EXPLANATION OF THE PLAN PLOT

There are two different formats for this plot depending upon whether the spin axis is eliptic normal or orbit normal. Starting in September 2003 the spin axis of the POLAR spacecraft will be ecliptic normal. Before September 2003 the spin axis was orbit normal, except during the summer of 2002 when it was ecliptic normal.

PLOT LAYOUT FOR ECLIPTIC NORMAL SPIN AXIS ORIENTATION

The instruments (VIS, UVI, PIXIE and SEPS) on the despun platform can only be operated when at least one of the Earth horizon sensors detects an Earth chord of sufficient width (~8 degrees). The purpose of this plot is to indicate when imaging is possible, the command status of the horizon sensors, and what object is being imaged (Earth, Moon, Jupiter or Saturn).

Earth Horizon Sensor 1 = HSA1

Earth Horizon Sensor 2 = HSA2

• Top panel: earth chords in degrees are plotted, black-HSA1, orange-HSA2. The black line at 8 degrees is for reference only.
• Second panel from Top: blue/yellow-green squares are HSA 1 and 2 field of view (fov) in degrees with respect to the spin plane, when the Earth chord is greater than 8 degrees. The spin plane is at zero degrees. The yellow-green boxes are the fov of the horizon sensors, while the blue boxes are the fov of the Sun sensor surrounding (not to be confused with the spacecraft's Sun sensors) each horizon sensor. The orange trace indicates the sun's location, the orange asterisks indicate when the sun is within 3 degrees of the Earth's horizon. The green trace indicates the moon's location, the blue asterisks indicate when the moon is at the horizon within 1.5 degrees.
• Third Panel from Top: is the HSA commanding, ~1 the HSA is turned on, ~0 the HSA is off. The black trace is for HSA 1, the orange trace is for HSA 2. The blue trace indicates when the platform is in maneuver mode. The dashed light-green trace indicates what science mode the spacecraft is in, 0.6 indicates science mode 1, while -0.2 indicates science mode 2.
• Bottom panel: shows when the spacecraft is in maneuver mode (black line segments) as a function of slew angle in degrees (pitch on plot). The yellow shaded region bounded by the red dashed curves is the Sun Danger Zone. During ecliptic normal configuration the imager's are always in Sun danger season. The green trace is the moon's location, and the blue trace is Jupiter's location, and the blue dashed trace in Saturn's location. The spacecraft can only be in maneuver mode when at least one of the horizon sensors is activated.

PLOT LAYOUT FOR ORBIT NORMAL SPIN AXIS ORIENTATION

The polar pointing plan plots consistent of 3 panels with orbital information at the bottom of the plot. The purpose of the top panel shows how various parameters vary thoughout the day as a function of latitude out of platform plane (see definitions). The information on this panel is independent of the bore sight pitch angle (see definitions). The middle panel shows how various parameters vary thoughout the day as a function of pitch angle in the platform plane. Obviously with the exception of the bore-sight pitch angle, the information on this panel is independent of the bore sight pitch angle. The purpose of this panel is to aid in plan development for magnetic field viewing, for avoidance of sun danger, and for the perigee pass. The lower panel is a blow up of the middle panel and its purpose is to aid in plan development for viewing the northern auroral oval.

• The black trace is bore sight pitch angle, asterisks indicate slew maneuvers.
• The red trace is the sun direction and sun danger boundaries (shaded in yellow).
• The dashed- red trace is the anti-sunward direction and the SEPS exposure boundaries ( shaded in gray).
• The blue trace is the (pitch angle, latitude) of and Earth centered dipole magnetic field direction.
• The blue dashed trace is the (pitch angle, latitude) of the anti- Earth centered dipole magnetic field direction.
• The brown trace is the location of Earth's horizon in the platform plane, it's symetric about nadir (0 degrees pitch angle).
• The green traces are the pitch angles that intersect the equatorial edge of the auroral oval, ( the middle trace is the closest approach to working definition of magnetic poles (see definitions). The Holzworth-Meng auroral oval model was used for Qindex of 6 to determine the equatorial edges of the oval.
• If two VERTICAL red lines appear on the plot, they indicate when polar is in the Earth's umbra.

Last updated on August 5, 2003