he term Opposition describes an alignment of the Earth, the Sun, and the Spacecraft with the
Earth in the middle. Therefore the Sun-Probe-Earth angle (SPE) is close to 0º but the Sun-Earth-Probe
angle (SEP) is close to 180º.
uring an opposition, there is minimal Solar interference to the radio signals travelling between the Earth and the spacecraft.
It is therefore a good opportunity to try to detect gravitational waves. The Ulysses Gravitational Wave Experiment (GWE) is
a radio science experiment designed to attempt to detect low frequency gravitational waves (in the mHz band). Possible
astrophysical sources in this frequency band are:
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Collapse and collisions of black holes in the nuclei of galaxies and quasars |
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Periodic wave trains emanating from massive orbiting binary black holes |
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An isotropic background of cosmological origin
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econd Opposition in February 1992 provided the best geometric conditions for the GWE. First Opposition was therefore used
as a period to test the radio science techniques. No GWE observations have been planned for subsequent oppositions.
lignment of Ulysses and the ACE, POLAR and SOHO spacecraft around the 5th Opposition of Ulysses in February 1998 also
provided a unique scientific opportunity. Extra coverage was scheduled to support the Multi-project Investigation During
the Alignment of Spacecraft (MIDAS) for the study of the evolution of Coronal Mass Ejections (CMEs), interstellar pickup
ions and other phenomena.