Citation
Abstract
The first in-situ measurements at a comet occurred on 11 September 1985 when the International Cometary Explorer (ICE) passed through the tail of Comet Giacobini-Zinner approximately 7870 km downstream of the nucleus, Encounter took place 7 years after the spacecraft’s original launch on 12 August 1978 as the International Sun Earth Explorer 3 (ISEE-3), part of a three-spacecraft project to study the interaction between the solar wind and the Earth’s magnetosphere. Transfer to an interplanetary trajectory (and the name change) was performed via a 119-km-altitude, gravity-assist, lunar swingby on 22 December 1983. Navigation support during interplanetary cruise and comet encounter was provided by orbit determination utilizing rauio metric data from the DSN 64-meter antennas in Goldstone, California and Madrid, Spain. Orbit solutions yielding predictions of 50-km geocentric delivery accuracy in the target aim plane were achieved during interplanetary cruise and at comet encounter using 6-to-12-week data arcs between periodic attitude-change maneuvers, One-sigma two-way range and range rate residuals were consistently 40 meters and 0.2 mm/s or better, respectively. Non-gravitational forces affected the comet’s motion during late August and early September 1985 and caused a 2300-km shift in the orbit of the comet relative to the spacecraft. This necessitated a final ICE orbit trim maneuver 3 days prior to encounter. Near-real-time assessment of two-way 2-GHz (S-band) Doppler pseudo-residuals during the June and July 1985 trajectory change maneuvers aided in calibration of the spacecraft’s thrusters in preparation for this final critical maneuver. Post-flight analysis indicates tail centerline passage was achieved within 10 seconds of the predicted time and geocentric position uncertainty at encounter was less than 40 km.
Details
- Volume
- 42-86
- Published
- August 15, 1986
- Pages
- 268–283
- File Size
- 1.1 MB