 launch date. Orbital will issue additional updates as warranted.

Dan Leone is the NASA reporter for SpaceNews, where he also covers other civilian-run U.S. government space programs and a growing number of entrepreneurial space companies. He joined SpaceNews in 2011.Dan earned a bachelor's degree in public communications...