How To Hack A Spacecraft To Die Gracefully

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Last week, the Rosetta spacecraft crashed into comet 67P/Churyumov-Gerasimenko after orbiting it since 2014. It was supposed to do that: the mission was at an end, and the mission designers wanted to end it by getting a close look at the surface of the comet. But this raises an interesting problem: how do you get a device that is designed to never stop to actually stop?

A spacecraft like Rosetta is built from the ground up to keep going, to reboot and go into a backup mode, phone home and wait for instructions if it encounters a problem. This is called a safe mode, and it has saved the spacecraft several times before. If it was left unfixed, when the spacecraft hit the comet, it would trigger a special safe mode called FDIR (Failure Detection, Isolation and Recovery) that would keep sending a diagnostic signal back to earth until the mission controllers responded.

But this mission was at an end, and if the probe was left constantly rebooting and transmitting a cry for help, it could interfere with other spacecraft using the same frequency. Even a weak signal could interfere with another spacecraft, so the designers wanted to shut it down completely.  So, they used an interesting approach: they patched the software on the spacecraft to stop it phoning home. The day before it was crashed into the comet, they sent it a patch that removed the safe mode and replaced it with a passive mode that hadn’t been used since before launch, where the spacecraft would simply sit and wait for instructions if it hit a problem. A few hours before the crash, this patch was activated, and the probe was now without a backup plan. So, when it hit the comet, it entered this passive mode, and it will stay in this mode for as long as the batteries last, forever waiting for a command to restart that will never come…

Thanks to [Daniel] for the tip!

Filed under: solar hacks

Homebrew Powerwall Sitting at 20kWh

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Every now and then a hacker gets started on a project and forgets to stop. That’s the impression we get from [HBPowerwall]’s channel anyway. He’s working on adding a huge number of 18650 Lithium cells to his home’s power grid and posting about his adventures along the way. This week he gave us a look at the balancing process he uses to get all of these cells to work well together. Last month he gave a great overview of the installed system.

His channel starts off innocently enough. It’s all riding small motor bikes around and having a regular good time.  Then he experiments a bit with the light stuff, like a few solar panels on the roof.  However, it seems like one day he was watching a news brief about the Powerwall (Tesla’s whole-home battery storage system) and was like, “hey, I can do that.”

After some initial work with the new substance it wasn’t long before he was begging, borrowing, and haggling for every used 18650 lithium battery cell the local universe in Brisbane, Australia could sell him. There are a ton of videos documenting his madness, but he’s all the way up to a partly off-grid house with a 20kWh battery bank, for which he has expansion plans.

There’s a lot of marketing flim flam and general technical pitfalls in the process of generating your own non-grid electricity. But for hackers in sunny areas who want to dump those rays into local storage this is an interesting blueprint to start with.

Filed under: home hacks, solar hacks

Characterizing a Death Ray… er, Solar Oven

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Many of you will probably at some point have looked at a satellite dish antenna and idly wondered whether it would collect useful amounts of heat if you silvered it and pointed it at the sun. Perhaps you imagine a handy source of  solar-cooked hotdogs, or maybe you’re a bit of a pyromaniac.

[Charlie Soeder] didn’t just think about it, he did it. Finding a discarded offset-focus DirecTV dish, he glued a grid of 230 inch-square mirror tiles to it and set to investigating  the concentrated solar energy at its focus. 

Cotton waste, newspaper, and scraps of fabric char and burn with ease. A cigarette is lit almost from end to end, and it burns a hole right through a piece of bamboo. Most of the energy is in the form of light, so transparent or reflective items need a little help to absorb it from something dark. He demonstrated this by caramelizing some sugar through adding a few bits of charcoal to it, once the charcoal becomes hot enough to caramelize the sugar around it the spreading dark colour causes the rest of the sugar to caramelize without further help.

Solar furnace calculationsSolar furnace calculations

To gain some idea of the power of his solar furnace, he recorded a time series of temperature readings as it heated up some water darkened with a bit of charcoal to absorb heat. The resulting graph had a flat spot as a cloud had passed over the sun, but from it he was able to calculate instantaneous power figures from just below 30W to just below 50W depending on the sun.

He records his progress in the video you’ll find below the break. Will we be the only ones casting around for a surplus dish after watching it?

We don’t seem to have had many satellite dish solar furnaces here on these pages, but we have had a more conventional solar oven or two. This dish-based solution would probably benefit from a sun tracker.

Filed under: green hacks, solar hacks

Working in Peace With an Off-Grid Office Shed

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Finding a good work space at home isn’t a trivial task, especially when you’ve got a wife and kid. A lot of us use a spare bedroom, basement, or garage as a space to work on our hobbies (or jobs). But, the lack of true separation from the home can make getting real work done difficult. For many of us, we need to have the mental distance between our living space and our working space in order to actually get stuff done.

This is the problem [Syonyk] had — he needed a quiet place to work that was separated from the rest of his house. To accomplish this, he used a Tuff Shed and set it up to run off-grid. The reason for going off-grid wasn’t purely environmental, it was actually more practical than trying to run power lines from the house. Because of the geology where he lives, burying power lines wasn’t financially feasible.

So, he poured a foundation, brought in a pre-assembled shed (a demo unit at a big discount), and got to work outfitting it for use as on office. The first step (and arguably a very important one), was to heavily insulate it. And, we do mean “heavily” — he used 3.5″ of rock wool (5.5″ on the ceiling) in addition to 2″ of foam board.

The insulation was essential, as the entire office is powered by solar panels (with a battery bank); keeping cooling and heating energy use down was paramount. Even with 2kW of panels, heating and cooling are still a huge portion of the energy usage, and he needed power to spare for his computer and other electronics. With the shed so well insulated, [Syonyk] has been able to keep the temperature inside at about 70ºF while the outside temperature is above 100ºF.

The rest of the build was straightforward, with sensible plywood walls and a desk taking up most of the space to hold his multiple computers. Of course, for the Hackaday crowd, a space like this would be best used for efficient hacking.

Filed under: green hacks, solar hacks

Star Track: A Lesson in Positional Astronomy With Lasers

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[gocivici] threatened us with a tutorial on positional astronomy when we started reading his tutorial on a Arduino Powered Star Pointer and he delivered. We’d pick him to help us take the One Ring to Mordor; we’d never get lost and his threat-delivery-rate makes him less likely to pull a Boromir.

As we mentioned he starts off with a really succinct and well written tutorial on celestial coordinates that antiquity would have killed to have. If we were writing a bit of code to do our own positional astronomy system, this is the tab we’d have open. Incidentally, that’s exactly what he encourages those who have followed the tutorial to do.

The star pointer itself is a high powered green laser pointer (battery powered), 3D printed parts, and an amalgam of fourteen dollars of Chinese tech cruft. The project uses two Arduino clones to process serial commands and manage two 28byj-48 stepper motors. The 2nd Arduino clone was purely to supplement the digital pins of the first; we paused a bit at that, but then we realized that import arduinos have gotten so cheap they probably are more affordable than an I2C breakout board or stepper driver these days. The body was designed with a mixture of Tinkercad and something we’d not heard of, OpenJsCAD.

Once it’s all assembled and tested the only thing left to do is go outside with your contraption. After making sure that you’ve followed all the local regulations for not pointing lasers at airplanes, point the laser at the north star. After that you can plug in any star coordinate and the laser will swing towards it and track its location in the sky. Pretty cool.

Filed under: Arduino Hacks, cnc hacks, news, solar hacks

Dual Axis Solar Tracker with Online Energy Monitor

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[Bruce Helsen] built this dual axis solar tracker as one of his final projects for school.

As can be experimentally verified in a very short timeframe, the sun moves across the sky. This is a particularly troublesome behavior for solar panels, which work best when the sun shines directly on them. Engineers soon realized that abstracting the sun away only works in physics class, and moved to the second best idea of tracking sun by moving the panel. Surprisingly, for larger installations the cost of adding tracking (and its maintenance) isn’t worth the gains, but for smaller, and especially urban, installations like [Bruce]’s it can still help.

[Bruce]’s build can be entirely sourced from eBay. The light direction is sensed via a very clever homemade directional light sensor. A 3D printer extruded cross profile sits inside an industrial lamp housing. The assembly divides the sky into four quadrants with a light-dependent resistor for each. By measuring the differences, the panel can point in the optimal direction.

The panel’s two axis are controlled with two cheap linear actuators. The brains are an Arduino glued to a large amount of solar support electronics and the online energy monitor component is covered by an ESP8266.

The construction works quite well. If you’d like to build one yourself the entire BOM, drawings, and code are provided on the instructables page.


Filed under: Arduino Hacks, solar hacks

Perovskite Solar: Coming Soon?

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Making solar cells out of silicon is difficult. There’s plenty of manufacturing steps, many of them at very high temperatures, and you need a high vacuum and a clean room. However, perovskite solar cells–cells made with hybrid organic-inorganic materials in a perovskite crystal structure–are relatively easy to make using wet chemistry involving solvents or vapor deposition.

In theory, silicon solar cells could be 30% efficient, but in reality, 25% seems to be a practical limit with commercial cells typically topping out at 20%. Perovskite cells are nearly that high now, and could be higher by stacking thin layers, each sensitive to different wavelengths of light.

A recent development at the Lawrence Berkeley National Laboratory may lead to even more efficient perovskite cells. Researchers found that certain crystal structures had a much higher efficiency than other structures. The problem now is figuring out how to produce the crystals to increase the prevalence of that structure.

That’s not the only problem, though. Perovskite cells degrade quickly. The materials used tend to be water soluble, and the cell breaks down in most environments. There has been work to make longer lasting cells. The current record for efficiency in a single-junction perovskite cell is 22.1%.

Researchers hope to solve the stability problem and produce highly efficient solar films using this technology. They envision light, transparent, and cheap solar cells that would be as easy to apply as wallpaper, covering any surface that has sun exposure.

If you want to try your hand at building your own perovskite cells, you might enjoy the videos below. Notice you can actually make the cells. Usually, when we see a DIY solar project, it starts with conventional solar panels. Unless, of course, it doesn’t create electricity.

Filed under: solar hacks

Open Source Solar

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What’s the size of a standard euro-palette, goes together in 15 minutes, and can charge 120 mobile phones at one time? At least one correct answer is Sunzilla, the open source solar power generator. The device does use some proprietary components, but the entire design is open source. It contains solar panels, of course, as well as storage capacity and an inverter.

You can see a video about the project below. The design is modular so you can pick and choose what you want. It also is portable, stackable, and easy to transport. The team claims they generate 900W of solar power and can store 4 kWh. Because of the storage device, the peak power out is 1600W and the output is 230V 50Hz AC.

The storage component is the heaviest part, of course. The entire thing weighs under 200 pounds without batteries. With them, the weight leaps to about 550 pounds.

Although the focus is on impoverished places, it would be easy to imagine a ham radio club using something like this for Field Day operations or working in disaster areas. Outdoor festivals could use something like this, too.

We have covered many solar power builds, but this one is particularly complete and modular. Then again, if all you want to do is heat your redneck hot tub, Sunzilla might be overkill.

Filed under: solar hacks
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