Prasad Kutty

Mars Entry Atmospheric Data System Trajectory Reconstruction Algorithms and Flight Results

The Mars Entry Atmospheric Data System is a part of the Mars Science Laboratory, Entry, Descent, and Landing Instrumentation project. These sensors are a system of seven pressure transducers linked to ports on the entry vehicle forebody to record the pressure distribution during atmospheric entry. These measured surface pressures are used to generate estimates of atmospheric quantities based on modeled surface pressure distributions. Specifically, angle of attack, angle of sideslip, dynamic pressure, Mach number, and freestream atmospheric properties are reconstructed from the measured pressures. Such data allows for the aerodynamics to become decoupled from the assumed atmospheric properties, allowing for enhanced trajectory reconstruction and performance analysis as well as an aerodynamic reconstruction, which has not been possible in past Mars entry reconstructions. This paper provides details of the data processing algorithms that are utilized for this purpose. The data processing algorithms include two approaches that have commonly been utilized in past planetary entry trajectory reconstruction, and a new approach for this application that makes use of the pressure measurements. The paper describes assessments of data quality and preprocessing, and results of the flight data reduction from atmospheric entry, which occurred on August 5th, 2012.

The aerodynamics of axisymmetric blunt bodies flying at angle of attack

The Mars Science Laboratory entry capsule is used as an example to demonstrate how a blunt body of revolution must be treated as asymmetric in some respects when flying at a non-zero trim angle of attack. A brief description of the axisymmetric moment equations are provided before solving a system of equations describing the lateral-directional moment equations for a blunt body trimming at an angle of attack. Simplifying assumptions are made which allow the solution to the equations to be rearranged to relate the roll and yaw stability with sideslip angle to the frequency of oscillation of the vehicle body rates. The equations show that for a blunt body the roll and yaw rates are in phase and proportional to each other. The ratio of the rates is determined by the static stability coefficients and mass properties about those axes. A trajectory simulation is used to validate the static yaw stability parameter identification equation and a simple method of identifying the oscillation frequency from the body rates. The approach is shown to successfully extract the modeled yaw stability coefficient along a simulated Mars entry. Mars Science Laboratory flight data results are presented from earlier work which indicate that results from both the validation case and flight data are in agreement with preflight predictions. A brief discussion of the dynamic stability is also provided. Trimming at a nonzero angle suggests that the typical axisymmetric models of the dynamic stability coefficients should be modified. However, further experimental or computational work must be done to separate damping due to body rates and wind relative rates before the correct lifting formulation would affect simulation results.

LDSD supersonic Flight Dynamics Test 1: Post-flight reconstruction

The Low Density Supersonic Decelerator projects first Supersonic Flight Dynamics Test (SFDT) occurred on June 28, 2014, off the west coast of Kauai, Hawaii, over the Pacific Ocean. The test vehicle traveled to speeds above Mach 4 and to an altitude of over 200,000 feet. This flight, although classified as a test architecture shake-out flight, tested two technologies: a robotic class Supersonic Inflatable Aerodynamic Decelerator and a Supersonic Disksail Parachute. The reconstruction team was tasked with collecting all relevant pre-flight and flight data to accurately reconstruct the trajectory and technology performance during the science phase of the flight. Furthermore, the reconstruction team has been involved with reconstructing and exploring all aerodynamic and test vehicle properties that affected the entire flight phase. This reconstruction provided insight into the technology performance, which is a key deliverable for the LDSD project, as well as provided insight into lessons learned for subsequent SFDT flights, in the fields of data recovery, reconstruction, and pre-flight trajectory simulations.

Mars Science Laboratory Aerodatabase Trajectory Reconstruction and Uncertainty Assessment

In this paper, a method of reconstruction and uncertainty quantification for entry, descent and landing trajectories is applied to the Mars Science Laboratory mission. The method, referred to as the aerodynamic database reconstruction, is a technique founded in previous planetary entry, descent and landing reconstruction analyses. The aerodynamic database algorithm estimates the ambient atmosphere states and wind-relative attitude (angle of attack and angle of sideslip) from the measured aerodynamic forces acting on the vehicle. At every flight condition for which measurements of the aerodynamic forces are available, as recorded by the on-board inertial measurement unit, the measured forces are compared to the forces tabulated in the aerodynamic database. The reconstructed values of atmosphere and wind-relative attitude are those that best reconcile the measured forces with the aerodynamic database. In this manner, state estimates are computed by leveraging data from both flight measurements and pre-flight models. Additionally, uncertainties of the state estimates are computed through an accompanying uncertainty assessment. The uncertainty quantification is an application of a fundamental technique that applies linear covariance propagation to transform input variances into output uncertainties. Flight data from the Mars Science Laboratory entry, descent and landing, having successfully completed on August 5th 2012, is used to reconstruct the in-flight atmosphere and wind-relative attitude of the Mars Science Laboratory trajectory. In order to assess the performance of the aerodynamic database reconstruction, comparisons of the estimated states are made against the extended Kalman filter reconstruction performed by the Mars Entry Descent and Landing Instrumentation reconstruction team. The state uncertainties are evaluated relative to the differences between the two reconstruction approaches in order to assess the accuracy of the estimated states.