Aerodynamic effects of bulbous bases
Aerodynamic characteristics of blunt space capsules and slender reentry bodies with bulbous bases
Ericsson, L. E.↗
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Computer simulation of the effect of dDAVP with saline loading on fluid balance after 24-hour head-down tilt
Fluid loading (FL) before Shuttle reentry is a countermeasure currently in use by NASA to improve the orthostatic tolerance of astronauts during reentry and postflight. The fluid load consists of water and salt tablets equivalent to 32 oz (946 ml) of isotonic saline. However, the effectiveness of this countermeasure has been observed to decrease with the duration of spaceflight. The countermeasure's effectiveness may be improved by enhancing fluid retention using analogs of vasopressin such as lypressin (LVP) and desmopressin (dDAVP). In a computer simulation study reported previously, we attempted to assess the improvement in fluid retention obtained by the use of LVP administered before FL. The present study is concerned with the use of dDAVP. In a recent 24-hour, 6 degree head-down tilt (HDT) study involving seven men, dDAVP was found to improve orthostatic tolerance as assessed by both lower body negative pressure (LBNP) and stand tests. The treatment restored Luft's cumulative stress index (cumulative product of magnitude and duration of LBNP) to nearly pre-bedrest level. The heart rate was lower and stroke volume was marginally higher at the same LBNP levels with administration of dDAVP compared to placebo. Lower heart rates were also observed with dDAVP during stand test, despite the lower level of cardiovascular stress. These improvements were seen with only a small but significant increase in plasma volume of approximately 3 percent. This paper presents a computer simulation analysis of some of the results of this HDT study.
NASA Discipline Cardiopulmonary↗
Property and Microstructural Characterization of Diboride Composites for High Temperature Aerospace Applications
Previous work on refractory diboride composites has shown these systems to have potential for use in high temperature leading edge applications for reusable reentry vehicles. These composites, based on compositions of HfB2 or ZrB2 with SiC particulate reinforcements, have shown good oxidation resistance in reentry environments. In this work we are investigating the effects of composition and microstructure on properties. Preliminary studies of composite mechanical properties and oxidation behavior will be discussed.
Gusman, Michael I.↗
A minimum heating flight mode for high lateral range space shuttle entries including the effects of transition
Minimum heating flight mode for high lateral range space shuttle reentry based on boundary layer transition criteria
Moote, J. D.↗
Estimates of Minimum Energy Requirements for Range-Controlled Return of a Nonlifting Satellite from a Circular Orbit
Existing expressions are used to obtain the minimum propellant fraction required for return from a circular orbit as a function of vacuum trajectory range. trajectory are matched to those of the atmospheric trajectory to obtain a complete return from orbit to earth. The results are restricted by the assumptions of (1) impulsive velocity change, (2) nearly circular transfer trajectory, ( 3) spherical earth, atmosphere, and gravitational field, (4) exponential atmospheric density variation with attitude, and (5) a nonrotating atmosphere. The solutions for the parameters of the vacuum Calculations are made t o determine the effects of longitudinal and lateral range on required propeUant fraction and reentry loading for a nonrotating earth and for several orbital altitudes. the single- and two-impulse method of return is made and the results indicate a "trade off" between propellant fraction required and landing- position accuracy. A comparison of An example of a return mission from a polar orbit is discussed where the initial deorbit point is the intersection of the North Pole horizon with the satellite orbit. Some effects of a rotating earth are also considered. It is found that, for each target-orbital-plane longitudinal difference, there exists a target latitude for which the required propellant fraction is a minimum.
Jackson, Charlie M., Jr.↗
Effect of re-entry vehicle environment on electromagnetic radiation.
RF/plasma interactions relative to reentry plasma diagnostics and microwave transmission, noting increased hot air susceptibility to RF breakdown
Chown, J. B.↗
Computation of flowfields for hypersonic flight at high altitudes
Recent direct simulation Monte Carlo methods are reviewed focusing on the nonequilibrium aspects of rarefied hypersonic flows typical of reentry conditions. The calculations identify the altitudes for which the onset of dissociation occurs, the magnitude of the surface temperature variations, the effect of the shock wave structure on the chemistry of a dissociating gas, and the radiation emisssion for reentry flowfields.
Moss, James N.↗
Aerodynamic investigation of some high-drag entry shapes at Mach 15.4
Effects of body shape, nose radius, and shoulder shape of reentry body on aerodynamic drag
DRAG COEFFICIENT↗
Effects of the plasma sheath on antenna performance.
Antenna radiation patterns and near field effects by solving aperture and plasma sheath problems independently in reentry communications
Hodara, H.↗
Behavior of structural joints and assemblies under thermal environment
Thermal environment effects on alignment behavior of structural joints and assemblies of reentry vehicle and Mars landing module
Crawford, R. G.↗
Monopropellant engine investigation for space shuttle reaction control system, volume 1
The results are presented of an investigation to determine the capability of a monopropellant hydrazine thruster to meet the requirements specified for the space shuttle reaction control system (RCS). Of those requirements, the major concern was whether the 100,000 seconds life could be achieved at thrust levels within the specified range. Although burn times in excess of 200,000 seconds have been demonstrated at low thrust levels, the corresponding total impulse values have been substantially lower than that required for the space shuttle RCS. Two other areas of concern, involving the catalyst, were: (1) the effects of the relatively high vehicle vibration levels on catalyst attrition and (2) the effect of exposure of the catalyst to air during atmospheric reentry of the vehicle.
Source record↗
Comparison of concurrent strain gage- and pressure transducer-measured flight loads on a lifting reentry vehicle and correlation with wind tunnel predictions
Concurrent strain gage and pressure transducer measured flight loads on a lifting reentry vehicle are compared and correlated with wind tunnel-predicted loads. Subsonic, transonic, and supersonic aerodynamic loads are presented for the left fin and control surfaces of the X-24B lifting reentry vehicle. Typical left fin pressure distributions are shown. The effects of variations in angle of attack, angle of sideslip, and Mach number on the left fin loads and rudder hinge moments are presented in coefficient form. Also presented are the effects of variations in angle of attack and Mach number on the upper flap, lower flap, and aileron hinge-moment coefficients. The effects of variations in lower flap hinge moments due to changes in lower flap deflection and Mach number are presented in terms of coefficient slopes.
Tang, M. H.↗
Numerical simulations of rarefied reentry flows
A review of recent calculations obtained with Bird's direct simulation Monte Carlo (DSMC) method is presented for the transitional flowfield encountered at reentry conditions. Consequently, the emphasis is the real-gas effects resulting from a highly energetic nonequilibrium flow. The DSMC calculations for both wide-angle and slender bodies are compared with continuum calculations. The wide-angle body calculations simulate the windward nose of the Shuttle Orbiter and projected aeroassisted orbital transfer vehicles. For the slender, blunted configurations, both two-dimensional and axisymmetric results are presented. Comparisons between the DSMC and continuum calculations show the altitude range where differences in flowfield structure and surface quantities become significant.
Moss, James N.↗
PNS predictions of axisymmetric hypersonic blunt-body and afterbody flowfields
A new space-marching full-body PNS algorithm capable of treating the complete blunt-body and afterbody flowfields over typical wide-bodied configurations is developed and demonstrated. A hybrid differencing scheme involving Flux-Vector Splitting (FVS) across embedded shocks and flowfield discontinuities, and central differencing in smooth (shock-free) regions is used. It is demonstrated that this new full-body PNS scheme can be marched from the spherical stagnation point over the entire body using bow-shock capturing, and provides an efficient and effective way for predicting blunt-body flowfields for various reentry application. The Mach 20 flow over a 30-deg sphere cone is predicted and comparisons are made with an existing VSL scheme for the blunt-body region and an existing PNS scheme for the conical afterbody region. The predicted flowfield and surface-measurable quantities are in excellent agreement, and demonstrate the accuracy and efficiency of the new full-body PNS scheme.
Bhutta, Bilal A.↗
Fuzzy Logic Trajectory Design and Guidance for Terminal Area Energy Management
The second generation reusable launch vehicle will leverage many new technologies to make flight to low earth orbit safer and more cost effective. One important capability will be completely autonomous flight during reentry and landing, thus making it unnecessary to man the vehicle for cargo missions with stringent weight constraints. Implementation of sophisticated new guidance and control methods will enable the vehicle to return to earth under less than favorable conditions. The return to earth consists of three phases--Entry, Terminal Area Energy Management (TAEM), and Approach and Landing. The Space Shuttle is programmed to fly all three phases of flight automatically, and under normal circumstances the astronaut-pilot takes manual control only during the Approach and Landing phase. The automatic control algorithms used in the Shuttle for TAEM and Approach and Landing have been developed over the past 30 years. They are computationally efficient, and based on careful study of the spacecraft's flight dynamics, and heuristic reasoning. The gliding return trajectory is planned prior to the mission, and only minor adjustments are made during flight for perturbations in the vehicle energy state. With the advent of the X-33 and X-34 technology demonstration vehicles, several authors investigated implementing advanced control methods to provide autonomous real-time design of gliding return trajectories thus enhancing the ability of the vehicle to adjust to unusual energy states. The bulk of work published to date deals primarily with the approach and landing phase of flight where changes in heading angle are small, and range to the runway is monotonically decreasing. These benign flight conditions allow for model simplification and fairly straightforward optimization. This project focuses on the TAEM phase of flight where mathematically precise methods have produced limited results. Fuzzy Logic methods are used to make onboard autonomous gliding return trajectory design robust to a wider energy envelope, and the possibility of control surface failures, thus increasing the flexibility of unmanned gliding recovery and landing.
Burchett, Bradley↗
Comparison with test data and application of aerodynamic coefficients computed for unfinned axisymmetric bodies using a modified viscous crossflow method
Aerodynamic coefficients computed using a modified viscous crossflow method are verified with test data and shown to compare favorably for the general class of sounding rocket reentry bodies. Next, several reentry predictions are compared with the actual reentry plus a discussion of characteristic traits shown in both. Then a detailed study of the effects of initial conditions on maximum dynamic pressure (q), q at Mach 1 and at 20,000 feet (nominal drogue deployment altitude) will be presented and discussed. These results prove that reentry simulations using this technique are applicable to sounding rocket reentry bodies.
Laudadio, J. F.↗
A Concept of a Manned Satellite Reentry Which is Completed with a Glide Landing
A concept for a manned satellite reentry from a near space orbit and a glide landing on a normal size airfield is presented. The reentry vehicle configuration suitable for this concept would employ a variable geometry feature in order that the reentry could be made at 90 deg. angle of attack and the landing could be made with a conventional glide approach. Calculated results for reentry at a flight-path angle of -1 deg. show that with an accuracy of 1 percent in the impulse of a retrorocket, the desired flight-path angle at reentry can be controlled within 0.02 deg. and the distance traveled to the reentry point, within 100 miles. The reentry point is arbitrarily defined as the point at which the satellite passes through an altitude of about 70 miles. Misalignment of the retrorocket by 10 deg. increased these errors by as much as 0.02 deg. and 500 miles. Intra-atmospheric trajectory calculations show that pure drag reentries starting with flight-path angles of -1 deg. or less produce a peak deceleration of 8g. Lift created by varying the angle of attack between 90 and 60 deg. is effective in decreasing the maximum deceleration and allows the range to the "recovery" point (where transition is made from reentry to gliding flight) to be increased by as much as 2,300 miles. A sideslip angle of 30 deg. allows lateral displacement of the flight path by as much as 60 deg. miles. Reaction controls would provide control-attitude alignment during the orbit phase. For the reentry phase this configuration should have low static longitudinal and roll stability in the 90 deg. angle-of-attack attitude. Control could be effected by leading-edge and trailing-edge flaps. Transition into the landing phase would be accomplished at an altitude of about 100,000 feet by unfolding the outer wing panels and pitching over to low angles of attack. Calculations indicate that glides can be made from the recovery point to airfields at ranges of from 150 to 200 miles, depending upon the orientation with respect to the original course.
Cheatham, Donald C.↗
Space tug propulsion system failure mode, effects and criticality analysis
For purposes of the study, the propulsion system was considered as consisting of the following: (1) main engine system, (2) auxiliary propulsion system, (3) pneumatic system, (4) hydrogen feed, fill, drain and vent system, (5) oxygen feed, fill, drain and vent system, and (6) helium reentry purge system. Each component was critically examined to identify possible failure modes and the subsequent effect on mission success. Each space tug mission consists of three phases: launch to separation from shuttle, separation to redocking, and redocking to landing. The analysis considered the results of failure of a component during each phase of the mission. After the failure modes of each component were tabulated, those components whose failure would result in possible or certain loss of mission or inability to return the Tug to ground were identified as critical components and a criticality number determined for each. The criticality number of a component denotes the number of mission failures in one million missions due to the loss of that component. A total of 68 components were identified as critical with criticality numbers ranging from 1 to 2990.
Boyd, J. W.↗