Todd White

Mars Science Laboratory Heat Shield Aerothermodynamics: Design and Reconstruction

The Mars Science Laboratory heat shield was designed to withstand a fully turbulent heat pulse using information from ground testing and computational analysis on a preflight design trajectory. Instrumentation on the flight heat shield measured in-depth temperatures to permit reconstruction of the surface heating. The data indicate that boundary-layer transition occurred at five of seven measurement locations before peak heating. Data oscillations at three pressure measurement locations may also indicate transition. This paper presents the heat shield temperature and pressure data, possible explanations for the timing of boundary-layer transition, and a comparison of reconstructed and computational heating on the actual trajectory. A smooth-wall boundary-layer Reynolds number that was used to predict transition is compared with observed transition at various heat shield locations. A single transition Reynolds number criterion does not uniformly explain the timing of boundary-layer transition observed duri...

Initial Assessment of Mars Science Laboratory Heatshield Instrumentation and Flight Data

The Mars Science Laboratory (MSL) Entry Descent and Landing Instrumentation (MEDLI) suite on MSL entry vehicle heatshield has successfully returned pressure, temperature, and thermal protection system (TPS) ablation data acquired during entry. This paper provides an initial assessment of MEDLI thermal instrumentation data that is comprised of in-depth temperatures in the TPS made of Phenolic-Impregnated Carbon Ablator (PICA). Temperatures are measured in-depth at seven different locations on the surface. The thermal sensor plugs are also characterized in arc jet facilities to quantify measurement uncertainties and biases. The assessment of flight data provides key insights into boundary layer transition to turbulence, surface recession, turbulent heating augmentation, stagnation point and apex laminar heating, and in-depth thermal response. A preliminary comparison with model results highlights inadequacies in our predictive capability. The peak temperature measured by near surface thermocouples was found to be 1049 C in the vicinity of apex region. Initial estimate of peak surface temperature with nominal model settings is about 1575 C. The peak heat flux was found to be on the leeside of the vehicle as predicted, but its value is sensitive to the recession model.

Reconstruction of Aerothermal Environment and Heat Shield Response of Mars Science Laboratory

An initial assessment and reconstruction of the Mars Science Laboratory entry aerothermal environment and thermal protection system response is performed using the onboard instrumentation suite called the Mars Science Laboratory entry, descent, and landing instrumentation. The analysis is performed using the current best-estimated trajectory. The Mars Science Laboratory Entry, Descent, and Landing Instrumentation suite in part provides in-depth temperature measurements at seven locations on the heat shield. The temperature data show the occurrence of boundary-layer transition to turbulence on the leeside forebody of the entry vehicle. The data also suggest that the thermal protection system recession is lower than nominal model predictions using diffusion limited surface oxidation. The model predictions of temperatures show an underprediction in the stagnation and apex regions and an overprediction in the leeside region. An estimate of time-varying aeroheating using an inverse reconstruction technique is ...

Direct Coupling of the NEQAIR Radiation and DPLR CFD Codes

The NEQAIR line-by-line radiation code is incorporated into the DPLR flow solver such that NEQAIR is now a callable subroutine of DPLR. The radiant energy source term computed by NEQAIR acts as an energy sink, reducing the convective and radiative heating rates, and brings the shock wave closer to the body. The effects of fluid dynamics/radiation coupling are examined by comparing coupled and uncoupled DPLR-NEQAIR results against FIRE II flight measurements and previous computations. Radiation coupling had the greatest effect at the 1643 s FIRE II trajectory point where the stagnation point total heating rate was reduced by 15.1 %. The coupled 1643 s results were closely correlated to the flight measurements. The change in stagnation point total heating rate was 6% at the 1636 and 1645 s trajectory points, and radiation coupling effects were essentially nonexistent at the 1651 s trajectory point. The coupled DPLR-NEQAIR surface heating rate profiles converged after only two updates of the radiant energy source term.

Preliminary Analysis of the Mars Science Laboratory's Entry Aerothermodynamic Environment and Thermal Protection System Performance

The Mars Science Laboratory (MSL) entry vehicle successfully landed on the Martian surface on August 5, 2012. A phenolic impregnated carbon ablator heatshield was used to protect the spacecraft against the severe aeroheating environments of atmospheric entry. This heatshield was instrumented with a comprehensive set of pressure and temperature sensors. The objective of this paper is to present the thermal ight data returned and provide a preliminary postight analysis of MSL’s aerothermal environment and heatshield thermal response. The ight temperature data are compared with the thermal response predictions by the same analytical models used in heatshield design. In addition to this direct comparison, a preliminary inverse analysis is performed where the time-dependent surface heating is estimated from ight-measured subsurface temperature data.

Post-flight Analysis of Mars Science Laboratory Entry Aerothermal Environment and Thermal Protection System Response

The Mars Science Laboratory rover landed at Gale Crater on August 5 th , 2012. The rover was protected from the extreme heating environments of Martian atmospheric entry by an ablative heatshield. This tiled Phenolic Impregnated Carbon Ablator heatshield was instrumented with a suite of sensors that monitored the in-depth ablator temperature response and the surface pressure at discrete locations. This paper presents a comparison of the flight data with post-entry analysis at the discrete sensor locations. From the flight data, we postulate that the heatshield experienced roughness-induced turbulent transition due to roughness elements around the heatshield tile and sensor plugs. We find that the analytical ablator material model performs well and can be used directly with the in-depth temperature data. Finally, we assess the performance of the ablation sensors, and predict the bondline temperature rise. The flight data from the instrumentation, along with the successful landing of the rover, confirms the performance of the heatshield and the conservative heatshield design and margins process.

Proposed Analysis Process for Mars Science Laboratory Heat Shield Sensor Plug Flight Data

The Mars Science Laboratory (MSL) mission is scheduled to enter the Martian atmosphere in August 2012. Aboard the heatshield is the MSL Entry Descent and Landing Instrumentation (MEDLI) system that includes a series of embedded sensor plugs to measure in-depth response of the thermal protection system (TPS). The general objectives of the MEDLI system are to assess the TPS performance and reconstruct the aerothermal environment experienced during entry. Some specific objectives, such as measuring TPS temperature, can be addressed with direct measurements. Other objectives, such as determining surface heating, must be inferred using measurements combined with analytical tools. This paper describes the specific objectives, the expected sensor responses to the entry environment based on aerothermal and material response simulations, and the reconstruction analysis process being developed for the flight data.

Mars Science Laboratory Heat Shield Instrumentation and Arc Jet Characterization

The Mars Science Laboratory (MSL) Entry Descent and Landing Instrumentation (MEDLI) suite on MSL entry vehicle heatshield has returned pressure, temperature, and thermal protection system (TPS) performance data acquired during entry. This paper presents performance and characterization data of the MEDLI Integrated Sensor Plug (MISP) embedded in Phenolic-Impregnated Carbon Ablator (PICA) heatshield. The sensor is characterized in arc jet facilities at MSL flight relevant conditions. The performance of the Hollow aErothermal Ablation and Temperature (HEAT) sensor in tracking a moving temperature isotherm through the thickness is evaluated. A close agreement between HEAT sensor depth and measured char depth in arc jet samples is also found. The growth of a fence due to Room-Temperature Vulcanizing (RTV) bonding agent around MISP plugs, which has significant impact on aerothermal reconstruction, is also quantified. The data presented will be used for improved reconstruction of the aerothermal environment and TPS response using MISP flight data.

Reconstruction of Mars Pathfinder Aeroheating and Heat Shield Response Using Inverse Methods

The Mars Pathfinder probe entered the Martian atmosphere in 1997 and contained instrumentation that provided measurements of the superlight ablator (SLA) heat shield subsurface temperature at different locations during the entry sequence. These measurements represented the first Martian aeroheating flight data since the Viking Lander missions. The objective of this paper is to reconstruct the Pathfinder entry vehicle’s aerothermal heating and heat shield material response using updated modeling tools and approaches in both direct and inverse manners. The direct approach consists of performing updated computational fluid dynamics calculations on a newly reconstructed entry trajectory to characterize the vehicle’s heating environment. From the calculated heating boundary conditions, the heat shield in-depth temperature response is computed using an updated thermal response and ablation model for the SLA material. These predictions are compared directly to the flight data. In addition to the direct compariso...

Inverse Estimation of the Mars Science Laboratory Entry Aerothermal Environment and Thermal Protection System Response

The Mars Science Laboratory entry vehicle successfully landed the Curiosity rover on the Martian surface on August 5, 2012. A phenolic impregnated carbon ablator heatshield was used to protect the spacecraft against the severe aeroheating environments of atmospheric entry. This heatshield was instrumented with a comprehensive set of pressure and temperature sensors. The objective of this paper is to perform an inverse estimation of the entry vehicle’s surface heating and heatshield material properties. The surface heating is estimated using the flight temperature data from the shallowest thermocouple. The sensitivity of the estimated surface heating profile to estimation tuning parameters, measurement errors, recession uncertainty and material property uncertainty is investigated. A Monte Carlo analysis is conducted to quantify the uncertainty bounds associated with the nominal estimated surface heating. Additionally, a thermocouple driver approach is employed to estimate heatshield material properties using the flight data from the deeper thermocouples while applying the shallowest thermocouple temperature as the surface boundary condition.