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!

Don't plug the pressure relief valve.

The pressure relief valve is one of my favourite pieces of safety equipment.

In this case, it's just a simple valve that's designed to leak if the pressure gets above a certain point on one side. By letting a small leak happen, you avoid having the pressure get higher than the tank or pipe is designed to handle. If the pressure in a tank gets higher than it's designed to handle, you get stuff like this:

They aren't only on large industrial systems though.

That one was a little bitty (5 gallon, according to the public safety notice I found it on) hot water tank that exploded. A full size hot water tank does a lot more damage, such as done by this 80 gallon commercial hot water tank installed for a school cafeteria. Did I mention you don't ever plug the pressure relief valve? It's there for a reason.

And because it involves explosions, mythbusters naturally did a couple of episodes to find out if a hot water tank really does launch itself like a rocket and if it really can punch through the 2nd floor then the roof of a 2-story house.

So yeah, if your hot water tank has a dripping valve, don't plug it—call the repairman and put a bucket under it until then.

The reverse of a pressure relief is a vacuum relief, which lets air into tanks that you're emptying. Like this one:

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.