The flight of the SpaceX Falcon 1 launch vehicle on March 21, named Demo2, from the U.S. Army Space and Missile Defense Command’s Reagan Test Site, Omelek Island, Kwajalein Atoll, Republic of the Marshall Islands in the Pacific Ocean was being closely monitored by engineers at the Wallops Flight Facility.
The payload consisted of two NASA experiments demonstrating critical elements to enable operationally responsive space access and lower cost range operations.
The first experiment, the Autonomous Flight Safety System (AFSS), is managed by NASA Wallops Flight Facility (WFF) and was jointly developed by WFF and NASA’s Kennedy Space Center. This on-board system is being designed to enhance and eventually replace costly range tracking components required for flight termination. The AFSS evaluated data from independent on-board navigation sensors, made flight termination decisions, and issued simulated Flight Termination System (FTS) commands. During the Falcon 1 launch, the AFSS was flown in a shadow mode and provided telemetry indicating whether the vehicle flew a nominal trajectory or whether potentially unsafe conditions existed. It was not connected to the Falcon 1 FTS.
The second experiment, the Low-Cost Tracking and Data Relay Satellite System (TDRSS) Transmitter (LCT2) was developed by WFF. The LCT2 is a low-cost, digital TDRSS transmitter for launch and flight vehicles that relays telemetry data to ground controllers using the NASA TDRSS communications network. It was implemented in the Demo2 payload to provide verification of AFSS functionality. NASA’s TDRSS network also is used for the space shuttle, satellite, and launch vehicle communication.
Despite the successful completion of compatibility testing with launch vehicle systems, a concern was raised on the day of the launch that the LCT2 could potentially interfere with the vehicle’s GPS subsystems. Since time was not available to conduct additional testing, a decision was made to fly with the LCT2 powered off. As a result, detailed response data from one of the two redundant AFSS processors was not available for post-test analysis.
At launch, the AFSS properly detected lift-off and enabled the appropriate flight termination mission rules. Both flight processors properly issued and released ARM and FIRE commands to the voting circuit when the vehicle instantaneous impact prediction intruded the test exclusion zone at L+4 minutes 27 seconds and exited it at L+5 minutes 9 seconds. Both processors issued ARM and FIRE functions associated with the erratic vehicle performance experienced later during flight.
Using the available telemetry data, the team can confirm that a termination command was issued due to a violation of a moving-gate rule established to identify erratic flight from in-plane vehicle failures. The erratic behavior rule firing occurred late in the second stage flight.
Although the Demo2 flight did not reach orbit, the engineering development team was able to exercise many elements of the AFSS Concept of Operations in the integration, test and launch operations environment of an Expendable Launch Vehicle.
A preliminary review of the flight data indicates that the team met test objectives that included successful operation and post-flight performance character-ization of the AFSS hardware and software elements. These are part of a system design that will ultimately comply with accepted range safety flight termination system standards.
The AFSS engineering team is currently engaged in a post-test analysis of the data. This will include conducting a detailed review of the in-flight telemetry data, correlating observed AFSS events with Falcon 1 vehicle telemetry data, cataloging and investigating in-flight anomalies, and collecting lessons learned.
The SpaceX Falcon1 launch along with the WFF payload demonstration was sponsored by the Defense Advanced Research Projects Agency (DARPA) Falcon Program.
The goal of this DARPA program is to develop and demonstrate an affordable responsive space lift capability.