Hi all -- Because of free-space path loss over the distance between Earth and Pluto, the New Horizons exploration spacecraft was only able to send data at a rate of 2 kbps.

Does anyone know what kind of compression NASA uses for New Horizons and other spacecraft?

It seems to mostly be imaging data, like the images of Pluto and its moon Charon. I'm curious if they're using something new and state of the art, or something old, and how it might be improved.

It sounds like they can upgrade their data compression codec in place:

Another exciting possibility is that we can dramatically augment New Horizons' capabilities by uploading new observing and onboard data-reduction software once the spacecraft's flyby software is no longer needed.
(From one of the mission webpages at John Hopkins University.)

Here's some data if you're interested, though it's post-decompression I think: