STEP-2 and HETI/SAC-B), and two partial failures, (USAF Microsat and STEP-2) followed by 30 consecutive successful flights for a total program success rate of 89 percent. The first partial failure on 17 July 1991 caused the seven USAF microsatellites to be delivered to a lower than planned orbit, significantly reducing the mission lifetime. The last mission failure on 4 November 1996 resulted in the loss of gamma-burst identifying satellite HETE (High Energy Transient Explorer) in 1996. The Pegasus XL, introduced in 1994 has lengthened stages to increase payload performance. In the Pegasus XL, the first and second stages are lengthened into the Orion 50SXL and Orion 50XL, respectively. Higher stages are unchanged; flight operations are similar. The wing is strengthened slightly to handle the higher weight. The standard Pegasus has been discontinued; the Pegasus XL is still active as of 2019. Pegasus has flown 44 missions in both configurations, launching 91 satellites as of October 12, 2019. Dual payloads can be launched, with a canister that encloses the lower spacecraft and mounts the upper spacecraft. The upper spacecraft deploys, the canister opens, then the lower spacecraft separates from the third-stage adapter. Since the fairing is unchanged for cost and aerodynamic reasons, each of the two payloads must be relatively compact. Other multiple-satellite launches involve "self-stacking" configurations, such as the ORBCOMM spacecraft. For their work in developing the rocket, the Pegasus team led by Antonio Elias was awarded the 1991 National Medal of Technology by U.S. President George H. W. Bush. The initial launch price offered was US$6 million, without options or a HAPS (Hydrazine Auxiliary Propulsion System) maneuvering stage. With the enlargement to Pegasus XL and the associated improvements to the vehicle, baseline prices increased. In addition, customers usually purchase additional services, such as extra testing, design and analysis, and launch-site support. As of 2015, the most recent Pegasus XL to be purchased — a planned June 2017 launch of NASA's Ionospheric Connection Explorer (ICON) mission — had a total cost of US$56.3 million, which NASA notes includes "firm-fixed launch service costs, spacecraft processing, payload integration, tracking, data and telemetry and other launch support requirements". A series of technical problems delayed this launch, which finally took place on 11 October 2019. In July 2019, it was announced that Northrop Grumman had lost the launch contract of the Imaging X-ray Polarimetry Explorer (IXPE) satellite to SpaceX. IXPE had been planned to