Results for “Earth entry” — Page 12

NASA NTRS1997

Entry Dispersion Analysis for the Stardust Comet Sample Return Capsule

Stardust will be the first mission to return samples from beyond the Earth-Moon system. The sample return capsule, which is passively controlled during the fastest Earth entry ever, will land by parachute in Utah. The present study analyzes the entry, descent, and landing of the returning sample capsule. The effects of two aerodynamic instabilities are revealed (one in the high altitude free molecular regime and the other in the transonic/subsonic flow regime). These instabilities could lead to unacceptably large excursions in the angle-of-attack near peak heating and main parachute deployment, respectively. To reduce the excursions resulting from the high altitude instability, the entry spin rate of the capsule is increased. To stabilize the excursions from the transonic/subsonic instability, a drogue chute with deployment triggered by an accelerometer and timer is added prior to main parachute deployment. A Monte Carlo dispersion analysis of the modified entry (from which the impact of off-nominal conditions during the entry is ascertained) shows that the capsule attitude excursions near peak heating and drogue chute deployment are within Stardust program limits. Additionally, the size of the resulting 3-sigma landing ellipse is 83.5 km in downrange by 29.2 km in crossrange, which is within the Utah Test and Training Range boundaries.

Desai, Prasun N.↗

NASA NTRS1976

Planetary/DOD entry technology flight experiments. Volume 3: Planetary entry flight experiments handbook

The environments produced by entry into Jupiter and Saturn atmospheres are summarized. Worst case design environments are identified and the effect of entry angle, type of atmosphere and ballistic coefficient variations are presented. The range of environments experienced during earth entry is parametrically described as a function of initial entry conditions. The sensitivity of these environments to vehicle ballistic coefficient and nose radius is also shown. An elliptical deorbit maneuver strategy is defined in terms of the velocity increment required versus initial entry conditions and apoapsis altitude. Mission time, ground track, and out of plane velocity penalties are also presented. Performance capabilities of typical shuttle launched boosters are described including the initial entry conditions attainable as a function of paylaod mass and apoapsis altitude.

Christensen, H. E.↗

NASA NTRS2010

Earth Return Navigation Analysis for Manned Spacecraft Using Optical and Radiometric Measurements

Future manned space missions will travel beyond low Earth orbit with more stringent navigation requirements and fewer navigation resources than used for the Apollo Program of the 1960s. A study has been performed to assess radiometric and optical tracking capabilities necessary to meet nominal and contingency Earth entry flight path angle requirements. Results indicate that 3 tracking stations will be insufficient for meeting nominal entry requirements, while the performance of a 6 station architecture is dependent on the entry geometry. Optical tracking results indicate that a narrow-angle camera is required for satisfying contingency Earth return requirements.

GN&C↗

NASA NTRSDate not supplied

Unsteady Aerodynamic Modeling of Atmospheric Entry Vehicles in Subsonic and Incompressible flow: A Frequency Response Approach

The determination of time-varying lift force and pitch moment generated by a purely pitching Earth-entry capsule is investigated. Experiments were conducted in the 12-foot Low-Speed Tunnel at NASA Langley Research Center, testing a range of oscillation frequencies at a zero-mean angle of attack with a pitching amplitude of 10 degrees. In light of these measurements, a closed-form set of analytically derived equations for lift and moment was used to develop a semi-empirical formulation, incorporating empirically determined values from the experimental runs. The equations are grounded in potential flow theory, Theodorsen's classical theory of unsteady aerodynamics, and the Joukowski theorem of conformal mapping. The unsteady aerodynamics generated by the oscillating body are then modeled by constructing frequency response functions, with quasi-steady forces and moments serving as inputs and unsteady forces and moments as outputs. The experimentally determined gain and phase variations characterize the unsteady nature of the flow and the system's response and flow time-lag to input flow parameters for a blunt-body entry vehicle. The final semi-empirical model is validated with a set of parameters beyond the initial test matrix.

Entry Systems Modeling↗

NASA NTRSDate not supplied

Unsteady Aerodynamic Modeling of Atmospheric Entry Vehicles in Subsonic and Incompressible Flow: A Frequency Response Approach

The determination of time-varying lift force and pitch moment generated by a purely pitching Earth-entry capsule is investigated. Experiments were conducted in the 12-foot Low-Speed Tunnel at NASA Langley Research Center, testing a range of oscillation frequencies at a zero-mean angle of attack with a pitching amplitude of 10 degrees. In light of these measurements, a closed-form set of analytically derived equations for lift and moment was used to develop a semi-empirical formulation, incorporating empirically determined values from the experimental runs. The equations are grounded in potential flow theory, Theodorsen's classical theory of unsteady aerodynamics, and the Joukowski theorem of conformal mapping. The unsteady aerodynamics generated by the oscillating body are then modeled by constructing frequency response functions, with quasi-steady forces and moments serving as inputs and unsteady forces and moments as outputs. The experimentally determined gain and phase variations characterize the unsteady nature of the flow and the system's response and flow time-lag to input flow parameters for a blunt-body entry vehicle. The final semi-empirical model is validated with a set of parameters beyond the initial test matrix.

Entry Systems Modeling↗

NASA NTRS2013

Multi-Mission Earth Vehicle Subsonic Dynamic Stability Testing and Analyses

Multi-Mission Earth Entry Vehicles (MMEEVs) are blunt-body vehicles designed with the purpose of transporting payloads from outer space to the surface of the Earth. To achieve high-reliability and minimum weight, MMEEVs avoid use of limited-reliability systems, such as parachutes, retro-rockets, and reaction control systems and rely on the natural aerodynamic stability of the vehicle throughout the Entry, Descent, and Landing (EDL) phase of flight. The Multi-Mission Systems Analysis for Planetary Entry (M-SAPE) parametric design tool is used to facilitate the design of MMEEVs for an array of missions and develop and visualize the trade space. Testing in NASA Langley?s Vertical Spin Tunnel (VST) was conducted to significantly improve M-SAPE?s subsonic aerodynamic models. Vehicle size and shape can be driven by entry flight path angle and speed, thermal protection system performance, terminal velocity limitations, payload mass and density, among other design parameters. The objectives of the VST testing were to define usable subsonic center of gravity limits, and aerodynamic parameters for 6-degree-of-freedom (6-DOF) simulations, for a range of MMEEV designs. The range of MMEEVs tested was from 1.8m down to 1.2m diameter. A backshell extender provided the ability to test a design with a much larger payload for the 1.2m MMEEV.

Glaab, Louis J.↗

NASA NTRS2006

Trajectory and Aeroheating Environment Development and Sensitivity Analysis for Capsule-shaped Vehicles

Recently, NASA's Exploration Systems Research and Technology Project funded several tasks that endeavored to develop and evaluate various thermal protection systems and high temperature material concepts for potential use on the crew exploration vehicle. In support of these tasks, NASA Langley's Vehicle Analysis Branch generated trajectory information and associated aeroheating environments for more than 60 unique entry cases. Using the Apollo Command Module as the baseline entry system because of its relevance to the favored crew exploration vehicle design, trajectories for a range of lunar and Mars return, direct and aerocapture Earth-entry scenarios were developed. For direct entry, a matrix of cases was created that reflects reasonably expected minimum and maximum values of vehicle ballistic coefficient, inertial velocity at entry interface, and inertial flight path angle at entry interface. For aerocapture, trajectories were generated for a range of values of initial velocity and ballistic coefficient that, when combined with proper initial flight path angles, resulted in achieving a low Earth orbit either by employing a full lift vector up or full lift vector down attitude. For each trajectory generated, aeroheating environments were generated which were intended to bound the thermal protection system requirements for likely crew exploration vehicle concepts. The trades examined clearly pointed to a range of missions / concepts that will require ablative systems as well as a range for which reusable systems may be feasible. In addition, the results clearly indicated those entry conditions and modes suitable for manned flight, considering vehicle deceleration levels experienced during entry. This paper presents an overview of the analysis performed, including the assumptions, methods, and general approach used, as well as a summary of the trajectory and aerothermal environment information that was generated.

Robinson, Jeffrey S.↗

NASA NTRS2012

Validation of Shock Layer Radiation: Perspectives for Test Cases

This paper presents a review of the analysis and measurement of radiation data obtained in the NASA Ames Research Center's Electric Arc Shock Tube (EAST) facility. The goal of these experiments was to measure the level of radiation encountered during atmospheric entry. The data obtained from these experiments is highlighted by providing the first spectrally and spatially resolved data for high speed Earth entry and measurements of the CO 4th positive band for conditions relevant to Mars entry. Comparisons of the EAST data with experimental results obtained from shock tunnels at JAXA and the University of Queensland are presented. Furthermore, the paper will detail initial analyses in to the influence and characterization of the measure non-equilibrium radiation.

Brandis, Aaron↗

NASA NTRS2013

TPSAS-NF1676L-16762-DND

Multi-Mission Earth Entry Vehicles (MMEEVs) are blunt-body vehicles designed with the purpose of transporting payloads from outer space to the surface of the Earth. To achieve high-reliability and minimum weight, MMEEVs avoid use of limited-reliability systems, such as parachutes and retro-rockets, instead using built-in impact attenuators to absorb energy remaining at impact to meet landing loads requirements. In the current effort, two different Rohacell foams were tested to determine their thermal conductivity in support of MMEEV design applications. These applications include thermal insulation during atmospheric entry, impact attenuation, and post-impact thermal insulation. Results indicate that for these closed-cell foams, the effect of impact is limited on thermal conductivity due to the venting of the virgin material gas and subsequent ambient air replacement. In addition, thermal conductivity results indicate a variation with temperature and are higher than manufacturer's specifications.

Lou Glaab↗

NASA NTRS1972

Plasma entry into the earth's magnetosphere.

Several recent observation and measurement results concerning plasma entry into the earth's magnetosphere are discussed in terms of only one magnetospheric model believed currently to provide a relatively self-consistent description for both high- and low-altitude surveys. Some of the criticisms the presented overall picture of the magnetosphere elicits in the light of present observational knowledge are examined, and major uncertainties are reviewed.

Frank, L. A.↗

NASA NTRS1993

Piloted Mars missions using cryogenic and storable propellants

The paper presents an analyses of piloted long-duration stay Mars missions using a chemical or nuclear thermal propulsion Earth-departure stage, storable propellant Mars arrival and departure stages (to avoid propellant boiloff), and an Earth entry vehicle, conducted for three-year segments from 2000 to 2020. The study initially determines the minimum initial mass in low-Earth orbit (IMLEO) missions and then investigates their radiation exposure levels and Mars parking orbit selection. The impact of reducing the outbound (Earth-Mars) transfer time on IMLEO and predicted radiation exposure levels is included. The results indicate that a vehicle using an advanced chemical propulsion system (Isp = 480 s) for Earth departure is feasible throughout 2000-2020 with an IMLEO less than 640 metric tons, while an Earth departure stage using a nuclear thermal propulsion (NTP) system with Isp of 925 s is even more appealing with IMLEO's less than 405 tons. Vehicles with 875 and 825 s specific impulse Earth departure stages have only slightly higher IMLEO's than the advanced NTP system (10 and 20 tons higher, respectively). Reducing the time spent in space may not always result in a significantly reduced level of radiation exposure, especially if the mission encounter dates are changed to a less favorable period of the solar cycle.

Striepe, Scott A.↗

NASA NTRS2005

Entry Abort Determination Using Non-Adaptive Neural Networks for Mars Precision Landers

The 2009 Mars Science Laboratory (MSL) will attempt the first precision landing on Mars using a modified version of the Apollo Earth entry guidance program. The guidance routine, Entry Terminal Point Controller (ETPC), commands the deployment of a supersonic parachute after converging the range to the landing target. For very dispersed cases, ETPC may not converge the range to the target and safely command parachute deployment within Mach number and dynamic pressure constraints. A full-lift up abort can save 85% of these failed trajectories while abandoning the precision landing objective. Though current MSL requirements do not call for an abort capability, an autonomous abort capability may be desired, for this mission or future Mars precision landers, to make the vehicle more robust. The application of artificial neural networks (NNs) as an abort determination technique was evaluated by personnel at the National Aeronautics and Space Administration (NASA) Johnson Space Center (JSC). In order to implement an abort, a failed trajectory needs to be recognized in real time. Abort determination is dependent upon several trajectory parameters whose relationships to vehicle survival are not well understood, and yet the lander must be trained to recognize unsafe situations. Artificial neural networks (NNs) provide a way to model these parameters and can provide MSL with the artificial intelligence necessary to independently declare an abort. Using the 2009 Mars Science Laboratory (MSL) mission as a case study, a non-adaptive NN was designed, trained and tested using Monte Carlo simulations of MSL descent and incorporated into ETPC. Neural network theory, the development history of the MSL NN, and initial testing with severe dust storm entry trajectory cases are discussed in Reference 1 and will not be repeated here. That analysis demonstrated that NNs are capable of recognizing failed descent trajectories and can significantly increase the survivability of MSL for very dispersed cases. NN testing was then broadened to evaluate fully dispersed entry trajectories. The NN correctly classified 99.7% of descent trajectories as abort or nonabort and reduced the probability of an unsafe parachute deployment by 83%. This second, broader testing phase is discussed in this paper.

Graybeal, Sarah R.↗

NASA NTRS2001

Dynamic Finite Element Predictions for Mars Sample Return Cellular Impact Test #4

The nonlinear, transient dynamic finite element code, MSC.Dytran, was used to simulate an impact test of an energy absorbing Earth Entry Vehicle (EEV) that will impact without a parachute. EEVOs are designed to return materials from asteroids, comets, or planets for laboratory analysis on Earth. The EEV concept uses an energy absorbing cellular structure designed to contain and limit the acceleration of space exploration samples during Earth impact. The spherical shaped cellular structure is composed of solid hexagonal and pentagonal foam-filled cells with hybrid graphite-epoxy/Kevlar cell walls. Space samples fit inside a smaller sphere at the center of the EEVOs cellular structure. Pre-test analytical predictions were compared with the test results from a bungee accelerator. The model used to represent the foam and the proper failure criteria for the cell walls were critical in predicting the impact loads of the cellular structure. It was determined that a FOAM1 model for the foam and a 20% failure strain criteria for the cell walls gave an accurate prediction of the acceleration pulse for cellular impact.

Fasanella, Edwin L.↗

NASA NTRS2003

Finite-Rate Ablation Boundary Conditions for Carbon-Phenolic Heat-Shield

A formulation of finite-rate ablation surface boundary conditions, including oxidation, nitridation, and sublimation of carbonaceous material with pyrolysis gas injection, has been developed based on surface species mass conservation. These surface boundary conditions are discretized and integrated with a Navier-Stokes solver. This numerical procedure can predict aerothermal heating, chemical species concentration, and carbonaceous material ablation rate over the heatshield surface of re-entry space vehicles. In this study, the gas-gas and gas-surface interactions are established for air flow over a carbon-phenolic heatshield. Two finite-rate gas-surface interaction models are considered in the present study. The first model is based on the work of Park, and the second model includes the kinetics suggested by Zhluktov and Abe. Nineteen gas phase chemical reactions and four gas-surface interactions are considered in the present model. There is a total of fourteen gas phase chemical species, including five species for air and nine species for ablation products. Three test cases are studied in this paper. The first case is a graphite test model in the arc-jet stream; the second is a light weight Phenolic Impregnated Carbon Ablator at the Stardust re-entry peak heating conditions, and the third is a fully dense carbon-phenolic heatshield at the peak heating point of a proposed Mars Sample Return Earth Entry Vehicle. Predictions based on both finite-rate gas- surface interaction models are compared with those obtained using B' tables, which were created based on the chemical equilibrium assumption. Stagnation point convective heat fluxes predicted using Park's finite-rate model are far below those obtained from chemical equilibrium B' tables and Zhluktov's model. Recession predictions from Zhluktov's model are generally lower than those obtained from Park's model and chemical equilibrium B' tables. The effect of species mass diffusion on predicted ablation rate is also examined.

Chen, Y.-K.↗

NASA NTRS1980

Development of the reentry flight dynamics simulator for evaluation of space shuttle orbiter entry systems

A nonlinear, six degree of freedom, digital computer simulation of a vehicle which has constant mass properties and whose attitudes are controlled by both aerodynamic surfaces and reaction control system thrusters was developed. A rotating, oblate Earth model was used to describe the gravitational forces which affect long duration Earth entry trajectories. The program is executed in a nonreal time mode or connected to a simulation cockpit to conduct piloted and autopilot studies. The program guidance and control software used by the space shuttle orbiter for its descent from approximately 121.9 km to touchdown on the runway.

Rowell, L. F.↗

NASA NTRS1999

Entry Trajectory Issues for the Stardust Sample Return Capsule

The Stardust mission was successfully launched on February 7, 1999. It will be the first mission to return samples from a comet. The sample return capsule, which is passively controlled during the fastest Earth entry ever, will land by parachute in Utah. The present study describes the analysis of the entry, descent, and landing of the returning sample capsule utilizing the final, launch configuration capsule mass properties. The effects of two aerodynamic instabilities are revealed (one in the high altitude free molecular regime and the other in the transonic/subsonic flow regime). These instabilities could lead to unacceptably large excursions in the angle-of-attack near peak heating and main parachute deployment, respectively. To reduce the excursions resulting from the high altitude instability, the entry spin rate of the capsule is increased. To stabilize the excursions from the transonic/subsonic instability, a drogue chute with deployment triggered by a gravity-switch and timer is added prior to main parachute deployment. A Monte Carlo dispersion analysis of the modified entry (from which the impact of off-nominal conditions during the entry is ascertained) predicts that the capsule attitude excursions near peak heating and drogue chute deployment are within Stardust mission limits. Additionally, the size of the resulting 3-sigma landing ellipse is 60.8 km in downrange by 19.9 km in crossrange, which is within the Utah Test and Training Range boundaries.

Desai, Prasun N.↗

NASA NTRS1999

Entry Trajectory Issues for the Stardust Sample Return Capsule

The Stardust mission was successfully launched on February 7, 1999. It will be the first mission to return samples from a comet. The sample return capsule, which is passively controlled during the fastest Earth entry ever, will land by parachute in Utah. The present study describes the analysis of the entry, descent, and landing of the returning sample capsule utilizing the final, launch configuration capsule mass properties. The effects of two aerodynamic instabilities are revealed (one in the high altitude free molecular regime and the other in the transonic/subsonic flow regime). These instabilities could lead to unacceptably large excursions in the angle-of-attack near peak heating and main parachute deployment, respectively. To reduce the excursions resulting from the high altitude instability, the entry spin rate of the capsule is increased. To stabilize the excursions from the transonic/subsonic instability, a drogue chute with deployment triggered by a gravity-switch and timer is added prior to main parachute deployment. A Monte Carlo dispersion analysis of the modified entry (from which the impact of off-nominal conditions during the entry is ascertained) predicts that the capsule attitude excursions near peak heating and drogue chute deployment are within Stardust mission limits. Additionally, the size of the resulting 3-sigma landing ellipse is 60.8 km in downrange by 19.9 km in crossrange, which is within the Utah Test and Training Range boundaries.

Desai, Prasun N.↗

NASA NTRS1996

[STS-75 Post Flight Presentation]

The flight crew of the STS-75 Space Shuttle, Cmdr. Andrew Allen, Pilot Scott Horowitz, Payload Cmdr. Franklin Chang-Diaz, Payload Specialist Umberto Guidoni (Italy), and Mission Specialists Jeffrey Hoffman, Maurizio Cheli (ESA) and Claude Nicollier (ESA), present a post flight analysis of their mission through the use of color slides and video footage. Prelaunch and launch activities are shown along with Earth entry and landing footage. Both middeck and payload bay microgravity experiments are shown and briefly discussed. The deployment and loss of the European Tethered Satellite experiment are presented and discussed. Earth views include the Nile Valley, Chad, the Himalayas and Mount Everest, and China. A unique moonset is also shown.

Source record↗