Engine Trouble Delays SpaceX’s Return To The ISS

October 27, 2020 by 20 Comments

A crewed mission to the International Space Station that was set to depart from Kennedy Space Center on Halloween has been pushed back at least several weeks as NASA and SpaceX investigate an issue with the company’s Merlin rocket engine. But the problem in question wasn’t actually discovered on the booster that’s slated to carry the four new crew members up to the orbiting outpost. This story starts back on October 2nd, when the computer aboard a Falcon 9 set to carry a next-generation GPS III satellite into orbit for the US Space Force shut down the engines with just two seconds to go before liftoff.

The fact that SpaceX and NASA have decided to push back the launch of a different Falcon 9 is a clear indication that the issue isn’t limited to just one specific booster, and must be a problem with the design or construction of the Merlin engine itself. While both entities have been relatively tight lipped about the current situation, a Tweet from CEO Elon Musk made just hours after the GPS III abort hinted the problem was with the engine’s gas generator:

As we’ve discussed previously, the Merlin is what’s known as an “open cycle” rocket engine. In this classical design, which dates back to the German V-2 of WWII, the exhaust from what’s essentially a smaller and less efficient rocket engine is used to spin a turbine and generate the power required to pump the propellants into the main combustion chamber. Higher than expected pressure in the gas generator could lead to a catastrophic failure of the turbine it drives, so it’s no surprise that the Falcon 9’s onboard systems determined an abort was in order.

Grounding an entire fleet of rockets because a potentially serious fault has been discovered in one of them is a rational precaution, and has been done many times before. Engineers need time to investigate the issue and determine if changes must be made on the rest of the vehicles before they can safely return to flight. But that’s where things get interesting in this case.

SpaceX hasn’t grounded their entire fleet of Falcon 9 rockets. In fact, the company has flown several of them since the October 2nd launch abort. So why are only some of these boosters stuck in their hangers, while others are continuing to fly their scheduled missions?

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Going For The Home Run Record With Explosive Help

October 27, 2020 by 6 Comments

The baseball home run distance challenge for crazy engineers is really heating up, with the two main (only?) competitors joining forces. [Shane] of [Stuff Made Here] and [Destin] of [Smarter Every Day] did a deep dive into [Shane]’s latest powder charged baseball bat, designed to hit a ball 600+ feet.

[Shane] built two new versions of his bat this time, using the lessons he learned from his previous V1 and V2 explosive bats. It still uses blank cartridges, but this time the max capacity was increased from three to four cartridges. For V3 a section of the bat was removed, and replaced with a four-bar linkage, which allowed the entire front of the bat to move. The linkage integrated a chamber for four blank cartridges that could be loaded almost like a double barrel shotgun and closed with a satisfying snap. Unfortunately the mass of the moving section was too much for the welds, and the entire front broke off on the first test, so the design was scrapped.

V4 returned to the piston concept of the initial version, except V4 contains two parallel pistons, in a metal bat, with a larger hitting surface. With two cartridges it worked well, but parts started breaking with three and four, and required multiple design updates to fix. [Destin] covered the physics of the project and took some really cool high speed video. He and [Jeremy Fielding] hold the current distance record of 617 ft with their crazy Mad Batter. Unfortunately on [Shane]’s final distance attempt the bat broke again, and the ball was lost in a field with tall grass beyond the 600-foot mark, so they could not confirm if the record was actually broken.

[Destin] and his team still remain the undisputed baseball velocity record holders, with their supersonic baseball canon. It sounds like there might be another collaboration between [Destin] and [Shane] in the future, and we’re definitely looking forward to the results of that crazy venture. Continue reading “Going For The Home Run Record With Explosive Help” →

Low-Tech Fix Saves Expensive, High-Tech TV From Junk Pile

October 27, 2020 by 67 Comments
Wiggling this connector caused the backlight to turn off and on.

[Tweepy]’s TV stopped working, and the experience is a brief reminder that if a modern appliance fails, it is worth taking a look inside because the failure might be something simple. In this case, the dead TV was actually a dead LED backlight, and the fix was so embarrassingly simple that [Tweepy] is tempted to chalk it up to negligently poor DFM (design for manufacture) at best, or even some kind of effort at planned obsolescence at worst.

What happened is this: the TV appeared to stop working, but one could still make out screen content while shining a bright light on the screen. Seeing this, [Tweepy] deduced that the backlight had failed, and opened up the device to see if it could be repaired. However, the reason for the backlight failure was a surprise. It was not the power supply, nor even any of the LEDs themselves; the whole backlight wouldn’t turn on because of a cheap little PCB-to-PCB connector, and the two small spring contacts inside that had failed.

The failed connector, once cut open, showed contacts in poor condition (click to enlarge). It was ditched for a soldered connection, and the TV lived again.

From the outside things looked okay, but wiggling the connector made the backlight turn on and off, so the connection was clearly bad. Investigating further, [Tweepy] saw that the contact points of the PCBs and the two little conductors inside the connector showed clear signs of arcing and oxidation, leading to a poor connection that eventually failed, resulting in a useless TV. The fix wasn’t to clean the contacts; the correct fix was to replace the connector with a soldered connection.

Using that cheap little connector doubtlessly saved some assembly time at the factory, but it also led to failure within a fairly short amount of time. Had [Tweepy] not been handy with a screwdriver (or not bothered to investigate) the otherwise working TV would doubtlessly have ended up in a landfill.

It serves as a good reminder to make some time to investigate failures of appliances, even if one’s repair skills are limited, because the problem might be a simple one. Planned obsolescence is a tempting doorstep upon which to dump failures like this, but a good case can be made that planned obsolescence isn’t really a thing, even if manufacturers compromising products in one way or another certainly is.

Inside The Top Secret Doughnut: A Visit To GCHQ

October 26, 2020 by 31 Comments

There’s an old joke that the world’s greatest secret agent was Beethoven. Didn’t know Beethoven was a secret agent? That’s why he was the greatest one! While most people have some idea about the CIA, MI6, and the GRU, agencies like the NRO and GCHQ keep a much lower profile. GCHQ (Government Communications Headquarters) is the United Kingdom’s electronic listening center housed in a 180 meter round doughnut. From there they listen to… well… everything. They are also responsible for codebreaking and can trace their origin back to Bletchley Park as well as back to the Great War. So what’s inside the Doughnut? National Geographic managed to get a tour of GCHQ and if you have any interest in spies, radios, cybersecurity, or codebreaking, it is worth having a look at it.

Of course, only about half of the GCHQ’s employees work in the Doughnut. Others are scattered about the UK and — probably — some in other parts of the world, too. According to the article, GCHQ had a hand in foiling 19 terrorist attacks, arresting at least two sex offenders, and prevented about £1.5 billion of tax evasion.

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Jetson Emulator Gives Students A Free AI Lesson

October 26, 2020 by 4 Comments

With the Jetson Nano, NVIDIA has done a fantastic job of bringing GPU-accelerated machine learning to the masses. For less than the cost of a used graphics card, you get a turn-key Linux computer that’s ready and able to handle whatever AI code you throw at it. But if you’re trying to set up a lab for 30 students, the cost of even relatively affordable development boards can really add up.

Spoiler: These things don’t exist.

Which is why [Tea Vui Huang] has developed jetson-emulator. This Python library provides a work-alike environment to NVIDIA’s own “Hello AI World” tutorials designed for the Jetson family of devices, with one big difference: you don’t need the actual hardware. In fact, it doesn’t matter what kind of computer you’ve got; with this library, anything that can run Python 3.7.9 or better can take you through NVIDIA’s getting started tutorial.

So what’s the trick? Well, if you haven’t guessed already, it’s all fake. Obviously it can’t actually run GPU-accelerated code without a GPU, so the library [Tea] has developed simply pretends. It provides virtual images and even “live” camera feeds to which randomly generated objects have been assigned.

The original NVIDIA functions have been rewritten to work with these feeds, so when you call something like net.Classify(img) against one of them you’ll get a report of what faux objects were detected. The output will look just like it would if you were running on a real Jetson, down to providing fictitious dimensions and positions for the bounding boxes.

If you’re a hacker looking to dive into machine learning and computer vision, you’d be better off getting a $59 Jetson Nano and a webcam. But if you’re putting together a workshop that shows a dozen people the basics of NVIDIA’s AI workflow, jetson-emulator will allow everyone in attendance to run code and get results back regardless of what they’ve got under the hood.

World’s Smallest Benchy Shows Off What 3D-Printing Can Do For “Microswimmers”

October 26, 2020 by 12 Comments

We’ve said it before, but we cast a wary eye at any superlative claims that come our way. “World’s fastest” or “world’s first” claims always seem to be quickly debunked, but when the claim of “World’s Smallest Benchy” is backed up by a tugboat that two dozen E. coli would have a hard time finding space on, we’re pretty comfortable with it.

Of course the diminutive benchmark was not printed just for the sake of it, but rather as part of a demonstration of what’s possible with “microswimmers”, synthetic particles which are designed to move about freely in microscopic regimes. As described in a paper by [Rachel P. Doherty] et al from the Soft Matter Physics lab at Leiden University, microswimmers with sizes on the order of 10 to 20 μm can be constructed repeatably, and can include a small area of platinum catalyst. The catalyst is the engine of the microswimmer; hydrogen peroxide in the environment decomposes on the catalyst surface and provides a propulsive force.

Artificial microswimmers have been around for a while, but most are made with chemical or evaporative methods which result in simple shapes like rods and spheres. The current work describes much more complex shapes — the Benchy was a bit of a flex, since the more useful microswimmers were simple helices, which essentially screw themselves into the surrounding fluid. The printing method was based on two-photon polymerization (2PP), a non-linear optical process that polymerizes a resin when two photons are simultaneously absorbed.

The idea that a powered machine so small could be designed and manufactured is pretty cool. We’d love to see how control mechanisms could be added to the prints — microfluidics, perhaps?

Simple Induction Heater Helps With Homebrew Shrink-Fitting

October 26, 2020 by 14 Comments

Machinists have a lot of neat shop tricks, but one especially interesting one is shrink-fitting tools. Shrink-fitting achieves an interference fit between tool and holder by creating a temperature difference between the two before assembly. Once everything returns to temperature, the two parts may as well be welded together.

The easiest way to shrink-fit machine tooling is with induction heating, and commercial rigs exist for doing the job. But [Roetz 4.0] decided to build his own shrink-fitting heater, and the results are pretty impressive. The induction heater itself is very simple — a 48 volt, 20 amp power supply, an off-the-shelf zero-voltage switching (ZVS) driver, and a heavy copper coil. When the coil is powered up, any metal within is quickly and evenly heated by virtue of the strong magnetic flux in the coil.

To use the shrinker, [Roetz 4.0] starts with a scrupulously clean tool holder, bored slightly undersized for the desired tool. Inside the coil, the steel tool holder quickly heats to a lovely deep brown color, meaning it has gotten up to the requisite 250-300°C. The tool is quickly dropped into the now-expanded bore, which quickly shrinks back around it. The advantage of this method over a collet or a chuck is clear in the video below: practically zero runout, and the tool is easily released after another run through the heater.

You say you’ve got no need for shrink-fitting tools? How about stuck bolts? Induction heaters work great there too.

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