Toward Precision Autonomous Spacecraft Recovery

From October 1991 to December 1996, a research program known as the Spacecraft Autoland Project was conducted at Dryden to determine the feasibility of autonomous spacecraft recovery using a ram-air parafoil system for the final stages of flight, including a precision landing. The latter characteristic was the focus of a portion of the project that called for development of a system for precision cargo delivery. NASA Johnson Space Center and the U. S. Army also participated in various phases of the program, with the Charles Stark Draper Laboratory of Cambridge, MA, developing Precision Guided Airdrop Software (PGAS) under contract to the Army.[989] Four generic spacecraft models (each called a Spacewedge, or simply Wedge) were built to test the concept’s feasibility. The proj­ect demonstrated precision flare and landing into the wind at a pre­determined location, proving that a flexible, deployable system that entailed autonomous navigation and landing was a viable and practical way to recover spacecraft.

Key personnel included R. Dale Reed, who participated in flight-test operations. Alexander Sim managed the project and documented the results. James Murray served as the principal Dryden investigator and as lead for all systems integration for Phases I and II. He designed and fabricated much of the instrumentation for Phase II and was the lead for flight data retrieval and analysis in Phases II and III. David Neufeld performed mechanical integration for the Wedge vehicles’ systems dur­ing all three phases and served as parachute rigger, among other duties. Philip Hattis of the Charles Stark Draper Laboratory served as the proj­ect technical director for Phase III. For the Army, Richard Benney was the technical point of contact, while Rob Meyerson served as the tech­nical point of contact for NASA Johnson and provided the specifica­tions for the Spacewedges.[990] The Spacewedge configuration consisted of a flattened biconic airframe joined to a ram-air parafoil with a cus­tom harness. In the manual control mode, the vehicle was flown using radio uplink. In the autonomous mode, it was controlled using a small computer that received inputs from onboard sensors. Selected sensor data were recorded onto several onboard data loggers.

Two Spacewedge shapes, resembling half cones with a flattened bot­tom, were used for four airframes that represented generic hypersonic vehicle configurations. Wedge 1 and Wedge 2 had sloping sides, and the underside of the nose sloped up slightly. Wedge 3 had flattened sides, to create a larger internal volume for instrumentation. The Spacewedge vehi­cles were 48 inches long, 30 inches wide, and 21 inches in height. The basic weight was 120 pounds, although various configurations ranged from 127 to 184 pounds during the course of the test program. Wedge 1 had a tubular steel structure, covered with plywood on the rear and underside that could withstand hard landings. It had a fiberglass-covered wooden nose and removable aluminum upper and side skins. Wedge 2, originally uninstrumented, was later configured with instrumentation. It had a fiberglass outer shell, with plywood internal bulkheads and bottom structure. Wedge 3 was constructed as a two-piece fiberglass shell, with a plywood and aluminum shelf for instrumentation.[991] A commercially available 288-square-foot ram-air parafoil of a type commonly used by sport parachutists was selected for Phase I tests. The docile flight charac­teristics, low wing loading, and proven design allowed the project team to concentrate on developing the vehicle rather than the parachute. With the exception of lengthened control lines, the parachute was not modi­fied. Its large size allowed the vehicle to land without flaring and without sustaining damage. For Phase II and III, a smaller (88 square feet) para­foil was used to allow for a wing loading more representative of space vehicle or cargo applications.

Spacewedge Phase I and II instrumentation system architecture was driven by cost, hardware availability, and program evolution. Essential items consisted of the uplink receiver, Global Positioning System (GPS) receiver and antenna, barometric altimeter, flight control computer, servo – actuators, electronic compass, and ultrasonic altimeter. NASA techni­cians integrated additional such off-the-shelf components as a camcorder, control position transducers, a data logger, and a pocket personal com­puter. Wedge 3 instrumentation was considerably more complex in order to accommodate the PGAS system.[992] Spacewedge control systems had programming, manual, and autonomous flight modes. The programming mode was used to initialize and configure the flight control computer. The manual mode incorporated a radio-control model receiver and uplink transmitter, configured to allow the ground pilot to enter either brake (pitch) or turn (yaw) commands. The vehicle reverted to manual mode whenever the transmitter controls were moved, even when the autono­mous mode was selected. Flight in the autonomous mode included four primary elements and three decision altitudes. This mode allowed the vehicle to navigate to the landing point, maintain the holding pattern while descending, enter the landing pattern, and initiate the flare maneu­ver. The three decision altitudes were at the start of the landing pattern, the turn to final approach, and the flare initiation.

NASA researchers initially launched Wedge 1 from a hillside near the town of Tehachapi, in the mountains northwest of Edwards, to evaluate general flying qualities, including gentle turns and landing flare. Two of these slope soar flights were made April 23, 1992, with approximately 15-knot winds, achieving altitudes of 10 to 50 feet. The test program was then moved to Rogers Dry Lake at Edwards and to a sport parachute drop zone at California City.115 A second vehicle (known as Inert Spacewedge, or Wedge 2) was fabricated with the same external geometry and weight as Wedge 1. It was initially used to validate parachute deployment, har­ness design, and drop separation characteristics. Wedge 2 was inexpen­sive, lacked internal components, and was considered expendable. It was first dropped from a Cessna U-206 Stationair on June 10, 1992. A sec­ond drop of Wedge 2 verified repeatability of the parachute deployment system. The Wedge 2 vehicle was also used for the first drop from a Rans S-12 ultralight modified as a RPV on August 14, 1992. Wedge 2 was later instrumented and used for ground tests while mounted on top of a van, becoming the primary Phase I test vehicle.116 Thirty-six flight tests were conducted during Phase I, the last taking place February 12, 1993. These flights, 11 of which were remotely controlled, verified the vehicle’s manual and autonomous landing systems. Most were launched from the Cessna U-206 Stationair. Only two flights were launched from the Rans S-12 RPV.

Phase II of the program, from March 1993 to March 1995, encom­passed 45 flights using a smaller parafoil for higher wing loading [993] [994] (2 lb/ft2) and incorporating a new guidance, control, and instrumentation system developed at Dryden. The remaining 34 Phase III flights evaluated the PGAS system using Wedge 3 from June 1995 to December 1996. The software was developed by the Charles Stark Draper Laboratory under contract to the U. S. Army to develop a guidance system to be used for precision offset cargo delivery. The Wedge 3 vehicle was 4 feet long and was dropped at weights varying from 127 to 184 pounds.[995] Technology developed in the Spacewedge program has numerous civil and military applications. Potential NASA users for a deployable, precision, autono­mous landing system include proposed piloted vehicles as well as plan­etary probes and booster-recovery systems. Military applications of autonomous gliding-parachute systems include recovery of aircraft ejec­tion seats and high-altitude, offset delivery of cargo to minimize danger to aircraft and crews. Such a cargo delivery system could also be used for providing humanitarian aid.[996] In August 1995, R. Dale Reed incor­porated a 75-square-foot Spacewedge-type parafoil on a 48-inch-long, 150-pound lifting body model called ACRV-X. During a series of 13 flights at the California City drop zone, he assessed the landing characteris­tics of Johnson Space Center’s proposed Assured Crew Return Vehicle design (essentially a lifeboat for the International Space Station). The instrumented R/C model exhibited good flight control and stable ground slide-out characteristics, paving the way for a larger, heavyweight test vehicle known as the X-38.[997]