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NASA NTRS1979

800 x 800 charge-coupled device /CCD/ camera for the Galileo Jupiter Orbiter mission

During January 1982 the NASA space transportation system will launch a Galileo spacecraft composed of an orbiting bus and an atmospheric entry probe to arrive at the planet Jupiter in July 1985. A prime element of the orbiter's scientific instrument payload will be a new generation slow-scan planetary imaging system based on a newly developed 800 x 800 charge-coupled device (CCD) image sensor. Following Jupiter orbit insertion, the single, narrow-angle, CCD camera, designated the Solid State Imaging (SSI) Subsystem, will operate for 20 months as the orbiter makes repeated encounters with Jupiter and its Galilean Satellites. During this period the SSI will acquire 40,000 images of Jupiter's atmosphere and the surfaces of the Galilean Satellites. This paper describes the SSI, its operational modes, and science objectives.

Clary, M. C.↗

NASA NTRS2010

Reactive Sequencing for Autonomous Navigation Evolving from Phoenix Entry, Descent, and Landing

Virtual Machine Language (VML) is an award-winning advanced procedural sequencing language in use on NASA deep-space missions since 1997, and was used for the successful entry, descent, and landing (EDL) of the Phoenix spacecraft onto the surface of Mars. Phoenix EDL utilized a state-oriented operations architecture which executed within the constraints of the existing VML 2.0 flight capability, compatible with the linear "land or die" nature of the mission. The intricacies of Phoenix EDL included the planned discarding of portions of the vehicle, the complex communications management for relay through on-orbit assets, the presence of temporally indeterminate physical events, and the need to rapidly catch up four days of sequencing should a reboot of the spacecraft flight computer occur shortly before atmospheric entry. These formidable operational challenges led to new techniques for packaging and coordinating reusable sequences called blocks using one-way synchronization via VML sequencing global variable events. The coordinated blocks acted as an ensemble to land the spacecraft, while individually managing various elements in as simple a fashion as possible. This paper outlines prototype VML 2.1 flight capabilities that have evolved from the one-way synchronization techniques in order to implement even more ambitious autonomous mission capabilities. Target missions for these new capabilities include autonomous touch-and-go sampling of cometary and asteroidal bodies, lunar landing of robotic missions, and ultimately landing of crewed lunar vehicles. Close proximity guidance, navigation, and control operations, on-orbit rendezvous, and descent and landing events featured in these missions require elaborate abort capability, manifesting highly non-linear scenarios that are so complex as to overtax traditional sequencing, or even the sort of one-way coordinated sequencing used during EDL. Foreseeing advanced command and control needs for small body and lunar landing guidance, navigation and control scenarios, work began three years ago on substantial upgrades to VML that are now being exercised in scenarios for lunar landing and comet/asteroid rendezvous. The advanced state-based approach includes coordinated state transition machines with distributed decision-making logic. These state machines are not merely sequences - they are reactive logic constructs capable of autonomous decision making within a well-defined domain. Combined with the JPL's AutoNav software used on Deep Space 1 and Deep Impact, the system allows spacecraft to autonomously navigate to an unmapped surface, soft-contact, and either land or ascend. The state machine architecture enabled by VML 2.1 has successfully performed sampling missions and lunar descent missions in a simulated environment, and is progressing toward flight capability. The authors are also investigating using the VML 2.1 flight director architecture to perform autonomous activities like rendezvous with a passive hypothetical Mars sample return capsule. The approach being pursued is similar to the touch-and-go sampling state machines, with the added complications associated with the search for, physical capture of, and securing of a separate spacecraft. Complications include optically finding and tracking the Orbiting Sample Capsule (OSC), keeping the OSC illuminated, making orbital adjustments, and physically capturing the OSC. Other applications could include autonomous science collection and fault compensation.

asteroid↗

NASA NTRS1973

Determination of meteor parameters using laboratory simulation techniques

Atmospheric entry of meteoritic bodies is conveniently and accurately simulated in the laboratory by techniques which employ the charging and electrostatic acceleration of macroscopic solid particles. Velocities from below 10 to above 50 km/s are achieved for particle materials which are elemental meteoroid constituents or mineral compounds with characteristics similar to those of meteoritic stone. The velocity, mass, and kinetic energy of each particle are measured nondestructively, after which the particle enters a target gas region. Because of the small particle size, free molecule flow is obtained. At typical operating pressures (0.1 to 0.5 torr), complete particle ablation occurs over distances of 25 to 50 cm; the spatial extent of the atmospheric interaction phenomena is correspondingly small. Procedures have been developed for measuring the spectrum of light from luminous trails and the values of fundamental quantities defined in meteor theory. It is shown that laboratory values for iron are in excellent agreement with those for 9 to 11 km/s artificial meteors produced by rocket injection of iron bodies into the atmosphere.

Friichtenicht, J. F.↗

NASA NTRS1993

Observation of intense wave bursts at very low altitudes within the Venus nightside ionosphere

Intense ELF (100 Hz) bursts were detected by the Pioneer Venus (PV) Orbiter plasma wave instrument during the final operations of the spacecraft prior to atmospheric entry. These bursts were detected at approx. 130 km altitude around 0400 local time. The wave activity lasted for several tens of seconds. Furthermore the bursts were not symmetric about periapsis, unlike instrument noise caused by neutral impacts on the spacecraft. The bursts had a vertical attenuation scale height of the order 1 km, consistent with that expected for whistler-mode waves propagating through a collisional ionosphere. Since the decay of the signals appears to be due to attenuation, the source must persist for several tens of seconds. The wave bursts could therefore be the signature of electromagnetic radiation entering the bottomside ionosphere from several distant sources, as would be expected if lightning were a relatively persistent phenomenon within the Venus atmosphere.

Strangeway, R. J.↗

NASA NTRS1993

Observation of Intense Wave Bursts at Very Low Altitudes Within the Venus Nightside Ionosphere

Intense ELF (100 Hz) bursts were detected by the Pioneer Venus Orbiter plasma wave instrument during the final operations of the spacecraft prior to atmospheric entry. These bursts were detected at approx. 130 km altitude around 0400 local time. The wave activity lasted for several tens of seconds. Furthermore the bursts were not symmetric about periapsis, unlike instrument noise caused by neutral impacts on the spacecraft. The bursts had a vertical attenuation scale height of the order 1 km, consistent with that expected for whistler-mode waves propagating through a collisional ionosphere. Since the decay of the signals appears to be due to attenuation, the source must persist for several tens of seconds. The wave bursts could therefore be the signature of electromagnetic radiation entering the bottomside ionosphere from several distant sources, as would be expected if lightning were a relatively persistent phenomenon within the Venus atmosphere.

Strangeway, R. J.↗

NASA NTRSDate not supplied

Recommended DSMC Collision Model Parameters for Planetary Entry

Hybrid simulation frameworks combining Computational Fluid Dynamics (CFD) and Direct Simulation Monte Carlo (DSMC) are frequently employed to efficiently perform high-fidelity simulations of environments consisting of both continuum and rarified flow. DSMC is a stochastic, particle-based method which solves the fundamental Boltzmann equation and is therefore necessary for high-Knudsen flow where continuum-based assumptions governing CFD break down. However, the DSMC methodology is generally computationally inefficient to model the continuum regime. In a CFD/DSMC hybrid approach, obtaining an accurate, high-fidelity solution hinges on the consistent treatment of transport properties and the thermo-chemical models employed within the two solvers. In principle, in regions where CFD and DSMC are both employed, the same gas mixture under the same conditions should have the same properties, regardless of simulation type. Observed differences should be due to non-equilibrium processes, rather than differences in physical models. The goal of this work is to provide a comprehensive DSMC transport database encompassing the vast majority of known gas species encountered during Earth or other planetary atmospheric entry. This goal is largely possible due to recently performed ab initio quantum chemistry calculations. Combined with other high-fidelity data, the planned database will consist of collision integral data for over 200 neutral and ionized species and over 20000 binary collisions. From these collision integrals, Nelder-Mead optimization is used to compute collision-specific Variable Soft Sphere (VSS) collision model parameters, fitted from 300 K to 20000 K. Initial comparisons of transport properties of relevant equilibrium gas mixtures show great agreement between CFD and DSMC-derived results. The completed database can be readily applied to model binary collisions of any gas mixture containing the included species over the specified temperature range, making it a valuable tool for future planetary probe modeling efforts. An example is shown below in Fig. 1. Equilibrium mixture transport properties for a 35-species mixture composed originally of 10% air and 90% pyrolysis species of a carbon-phenolic ablator material [4] are computed using both fitted VSS Parameters and the original CFD collision integral values. Deviations in computed properties between the two approaches are less than 5% for the entire temperature range.

M. R. Gosma↗

NASA NTRS2004

The Complex Exposure History of a Very Large L/LL5 Chondrite Shower: Queen Alexandra Range 90201

Compared to iron meteorites, large stony meteorites (less than 100 kg) are relatively rare. Most large stony meteoroids fragment during atmospheric entry, producing large meteorite showers. Interestingly, many of these large chondrites, such as Bur Gheluai, Gold Basin, Jilin and Tsarev appear to have a complex exposure history with a first-stage exposure on the parent body. The question is whether complex exposure histories are simply more readily detected in large objects or large objects are more likely to experience a complex exposure. Investigation of these two hypotheses is the motivation for this work in which we report on the exposure history of QUE 90201, a large L/LL5 chondrite shower found near Queen Alexandra Range, Antarctica. Previous cosmogenic nuclide studies have led to the consensus that most of the approx. 2000 L5 and LL5 chondrites from the QUE area are derived from a single object with a pre-atmospheric radius of 1-2 m. The terrestrial age of the QUE 90201 shower was determined at 125 20 kyr. Here, we present a more complete set of cosmogenic radionuclide results in the metal and stone fractions of eleven L/LL5 chondrites from the QUE stranding area, as well as noble gases in seven of these samples. The main goal of this work is to unravel the cosmic-ray exposure history of the QUE 90201 meteoroid. In addition, we will discuss the pre-atmospheric size and exposure history of QUE 93013 (H5) and 93081 (H4) with similar shielding conditions as the QUE 90201 shower and a terrestrial age of 145 +/- 25 kyr.

Welten, K. C.↗

NASA NTRS2020

InSight Aerothermal Environment Assessment

The Mars Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) spacecraft, which successfully touched down on the planet surface on November 26, 2018, was proposed as a near build-to-print copy of the Mars Phoenix vehicle to reduce the overall cost and risk of the mission. Since the lander payload and the atmospheric entry trajectory were similar enough to those of the Phoenix mission, it was expected that the Phoenix thermal protection material thickness would be sufficient to withstand the entry heat load. However, allowances were made for increasing the heatshield thickness because the planned spacecraft arrival date coincided with the Mars dust storm season. The aftbody Thermal Protection System (TPS) components were not expected to change. In a first for a US Mars mission, the aerothermal environments for InSight included estimates of radiative heat flux to the aftbody from the wake. The combined convective and radiative heat fluxes were used to determine if the as-flown Phoenix thermal protection system (TPS) design would be sufficient for InSight. Although the radiative heat fluxes on the aftbody were predicted to be comparable to, or even higher than the local convective heat fluxes, all analyses of the aftbody TPS showed that the design would still be adequate. Aerothermal environments were computed for the vehicle from post-flight reconstruction of the atmosphere and trajectory and compared.

Beck, Robin↗

NASA NTRS2020

InSight Aerothermal Environment Assessment

Beck, Robin A. S.↗

NASA NTRSDate not supplied

A Holistic DSMC Transport Database for Re-Entry and Ablation Modeling

Hybrid simulation frameworks combining Computational Fluid Dynamics (CFD) and Direct Simulation Monte Carlo (DSMC) are frequently employed to efficiently perform high-fidelity solutions of environments containing combined continuum/rarified flow. The use of DSMC, a stochastic, particle-based method, is necessary for high-Knudsen flow where continuum-based assumptions governing CFD break down. However, the DSMC methodology is generally very computationally inefficient to model the continuum regime. In a CFD/DSMC hybrid approach, obtaining an accurate, high-fidelity solution hinges on the consistent treatment of transport properties and the used thermo-chemical models employed within the two solvers. In principle, in regions where CFD and DSMC are both employed, the same gas mixture under the same conditions should have the same properties, regardless of simulation type. Observed differences should be due to non-equilibrium processes, rather than differences in physical models. While the transport models governing CFD and DSMC simulations are starkly different, they can effectively be linked via their use of reduced Chapman-Enskog collision integrals. In CFD, these integrals are typically stored as fitted polynomial expressions and used to directly compute gas transport properties via mixing rules or the full Chapman-Enskog formulation. In DSMC, they can be used to derive the collision parameters needed for the phenomenological collision cross-section models that govern particle interactions, via a Nelder-Mead optimization scheme. The goal of this work is to provide a unified DSMC transport database encompassing the vast majority of known gas species encountered during atmospheric entry, on Earth or any other Solar body. This goal is largely possible due to recently performed ab-initio quantum chemistry calculations. Combined with other high-fidelity literature sources, the planned database will consist of collision integral data for over 200 neutral and ionized species and over 17000 binary collisions. From these collision integrals, Nelder-Mead optimization is used to compute Variable Soft Sphere (VSS) collision model parameters for DSMC, fitted from 300 K to 20000 K. Initial comparisons of transport properties of relevant equilibrium gas mixtures show great agreement between CFD and DSMC-derived results. The completed database will be able to be readily applied to model binary collisions of any gas mixture containing the included species over the specified temperature range, making it a valuable tool for future planetary probe modeling efforts. An example is shown below. Equilibrium mixture transport properties for a 19-species Titan atmospheric model [4] are computed using both fitted VSS parameters and the original CFD collision integral values. Deviations in computed properties between the two approaches is less than 5% for the entire temperature range.

M R Gosma↗

NASA NTRS2015

Near Earth Asteroid Characteristics for Asteroid Threat Assessment

Information about the physical characteristics of Near Earth Asteroids (NEAs) is needed to model behavior during atmospheric entry, to assess the risk of an impact, and to model possible mitigation techniques. The intrinsic properties of interest to entry and mitigation modelers, however, rarely are directly measureable. Instead we measure other properties and infer the intrinsic physical properties, so determining the complete set of characteristics of interest is far from straightforward. In addition, for the majority of NEAs, only the basic measurements exist so often properties must be inferred from statistics of the population of more completely characterized objects. We will provide an assessment of the current state of knowledge about the physical characteristics of importance to asteroid threat assessment. In addition, an ongoing effort to collate NEA characteristics into a readily accessible database for use by the planetary defense community will be discussed.

Atmospheric↗

NASA NTRS1994

The End of Comet Shoemaker-Levy 9

The pieces of the former Comet Shoemaker-Levy 9 struck Jupiter during the week of July 16-22 1994. We divide the general impact phenomena into four phases: (1) Atmospheric entry should have been accompanied by an entry flash, probably only detectable by the Galileo spacecraft. (2) Aerodynamic forces cause the impactor to explode. We show that the apparent altitude of the explosions is consistent with the analytical model proposed by Zahnle and Chyba et al, with numerical models calculated by Mac Low and Zahnle and Yabe et al., and with dynamically-based estimates of fragment masses Suggested by Scotti and Melosh and Asphaug and Benz. (3) The explosion produces a fireball that propagates most quickly up the wake, as predicted by Takata et al. and Crawford et al. The fireball's luminosity fades over a timescale of 30-60 seconds. (4) Each explosion produced a plume that reached thousands of kilometers above the cloud-tops. The plumes appear to have been dusty and SO illuminated when they reached sunlight. The plumes rose and fell over a period of ten or twenty minutes, governed by the simple laws of ballistics. When plume material (dust) fell back on the atmosphere it was reheated and glowed brightly in the thermal infrared for a period of order ten to twenty minutes; a large fraction of the impact energy was spent thus. Geometry introduces additional factors that complicate interpretation of the observed light curves.

Zahnle, K. J.↗

NASA NTRS2015

Structural Testing of a 6m Hypersonic Inflatable Aerodynamic Decelerator System

NASA is developing low ballistic coefficient technologies to support the Nations long-term goal of landing humans on Mars. Current entry, decent, and landing technologies are not practical for this class of payloads due to geometric constraints dictated by current and future launch vehicle fairing limitations. Hypersonic Inflatable Aerodynamic Decelerators (HIADs) are being developed to circumvent this limitation and are now considered a leading technology to enable landing of heavy payloads on Mars. At the beginning of 2014, a 6m diameter HIAD inflatable structure with an integrated flexible thermal protection system (TPS) was subjected to a static load test series to verify its structural performance under flight-relevant loads. The inflatable structure was constructed into a 60 degree sphere-cone configuration using nine inflatable torus segments composed of fiber-reinforced thin films. The inflatable tori were joined together using adhesives and high-strength textile woven structural straps. These straps help distribute the load throughout the inflatable structure. The 6m flexible TPS was constructed using multiple layers of high performance materials that are designed to protect the inflatable structure from heat loads that would be seen in flight during atmospheric entry. A custom test fixture was constructed to perform the static load test series. The fixture consisted of a round structural tub with enough height and width to allow for displacement of the HIAD test article as loads were applied. The bottom of the tub rim had an airtight seal with the floor. The rigid centerbody of the HIAD was mounted to a pedestal in the center of the structural tub. Using an impermeable membrane draped over the HIAD test article, an airtight seal was created with the top rim of the static load tub. This seal allowed partial vacuum to be pulled beneath the HIAD resulting in a uniform static pressure load applied to the outer surface. Using this technique, the test article was subjected to loads of up to 50,000lbs. During the test series an extensive amount of instrumentation was used to provide a rich data set, including deflected shape, structural strap loads, torus cord loads, inflation pressures, and applied static load. In this paper the 2014 6m HIAD static load test series will be discussed in detail, including the design of the 6m HIAD test article, the test setup, and test execution. Analysis results will be described supporting the conclusions that were drawn from the test series..

Hypersonic↗

NASA NTRSDate not supplied

Stagnation Point Convective Heating Correlations for Entry Into H2/He Atmospheres

New convective heating correlations have been developed over a broad range of entry conditions into H2/He atmospheres. The correlations are based on calculations of stagnation point convective heat fluxes over a large range of velocities, densities, and effective nose radii. The heat fluxes and corresponding flowfields are computed using NASA’s hypersonic computational fluid dynamics code, DPLR. Cases in this study have been computed using both a temperaturelimited, radiative equilibrium wall and a cold wall temperature boundary condition. The results for the scaled heat flux, as a function of the difference in freestream and wall enthalpies, show a clear deviation from the linear trend predicted by the method of Sutton and Graves. Therefore, updated non-linear correlations are proposed for the prediction of stagnation point convective heat fluxes. Generally, these updated correlations predict lower heat loads and therefore smaller required TPS thicknesses when compared to previous correlations for a range of test cases in the Neptune, Saturn, and Uranus atmospheres.

Alex T. Carroll↗

NASA NTRSDate not supplied

Stagnation Point Convective Heating Correlations for Entry Into H2/He Atmospheres

New convective heating correlations have been developed over a broad range of entry conditions into H2/He atmospheres. The correlations are based on calculations of stagnation point convective heat fluxes over a large range of velocities, densities, and effective nose radii. The heat fluxes and corresponding flow fields are computed using NASA’s hypersonic computational fluid dynamics code, DPLR. Cases in this study have been computed using both a temperature limited, radiative equilibrium wall and a cold wall temperature boundary condition. The results for the scaled heat flux, as a function of the difference in freestream and wall enthalpies, show a clear deviation from the linear trend predicted by the method of Sutton and Graves. Therefore, updated non-linear correlations are proposed for the prediction of stagnation point convective heat fluxes. Generally, these updated correlations predict lower heat loads and therefore smaller required TPS thicknesses when compared to previous correlations for a range of test cases in the Neptune, Saturn, and Uranus atmospheres.

Alex T. Carroll↗

NASA NTRS2012

Ground Contact Model for Mars Science Laboratory Mission Simulations

The Program to Optimize Simulated Trajectories II (POST 2) has been successful in simulating the flight of launch vehicles and entry bodies on earth and other planets. POST 2 has been the primary simulation tool for the Entry Descent, and Landing (EDL) phase of numerous Mars lander missions such as Mars Pathfinder in 1997, the twin Mars Exploration Rovers (MER-A and MER-B) in 2004, Mars Phoenix lander in 2007, and it is now the main trajectory simulation tool for Mars Science Laboratory (MSL) in 2012. In all previous missions, the POST 2 simulation ended before ground impact, and a tool other than POST 2 simulated landing dynamics. It would be ideal for one tool to simulate the entire EDL sequence, thus avoiding errors that could be introduced by handing off position, velocity, or other fight parameters from one simulation to the other. The desire to have one continuous end-to-end simulation was the motivation for developing the ground interaction model in POST 2. Rover landing, including the detection of the postlanding state, is a very critical part of the MSL mission, as the EDL landing sequence continues for a few seconds after landing. The method explained in this paper illustrates how a simple ground force interaction model has been added to POST 2, which allows simulation of the entire EDL from atmospheric entry through touchdown.

Raiszadeh, Behzad↗

NASA NTRS2022

Mars 2020 Entry, Descent, and Landing as Observed by Radio Science Techniques at UHF and X-band Frequencies

On February 18, 2021, NASA’s Mars 2020 Rover “Perseverance” conducted the Entry, Descent, and Landing (EDL) sequence to land safely on the surface of Mars at Jezero Crater. Due to the criticality of the EDL sequence, redundant telecommunications strategies were utilized to observe the event. The rover transmitted an X-band (8.4 GHz) signal encoded with Multiple Frequency Shift Keying tones direct-to-Earth and a UHF (401.5 MHz) signal with 8 kbps encoded telemetry to orbiters, which relayed the signal back to Earth at X-band. NASA’s Deep Space Network complexes at Goldstone, California and Madrid, Spain received the direct-to-Earth X-band signal. Two of the largest steerable radio telescopes in the world, the 100-meter Green Bank Telescope in West Virginia and the Effelsberg 100-meter Radio Telescope in Germany also received the UHF carrier signal on Earth. During the EDL event, full spectrum recordings of the UHF and X-band signals were captured at these observatories using open-loop receivers. Real-time and post-processing signal analysis to determine power level, received frequency, and Doppler shift allowed determination of the spacecraft’s health and safety state during critical sequences, including event detection such as atmospheric entry, plasma blackouts, and parachute deployment. Simultaneous observations of the UHF and X-band radio links allow for redundancy in the event of a fault and greatly improve confidence in Doppler event detection.

Gladden, Roy↗

NASA NTRS1994

Galileo Preparing for Jupiter Arrival

The most critical events of the Galileo mission occur on Jupiter arrival day, December 7, 1995. In chronological order, these one-time events are: a 1000 km flyby of the innermost Galilean satellite Io, the 75-minute Atmospheric Entry Probe mission, and the Orbiter's Jupiter Orbit Insertion (JOI) maneuver. In addition, extensive, unique Orbiter science observations are planned because this is the only time Galileo will encounter Io, fly through the Io torus, and will be so close to Jupiter -- three times closer than at any of the perijove passes in the orbital mission. All of these events occur in what will be by far the most intense radiation environment Galileo will ever see. The focus of this paper is the extraordinary preparations being made to maximize the reliability of the most critical events in order to ensure a successful probe mission and Orbiter Insertion while also gathering unique arrival day Orbiter science. The paper also provides a mission status report including the return of the asteroid Ida data and the Galileo direct line-of-sight observations of Comet Shoemaker-Levy fragments impacting Jupiter in July 1994.

Galileo↗