Since the first V2 rocket sailed above the Kármán line back in 1944 and right up until the modern era, the trajectory of most space-bound rockets was more or less the same: after expending their propellants they would either crash into some desolate steppe or plunge into the ocean. In either event, the rocket was disposable. The important bit up top might go on to explore the stars or send a human crew off on their mission, but the booster rocket that lifted the spacecraft out of the atmosphere was always going to be sacrificed for the cause.

But in the 1970s NASA had a wild idea: what if we didn’t smash a brand-new rocket valued at millions of dollars into the ocean every time we wanted to put something in orbit? Instead, they would build a hybrid space vehicle that blended the vertical takeoff and raw power of a rocket with the capabilities of an airplane, allowing it and whatever it was carrying to make a gentle runway landing at the end of its mission. As such, the Space Shuttle was born.

With the benefit of hindsight, we now know the Shuttle wasn’t quite the spaceflight revolution that NASA had hoped for. The age of reusable rockets didn’t truly begin until 2015, when SpaceX landed the first stage of their Falcon 9. To date they’ve repeated the feat nearly 600 times, all the while increasing the reliability and speed of their operations. Today the Falcon 9 is the most prolific launch vehicle in history, and nearly every other rocket in active development is being designed to include some element of reusability.

Most recently, China demonstrated that they could recover their Long March 10B rocket by gently bringing it down into what amounts to a giant butterfly net. While it might seem a bit quaint compared to rockets that land on their tails like something out of a 1950s sci-fi movie, the idea offers considerable promise.

There and Back Again

But why did it take 70+ years before we were able to regularly refly orbital-class rockets? It’s not that there’s anything inherently complex about reusing a spent rocket. Sure, there’s a case to be made that material science improvements have made the engines robust enough for repeated use. But even if you had to rebuild the engines after each flight it would still be better than slamming the whole vehicle into the ocean. Similarly, there’s nothing particularly unique about the structure of the Falcon 9 that enables it to fly multiple times — it’s a big metal tube with tanks inside of it, just like essentially every rocket that has flown before it.

The revolutionary technology demonstrated by SpaceX in 2015 didn’t have anything to do with making their rocket go up, it was that they were able to safely bring it back without damaging or physically altering it. The Falcon 9 first stage that came back to Earth was in the same condition it was when it left the launch pad eight minutes or so earlier, albeit with empty propellant tanks and a layer of soot on the outside.

As such, most of the variability we see when comparing the reuse of past, present, and future rockets comes not from how the vehicle ascends, but how it ultimately comes to rest back down on Earth.

Splashdown is Easy, But Rough

Without question, the easiest way to recover a rocket intact is to simply slow it down before it hits the surface of the ocean using parachutes This is how all American crewed capsules, and more applicably the Space Shuttle’s Solid Rocket Boosters (SRBs), have been recovered after their flights.

But even when descending under multiple huge parachutes, splashdown isn’t exactly a gentle event. It could probably best be described as “survivable”, in that the vehicle and crew will come through the experience in one piece, but neither is likely to be terribly happy about it.

The situation of course ends up being even worse for the rocket, as its structure is going to be subjected to the brunt of the impact force. Additionally, a complex aerospace vehicle getting partially submerged in salt water is a recipe for corrosion and electrical issues, to say nothing of the thermal shock the hot engines will experience when getting dunked.

One could argue that the only reason this method of recovery worked for the Shuttle SRBs is because of their relative simplicity when compared to a liquid-fueled rocket capable of independent flight. At the risk of oversimplifying the structure of the SRB, at splashdown it was effectively a hollow tube with minimal avionics and thrust vector control (TVC) hardware that could simply be replaced before the next flight.

Still, the NASA document Solid Rocket Booster (SRB) Refurbishment Practices goes over the considerable work required to bring each booster back to flight status after coming down in the ocean. Given the challenges of refurbishing the boosters, it’s perhaps unsurprising that NASA elected to forgo their reuse on the Space Launch System despite its SRBs being largely identical to their Shuttle predecessors.

Teaching Rockets New Tricks

In the very early days, while they were still trying to reach orbit with the Falcon 1, SpaceX had actually considered a Shuttle SRB-style recovery procedure. But in the end they decided to outfit the Falcon 9 with deployable landing legs and the rest, as they say, is history.

Landing legs allow a rocket to come down on effectively any flat surface, be it a concrete pad next to the launch facility or a floating platform. But there are some fairly serious drawbacks to this approach. For one thing, the requirement for precise terminal guidance means parachutes are out of the question. The rocket needs fins, attitude thrusters, or other control surfaces to come down on the center of the pad.

It also means the rocket needs to perform a propulsive landing. That is, use its own primary engines to bring its velocity on touchdown to as close to zero as possible. This in turn requires engines that can not only restart in flight — a capability that has not traditionally been required by first stage boosters — but are able to throttle down low enough to control the rocket’s descent without simply pushing it back upwards. It’s difficult to overstate how unnatural a state of operation this is for a rocket. Indeed, it’s the antithesis of how nearly every rocket has operated since the Song Dynasty started experimenting with gunpowder in the 10th century.

Even if you can accomplish all that, the true cost of landing a rocket is in the extra mass. Although the legs will be stowed away and unused for 99.8% of the rocket’s flight time, it still has to lug all that weight uphill. If that wasn’t bad enough, there’s also the extra weight of whatever control mechanism is in place to guide the rocket’s descent trajectory as well as the propellant that needs to be kept in reserve for the landing burn.

All told, landing a rocket on legs comes with a massive payload penalty. In the case of the Falcon 9, the rocket’s maximum capacity to Low Earth Orbit (LEO) in its expendable configuration is approximately 22,800 kg (50,300 lb). But when outfitted with the hardware necessary to land, that number is reduced by nearly 25% to 17,500 kg (38,600 lb).

Dropping the Dead Weight

There was a time, not so very long ago, when critics doubted the financial viability of recovering and reusing rockets like the Falcon 9. But today, reuse has gone from theoretical to standard operating procedure. Outside of a few Old Space holdouts, it’s top of mind for every launch provider and critical for remaining competitive in a fast-moving commercial market. In November, Blue Origin even managed to land their New Glenn heavy-lift rocket on only its second flight.

So at this point the question isn’t whether or not future rockets will be reusable, but rather, what is the most efficient way to achieve that reusability?

With that in mind, it’s easy to see the appeal of China’s net recovery. While the rocket must still perform a propulsive descent — although in theory the necessary positional accuracy, and therefore the technical challenge, is somewhat reduced — it doesn’t need to have landing legs installed. This mass savings increases the vehicle’s useful payload capacity, which in turn makes it more profitable to operate. Achieving the same end goal while being easier and cheaper is an improvement in anyone’s book.

Admittedly, having the rocket come down in a huge net adds a certain amount of whimsy to the whole endeavor, but the overall logic is sound enough. It should also be said that SpaceX, for all the success they’ve had with landing their Falcon 9 on a set of deployable legs, are themselves planning on catching both the first and second stages of their next-generation Starship vehicle. Instead of a net, their goal is to pluck the rocket out of the air with a huge robotic pincer mechanism.

One is reminded of the old joke about how the Americans and Russians approached the problem of writing in space: NASA spent millions of dollars developing a pen that would work in microgravity, while their Russian counterparts simply used pencils. If China can demonstrate the ability to reuse a rocket they snagged in their net, the more elaborate methods of recovery employed by American rockets may one day look like a similarly overengineered solution.

Having the information shown on the display of a digital multimeter also recorded off-screen can be incredibly useful, but unless the device exposes something like SCPI on a network interface, you will have to get creative. In the case of the budget ANENG AN870 digital multimeter (DMM), [Bits und Bolts] really wanted to show its display clearly as an overlay in OBS instead of just the camera view, but with said DMM not offering an easy way he had to resort to just copying the data sent to its multiplexed LCD.

The GitHub project page contains the background information, as well as the instructions if you too have this DMM. It might of course also be useful as the jumping off point for your own DMM modification. In total the project requires three modules: an RP2040 Zero and HC-12 433 MHz transceiver on the DMM side, and another HC-12 plus ESP32-C3 module on the receiving side. A boost module is also added to generate 3.3 V out of the 2.4 V – 3 V provided by the meter’s two AA cells.

To be able to read the LCD signal lines, a custom PCB was created that is installed inside the DMM. With the LCD’s segments mapped, this meant being able to send a perfect copy of the display’s state to the ESP32-C3 and from there making it available via WiFi.

WHOOP does not have the presence in the wearable space as other brands, but in certain circles, it’s a household name. Their business model requires you to have a yearly app subscription to use their fitness tracker, but here at Hackaday, we are big fans of actually owning the devices you buy — which is why we were happy to hear about an open source and subscription free WHOOP compatible app!

The goal of the so-called OpenStrap project is not to re-create the WHOOP app. Rather, the algorithms and processing methods are developed from scratch, based on public research. It’s all calculated locally on a 1 Hz interval, based on the data the WHOOP 4.0 device feeds the app. As such, the health data collected from the watch, never leaves the phone. While not the main goal of the project, the privacy improvement of the app’s serverless nature cannot be overstated. However, to display metrics, you first need to get data off the WHOOP to begin with.

The crux of the issue with making the WHOOP 4.0 work without the official app is the reliance on proprietary Bluetooth protocols. Fortunately, the protocol itself ended up being relatively simple. The WHOOP 4.0 amounts to little more than a series of sensors that sit on the user’s wrist. As such, the app can subscribe to the Bluetooth feed and decode the data, right? Well, the devil is always in the details with such things, and the protocol came with its fair share of quirks. The hardware clock needs to be synchronized, or it simply defaults to zero Unix time. Moreover, the analog sensors like, ambient temperature are given in relative ADC values, and are not terribly useful without calibration. Regardless, the result of the reverse engineering effort speaks for itself with the OpenStrap app able to recreate much of the functionality in WHOOP’s official app.

Quite often, devices reliant on proprietary apps are little more than manufactured e-waste. While we don’t expect many of you to actually own a WHOOP 4.0, we do hope to see the OpenStrap project keep at least a few out of the landfill in the future.

Having a pump in a remote location where you aren’t constantly monitoring it is a common scenario, which can be unfortunate when said pump runs into problems like a dry well, jammed impeller or power issues. This is where pump monitors like the older SymCom (now Littelfuse) PumpSaver Plus 233P will protect the pump if such conditions are detected. Of course, the infrared communication port on it uses an undocumented protocol that was meant to be used with a long-since discontinued handheld device. Ergo [Elizabeth Camporeale] saw fit to reverse-engineer this protocol.

In the installation manual for this device this Informer unit is briefly mentioned along with the information it will display on its screen, making it clear that it’s quite literally just there to act as a display for the information that’s constantly generated on this interface. Naturally, this is incredibly useful if you wish to tie the system into a wider monitoring and automation system.

Somewhat unusual, this IR interface on the used 233P-1.5 unit turned out to be use a 5,000 baud NRZ, MSB-first protocol, with the juicy details fully documented and a Python-based decoder implementation provided.

Naturally [Elizabeth] didn’t just reverse-engineer this for the fun of it, but also for ESPHome integration. This uses a setup as can be seen in the top image, with an ESP32-C6 module providing the processing power and Wi-Fi, with a standard phototransistor recording the data pumped out by the pump monitor.

Even with Amazon’s Echo Show devices running Linux in the form of the Android-derived FireOS, using them for non-Amazon approved purposes can be a chore at best. In the case of the Echo Show 8 even simple workarounds using ADB and the bootloader have been locked-down, requiring more drastic measures. Here [Vowed] over at the XDA forums shows off one such hack, involving directly tapping into the device’s eMMC.

Suffice it to say that this is not a hack for the faint of heart, with even the iFixit teardown guide for this device being rather daunting. Even after you get access to the mainboard, you still have to remove or cut open the metal can that covers the eMMC, so that you can unleash an eMMC programmer on it. It’s best to make sure to make a backup image of the original contents too, just in case you have to restore things.

With the shield out of the way you can solder fine wires to pads that connect to the eMMC to program it. You also have to solder wires to pads for the UART, though if you’re fancy you can also create a custom pogo pin adapter. With a serial connection established to the original firmware you can then enable features like ADB, and courtesy of the connected eMMC adapter it’s possible to directly alter system files to make rooting as easy as possible.

In addition to rooting the system you can also do a straight replacement of the eMMC contents, such as the demonstrated Debian installation. Even if not the most easy of mods, it’s good to see that it’s possible to repurpose these devices.

(Top image: Amazon Echo Show 8 3rd generation mainboard. Credit: iFixit, CC BY-NC-SA 3.0.)

Sold by German DIY store OBI, the OBI Energy Tracker is a €15 set of two devices, one of which you essentially stick on top of your existing electricity meter. This then allows for electricity usage to be measured and tracked, with the data sent to the second, gateway device. This latter cloud-bound device is linked to an OBI account via the heyOBI app. This correspondingly called for the gateway device to be reverse-engineered and freed from its cloud-based shackles, a task that [Aaron Christophel] happily took upon himself.

The whole process is also covered in two videos, with the first providing all the essentials on reprovisioning the original firmware for a local MQTT server in English, while the second, German-language video focuses on custom firmware for the ESP32-C3 inside of the gateway device.

Inside the reader device is a Cortex-M0+-based BAT32G135 MCU that communicates with the meter via its IR protocol. This is then communicated via 868 MHz LoRa to the gateway device that will be placed somewhere within Wi-Fi reach by the user. Inside this latter device is as mentioned the ESP32-C3, which by default runs firmware that communicates via secure MQTT with an AWS cloud instance for the typical cloud-based shenanigans.

The aforementioned reprovisioning option doesn’t require firmware flashing, just a handful of steps to follow. This involves fetching the 32-bit TEA key, generating your own PKI, running your own MQTTS-capable broker and having the provided Python script handle the rest from there.

Flashing custom firmware is the other option, with straightforward UART/JTAG reflashing sadly disabled by the manufacturer. With the effort required here you could perhaps argue that simply connecting the reader device to a custom gateway device might be a lot easier, especially if you already have a LoRa transceiver and associated hardware.

Watching [sprite_tm]’s build of a handheld 486-based gaming computer, we got to thinking about retro computers and the eternal questions of how much of the computer needs to be actually “old” for it it be retro. Where is the soul of a retro computer? The CPU? The old yellowing plastic case? Maybe it depends on what you’re trying to get out of the hobby.

There is of course a spectrum of people playing around with old computers. For some people, let’s call them “vintage computer enthusiasts”, half of the fun is in keeping the actual old hardware running. This group tends to know what teletype lubricant smells like, and how to tell which capacitors need replacing.

For others, “team retro”, the joy is in using the machine itself, whether that be teaching the old dogs new tricks, or simply loading up nostalgic video games. Team retro is more content with emulations or emulations that are wrapped up neatly in hardware workalikes. They know which registers need POKEing, and whether or not Commander Keen is running at the right framerate.

I think [sprite_tm]’s project falls in with yet another camp, the retro-reengineers. Here, the idea is to step through the engineering lessons of the past by re-designing something from a bygone era. So when [sprite_tm] went with a period 486 CPU backed up by a modern FPGA, perhaps ironically borrowing code from the modern MiSTer project, it makes sense for his goals. Retro-reengineers know the bus architecture and the memory timings, and they are reinventing the wheel as a learning experience. Or in the case of [Voja Antonic]’s imaginary four-bit machine, it’s a teaching experience.

How you work often reflects what you’d like to get out of the project, and at Hackaday, of course, we love all of the above! We’ve identified at least three broad schools of fooling around with old computers. Are we missing any?

Many of us remember back in our school days taking tests and filling out answers on a Scantron sheet, those long rows of A, B, C, D, and E that had to be filled in with a #2 pencil. Ever wonder why it needed a #2 pencil, or what the point of using a Scantron was at all? That question is answered in the latest video from [SimonRetro], where he takes a look at the Scantron and how it works.

One of the more interesting things about the Scantron is that it’s such a standalone device. No software needed, no keypad to mess with just two rocker switches. The on/off switch is also the way you tell it to forget the last answer sheet and allow you to program in a new test. Upon booting, you feed in a Scantron sheet with some specific boxes filled in, and then it’s programmed and ready to take in and grade all the students’ answers. Opening up the Scantron reveals it’s pretty interesting inside: one control board with early-’90s-era chips. There’s also a lightbulb (no LEDs) shining through the six reading sections of the card, as well as an arrangement of belts and motors to move the card through the machine. The printer is a seven-pin printer used in conjunction with a pair of ink rollers to print out the results on the cards.

[SimonRetro] also went ahead and tried different ways to mark the sheets including pens, Sharpies, colored pencils, and different thicknesses of pencils besides the #2 to see which would and wouldn’t work in the Scantron. Thanks [SimonRetro] for exploring this machine from many of our childhoods and sharing its inner workings. Be sure to check out some of our other reverse engineering articles that explore how classic devices work.