What does one do when frustrated at the lack of affordable, open source portable trackers? If you’re [OG-star-tech], you design your own and give it modular features that rival commercial offerings while you’re at it.

What’s a star tracker? It’s a method of determining position based on visible stars, but when it comes to astrophotography the term refers to a sort of hardware-assisted camera holder that helps one capture stable long-exposure images. This is done by moving the camera in such a way as to cancel out the effects of the Earth’s rotation. The result is long-exposure photographs without the stars smearing themselves across the image.

Interested? Learn more about the design by casting an eye over the bill of materials at the GitHub repository, browsing the 3D-printable parts, and maybe check out the assembly guide. If you like what you see, [OG-star-tech] says you should be able to build your own very affordably if you don’t mind 3D printing parts in ASA or ABS. Prefer to buy a kit or an assembled unit? [OG-star-tech] offers them for sale.

Frustration with commercial offerings (or lack thereof) is a powerful motive to design something or contribute to an existing project, and if it leads to more people enjoying taking photos of the night sky and all the wonderful things in it, so much the better.

Anybody who has set up a satellite TV antenna will tell you that alignment is critical when picking up a signal from space. With a satellite dish it’s a straightforward task to tweak the position, but what happens if the dish in question is out beyond the edge of the Solar System?

We told you a few days ago about this exact issue currently facing Voyager 2, but we’re guessing Hackaday readers will want to know a little bit more about how a 50+ year old spacecraft so far from home can still sort out its antenna. The answer lies in NASA Technical Report 32-1559, Digital Canopus Tracker from 1972, which describes the instrument that notes the position of the star Canopus, which along with that of the Sun it can use to calculate the antenna bearing to reach Earth. The report makes for fascinating reading, as it describes how early-1970s technology was used to spot the star by its specific intensity and then keep it in its sights. It’s an extremely accessible design, as even the part numbers are an older version of the familiar 74 logic.

So somewhere out there in interstellar space beyond the boundary of the Solar System is a card frame full of 74 logic that’s been quietly keeping an eye on a star since the early 1970s, and the engineers from those far-off days at JPL are about to save the bacon of the current generation at NASA with their work. We hope that there are some old guys in Pasadena right now with a spring in their step.

Read our coverage of the story here.

Important safety tip: When you’re sending commands to the second-most-distant space probe ever launched, make really, really sure that what you send isn’t going to cause any problems.

According to NASA, that’s just what happened to Voyager 2 last week, when uplinked commands unexpectedly shifted the 46-year-old spacecraft’s orientation by just a couple of degrees. Of course, at a distance of nearly 20 billion kilometers, even fractions of a degree can make a huge difference, especially since the spacecraft’s high-gain antenna (HGA) is set up for very narrow beamwidths; 2.3° on the S-band channel, and a razor-thin 0.5° on the X-band side. That means that communications between the spacecraft and the Canberra Deep Space Communication Complex — the only station capable of talking to Voyager 2 now that it has dipped so far below the plane of the ecliptic — are on pause until the spacecraft is reoriented.

Luckily, NASA considered this as a possibility and built safety routines into Voyager‘s program that will hopefully get it back on track. The program uses the onboard star tracker to get a fix on the bright star Canopus, and from there figures out which way the spacecraft needs to move to get pointed back at Earth. The contingency program runs automatically several times a year, just in case something like this happens.

That’s the good news; the bad news is that the program won’t run again until October 15. While that’s really not that far away, mission controllers will no doubt find it an agonizingly long time to be incommunicado. And while NASA is outwardly confident that communications will be restored, there’s no way to be sure until we actually get to October and see what happens. Fingers crossed.

Getting a closer look at the Moon isn’t particularly difficult; even an absolute beginner can point a cheap telescope towards our nearest celestial neighbor and get some impressive views. But if you’re looking to explore a bit farther, and especially if you want to photograph what you find out there amongst the black, things can get complicated (and expensive) pretty quick.

While building this 3D printed automated telescope designed [Greg Holloway] isn’t necessarily cheap, especially once you factor in what your time is worth, the final product certainly looks to be considerably streamlined compared to most of what’s available in the commercial space. Rather than having to lug around a separate telescope, tripod, motorized tracker, and camera, you just need this relatively compact all-in-one unit.

It’s taken [Greg] six months to develop his miniature observatory, and it shows. The CAD work is phenomenal, as is the documentation in general. Even if you’re not interested in peering into the heavens, perusing the Instructables page for this project is well worth your time. From his tips on designing for 3D printing to information about selecting the appropriate lens and getting it mated to the Raspberry Pi HQ Camera, there’s a little something for everyone.

Of course if you are looking to build your own motorized “GOTO” telescope, then this is must-read stuff. [Greg] has really done his homework, and the project is a fantastic source of information about motor controllers, wiring, hand controllers, and the open source firmware you need to tie it all together. Many of the ideas he’s outlined here could be applicable to other telescope projects, or really, anything that needs to be accurately pointed to the sky. If you’d like to get started with night sky photography and aren’t picky about what kind of things you capture, we’ve seen a number of projects that simply point a camera towards the stars and wait for something to happen.

[Thanks to Eugene for the tip.]

Keeping track of position is crucial in a lot of situations. On Earth, it’s usually relatively straight-forward, with systems having been developed over the centuries that would allow one to get at least a rough fix on one’s position on this planet. But for a satellite out in space, however, it’s harder. How do they keep their communications dishes pointed towards Earth?

The stars are an obvious orientation point. The Attitude and Articulation Control Subsystem (AACS) on the Voyager 1 and 2 space probes has the non-enviable task of keeping the spacecraft’s communication dish aligned precisely with a communications dish back on Earth, which from deep space is an incomprehensibly tiny target.

Back on Earth, the star tracker concept has become quite popular among photographers who try to image the night skies. Even in your living room,  VR systems also rely on knowing the position of the user’s body and any peripherals in space. In this article we’ll take a look at the history and current applications of this type of position tracking.

Celestial Navigation

Celestial navigation has been practiced for thousands of years. In theory, all you need is your eyes and some knowledge of how the Sun, Moon and stars move in the skies throughout the seasons to get a sense of direction. But this doesn’t tell you your position on the Earth’s surface.

For most of human history, ships would stay within sight of the coast and rarely cross large bodies of water. When they did crossings, they would often use dead reckoning, using one’s known position, heading and speed. Although the concept of latitude had been around for a while, measuring latitude accurately required angle-finding instruments, such as an astrolabe, invented around 200 BC, or a sextant, invented in the 16th century.

An astrolabe, sextant, or similar measures the angles between known celestial bodies, from which the latitude can be deduced. The determining of longitude was a major question that ultimately came down to having an accurate clock, as longitude and solar time are directly related. The invention of timepieces that were both accurate and could be used on a ship or moving vehicle would not be solved until the 19th century when they became reliable and affordable enough that alternatives (lunar distance method) fell out of favor.

Finding one’s way in space

Although navigating in the mindbogglingly massive vacuum of space may seem harder than navigating on Earth, essentially the same principles apply. The most important thing is to have at least one point of reference. In the case of Earth-based navigation, this can be the Sun, the Moon or any bright star with a known trajectory and location in the sky.

For a space probe, the common metaphor of ‘sailing the ocean of stars’ is rather apt when it comes to navigation. The Attitude and Articulation Control Subsystem (AACS) as it is known on the Voyager, Cassini, and other spacecraft form the core of the navigation and positioning system. In the case of Cassini, it uses a number of sensors, including Stellar Reference Units (SRU), Inertial Reference Units (IRU) and Sun sensors (SSA). These SRUs are CCD-based star trackers that together with the other units keep the spacecraft aware of its relative position in space.

The Voyager spacecraft use a similar AACS system, as did other spacecraft in the past and probes after Voyager 1 and Voyager 2. For attitude reference, star trackers, star scanners, solar trackers, sun sensors, and planetary limb trackers are used. Voyager’s AACS uses a sun sensor for yaw and pitch reference, and a star tracker to continuously track a bright star at right angles for roll reference. Galileo references a star scanner that rotates with the spinning part of the spacecraft. Magellan used a star scanner to obtain a fix on two bright stars during a special maneuver every few orbits.

It isn’t just in space where star trackers are useful, either. In order to take photographs of the Milky Way and the night sky, the film or camera sensor requires long exposure times in order to gather sufficient light from the (faint) star light. Because the Earth rotates continuously, the position of the stars is shifting, and this makes a blurred mess over even a ten second exposure time, let alone half a minute or longer. In the old days, rotating the camera or telescope along with the stars was done by aligning a pivot with the earth’s axis and turning it at a preset rotation speed for one’s location on Earth. More modern astrophotography rigs use a photo sensor that keeps a fix on one or more stars, moving the camera that is mounted on top of the tracker with just the right amount to get a sharp image.

Bodies in Space

For the moment at least, the Final Frontier when it comes to tracking one’s position is not outer space, but our living rooms. Significant R&D money is being invested in creating an ever more realistic and natural Virtual Reality (VR) experience. This requires that the system can keep track of not only where the user is looking in the virtual world, but also where their appendages are currently located.

In VR positional tracking aims to determine the yaw, pitch, and roll of displays, controllers, or body parts. Here there are two main options: either sensors on the user keep track of markers in their surroundings, like the Oculus Rift S does, or sensors that surround the user keep track of markers on the user’s body or on the controllers, like the Oculus Rift CV1‘s aptly named Constellation system. Of course, each solution comes with its own set of advantages and disadvantages (and aggravated users).

Methods for motion capture, often used for (CGI) films and video games, operate similarly. The big difference between VR and motion capture is that for motion capture it is acceptable to gear the subject up in special suits with markers, while also often including the finer details of facial movements, something that is less interesting in VR than tracking the movement of one’s digits. You don’t want to spend twenty minutes suiting up just to play a game.

Good Tracking Goes Places

Whether navigating a celestial body’s surface, the space between the stars, or a virtual reality while flailing wildly in the living room amidst curious glances from your pets, the challenges posed by determining position and orientation remain. Only the actual space that is being navigated changes.

Improved navigation on Earth has led humankind to explore and settle virtually every bit of land on this planet, to create accurate maps, and to locate ourselves in the Earth’s oceans, land, and skies with ever-increasing precision. Over time we learned to create our own markers in addition to the Sun and stars, using light houses, radio beacons, and ultimately a constellation of satellites to enable navigation.

In space, our probes don’t just navigate by stars alone anymore either. The NASA Deep Space Network provides both communication and tracking services to any spacecraft inside our solar system, and beyond. At this point in time, only the network’s largest 70-meter antenna can still communicate with and track the Voyager probes as they venture ever further into deep space.

It’s an interesting inversion that what allowed early sailors to navigate the seven seas and later space probes to navigate the solar system is now used to keep track of you in your living room as you explore the worlds that exist within our collective imagination.

If you want to take beautiful night sky pictures with your DSLR and you live between 15 degrees and 55 degrees north latitude you might want to check out OpenAstroTracker. If you have a 3D printer it will probably take about 60 hours of printing, but you’ll wind up with a pretty impressive setup for your camera. There’s an Arduino managing the tracking and also providing a “go to” capability.

The design is over on Thingiverse and you can find code on GitHub. There’s also a Reddit dedicated to the project. The tracker touts its ability to handle long or heavy lenses and to target 180 degrees in every direction.

Some of the parts you must print are specific to your latitude to within 5 degrees, so if you live at latitude 43 degrees, you could pick the 40-degree versions of the parts. So far though, you must be in the Northern hemisphere between 15 and 55 degrees.

What kind of images can you expect? The site says this image of Andromeda was taken over several nights using a Soligor 210mm f/4 lens with ISO 800 film.

Not bad at all! Certainly not the view from our $25 department store telescope.

If you’d rather skip the Arduino, try a cheap clock movement. Or you can replace the clock and the Arduino with yourself.