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At least 379 records · Page 21

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NASA NTRS1973

An analysis of atmospheric entry trajectories for manned and unmanned missions to the planet Venus

A unified atmospheric density model is presented for the planet Venus, and this model is compatible with Russian and American data obtained during the 1967 Venus launch opportunity. Trajectory characteristics involved in atmospheric entry are discussed with reference to roll-control modulation and entry corridor. Subsequent to a trajectory-oriented discussion of potential Venus mission characteristics, a parametric analysis of manned and unmanned vehicle entry trajectories into the Venusian atmosphere is presented. A sensitivity analysis with reference to atmospheric density deviations is included to show the dependence of corridor depth on the atmospheric density profile.

Craig, M. K.↗

NASA NTRS1972

Radiative and convective heating during Venus entry.

Determination of the stagnation region heating of probes entering the Venusian atmosphere. Both convective and radiative heat-transfer rates are predicted, and account is taken of the important effects of radiative transport in the vehicle shock layer. A nongray radiative transport model is utilized which parallels a four-band treatment previously developed for air (Page et al., 1969), but includes two additional bands to account for the important CO(4+) molecular band system. Some comparisons are made between results for Venus entry and results for earth entry obtained using a viscous earth entry program.

Page, W. A.↗

NASA NTRS1973

Scientific considerations for a common Saturn/Uranus atmospheric entry probe.

Development of a scientific rationale for an atmospheric probe designed to be capable of entry into either Saturn or Uranus. The effects of the NASA Monograph model atmospheres (SP 8091 and SP 8103) on the entry and descent trajectory specify instrument sampling design. The cool model atmospheres require descents to the vicinity of 20 bars to satisfy the objectives while about 4 bars is sufficient for the warm models. The measurement performance for a descent sampling time of 44 minutes shows that the atmosphere can be reconstructed from measured data. The required total probe entry weight is 103 kg, of which about 15 kg is for the science instruments. The descent data rate varies from 32 to 51 bps, depending upon the mode of transmitting preentry data. The resulting common probe can be redirected in flight between Saturn and Uranus.

Ledbetter, K. W.↗

NASA NTRS1973

Space shuttle GN and C equation document: Entry and transition guidance

The entry-guidance routine presented is designed to take the orbiter vehicle from entry interface through the critical heating phase of entry down to the start of the approach phase. The material includes: (1) a functional flow diagram, (2) input and output variables, (3) a description of equations, and (4) detailed flow diagrams.

Marcus, F. J.↗

NASA NTRS1973

Developing a technology base in planetary entry aerothermodynamics

The long-range objectives of the entry technology program are to insure that an adequate technology base for a great variety of mission options exists. Consideration has been given to the entry of vehicles into the atmospheres of all the planets with the exception of Pluto. The experimental facilities for the studies are discussed, giving attention to shock tubes, the planetary entry radiation facility, ballistic ranges, the expansion tube, and arc jet facilities. Flight experiments are considered along with computational analyses and engineering approximations.

Olstad, W. B.↗

NASA NTRS1974

Hydrogen ionization in the shock layer for entry into the outer planets

Approximate assessments are presented for the chemical state of the shock layer with respect to the hydrogen ionization reaction for representative entries into Saturn, Uranus, and Jupiter. It is shown that, except for a steep entry into the Saturn nominal atmosphere, the computation of all entry probe gascaps for the outer planets can probably be considered on either a frozen or chemical equilibrium basis.

Howe, J. T.↗

NASA NTRS1974

Selected optimal shuttle entry computations

Parameterization and the Davidon-Fletcher-Powell method are used to study the characteristics of optimal shuttle entry trajectories. Two problems of thermal protective system weight minimization are considered: roll modulation and roll plus an angle-of-attack modulation. Both problems are targeted for the edges of the entry footprint. Results consistent with constraints on loads and control bounds are particularly well-behaved and strongly support 'energy' approximation results obtained for the case of symmetric flight by Kelley and Sullivan (1973). Furthermore, results indicate that optimal shuttle entry trajectories should be easy to duplicate and to analyze by using simple techniques.

Sullivan, H. C.↗

NASA NTRS1975

Apollo experience report: Guidance and control systems: Command and service module entry monitor subsystem

The conceptual aspects of the command and service module entry monitor subsystem, together with an interpretation of the displays and their associated relationship to entry trajectory control, are presented. The entry monitor subsystem is described, and the problems encountered during the developmental phase and the first five manned Apollo flights are discussed in conjunction with the design improvements implemented.

Reina, B., Jr.↗

NASA NTRS1975

Outer planet atmospheric entry probes - An overview of technology readiness

Entry probe systems for characterizing, by in situ measurements, the atmospheric properties, chemical composition, and cloud structure of the planets Saturn, Uranus, and Jupiter are examined from the standpoint of unique mission requirements, associated subsystem performance, and degree of commonality of design. Past earth entry vehicles (PAET) and current planetary spacecraft (Pioneer Venus probes and Viking lander) are assessed to identify the extent of potential subsystem inheritance, as well as to establish the significant differences, in both form and function, relative to outer planet requirements. Recent research results are presented and reviewed for the most critical probe technology areas, including: science accommodation, telecommunication, and entry heating and thermal protection. Finally presented is a brief discussion of the use of decision analysis techniques for quantifying various probe heat-shield test alternatives and performance risk.

Vojvodich, N. S.↗

NASA NTRS1975

Orbiter entry trajectory corridors: 32000 pound payload, 67.5 percent center of gravity

Thermal and equilibrium glide boundaries were used to analyze and/or design shuttle orbiter entry trajectories. Plots are presented of orbiter thermal and equilibrium glide boundaries in the drag/mass-relative velocity dynamic pressure-relative velocity, and altitude-relative velocity planes for an orbiter having a 32,000 pound payload and a 67.5% center of gravity location. These boundaries were defined for control points 1 through 4 of the shuttle orbiter for 40 deg-30 deg and 38 deg-28 deg ramped angle of attack entry profiles and 40 deg, 38 deg, 35 deg, 30 deg, 28 deg, and 25 deg constant angle of attack entry profiles each at 20 deg, 15 deg, and 10 deg constant body flap settings.

Treybig, J. H.↗

NASA NTRS1976

Space Shuttle Orbiter entry guidance and control system sensitivity analysis

An approach has been developed to determine the guidance and control system sensitivity to off-nominal aerodynamics for the Space Shuttle Orbiter during entry. This approach, which uses a nonlinear six-degree-of-freedom interactive, digital simulation, has been applied to both the longitudinal and lateral-directional axes for a portion of the orbiter entry. Boundary values for each of the aerodynamic parameters have been identified, the key parameters have been determined, and system modifications that will increase system tolerance to off-nominal aerodynamics have been recommended. The simulations were judged by specified criteria and the performance was evaluated by use of key dependent variables. The analysis is now being expanded to include the latest shuttle guidance and control systems throughout the entry speed range.

Stone, H. W.↗

NASA NTRS1976

Aerothermal environment for Jovian entry probes

Results are presented that describe the aerothermal environment encountered by the forebody of probes during Jovian entry. Two probe configurations are considered: a 55 deg half-angle spherically blunted cone and a 50 deg half-angle hyperboloid. The main emphasis is focused on defining the heating environment during entry and on determining the effectiveness of coupled ablation injection in reducing the surface heating rate. This is accomplished by calculating both the convective and radiative heating at several points along the entry trajectory both with and without coupled ablation injection. Results are presented for both laminar and turbulent calculations.

Moss, J. N.↗

NASA NTRS1978

Effects of atmospheric structure on radiative heating for Jupiter entry probe

New estimates of the radiative heat load to a Jupiter entry probe have been obtained for revised models of Jupiter's atmosphere based on the latest data from Pioneer 10 and 11 missions and earth-based experiments. The new estimates of the radiative heat load are compared with results obtained for the previous atmospheric models. The changes in Jupiter's atmospheric models cause a substantial reduction in the radiative heat load for the atmosphere denoted as 'cool', but only moderate reductions for the atmospheres denoted as 'nominal' and 'warm'. Results are also presented showing the effects of inertial entry angle for off-equatorial entries in the revised model atmospheres.

Sutton, K.↗

NASA NTRS1978

Radiative flux penetration through a blown shock layer for Jupiter entry conditions

A study is made of the radiative blockage due to carbonaceous ablation injection for a probe entering the Jupiter atmosphere. This is accomplished by calculating the stagnation-point blockage factors for three entry trajectories that account for variations in probe configuration, atmospheric gas composition, and entry conditions. The radiative blockage within the relatively cool ablation layer is shown to be large and to be primarily dependent upon the absorption of the C2 and C3 species. The C3 absorption is significant, particularly when the new experimental data for C3 spectral absorption properties are used. Also, the stagnation-point radiative blockage factors are shown to correlate well in terms of the no-injection radiative heating rates for various entry conditions.

Moss, J. N.↗

NASA NTRS1979

Investigation of air stream from combustor-liner air entry holes, 3

Jets flowing from air entry holes of the combustor liner of a gas turbine were investigated. Cold air was supplied through the air entry holes into the primary hot gas flows. The mass flow of the primary hot gas and issuing jets was measured, and the behavior of the air jets was studied by the measurement of the temperature distribution of the gas mixture. The air jets flowing from three circular air entry holes, single streamwise long holes, and two opposing circular holes, parallel to the primary flow were studied along with the effects of jet and gas stream velocities, and of gas temperature. The discharge coefficient, the maximum penetration of the jets, the jet flow path, the mixing of the jets, and temperature distribution across the jets were investigated. Empirical expressions which describe the characteristics of the jets under the conditions of the experiments were formulated.

Aiba, T.↗

NASA NTRS1979

Proposed methods for the reconstruction of the Pioneer/Venus probe entry trajectories

In connection with the Pioneer Venus Project, an orbiter and an array of atmospheric probes are sent to Venus in separate launches during 1978. The four probes, which are transported to the planet on an instrumented Bus are released approximately 20 days prior to encounters. There are three identical small probes and a large probe. Each is designed to make in-situ atmospheric measurements. One of the principal scientific objectives of the Pioneer Venus (P/V) multiprobe mission is the determination of the structure and composition of the Venusian atmosphere down to the planet surface. To enhance the science return it is of paramount importance to be able to accurately determine the spacecraft entry trajectories. In addition to the in-situ spacecraft measurements, earth-based Doppler data are available. The process felt to be most applicable for the P/V multiprobe entry trajectory reconstruction is considered, with emphasis placed on the highly dynamic upper entry segment of the trajectory.

Findlay, J. T.↗

NASA NTRS1978

Shuttle entry guidance

This paper describes the design of the entry guidance for the Space Shuttle Orbiter. This guidance provides the steering commands for trajectory control from initial penetration of the earth's atmosphere until the terminal area guidance is activated at an earth-relative speed of 2500 fps. At this point, the Orbiter is at a distance of about 50 nmi from the runway threshold, and at an altitude of about 80,000 ft. The entry guidance design is based on an analytic solution of the equations of motion defining the drag acceleration profile that meets the terminal criteria of the entry flight while maintaining the flight within systems and operational constraints. Guidance commands, which are based on a control law that ensures damping of oscillatory type trajectory motion, are computed to steer the Orbiter to this drag acceleration profile.

Harpold, J. C.↗

NASA NTRS1979

Nonequilibrium radiative heating of a Jovian entry body

The influence of nonlocal thermodynamic equilibrium (NLTE) radiative transfer on radiative and convective heating of a Jovian entry body is investigated. The flow in the shock layer is assumed to be axisymmetric, viscous, and in chemical equilibrium. The chemical species considered for the collisional deactivation processes are H2, H, H+. The NLTE radiative transfer equations are derived for multilevel energy transitions. The rotational and vibrational energy modes are assumed to be in local thermodynamic equilibrium. The results indicate that higher-level energy transitions have little influence on the overall NLTE results. The NLTE results, however, are found to be greatly influenced by the temperature distributions in the shock layer. The convective and radiative heating to the entry body are reduced significantly because of the NLTE conditions; the reduction in convective heating, however, is relatively small. The influence of NLTE is found to be greater at higher entry altitudes.

Tiwari, S. N.↗