The General Mission Analysis Tool (GMAT) is the world's only enterprise, multi-mission, open source software system for space mission design, optimization, and navigation. The system supports missions in flight regimes ranging from low Earth orbit to lunar, libration point, and deep space missions. GMAT is developed by a team of NASA, private industry, public, and private contributors and is used for real-world mission support, engineering studies, as a tool for education, and public engagement.

A blog dedicated to observing, mostly classified, satellites.
Found on https://hackaday.io/event/192573-satellite-hunting-hack-chat

Just one of the many interesting articles written by Ken Shiriff, who also has chip photos together with detailed information about the corresponding circuit, e.g.
https://www.righto.com/2022/04/reverse-engineering-lm185-voltage.html

Found via the author's blog https://www.dl1ye.com/posts/2021-04-29-universal-lnb-biastee/ which in turn was found when searching for a bias tee.

Found via an ad, Omega is teaming with Privateer https://gothammag.com/omega-privateer-space-travel-junk-wayfinder

Digital orrery, showing planets, moons, asteroids and some spacecraft.

Review of
Eyles, Don. Sunburst and Luminary. Boston: Fort Point Press, 2018. ISBN 978-0-9863859-3-3.
http://www.sunburstandluminary.com/SLhome.html

The next blog entry is interesting as well.
https://www.fourmilab.ch/fourmilog/archives/2019-11/001848.html
Crossfield, Albert Scott and Clay Blair. Always Another Dawn. Seattle, CreateSpace, [1960] 2018. ISBN 978-1-7219-0050-3.

GMAT is designed to model, optimize, and estimate spacecraft trajectories in flight regimes ranging from low Earth orbit to lunar applications, interplanetary trajectories, and other deep space missions. Analysts model space missions in GMAT by first creating resources such as spacecraft, propagators, estimators, and optimizers.

Abstract: The Breakthrough Starshot project proposes using radiation-pressure propulsion to send multiple spacecraft in the gram-range mass to interstellar targets. There are numerous engineering challenges to accomplishing this mission, but their project discusses speeds and accelerations previously only discussed for cannon projectiles and particle physics experiments. This article examines the problem from first principles to see if the project is even orders-of-magnitude possible. A preliminary check on their numbers seems to confirm that the project is possible in principle.
https://stkwans.blogspot.com/2012/04/program-66.html is about the Apollo guidance computer.
https://stkwans.blogspot.com/2012/09/a-review-of-adxl345-and-bma180.html

Information about visual satellite observation.