Now the eyes of space explorers are turned once more towards the Moon, there are a whole host of new engineering challenges facing engineers working on lunar missions. One such challenge relates to how any proposed Moon base might be built, and as European Space Agency (ESA) researchers turn their mind to the problem they’ve taken a uniquely European approach. They’ve made some LEGO bricks.

Sadly lunar regolith is in short supply in Europe at the moment, so as a stand-in they’ve ground up a meteorite, mixed the powder with a polymer, and 3D printed their bricks. The LEGO write-up is a little long on frothy writing style and a little short on the science, but it seems that they clutch in exactly the same way as the official bricks from Billund, and can be assembled just as you would a normal set of bricks.

It’s with some regret that we have to concede that Europe’s off-planet outpost won’t be crewed by LEGO people in a base made from LEGO bricks, but we applaud them for doing this as a practical test given the limited supply of starter material. LEGO themselves have snagged some of them to display in a range of their flagship stores, so we hot-footed it down to London to catch some pictures. What we found is a single brick in a glass case, sadly looking very like any other 3D printed brick in a shiny grey medium. It’s probably the most expensive brick in the world though, so we doubt they’ll be available to buy any time soon.

If you’re hungry for more of all things LEGO, we can do no better than suggest a trip to the mother lode, in Billund, Denmark.

After Space Shuttle Atlantis’ drive-by repair of the Hubble Space Telescope (HST) in May of 2009, the end of the STS program meant that the space telescope had to fend for itself with no prospect for any further repair missions. The weakest point turned out to be the gyroscopes, with of the original six only three functioning until May 24th of 2024 when one failed and couldn’t be reset any more. To make the most out of the HST’s remaining lifespan, NASA decided to transition again to single-gyroscope operation, with the most recent imaging results showing that this enables HST to return to its science mission.

Although the HST has operated with a reduced number of gyroscopes before, while awaiting its (much delayed) 2009 Servicing Mission 4, this time around it would appear that no such aid is coming. Although HST is still very much functional even after recently celebrating its 34th year in space, there is a lot of debate about whether another servicing mission could be organized, or whether HST will be deorbited in a number of years. Recently people like [Jared Isaacman] have suggested ideas for an STS servicing mission, with [Jared] even offering to pay for the entire servicing mission out of pocket.

While there is an argument to be made that a Crew Dragon is a poor substitute for a Shuttle with its big cargo bay, airlock and robotic arm, it’s promising to see at least that for now HST can do what it does best with few compromises, while we may just see Servicing Mission 5 happening at some point before that last gyro kicks the bucket.

Recently ESA published the results of a proof-of-concept study into monitoring marine litter using existing satellites, with promising results for the Mediterranean study area. For the study, six years of historical data from the Sentinel-2 satellite multispectral imaging  cameras were used, involving 300,000 images with a resolution of 10 meters. The focus was on litter windrows as common collections of litter like plastic, wood and other types of marine debris that float on the surface, forming clearly visible lines that can be meters wide and many times as long.

These were processed as explained in the open access paper in Nature Communications by [Andrés Cózar] and colleagues. As marine litter (ML) tends to be overwhelmingly composed of plastic, this eases the detection, as any ML that’s visible from space can generally be assumed to be primarily plastic litter. This was combined with the spectral profile of common plastics, so that other types of floating materials (algae, driftwood, seafoam, etc.) could be filtered out, leaving just the litter.

This revealed many of these short-lived litter windrows, with spot confirmation from ships in the area. Some of the windrows were many kilometers in length, with an average of around 1 km.

Although just a PoC, it nevertheless shows that monitoring such plastic debris from space is quite doable, even without dedicated satellites. As every day tons more plastics make their way into the oceans, this provides us with the means to at least keep track of the scope of the problem. Even if resolving it and the associated microplastics problem is still a far-off dream.

Although there is a lot of space in Earth orbit, there are also some seriously big man-made objects in those orbits, some of which have been there for decades. As part of efforts to remove at least some of this debris from orbit, Astroscale’s ADRAS-J (“Active Debris Removal by Astroscale-Japan”) satellite has been partaking in JAXA’s Commercial Removal of Space Debris Demonstration (CRD2). After ADRAS-J was launched by a Rocket Lab Electron rocket on February 18, it’s been moving closer to its target, with June 14th seeing an approach by roughly 50 meters, allowing for an unprecedented photo to be made of the H-2A stage in orbit. This upper stage of a Japanese H-2A rocket originally launched the GOSAT Earth observation satellite into orbit back in 2009.

The challenges with this kind of approach is that the orbital debris does not actively broadcast its location, ergo it requires a combination of on-ground and on-satellite tracking to match the orbital trajectory for a safe approach. Here ADRAS-J uses what is called Model Matching Navigation (MNM), which uses known visual information to compare it with captured images, to use these to estimate the relative distance to the target.

Although the goal of ADRAS-J is only to study the target from as closely as possible, the next phase in the CRD2 program would involve actively deorbiting this upper stage, with phase start projected to commence in 2026.

Thanks to [Stephen Walters] for the tip.

As humanity’s furthest reach into the Universe so far, the two Voyager spacecraft’s well-being is of utmost importance to many. Although we know that there will be an end to any science mission, the recent near-death experience by Voyager 1 was a shocking event for many. Now it seems that things may have more or less returned to normal, with all four remaining scientific instruments now back online and returning information.

Since the completion of Voyager 1’s primary mission over 43 years ago, five of its instruments (including the cameras) were disabled to cope with its diminishing power reserves, with two more instruments failing. This left the current magnetometer (MAG), charged particle (LECP) and cosmic ray (CRS) instruments, as well as the plasma wave subsystem (PWS). These are now all back in operation based on the returned science data after the Voyager team confirmed previously that they were receiving engineering data again.

With Voyager 1 now mostly back to normal, some housekeeping is necessary: resynchronizing the onboard time, as well as maintenance on the digital tape recorder. This will ensure that this venerable spacecraft will be all ready for its 47th anniversary this fall.

Thanks to [Mark Stevens] for the tip.

Danswer is an open-source AI-powered workplace search engine that allows you to quickly find information across your company’s documents, apps, and employees. It offers integration with over 25 workplace apps including Slack, providing AI-generated answers backed by your team’s own data sources to prevent hallucinations. Danswer can be self-hosted for free using Docker or run […]

Source

Wandering round the field at EMF Camp, our eye was caught by an unusual sight, at least to European eyes. The type of campervan body which sits on the back of a pickup truck is not particularly common on this side of the Atlantic, but there one was, fitted out as a mobile makerspace. If that wasn’t enough, this one is for sale.

Here at Hackaday we’re neither estate agents or in the want-ads business, so we’re unaccustomed to property promotion. We’re still not immune to the attraction of a portable makerspace to take to events though, and this one provides a very practical basis. It started life as what Brits call a Luton van body, a box van, and inside it’s gained a small kitchen, benches and shelves either side, and up in the space over the cab, a double bed. Sadly the laser cutter and 3D printers aren’t included.

If you live in Southern England and you want to be the envy of everyone at your next hacker camp, an email to richjmaynard at gmail dot com with a sensible offer might secure it. We would be first in the queue if we had the space, because what Wrencher scribe wouldn’t want an office like this!

Reaching orbit around Earth is an incredibly difficult feat. It’s a common misconception that getting into orbit just involves getting very high above the ground — the real trick is going sideways very, very fast. Thus far, the most viable way we’ve found to do this is with big, complicated multi-stage rockets that shed bits of themselves as they roar out of the atmosphere.

Single-stage-to-orbit (SSTO) launch vehicles represent a revolutionary step in space travel. They promise a simpler, more cost-effective way to reach orbit compared to traditional multi-stage rockets. Today, we’ll explore the incredible potential offered by SSTO vehicles, and why building a practical example is all but impossible with our current technology.

A Balancing Act

The SSTO concept doesn’t describe any one single spacecraft design. Instead, it refers to any spacecraft that’s capable of achieving orbit using a single, unified propulsion system and without jettisoning any part of the vehicle.

Today’s orbital rockets shed stages as they expend fuel. There’s one major reason for this, and it’s referred to as the tyranny of the rocket equation. Fundamentally, a spacecraft needs to reach a certain velocity to attain orbit. Reaching that velocity from zero — i.e. when the rocket is sitting on the launchpad — requires a change in velocity, or delta-V. The rocket equation can be used to figure out how much fuel is required for a certain delta-V, and thus a desired orbit.

The problem is that the mass of fuel required scales exponentially with delta-V. If you want to go faster, you need more fuel. But then you need even more fuel again to carry the weight of that fuel, and so on. Plus, all that fuel needs a tank and structure to hold it, which makes things more difficult again.

Work out the maths of a potential SSTO design, and the required fuel to reach orbit ends up taking up almost all of the launch vehicle’s weight. There’s precious mass left over for the vehicle’s own structure, let alone any useful payload. This all comes down to the “mass fraction” of the rocket. A SSTO powered by even our most efficient chemical rocket engines would require that the vast majority of its mass be dedicated to propellants, with its structure and payload being tiny in comparison. Much of that is due to Earth’s nature. Our planet has a strong gravitational pull, and the minimum orbital velocity is quite high at about 7.4 kilometers per second or so.

Stage Fright

Historically, we’ve cheated the rocket equation through smart engineering. The trick with staged rockets is simple. They shed structure as the fuel burns away. There’s no need to keep hauling empty fuel tanks into orbit. By dropping empty tanks during flight, the remaining fuel on the rocket has to accelerate a smaller mass, and thus less fuel is required to get the final rocket and payload into its intended orbit.

So far, staged rockets have been the only way for humanity to reach orbit. Saturn V had five stages, more modern rockets tend to have two or three. Even the Space Shuttle was a staged design: it shed its two booster rockets when they were empty, and did the same with its external liquid fuel tank.

But while staged launch vehicles can get the job done, it’s a wasteful way to fly. Imagine if every commercial flight required you to throw away three quarters of the airplane. While we’re learning to reuse discarded parts of orbital rockets, it’s still a difficult and costly exercise.

The core benefit of a SSTO launch vehicle would be its efficiency. By eliminating the need to discard stages during ascent, SSTO vehicles would reduce launch costs, streamline operations, and potentially increase the frequency of space missions.

Pushing the Envelope

It’s currently believed that building a SSTO vehicle using conventional chemical rocket technology is marginally possible. You’d need efficient rocket engines burning the right fuel, and a light rocket with almost no payload, but theoretically it could be done.

Ideally, though, you’d want a single-stage launch vehicle that could actually reach orbit with some useful payload. Be that a satellite, human astronauts, or some kind of science package. To date there have been several projects and proposals for SSTO launch vehicles, none of which have succeeded so far.

One notable design was the proposed Skylon spacecraft from British company Reaction Engines Limited. Skylon was intended to operate as a reusable spaceplane fueled by hydrogen. It would take off from a runway, using wings to generate lift to help it to ascend to 85,000 feet. This improves fuel efficiency versus just pointing the launch vehicle straight up and fighting gravity with pure thrust alone. Plus, it would burn oxygen from the atmosphere on its way to that altitude, negating the need to carry heavy supplies of oxygen onboard.

Once at the appropriate altitude, it would switch to internal liquid oxygen tanks for the final acceleration phase up to orbital velocity. The design stretches back decades, to the earlier British HOTOL spaceplane project. Work continues on the proposed SABRE engine (Syngergetic Air-Breathing Rocket Engine) that would theoretically propel Skylon, though no concrete plans to build the spaceplane itself exist.

Lockheed Martin also had the VentureStar spaceplane concept, which used an innovative “aerospike” rocket engine that maintained excellent efficiency across a wide altitude range. The company even built a scaled-down test craft called the X-33 to explore the ideas behind it. However, the program saw its funding slashed in the early 2000s, and development was halted.

McDonnell Douglas also had a crack at the idea in the early 1990s. The DC-X, also known as the Delta Clipper, was a prototype vertical takeoff and landing vehicle. At just 12 meters high and 4.1 meters in diameter, it was a one-third scale prototype for exploring SSTO-related technologies

It would take off vertically like a traditional rocket, and return to Earth nose-first before landing on its tail. The hope was that the combination of single-stage operation and this mission profile would provide extremely quick turnaround times for repeat launches, which was seen as a boon for potential military applications. While its technologies showed some promise, the project was eventually discontinued when a test vehicle caught fire after NASA took over the project.

Ultimately, a viable SSTO launch vehicle that can carry a payload will likely be very different from the rockets we use today. Relying on wings to generate lift could help save fuel, and relying on air in the atmosphere would slash the weight of oxidizer that would have to be carried onboard.

However, it’s not as simple as just penning a spaceplane with an air-breathing engine and calling it done. No air breathing engine that exists can reach orbital velocity, so such a craft would need an additional rocket engine too, adding weight. Plus, it’s worth noting a reusable launch vehicle would also still require plenty of heat shielding to survive reentry. One could potentially build a non-reusable single-stage to orbit vehicle that simply stays in space, of course, but that would negate many of the tantalizing benefits of the whole concept.

Single-stage-to-orbit vehicles hold the promise of transforming how we access space by simplifying the architecture of launch vehicles and potentially reducing costs. While there are formidable technical hurdles to overcome, the ongoing advances in aerospace technology provide hope that SSTO could become a practical reality in the future. As technology marches forward in materials, rocketry, and aerospace engineering in general, the dream of a single-stage path to orbit remains a tantalizing future goal.

---

Featured Image: Skylon Concept Art, ESA/Reaction Engines Ltd

For many decades, the USA has been at the forefront of astronomy, whether with ground-based telescopes or space-based observatories like Hubble and the JWST. Yet this is now at risk as US astronomers are forced to choose between funding either the Giant Magellan Telescope (GMT) or the Thirty Meter Telescope (TMT) as part of the US Extremely Large Telescope (USELT) program. This rightfully has the presidents of Carnegie Science and Caltech – [Eric D. Isaacs] and [Thomas F. Rosenbaum] respectively – upset, with their opinion piece in the Los Angeles Times going over all the reasons why this funding cut is a terrible idea.

The slow death of US astronomy is perhaps best exemplified by the slow death and eventual collapse of the Arecibo radio telescope. Originally constructed as a Cold War era ICBM detector, it found grateful use by radio astronomers, but saw constant budget cuts and decommissioning threats. After Arecibo’s collapse, it’s now China with its FAST telescope that has mostly taken the limelight. In the case of optical telescopes, the EU’s own ELT is expected to be online in 2028, sited close to the GMT in the Atacama desert. The TMT would be sited in Hawai’i.

Of note is also that the TMT and GMT are both not solely US-funded at this point in time, but rather a partnership with a range of other nations, including Australia, Chile, South Korea, China, Canada, Japan, India and others. Even if the US only contributes funds to either telescope, the other partners may decide to pick up the slack, however the TMT project is currently in dire straits as the selected site on Mauna Kea has run into severe local resistance. This may force the TMT project to be sited elsewhere.

GMT and ESO’s ELT would seem to overlap significantly in terms of functionality and observed parts of the sky, making the TMT perhaps the most useful choice for US astronomers if they cannot have both. No matter what choice is made, however, it’ll mean more US budget cuts for astronomy and more US astronomers having to schedule observation time at EU and Asian observatories. Ultimately the USA as the guiding star in astronomy may significantly diminish, along with the positive effects of this status in the scientific community.

There have been all kinds of wild ideas to get spacecraft into orbit. Everything from firing huge cannons to spinning craft at rapid speed has been posited, explored, or in some cases, even tested to some degree. And yet, good ol’ flaming rockets continue to dominate all, because they actually get the job done.

Rockets, fuel, and all their supporting infrastructure remain expensive, so the search for an alternative goes on. One daring idea involves using airships to loft payloads into orbit. What if you could simply float up into space?

Lighter Than Air

The concept sounds compelling from the outset. Through the use of hydrogen or helium as a lifting gas, airships and balloons manage to reach great altitudes while burning zero propellant. What if you could just keep floating higher and higher until you reached orbital space?

This is a huge deal when it comes to reaching orbit. One of the biggest problems of our current space efforts is referred to as the tyranny of the rocket equation. The more cargo you want to launch into space, the more fuel you need. But then that fuel adds more weight, which needs yet more fuel to carry its weight into orbit. To say nothing of the greater structure and supporting material to contain it all.

Carrying even a few extra kilograms of weight to space can require huge amounts of additional fuel. This is why we use staged rockets to reach orbit at present. By shedding large amounts of structural weight at the end of each rocket stage, it’s possible to move the remaining rocket farther with less fuel.

If you could get to orbit while using zero fuel, it would be a total gamechanger. It wouldn’t just be cheaper to launch satellites or other cargoes. It would also make missions to the Moon or Mars far easier. Those rockets would no longer have to carry the huge amount of fuel required to escape Earth’s surface and get to orbit. Instead, they could just carry the lower amount of fuel required to go from Earth orbit to their final destination.

Of course, it’s not that simple. Reaching orbit isn’t just about going high above the Earth. If you just go straight up above the Earth’s surface, and then stop, you’ll just fall back down. If you want to orbit, you have to go sideways really, really fast.

Thus, an airship-to-orbit launch system would have to do two things. It would have to haul a payload up high, and then get it up to the speed required for its desired orbit. That’s where it gets hard. The minimum speed to reach a stable orbit around Earth is 7.8 kilometers per second (28,000 km/h or 17,500 mph). Thus, even if you’ve floated up very, very high, you still need a huge rocket or some kind of very efficient ion thruster to push your payload up to that speed. And you still need fuel to generate that massive delta-V (change in velocity).

For this reason, airships aren’t the perfect hack to reaching orbit that you might think. They’re good for floating about, and you can even go very, very high. But if you want to circle the Earth again and again and again, you better bring a bucketload of fuel with you.

Someone’s Working On It

Nevertheless, this concept is being actively worked on, but not by the usual suspects. Don’t look at NASA, JAXA, SpaceX, ESA, or even Roscosmos. Instead, it’s the work of the DIY volunteer space program known as JP Aerospace.

The organization has grand dreams of launching airships into space. Its concept isn’t as simple as just getting into a big balloon and floating up into orbit, though. Instead, it envisions a three-stage system.

The first stage would involve an airship designed to travel from ground level up to 140,000 feet. The company proposes a V-shaped design with an airfoil profile to generate additional lift as it moves through the atmosphere. Propulsion would be via propellers that are specifically designed to operate in the near-vacuum at those altitudes.

Once at that height, the first stage craft would dock with a permanently floating structure called Dark Sky Station. It would serve as a docking station where cargo could be transferred from the first stage craft to the Orbital Ascender, which is the craft designed to carry the payload into orbit.

The Orbital Ascender itself sounds like a fantastical thing on paper. The team’s current concept is for a V-shaped craft with a fabric outer shell which contains many individual plastic cells full of lifting gas. That in itself isn’t so wild, but the proposed size is. It’s slated to measure 1,828 meters on each side of the V — well over a mile long — with an internal volume of over 11 million cubic meters. Thin film solar panels on the craft’s surface are intended to generate 90 MW of power, while a plasma generator on the leading edge is intended to help cut drag. The latter is critical, as the craft will need to reach hypersonic speeds in the ultra-thin atmosphere to get its payload up to orbital speeds. To propel the craft up to orbital velocity, the team has been running test firings on its own designs for plasma thrusters.

The team at JP Aerospace is passionate, but currently lacks the means to execute their plans at full scale. Right now, the team has some experimental low-altitude research craft that are a few hundred feet long. Presently, Dark Sky Station and the Orbital Ascender remain far off dreams.

Realistically, the team hasn’t found a shortcut to orbit just yet. Building a working version of the Orbital Ascender would require lofting huge amounts of material to high altitude where it would have to be constructed. Such a craft would be torn to shreds by a simple breeze in the lower atmosphere. A lighter-than-air craft that could operate at such high altitudes and speeds might not even be practical with modern materials, even if the atmosphere is vanishingly thin above 140,000 feet.  There are huge questions around what materials the team would use, and whether the theoretical concepts for plasma drag reduction could be made to work on the monumentally huge craft.

Even if the craft’s basic design could work, there are questions around the practicalities of crewing and maintaining a permanent floating airship station at high altitude. Let alone how payloads would be transferred from one giant balloon craft to another. These issues might be solvable with billions of dollars. Maybe. JP Aerospace is having a go on a budget several orders of magnitude more shoestring than that.

One might imagine a simpler idea could be worth trying first. Lofting conventional rockets to 100,000 feet with balloons would be easier and still cut fuel requirements to some degree. But ultimately, the key challenge of orbit remains. You still need to find a way to get your payload up to a speed of at least 8 kilometers per second, regardless of how high you can get it in the air. That would still require a huge rocket, and a suitably huge balloon to lift it!

For now, orbit remains devastatingly hard to reach, whether you want to go by rocket, airship, or nuclear-powered paddle steamer. Don’t expect to float to the Moon by airship anytime soon, even if it sounds like a good idea.

Our own Dan Maloney has been on a Voyager kick for the past couple of years. Voyager, the space probe. As a long-term project, he has been trying to figure out the computer systems on board. He got far enough to write up a great overview piece, and it’s a pretty good summary of what we know these days. But along the way, he stumbled on a couple old documents that would answer a lot of questions.

Dan asked JPL if they had them, and the answer was “no”. Oddly enough, the very people who are involved in the epic save a couple weeks ago would also like a copy. So when Dan tracked the document down to a paper-only collection at Wichita State University, he thought he had won, but the whole box is stashed away as the library undergoes construction.

That box, and a couple of its neighbors, appear to have a treasure trove of documentation about the Voyagers, and it may even be one-of-a-kind. So in the comments, a number of people have volunteered to help the effort, but I think we’re all just going to have to wait until the library is open for business again. In this age of everything-online, everything-scanned-in, it’s amazing to believe that documents about the world’s furthest-flown space probe wouldn’t be available, but so it is!

It makes you wonder how many other similar documents – products of serious work by the people responsible for designing the systems and machines that shaped our world – are out there in the dark somewhere. History can’t capture everything, and it’s down to our collective good judgement in the end. So if you find yourself in a position to shed light on, or scan, such old papers, please do! And then contact some nerd institution like the Internet Archive or the Computer History Museum.

Although we have a gaggle of space telescopes floating around these days, there is still a lot of value in ground-based telescopes. These generally operate in the visible light spectrum, but infrared ground-based telescopes can also work on Earth, assuming that you put them somewhere high in an area where the atmosphere is short on infrared-radiation absorbing moisture. The newly opened Universe of Tokyo Atacama Observatory (TAO) with its 6.5 meter silver-coated primary mirror is therefore placed on the summit of Cerro Chajnantor at 5,640 meters, in the Atacama desert in Chile.

This puts it only a few kilometers away from the Atacama Large Millimeter Array (ALMA), but at a higher altitude by about 580 meters. As noted on the University of Tokyo project site (in Japanese), the project began in 1998, with a miniTAO 1 meter mirror version being constructed in 2009 to provide data for the 6.5 meter version. TAO features two instruments (SWIMS and MIMIZUKU), each with a specific mission profile, but both focused on deciphering the clues about the Universe’s early history, a task for which infrared is significantly more suitable due to redshift.

After more than four decades in space and having traveled a combined 44 billion kilometers, it’s no secret that the Voyager spacecraft are closing in on the end of their extended interstellar mission. Battered and worn, the twin spacecraft are speeding along through the void, far outside the Sun’s influence now, their radioactive fuel decaying, their signals becoming ever fainter as the time needed to cross the chasm of space gets longer by the day.

But still, they soldier on, humanity’s furthest-flung outposts and testaments to the power of good engineering. And no small measure of good luck, too, given the number of nearly mission-ending events which have accumulated in almost half a century of travel. The number of “glitches” and “anomalies” suffered by both Voyagers seems to be on the uptick, too, contributing to the sense that someday, soon perhaps, we’ll hear no more from them.

That day has thankfully not come yet, in no small part due to the computers that the Voyager spacecraft were, in a way, designed around. Voyager was to be a mission unlike any ever undertaken, a Grand Tour of the outer planets that offered a once-in-a-lifetime chance to push science far out into the solar system. Getting the computers right was absolutely essential to delivering on that promise, a task made all the more challenging by the conditions under which they’d be required to operate, the complexity of the spacecraft they’d be running, and the torrent of data streaming through them. Forty-six years later, it’s safe to say that the designers nailed it, and it’s worth taking a look at how they pulled it off.

Volatile (Institutional) Memory

That turns out that getting to the heart of the Voyager computers, in terms of schematics and other technical documentation, wasn’t that easy. For a project with such an incredible scope and which had an outsized impact on our understanding of the outer planets and our place in the galaxy, the dearth of technical information about Voyager is hard to get your head around. Most of the easily accessible information is pretty high-level stuff; the juicy technical details are much harder to come by. This is doubly so for the computers running Voyager, many of the details of which seem to be getting lost in the sands of time.

As a case in point, I’ll offer an anecdote. As I was doing research for this story, I was looking for anything that would describe the architecture of the Flight Data System, one of the three computers aboard each spacecraft and the machine that has been the focus of the recent glitch and recovery effort aboard Voyager 1. I kept coming across a reference to a paper with a most promising title: “Design of a CMOS Processor for use in the Flight Data Subsystem of a Deep Space Probe.” I searched high and low for this paper online, but it appears not to be available anywhere but in a special collection in the library of Witchita State University, where it’s in the personal papers of a former professor who did some work for NASA.

Unfortunately, thanks to ongoing construction, the library has no access to the document right now. The difficulty I had in rounding up this potentially critical document seems to indicate a loss of institutional knowledge of the Voyager program’s history and its technical origins. That became apparent when I reached out to public affairs at Jet Propulsion Lab, where the Voyagers were built, in the hope that they might have a copy of that paper in their archives. Sadly, they don’t, and engineers on the Voyager team haven’t even heard of the paper. In fact, they’re very keen to see a copy if I ever get a hold of it, presumably to aid their job of keeping the spacecraft going.

In the absence of detailed technical documents, the original question remains: How do the computers of Voyager work? I’ll do the best I can to answer that from the existing documentation, and hopefully fill in the blanks later with any other documents I can scrape up.

Good Old TTL

As mentioned above, each Voyager contains three different computers, each of which is assigned different functions. Voyager was the first unmanned mission to include distributed computing, partly because the sheer number of tasks to be executed with precision during the high-stakes planetary fly-bys would exceed the capabilities of any single computer that could be made flyable. There was a social engineering angle to this as well, in that it kept the various engineering teams from competing for resources from a single computer.

To the extent that any one computer in a tightly integrated distributed system such as the one on Voyager can be considered the “main computer,” the Computer and Command Subsystem (CCS) would be it. The Voyager CCS was almost identical to another JPL-built machine, the Viking orbiter CCS. The Viking mission, which put two landers on Mars in the summer of 1976, was vastly more complicated than any previous unmanned mission that JPL had built spacecraft for, most of which used simple sequencers rather than programmable computers.

On Voyager, the CCS is responsible for receiving commands from the ground and passing them on to the other computers that run the spacecraft itself and the scientific instruments. The CCS was built with autonomy and reliability in mind, since after just a few days in space, the communication delay would make direct ground control impossible. This led JPL to make everything about the CCS dual-redundant — two separate power supplies, two processors, two output units, and two complete sets of command buffers. Additionally, each processor could be cross-connected to each output unit, and interrupts were distributed to both processors.

There are no microprocessors in the CCS. Rather, the processors are built from discrete 7400-series TTL chips. The machine does not have an operating system but rather runs bare-metal instructions. Both data and instruction words are 18 bits wide, with the instruction words having a 6-bit opcode and a 12-bit address. The 64 instructions contain the usual tools for moving data in and out of registers and doing basic arithmetic, although there are only commands for adding and subtracting, not for multiplication or division. The processors access 4 kilowords of redundant plated-wire memory, which is similar to magnetic core memory in that it records bits as magnetic domains, but with an iron-nickel alloy plated onto the surface of wires rather than ferrite beads.

The Three-Axis Problem

On Voyager, the CCS does almost nothing in terms of flying the spacecraft. The tasks involved in keeping Voyager pointed in the right direction are farmed out to the Attitude and Articulation Control Subsystem, or AACS. Earlier interplanetary probes such as Pioneer were spin-stabilized, meaning they maintained their orientation gyroscopically by rotating the craft around the longitudinal axis. Spin stabilization wouldn’t work for Voyager, since a lot of the science planned for the mission, especially the photographic studies, required a stable platform. This meant that three-axis stabilization was required, and the AACS was designed to accommodate that need.

The physical design of Voyager injected some extra complexity into attitude control. While previous deep-space vehicles had been fairly compact, Voyager bristles with long booms. Sprouting from the compact bus located behind its huge high-gain antenna are booms for the three radioisotope thermoelectric generators that power the spacecraft, a very long boom for the magnetometers, a shorter boom carrying the heavy imaging instruments, and a pair of very long antennae for the Plasma Wave Subsystem experiment. All these booms tend to wobble a bit when the thrusters fire or actuators move, complicating the calculations needed to stay on course.

The AACS is responsible for running the gyros, thrusters, attitude sensors, and actuators needed to keep Voyager oriented in space. Like the CCS, the AACS has a redundant design using TTL-based processors and 18-bit words. The same 4k of redundant plated-wire memory was used, and many instructions were shared between the two computers. To handle three-axis attitude control in a more memory-efficient manner, the AACS uses index registers to point to the same block of code multiple times.

Years of Boredom, Minutes of Terror

Rounding out the computers of Voyager is the Flight Data Subsystem or FDS, the culprit in the latest “glitch” on Voyager 1, which was traced to a corrupted memory location and nearly ended the extended interstellar mission. Compared with the Viking-descended CCS and AACS, the FDS was to be a completely new kind of computer, custom-made for the demands of a torrent of data from eleven scientific experiments and hundreds of engineering sensors during the high-intensity periods of planetary flybys, while not being overbuilt for the long, boring cruises between the planets.

The FDS was designed strictly to handle the data to and from the eleven separate scientific instruments on Voyager, as well as the engineering data from dozens of sensors installed around the spacecraft. The need for a dedicated data computer was apparent early on in the Voyager design process, when it became clear that the torrent of data streaming from the scientific platforms during flybys would outstrip the capabilities of any of the hard-wired data management systems used in previous deep space probes.

It was evident early in the Voyager design process that data-handling requirements would outstrip the capabilities of any of the hard-wired data management systems used in previous deep space probes. This led to an initial FDS design using the same general architecture as the CCS and AACS — dual TTL processors, 18-bit word width, and the same redundant 4k of plated-wire memory.  But when the instruction time of a breadboard version of this machine was measured, it turned out to be about half the speed necessary to support peak flyby data throughput.

To double the speed, direct memory access circuits were added. This allowed data to move in and out of memory without having to go through the processor first. Further performance gains were made by switching the processor design to CMOS chips, a risky move in the early 1970s. Upping the stakes was the decision to move away from the reliable plated-wire memory to CMOS memory, which could be accessed much faster.

The speed gains came at a price, though: volatility. Unlike plated-wire memory, CMOS memory chips lose their data if the power is lost, meaning a simple power blip could potentially erase the FDS memory at the worst possible time. JPL engineers worked around this with brutal simplicity — rather than power the FDS memories from the main spacecraft power systems, they ran dedicated power lines directly back to the radioisotope thermoelectric generators (RTG) powering the craft. This means the only way to disrupt power to the CMOS memories would be a catastrophic loss of all three RTGs, in which case the mission would be over anyway.

Physically, the FDS was quite compact, especially for a computer built of discrete chips in the early 1970s. Unfortunately, it’s hard to find many high-resolution photos of the flight hardware, but the machine appears to be built from eight separate cards that are attached to a card cage. Each card has a row of D-sub connectors along the top edge, which appear to be used for card-to-card connections in lieu of a backplane. A series of circular MIL-STD connectors provide connection to the spacecraft’s scientific instruments, power bus, communications, and the Data Storage Subsystem (DSS), the digital 8-track tape recorder used to buffer data during flybys.

Next Time?

Even with the relative lack of information on Voyager’s computers, there’s still a lot of territory to cover, including some of the interesting software architecture techniques used, and the details of how new software is uploaded to spacecraft that are currently almost a full light-day distant. And that’s not to mention the juicy technical details likely to be contained in a paper hidden away in some dusty box in a Kansas library. Here’s hoping that I can get my hands on that document and follow up with more details of the Voyager computers.

It shouldn’t be a surprise that the idea of a planetarium originated with an electrical engineer, [Oskar von Miller] from the Deutsches Museum in Munich. According to [Allison Marsh] in IEEE Spectrum, he thought about the invention in 1912 as a way to demonstrate astronomical principles to the general public. While it seems obvious today that you can project the night sky onto a dome, it was a novel thought in 1912. So novel that the Carl Zeiss company first told [von Miller] to take a hike. But they eventually reconsidered and built the first planetarium, the Model I.

The engineer for Zeiss was a mechanical engineer by the name of [Walther Bauersfeld]. He was familiar with mechanical devices — orreries — that tracked the motion of the stars and planets. The goal was to translate those movements into a moving projection of light.

The practical realization of the projector required two independent projection spheres. One projected the stars and moved as a unit. It also held a cage that moved differently with projectors for the planets. Other separate projectors handled things like the Milky Way. There were 180 stars and the orbit of Saturn, just as an example was over 11 meters in diameter.

Even the domed projection room required innovative design. All of this would be easy with modern computers, but doing it all with gears seems quite a task. World War I slowed progress, but the Deutsches Museum committee saw an early demonstration of the device in late 1923. They were impressed.

Of course, the planetarium went on to become a…well, a star of science museums. Of course, there were improvements over time. Today, there are more than 4,000 planetariums worldwide. While [von Miller] and the Zeiss company made the first modern planetarium, mechanical devices date back to the time of [Archimedes], although they weren’t optical. However, in 1229, Emperor Frederick II acquired a tent with holes in it representing stars that rotated to show the movement of heavenly bodies.

Want to build your own private planetarium? [Gabby] did. You might want to grab some magnets.

In what is probably the longest-distance tech support operation in history, the Voyager mission team succeeded in hacking their way around some defective memory and convincing their space probe to send sensor data back to earth again. And for the record, Voyager is a 46-year old system at a distance of now 24 billion kilometers, 22.5 light-hours, from the earth.

While the time delay that distance implies must have made for quite a tense couple days of waiting between sending the patch and finding out if it worked, the age of the computers onboard probably actually helped, in a strange way. Because the code is old-school machine language, one absolutely has to know all the memory addresses where each subroutine starts and ends. You don’t call a function like do_something(); but rather by loading an address in memory and jumping to it.

This means that the ground crew, in principle, knows where every instruction lives. If they also knew where all of the busted memory cells were, it would be a “simple” programming exercise to jump around the bad bits, and re-write all of the subroutine calls accordingly if larger chunks had to be moved. By “simple”, I of course mean “incredibly high stakes, and you’d better make sure you’ve got it right the first time.”

In a way, it’s a fantastic testament to simpler systems that they were able to patch their code around the memory holes. Think about trying to do this with a modern operating system that uses address space layout randomization, for instance. Of course, the purpose there is to make hacking directly on the memory harder, and that’s the opposite of what you’d want in a space probe.

Nonetheless, it’s a testament to careful work and clever software hacking that they managed to get Voyager back online. May she send for another 46 years!

A cornerstone of early 1970s rock music culture was the British singer David Bowie in his Ziggy Stardust persona, along with his backing band the Spiders from Mars. You can tell that the PR department at the European Space Agency were beside themselves with glee at the opportunity to reference them when their Mars Express spacecraft snapped a picture of some of the planets surface structures which bear a passing resemblance to Earth-bound spiders. We can’t blame them, we’d have done the same.

While these spiders are definitely not arachnid in origin, they are no less interesting. Over the Martian winter there form layers of carbon dioxide ice, which turn to gas under the influence of the Sun. This gas becomes trapped underneath layers of ice, until it forms sufficient pressure to burst through and escape. In doing so it brings up dark dust which settles along fissures in the ice, leading to the spider-like patterns when viewed from orbit.

So no life on Mars then, at least as yet. But it’s an interesting observation, and another little piece in the puzzle of understanding our planetary neighbor, as well as an excuse for a classic rock earworm. Meanwhile, this isn’t the first time we’ve reported on the ESA Mars probes.

After many tense months, it seems that thanks to a gaggle of brilliant engineering talent and a lucky break the Voyager 1 spacecraft is once more back in action. Confirmation came on April 20th, when Voyager 1 transmitted its first data since it fell silent on November 14 2023. As previously suspected, the issue was a defective memory chip in the flight data system (FDS), which among other things is responsible for preparing the data it receives from other systems before it is transmitted back to Earth. As at this point in time Voyager 1 is at an approximate 24 billion kilometers distance, this made for a few tense days for those involved.

The firmware patch that got sent over on April 18th contained an initial test to validate the theory, moving the code responsible for the engineering data packaging to a new spot in the FDS memory. If the theory was correct, this should mean that this time the correct data should be sent back from Voyager. Twice a 22.5 hour trip and change through Deep Space and back later on April 20th the team was ecstatic to see what they had hoped for.

With this initial test successful, the team can now move on to moving the remaining code away from the faulty memory after which regular science operations should resume, and giving the plucky spacecraft a new lease on life at the still tender age of 46.