The Low-Density Supersonic DeceleratororLDSD is a reentry vehicle designed to test techniques for atmospheric entryonMars. The disc-shaped LDSD uses an inflatable structure called the Supersonic Inflatable Aerodynamic Decelerator (SIAD), which is essentially a donut-shaped balloon, to create atmospheric drag in order to decelerate the vehicle before deploying a large supersonic parachute.[2] The goal of the $230 m project is to develop a reentry system capable of landing 2- to 3-ton payloads on Mars, as opposed to the 1-ton limit of the currently used systems.[3]
The test flight took place on June 28, 2014, with the test vehicle launching from the United States Navy's Pacific Missile Range FacilityonKauaʻi, Hawaiʻi, at 18:45 UTC (08:45 local).[4] A high-altitude helium balloon, which when fully inflated has a volume of 975,000 cubic meters (34,430,000 cu ft),[1] lifted the vehicle to 36,500 meters (119,900 ft).[6] The vehicle detached at 21:05 UTC (11:05 local),[4] and four small, solid-fuel rocket motors spun up the vehicle to provide stability.[6]
A half second after spin-up, the vehicle's Star 48B solid-fuel motor ignited, powering the vehicle to Mach 4.32 and a peak altitude of 58,200 meters (190,900 ft).[6] Immediately after rocket burn-out, four more rocket motors despun the vehicle.[1] Upon slowing to Mach 4.08, the 6-meter (20 ft) tube-shaped Supersonic Inflatable Aerodynamic Decelerator (SIAD-R configuration) deployed.[6] SIAD is intended to increase atmospheric drag on the vehicle by increasing the surface area of its leading side, thus increasing the rate of deceleration.[7]
Upon slowing to Mach 2.54 (around 86 seconds after SIAD deployment[1]), the Supersonic Disksail (SSDS) parachute was deployed to slow the vehicle further.[6] This parachute measures 30.5 meters (100 ft) in diameter, twice the area of the one used for the Mars Science Laboratory mission.[8] However, it began tearing apart after deployment,[9] and the vehicle impacted the Pacific Ocean at 21:35 UTC (11:35 local) travelling 32 to 48 kilometers per hour (20 to 30 mph).[4][10] All hardware and data recorders were recovered.[7][10] Despite the parachute incident, the mission was declared a success; the primary goal was proving the flight worthiness of the test vehicle, while SIAD and SSDS were secondary experiments.[7]
A second test flight of LDSD took place in June 2015, at the Pacific Missile Range Facility. This test focused on the 6-meter (20 ft) SIAD-R and Supersonic Ringsail (SSRS) technologies, incorporating lessons learned during the 2014 test.[11] Changes planned for the parachute included a rounder shape and structural reinforcement.[9] After several weather-related scrubs, the flight occurred on June 8.[12][13] As in the first test, the SIAD structure inflated successfully but the parachute was damaged during deployment,[14][3] this time after 600 ms and at 80,000 pounds (36,000 kg) drag.[15]
