ISS / SL-12 DEB avoided close encounter - 2020-07-03

On July 3, 2020 the ISS performed an unscheduled reboost (please, see ISS reboosts).
According to the book The International Space Station: Operating an Outpost in the New Frontier, page 145, a DAM must be performed when there is a sufficiently high probability that a debris penetrates an imaginary box of space around the ISS, usually called "pizza box".
An exhaustive search across the entire Space-Track.org catalog detected a very high risk of a potential collision with the SL-12 DEB object (NORAD id 27923).


Here's the trajectories of the SL-12 debris in the ISS-Centered TEME frame (the +Z axis points in the direction of the true Earth's north pole).
The yellow circle represents the ISS and the black lines represent the SL-12 DEB predicted trajectories calculated with the CSpOC's SGP4 library and the TLEs listed in the table at the bottom.

The popup label that appears when you hover the mouse over the trajectories shows the UTC time (the date is July 3) and the distance between the objects (km).

Here's the same graph as above, but in the ISS-Centered RIC frame (the ISS velocity vector is almost exactly coincident with the +I axis).
The semi transparent red box represents the pizza box. The graph clearly shows that without a corrective maneuver, SL-12 DEB would have severely violated the pizza box.


Here's the list of the TLEs used for the calculations and the values obtained with the CSpOC's SGP4 library.

Explanation of the columns

UTC: time of the minimum distance between the two objects;
TLEISS and TLESL12 [DoY]: TLE used for the calculations;
Dmin [km]: minimum distance between the two objects;
Drad [km]: radial distance between the two objects at the time of the closest approach; it's the difference between the magnitude of the two radius vectors (Drad < 0 means that SL-12 DEB is below the ISS);
Rel spd [km/s]: relative speed between the two objects;
AgeISS and AgeSL12 [hours]: difference between the time of the closest approach and the TLE epoch.

There are 130 rows and 87 of them (67%) violate the pizza box.

The average values are: UTC = 2020-07-03 18:28:09.155, Dmin = 2.3 km and |Drad| = 415 m.