Carbon survey

Tomorrow, NASA launches the OCO-2 satellite, which will make a detailed map of how much CO₂ is in the atmosphere at various points on the globe. They plan to combine that data with data from other existing satellites, atmospheric sampling, and ground sampling, with the goal of finding out where CO₂ is being produced and where it's being absorbed—in very high resolution, about 3 km² per measurement, or, smaller than a big coal-fired power plant.

The satellite will be in a polar orbit which allows it to fly over every single spot on earth every 16 days, which means it will generate a complete map of CO₂ concentrations every 16 days—less the areas that were covered in cloud when it flew over on that cycle. This repeated mapping also means that seasonal variations can be tracked, to separate a long-term trend from a seasonal fluctuation.

OCO-2 measures CO₂ by measuring how much light is absorbed by the CO₂ as sunlight travels down to the surface, reflects off the planet, and bounces back up to the satellite. So, cloud cover interferes with the measurement, and repeated mapping is one of the ways they're compensating for that.

Chilly chemical properties

Because it's the middle of winter here in Canada, I think today is a good day to talk about refrigeration.

Just kidding. Actually it's because the ISS had to replace a piece of its refrigeration system last week, and I thought that was a good excuse to talk about refrigeration.

Most modern refrigeration involves the chemical property \(\Delta H_{vap}\), or enthalpy (heat) of vaporization. Every substance has a heat of vaporization, and the amount of heat energy required to vaporize a substance is independent of what temperature the substance boils at. To choose a rather extreme contrast, water boils at 100C while lead boils at 1750C, but water requires 539cal/g to convert from liquid to gas while lead only needs 208cal/g, less than half that required by water. This amount of heat does not account for how much is required to get to the boiling point, and if you remember your high school chemistry, the temperature does not change with the additional heat input while it changes from liquid to gas.

The basic principle in use here is that when a substance evaporates, it draws heat energy from its surroundings (or the more familiar form: when you add heat to a substance, it will evaporate), and when a substance condenses, it releases heat energy back to its surroundings. Put an insulated barrier between these two sides of the process, and you have refrigerators, freezers, and air conditioners which get colder "inside" and warmer "outside".

Two rovers

Once again, there are two rovers alive and well on the surface of Mars.

Just over eight hours ago, Curiosity landed on Mars. It was an odd mixture of tension and knowing that no matter what we saw, it was all 14 minutes in the past and there was absolutely nothing anybody could do.

Two rovers? You haven't forgotten Opportunity, have you? Eight and a half earth years old (five martian winters) and still going strong.

Not a sunrise, but a galaxy rise

I just discovered the "Symphony of Science" series of music videos. Gorgeous visuals in this one, both on the screen and inspired in my head by the lyrics.

I don't really have much to say about it, except that it makes me happy when I watch it. This music video has lyrics made entirely from recordings of things said by Carl Sagan (with a verse by Stephen Hawking), with their tone digitally altered to fit the melody.

Recycling water

It may be something we don't like to think about, but one of the things the astronauts have to do while in orbit will be coming more and more to Earth. Fresh water is limited, and getting more so with time. Water conservation helps, but it may not be enough in the future.

Whether they are dependent on well water or surface water, many cities have to worry about having enough water to last through the dry season as the water levels drop. Water restrictions are common in some areas; where I grew up, part of the summer routine was that you couldn't water your lawn whenever you wanted, but only on certain days. Sometimes there was an outright ban on watering lawns if the river level was too low.

At the same time, the volume of water leaving a city's wastewater treatment plant is a substantial part of what the city brought in to start with, and grows with population more than the season.

As wastewater treatment technology improves, the sewage plant's discharge gets cleaner and cleaner, so why not use it as feed for our clean water treatment system?

Science fiction fans, rejoice!

All I can really say about this is, WOW.

NASA's Kepler team has found loads of planet candidates to date (about 2300) by measuring variations in brightness in the star as the planet orbits. They've confirmed a bunch of them as well, so we know there are other planets out there. And just in case you think 2300 is a low number considering how many stars are in the sky, keep in mind that the Kepler telescope has been staring at a patch of sky about the size of your outstretched hand the entire time. I don't know about you, but I can't even see 2300 stars in that kind of an area, and the Kepler telescope has found that many planet candidates.

Now they've found one in its star's habitable zone - where liquid water can exist.

If you take a look at their news story, they show our solar system with the habitable zone defined - Venus is too close to the sun to be habitable, but Earth and Mars are both in the right area. This is why they've been sending robots to Mars to look for evidence of past water. Past water, because Mars' atmosphere is much too thin to retain enough heat to have present water, but it does have present ice in the form of its polar ice caps (as well as solid CO₂, dry ice).

It remains to be seen whether this planet has an atmosphere which will hold in enough heat to maintain liquid water, but at least its orbit is in the right place for this even to be an option. Composition of some planets' atmospheres (mostly the early Jupiter-sized ones so far) has been studied using infrared absorption spectra, which is a whole level of nifty that I would need to study for a while to understand.

The Voyagers are still going strong

This pair was aptly named. Launched in 1977, the Voyagers are still cruising, still doing science, still sending back photos and data, still occasionally making the news. Just this past summer, they discovered bubbles in the outer edge of the sun's magnetic field, way out at the boundary of the solar system.

The most recent news is more mundane and administrative in one sense, and pretty darn amazing in another sense. The Voyagers have now switched the last set of thrusters to the backup set. Sounds kind of boring, until you realize that this means the longest lasting of the primary set of thrusters lasted for 33 years. Without maintenance. Yeah, try that with your car.

Every time I look at this set of twins, they amaze me. They were designed from the start to be deep space probes; these are the ones who carry the famous golden record (and the needle to play it—yes, it is in fact a phonograph record, only made out of gold instead of vinyl) and took the first ever picture of both the earth and the moon in the same frame. (Links at the bottom of that page to larger versions of the photo.) They're also the only spacecraft ever to have visited Uranus (1986) and Neptune (1989). Everything we know about those two planets beyond distant telescope viewing, we owe to Voyager 2.

Apparently now that they're fully switched to the backup thrusters, they can shut off the heat to the primaries and save power, and expect to get at least another 10 years out of the backup thrusters. Did I mention the backup thrusters weren't maintained for over 30 years either, and they worked fine when NASA turned them on? This just boggles my mind.

I am curious to see what they find when they finally cross out of our sun's area of influence and get into interstellar space, and I really hope their thrusters last that long. (The thrusters in question aren't their drive, they're for aiming the antenna so they can keep talking to Earth.) They just keep on finding new things!

Gravitational assumptions

I was working on some fluid flow at work the other day, and while trying to determine whether I could use gravity flow between a series of tanks or whether I had to put a pump in there somewhere, I wondered how a chemical plant built in microgravity would work.

Fluids or solids move because they have potential energy. (Once they're moving they also have kinetic energy.) So what kind of potential energy could, say, a pipe full of water have, if it didn't have gravitational potential and thus couldn't do any kind of gravity flow?

The first thing I thought of was pressure; this is how pumps overcome gravity and lift liquids uphill. Absent gravity, building up pressure at one end of a pipe would push the fluid toward the other, lower pressure end.

Up, up, a little bit higher

In honour of today's shuttle launch, I thought I'd start off with a bang, or at least a roar of fire: rocket fuel!

The shuttle uses two different styles of rockets with two very different types of fuel: liquid and solid. The shuttle itself has three big rocket engines that run on liquid hydrogen and liquid oxygen, stored in the big orange external tank, while the rest of the thrust is provided by solid fuel in the solid rocket boosters, a mixture of ammonium perchlorate (NH₄ClO₄), aluminum, iron oxide, and some binders to hold it in its moulded shape.

The liquid fuel engines fire first; they are the controllable ones. If there's a problem, they can be shut down. Once the solid fuel starts burning, they only stop by running out of fuel - and the solid rockets provide the majority of the boost to get the shuttle off the ground.

And since this is a chemical engineer's blog, I'm going to do some calculations around the chemistry of those engines. Of course, this won't be nearly enough to design your own rocket engine from, but then I'm just doing this for fun, I'm not a rocket scientist.