LDSD (Low-Density Supersonic Decelerator) TV-2

The Low-Density Supersonic Decelerator (LDSD) program, managed by NASA, aimed to advance technologies for landing heavier payloads on Mars. This was achieved by testing a series of supersonic decelerator systems under atmospheric conditions resembling those on Mars. The program employed a combination of high-altitude balloon launches, rocket propulsion, and supersonic reentry tests.

The second test vehicle for the LDSD program, which can be seen in the image at left, was composed by a blunt body of 4.7 meters in diameter, incorporating a robust suite of technologies for deployment, stabilization, and data collection during supersonic descent.

The vehicle's aerodynamic profile included a 6-meter diameter Supersonic Inflatable Aerodynamic Decelerator (SIAD-R) and a 30.5-meter Supersonic Ringsail Parachute (SSRS). The SIAD-R, constructed from Kevlar-29 broadcloth coated with silicone RTV, acted as a rigid aerodynamic torus upon inflation, thanks to a network of internal cords enhancing stiffness. This inflatable decelerator was pressurized using an onboard system of gas generators, reaching a peak internal pressure of 31 kPa. The SIAD-R featured a burble fence to improve flow stability during supersonic flight. Its rapid inflation sequence ensured minimal disturbances during deployment, with the cold and hot gas generators initiating inflation in under one second.

The Ringsail parachute design comprised 96 gores in a 20-panel configuration with varying fullness across panels to optimize aerodynamic efficiency. The materials included Kevlar for structural elements and ripstop Nylon for canopy sections, chosen for their strength and low permeability. The parachute's deployment was achieved through a trailing ballute system, which served as a supersonic pilot for extracting the parachute from the vehicle.

The vehicle's instrumentation suite was comprehensive, including high-speed and high-resolution cameras for capturing deployment and inflation dynamics, inertial measurement units (IMUs), thermocouples, and pressure transducers. These systems provided real-time telemetry and post-flight data to evaluate aerodynamic performance, deployment accuracy, and structural integrity.

Propulsion was provided by a STAR-48 solid rocket motor, which accelerated the vehicle to Mach 4 and an altitude of 52 kilometers before initiating the test sequence. Spin-up motors stabilized the vehicle, achieving rotational speeds of 300 degrees per second, before the motor's burnout triggered the primary test phase. The vehicle was despun using onboard mechanisms to prepare for decelerator deployment.

The structural and thermal integrity of the vehicle was tested under high dynamic pressure and supersonic conditions. Aerodynamic coefficients and thermodynamic behavior were reconstructed using data from onboard sensors and external tracking systems, confirming the vehicle's stability and the effectiveness of its decelerators under Mars-equivalent atmospheric conditions.

Balloon launched on: 6/8/2015 at 17:44 utc
Launch site: Pacific Missile Range Facility, Barking Sands, Kauai, Hawaii, US  
Balloon launched by: Columbia Scientific Balloon Facility (CSBF)
Balloon manufacturer/size/composition: Zero Pressure Balloon Raven Aerostar - 39.570.000 cuft
Flight identification number: 663NT
End of flight (L for landing time, W for last contact, otherwise termination time): 6/8/2015 at 21:35 utc
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 3 h 50 m
Landing site: Over the Pacific Ocean, W of Kauai, Hawaii

The second high-altitude, supersonic flight dynamics test (SFDT-2) of the LDSD project occurred on June 8, 2015, at the Pacific Missile Range Facility in Hawaii. This test sought to improve upon the initial flight by validating advancements in supersonic parachute technology and other decelerator systems.

The balloon for SFDT-2 carried the test vehicle, a 4.7 m blunt body, to a float altitude of approximately 36.6 km. Weather conditions and trajectory predictions were carefully analyzed to ensure compliance with operational and safety constraints. The balloon's ascent rate and wind conditions were continuously monitored, with ballast drops conducted to maintain a positive ascent rate through the tropopause. The balloon achieved float altitude at 10:21 HST, where it stabilized before the test vehicle release.

The test vehicle was armed and powered for the drop approximately 30 minutes prior to release. At 11:35 Hawaiian time, the vehicle was released, marking the beginning of the powered flight phase. Spin-up motors initiated rotation for stability before the ignition of the STAR-48 solid rocket motor. The vehicle accelerated to Mach 4.17, reaching an altitude of 52.2 km at burnout. A despin maneuver stabilized the vehicle for the test phase.

The Supersonic Inflatable Aerodynamic Decelerator (SIAD-R) was deployed at Mach 3.09, following updated triggering logic based on altitude and velocity at motor burnout. The SIAD inflated rapidly and uniformly, transitioning the vehicle into a more aerodynamically stable configuration. Subsequently, a trailing ballute deployed the 30.5 m Supersonic Ringsail Parachute (SSRS), which decelerated the vehicle to subsonic speeds.

Instrumentation provided real-time telemetry and high-speed imagery, capturing critical deployment, inflation, and flight dynamics of the SIAD and parachute. The SSRS achieved partial success in its deployment, with data collection supporting future design improvements.

The vehicle descended to the ocean and splashed down 16 minutes after release. Recovery operations retrieved the test vehicle, parachute, and balloon carcass, though the vehicle sustained impact damage. Despite challenges, SFDT-2 collected valuable data to refine deceleration systems for Mars missions, demonstrating significant progress in supersonic parachute technology.

• Low-Density Supersonic Decelerator NASA website
• Aerodynamic Models for the Low Density Supersonic Decelerator (LDSD) Test Vehicles 2016 AIAA Aviation Conference
• Summary of the Second High-Altitude, Supersonic Flight Dynamics Test for the LDSD Project 2016 IEEE Aerospace Conference
• Supersonic Flight Dynamics Test 2: Trajectory, Atmosphere, and Aerodynamics Reconstruction AAS Paper 16-217, NF1676L-22612