natep

To answer your question about software upload, the PSP has 3 redundant CPUs (primary, hot spare, backup spare), and each has multiple boot images. To upload software, the team uploads it to an inactive image of the backup spare CPU, promotes it to hot spare for long enough to collect the data it needs, reboots it into the new image, and then rotates it into the primary role, which is a seamless transition unless something goes wrong, and then the new hot spare takes over again within a second. Once they're sure the software is working, they can update the other CPUs. Before any of this, new software is tested on identical hardware set up on the ground with physics simulations.

> See the "Guidance and Control" and "Communications" section of the NH > Spacecraft Systems page for a detailed answer. > > The short version is that it uses a combination of star trackers and IMUs > (Inertial Measurement Units). The star trackers analyze pictures of the > surrounding star field to determine how it is pointing instantaneously, and > the IMUs track how it is rotating in between each of those instants. This > determines the attitude (which way it is pointing). > > For position determination, "ranging" tones are sent from the earth and > echoed back by the craft. This combined with the angle that the dish is > pointing at to get the strongest signal tells the operators where the craft > is in space. This information is fed back to the craft, which has an on- > board physics simulation, and predicts where it will be until the next > ranging event. > > Now, you might have noticed that I didn't mention Pluto once. That is > because this system (minus the exact details) is used by pretty much every > spacecraft, from those around Earth, to New Horizons, and beyond.

As far as the final approach goes, the core sequence started July 7[1], and no adjustments were made to it. They even had a TCM opportunity before that in case of a possible collision, that I heard was skipped.