Stargazer is a Lockheed L-1011 TriStar built in 1974, that was modified in 1994 for use by Orbital Sciences (now part of Northrop Grumman) as a mother ship for the Pegasus, a small-lift launch vehicle.

The first attempt on December 12 was scrubbed due to issues with the hydraulic system responsible for separating the Pegasus rocket from the launch aircraft.

The launch was originally scheduled for June 2017 but was scrubbed when an anomalous piece of vehicle data was observed during a ferry flight.

The data was related to the rudder position of the Pegasus XL rocket and was observed during a routine in-flight vehicle health check.

In May 1992 Orbital Sciences acquired the plane and had Marshall Aerospace in the UK implement accommodations for the Pegasus system.