README.txt

# 42 - Spacecraft Simulation

42 is a comprehensive general-purpose simulation of spacecraft attitude and
orbit dynamics. Its primary purpose is to support design and validation of
attitude control systems, from concept studies through integration and test. 42
accurately models multi-body spacecraft attitude dynamics (with rigid and/or
flexible bodies), and both two-body and three-body orbital flight regimes,
modelling environments from low Earth orbit to throughout the solar system. 42
simulates multiple spacecraft concurrently, facilitating studies of rendezvous,
proximity operations, and precision formation flying. It also features
visualization of spacecraft attitude.

Features:

  - Multi-body dynamics (tree topology, rotational and/or translational
    joints)
  - Rigid and/or flexible bodies
  - Multiple spacecraft (prox ops, formation flying, or independent)
  - Inter-spacecraft and spacecraft-surface contact forces support landers,
    rovers, and spacecraft servicing scenarios
  - Two-body or three-body orbits, anywhere in the solar system
  - Optional visualization
  - Socket-based interprocess comm (IPC) interface to other apps
  - Fast setup for concept studies
  - Rigorous and full-featured to support full spacecraft life cycle

## Installation

If you're installing on Windows, see the files "Install-msys.txt" and "Install Ubuntu on Win10.txt" in the Docs folder.

The compiler will attempt to detect what platform you're on (Linux, OSX, or
Msys), but its success rate isn't great. If you have errors on the first
compile or run, try editing your Makefile to manually set your `42PLATFORM`.

42 supports both the GLUT and GLFW libraries, which handle the platform-specific parts of graphics processing.  There was a period of time when newer Macs with Retina displays needed the GLFW graphics libraries, but the problem with GLUT has since been fixed.  GLFW is available from MacPorts, Homebrew, and probably elsewhere.  The GLUT libraries are also readily available if not already installed on your system.  Graphics are optional, settable in the Makefile by GUIFLAG.

## Getting Started

See the overview, "42 Overview.pdf", in the Docs folder. Also recommended:

- Nomenclature.pdf
- POV Menu.pdf
- Key Bindings.txt
- FSW Models.pdf
- Flight Regimes.pdf

The default folder for inputs and outputs is "InOut". Look there for sample
input files. "Inp_Sim.txt" is the top-level input file.

The input/output folder may be changed for a sim run by running 42 with an
argument. For example, enter this at the command prompt:

    42 Demo

## Common Problems

1) 42 expects the input files to be plain vanilla text files. If your text
editor adds formatting, makes straight quotes into smart quotes, etc, 42 may get
confused. The most common symptom is generating the "Bogus input in
DecodeString" error.

2) Also text-related, 42 is very simple-minded about reading the input files.
Adding extra lines, or accidentally deleting a line, or swapping lines, will
throw things out of synch. Again, the most common symptom is the "Bogus input in
DecodeString" error. Use your debugger to trace back where the error was
generated. (The actual mistake may be at that line, or may be somewhere
upstream.)

3)  Line endings.  Natively, Windows uses CRLF, OSX uses CR, and *nix uses LF (I think I got those right...)  Text editors, etc, are better these days at tolerating unexpected line endings than they used to be, but this is something you should check if something goes awry.  For example, there are reports that git, in an effort to be helpful, might regularize your line endings.  This might cause some text files to fail being read in properly by 42 on other platforms.  One reported outcome is graphics shader code not compiling correctly, resulting in gray worlds or other graphics issues.  Something to watch for.