Hannah S. Alpert | Search NASA

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A TPS Design Analysis of Entry Probe Delivery from Orbit for Ice Giant Missions

Previous investigation of direct delivery of a probe into Neptune’s atmosphere showed said approach to be challenging due to high stagnation pressures and heat loads. Entering at a high entry flight path angle (EFPA) results in stagnation pressure beyond current Heatshield for Extreme Entry Environment Technology (HEEET) qualification, while entering at a lower EFPA results in higher heat loads, leading to required HEEET thicknesses beyond manufacturing capabilities. Aerocapture is an enticing alternative entry scenario because it enables a fast trip and the placement of a payload in orbit around Neptune that can also reach Triton. Here, we investigate entry conditions associated with delivering a probe from orbit to assess feasibility. We consider whether 1) this entry scenario results in reasonable conditions, and 2) HEEET single insulating layer (mid-density carbon phenolic, 3MDCP) can be used to decrease mass, risk, and cost.

Hannah S. Alpert↗

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Thermal Modeling of a Novel Air-Cooled Temperature Swing Adsorption Compressor (AC-TSAC)

Contaminant removal technology, such as the Carbon Dioxide Removal Assembly (CDRA) on the International Space Station (ISS), is critical to Environmental Control and Life Support Systems (ECLSS), which enable humans to live and work in outer space. The CDRA includes an adsorbent bed, which absorbs CO 2 from the cabin air and releases it to a Sabatier reactor for water production when thermally cycled. An effective system would heat and cool the adsorbent quickly and uniformly to maximize the amount of CO 2 removed from the cabin and delivered to the Sabatier reactor. Air-Cooled Temperature Swing Adsorption Compressors (AC-TSAC) are promising for use downstream of the CDRA because they are a simple alternative to more mechanically-complex compressors, which are currently in use on the ISS. The current investigation addresses the thermal modeling of potential AC-TSAC designs. An initial thermal model was created and validated by comparing the model outputs to experimental data for the heating phase. Several design trades were conducted, including bed geometry (rectangular vs. cylindrical), bed structural material (i.e., the material that makes up the walls and shelves), and configuration of heat spreading elements within the bed. Also investigated is AC-TSAC performance sensitivity to the thermal conductivity of the adsorbent material and the heat pipes as well as the input power for heating. The results from these studies will inform the design of the next generation of the AC-TSAC, and the thermal modeling results will be further validated through testing.

Hannah S. Alpert↗

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Post-Flight Quantification of LOFTID Aeroshell Deflection Using Feature Tracking

The Low-Earth Orbit Flight Test of an Inflatable Decelerator (LOFTID) was a flight demonstration of the Hypersonic Inflatable Aerodynamic Decelerator (HIAD) technology, which has the potential to enable delivery of heavy payloads to Mars, Venus, and Titan, as well as return to Earth. Unlike rigid aeroshells that are constrained by the diameter of the launch vehicle shroud, inflatable aeroshells can be deployed to a much larger drag area, thus allowing a more massive spacecraft to begin its deceleration at higher altitudes and experience less heating. On November 10, 2022, the LOFTID reentry vehicle launched aboard a United Launch Alliance Atlas V rocket to low-Earth orbit. The aeroshell was inflated to its full 6-meter diameter, and the vehicle then successfully re-entered the atmosphere, landing in the Pacific Ocean. The aeroshell was composed of seven tori bound together by high strength straps to create a 70-degree half-angle sphere-cone, and the forebody was covered with a flexible thermal protection system (FTPS) (Fig. 1). The centerbody of the vehicle housed six visual cameras. Each camera was made up of 1920 x 1080 pixels and had a field-of-view (FOV) of 85.4° x 55.6°, resulting in a resolution of less than 0.1" at all locations on the aftbody side of the aeroshell. The approximate locations of the cameras and their associated FOVs is shown in Fig. 2. The high loads experienced during flight resulted in the cone of the aeroshell deflecting. This behavior was seen during the static load testing of the aeroshell in May 2021, in which loads ranging from 1,000 to 20,000 lbf were applied, and deflections of up to ~1.7° were observed. The LOFTID team was interested in estimating the deflection of the aeroshell during the its entry into Earth's atmosphere. Before launch, 1"-diameter black circles were drawn on select structural straps for tracking with the visual cameras; the change in position of these features could then be used to calculate aeroshell deflection angle.

Hannah S. Alpert↗

NASA NTRSDate not supplied

Post-Flight Quantification of LOFTID Aeroshell Deflection Using Feature Tracking

The Low-Earth Orbit Flight Test of an Inflatable Decelerator (LOFTID) was a flight demonstration of the Hypersonic Inflatable Aerodynamic Decelerator (HIAD) technology, which has the potential to enable delivery of heavy payloads to Mars, Venus, and Titan, as well as return to Earth. Unlike rigid aeroshells that are constrained by the diameter of the launch vehicle shroud, inflatable aeroshells can be deployed to a much larger drag area, thus allowing a more massive spacecraft to begin its deceleration at higher altitudes and experience less heating. On November 10, 2022, the LOFTID reentry vehicle launched aboard a United Launch Alliance Atlas V rocket to low-Earth orbit. The aeroshell was inflated to its full 6-meter diameter, and the vehicle then successfully re-entered the atmosphere, landing in the Pacific Ocean. The aeroshell was composed of seven tori bound together by high strength straps to create a 70-degree half-angle sphere-cone, and the forebody was covered with a flexible thermal protection system (FTPS) (Fig. 1). The centerbody of the vehicle housed six visual cameras. Each camera was made up of 1920 x 1080 pixels and had a field-of-view (FOV) of 85.4° x 55.6°, resulting in a resolution of less than 0.1" at all locations on the aftbody side of the aeroshell. The approximate locations of the cameras and their associated FOVs is shown in Fig. 2. The high loads experienced during flight resulted in the cone of the aeroshell deflecting. This behavior was seen during the static load testing of the aeroshell in May 2021, in which loads ranging from 1,000 to 20,000 lbf were applied, and deflections of up to ~1.7° were observed. The LOFTID team was interested in estimating the deflection of the aeroshell during the its entry into Earth's atmosphere. Before launch, 1"-diameter black circles were drawn on select structural straps for tracking with the visual cameras; the change in position of these features could then be used to calculate aeroshell deflection angle.

Hannah S. Alpert↗

NASA NTRSDate not supplied

Supersonic Free-Flight Dynamics Testing in the Stratosphere

A new technique for obtaining stratospheric free-flight dynamics data for atmospheric entry capsules is described. The Stratospheric Projectile Experiment of Entry Dynamics (SPEED) represents a new approach to characterizing the free-flight dynamics of vehicles in the supersonic and transonic regime of flight. The SPEED test architecture leverages a stratospheric balloon and 3D-printed flight system in a novel two-stage configuration to deliver test articles to supersonic conditions in the atmosphere which achieve dynamic similitude with a full-scale vehicle. Designed to address the limitations of existing test facilities, SPEED captures the complete time evolution of a vehicle’s dynamic state while producing a statistically significant number of observed flight trajectories to address the stochastic nature of the wake-driven dynamic stability phenomenon. SPEED was developed over two years at NASA Ames Research Center. The inaugural flight of the SPEED test platform was conducted in the summer of 2024 where scaled capsules of the Mars Sample Return Earth Entry System and Dragonfly entry vehicle were tested. This paper describes the motivation for a new test architecture, operational constraints and achievable flight test envelopes, the design and development of the SPEED concept, and results from the demonstration flight. Techniques for estimating the dynamic aerodynamic characteristics and atmospheric conditions for each test article individually and as a collective are also discussed.

Entry Vehicle↗

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Thermal Protection Systems (TPS) for High Velocity Earth Entry Missions

The fastest man-made object to re-enter into Earth’s atmosphere, with an entry velocity of 12.8 km/s, was the Stardust capsule, which returned samples from the comet Wild 2. Sample return missions offer high and long-lasting science yield; as such, they are discussed repeatedly in the latest planetary science decadal survey, titled Origins, Worlds, and Life. An advantage of sample return missions over in situ measurements is the ability to use state-of-the-art instruments that are not limited in power, size, or complexity; conversely, in situ measurements rely on instruments optimized to fit within the limitations of the spacecraft. Additionally, sample return provides the opportunity to revisit samples as analysis techniques improve as well as to further investigate unanticipated or ambiguous results. As launch vehicle and propulsion technologies continue to advance, it is becoming feasible to consider sample return missions from further out in the Solar System beyond Mars orbit. However, returning samples from increasingly distant destinations comes with high entry velocities, and thus requires ever more capable thermal protection systems (TPS). Evaluating the capabilities of existing mature TPS materials for a range of entry conditions and sample return aeroshell configurations is key to establishing the feasibility of future mission proposals. As such, this presentation describes the comprehensive trade study done to evaluate the feasibility of high velocity Earth entry missions with the currently available TPS materials.

Hannah S. Alpert↗

NASA NTRSDate not supplied

A Green’s Function Sensor Fusion Approach for Evaluating Spacecraft Entry Heating From on-Board Thermal Instrumentation

During atmospheric entry, distributed thermal measurements are critical to enable the evaluation of heat loads on spacecraft thermal protection systems (TPS). In recent space exploration missions, Schmidt-Boelter-type heat flux gauges have been integrated into the TPS alongside conventional temperature measurement instrumentation to measure total (convective and radiative) and radiative heat transfer rates1,2. While direct heat flux sensors (HFS) are able to provide valuable information detailing the thermal loads experienced by spacecraft, the interpretation of these measurements in unsteady, convective environments requires a correction factor to account for local heating augmentations at the cold wall HFS surface2,3. Current efforts to estimate cold wall correction factors, and thus recover the hot wall TPS heat flux, rely on time-marching computational fluid dynamics (CFD) simulations2. Simulation-based methods are susceptible to large uncertainties, however, as they require estimations of vehicle trajectory, gas kinetics, wall catalysis models, and other flight conditions as input parameters2,4. Furthermore, CFD simulations are computationally expensive and cannot efficiently survey all possible entry scenarios, exacerbating the uncertainty of reconstructed hot wall heat flux values. These drawbacks motivate the development of alternative hot wall heat flux reconstruction methods that are not reliant on CFD-based correction factors.

Kenneth McAfee↗

NASA NTRSDate not supplied

Reconstruction of Thermal Protection System Aeroheating using a Green’s Function Approach

Inverse heat transfer (IHT) techniques are often used to reconstruct the surface heating conditions on spacecraft thermal protection systems (TPS) during atmospheric entry. Current IHT techniques for entry spacecraft applications, however, demand substantial computational resources, and are impractical for analyses such as uncertainty quantification and real-time health monitoring. In this paper, a Green’s function sensor fusion approach is used to reconstruct the TPS surface aeroheating conditions on experimental spaceflight and ground test systems from collocated temperature and heat flux sensors embedded in the TPS. The algorithm leverages Green’s functions to model the heat conduction within the spacecraft TPS and stabilizes the recovery of the surface heating condition using the direct heat flux sensor measurement. The algorithm is validated using arc-jet ground test data and applied to the reconstruction of the Mars 2020 backshell heating during Martian atmospheric entry. The performance of the algorithm is benchmarked against a current state-of-the-art IHT framework, FIAT_Opt. The Green’s function-based reconstruction algorithm recovers the net hot-wall heat flux absorbed by the TPS and the incident heat flux from the atmospheric entry environment in close agreement with FIAT_Opt. Notably, computation of the surface heating condition is completed in three orders of magnitude less time with the Green’s function sensor fusion approach using a consumer-grade PC, versus with FIAT_Opt running on a high performance computer cluster. The efficiency of the algorithm is leveraged to compute the uncertainty contributions of input parameters to the total uncertainty in reconstructed Mars 2020 backshell heating for the full atmospheric entry heat pulse. The sensitivity analysis uncovers that, at different times throughout the entry heat pulse, uncertainties in the TPS specific heat, thermal conductivity, and emissivity are all dominant drivers of the reconstruction uncertainty. These results demonstrate Green’s functions and sensor-fusion techniques as promising IHT approaches to reconstruct atmospheric entry environments from TPS-embedded measurements, and highlight how these techniques may give access to post-flight analyses previously hindered by the prohibitive cost of current methods.

Kenneth McAfee↗

NASA NTRSDate not supplied

Reconstruction of Thermal Protection System Aeroheating using a Green’s Function Approach

Inverse heat transfer (IHT) techniques are often used to reconstruct the surface heating conditions on spacecraft thermal protection systems (TPS) during atmospheric entry. Current IHT techniques for entry spacecraft applications, however, demand substantial computational resources, and are impractical for analyses such as uncertainty quantification and real-time health monitoring. In this paper, a Green’s function sensor fusion approach is used to reconstruct the TPS surface aeroheating conditions on experimental spaceflight and ground test systems from collocated temperature and heat flux sensors embedded in the TPS. The algorithm leverages Green’s functions to model the heat conduction within the spacecraft TPS and stabilizes the recovery of the surface heating condition using the direct heat flux sensor measurement. The algorithm is validated using arc-jet ground test data and applied to the reconstruction of the Mars 2020 backshell heating during Martian atmospheric entry. The performance of the algorithm is benchmarked against a current state-of-the-art IHT framework, FIAT_Opt. The Green’s function-based reconstruction algorithm recovers the net hot-wall heat flux absorbed by the TPS and the incident heat flux from the atmospheric entry environment in close agreement with FIAT_Opt. Notably, computation of the surface heating condition is completed in three orders of magnitude less time with the Green’s function sensor fusion approach using a consumer-grade PC, versus with FIAT_Opt running on a high performance computer cluster. The efficiency of the algorithm is leveraged to compute the uncertainty contributions of input parameters to the total uncertainty in reconstructed Mars 2020 backshell heating for the full atmospheric entry heat pulse. The sensitivity analysis uncovers that, at different times throughout the entry heat pulse, uncertainties in the TPS specific heat, thermal conductivity, and emissivity are all dominant drivers of the reconstruction uncertainty. These results demonstrate Green’s functions and sensor-fusion techniques as promising IHT approaches to reconstruct atmospheric entry environments from TPS-embedded measurements, and highlight how these techniques may give access to post-flight analyses previously hindered by the prohibitive cost of current methods.

Kenneth McAfee↗