Paul F. Wercinski

Surface Heating from Remote Sensing of the Hypervelocity Entry of the NASA GENESIS Sample Return Capsule

An instrumented aircraft and ground-based observing campaign was mounted to measure the radiation from the hypervelocity (11.0 km/s) reentry of the Genesis Sample Return Capsule prior to landing on the Utah Test and Training Range on September 08, 2004. The goal was to validate predictions of surface heating, the physical conditions in the shock layer, and the amount and nature of gaseous and solid ablation products as a function of altitude. This was the first hypervelocity reentry of a NASA spacecraft since the Apollo era. Estimates of anticipated emissions were made. Erroneous pointing instructions prevented us from acquiring spectroscopic data, but staring instruments measured broadband photometric and acoustic information. A surface-averaged brightness temperature was derived as a function of altitude. From this, we conclude that the observed optical emissions were consistent with most of the emitted light originating from a gray body continuum, but with a surface averaged temperature of 570 K less than our estimate from the predicted heat flux. Also, the surface remained warm longer than expected. We surmise that this is on account of conduction into the heat shield material, ablative cooling, and finite-rate wall catalycity. Preparations are underway to observe a second hypervelocity reentry (12.8 km/s) when the Stardust Sample Return Capsule returns to land at U.T.T.R. on January 15, 2006.

A Web-based Analysis System for Planetary Entry Vehicle Design

An integrated analysis environment for designing planetary entry vehicles has been developed. The system uses a Web-based graphical user interface, so that members of a geographically dispersed design team, with heterogeneous hardware, can readily access analysis modules located at other sites. The analyses and their implementation are briefly described. A sample application illustrates the value of this system, and indicates where further development effort would provide significant return.

Digital Still Snapshots of the Stardust Sample Return Capsule Entry

of the observed broadband flux is due to gray body radiation from the hot surface of the thermal protection system, exceptintheverybeginningwhenstrongemissionlines ofzincfromanablating paintlayercontributedsignificantly to the blue band. The measured flux in the green band was used to measure the surface-averaged temperature variation during flight, and the corresponding flux in the blue and red bands were used to verify the expected wavelength dependence of the gray body emission.

Venus In Situ Explorer Mission design using a mechanically deployed aerodynamic decelerator

The Venus In Situ Explorer (VISE) Mission addresses the highest priority science questions within the Venus community outlined in the National Research Councils Decadal Survey. The heritage Venus atmospheric entry system architecture, a 45° sphere-cone rigid aeroshell with a carbon phenolic thermal protection system, may no longer be the preferred entry system architecture compared to other viable alternatives being explored at NASA. A mechanically-deployed aerodynamic decelerator, known as the Adaptive Deployable Entry and Placement Technology (ADEPT), is an entry system alternative that can provide key operational benefits and risk reduction compared to a rigid aeroshell. This paper describes a mission feasibility study performed with the objectives of identifying potential adverse interactions with other mission elements and establishing requirements on decelerator performance. Feasibility is assessed through a launch-to-landing mission design study where the Venus Intrepid Tessera Lander (VITaL), a VISE science payload designed to inform the Decadal Survey results, is repackaged from a rigid aeroshell into the ADEPT decelerator. It is shown that ADEPT reduces the deceleration load on VITaL by an order of magnitude relative to a rigid aeroshell. The more benign entry environment opens up the VISE mission design environment for increased science return, reduced risk, and reduced cost. The ADEPT-VITAL mission concept of operations is presented and details of the entry vehicle structures and mechanisms are given. Finally, entry aerothermal analysis is presented that defines the operational requirements for a revolutionary structural-TPS material employed by ADEPT: three-dimensionally woven carbon cloth. Ongoing work to mitigate key risks identified in this feasibility study is presented.

Variable temperature performance of a Si(Li) detector stack

New experimental data is presented which displays /sup 137/Cs resolution of both single Si(Li) devices and a detector stack 2 cm in height as a function of temperature (85 K/spl les/T/spl les/245 K). We also discuss variations in photopeak shape which indicate that detector charge collection may be temperature dependent over the range of interest. >

Results from a Si(Li) gamma ray detector stack for future Mars missions

The authors present Monte Carlo analysis and experimental data from a novel lithium-drifted silicon detector stack for gamma ray spectroscopy instrumentation in future Mars surface landers and other planetary missions. The Monte Carlo analysis shows full energy photopeaks even in the range of approximately 100 keV to 2 MeV where. in Si, Compton scattering, dominates the absorption processes. Laboratory data are shown for an experimental detector stack of four planar Si(Li) devices, each 5 mm thick with an active area 2 cm in diameter. All the experimental data were collected with maximum temperature of the stack at 175 K. Background reduction was achieved by using the detector of the stack closest to the source in anticoincidence. Experimental data from the stack are compared with the Monte Carlo model for /sup 137/Cs (662 keV). >

MeV gamma ray detection algorithms for stacked silicon detectors

By making use of the signature of a gamma ray event as it appears in a stack of N=5 to 20 lithium-drifted silicon detectors and applying smart selection algorithms, gamma rays in the energy range of 1 to 8 MeV can be detected with good efficiency and selectivity. Examples of the types of algorithms used for different energy regions include the simple sum mode, the sum-coincidence mode used in segmented detectors, unique variations of sum-coincidence for an N-dimensional vector event, and a new and extremely useful mode for double escape peak spectroscopy at pair-production energies. The latter algorithm yields a spectrum similar to that of the pair spectrometer, but without the need for the dual external segments for double escape coincidence, and without the large loss in efficiency of double escape events. Background events due to Compton scattering are largely suppressed. Monte Carlo calculations were used to model the gamma ray interactions in the silicon in order to enable testing of a wide array of different algorithms on the event N-vectors for a large-N stack. >

Human Mars mission design study utilizing the adaptive deployable entry and placement technology

The Adaptive Deployable Entry and Placement Technology (ADEPT) is being considered as an entry, descent and landing (EDL) system to enable Human Mars class missions. ADEPT is a mechanically deployable decelerator that makes use of a 3 d woven carbon fabric as both heat shield and primary structure. The Human Mars Mission design study is focused, in part, on assessing the viability of ADEPT and identifying technical challenges, operational constraints, and critical risk mitigation activities. Study inputs included definition of the ground rules and assumptions, associated mission timelines and high level functional requirements. These inputs enabled the clarification of the concept of operations along with the design constraints and environments. Subsystem trades, mass sizing and integrated flight performance assessments enabled determination of a feasible mission architecture. Key outputs from the design study include a parametric mass model, driving requirements, key performance parameters and critical risks. These findings enable us to determine strategies for technical maturation and risk mitigation that can be assessed against resource and programmatic constraints to aid in advanced planning for human exploration of Mars.

Development challenges of game-changing entry system technologies from concept to mission infusion

NASAs Space Technology Mission Directorate (STMD) and the Game Changing Development Program (GCDP) were created to develop new technologies. This paper describes four entry system technologies that are funded by the GCDP and summarizes the lessons learned during the development. The investments are already beginning to show success, mission infusion pathways after five years of existence. It is hoped that our experience and observations, drawn from projects supported by the GCD program/STMD, Orion and SMD can help current and future technology development projects. Observations on fostering a culture of success and on constraints that limit greater success are also provided.

Nano-ADEPT aeroloads wind tunnel test

A wind tunnel test of the Adaptable Deployable Entry and Placement Technology (ADEPT) was conducted in April 2015 at the US Armys 7×10 Foot Wind Tunnel located at NASA Ames Research Center. Key geometric features of the fabric test article were a 0.7 m deployed base diameter, a 70° half-angle forebody cone angle, eight ribs, and a nose-to-base radius ratio of 0.7. The primary objective of this wind tunnel test was to obtain static deflected shape and pressure distributions while varying pretension at dynamic pressures and angles of attack relevant to entry conditions at Earth, Mars, and Venus. Other objectives included obtaining aerodynamic force and moment data and determining the presence and magnitude of any dynamic aeroelastic behavior (buzz/flutter) in the fabric trailing edge. All instrumentation systems worked as planned and a rich data set was obtained. This paper describes the test articles, instrumentation systems, data products, and test results. Four notable conclusions are drawn. First, test data support adopting a pre-tension lower bound of 10 lbf/in for Nano-ADEPT mission applications. Second, test results indicate that the fabric conditioning process needs to be reevaluated. Third, no flutter/buzz of the fabric was observed for any test condition and should also not occur at hypersonic speeds. Fourth, translating one of the gores caused ADEPT to generate lift without the need for a center of gravity offset. At hypersonic speeds, the lift generated by actuating ADEPT gores could be used for vehicle control.