Wikipedia's Long Range Reconnaissance Imager says that LORRI is a:
...telescope aboard the New Horizons spacecraft for imaging. LORRI has been used to image Jupiter, its moons, Pluto and its moons, and Arrokoth since its launch in 2006. LORRI is a reflecting telescope of Ritchey-Chrétien design, and it has a main mirror diameter of 20.8 cm (8.2 inches) across. LORRI has a narrow field of view, less than a third of a degree. Images are taken with a CCD capturing data with 1024 × 1024 pixels. LORRI is a telescopic panchromatic camera integrated with the New Horizons spacecraft, and it is one of seven major science instruments on the probe. LORRI does not have any moving parts and is pointed by moving the entire New Horizons spacecraft.
Later in design it says:
The design can take images at very low light levels required for the mission, including light levels 1/900 those of Earth when it is at Pluto. For the Arrokoth encounter the longest exposure time (up to ten seconds for the Pluto flyby) was increased. This was accomplished after the Pluto flyby by the team, to support taking images in even lower light levels.
After the Pluto flyby, exposure times of at least 30 seconds were made possible, which was also useful for taking reconnaissance images and enabling imaging down to a magnitude of 21.
LORRI is pointed by moving the entire spacecraft, which limits the exposure time. The spacecraft does not have reaction wheels and is stabilized by thrusters.
Seeing a +21 magnitude star with a 20.8 cm telescope will require a long exposure time as mentioned. I am surprised that thrusters alone can stabilize this spacecraft and therefore this telescope so well without the use of any other attitude control system.
Unlike the push-broom cameras popular on some deep space spacecraft that use slow spacecraft rotation to scan their 1D CDD across a field for imaging purposes, LORRI is a "normal" 2D CCD camera and so requires steady pointing during an exposure.
Question: How (the heck) can thrusters alone stabilize New Horizons well enough to take high magnification 30 second long exposures in order to see +21 mag. objects?
Are there any special tricks to this? Perhaps firing opposite thrusters for very slightly different times rather than trying to fire only one for a very short time? Are there any other sources of torque that are used to fine-null any rotation during the up to 30 second long exposures?
From Wikipedia's [New Horizons; Propulsion and attitude control] (https://en.m.wikipedia.org/wiki/New_Horizons):
There are 16 thrusters on New Horizons: four 4.4 N (1.0 lbf) and twelve 0.9 N (0.2 lbf) plumbed into redundant branches. The larger thrusters are used primarily for trajectory corrections, and the small ones ... are used primarily for attitude control.