Spin Dynamics Issues (1 of 4)
Stochastic and other Hard-to-Model Perturbations
Fuel sloshing
Variability of solar irradiance
variations on all timescales
short-term fluctuations are stochastic
variation ~0.1 percent over long
timescales
variation ~0.01 percent over short
timescales
Earth radiation pressure
visible
infrared
variability due to weather
complicated torques
spacecraft not protected by shield
optical ports
AKM hole
Nutation damping mechanism stiction and/or
other undesirable behaviors
Magnetic torques near magnetopause
Spin Dynamics Issues (2 of 4)
Solar Shield
Shield (panels, teflon tape, & webbing) &
flattop albedos
variable over time as materials age
spatial inhomogeneities
AKM: hole or cover?
Variations in effective shield angle
nonuniform in circumference
slow variation over time
fast variation -- flapping modes (eclipses)
Shield geometry perturbations
solar panels
potato chipping
dynamic modes
radial (flapping)
twisting
what are the timescales for
damping?
interpanel membranes
sagging
flapping?
Spin Dynamics Issues (3 of 4)
Thermal radiation torques
Axis of shield misaligned with spacecraft spin
axis
Trim tab problems
nonuniform axis directions
mechanism slop?
Perturbations Due to Events
Eclipses
Geotail particle bursts
"wind" gusts
potentials across spacecraft surfaces
cause electrical currents which cause
magnetic torques
caused Echo spinup
very large bursts from fast CME events
a few times per year around solar max
potential for spacecraft damage?
Magnetopause crossings
relatively rare at geosynch (a few times a
year)
short duration (~15 min) exposure to full
blast of the solar wind
Micrometeoroid hits
Spin Dynamics Issues (4 of 4)
Other Smooth Perturbations
Spin axis not aligned with principal axis
Spacecraft thermal radiation torques
Sun shield
thermal radiators
telescope viewports
Gravity gradient torques
Movement of center of gravity as fuel is
expended
Variations of Sun direction due to
Sun-tracking dynamics
Variation of solar radiation pressure as
spacecraft orbits around the Earth
Magnetic torques
Lunar torques
Jitter
