UNCERTAINTY ANALYSIS
The current uncertainty analyses for the CONTOUR target comets uses actual data during the observed intervals employed for the orbit updates as well as simulated, future observations assumed to take place during favorable observing circumstances prior to the respective encounter times.  

To account for unmodeled error sources, all observations were given data noise values that have been slightly increased above the RMS values resulting from the orbital computations.  It was assumed that the transverse nongravitational parameter (A2) was included in the orbit solution but that the radial nongravitational parameter (A1) was not.  This latter parameter was then "considered." That is, the uncertainty in A1 was allowed to corrupt the uncertainties in the comet's position.  

One sigma position uncertainties are expressed in the comet-centered, rotating coordinate system (R,T,N) and in the plane-of-sky (POS) system.  The heliocentric RTN coordinate system is defined by a Sun-comet unit vector (R), a unit vector normal to R and also normal to the comet's orbit plane (N) and by a transverse unit vector (T) that completes the right handed, orthogonal system such that T = N x R.  In the plane-of-sky coordinate system, the RA and DEC coordinates lie in the plane of sky as viewed from Earth with RA pointing in the direction of increasing right ascension and DEC pointing in the direction of increasing declination.  The R vector is directed in the range direction, from the Earth to the comet. The planar uncertainty ellipses can be properly oriented in space with the angles Theta1, measured from R toward T in the RTN system, and Theta2, measured from RA towards DEC in the plane-of-sky system

The SET3 covariance matrices for the three comets are appended in Table 2.



























Table 1.  Summary of CONTOUR comet Ephemeris Uncertainties (km) for the nominal encounter times of Nov. 12.5, 2003 (2P/Encke), June 19.5, 2006 (73P/SW3) and Aug. 15.0, 2008 (6P/d'Arrest).  The given values represent 1-sigma estimates in km of the uncertainty ellipsoid axes in the particular coordinate system.
______________________________________________________________________________

RTN Coordinate System					Orbit Plane        
								Error Ellipsoid Semi Axes

			R	T	N	Major	Minor	Theta1
Encke (optical only)		174	 94	41	185	69	158 deg.

SW3 (optical only)		188	210	 33	280	35	132	
SW3 (optical & radar)		 69	 63	174 	 93	 7	138

D'Arrest (optical)		507	398	 27	641	67	142
D'Arrest (optical & radar)	 39	246	163	249	10	 81
 
______________________________________________________________________________

POS Coordinate System					Plane of sky        
								Error Ellipsoid Semi Axes

			RA	DEC	R	Major	Minor	Theta2
Encke (optical only)		143	 66	126	143	65	174 deg.

SW3 (optical only)		146	120	212	186	34	 39
SW3 (optical & radar)		 36	192	 30	194	14	100

D'Arrest (optical)		256	 74	587	265	28	165
D'Arrest (optical & radar)	230	188	 19	294	40	141