Engineering topics

Ananda, M. P.

Publications and source records attributed to Ananda, M. P..

8 records

NASA NTRS1983

Simultaneous dual baseline differential VLBI

Attention is drawn to the benefits of simultaneous dual baseline radio interferometric measurements for low altitude planetary orbiter navigation. The radio interferometric data types constitute a valuable addition to conventional tracking data in the establishment of orbit-plane orientation, thanks to their measurement of inertial reference cross-track velocity. The present results show that only a few Delta-VLBI measurements, taken at either end of a conventional tracking arc, suffice for the realization of a positional accuracy of better than 1 km for the case of a Venus Orbiting Imaging Radar-type planetary orbiter. This is comparable to Deep Space Net accuracies, despite the use of a shorter baseline.

Mohan, S. N.↗

NASA NTRS1980

A low-order global gravity field of Venus and dynamical implications

An estimate of sixth-degree and sixth-order harmonic coefficients of the global gravity field of Venus is obtained by processing the long periodic variations of the mean orbital elements of the Pioneer Venus orbiter. Approximately 220 days of data are included in this reduction, which provides almost complete longitudinal coverage. Oblateness is estimated to be -5.97 + or - 3.2 x 10 to the -6. It is noted that the amplitudes of other coefficients are similar to the predicted coefficients using Kaula's rule under equal stress assumption. Atmospheric density values as a function of altitude are obtained to help model drag perturbation. A radial acceleration map at 100 km above the Venus surface is generated, and correlation between gravity anomalies and major topographic features is observed. Spectral analysis of the harmonic model suggests that the interior density anomalies are like those on earth. The orientation angles of the principal axes of the moments of inertia are computed, and deviation of the maximum moment of inertia axis from the spin axis is observed to be small (less than 5 deg). It is found that the minimum moment of inertia axis passes through the Aphrodite and Beta regions.

Ananda, M. P.↗

NASA NTRS1980

An evaluation of Galileo-Viking differenced range in Galileo-Mars flyby navigation

A summary and evaluation of the Galileo-Mars flyby navigation techniques is presented. The navigational requirements of Galileo as it swings by Mars are going to be met with interferometric angular measurements (VLBI) and range and range-rate measurements. Like VLBI, dual spacecraft differenced range is less sensitive to Mars ephemeris errors and tracking station location errors than conventional range and Doppler. Similarly, differenced range provides angular information about the separation between the Mars Viking Lander I and the Galileo spacecraft. In covariance studies, dual spacecraft range coupled with conventional range and Doppler is shown to estimate the Galileo-Mars flyby distance to better than 10 km which is comparable to the VLBI performance. For the Galileo-Mars flyby, dual spacecraft differenced range promise to be an excellent backup to VLBI if the Mars Viking Lander remains operational.

Winn, F. B.↗

NASA NTRS1980

Interplanetary beacon for deep space navigation

The utilization of the Viking lander as a beacon for navigating the Galileo spacecraft for its Mars flyby is investigated. Covariance analyses show that the improvement in the flyby navigation accuracy is significant compared with the conventional radiometric navigation. A validation experiment using Viking lander and orbiter indicates that the expected accuracy can be obtained.

Ananda, M. P.↗

NASA NTRS1977

An improved lunar moment of inertia determination - A proposed strategy

A strategy for determining an improved lunar moment of inertia is proposed. An improved uncertainty in the lunar inhomogeneity parameter could reduce the core density error from 4.20 gr/cu cm to 0.1 gm/cu cm for the case of a lunar density model having a 300 km core radius. The current error of 0.0025 for the lunar inhomogeneity parameter is mostly due to the uncertainties in the C20 and C22 gravity harmonics. An optimum reduction strategy for obtaining an order of magnitude improvement in the gravity estimates is based on covariance analyses of Doppler data. The long-arc reduction method is shown to provide better results than the short-arc technique, and the use of an orbit with a 7000 km semimajor axis along with certain terms of up to degree and order eight is recommended.

Ananda, M. P.↗

NASA NTRS1977

Lunar gravity - A mass point model

A point-mass representation of a quasi-global lunar gravity field is developed by processing Apollo 15 and 16 subsatellite and Lunar Orbiter 5 Doppler tracking data. The model is generated by reducing the long-period variations in the mean orbital elements. The model consists of 117 point masses distributed over the region of + or - 30 deg in latitude about the lunar equator and resolves all the previously known 'mascons' on the near side as broad positive-gravity regions. The near-side acceleration map evaluated at 100 km above the lunar surface shows good agreement with line-of-sight acceleration results. The lunar far-side gravity map shows strong broad positive-gravity regions for the highland areas. However, all the major ringed basins are resolved as localized negative anomalies in contrast with the near-side basins. This model does not indicate any evidence for the existence of any mascon-type feature on the lunar far-side.

Ananda, M. P.↗

NASA NTRS1977

Lunar gravity - A long-term Keplerian rate method

Nearside tracking data from Apollo subsatellites and Lunar Orbiter 5 are used to construct a model of the farside lunar gravity field. An indirect method of calculating the average effect of all the gravity anomalies which affect spacecraft orbits is reduced to a linear estimation problem by eliminating the integration of spacecraft dynamics. Doppler frequency shifts between the lunar satellite and earth-based tracking station are used to measure the line of sight velocity component between the orbiter and the tracker; gravity determination is then performed in a weighted least squares estimator which employs the orbital rates as data and formulates the normal equations using the associated Keplerian state. Simulations performed demonstrate that farside gravity features can be economically determined by use of gravity estimates obtained from long-period models of nearside orbiting tracks.

Ferrari, A. J.↗

NASA NTRS1972

Outer planet satellite ephemeris development.

Discussion of the possible effectiveness of an earth-based ephemeris development program for the outer planet natural satellites. Technologies for obtaining and reducing photographic plates are available and new satellite theories needed for data processing are being developed. It is shown that satellite ephemeris accuracies could be reduced to hundreds of km by the end of the 1970s. An earth-based program would have great benefits to future outer planet missions requiring this level of accuracy.

Duxbury, T. C.↗