Proposed Priority Science Operations Topic

SPOT No. 8: Topic 'Observations of Comet Hale-Bopp'

Topic Description

Goal: To utilize the imagers on the Polar spacecraft to observe Comet Hale-Bopp during its closest approach to the Sun. We have a unique opportunity to observe Comet Hale-Bopp over a broad range of wavelengths from the visible to near ultraviolet to far ultraviolet to soft x-rays. It is extremely fortuitous that Comet Hale-Bopp crosses the orbital plane of the Polar spacecraft on approximately April 2, 1997. This is within a few days of its closest approach to the Earth (March 22-23, 1997) and within a day of its perihelion (April 1, 1997). As a consequence, Polar spacecraft attitude re-orientations will not be required.

Epoch/Orbit CHARACTERISTICS

For the period (Year/Day of Year) 97/086 to 97/092, the Polar platform should be pointed to allow observations of Comet Hale-Bopp for 1 hour of each orbit. These 1 hour observation periods should occur near apogee to eliminate the need for platform slews during the observation period and allow sufficient time to acquire images that can be summed to obtain maximum sensitivity. The ephemeris of Comet Hale-Bopp is available.

POLAR DATA REQUIRED

VIS will be operated to obtain a complete set of images in 11 different wavelengths during each observation period. UVI and PIXIE should be operated in the mode that is most appropriate to achieve the maximum science return.

POLAR De-Spun PLATFORM OPERATIONS

A test run to verify pointing and camera operations will occur on 97/084. Observation of Comet Hale-Bopp will begin on 97/086 and continue through 97/092. The following table contains the current plan for Comet Hale-Bopp observations with the imaging instruments on the Polar spacecraft where long - the angle between the comet(sun) direction and nadir direction projected into the platform plane lat - the angle between the comet(sun) direction and the anti-spin axis vector. NOTE: in this coordinate system UVI has a 'lat' offset of -1.46 degrees. angle sun-comet - is the angle between the comet and the sun from the Polar spacecraft viewpoint.

						    Length of     
		  				    Observation
 POLAR apogee   Comet           Sun        ANGLE    Centered on
 time        long     lat   long    lat  Sun-Comet  Apogee time 
 yydddhhmm  (deg.)  (deg.) (deg.) (deg.)  (deg.)    (minutes)	 Comments

 970840151   134.0   12.4   88.3   20.0    44.4		60	Test Run

 970860642   133.6    8.6   89.4   18.0    43.9		60  	Begin Comet 
 970870018   133.5    7.3   89.8   17.4    43.7		60	Observations
 970871757   133.2    6.1   90.0   16.7    43.5		60
 970881133   133.1    4.8   90.4   16.1    43.3		60
 970890509   133.0    3.6   90.9   15.4    43.1		30	Short run*
 970892245   133.0    2.3   91.3   14.8    42.9		30	Short run*
 970901624   132.7    1.1   91.5   14.1    42.7		60
 970911000   132.6   -0.1   91.9   13.4    42.5		60
 970920336   132.5   -1.3   92.4   12.8    42.3		30	Short run*
 970922112   132.4   -2.5   92.7   12.1    42.1		60	End Comet
								Observations

* Short runs (30 minutes as opposed to 60 minutes) are due to overall
  mission science constraints.

A plot of the comet latitude vs. DOY is available.

Investigator: John B. Sigwarth
The University of Iowa
Department of Physics and Astronomy
Iowa City IA 52242-1479
319-335-1867