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NASA NTRS1994

GRTS operations monitor/control system

An Operations Monitor/Control System (OMCS) was developed to support remote ground station equipment. The ground station controls a Tracking Data Relay Satellite (TDRS) relocated to provide coverage in the tracking system's zone of exclusion. The relocated satellite significantly improved data recovery for the Gamma Ray Observatory mission. The OMCS implementation, performed in less than 11 months, was mission critical to TDRS drift operations. Extensive use of Commercial Off The Shelf (COTS) hardware and software products contributed to implementation success. The OMCS has been operational for over 9 months with no significant problems. This paper will share our experiences in OMCS development and integration.

Rohrer, Richard A.↗
NASA NTRS1994

Venus spherical harmonic gravity model to degree and order 60

The Magellan and Pioneer Venus Orbiter radiometric tracking data sets have been combined to produce a 60th degree and order spherical harmonic gravity field. The Magellan data include the high-precision X-band gravity tracking from September 1992 to May 1993 and post-aerobraking data up to January 5, 1994. Gravity models are presented from the application of Kaula's power rule for Venus and an alternative a priori method using surface accelerations. Results are given as vertical gravity acceleration at the reference surface, geoid, vertical Bouguer, and vertical isostatic maps with errors for the vertical gravity and geoid maps included. Correlation of the gravity with topography for the different models is also discussed.

Konopliv, Alex S.↗
NASA NTRS1973

Data-aided carrier tracking loops

The characteristics of a data-aided carrier tracking loop are discussed. The loop signal to noise ratio is improved in a phase-locked loop used for tracking a carrier an angle modulated communications system by a quadrature channel added to the phase locked loop. A d.c. signal derived from the quadrature channel is added to the signal fed back to the voltage controlled oscillator in the otherwise conventional phase-locked loop.

Lindsey, W. C.↗
NASA NTRS1976

Recovery of atmospheric parameters from the Apollo/Soyuz-ATS-F radio occultation data

As part of the Apollo-Soyuz Test Project, Apollo was tracked in the satellite-to-satellite tracking mode by ATS-F. The tracking data obtained at occultation of Apollo by the earth has been used in this study to compute atmospheric parameters like pressure and temperature. The results of the numerical inversion have been compared with data from a radiosonde station near the occultation site. Near the surface of the earth, the refractivity computed from occultation data agreed with the radiosonde-derived values to within 3%. A pressure profile deduced from the refractivity profile by using a simplified model of the atmosphere showed good agreement with radiosonde measurements.

Rangaswamy, S.↗
NASA NTRS1994

Mean sea surface and geoid gradient comparisons with TOPEX altimeter data

Cycles 4 to 54 of TOPEX data have been analyzed through comparisons with the mean sea surface given on the disturbed geophysical data record (GDR). Two inverted barometer correction procedures were considered for the data reduction. One used a constant atmospheric pressure for all data while the one adopted for use, for most computations, introduced a cycle average pressure. The maximum difference between the two estimates was 3.0 cm with a clear annual signal. With the modified correction the TOPEX sea surface was compared to The Ohio State University (OSU) mean sea surface, given on the GDR, to estimate three translations ( delta x = -2.3 cm; delta y = 25.0 cm; delta z = -0.3 cm) and a bias (43.3 cm) between the two surfaces. The only significant translation is delta y which indicates the reference frame of the TOPEX system differs from that used in the OSU mean sea surface system. The bias between the TOPEX mean sea surface and the OSU mean sea surface was used to estimate an equatorial radius of 6,378,136.55 m based on an 18-cm biased estimate of the TOPEX altimeter. Examination of the average difference, by cycle, between the TOPEX sea surface and the OSU mean sea surface suggested a bias change of 3.1 +/- 2.2 mm/yr with a positive sign indicating the average ocean surface is rising or the altimeter measured distance is decreasing. Models were implemented that solved directly for a bias, bias rate annual/semiannual, and tide correction terms. The computations indicated that a simultaneous solution for this bias, bias rate, and annual/semiannual terms gave the most accurate results. Nonsimultaneous solutions led to slightly different bias rate values. The root mean square difference between the TOPEX sea surface and OSU sea surface, after translation and bias correction, was +/- 17 cm for a typical cycle. Some locations were indentified where the difference could reach 2.3 cm and were repeated over several cycles indicating errors in the mean sea surface. Most of the large differences occur in regions lacking altimeter data prior to the TOPEX/POSEIDON mission and/or areas of significant bathymetric signature. Geoid gradients are needed for the reduction of individual track data to a reference track. The accuracy of the determination of such gradients was determined through the comparison of predicted along-track gradients to the observed gradients. Among four mean sea surfaces tested the best agreement was found with the OSU mean sea surface placed on the TOPEX geophysical data record.

Rapp, Richard H.↗
NASA NTRS1976

Improvements in navigation resulting from the use of dual spacecraft radiometric data

If two spacecraft lying along similar geocentric lines-of-sight are simultaneously tracked by two nearby ground stations (dual spacecraft two-station tracking), navigational capabilities may be substantially improved. A thorough accuracy analysis study of dual spacecraft tracking using simulated tracking data based on the trajectories of Viking and Mariner Jupiter-Saturn '77(MJS '77) missions has been carried out. Results of the study reveal the following advantages: (1) cancellation of platform parameter and transmission media modelling errors in short arc solutions, (2) accurate encounter guidance for the trailing spacecraft, (3) reduction of total tracking time requirements, and (4) rapid determination of the orbit following a maneuver on either spacecraft. It is shown that dual spacecraft data types can improve navigational capabilities by a factor of 5 to 10, under the conditions of small angular separation (not exceeding 3 degrees) of the two spacecraft and well determined trajectory of the reference spacecraft. The research to carry out and the data to obtain before the new technique can be used in interplanetary navigation are pointed out.

Chao, C. C.↗
NASA NTRS1971

Navigation analysis for Viking 1979, option B

A parametric study performed for 48 trans-Mars reference missions in support of the Viking program is reported. The launch dates cover several months in the year 1979, and each launch date has multiple arrival dates in 1980. A plot of launch versus arrival dates with case numbers designated for reference purposes is included. The analysis consists of the computation of statistical covariance matrices based on certain assumptions about the ground-based tracking systems. The error model statistics are listed in tables. Tracking systems were assumed at three sites: Goldstone, California; Canberra, Australia; and Madrid, Spain. The tracking data consisted of range and Doppler measurements taken during the tracking intervals starting at E-30(d) and ending at E-10(d) for the control data and ending at E-18(h) for the knowledge data. The control and knowledge covariance matrices were delivered to the Planetary Mission Analysis Branch for inputs into a delta V dispersion analysis.

Mitchell, P. H.↗
NASA NTRS2014

Three Orbital Burns to Molniya Orbit via Shuttle Centaur G Upper Stage

An unclassified analytical trajectory design, performance, and mission study was done for the 1982-86 joint NASA-USAF Shuttle/Centaur G upper stage development program to send performance-demanding payloads to high orbits such as Molniya using an unconventional orbit transfer. This optimized three orbital burn transfer to Molniya orbit was compared to the then-baselined two burn transfer. The results of the three dimensional trajectory optimization performed include powered phase steering data and coast phase orbital element data. Time derivatives of the orbital elements as functions of thrust components were evaluated and used to explain the optimization's solution. Vehicle performance as a function of parking orbit inclination was given. Performance and orbital element data was provided for launch windows as functions of launch time. Ground track data was given for all burns and coasts including variation within the launch window. It was found that a Centaur with fully loaded propellant tanks could be flown from a 37deg inclination low Earth parking orbit and achieve Molniya orbit with comparable performance to the baselined transfer which started from a 57deg inclined orbit: 9,545 lb vs. 9,552 lb of separated spacecraft weight respectively. There was a significant reduction in the need for propellant launch time reserve for a one hour window: only 78 lb for the three burn transfer vs. 320 lb for the two burn transfer. Conversely, this also meant that longer launch windows over more orbital revolutions could be done for the same amount of propellant reserve. There was no practical difference in ground tracking station or airborne assets needed to secure telemetric data, even though the geometric locations of the burns varied considerably. There was a significant adverse increase in total mission elapsed time for the three vs. two burn transfer (12 vs. 11/4 hrs), but could be accommodated by modest modifications to Centaur systems. Future applications were discussed. The three burn transfer was found to be a viable, arguably preferable, alternative to the two burn transfer.

Orbital trajectory design↗
NASA NTRS2015

Three Orbital Burns to Molniya Orbit Via Shuttle_Centaur G Upper Stage

An unclassified analytical trajectory design, performance, and mission study was done for the 1982 to 1986 joint National Aeronautics and Space Administration (NASA)-United States Air Force (USAF) Shuttle/Centaur G upper stage development program to send performance-demanding payloads to high orbits such as Molniya using an unconventional orbit transfer. This optimized three orbital burn transfer to Molniya orbit was compared to the then-baselined two burn transfer. The results of the three dimensional trajectory optimization performed include powered phase steering data and coast phase orbital element data. Time derivatives of the orbital elements as functions of thrust components were evaluated and used to explain the optimization's solution. Vehicle performance as a function of parking orbit inclination was given. Performance and orbital element data was provided for launch windows as functions of launch time. Ground track data was given for all burns and coasts including variation within the launch window. It was found that a Centaur with fully loaded propellant tanks could be flown from a 37 deg inclination low Earth parking orbit and achieve Molniya orbit with comparable performance to the baselined transfer which started from a 57 deg inclined orbit: 9,545 versus 9,552 lb of separated spacecraft weight, respectively. There was a significant reduction in the need for propellant launch time reserve for a 1 hr window: only 78 lb for the three burn transfer versus 320 lb for the two burn transfer. Conversely, this also meant that longer launch windows over more orbital revolutions could be done for the same amount of propellant reserve. There was no practical difference in ground tracking station or airborne assets needed to secure telemetric data, even though the geometric locations of the burns varied considerably. There was a significant adverse increase in total mission elapsed time for the three versus two burn transfer (12 vs. 1-1/4 hr), but could be accommodated by modest modifications to Centaur systems. Future applications were discussed. The three burn transfer was found to be a viable, arguably preferable, alternative to the two burn transfer.

Orbital trajectory design↗
NASA NTRS1984

Somali current studied from SEASAT altimetry

Mesoscale variability has been obtained for the world ocean from satellite altimetry by using the repetitive tracks data of SEASAT. No significant results were obtained for the Somali current area for two main reasons: the repetitive tracks are too sparse to cover the expected eddy pattern and these data were obtained in late September and early October when the current is strongly decaying. The non-repetitive period of SEASAT offers the possibility to study a dozen of tracks parallel to the eddy axis or crossing it. These are used here to deduce the dynamic topography of the Somali current. Data error reduction and tide and orbit corrections are addressed. A local geoid was built using a collocation inverse method to combine surface gravity data and altimetry: the repetitive tracks show no variability (which confirms that the current is quasi-inexistent at that time) and can be used as data for the local geoid. This should provide a measure of the absolute dynamic topography of the Somali current.

Perigaud, C.↗
NASA NTRS1980

Precision orbit analyses in support of the Seasat altimeter experiment

It is noted that major improvements have been made in the Goddard Space Flight Center (GSFC) geodynamic models for Seasat. It is pointed out that the dominant error source in Seasat ephemeris computation is currently the uncertainty in modeling the earth's gravity field. Attention is also given to significant errors arising from atmospheric drag and solar radiation pressure modeling. It is noted that a comparison of GSFC and Naval Surface Weapons Center (NSWC) Seasat ephemerides indicate the presence of an unexplained difference of about 4 m in the location of the center of mass along the Z axis. This difference is consistent with that obtained with earlier geoid and station coordinated comparisons performed by other investigators. It is expected that future combinations of Seasat and GEOS-3 altimeter data, together with laser and Unified S-Band tracking data, will ultimately produce a gravity field which allows computations of a global Seasat ephemeris with an rms radial accuracy of about 50 cm.

Marsh, J. G.↗
NASA NTRS1984

Radar data smoothing filter study

The accuracy of the current Wallops Flight Facility (WFF) data smoothing techniques for a variety of radars and payloads is examined. Alternative data reduction techniques are given and recommendations are made for improving radar data processing at WFF. A data adaptive algorithm, based on Kalman filtering and smoothing techniques, is also developed for estimating payload trajectories above the atmosphere from noisy time varying radar data. This algorithm is tested and verified using radar tracking data from WFF.

White, J. V.↗
NASA NTRS1985

Viking Radio Science Data Analysis and Synthesis

The objectives of the analysis of the Viking radio tracking data are: (1) the study of Mars, its rotation, topography, and internal structure; (2) the development of a general dynamical model of the solar system; and (3) tests of the fundamental laws of gravitation. The central element in the data analysis is the Planetary Ephemeris Program (PEP) which embodies the mathematical models of the solar system. The asteroid model in PEP is changed to better estimate the mass of a fictitious uniform ring and the masses of eight separate asteroids. A model of the rotation of Mars include a secular rate of change of the period and both annual and semiannual variations in the phase of rotation. Other modifications to this model are discussed.

Shapiro, I. I.↗
NASA NTRS1975

Applications of satellite-to-satellite tracking to orbit determination and geopotential recovery

Recent simulations have demonstrated the applicability of satellite-to-satellite tracking data to the related problems of orbit determination and geopotential recovery. Specifically, satellite-to-satellite tracking between an earth orbiting satellite and a satellite at geosynchronous altitude (36000 km) produces long continuous data arcs which are not available by means of ground-based tracking. This facility, in conjunction with correct estimation techniques, yields exceptional orbit determination accuracy. The data type also has considerable applicability to geopotential determination when the low satellite has a high inclination.

Argentiero, P.↗
NASA NTRS1974

C-band station coordinate determination for the Geos-C altimeter calibration area

Dynamical orbital techniques were employed to estimate the center-of-mass station coordinates of six C-band radars located in the designated primary Geos-C radar altimeter calibration area. This work was performed in support of the planned Geos-C mission (December 1974 launch). The sites included Bermuda, Grand Turk, Antigua, Wallops Island (Virginia), and Merritt Island (Florida). Two sites were estimated independently at Wallops Island yielding better than 40 cm relative height recovery, with better than 10 cm and 1m (relative) recovery for phi and lambda, respectively. The tracking data used in this analysis were taken during 1969 when the radars tracked the Geos-II transponder. In all, over 120 passes of data were used. Range biases were estimated. Error analysis and comparisons with other investigators indicate that better than 2m (1 sigma) relative recovery has been achieved at all sites.

Klosko, S. M.↗
NASA NTRS1977

Recovery of refractivity profiles and pressure and temperature distributions in the lower atmosphere from satellite-to-satellite radio occultation data

The feasibility of recovering parameters from one-way range rate between two earth orbiting spacecraft during occultation of the tracking signal by the earth's lower atmosphere. The tracking data is inverted by an integral transformation (Abel transform) to obtain a vertical refractivity profile above the point of closest approach of the ray connecting the satellites. Pressure and temperature distributions can be obtained from values of dry refractivity using the hydrostatic equation and perfect gas law. Two methods are investigated for recovering pressure and temperature parameters. Results show that recovery is much more sensitive to satellite velocity errors than to satellite position errors. An error analysis is performed. An example is given demonstrating recovery of parameters from radio occultation data obtained during satellite-to-satellite tracking of Nimbus 6 by the ATS 6 satellite.

Murray, C. W., Jr.↗
NASA NTRS1972

Space station data flow

The results of the space station data flow study are reported. Conceived is a low cost interactive data dissemination system for space station experiment data that includes facility and personnel requirements and locations, phasing requirements and implementation costs. Each of the experiments identified by the operating schedule is analyzed and the support characteristics identified in order to determine data characteristics. Qualitative and quantitative comparison of candidate concepts resulted in a proposed data system configuration baseline concept that includes a data center which combines the responsibility of reprocessing, archiving, and user services according to the various agencies and their responsibility assignments. The primary source of data is the space station complex which provides through the Tracking Data Relay Satellite System (TDRS) and by space shuttle delivery data from experiments in free flying modules and orbiting shuttles as well as from the experiments in the modular space station itself.

Source record↗