Roman Telescope Saves Fuel, Doubles Mission

September 30, 2026 by Zoe Skyforest 14 Comments

Contemplate the events that might end a space mission, and you might picture something dramatic: detonation on the pad, a dead guidance system, or micrometeoroids shattering delicate solar panels. More often, though, the ending is far more mundane. Plenty of perfectly healthy spacecraft have been retired simply because the fuel tanks ran dry. That’s why mission planners guard every kilogram of go juice so jealously, and why careful preparation in a mission is critical to long-term success.

Which brings us to NASA’s Nancy Grace Roman Space Telescope. Barely two weeks after its August 30 launch on a Falcon Heavy, the mission team announced that Roman now has enough fuel for at least 22 years of science operations. That’s well over double its original 10-year fuel budget. It’s a huge gain, so let’s explore how NASA pulled it off.

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The FPGA Chronicles: Exploring The Tang Nano 20K

September 28, 2026 by Al Williams 36 Comments

FPGAs used to be mysterious, expensive devices, but these days you can buy surprisingly capable boards for very little money. Some years ago, I did an FPGA Bootcamp over on Hackaday.io. Much of that material still applies, but the hardware is dated. So I decided it was time to update it, using the inexpensive Tang Nano 20K and its GOWIN GW2AR-18 FPGA as the main platform, with perhaps a few excursions into other FPGAs.

History and Motivation

Once upon a time, if you wanted to have a custom IC, you went with a wheelbarrow full of money to a semiconductor company. However, some smart person at a semiconductor fab eventually realized they could make a chip with a lot of uncommitted blocks on it and then, for a custom chip, only design the wiring that connected them together. This still required a wheelbarrow full of money, but it was a smaller wheelbarrow.

Then one day, someone realized they could do the same thing but make the electrical connections between the blocks configurable. Maybe have fuses you can blow, or use EEPROM or RAM cells to remember which blocks are connected to which. It is complicated, sure, but then you can make many of these chips and sell them to people who could, in theory, make their own custom chips without your help.

When do you need an FPGA? A classic classroom exercise for an FPGA, for example, is a traffic light because it shows off how to do state machines, which are important for some kinds of FPGA designs. But other than as a learning example, why would you do this? Even a simple 8-bit CPU can handle a traffic light.

Suppose instead that you have hundreds of digital sensors on a rocket, and any one of them must raise an alarm within a few microseconds. A processor has to sample inputs in groups, service interrupts, or rely on extra hardware. An FPGA can simply implement the equivalent of one enormous OR gate. It watches every input continuously, and unrelated logic elsewhere in the FPGA does not steal execution time from it. Can you do it with a microcontroller? Probably, but not easily. For some classes of problems, an FPGA is the better answer.

Of course, you can also build a CPU on your FPGA and some FPGAs have CPUs in the same package. This is often a sweet spot because then things that are easy to do in software, you do in software. Things that are easier to do in hardware, you do in the FPGA.

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After Decades, NASA May Finally Replace Mars Relays

September 24, 2026 by Tom Nardi 19 Comments

We’ve yet to find any definitive evidence that there’s biological life on present-day Mars, but to say it’s a dead planet isn’t exactly accurate. Since the first Viking lander touched down in 1976, a revolving cast of humanity’s robotic envoys have worked on and around the Red Planet — and as access to space becomes cheaper and more routine, the mechatronic population of Mars will continue to grow.

Given the number of landers, rovers, and orbiting spacecraft that have been sent to study Mars over the last 50 years, you might be surprised to find that the communications systems in place to transmit all that critical scientific data back to Earth aren’t nearly as robust as you’d think. While it’s understandable that the first craft to arrive at Mars had to operate in isolation, even the flagship Perseverance and Curiosity rovers carry their own high-gain radio systems so they can communicate directly with Earth. Given the incredible premium put on the mass of an interplanetary craft, each mission that needs to bring along its own link back to Earth effectively reduces its payload of much scientific equipment.

It’s not that satellites in orbit around the planet aren’t used to relay signals between Martian ground assets and their controllers back on Earth. In fact these relay links are used extensively for bandwidth-intensive tasks such as image transfers. But it’s also true that the craft currently available to act as intermediaries between the two planets aren’t terribly well suited to the task. The current fleet of Mars orbiters were conceived primary as research vehicles, and so every decision regarding their design and positioning around the planet was made with that goal in mind. What relatively limited capability they do have as communication relays is further hindered by the age of their hardware.

But after decades of false starts and shifting budgets, NASA is closer than ever to finally establishing the Mars Telecommunications Network, a dedicated high-bandwidth communication relay that will ensure current and future missions always have a way to phone home.

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Hunting The Wild Vibrotruck

September 9, 2026 by Elliot Williams 46 Comments

A few weeks ago, my wife was out walking the dog, and she sent me four or five photos of small orange boxes planted all around our neighborhood. (OK, I’ll bite!) They had little cards on them explaining that they were geophones, and a QR code on them that lead to a website with all the details. Munich was getting a large-scale seismic survey to map out our underground water, with the aim of using it for geothermal heat and power in the near future.

A geophone in its native habitat.

How do you map up to five kilometers under the earth? You pound the ground, sending shockwaves downward, and then listen for their reflections. At the boundaries between different layers, the change in the speed of sound in the different media cause reflections. Calculating the time it took for a given reflection to reach you lets you figure out how deep the layer boundary is.

The seismic survey procedure goes like this: geophones are set out at roughly 20 m intervals in lines spaced around 300 m apart that run roughly north-south, while “vibrotrucks” drive a roughly east-west course, creating mini-earthquakes every 20 meters along the way. Covering a surface of 1,000 km^2 with over 120,000 sample locations and exciting them 86,000 times is going to take a while. Lucky for me, they started in my part of town.

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“I’m Not Dead Yet!” Reverse Polish Notation Calculators You Can Still Buy

September 2, 2026 by Al Williams 77 Comments

If you used a scientific calculator in the 1970s or 1980s, there was a fair chance that it worked differently from almost every calculator you see today. Instead of typing:

2 + 3 =

you entered:

2 ENTER 3 +

There wasn’t even an equals key. Hewlett-Packard made this system — Reverse Polish Notation, or RPN — practically synonymous with serious scientific calculators until other players like TI and Casio got serious. Once you got used to it, ordinary algebraic calculators could feel annoyingly clumsy.

Today, RPN calculators look like a nearly extinct species. HP left the calculator market, licensing the HP calculator line to Moravia Consulting. Old HP-15Cs, 16Cs, 32Ss, 42Ss, and 48s have become collectibles. But RPN isn’t dead. You can still buy new hardware, build your own, or turn almost any computer or phone into a very capable RPN machine. There are reasons some of us still want to.

But Why Polish?

The name goes back to Polish logician [Jan Łukasiewicz], who devised a notation in which operators precede their operands. Instead of writing:

A + B

you can write:

+ A B

The big advantage is that parentheses aren’t required. The structure of the expression tells you exactly what operates on what. Reverse Polish notation simply puts the operator at the other end:

A B +

[Łukasiewicz] wasn’t designing calculators, of course, but the same idea turned out to be extremely convenient for computers and calculators. Your software doesn’t have to remember what operation is in progress. Each operator is ready to go and can simply work on the operands that you’ve already read.

RPN isn’t exactly the way people calculate with pencil and paper, and it certainly wasn’t derived from the slide rule, but there is a similarity in the way you work. With a slide rule, you generally establish some value, operate on it, and continue from the result. When doing a long-hand calculation, you often calculate a subexpression, write down the answer, and use that answer in the next step. You will probably start with the inner parenthesis and work outward, just like someone with an RPN calculator does. RPN formalizes that process with a stack.

Suppose you want:

(3 + 4) × (5 + 6)

On a conventional calculator, you either need parentheses, or you have to calculate one result and remember it. On an RPN calculator:

3 ENTER

4 +

5 ENTER

6 +

×

The first + leaves 7 on the stack. The second leaves 11 above it. The multiply consumes both and leaves 77.

Notice what’s missing: parentheses, an equals key, and any need to tell the calculator about precedence. This isn’t much of a win for a five-key calculation. It becomes more apparent with something like computing the value of a bunch of parallel resistors:

R=1/(1/R1+1/R2+1/R3…)

An RPN user can calculate each reciprocal, add it to the running result on the stack, and finally take the reciprocal. Intermediate answers stay in the calculator naturally instead of being stuffed into memory registers or enclosed in increasingly impressive collections of parentheses.

Is RPN better? Calculator users have been arguing about that for half a century. But once RPN gets wired into your fingers, it can be surprisingly hard to give up.

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What’s Mu Metal?

August 31, 2026 by Al Williams 28 Comments

If you tear into old TVs or recording equipment, you may see shields made from some exotic-looking metal. Old timers will tell you it’s called mu metal, and its purpose is to — sort of — shield things from magnetic fields. The qualification is important. Unlike a conductive RF shield, mu metal doesn’t really stop a magnetic field. Instead, it gives magnetic flux an easier path to follow around whatever you’re trying to protect.

What’s In The Metal?

Mu metal belongs to a family of soft magnetic nickel-iron alloys. A typical modern formulation is about 80% nickel and 15% iron, with molybdenum and a few other elements making up most of the remainder. What makes it useful is its extremely high magnetic permeability. Commercial material can have relative permeability around 100,000 or more, and some specialty alloys can reach even higher.

You can think about reluctance as the magnetic equivalent of resistance. Put a high-permeability shell around something sensitive, and magnetic flux would much rather travel through the shell than through the space inside it, just like current tends to take the path of least resistance.

This works particularly well for DC and low-frequency fields, exactly where your usual copper or aluminum EMI shield isn’t much help.

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An Early History Of Space Stations: The Brick Moon Made Real

August 20, 2026 by Al Williams 21 Comments

People have lived in space stations for decades now, but something is wrong with them. Where are the big rotating wheels? You know the ones. They show up in old paintings of the future and, perhaps most memorably, in 2001: A Space Odyssey. Spin a great wheel in space, and people can stroll around inside with something that feels suspiciously like gravity. It seems like an obvious idea.

It is also an old idea. Much older than actual spaceflight, in fact. But to find the beginning of the space station, we have to go back to a time when powered aircraft were still several decades in the future.

A Moon Made of Bricks

In 1869, Edward Everett Hale published The Brick Moon in The Atlantic Monthly. The moon in question wasn’t natural. Hale imagined building a 200-foot-diameter sphere made from bricks and putting it into orbit as a navigation aid. Sailors could sight it and use its known orbit to determine their longitude. There was only one small problem: the thing was accidentally launched with people aboard.

That makes The Brick Moon generally regarded as not only the first fictional artificial satellite, but also the first fictional space station. Hale followed it in 1870 with Life on the Brick Moon, describing how the accidental colonists got along up there.

Hale didn’t have rockets. He proposed flinging the thing into the sky with giant flywheels, but, then again, it was 1869, so we’re inclined to cut him some slack. As the 19th century turned into the 20th, however, people started doing the math.

Konstantin Tsiolkovsky is best remembered for putting rocket flight on a sound theoretical footing. The Russian schoolteacher wrote extensively about orbital flight and space habitation, envisioning people living in orbit long before anyone had demonstrated that a liquid-fueled rocket actually worked. His ideas included rotating habitats to provide artificial gravity.

Hermann Oberth’s 1923 book Die Rakete zu den Planetenräumen — The Rocket into Planetary Space — Oberth went beyond fiction and seriously considered a permanently inhabited station. He envisioned it being periodically supplied by smaller rockets, serving as an observation and communications platform, and even acting as a jumping-off point for trips farther into space. He also suggested spinning the station to give the crew artificial gravity.

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