What I Learned Today

Recently I enjoyed working through Coursera’s Rocket Science for Everyone taught by Prof. Marla Geha.

The course reminds us that achieving orbit is all about going horizontally fast enough that you “miss” the Earth’s surface. For our planet’s mass, to achieve low Earth orbit, that speed is about 7.6 km/sec. I was interested to learn that given our available chemical propulsion options, we almost didn’t make it to orbit.

The rocket equation defines the change in velocity (delta_v) that you get from a given fuel and rocket design:

delta_v = v_exhaust ln(rocket mass [initial] / rocket without fuel mass [final] )

Exhaust velocity (v_exhaust) is how fast material is pushed out of the rocket, given the fuel you are using. This value for our propellants is about 2-3 km/sec, which means you need something greater than 95% fuel in order to get to 7.6 km/sec and achieve low Earth orbit! (By making that natural log of the mass ratio large enough)

Fortunately, smart people figured out that you can work around this limit using multiple stages and discarding spent containers to improve your mass ratio as you go. But if our planet had been more massive, we would have had to get a lot more creative to find something that would work.

Another bonus: launching near the equator and west to east gives you 0.5 km/sec for “free” (if you want an equatorial orbit). But Vandenberg Air Force Base (not equatorial) is a good launch site if you want a polar orbit instead (no freebies).

I also learned that GPS satellites are not out at geostationary orbit (which would allow them always to be in view, and only require three total to cover the Earth) because they didn’t want to have to build ground stations for them all over the Earth (i.e., in other countries) but instead just in the U.S. Interesting.

Great class – I recommend it!

While visiting Montreal, I found this fascinating American typewriter on display at the small museum tucked into a grand Bank of Montreal building:

The compact size and unusual key layout caught my eye. I looked it up later and found out that it’s a Blickensderfer typewriter, invented in 1892 by George Canfield Blickensderfer. (Note that the caption says 1884 but I’m guessing this is a typo, since the Model 5 was not introduced until 1893, and the Model 7, which is what appears in the photo, was introduced in 1897.) It featured a lot of innovations compared to existing typewriters, including a much more compact size, fewer parts, lighter weight, the careful choice of keyboard layout, and a rotating typewheel that contained all of the letters and symbols in one place, in contrast to the individual key-arms with one letter per arm! The typewheel meant that you could change the machine’s entire font by swapping it for another typewheel.

The keyboard layout was carefully chosen. “Blickensderfer determined that 85% of words contained these letters, DHIATENSOR,” (Wikipedia) and so those letters were used for the home (bottom) row of the keyboard. The earlier QWERTY layout (1874) was designed to minimize the chance of the key-arms hitting each other, something the Blickensderfer model did not have to worry about.

I’d love to get to type on one of these machines. I’d have to re-learn touch typing with the different layout, but what a marvelous machine, packed with ingenuity!

It’s still early times, but what a captivating thought!

Last year, DARPA created the LunA-10 study, a 10-year effort that “aims to rapidly develop foundational technology concepts that move away from individual scientific efforts within isolated, self-sufficient systems, toward a series of shareable, scalable systems that interoperate.”

So far, our trips to the Moon have been isolated visits, but if we’d like to get serious about sustained activity, additional infrastructure (for mobility, communication, energy generation, etc.) would surely be useful.

Recently, Northrop Grumman provided some details about their part of LunA-10, which aims to develop a framework for a railroad network on the Moon. How cool is that? I’d love to be part of that study.

LunA-10 participant updates are planned to be shared at the Lunar Surface Innovation Consortium meeting, final reports from each of the LunA-10 participants will be due in June – here’s hoping they’re made publicly available.

Recently I had the pleasure of taking a free online course offered by the Transportation Safety Institute (TSI) called Rail Nomenclature. As a big train fan, it was a delightful opportunity to learn about terminology related to trains and rail systems and to get more insight into how they work.

The introduction to the course quoted George Bernard Shaw as motivation:

“The single biggest problem in communication is the illusion that it has take place.”

… which has so many implications beyond just terminology for railroads! I agree!

I learned a lot from this course. For example, did you know that we have both the Federal Railroad Administration (in charge of transport of people (Amtrak) and freight via railroad) and the Federal Transit Administration (in charge of public transit, which includes buses, subways, commuter rail, etc.)? I was intrigued to learn that the U.S. has 47 rail transit systems, 4000 miles of track, and 4.2B trips per year – more than airlines, but fewer than buses. (This is just for systems controlled by the FTA, so the numbers exclude Amtrak numbers.)

The course covered terminology used to describe train cars themselves, parts of the track, signal systems, power systems, and more. There was quite a bit of detail about braking systems in particular – important if you’ve got several tons generating momentum to dissipate when you want to stop. When the train is going more than 3 mph, it uses “dynamic” brakes in which the motors driving the wheels stop and become generators instead. If electrical storage is available, they can serve as regenerative brakes. When the train is going more slowly, it employs friction brakes (e.g., calipers squeeze pads against the wheels to slow their rotation). Both of these brake types are familiar to car owners. However, the train has a third option for emergencies: track brakes, in which the train uses strong magnets to press metal shoes directly onto the rail for additional drag (I guess this would be like toe stops on roller skates :) ).

Another cool fact is that the rails do double duty: not only do they provide a surface for the train to roll on, but they also provide a medium for signaling. This can be as simple as a track circuit: if you run power through a segment of metal track with no train on it, the circuit is closed and the corresponding signal can show a green light indicating the track is unoccupied. When a train enters that segment, its axles short the rails together and current drops, triggering the signal light to change to red. Thus, any train approaching that segment gets an automatic warning of whether the track ahead is occupied, even if the approaching train cannot be seen. No person or computer is needed to actively monitor it. (If power to the track fails, the signal defaults to red.)

More courses are available through the TSI course catalog. This particular class required Flash and was a little difficult at first to get working due to popups etc. However, the course instruction was very visual and fun to follow along – it used Flash to animate drawings of the concepts as they were discussed. I don’t know if they plan to revamp the course, since Flash support ends on December 31, 2020. You might want to check it out now before it’s gone! You get a certificate at the end, of course. :)

I have a lawn mower (reel mower) that is purely mechanical: you push it and as it moves it spins five curved blades that chop up the grass. It has no engine and uses no gas or electricity. Mowing the lawn with it is a nice exercise: you push it along and it makes a quiet snick-snick-snick sound as it cuts the grass. I’m very fond of it!

Yet over the years the blades grow dull. I figured I’d need to take it to a sharpening service, but then I found this Instructable that shows you how to sharpen a reel mower yourself. It’s quite clever *and* easy to do! You use the mower to “lap” its own curved blades, meaning to sharpen and align them by running them backwards against the fixed blade (“bed knife”). As advertised, this was straightforward: I swapped the gears on the two wheels, adjusted the bed knife (this was actually the trickiest part for me), smeared on “grinding compound” (I ordered this Permatex compound for just $4!), and then pushed the mower around for a while with its blades grinding each other smooth/sharp. In this process I also got to study just how the mower works (I love decoding machines) and to admire the built-in ingenuity and simplicity of it.

At least, that’s what it was supposed to do. After I’d pushed it for a while, I felt the blades with my finger. They had turned shiny (see picture at right), but didn’t feel sharp. I decided to give it a try. I swapped the gears back, readjusted the bed knife, and took my mower out to the lawn. And whoa! It cut the grass WAY BETTER than it had for a long time. In fact it cut it much shorter than before – I think with dull blades it was bending the grass over and cutting it longer. I had *wondered* why I had to leave the mower on the lowest height to get anything reasonable. Now I can set it to a higher (correct) setting and get the desired grass height. Very satisfying!