After a long hiatus, and two more recent delays, a Pegasus XL winged-launch vehicle successfully achieved orbit after being air dropped from a converted Lockheed L-1011 Tristar passenger jet. The launch took place at 1337 GMT on 15 December 2016 over the Atlantic Ocean. Aboard were eight small satellites of the NASA sponsored Cyclone Global Navigation Satellite System (CGNSS) to measure sea winds from low Earth orbit. Built by the Southwest Research Institute (SwRI) in conjunction with the University of Michigan, CYGNSS will use GPS signals to derive the roughness of the ocean surface, from which wind speed is retrieved.
Originally, the launch of the Pegasus XL launch vehicle was to have occurred on 12 December, but had an “abort” before its planned air drop on 12 December 2016 putting a stop to the mission. Although the L-1011 carrier aircraft took off from Cape Canaveral on time, the launch was aborted at T-5 minutes due to an anomaly with the hydraulic pump which controls the release of the launch vehicle from the carrier aircraft. The pump was apparently working before the aircraft took off. In the end the launch was delayed until the 14 December while a part was replaced. However, another delay, this time related to a fault discovered on the spacecraft software, moved the launch to 15 December.
Note: Seradata usually awards an “abort” event in the case where a launch is prevented from happening within the last minute of the countdown. This period we assume is when the vehicle is “ready to go”. Any failures within this period are regarded as “launch failures”. The exception to this rule is for air launched vehicles in which we assume that the “launch” has already entered a “ready to go” status, once the carrier aircraft is airborne. To date Pegasus has had eight “aborts” of which four were outside the final minute of countdown before launch (i.e. T – 60s or more) as with the example above.
