Dragon Is The Latest, And Final, Craft To Reboost ISS

September 11, 2025 by Tom Nardi 41 Comments

The International Space Station has been in orbit around the Earth, at least in some form, since November of 1998 — but not without help. In the vacuum of space, an object in orbit can generally be counted on to remain zipping around more or less forever, but the Station is low enough to experience a bit of atmospheric drag. It isn’t much, but it saps enough velocity from the Station that without regular “reboosts” to speed it back up , the orbiting complex would eventually come crashing down.

Naturally, the United States and Russia were aware of this when they set out to assemble the Station. That’s why early core modules such as Zarya and Zvezda came equipped with thrusters that could be used to not only rotate the complex about all axes, but accelerate it to counteract the impact of drag. Eventually the thrusters on Zarya were disabled, and its propellant tanks were plumbed into Zvezda’s fuel system to provide additional capacity.

An early image of ISS, Zarya module in center and Zvezda at far right.

Visiting spacecraft attached to the Russian side of the ISS can transfer propellant into these combined tanks, and they’ve been topped off regularly over the years. In fact, the NASA paper A Review of In-Space Propellant Transfer Capabilities and Challenges for Missions Involving Propellant Resupply, notes this as one of the most significant examples of practical propellant transfer between orbital vehicles, with more than 40,000 kgs of propellants pumped into the ISS as of 2019.

But while the thrusters on Zvezda are still available for use, it turns out there’s an easier way to accelerate the Station; visiting spacecraft can literally push the orbital complex with their own maneuvering thrusters. Of course this is somewhat easier said than done, and not all vehicles have been able to accomplish the feat, but over the decades several craft have taken on the burden of lifting the ISS into a higher orbit.

Earlier this month, a specially modified SpaceX Cargo Dragon became the newest addition to the list of spacecraft that can perform a reboost. The craft will boost the Station several times over the rest of the year, which will provide valuable data for when it comes time to reverse the process and de-orbit the ISS in the future.

Continue reading “Dragon Is The Latest, And Final, Craft To Reboost ISS” →

FreeCAD Foray: Good Practices

September 11, 2025 by Arya Voronova 23 Comments

Last time, we built a case for a PCB that handles 100 W of USB-C power, an old project that I’ve long been aiming to revive. It went well, and I’d like to believe you that the article will give you a much-needed easy-to-grasp FreeCAD introduction, Matrix knowledge upload style, having you designing stuff in no time.

Apart from my firm belief in the power of open-source software, I also do believe in social responsibilities, and I think I have a responsibility to teach you some decent FreeCAD design practices I’ve learned along the way. Some of them are going to protect your behind from mistakes, and some of them will do that while also making your project way easier to work with, for you and others.

You might not think the last part about “others” matters, but for a start, it matters in the ideal world that we’re collectively striving towards, and also, let’s be real, things like documentation are half intended for external contributors, half for you a year later. So, here’s the first FreeCAD tip that will unquestionably protect you while helping whoever else might work with the model later.

Okay, we’re all hackers, so I’ll start with zero-th FreeCAD tip – press Ctrl+S often. That’ll help a ton. Thankfully, FreeCAD’s autorecovery system has made big leaps, and it’s pretty great in case FreeCAD does crash, but the less you have to recover, the better. Now, onto the first tip.

Continue reading “FreeCAD Foray: Good Practices” →

FLOSS Weekly Episode 846: Mastering Embedded Linux Programming

September 10, 2025 by Jonathan Bennett 2 Comments

This week Jonathan and Dan chat with Frank Vasquez and Chris Simmonds about Embedded Linux, and the 4th edition of the Mastering Embedded Linux Programming book. How has this space changed in the last 20 years, and what’s the latest in Embedded Linux?

Continue reading “FLOSS Weekly Episode 846: Mastering Embedded Linux Programming” →

Bare Metal STM32: The Various Real Time Clock Flavors

September 10, 2025 by Maya Posch 8 Comments

Keeping track of time is essential, even for microcontrollers, which is why a real-time clock (RTC) peripheral is a common feature in MCUs. In the case of the STM32 family there are three varieties of RTC peripherals, with the newest two creatively called ‘RTC2′ and RTC3’, to contrast them from the very basic and barebones RTC that debuted with the STM32F1 series.

Commonly experienced in the ubiquitous and often cloned STM32F103 MCU, this ‘RTC1’ features little more than a basic 32-bit counter alongside an alarm feature and a collection of battery-backed registers that requires you to do all of the heavy lifting of time and date keeping yourself. This is quite a contrast with the two rather similar successor RTC peripherals, which seem to insist on doing everything possible themselves – except offer you that basic counter – including giving you a full-blown calendar and today’s time with consideration for 12/24 hour format, DST and much more.

With such a wide gulf between RTC1 and its successors, this raises the question of how to best approach these from a low-level perspective.

Continue reading “Bare Metal STM32: The Various Real Time Clock Flavors” →

The Android Linux Commander

September 9, 2025 by Al Williams 7 Comments

Last time, I described how to write a simple Android app and get it talking to your code on Linux. So, of course, we need an example. Since I’ve been on something of a macropad kick lately, I decided to write a toolkit for building your own macropad using App Inventor and any sort of Linux tools you like.

I mentioned there is a server. I wrote some very basic code to exchange data with the Android device on the Linux side. The protocol is simple:

All messages to the ordinary Linux start with >
All messages to the Android device start with <
All messages end with a carriage return

Security

You can build the server so that it can execute arbitrary commands. Since some people will doubtlessly be upset about that, the server can also have a restrictive set of numbered commands. You can also allow those commands to take arguments or disallow them, but you have to rebuild the server with your options set.

There is a handshake at the start of communications where Android sends “>.” and the server responds “<.” to allow synchronization and any resetting to occur. Sending “>#x” runs a numbered command (where x is an integer) which could have arguments like “>#20~/todo.txt” for example, or, with no arguments, “>#20” if you just want to run the command.

If the server allows it, you can also just send an entire command line using “>>” as in: “>>vi ~/todo.txt” to start a vi session.

Continue reading “The Android Linux Commander” →

FreeCAD Foray: From Brick To Shell

September 9, 2025 by Arya Voronova 18 Comments

Over a year ago, we took a look at importing a .step file of a KiCad PCB into FreeCAD, then placing a sketch and extruding it. It was a small step, but I know it’s enough for most of you all, and that brings me joy. Today, we continue building a case for that PCB – the delay is because I stopped my USB-C work for a fair bit, and lost interest in the case accordingly, but I’m reviving it now.

Since then, FreeCAD has seen its v 1.0 release come to fruition, in particular getting a fair bit of work done to alleviate one of major problems for CAD packages, the “topological naming problem”; we will talk about it later on. The good news is, none of my tutorial appears to have been invalidated by version 1.0 changes. Another good news: since version 1.0, FreeCAD has definitely become a fair bit more stable, and that’s not even including some much-needed major features.

High time to pick the work back up, then! Let’s take a look at what’s in store for today: finishing the case in just a few more extrusions, explaining a few FreeCAD failure modes you might encounter, and giving some advice on how to make FreeCAD for you with minimum effort from your side.

Continue reading “FreeCAD Foray: From Brick To Shell” →

Ore Formation Processes, Part Two: Hydrothermal Boogaloo

September 8, 2025 by Tyler August 2 Comments

There’s a saying in mine country, the kind that sometimes shows up on bumper stickers: “If it can’t be grown, it has to be mined.” Before mining can ever start, though, there has to be ore in the ground. In the last edition of this series, we learned what counts as ore (anything that can be economically mined) and talked about the ways magma can form ore bodies. The so-called magmatic processes are responsible for only a minority of the mines working today. Much more important, from an economic point of view, are the so-called “hydrothermal” processes.

Come back in a few million years, and Yellowstone will be a great mining province.
Image: “Gyser Yellowstone” by amanderson2, CC BY 2.0

When you hear the word “hydrothermal” you probably think of hot water; in the context of geology, that might conjure images of Yellowstone and regions like it : Old Faithful geysers and steaming hot springs. Those hot springs might have a role to play in certain processes, but most of the time when a geologist talks about a “hydrothermal fluid” it’s a lot hotter than that.

Is there a point on the phase diagram that we stop calling it water? We’re edging into supercritical fluid territory, here. The fluids in question can be hundreds of degrees centigrade, and can carry things like silica (SiO2) and a metal more famous for not dissolving: gold. Perhaps that’s why we prefer to talk about a “fluid” instead of “water”. It certainly would not behave like water on surface; on the surface it would be superheated steam. Pressure is a wonderful thing.

Let’s return to where we left off last time, into a magma chamber deep underground. Magma isn’t just molten rock– it also contains small amounts of dissolved gasses, like CO2 and H2O. If magma cools quickly, the water gets trapped inside the matrix of the new rock, or even inside the crystal structure of certain minerals. If it cools slowly, however? You can get a hydrothermal fluid within the magma chamber.

Continue reading “Ore Formation Processes, Part Two: Hydrothermal Boogaloo” →