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At least 1,531 records · Page 85
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Buckling analysis of the quadripod structure for the NASA 70-meter antenna

As part of the effort to extend the diameter of three Deep Space Network large earth antennas from 64 meters to 70 meters, a slim profiled quadripod structure was designed to support a 7.7 meter diameter subreflector for the 70 meter antenna. The new quadripod design, which particularly emphasizes reduced radio frequency blockage, is achieved by means of a narrow cross sectional profile of the legs. Buckling analysis, using NASTRAN, was conducted in this study to verify the safety margin for the quadripod structural stability.

Chian, Chian T.↗
NASA NTRS1987

The Telecommunications and Data Acquisition Report

Developments in programs managed by the Jet Propulsion Laboratory's Office of Telecommunications and Data Acquisition are discussed. Topics discussed include sorption compression/mechanical expanded hybrid refrigeration, calculated 70-meter antenna performance for offset L-band, systolic arrays and stack decoding, and calibrations of Deep Space Network antennas.

Posner, E. C.↗
NASA NTRS1987

Power supply conditioning circuit

A power supply conditioning circuit that can reduce Periodic and Random Deviations (PARD) on the output voltages of dc power supplies to -150 dBV from dc to several KHz with no measurable periodic deviations is described. The PARD for a typical commercial low noise power supply is -74 dBV for frequencies above 20 Hz and is often much worse at frequencies below 20 Hz. The power supply conditioning circuit described here relies on the large differences in the dynamic impedances of a constant current diode and a zener diode to establish a dc voltage with low PARD. Power supplies with low PARD are especially important in circuitry involving ultrastable frequencies for the Deep Space Network.

Primas, L. E.↗
NASA NTRS1987

Sorption compressor/mechanical expander hybrid refrigeration

Experience with Deep Space Network (DSN) ground-based cryogenic refrigerators has proved the reliability of the basic two-stage Gifford-McMahon helium refrigerator. A very long life cryogenic refrigeration system appears possible by combining this expansion system or a turbo expansion system with a hydride sorption compressor in place of the usual motor driven piston compressor. To test the feasibility of this system, a commercial Gifford-McMahon refrigerator was tested using hydrogen gas as the working fluid. Although no attempt was made to optimize the system for hydrogen operation, the refrigerator developed 1.3 W at 30 K and 6.6 W at 60 K. The results of the test and of theoretical performances of the hybrid compressor coupled to these expansion systems are presented.

Jones, J. A.↗
NASA NTRS1987

Compound-taper feedhorn for the DSN 70-meter antennas

A novel X-band feedhorn was designed for the Deep Space Network (DSN) 70-meter antennas. The feedhorn is a compound-taper structure consisting of a corrugated flared section and a corrugated straight section. This feedhorn is designed to closely initiate the characteristics of the standard feedhorn, while providing the proper phase center location, without adding any significant loss to the system. The use of the existing feedhorn and the ease of manufacturing the corrugated straight section have resulted in major overall cost savings.

Manshadi, F.↗
NASA NTRS1987

X-band phase calibration generator coupler

A new type of phase calibration generator (PCG) coupler was developed for the Deep Space Network (DSN) X-band antennas that can be located directly behind the feedhorn. The advantage of this is that the calibration includes more of the system. The disadvantage is that the overmoded waveguide at this location must be coupled in a mode-selective manner. Low-power and high-power PCG couplers have been successfully produced, and the RF test results from a PCG coupler are given.

Stanton, P. H.↗
NASA NTRS1987

DSN 63 64-meter antenna S- and X-band efficiency and system noise temperature calibrations, July 1986

The Deep Space Network (DSN) 64-meter antenna in Spain (DSN 63) has been calibrated prior to its upgrading to a 70-meter high efficiency configuration in preparation for the Voyager Neptune encounter in August 1989. The S-band (2285 MHz) and X-band (8420 MHz) effective area efficiency and system noise temperature calibrations were carried out during July 1986 to establish a baseline system performance for this station. It is expected that the 70-meter will result in at least a 1.9 dB G/T improvement at X-band relative to the 64-meter baseline reference.

Slobin, S. D.↗
NASA NTRS1987

DSS 43 64-meter antenna S- and X-band efficiency and system noise temperature calibrations, January 1987

The Deep Space Network (DSN) 64-meter antenna in Australia has been calibrated prior to its upgrading to a 70-meter configuration in preparation for the Voyager Neptune encounter in August 1989. The S-band (2285 MHz) and X-band (8420 MHz) antenna area efficiency and system noise temperature calibrations were carried out during December 1986 and January 1987 to establish a baseline system performance for this station.

Slobin, S. D.↗
NASA NTRS1987

DSS 43 antenna gain analysis for Voyager Uranus encounter: 8.45-GHz radio science data correction

A malfunction of the Deep Space Network (DSN) 64-meter antenna in Australia forced the antenna to operate with a mispositioned subreflector during the Voyager Uranus encounter period (January 24, 1986). Because of changing main reflector shape and quadripod position as a function of elevation angle, the antenna gain and pointing were not as expected, and the 8.45 GHz received signal level changed during the pass. The study described here used the Geometrical Theory of Diffraction (GTD) analysis to determine actual antenna gain and pointing during that period in an attempt to reconstruct the radio science data. It is found that the 1.4 dB of signal variation can be accounted for by antenna geometry changes and pointing error. Suggested modifications to the values measured during the pass are presented. Additionally, an extremely useful tool for the analysis of gravity deformed reflectors was developed for use in future antenna design and analysis projects.

Slobin, S. D.↗
NASA NTRS1986

DSN tracking support to the international cometary explorer

The tracking of the ICE spacecraft at its encounter with the comet Giacobini-Zinner posed a major problem for the Deep Space Network (DSN). At the comet, ICE was nearly 50 times as distant from the earth as it was during its designed mission. Its signal strength at the ground was diminished by almost 2500 times from its designed level. The paper describes how the DSN met this challenge by combining antennas in arrays and cooperating with the Arecibo Observatory in Puerto Rico and the Usuda 64m antenna in Japan.

Reid, M. S.↗
NASA NTRS1986

The spacecraft encounters of Comet Halley

The characteristics of the Comet Halley spacecraft 'fleet' (VEGA 1 and VEGA 2, Giotto, Suisei, and Sakigake) are presented. The major aims of these missions were (1) to discover and characterize the nucleus, (2) to characterize the atmosphere and ionosphere, (3) to characterize the dust, and (4) to characterize the nature of the large-scale comet-solar wind interaction. While the VEGA and Giotto missions were designed to study all four areas, Suisei addressed the second and fourth. Sakigake was designed to study the solar wind conditions upstream of the comet. It is noted that NASA's Deep Space Network played an important role in spacecraft tracking.

Asoka Mendis, D.↗
NASA NTRS1986

Navigating the International Cometary Explorer for encounter with Comet Giacobini-Zinner

The navigation of the International Cometary Explorer for its encounter with Comet Giacobini-Zinner, provided by orbit determination using radio metric data from the 64-m Deep Space Network antennas in California and Spain, is discussed. Orbital solutions providing predictions of 50-km geocentric delivery accuracy in the target plane were achieved using 6-12 week data arcs between periodic attitude change maneuvers. The one-sigma two-way range and range rate were found to be 40 m and 0.2 mm/s or better, respectively. Post-flight analysis shows tail centerline passage to be achieved within 10 s of the predicted time, and a geocentric position uncertainty at the encounter of better than 40 km is found.

Efron, L.↗
NASA NTRS1986

VEGA Pathfinder navigation for Giotto Halley encounter - An application of VLBI techniques

Results of the VEGA Pathfinder concept which was used to successfully target the European Space Agency's Giotto spacecraft to a 600 km encounter with the comet Halley are presented. Pathfinder was an international cooperative navigation activity involving USSR, European and U.S. space agencies. The final Giotto targeting maneuver was based on a comet location determined from optical data acquired by the earlier arriving Soviet VEGA spacecraft. Inertial pointing angles extracted from optical images of the comet nucleus were combined with a precise estimate of the VEGA encounter orbits determined using VLBI data acquired by NASA's Deep Space Network to predict the location of Halley at Giotto encounter. This article describes the VLBI techniques used to determine the VEGA orbits and shows that the insensitivity of the VLBI data strategy to unmodeled dynamic error sources resulted in estimates of the VEGA orbits with an accuracy of 50 km.

Ellis, Jordan↗
NASA NTRS1986

Management experience of an international venture in space The Ulysses mission

The management of the Ulysses project, a probe which will fly a solar polar orbit, is described. The 5-yr mission will feature a flyby of Jupiter to deflect the spacecraft into a high-inclination orbit. Data on the solar corona, solar wind, the sun-wind interface, the heliospheric magnetic field, solar and nonsolar cosmic rays, etc., will be gathered as a function of the solar latitude. NASA will track and control the probe with the Deep Space Network. JPL provides project management for NASA while the Directorate of Scientific Programs performs ESA management functions. The DOE will provide a radioisotope thermoelectric generator while NASA and ESA each supply half the scientific payload. A NASA-ESA Joint Working Group meets about twice per year to monitor the project and discuss the technical and scientific requirements. Safety issues and measures which are being addressed due to the presence of the Pu-238 heat source for the RTG are discussed.

Yoshida, Ronald Y.↗
NASA NTRS1986

Carrier tracking by smoothing filter improves symbol SNR

The potential benefit of using a smoothing filter to estimate carrier phase over use of phase locked loops (PLL) is determined. Numerical results are presented for the performance of three possible configurations of the deep space network advanced receiver. These are residual carrier PLL, sideband aided residual carrier PLL, and finally sideband aiding with a Kalman smoother. The average symbol signal to noise ratio (SNR) after losses due to carrier phase estimation error is computed for different total power SNRs, symbol rates and symbol SNRs. It is found that smoothing is most beneficial for low symbol SNRs and low symbol rates. Smoothing gains up to 0.4 dB over a sideband aided residual carrier PLL, and the combined benefit of smoothing and sideband aiding relative to a residual carrier loop is often in excess of 1 dB.

Pomalaza-Raez, Carlos A.↗
NASA NTRS1986

An analysis and intercomparison of VLBI nutation estimates

Nutation estimates from long duration VLBI experiments conducted by the Deep Space Network and reduced at JPL were compared with similar estimates from the IRIS/Polaris data reduced at Harvard. The two series were found to have an rms difference of 1.6 milliarcsec or less, and both exhibited the existence of seasonal errors in the IAU 1980 nutation theory. Most of the observed seasonal discrepancies could be removed by changing the period of the free core resonance to 431.5 solar days. The VLBI data constrain the resonance damping time to be at least one decade, and possibly much longer. Any free core nutation has an amplitude of less than 1 milliarcsec. Crude estimates of the atmospheric forcing of this resonance indicate that meteorological forcing could easily explain the observed free core nutation.

Eubanks, T. M.↗
NASA NTRS1987

Measurement technique of the Giotto radio science experiment

The paper describes the technique used to record time delay and waveform measurements for the Giotto radio science experiment of ESA's mission to comet Halley. The data were taken by using either two-way measurements (during pre- and post-encounter) or one-way measurements (during encounter with comet Halley), the downlink of the radio signal of the Giotto spacecraft being received at 8.4 GHz by the 64 m tracking stations of NASA's Deep Space Network (DSN). The waveform measurements were obtained at a sampling frequency of 50 kHz with an open-loop receiver assembly at DSN station Canberra as recently used for the Voyager/Uranus fly-by. Performance and calibration data are given as relevant to the radio subsystems on the ground and aboard Giotto.

Edenhofer, P.↗
NASA NTRS1987

Planning the Voyager spacecraft's mission to Uranus

The application of the systems engineering process to the planning of the Voyager spacecraft mission is described. The Mission Planning Office prepared guidelines that controlled the use of the project and multimission resources and spacecraft consumables in order to obtain valuable scientific data at an acceptable risk level. Examples of mission planning which are concerned with the design of the Deep Space Network antenna, the uplink window for transmitting computer command subsystem loads, and the contingency and risk assessment functions are presented.

Plagemann, Stephen H.↗