Engineering topics
McElrath, T. P.
Publications and source records attributed to McElrath, T. P..
PHOBOS Exploration using Two Small Solar Electric Propulsion (SEP) Spacecraft
Phobos Surveyor Mission concept provides an innovative low cost, highly reliable approach to exploring the inner solar system 1/16/2013 3 Dual manifest launch. Use only flight proven, well characterize commercial off-the-shelf components. Flexible mission architecture allows for a slew of unique measurements.
Asteroid 5535 Annefrank size, shape, and orientation: Stardust first results
The NASA Discovery Stardust spacecraft flew by the main belt asteroid 5535 Annefrank at a distance of 3100 km and a speed of 7.4 km/s in November 2002 to test the encounter sequence developed for its primary science target, the comet 81P/Wild2. During this testing, over 70 images of Annefrank were obtained, taken over a phase angle range from 40 to 140 degrees.
Asteroid 5535 Annefrank size, shape and orientation: STARDUST preliminary results
The NASA Discovery STARDUST spacecraft flew by the main belt asteroid 5535 Annefrank in November 2002 to test the encounter sequence developed for its primary science target, the comet 81P/Wild 2.
2001 Mars Odyssey orbit determination during interplanetary cruise
This paper will discuss the orbit determination processes and results of Mars Odyssey from launch to orbit insertion at Mars.
2001 Mars Odyssey orbit determination during interplanetary cruise
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Determination of Position of Jupiter From Very-Long Baseline Interferometry Observations of Ulysses
Very-long baseline interferometry (VLBI) observations of the Ulysses spacecraft near its encounter with Jupiter on 1992 February 8 were made to determine the angular position of Jupiter with respect to well known extragalactic radio sources. Spacecraft range and Doppler data were used to determine the position of the spacecraft with respect to Jupiter. Thirty-one VLBI observations of the spacecraft were made within 30 days of Ulysses closest approach to Jupiter, using the California-Spain and California-Australia baselines of NASA's Deep Space Network. When combined, these data determine the position of Jupiter at the time of encounter with an accuracy of 0.003 min in right ascension and 0.005 sec in declination. In addition, the Earth-Jupiter distance was determined with 20 m accuracy.
Galileo at Jupter: Delivery Accuracy
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(abstract) ARGOS: a System to Monitor Ulysses Nutation and Thruster Firings from Variations of the Spacecraft Radio Signal
Ulysses is a spin-stabilized spacecraft that experienced significant nutation after its launch in October 1990. This was due to the Sun-spacecraft-Earth geometry, and a study of the phenomenon predicted that the nutation would again be a problem during 1994-95. The difficulty of obtaining nutation estimates in real time from the spacecraft telemetry forced the ESA/NASA Ulysses Team to explore alternative information sources. The work performed by the ESA Operations Team provided a model for a system that uses the radio signal strength measurements to monitor the spacecraft dynamics. These measurements (referred to as AGC) are provided once per second by the tracking stations of the DSN. The system was named ARGOS (Attitude Reckoning from Ground Observable Signals) after the ever-vigilant, hundred-eyed giant of Greek Mythology. The ARGOS design also included Doppler processing, because Doppler shifts indicate thruster firings commanded by the active nutation control carried out onboard the spacecraft. While there is some visibility into thruster activity from telemetry, careful processing of the high-sample-rate Doppler data provides an accurate means of detecting the presence and time of thruster firings. DSN Doppler measurements are available at a ten-per-second rate in the same tracking data block as the AGC data.
Determination of Position of Jupiter from VLBI Observations of
Very-Long Baseline Interferometry (VLBI) observations of the.