Delta IV Upper Stage : What are all these parts for?

[EzinX]

Found this fascinating image on wikipedia :

Why are there miles of wiring, using what look like fairly heavy insulation and connectors? What's in the various boxes visible in the image? What about the spherical red tanks? Or the cylindrical ones located higher up?

Part of my questioning is, I just wonder what all that stuff is for. The second bit is that I thought with rocket engineering, you would want to save every gram. I see an awful lot of stuff

that doesn't look like it is as low mass as it could theoretically be : you could in theory store the same compressed gas volume that's in those red tanks in a smaller number of larger tanks. You could replace what look like analog signal cables bundles with digitizing the sensor data closer to the sensor and use lighter digital bus cables. So I wonder how much performance you lose, although I guess the reasoning is that reliability is a much more important goal than saving a few kilograms on the control and sensor systems.

[Voidryder]

Wooo-weee, you sure ask a lot of questions. I'm going to do my best to try and answer you based upon my years of building (been playing KSP since 0.17) some of the most advanced rockets known (to me).

First and first most, you need to have bright shiny parts. Lots and lots of bright shiny parts or it just won't fly. As you can see, the stage in the picture is bright and shiny. She is gonna fly just fine.

Second, you need to use the four basic rocket colors - white, black, silver and red.

Let's break those colors down by function:

• White is used for big parts that hold fuelly stuff and smaller important parts like electronic brains-thingies.
  
• Black is used for making parts stronger. It's been scientifically proven that painting a part black adds 20% to it's shear and/or tensile strength.
  
• Silver is for reflecting sunlight. Space is dark and reflecting sunlight helps when your astronauts forget where they left their rocket.
  
• But the most important color is Red. Red makes things go fast. Note the rocket nozzle is red. This baby is all about speed.
  

Now you can see in the picture the rocket engineers used yet another color - gold. Gold can be used to signify several different things. One is that this rocket cost a lot of money so don't screw up the launch or your fired. Helps motivate the pad crew. The other reason is gold is important looking. Let's everyone know that your rocket is...um...important.

Now that we got the basics of rocket design out of the way, let's address some of your specific questions.

1) Using analog parts versus digital: Seriously, don't tell me that you haven't experienced a dead zone on a cell phone. That be digital. But my old analog radio still can pick up Radio Havana late at night from 200 klicks away with the right tinfoil antenna. Analog - why fix what ain't broke.

2) A lot of small tanks or a few big ones: It's all about weight. A single worker can lift and bolt a smaller tank in place by themselves. Go bigger and you gotta hire more workers. Cost savings is the name of the game in rocket building.

So I hoped this helped take some of the mystery out of why rockets look so complicated.

See ya in The Black.

[kerbiloid]

Btw, http://en.wikipedia.org/wiki/Delta_Cryogenic_Second_Stage

contains another Kerbal-oriented link: https://web.archive.org/web/20110722081616/http://www.ulalaunch.com/site/docs/product_cards/guides/DeltaIVPayloadPlannersGuide2007.pdf

and it's not too bad.

[Lunniy Korabl]

Since it's capable of deorbiting itself, I'd imagine there's navigation and RCS stuff all crammed in there. It's basically a fully functional spacecraft wrapped around an upper stage.

[Kryten]

Since it's capable of deorbiting itself, I'd imagine there's navigation and RCS stuff all crammed in there.

All upper stages have independent avionics, since most spacecraft aren't build to handle this kind of navigation. Only recent exception is the MDU stage used on Phobos-Grunt, with predictable results when the P-G flight computer failed.

Edited December 4, 2014 by Kryten

[Nibb31]

Those red tanks are probably the helium tanks to provide pressure to the fuel tanks. Upper-stage engines are typically pressure-fed, especially when they are restartable, because you can't count on gravity to ensure ullage.

The reason there are several small ones instead of one big one is probably cost, integration, and spreading the mass. You could probably have a larger tank, but it would affect your CoM, or it would be more expensive, and maybe harder to move around and install.

A rocket stage needs performance, but it also needs reliability and needs to be reasonably cheap. It's the combination of all those factors that makes rocket design complicated. Pretty much everything in rocket design has a reason. The people who make this stuff are smart. Different designs are the results of different decisions made on different requirements, but in the end, there are rarely "stupid" designs.

Edited December 4, 2014 by Nibb31

[rhoark]

The RL-10B2 engine on the IUS uses an expander cycle. The poofy looking tank the engine sits on holds LOX, while the white cylindrical tank holds LH2. The red spheres hold helium to actuate valves, pressurize the LOX tank, and purge water from the system after shutdown. (Water is the combustion byproduct and will freeze and block lines if not purged.) The red cylinders are probably hydrazine for RCS. The LH2 tank is pressurized by gas tapped off the combustion chamber. The black box top/center looks like a computer. There's a schematic of the RL-10B2 on page 9 of this: https://webfiles.uci.edu/dbeerer/rockets/RL10.pdf

[Nuke]

heres my thoughts:

i bet the red tanks are pressurant for the fuel tanks (probibly helium).

the wiring is likely well insulated. it has to shield the signals from crosstalk, and it also has to cope with extremes in temperature. this results in thick wiring.

most of the wires likely go to on board sensors from all over the stage. many of those senors probibly are digital (protocols like i2c, spi, canbus, etc) and so have all the signal wires and power wound into one wiring harness. these days analog sensors are usually packaged with an analog to digital converter so that the signals can be converted on chip before being exposed to the noisy environment of wires. it makes little since to use analog wiring.

some of the wires may also run high power devices like servo valves, solenoids, relays, pumps, etc and so have thick diameters to better suit the higher power devices. some also look like your main power busses which also need to be thick.

[Guest]

Actually, you're all wrong about the red parts. If you see the full-res image, you could read the writing on them. Everything red will be gone before the flight. The protective blanket on the nozzle, the tanks, protective caps, everything. On takeoff, there should be no red elements on any aircraft (besides the paintjob). The tanks are likely there to keep the tanks pressurized, IIRC, the DCSS uses balloon tanks, which are not supported by any sort of structure. This means they need to be pressurized, or they'd collapse.

Hydrazine tanks might not be installed yet. For ullage, the DCSS uses boiloff hydrogen, so the hydrazine load would be very small. The movable nozzle extension is also missing (the black things are guide rails for it).

As for the wiring, it doesn't weigh that much. Besides, this is Delta IV's "instrument unit" containing computers that fly the rocket. It's expected that there'll be a lot of wires in the thing's main control system. They can't be too flimsy, or they'd run into trouble with cosmic rays.

[rhoark]

Like the nozzle, its a covering that will be removed from the bottles, not the bottles themselves.