Guidance of a Moon lander: PID-based vs TGO-based

As part of my Moon lander guidance software, I am making several small prototypes for each subsystems, in order to test ideas, learn and choose the best option. While I progress on the overall project, I have already learned a lot of things and wanted to share some of them. In this article, I will talk about how to control the altitude and vertical velocity of a spacecraft in order to guide it to a soft landing. Read the 3910 words...

Symbolic maths in Python: Attacking a castle with SymPy

While working on my Moon lander guidance software, I am making several small prototypes to test ideas. One of them involves testing several control laws (of the acceleration), which implies quite a lot of manual calculations (to integrate to obtain the velocity and position). Doing these calculations by hand is tedious and error prone, and I thought about using a symbolic math program. Usually, a programming language can not manipulate variables without predefined values, but I found a Python library which can: SymPy. Read the 2027 words...

Software quality notes: nested "for" loops considered harmful

While working on Exomars as a software engineer, I was notified an issue to fix. I thought it was an interesting one, and spent some moments to think about how it could have been prevented in the first place. I care about code quality, and always try to build reliable software. For this purpose, I do not believe in rockstar developers (we are all fallible humans), but rather in (automatically enforced) processes and tools. Read the 1135 words...

Guidance software of a Moon lander: preliminary study

I have always struggled during my control theory classes, and almost failed one (out of the three I attended). With this history, some people would have developed a hatred for this subject, but I personally felt in love with it: I have always found it magical to be able to control physical things with software. I love making a pile of silicon1 do things by itself, and developing control algorithms makes it possible to build robots and other automated machines. Read the 2516 words...

Hello World with Rust and WebAssembly

For the second part of my Rust & WebAssembly journey, I will write a basic hello world project. Note: you can jump to the demo by clicking here. This will give me the opportunity to demonstrate how to write a simple Wasm module in Rust. I will focus on a simple frontend and ignore the backend: no complicated GET or POST requests, no websockets, etc. This article will present how to build a simple game, such as Matt’s Pont. Read the 3047 words...

Introduction to Rust and WebAssembly

In this article, I would like to talk about two technologies I’ve been playing with recently: the Rust programming language and the WebAssembly standard. I’ll start by presenting each of these two technologies and which problems they are trying to solve. Then, I’ll explain what are the advantages of a Rust-powered Wasm module, and why it can be useful. Finally, I’ll provide links to interesting documentation. WebAssembly Since many years, client side web applications, implemented in JavaScript, have been becoming larger and larger. Read the 1227 words...

"Too much precision" bug

Introduction Context I am currently working on the Rosalind Franklin rover, part of the Exomars 2022 mission to Mars. I develop a software layer to integrate the autonomous navigation algorithms (developed by CNES) with the hardware rover (built by Airbus). CNES has been working on image processing algorithms to give some autonomy to robots. Their expertise is being used, among other projects, in Exomars. Airbus is developing the actual rover, and has defined some APIs to be exposed to allow executing CNES’s algorithms. Read the 2833 words...

Calculating the distance to the Moon

On 13th sept 2019, Pauline Acalin, a spaceflight photojournalist, posted two pictures of the Moon, taken 8.5 hours apart. Scott Manley commented “I should try measuring the distance to the Moon with this”. That’s was more than enough to get me started to attempt to do exactly this. After months of procrastination, here is finally an article with my findings and the detailed steps to reproduce them. “Rotating planets come in handy when you want to make a giant stereoscopic gif of the moon […]” - Pauline Acalin Introduction The size of the Earth will be assumed to be known. Read the 1199 words...

Flying to the moon with Apollo

About 50 years ago, humans landed on the Moon for the first time. I initially wanted to write on this subject because I like rockets and space, but this anniversary is a nice coincidence. Going to the Moon is not an easy endeavor. It requires an outstanding number of subsystems and components to work flawlessly, and many maneuvers to execute right as planned. Each time a rocket takes off, an engineering miracle happens. Read the 4558 words...

Future space articles

This article is a little teasing on future articles that I might write. After two articles on Kubernetes, I am going to switch to aerospace themed articles. Nonetheless, they will probably be fairly focused on software. Since a few years, I am getting more interested in space. Of course, I watched Scott Manley’s videos, played KSP, etc. But nowadays I like to design missions or spacecrafts with back-of-the-envelope estimations, perform computations and simulations. Read the 298 words...