C/1999 S4 LINEAR
more info
Comet C/1999 S4 was discovered on 27 September 1999 with Lincoln Laboratory Near-Earth Asteroid Research project, that is 10 months before its perihelion passage. It was observed until 31 July 2000.
It was the first Oort Cloud comet to have been captured by the Hubble Space Telescope during its fragmentation process. Nucleus decay started around 5/6 July 2000 after the comet first brightened because of its violent outburst, and many chunks were then observed along its orbit. Around 20 July, the comet brightened once again and the main component finally started to disintegrate three days later.
Therefore, preffered solution given here is based on pre-perihelion data spanning over 0.770 yr in a range of heliocentric distances from 4.33 au to 0.861 au (5 July 2000).
Comet had its closest approach to the Earth on 22 July 2000 (0.372 au), 4 days before perihelion passage.
This was Oort spike comet.
See also Sekanina 2019 and Królikowska 2020

solution description
number of observations 1116
data interval 1999 09 27 – 2000 07 05
data arc selection data generally limited to pre-perihelion (PRE)
range of heliocentric distances 4.33 au – 0.77au
type of model of motion NS - non-gravitational orbits for standard g(r)
data weighting YES
number of residuals 2221
RMS [arcseconds] 0.57
orbit quality class 1b
orbital elements (heliocentric ecliptic J2000)
Epoch 2000 08 04
perihelion date 2000 07 26.17152264 ± 0.00091088
perihelion distance [au] 0.76514526 ± 0.00000487
eccentricity 0.99953226 ± 0.00003237
argument of perihelion [°] 151.049212 ± 0.000916
ascending node [°] 83.194208 ± 0.000806
inclination [°] 149.38983 ± 0.000161
recip semi-major axis [10-6 au-1] 611.30 ± 42.30
Upper panel: Time distribution of positional observations with corresponding heliocentric (red curve) and geocentric (green curve) distance at which they were taken. The horizontal dotted line shows the perihelion distance for a given comet whereas vertical dotted line - the moment of perihelion passage.
Lower panel (panels): O-C diagram for this(two) solution (solutions) given in this database, where residuals in right ascension are shown using magenta dots and in declination by blue open circles.
non-gravitational parameters
A1 [10-8au/day2] 9.3198 ± 0.5227
A2 [10-8au/day2] -0.95107 ± 0.24266
A3 [10-8au/day2] 0.84772 ± 0.2097
m -2.15
n 5.093
k -4.6142
r0 [au] 2.808
α 0.1113