Recovering Pegasus-I was an extremely interesting part of the mission. This article goes into how it is done, and the fully story is here.
During the flight we immediately lost the Ham Radio, which was our backup GPS, and we were flying only on the onboard primary GPS. The craft had turned NE from East as expected, but with the mission altitude objective reached and difficultly of the terrain 17 miles East of Othello, WA, we decided to begin the descent stage.
Figure 1 is a map of 5 minute intervals of the flight path.
The winds gods were kind to us that day and you can see in Figure 2 that the radial distance of the flight was not very far.
The maximum altitude achieved by Pegasus-I was 84,899 feet, which gave us about 13 minutes during the descent stage before the craft lands. Once we cut down the craft, we begin a rapid descent in rarified air (not much friction) and rate of descent progressively slows as the air becomes denser at lower altitudes. The initial descent rate was over 200 mph and telemetry tells us the yaw, i.e., the rotation parallel to the ground was spinning wildly, while the roll and pitch were bumpy, but relatively stable.
During the descent the latitude and longitude from the primary GPS cut out at an air pressure of 38.8 millibars, due to an antenna becoming loosened. The rapidly spinning yaw likely put significant horizontal force on the antenna. The last recorded air pressure was 37.2 millibars at an altitude of 75,555 feet. Pegasus had dropped 9,344 feet in just 36 seconds at average of 256 ft/sec or 180 mph.
When GPS cut out, we were in dismay. Regardless of the other telemetry still pouring in, we did not have the location of the craft. The chase team exited the vehicle and began scanning the sky by sweeping from West to North, the expected landing zone. While this was actually the correct place to look, the cloud ceiling was only about 1,000 feet, which meant we had less than a minute to visually identify the craft. Figure 3 shows the position of the craft when we lost GPS, the position of the chase team and the last recorded position of the craft, which the chase team was not aware at the time.
After arriving home 3 days later, I was checking the telemetry we captured from Pegasus-I. First, I looked at the moment the GPS cut out, Figure 4.
I scanned further down and noticed this with only 26 seconds left in the flight, Figure 5.
Cross checking the air pressure with the location and topo map, it was apparent that landing point was consistent with the air pressure. Further analysis showed that the points between where the GPS cut out and came back online where in the expected location due to wind velocities and descent rate. The expected location was mapped in Figure 6 and sent to Mark to attempt recovery 7 days after the flight.
Figure 7 shows the last GPS coordinates and where Mark actually found the craft undamaged. The fact that we were streaming and capturing the telemetry enabled us to locate the craft and oddly enough provided and interesting story about the role our real-time IOT technology played in recovery.