EARLY ORBIT CAMPAIGN ENGINEERING DATA
This plot of the time difference between Horizon
Crossing Indicator limb crossings shows spin-axis nutation being damped
out during the first few orbits. The broad envelope of the line at left
is due to nutation; as time passes it reduces in amplitude and finally
becomes a narrow trace, showing that the passive alcohol-filled ring nutation
damper is doing its job.
Spin period of the satellite during the second
day of operation. The trend is due to the gradual slowing of the spin while
the once-per-orbit fluctuations are due to expansion and contraction of
the spacecraft in response to heating and cooling during the day/night
Right ascension and declination of the spacecraft
spin axis over the course of four orbits. The spin axis is making a twice-per-orbit
cycle about a point near orbit normal, with an amplitude of about one degree.
This may be due to the residual magnetism of the spacecraft and its torque
rods. With the axial torque rod last activated in the negative state, the
spin axis epicenter is precessing at almost the same rate as orbit normal,
the motion of which is shown on the plot as a heavy, straight line.
Plots of Spacecraft temperatures for three
locations on the 4th day of operation. The top plot is the central baseplate
temperature (on the launch adapter side). It shows about a 4 degree C day/night
amplitude. It is cooling slightly over time because just before this interval
all 4 solar array string circuits were on, which dumps more heat through
the batteries. With 3 circuits on the central plate is equilibrating to
a 16-20 C range. The batteries, subsytem electronics boxes, and instruments
are closely following the central plate temperatures. The second plot shows
the launch adapter ring temperature. The launch adapter is on the sun side
of the spacecraft, and the marmon clamp is fairly absorptive, so 20 degree
swings are seen. These fluctuations are not conducted significantly to
the central plate, however. The third plot shows a solar panel temperature
changing by about 40 degrees. This is as designed - the solar panels are
insulated from the rest of the spacecraft, so the components do not see
these temperature swings.
Solar array current and shunt current during
the solar eclipse of 26 February, 1998. The spacecraft passed through a
region of partial eclipse six orbits after launch. A slight dip can be
discerned in the total array current generated, while the shunting of excess
current went almost to zero.
Solar sensor data from 28 February 1998 (the
third day of operation), with 200 spins overplotted. The solar beta angle
is 28.5 degrees, the SXP offset angle is 22.5 degrees, and the spacecraft
is 1 degree off orbit normal, resulting in a maximum Y-axis measurement
of 5 degrees.