C/1999 S4 LINEAR
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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
detectability of NG effects in the comet's motion comet lost close to perihelion or split comet
type of model of motion GR - gravitational orbit
data weighting YES
number of residuals 2223
RMS [arcseconds] 0.63
orbit quality class 1a
orbital elements (barycentric ecliptic J2000)
Epoch 1702 08 07
perihelion date 2000 07 25.54127866 ± 0.00008163
perihelion distance [au] 0.76100540 ± 0.00000035
eccentricity 0.99998069 ± 0.00000073
argument of perihelion [°] 151.121006 ± 0.000036
ascending node [°] 83.187049 ± 0.000020
inclination [°] 149.276053 ± 0.000017
reciprocal semi-major axis [10-6 au-1] 25.37 ± 0.97
file containing 5001 VCs swarm
1999s4a7.bmi
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.
Six 2D-projections of the 6D space of original swarm including 5001 VCs. Each density map is given in logarithmic scale presented on the right in the individual panel.