Mairead Stackpoole

Post-Flight Evaluation of Stardust Sample Return Capsule Forebody Heatshield Material

Phenolic Impregnated Carbon Ablator (PICA) was developed at NASA Ames Research Center under the lightweight ceramic ablator development program in the ’80s. PICA’s low density (~ 0.27g/cc), coupled with efficient ablative capability at high heat fluxes, makes it an enabling technology for the Stardust mission. This paper discusses the evaluation of three cores extracted post flight from key locations on the forebody heatshield of the Stardust Sample Return Capsule (SRC). Core locations included a near stagnation core, a flank core, and a segment taken from the shoulder of the heatshield. Evaluation included density profiles, recession determination, a thermal analysis profile, PICA bondline examination, strength assessment of remaining virgin PICA, an emissivity profile, a chemical analysis profile, and a microstructural analysis. Results show good agreement in comparisons of experimental density profiles and profiles derived from FIAT and in recession comparisons from measured values and FIAT predictions for the flank core. In general, the PICA material examined in the cores is in good condition and intact. Impact damage is not evident, and the only degradation observed was that caused by heating on entry. A substantial amount of virgin PICA was present in all cores examined.

Post-Flight Analysis of the Stardust Sample Return Capsule Earth Entry

This paper presents an overview of post-flight activities for assessing the entry performance of the Stardust Sample Return Capsule and the analysis tools used to design it. Three sources of information are leveraged: the recovered return capsule thermal protection system, airborne observations of the entry using instruments that provide spectral resolution of the hot return capsule and shock layer gasses, and radar signature during the terminal descent stage. The paper describes the objectives of the post-flight analysis, the information sources, and the methods of analysis. Sample results from detailed analyses are presented.

Investigation of Performance Envelope for Phenolic Impregnated Carbon Ablator (PICA)

The present work provides the results of a short exploratory study on the performance of Phenolic Impregnated Carbon Ablator, or PICA, at high heat flux and pressure in an arcjet facility at NASA Ames Research Center. The primary objective of the study was to explore the thermal response of PICA at cold-wall heat fluxes well in excess of 1500 W/cm (exp 2). Based on the results of a series of flow simulations, multiple PICA samples were tested at an estimated cold wall heat flux and stagnation pressure of 1800 W/cm (exp 2) and 130 kPa, respectively. All samples survived the test, and no failure was observed either during or after the exposure. The results indicate that PICA has a potential to perform well at environments with significantly higher heat flux and pressure than it has currently been flown.

Remote Recession Measurements of Wire-Seeded PICA Samples in an Arc-Jet Flow [STUB]

Various methods for remote recession sensing of PICA have been developed and several seeding methods have been tested. The most recent method involved seeding the ablator with wires fed to the sample from the backside with a defined amount of PICA left towards the upstream front of the sample. This seed method mimics the installation of in-depth thermocouples as they are frequently used in ground testing and flight. Arc-jet tests were conducted in the NASA Langley HYMETS facility at a heat flux of 320 W/cm. The emission of the post-shock layer was observed in spectral resolution from the side along an optical axis perpendicular to the arc-jet flow and from the front, looking at the sample surface from an upstream position. Various metallic seed materials with different melting points were used. In addition to the emission spectroscopy measurements, the samples were monitored during the tests through pyrometry and videography. The time resolved response of the seeded material is described and compared to earlier tests with different seeding methods. The combination of seed materials was found to be critical for the selection of emission signatures characteristic for the material recession which can be isolated in the final emission spectra.