#lasersheet

The first lab session featured the Car Mirrors team doing the awfully glamorous work of cleaning out the crusty old water channel dye setup. I have no idea how long that crust had been developing, but luckily it came off fairly easily with some hot water (no elbow grease required!)

The water channel in its original state looked like a bad elementary school art project, with black stains all over the bottom of the bucket. Rinsing that out was a treat, and the bubbling black water reminded me of a horror film. Like I said, though, it all washed off fairly easily with some hot water, and only minor scrubbing was necessary to remove a clot of dye that had stuck to the bottom of the bucket.

This final dial setup is shown above. Somewhere among the mess of tubes you can see a dirty tube. That one appeared to have mold in it, and try as we might, we couldn’t clear the apparent blockage in the tube. So we decided the best course of action was to chalk up that one bottle as a loss and limit ourselves to two bottles.

All clean!

On Wednesday, Dr. Doig was absent, so we set out using what we had discussed last with him about where to go with the project. Another team was using the water channel, so we decided to scout out potential places to run a truck through at moderate speeds. We started pretty close to the wind tunnel to minimize the amount of extension-cord tomfoolery needed to set the smoke machine up. This is the view from down the service road:

So I was fairly surprised that the path was actually wide enough to fit a car (or truck) through. Of course, moving at neighborhood speeds like we’re planning to makes this a safety risk for people leaving their labs. The doors won’t suddenly open into the vehicle, but anyone walking out would be in for a surprise. An alternative to running the vehicle down the length of the walkway is to have it start from that reddish bush behind the spacecraft environment students. It probably wouldn’t be possible to get much higher than 20-25 mph (~40 kmh) before needing to stop before the bus/service road, and if we mount the laser sheet on the wall of the prop lab yard, shown below:

There wouldn’t be much time to stop before said service road.

One other option is the yard in between all the aero labs. There’s a more open space for the vehicle to run, and if the laser sheet is mounted to the fence seen, there should be slightly more time to stop. So, we have three options to drive the vehicle down during testing time that would be of at minimum dubious safety standards. If none of those work, the “wind tunnel option” (stationary body and moving air) shouldn’t be too hard to recreate with a leafblower, but I don’t know how the turbulence from a leafblower would impact the smoke. Perhaps if there was some leftover flow straightener honeycomb? Decisions decisions...

Of the many idle conversations we have in the conference room, one involved none other than Santa Claus

Specifically, we were discussing the rules of the Santa Clause (the Tim Allen movie) and his magical weight gain, but I can turn this discussion to sciency talk pretty easily.

Suppose there are just under 2 billion children under age 14 in the world. Now, Christians make up about 30 percent of the world population. At that clip, there would be about 600 million Christian kiddos on Christmas Eve. Lets assume this is a very generous year for St. Nick, and 9/10 of the children make the Nice List™. If all 540 million children were split at 2 to a household, that’s 270 million households to visit. Upon trying to look this distance up, I realized I’ve run into the Traveling Salesman Problem, and I didn’t really want to go down that rabbit hole for just a Tumblr post, so I’m going to cheat, and use these numbers for how far Mr. Claus has to travel in a night. So he’s got to travel 3 million miles (~5 million km) in 32 hours, and I will be generous to Santa’s delivery skills and say that he spends only 25% of his time delivering, and the rest traveling. That leaves him 24 hours to travel those 5 million km. That translates to a speed of 5787 m/s-at STP that’s Mach 170!

I wanted to translate this number into power requirements using the weight of 9 Reindeer + 1 Sleigh + 1 Obese Male (ignoring gifts of course) but then I realized I’d have to make assumptions about the shape and drag of Santa’s sleigh so I decided against that. What I can tell you is that traveling at this Mach number, design considerations must be made to prevent both the vaporization of your reindeer, and whatever heat shield you try to put in front of them. There’s also the issue of the shock wave. Traveling at Mach 170 would create a Mach wave behind the, uh, craft, at an angle of .33 degrees to the horizontal. If Santa wants to avoid hitting airliners, he should fly at an altitude of 20000 m (the U-2 had an “operational ceiling” of “70000 ft” *wink wink*. This is just over 21000 m, but Santa shouldn’t run into another super secret spy aircraft. Until he flies over Russia, anyway). Anyway, at an altitude of 20000 m, a Mach wave at .33 degrees to the horizontal should strike the ground 3400 km behind Santa. This is just about a quarter of the diameter of the Earth. I think that even when you consider the spherical nature of the Earth, the Mach wave should actually hit the ground, instead of careening off into space, guaranteeing that Santa blasts out every window on every building around the world once a year. Of course, he’s probably not traveling that high to just jump between neighboring houses, but to go across the Atlantic Ocean (which takes anywhere from half a second to a full second at these speeds, by the way), he’ll probably be able to reach his cruising altitude.