I was watching the HBO miniseries “From the Earth to the Moon” which has a lot of vintage footage of Saturn 1B and Saturn V launches. I understand that all the stuff that looks like ice… is ice… from the very cold propellant in the rocket. But what is all the “smoke” or stuff that looks like liquid oxygen pouring out of the rocket? I vaguely remember hearing that for some reason, they had to really overfill the rocket with liquid oxygen due to micro cracks or something - and that all that junk pouring out was just spill over… but I am not sure. So what is all that stuff?
I believe that’s air being rapidly compressed, which causes it to form a vapor cloud. You see the same thing on fighter jets when pulling high G-forces.
A “vapor cloud” is not visible. Perhaps you are thinking of condensation or fog, which is a cloud of liquid water droplets.
Moreover, compression of air results in adiabatic heating, which will not result in condensation. The relevant phenomenon is expansion, which results in adiabatic cooling and associated condensation. This expansion/condensation is what you are seeing on the upper surface of fighter jets operating at high angles of attack; it’s also what you see in planes traveling at approximately the speed of sound, as well as in the shock waves from very large bombs detonated in humid environs; in both cases, the condensation occurs in an expansion wave following immediately behind the shock front.
To the OP: can you provide more detail about what you are seeing? My guess right now is that it’s almost certainly condensation/fog, but without knowing more, it could be from several causes:
- the skin of the rocket is extremely cold because of the liquid oxygen inside; that’s why the ice is there, and there’s certainly condensation/fog forming in the air as well. You can get the same effect with a very cold beer in calm air on a humid day, where fog gently glides down the side of the bottle and away on the table.
-liquid oxygen coming out of the rocket bell prior to ignition causes local cooling, resulting in condensation/fog that can be seen.
-dynamic expansion of the air downdraft after the engines start. The exhaust gases flowing downward at Ludicrous Speed drags ambient air down with it; that air expands as it gets up to speed, so maybe you’re seeing condensation/fog in that air.
So…exactly when (before/after ignition) and where (around fuselage, around engine bells, or coming out of engine bells) are you seeing this stuff?
I assumed he meant before ignition. I’ve always thought that the ‘fog’ was LOX being vented and falling down along the sides of the rocket. (I should know this, but this is one of my infamous pre-coffee posts and I don’t remember and am moving too slowly to look it up in one of my books.)
If it’s after ignition, just at liftoff, then it’s the ice pulverised into a powder that is falling off.
One should note that a very cold undisturbed beer on a hot humid day is just theoretical construct. Those conditions have only been approached (but never reached) under extremely precise and controlled laboratory conditions. In nature it will never happen.
If you’re asking about what’s venting out the side before launch, it was oxygen. That had to be put into the rocket, at cryogenic temperatures, hours or even days before launch, and more had to be put in than would be needed for the flight because of inevitable gradual warming and evaporation. Venting off the vapor prevented tank pressures from exceeding limits. What you saw was condensation from the humid Florida air caused by contact with the still-cold oxygen vapor.
What I had in mind is in this youtube video http://www.youtube.com/watch?v=wvWHnK2FiCk
at around 2:01 - 2:14 right before “U S A” goes by vertically. All that smokey stuff just pouring off the rocket, which I assume is condensation or liquid oxygen from the thread. What an amazing launch. If this is real time, I think I would have messed my pants waiting for it to get off the ground - I was not quite born in time to see one of these live.
At about 2:01 to 2:13
Fog. Just like the cold beer analogy. The florida coast is an obscenely humid place (right now Weather Underground says Titusville is at 80 degrees and 92% relative humidity!), and the Saturn - with big tanks of LO2 - is one big-ass, ice-cold beer.
You’ll notice that the fog/ice is present mostly on the lower part of the second stage, and the upper part of the first stage. That’s consistent with this schematic, which identifies that area as the LO2 tanks for first and second stage. By the time you get to the ribbed section in your video (2:09), the fog is gone; that ribbed section joins the bottom of the first-stage LO2 tank with the top of the first-stage kerosene tank (see schematic). The kerosone, unlike the LO2, is not supercooled, and so you don’t see the fog/ice forming on the exterior of that portion of the rocket.
Thanks folks.
http://www.boston.com/bigpicture/2009/07/remembering_apollo_11.html
Photo 13.
Just in case someone wants to amend this post. Fog really forms that quickly?
Look where the fog is in your photo - the area between the two striped sections on the lower 1/3 of the rocket - and then check out the schematic (link in my previous post): that’s exactly the location of the LO2 tank for first-stage. The LO2 tank for second-stage is much shorter, and according to the schematic, only comes into close proximity with the outer skin of the rocket at the top of the ribbed joiner section. In your photo, that’s the top edge of the black-and-white striped section just below the vertical red “UNITED STATES” label. And you can see there’s actually a bit of frost/ice forming there, too.
As to whether fog can form that quickly…yes, when temps are that low. This is not an ice cube from your freezer at 0F; Liquid oxygen has a boiling point of nearly -300 degrees Fahrenheit. A bucket of liquid nitrogen (similar boiling point) in a chem lab will cause much the same sort of heavy fog/icing.
In your photo, you can even see ice/fog rolling down the right side of the launch gantry. my assumption here is that this is from the pipeline that had been used to bring LO2 to the tanks on the rocket; just like the rocket itself, the super-cold pipe is shedding fog, and - during liftoff - the vibrations are pulverizing the accumulated ice/frost into a cloud of dust (bigger chunks are visible farther down in the debris stream).
Wouldn’t the LO2 be less of a problem than the liquid hydrogen H2 in the second and third stage tanks? I understand they had problems with air condensing on the parts of the tanks where the H2 was.
This apparently was a design issue on the space shuttle’s external tank. There is of course the infamous foam insulation over the entire tank’s exterior surface to limit water-ice formation, but supposedly extra insulation is required on/near the LH2 tank to prevent liquifaction of air.
Possibly the Saturn designers employed the same solution, with the result that the skin temperatures in the vicinity of the 2nd/3rd stage LH2 tanks were not as low as the skin temps near the LO2 tanks. There is still some fog rolling off of that area; see Youtube video @1:51, corrugated black ring (near top of frame) is top of third stage LH2 tank. Fog may also be emanating from the white-painted areas, though it’s difficult to tell for certain in the video.
Is the fueling done at the last minute? Is that because it might warm up?
For the space shuttle, the orbital maneuvering engines (large pods on either side of the vertical stabilizer, and other nozzles all over the exterior of the orbiter) use nasty, toxic, super-reactive fuels; that stuff is loaded shortly before liftoff simply because it’s dangerous stuff.
The solid boosters (tall white sticks on either side of the space shuttle’s big orange fuel tank) are pre-filled with solid fuel at the contractor’s facility in Utah weeks (months?) before a launch.
I was unable to find when exactly they load the LH2 and LO2 for the a space shuttle launch. I’m pretty sure it’s loaded within 24 hours of launch, but not because it might warm up. As long as there’s liquid H2 or O2 in the tanks, the temperatures of those liquids will not exceed their respective boiling points (hundreds of degs. below zero). But as they absorb ambient heat they will continue to boil off, reducing the total mass available to power the engines.
I suspect the same would be true of the Saturn rocket. The kerosene for the first stage could be loaded whenever convenient (subject to fire hazard concerns), but the LO2 and LH2 would want to be transferred to the rocket relatively late in the game.
Pretty close, if you stretch “last minute.” If you look at cutaway diagrams of the Saturn V stages, you’ll see that basically each one is mostly a big fuel tank, with an engine at the bottom. It takes a long time to fuel that up – several hours at least.
As for the reason why – that’s basically the last thing they had to do. Dry, the fully assembled Saturn V weighs 430 thousand pounds. When fueled up, the weight increased to 6.2 million pounds. So obviously, it’s a lot more feasible to stack it, check it out, and move it to the pad empty. (The rocket was assembled in the Vehicle Assembly Building, three and a half miles away from the launch pad.) Yes, fuel temperature was an issue, but I don’t think you’d say it was the reason they fueled the bird last thing. There just wasn’t anything more to do once the fuel was on board except strap the astronauts in and flip the switch.
Note that they were also topping off the fuel until right before launch (within an hour, if not less) because it bubbled away.
–Cliffy
Update: I was poking around the site I linked to earlier, and it contains the Saturn V News Reference, a briefing document written in the '60’s by the major contractors on the rocket. I’ve been poking around a little, and it says that the fuel of the Apollo craft (that is the Command-Service and Lunar Modules) and the small auxiliary engines along the Saturn rocket for guidance and to separate spent stages, etc., are fueled “before launch day.” The kerosene which is the fuel for the first stage of the Saturn V is pumped in the day before launch (the rocket already on the pad for a couple days at this point). The rest – liquid hydrogen fuel for the top two stages and liquid oxygen oxidizer for all three – are cryogenic (hundreds of degrees below zero), and they’re the ones that boil away. It says they start fueling several hours before launch (I think it said 7 hrs., but now I can’t find the reference). It takes 4 1/2 hrs. to complete fueling, but the cryogenics keep boiling off, so they’re constantly replenished up to 70 seconds before launch. Dang.
–Cliffy
I’ve always wondered what the Estes order number is for the SRBs and how much it’d cost buy one.
Just to be completely tedious, I ran the numbers.
Based on the specs of a space shuttle SRB, and the model rocket motor classification scheme, I came up with the specs for a model rocket engine comparable to the SRB as:
X-10,700,000-218
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