Engineering topics
Tanner, Christopher L.
Publications and source records attributed to Tanner, Christopher L..
Reconstructed Parachute System Performance During the Second LDSD Supersonic Flight Dynamics Test
NASA’s Low-Density Supersonic Decelerators project (LDSD) has developed and tested four new aerodynamic decelerator technologies for future Mars missions: two attached toroidal inflatable decelerators, a ballute, and a large supersonic parachute. On June 8, 2015, the project conducted a high-altitude, supersonic flight test of a 30.5-meter supersonic Ringsail (SSRS) canopy at the US Navy’s Pacific Missile Range Facility (PMRF) on Kauai, HI. This test, the second in a series of Supersonic Flight Dynamics Tests (SFDT-2), allowed the LDSD project to test the deployment and performance of its parachute decelerator system in the wake of a representative test vehicle (a 4.7-meter aeroshell and 6-meter toroidal inflatable aerodynamic decelerator) at conditions relevant to Mars entry for the second time. The parachute decelerator system consisted of the SSRS main parachute and a 4.4-meter ballute (called the parachute deployment device, or PDD) for its extraction. The ballute was mortar-deployed at a Mach number of 2.78 and a dynamic pressure of 493 Pa, and inflated with the aid of a water-methanol based gas generator. After flying in the wake of the test vehicle for ten seconds, the PDD was released and allowed to extract the main parachute pack. The SSRS reached line-stretch at a Mach number of 2.37 and dynamic pressure of 602 Pa. Following full inflation, the propagation of a tear in the canopy led to the failure of the parachute skirt band and to the subsequent failure of the vent band. The test vehicle was instrumented with load sensors, inertial sensors, and high-speed and high resolution cameras that provided data on the performance of the PDD and SSRS through deployment, inflation, and flight. This paper describes the resulting reconstructed behavior of the PDD and SSRS during deployment and inflation, their aerodynamic performance on SFDT-2, the failure of the SSRS shortly after full inflation, and the LDSD project’s investigation into its underlying causes.
Pyrotechnically Actuated Gas Generator Utilizing Aqueous Methanol
A gas-generating device was developed to supplement the ram-air inflation of a supersonic ballute. The device is designed to initially pressurize the ballute following deployment, exposing and orienting its ram-air inlets to free-stream air for complete inflation. The supplemental pressurization decreases the total inflation time, and increases the likelihood of a successful inflation. The device contains a reservoir filled with an aqueous mixture of methanol that, when released in to the interior of the ballute, rapidly vaporizes due to the low ambient pressure. Upon activation of the device, a pair of redundant ring mechanisms initiate pyrotechnic charges that pressurize and rupture the reservoir, resulting in ejection of the methanol in to the ballute. In addition to its role in inflation, the device serves as the structural connection to the ballute. Analytical models were developed for the inflation capability of the device, which were verified using vacuum chamber testing of developmental hardware. Static, deployment, and environmental testing demonstrated the functionality of the ring mechanism and reservoir under several temperature and pressure conditions. Finally, the device was successfully operated during the first Supersonic Flight Dynamics Test (SFDT) of NASA's Low Density Supersonic Decelerator (LDSD) project. The design architecture is scalable to accommodate different quantities of gas generation, can be adjusted to operate in a variety of temperature and atmospheric pressure regimes, and provides a robust device that may be installed with minimal risk to personnel or hardware.
Pilot Deployment of the LDSD Parachute via a Supersonic Ballute
The Low Density Supersonic Decelerator (LDSD) Project required the use of a pilot system due to the inability to mortar deploy its main supersonic parachute. A mortar deployed 4.4 m diameter supersonic ram-air ballute was selected as the pilot system for its high drag coefficient and stability relative to candidate supersonic parachutes at the targeted operational Mach number of 3. The ballute underwent a significant development program that included the development of a new liquid methanol-based pre-inflation system to assist the ballute inflation process. Both pneumatic and pyrotechnic mortar tests were conducted to verify orderly rigging deployment, bag strip, inflation aid activation, and proper mortar performance. The ballute was iteratively analyzed between fluid and structural analysis codes to obtain aerodynamic and aerothermodynamic estimates as well as estimates of the ballute's structural integrity and shape. The ballute was successfully flown in June 2014 at a Mach number of 2.73 as part of the first LDSD supersonic flight test and performed beyond expectations. Recovery of the ballute indicated that it did not exceed its structural or thermal capabilities. This flight set a historical precedent as it represented the largest ballute to have ever been successfully flown at this Mach number by a NASA entity.
Aerodynamic Stability and Performance of Next-Generation Parachutes for Mars Descent
The Low Density Supersonic Decelerator Project is developing a next-generation supersonic parachute for use on future Mars missions. In order to determine the new parachute configuration, a wind tunnel test was conducted at the National Full-scale Aerodynamics Complex 80- by 120-foot Wind Tunnel at the NASA Ames Research Center. The goal of the wind tunnel test was to quantitatively determine the aerodynamic stability and performance of various canopy configurations in order to help select the design to be flown on the Supersonic Flight Dynamics tests. Parachute configurations included the diskgap- band, ringsail, and ringsail-variant designs referred to as a disksail and starsail. During the wind tunnel test, digital cameras captured synchronized image streams of the parachute from three directions. Stereo hotogrammetric processing was performed on the image data to track the position of the vent of the canopy throughout each run. The position data were processed to determine the geometric angular history of the parachute, which were then used to calculate the total angle of attack and its derivatives at each instant in time. Static and dynamic moment coefficients were extracted from these data using a parameter estimation method involving the one-dimensional equation of motion for a rotation of parachute. The coefficients were calculated over all of the available canopy states to reconstruct moment coefficient curves as a function of total angle of attack. From the stability curves, useful metrics such as the trim total angle of attack and pitch stiffness at the trim angle could be determined. These stability metrics were assessed in the context of the parachute's drag load and geometric porosity. While there was generally an inverse relationship between the drag load and the stability of the canopy, the data showed that it was possible to obtain similar stability properties as the disk-gap-band with slightly higher drag loads by appropriately tailoring the geometric porosity distribution.
Aerodynamic Characterization of New Parachute Configurations for Low-Density Deceleration
The Low Density Supersonic Decelerator project performed a wind tunnel experiment on the structural design and geometric porosity of various sub-scale parachutes in order to inform the design of the 110ft nominal diameter flight test canopy. Thirteen different parachute configurations, including disk-gap-band, ring sail, disk sail, and star sail canopies, were tested at the National Full-scale Aerodynamics Complex 80- by 120-foot Wind Tunnel at NASA Ames Research Center. Canopy drag load, dynamic pressure, and canopy position data were recorded in order to quantify there lative drag performance and stability of the various canopies. Desirable designs would yield increased drag above the disk-gap-band with similar, or improved, stability characteristics. Ring sail parachutes were tested at geometric porosities ranging from 10% to 22% with most of the porosity taken from the shoulder region near the canopy skirt. The disk sail canopy replaced the rings lot portion of the ring sail canopy with a flat circular disk and wastested at geometric porosities ranging from 9% to 19%. The star sail canopy replaced several ringsail gores with solid gores and was tested at 13% geometric porosity. Two disk sail configurations exhibited desirable properties such as an increase of 6-14% in the tangential force coefficient above the DGB with essentially equivalent stability. However, these data are presented with caveats including the inherent differences between wind tunnel and flight behavior and qualitative uncertainty in the aerodynamic coefficients.
Subsonic and Transonic Wind Tunnel Testing of Two Inflatable Aerodynamic Decelerators
Two inflatable aerodynamic decelerator designs were tested in the Transonic Dynamics Tunnel at the NASA Langley Research Center: a tension cone and an isotensoid. The tension cone consists of a flexible tension shell attached to a torus and the isotensoid employs a ram-air inflated envelope. Tests were conducted at Mach numbers from 0.3 to 1.08 and Reynolds numbers from 0.59 to 2.46 million. The main objective of these tests was to obtain static aerodynamic coefficients at subsonic and transonic speeds to supplement supersonic aerodynamic data for these same two designs. The axial force coefficients of both designs increased smoothly from subsonic through transonic Mach numbers. Dynamic data show significant oscillation of the tension cone and minimal oscillation of the isotensoid. The transonic and subsonic data will be used to assemble an inflatable decelerator aerodynamic database for use in computational analyses and system studies.
Structural Verification and Modeling of a Tension Cone Inflatable Aerodynamic Decelerator
Verification analyses were conducted on membrane structures pertaining to a tension cone inflatable aerodynamic decelerator using the analysis code LS-DYNA. The responses of three structures - a cylinder, torus, and tension shell - were compared against linear theory for various loading cases. Stress distribution, buckling behavior, and wrinkling behavior were investigated. In general, agreement between theory and LS-DYNA was very good for all cases investigated. These verification cases exposed the important effects of using a linear elastic liner in membrane structures under compression. Finally, a tension cone wind tunnel test article is modeled in LS-DYNA for which preliminary results are presented. Unlike data from supersonic wind tunnel testing, the segmented tension shell and torus experienced oscillatory behavior when subjected to a steady aerodynamic pressure distribution. This work is presented as a work in progress towards development of a fluid-structures interaction mechanism to investigate aeroelastic behavior of inflatable aerodynamic decelerators.