yee@trident.arc.nasa.gov (Peter E. Yee) (07/20/89)
Voyager Status Report
July 18, 1989
Neptune's new moon, 1989 N1, is becoming a new guidepost
for the Voyager navigation team and is a candidate to help
better determine the location of Neptune itself.
Neptune was discovered in 1846, and the planet takes 165
years to orbit the Sun; thus, Neptune won't return to the
position where astronomers first saw it until 2011. This
leaves great uncertainty in the precise knowledge of
Neptune's orbit that Voyager navigators need to get the
spacecraft to the targeted area of the planet at the right
time. But the new Neptunian moon, 1989 N1, will provide the
navigation team with a better idea of Neptune's exact
location.
The discovery of the moon fulfilled expectations of
Voyager navigators who were hoping to find at least one new
object in the Neptune system whose orbit could potentially be
used to gauge the relative positions of Triton, Neptune and
various background stars, said Don Gray, Voyager Navigation
Team Chief.
Many of the images coming back from the spacecraft are
optical navigation frames. Ideally, the frames show a moon
against a field of stars. Using stars as dim as 10th
magnitude as reference points, the Voyager navigators
progressively update and refine the location of Neptune and
its moons. This new information is then integrated into
commands that adjust Voyager's flight path and retarget the
spacecraft's observations, if necessary.
The next trajectory correction maneuver is being
designed and will be uplinked to the spacecraft late next
week. The maneuver is one of the final three that will be
conducted between now and closest approach to bring the
spacecraft within about 100 miles (150 kilometers) of the
point at which it's aimed -- about 3,000 miles (4,850
kilometers) from Neptune's cloud tops.
DISTANCE TO EARTH: 2,686,949,000 miles
DISTANCE TO NEPTUNE: 33,805,000 miles
HELIOCENTRIC VELOCITY: 42,192 mph