Software tools for space exploration available online

Question

There are a lot of calculators, simulators, plotters, visualizers, and libraries of bits of code and models and such online. Many of us are aware of a bunch of them, and they are great learning tools and aids for projects of all kinds. So, in the spirit of other very popular posts here, I'd like to propose we collect a list of them and update it as new things are found.

In particular, like these questions:

Resources and references on the topic of space exploration

Collection of space exploration related infographics

The Resources and references list has a set of answers that split the material into sections, each of which is a community wiki (people collaborate to add material to the answer and the usual point system doesn't apply). That seems like it would be effective here too.

I started two answers, one for tools that can be used in a browser, and one for things that are downloaded for use. Possibly it would be useful to distinguish between free and for sale material too.

All resources made available on this page are user-recommended. They have not been vetted by Stack Exchange or the moderators of this site. Use at your own risk. A disclaimer about RedShell analytics software (widely considered spyware) is posted on Kerbal Space Program (KSP) below. The presence of that disclaimer is not an indication that the other resources are clean. It exists only because the community was made aware of the issue in that instance.

Answer 1

Online Tools

• NASA's Data Portal has a catalog of NASA datasets and APIs
• JPL Horizons calculates ephemerides for tracked solar system objects
• Lagrange Point Finder at orbitsimulator.com.
• Trajectory Browser from NASA Ames.
• Delta-V and Fuel calculator for transfer from LEO to MEO or GEO
• Asterank - NEOs and asteroids mining value & trajectory database from Planetary Resources.
• Satellite orbit calculator - orbital radius, period, and flight velocity from the orbital altitude.
• Stuff in Space - An interactive, searchable display of most satellites orbiting Earth, giving basic data of each satellite
• FlightClub - An orbital launch simulator and data visualizer. Example of the SES-10 Falcon 9 launch and first stage re-entry.
• QuickMap - High quality lunar maps.

Answer 2

Source Code

• Apollo 11 Guidance Computer on github.
• NASA Open Source Software from Code NASA.
• CLARAty Reusable Robotic Software from NASA JPL.
• ESA Summer of Code in Space 2016 Projects from ESA SOCIS.
• NASA API for creating applications using NASA databases
• Kubos open source satellite platform on github.

Answer 3

Mission design libraries and toolkits

These pieces of software are useful for mission design simulations. They are not standalone (but some examples may exist): they require various levels of programming to tailor to specific missions.

• SPICE, the ephemerides library by NAIF, used by NASA JPL for all their missions. In C, documentation is here. SpiceyPy provides a Python interface to SPICE.
• Basilisk, a modular C/C++ astrodynamics simulation framework with Python scripting. Likely the highest fidelity attitude control simulation, algorithms used in ADCS of the upcoming EMM mission.
• smd, a mission propagator for continuous thrusting via way-point targeting. Can also be used for statistical orbital determination given range and range-rate information. Written in Go.
• poliastro a set of Python routines for astrodynamics with an emphasis on interplanetary mission design.

Answer 4

Downloads

• Gravity Simulator at orbitsimulator.com
• Celestia space simulation software, also
  • Celestia Motherlode add-ons of spacecraft, extra-solar objects, and fictional objects for Celestia
• NASA Eyes to see what spacecraft are doing in the Solar System and beyond.
• Stellarium An open source planetarium software for showing the night sky.
• Gpredict An open source program for showing and tracking artificial satellites.
• NASA Software NASA software made available to the public for free

Answer 5

Simulator Games

• Kerbal Space Program, a space travel simulator with fairly realistic physics. It also has a ton of mods and add-ons, a very active forum, and a good wiki, all accessible here. KSP is a commercial product

D̶I̶S̶C̶L̶A̶I̶M̶E̶R̶:̶ ̶K̶e̶r̶b̶a̶l̶ ̶S̶p̶a̶c̶e̶ ̶P̶r̶o̶g̶r̶a̶m̶ ̶h̶a̶s̶ ̶t̶h̶e̶ ̶R̶e̶d̶S̶h̶e̶l̶l̶ ̶a̶n̶a̶l̶y̶t̶i̶c̶s̶ ̶s̶o̶f̶t̶w̶a̶r̶e̶ ̶e̶m̶b̶e̶d̶d̶e̶d̶ ̶i̶n̶ ̶i̶t̶,̶ ̶w̶i̶d̶e̶l̶y̶ ̶c̶o̶n̶s̶i̶d̶e̶r̶e̶d̶ ̶t̶o̶ ̶b̶e̶ ̶s̶p̶y̶w̶a̶r̶e̶.̶ ̶I̶t̶ ̶m̶a̶y̶ ̶c̶o̶l̶l̶e̶c̶t̶ ̶h̶a̶s̶h̶e̶d̶ ̶I̶P̶ ̶a̶d̶d̶r̶e̶s̶s̶ ̶i̶n̶f̶o̶r̶m̶a̶t̶i̶o̶n̶,̶ ̶o̶p̶e̶r̶a̶t̶i̶n̶g̶ ̶s̶y̶s̶t̶e̶m̶,̶ ̶s̶c̶r̶e̶e̶n̶ ̶r̶e̶s̶o̶l̶u̶t̶i̶o̶n̶,̶ ̶t̶i̶m̶e̶z̶o̶n̶e̶,̶ ̶c̶o̶m̶p̶u̶t̶e̶r̶ ̶l̶a̶n̶g̶u̶a̶g̶e̶ ̶s̶e̶t̶t̶i̶n̶g̶,̶ ̶i̶n̶s̶t̶a̶l̶l̶e̶d̶ ̶f̶o̶n̶t̶s̶,̶ ̶i̶n̶s̶t̶a̶l̶l̶e̶d̶ ̶b̶r̶o̶w̶s̶e̶r̶s̶,̶ ̶a̶n̶d̶ ̶p̶o̶s̶s̶i̶b̶l̶y̶ ̶e̶v̶e̶n̶ ̶g̶a̶m̶e̶r̶ ̶t̶a̶g̶.̶ ̶I̶t̶ ̶i̶s̶ ̶r̶e̶p̶o̶r̶t̶e̶d̶l̶y̶ ̶G̶D̶P̶R̶-̶c̶o̶m̶p̶l̶i̶a̶n̶t̶.̶

Removed in the "Kerbal Space Program 1.4.4 and Making History 1.3" Patch.

• Orbiter, also an accurate space travel simulator, but based on the real solar system and real space craft. It also has a lot of mods and add-ons, and an active forum.