As always, participation in the annual Retrochallenge begins with nostalgia for those computers whose time has come and gone; it usually ends as an exercise in masochism.
My goal, this time around, is to convince my aging Apple II Plus that it can simulate a spacecraft with some degree of fidelity. Having said that, I’m setting my sights pretty low since I’m only seeking to simulate the flight dynamics and underlying physics of ballistic and orbital flight. Unlike Kerbal Space Program or the mighty (and inscrutable) Orbiter, I’m not looking for photo-realistic graphics or high-end animation.
The core of the simulation is a data structure representing the spacecraft’s overall status at a single point in time: Three-dimensional coordinates for its present location, a set of state-vectors indicating its relative motion, and spacecraft attitude (roll, pitch, and yaw.) Other information describing the vehicle status includes its internal and external environment, fuel and oxidizer status, electrical power system status, communication parameters, and general spacecraft “health.” At the moment, I’m trying to develop a spreadsheet (in VisiCalc, of course!) that brings all this data together in a single place. From there, actual software development begins — mostly in Applesoft BASIC but may also entail 6502 assembly language and FORTRAN (if I can get the UCSD Pascal System running on real hardware.)
Here we go!