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Braking system, which employs angular accelerometer to control wheel braking and results in low level of tire slip, has been developed and tested. Tests indicate that system is feasible for operations on surfaces of different slipperinesses. System restricts tire slip and is capable of adapting to rapidly-changing surface conditions.
High drag satellites frequently require precise verification of orbital maneuvers and the accurate prediction of perigee height. An in-flight ground support system designed to monitor and compute orbital state and maneuvers is described. The use of on-board three-axis accelerometer data in a flight support software system to perform on-line maneuver analysis and atmospheric model updating is discussed. In addition, automated analytic techniques to rapidly and accurately predict perigee height following a maneuver are described, as well as semianalytic averaging techniques designed to predict a decaying orbital state for mission control.
A Kearfott pendulous accelerometer was integrated with a United Aircraft pulse torque servo assembly (PTSA) forced binary loop. The test objective was to measure dynamic errors due to anisoinertia and OA coupling effects. The instrument and its torque loop are described, and the technique for isolating the anisoinertia error from centripetal acceleration effects is discussed in detail. The measured anisoinertia error coefficient was 3.0 cm, and the testing confirmed that no rectified OA coupling error was present.
The Applications Technology Satellite-6 (ATS-6) flight accelerometers were designed to provide data for verifying the basic spacecraft vibration modes during launch, to update the analytical model of the ATA structure, and to provide a capability for detection and diagnosis of inflight and anomalies. The experiment showed accelerations less than 2.5 g during liftoff and 1.1 g or less during staging with frequencies below 80 Hz. Measured values were generally within 1 g of predicted.
Five accelerometers mounted near the adapter base of the Titan 3-C launch vehicle and three on the hub of the ATS-F spacecraft provided (1) data for verifying basic spacecraft mode shapes and frequencies during powered flight while attached to the launch vehicle; (2) failure mode detection and diagnostic information on in-flight anomalies; and (3) data to be used in the design of future spacecraft to be flown on the Titan 3-C. Because data from the instruments mounted on the spacecraft hub passed through an in-flight disconnect at the separation plane between the transtage and ATS-F, the moment this connector was broken, the signal to the telemetry system showed a step function change. By monitoring these telemetry traces on the ground at appropriate times during flight sequences, a positive indication of spacecraft separation was obtained. Flight data showing dynamic response at spacecraft launch vehicle interface and at the top of ATS spacecraft during significant launch events are presented in tables.
Low-cost, rugged lightweight accelerometer has been developed that converts mechanical motion into digitized optical outputs and is immune to electromagnetic and electrostatic interferences. Instrument can be placed in hostile environment, such as engine under test, and output led out through miscellany of electrical fields, high temperatures, etc., by optic fiber cables to benign environment of test panel. There, digitized optical signals can be converted to electrical signals for use in standard electrical equipment or used directly in optical devices, such as optical digital computer.
An exact knowledge of the earth's gravity field is needed for advanced studies related to solid earth and ocean physics. A study (GRAVSAT-A) is currently considered by NASA to determine the gravity field with an accuracy of 2-3 mgal change and a resolution of 100 km using satellite to satellite range rate tracking techniques. The present investigation has the objective to prepare the foundation of an advanced GRAVSAT-B mission in the 1990s with an accuracy of about 1 mgal and a resolution of about 50 km. It is possible that satellite to satellite tracking will not be able to satisfy these requirements. However, it appears that a new technology, called "high sensitivity gradient gradiometry", could be employed to achieve the aims of the GRAVSAT-B mission. Attention is given to a new type of gravity gradiometer using superconducting microwave cavity oscillator accelerometers.
A description of the High Resolution Accelerometer Package (HiRAP) experiment, designed to measure rarefied flow aerodynamic accelerations, is given. The ground test calibration factors, as well as post-flight data processing techniques to extract aerodynamic accelerations, are discussed and applied to the recorded reentry data of the recent STS-6 Shuttle Orbiter flight. The ratio of the measured normal-to-axial aerodynamic accelerations during reentry is used to obtain the first flight measurement of the lift-to-drag ratio (L/D) of a winged entry vehicle in the rarefied flow flight regime. The preliminary result for the free-molecule flow L/D is 0.10 + or - 0.03. The initial flight results on L/D are compared with current predictions which are based upon theoretical and empirical considerations. The measured free-molecule flow L/D value is higher than predicted by a factor of about three, indicating that surface reflection is not completely diffuse as currently assumed. In the rarefied flow transition regime, the Shuttle data book-bridging formula fits the flight data adequately. Upper altitude density profiles are also deduced from the measurements and presented. The density profiles show a wave phenomena with amplitude of about 60 percent, relative to a standard model.
Resonant frequency of microwave superconducting cavity sensitive to gravitation and acceleration. Sensitive accelerometer assembled by combining superconducting microwave cavity and conventional microwave semiconductor oscillator circuit. Device measures acelerations as small as 10-10 cm/S2 (10-13 g's). Also configured to measure small gradients in gravitational field of Earth.
A new thermospheric wind measurement technique is reported which is based on a Satellite Electrostatic Triaxial Accelerometer (SETA) system capable of accurately measuring accelerations in the satellite's in-track, cross-track and radial directions. Data obtained during two time periods are presented. The first data set describes cross-track winds measured between 170 and 210 km during a 5-day period (25 to 29 March 1979) of mostly high geomagnetic activity. In the second data set, cross-track winds and neutral densities from SETA and exospheric temperatures from the Millstone Hill incoherent scatter radar are examined during an isolated magnetic substorm occurring on 21 March 1979. A polar thermospheric wind circulation consisting of a two cell horizontal convection pattern is reflected in both sets of cross-track acceleration measurements. The density response is highly asymmetric with respect to its day/night behavior. Latitude structures of the density response at successive times following the substorm peak suggest the equatorward propagation of a disturbance with a phase speed between 300 and 600 m/s. A deep depression in the density at high latitudes (less than 70 deg) is evident in conjunction with this phenomenon. The more efficient propagation of the disturbance to lower latitudes during the night is probably due to the midnight surge effect.
This report presents a process for extracting the aerodynamic accelerations of the Shuttle Orbiter Vehicle from the High Resolution Accelerometer Package (HiRAP) flight data during reentry. The methods for obtaining low-level aerodynamic accelerations, principally in the rarefied flow regime, are applied to 10 Orbiter flights. The extraction process is presented using data obtained from Space Transportation System Flight 32 (Mission 61-C) as a typical example. This process involves correcting the HiRAP measurements for the effects of temperature bias and instrument offset from the Orbiter center of gravity, and removing acceleration data during times they are affected by thruster firings. The corrected data are then made continuous and smooth and are further enhanced by refining the temperature bias correction and removing effects of the auxiliary power unit actuation. The resulting data are the current best estimate of the Orbiter aerodynamic accelerations during reentry and will be used for further analyses of the Orbiter aerodynamics and the upper atmosphere characteristics.
An accelerometer based on a spring-suspended reference mass and its precise relative motion measurement by means of 3 two-dimensional position sensitive detectors (PSD) is described. A breadboard model achieves a resolution (longterm linearity) of 25 nm in one direction. Due to the physical principle of the PSD, the second layer is slightly less sensitive than the top layer; accordingly for gravity gradient detection the more sensitive layer is selected for the Z/X component detection. At 10 Hz sampling rate an acceleration gradient of under 10 to the minus 12th power g (i.e., 0.01 E or 0.001 Gal/km) is considered to be detectable.
The LPL stellar accelerometer, an interferometrically calibrated spectrometer, is described. Particular attention is given to light feed, image scrambling, and interferometric wavelength calibration. Changes in radial velocity are inferred from changes in the relative intensities of starlight transmitted through the Fabry-Perot.
The Materials Science Laboratory-2 (MSL-2) mission flew the Marshall Space Flight Center-developed Linear Triaxial Accelerometer (LTA) on the Space Transportation System (STS) 61-C Shuttle mission launched January 21, 1986. Flight data were analyzed to verify the quietness of the MSL carrier and to characterize the acceleration environment for future MSL users. The MSL was found to introduce no significant experiment acceleration; and the effects of crew treadmill exercise, Orbiter vernier engine firings, and other routine flight occurrences were established. The LTA was found to be well suited for measuring nominal to very quiet STS acceleration levels at frequencies below 50 Hz. Special processing was used to examine the low-frequency spectrum and to establish the effective rms amplitude associated with dominant frequencies.
An electrostatically suspended proof mass in the Miniature Electrostatic Accelerometer (MESA) is used to measure acceleration in the submicro-g range. Since no fixed mechanical suspension (such as springs or strings) is used, the constrainment scaling can be changed electrically after being placed in orbit. A single proof mass can sense accelerations in three axes simultaneously. It can survive high-g pyrotechnic-generated shocks and launch environments while unpowered.
Given here is a condensed version of the results and conclusions that developed during the Workshop. Upper limits of residual accelerations that can be tolerated during materials processes, presented as acceptable and as desirable limits, are shown. Designs and capabilities of various accelerometers, and their inherent problems, are compared. Results of acceleration measurements on Spacelab flights are summarized, and expected acceleration levels on the Space Station under various conditions are estimated.
Silicon micromachining etching techniques were utilized to batch-fabricate hundreds of general purpose microaccelerometers on a single silicon substrate. Piezoresistive sensing elements were aligned to the back-side patterns using an IR mask aligner and then diffused into the areas of maximum stress. Capping of the two-arm cantilever beam structure was achieved using a combination of electrostatic bonding and low temperature glass films. Overrange protection, critical damping, and overall protection from the outside environment are achieved by controlling the cavity depths of the top and bottom covers. Temperature compensation, amplification, and filtering are performed by a companion LSI chip that is interfaced to the accelerometer by conventional wire-bonding techniques.
Motion of ball in liquid indicates acceleration. Passive accelerometer measures small accelerations along cylindrical axis. Principle of operation based on Stokes' law. Provides accurate measurements of small quasi-steady accelerations. Additional advantage, automatically integrates out unwanted higher-frequency components of acceleration.