Piston, Jet, and Rocket Engines

Engines! So interesting. We learned about the basic four-stroke engine, as well as diesel engines, during our Train Unit. And early planes used this type of piston engine. See this animation for a demonstration.

(In fact, this is one of our favorite sites ever—it shows animations of different kinds of engines at work. Certain of the children could watch this site, mesmerized, for hours at a time. :))

Later, the jet engine was invented, and there are several types of jet engine: Turbofan/turbojet engines (high- and low-bypass); Turboprops; and Turboshafts. It took us a while to get them straight, but this site does a good job of explaining the differences.

Here's another site that talks about types of jet engine.

We also learned about ramjets and scramjets which are used in rocket propulsion and hypersonic flight.

Here's a "boring" (self-described) animation of a jet engine at work. :)

This site has some good information on engines.

As does this one, including parts of an engine.

Here's a simple activity to demonstrate how rocket propulsion works. We tried this with a long balloon and with a round one. The round one worked MUCH better (more volume of air, I suppose).

The balloon being propelled along the string!

A video about how jet engines work. And on the same subject, another video we really liked.

Sonic booms are so interesting! Here are two videos about them.

ATK Rocket Display

As we were driving toward Promontory Summit, we saw several signs with pictures of rockets and "ATK" on them. We wondered if we were near some sort of explosives or rocket factory, but we'd never heard of ATK and didn't see anything that looked recognizable. We thought no more of it until we were driving back from the Golden Spike historic site, and Sebby said, "Look at that long white rocket!" I was not inclined to believe there would be such a thing, out in the middle of the desert, but after we went around a few more bends in the road, there it was! Something long, white, and pointy. We decided we had to go investigate.

It wasn't difficult to find, as there were road signs that said "Rocket Display--2 miles." We just followed them and soon arrived at a large, office-building-y facility, with a bunch of rockets strewn around in front. We parked in visitor parking and went to look around. The rockets and motor casings all have signs in front of them, and helpful diagrams showing you which components they are. It was awesome! 

It was so windy and there were tumbleweeds everywhere! We passed a million of them on the road.

Later I mentioned this place to a couple people, who both said, "Oh, Thiokol?" in a knowledgable way. Which I'd never heard of either, but I guess that's its parent company, or what it used to be called, or something. ATK stands for Alliant Techsystems, apparently, and they have several facilities in Utah. What we had run into was the ATK Propulsion Systems facility. It's nice of them to put out their rockets for people to look at, way out there in the middle of nowhere! The other thing you should do while in the area, I've heard, is look at the Spiral Jetty (if it's not underwater, that is). But we didn't do it, regrettably.

Patriot Missile

Motor casing

And our very favorite (Malachi was ecstatic to see this in person!)---the reusable solid rocket motor. (This picture shows the exit cone.) This is one of the motors that goes on the outside of the space shuttle, like this:

It was so enormous! We loved it. And it was the perfect place to eat our lunch. :)

Playing Astronaut

Re-entry parachute check

One of my favorite things to watch is the way the children play whatever we are currently learning about. Of course, these Solar System weeks were FULL of astronaut and space play. I love this astronaut kit Abraham made for Malachi. Note the "launch hole" (!!) he climbs inside of to launch from (this is to protect bystanders from being burned by his rocket boosters firing!)

Ready for launch (wearing jetpack)

Take-off!

Seb dressed in his astronaut gear

Junie doesn't want to be left out

Daisy with rocket and launch tower she built from blocks

Nuclear Submarines and Nuclear Rocket Propulsion

We were very interested in other uses of nuclear fission technology (besides in power plants). There are two areas in particular we learned about: nuclear submarines and nuclear-powered rockets.

Submarines are now powered by nuclear reactors almost exclusively, we learned, as they allow the subs to stay underwater for such long periods (the fuel doesn't require oxygen as a combustion engine would!) and thus allow great stealth. This site has a great video on the subject; we also had a couple books.

It was funny, a couple weeks later: I was reading the children a book about dolphins, and it said they used high-pitched sounds to bounce off objects to help them navigate, a technique called echolocation. As we'd talked about this before with our Night unit, I asked, "What other animal uses echolocation?" Seb immediately shot his hand in the air and stopped me almost mid-sentence. "Nuclear submarines!" he said. "Oh, and bats." Yes, Sebby thinks nuclear submarines are animals. How sweet. :)

The information we had on nuclear rockets was sketchier. We read about the Orion project, after WWII, which explored the idea of using nuclear bombs to propel rockets. It was eventually scrapped in favor of the Saturn rocket series (chemically propelled) but we kept finding references to the fact that "nuclear technology is also used in rockets today." However, we couldn't find many details about this, even on the NASA site!  Luckily I have a physicist brother that I can turn to. Hooray for Karl! I reproduce our conversation here, not because I think it will be particularly interesting to most, but in case someone who doesn't have a physicist brother is searching for the same information.

Karl's answers appear in blue:

Karl, 

Is there an easy way to explain our current nuclear rocket technology? We learned about the Orion project in the 1950s-70s, which proposed using tiny fission bombs to propel a rocket. After that project was cancelled, we learned, nuclear rocket propulsion was mostly abandoned---but then we read that the Russians have been using nuclear power for their rockets for some time, and that the New Horizons spacecraft also uses nuclear power for some things. But we can't find details. We assume it's not the tiny nuclear bomb thing, and the boys surmised that maybe it was a mini nuclear reactor, like they use in nuclear submarines. Do any rockets use this, and if so, how? (They don't have propellers for the turbines to turn, do they?)

First, I'd never heard of the Orion project.  It sounds dangerous!  I'm not surprised it never came to fruition.

We tried to read about the New Horizon spacecraft, and it talked about radioisotope technology, but very vaguely. Does this mean they AREN'T using a reactor, but instead just using the natural radioactive decay of plutonium to create heat? And then what is the heat used for? And wouldn't that be too slow/weak of a power source to fuel a rocket? There was a bunch of stuff on the NASA site about how safe! and not scary! this technology is, but not much about how it actually worked.

Every use of radioisotopes harnesses their heat.  In a fission reactor, you get a lot of Pu and a lot of heat, and you superheat steam with it and drive a turbine which turns an electric generator.  You are correct, there are no turbines on spacecraft.

If no steam and no turbines, what is left?  There are thermopiles and thermovoltaics.

Thermopiles are multiple thermocouples in series and parallel to generate the needed voltage and current (Seebeck effect).  An example of a thermopile is in your gas fireplace if you have one.  The little rod poking into your pilot light is a thermopile, and it generates enough electricity to open the gas valve.  Your fireplace will run even with the power out. 

A thermovoltaic works like a photovoltaic (photocell) where the "light" is very long wavelength (IR) light from the hot radioisotope.  These are less common. 

Some spacecraft that use thermopiles: Cassini, New Horizons, Curiosity. 

When we say the spacecraft are powered by these devices, we refer to generating electricity for the on-board systems: communication, navigation, attitude control, etc.  Not propulsion.  They are sent on their way using conventional rocket propulsion.  The entire future trajectory is set in the first few minutes of flight!  It does use small jets of hydrazine for attitude correction. 

The boys also wanted to know, are there any plans to use the "tiny bomb" type of rocket in the future? Or to use a fission reactor, if they aren't already using them?  

No plans that I know of, and I'd be surprised to ever see it. 

Karl.

Next we wondered:

Thank you! Very helpful. We are disappointed there is no nuclear propulsion method. Wouldn't that be able to get us much farther into space, if it could be done?

And Karl answered:

I don't really know how much better that would work.  Propulsion is all about Newton's 2nd law: action, reaction.  The only way you can go forward in space is to send some mass backward.  An explosion sends some mass backward, very fast.  But not all the energy coming from the explosion can be turned into motion.  A more spectacular explosion does not result in any more motion. 

If you want to get the most bang for the buck, so to speak, I believe you want to be gentle.  That is, you want to get the maximum eventual speed for a given amount of propellant since you can only take a finite amount of propellant with you.  I believe the best engine in that sense is the ion engine.  A heavy gas atom is ionized and accelerated through a potential.  As it exits the engine, an electron is added to the ion to make it neutral again, and therefore not attracted back to the spacecraft.  Therefore, the entire mass of the gas atom minus the tiny fraction that is the electron mass is converted into forward momentum. 

It takes years for these to accelerate to an appreciable speed, but they will get us farthest into space because of the efficient use of the propellant.  (To get away from earth's gravity, you do need to do something violent to create enough acceleration at first.) 

Karl.

So! There you have it. Thank you Karl, for a concise explanation of nuclear-powered rockets that anyone can understand! After all, it's not rocket science! (Ha ha! Sorry, I can't help myself. We kept that joke going for several days. We had a book called This is Rocket Science that set us off.)

Here is a bit more information, from the NASA site.

And an interesting video about a small reactor for deep space exploration.