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Post by ka9q on Nov 7, 2011 20:06:14 GMT -4
Thanks, Jay.
Had JW been at all honest, he would acknowledge those videos from Delta II hypergolic upper stages firing in space. There is absolutely no visible plume at all. The only clue that anything is even happening is the glow of the engine nozzle extension. Also, a bit of debris (ice, etc) occasionally falls off, demonstrating that the stage is under acceleration.
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Post by JayUtah on Nov 7, 2011 22:51:32 GMT -4
The Delta II is especially valid because its second stage is the same motor as the LM APS for all intents and purposes. I like the Titan, but its thrust chamber and nozzle are strictly old school. The Delta II is as faithful a modern demonstration as you can get.
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Post by ka9q on Nov 8, 2011 6:22:27 GMT -4
Right. I think I read that the hypergolic version of the Delta second stage engine was actually derived from the LM APS engine.
There may be other second stage engines for the Delta, but the hypergolic version is by far the most popular because of its inherent restart capability.
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Post by trebor on Nov 8, 2011 15:52:26 GMT -4
The RP1/LOX plume is incandescent in the atmosphere, but is not in near vacuum. Watch this video of the Apollo launch. Shortly after launch the plume is long, thin and bright. By T+1:45 (altitude ~20km) the plume has spread-out considerably due to the lower pressure, but is still glowing. By T+2:20 (altitude 46km), the plume is very wide and the particles (basically soot) are no longer incandescent. There is also this nice video of a Space X launch : www.youtube.com/watch?v=GHs6QyB5GWMIt shows very clearly the change in the plume with altitude. Edit: And a Delta II: www.youtube.com/watch?v=IvB-8CWw9eURight at the end you see the second stage start up.
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Nov 8, 2011 16:19:18 GMT -4
I've also noticed that the portion of a Titan II plume where the two nozzle plumes overlap is noticeably brighter than the individual plumes. Why is that? Since none of the Apollo spacecraft engines had twin nozzles, this effect would not be present in any Apollo footage so it's another reason Jarrah's selection of Titan II footage is dishonest, as is the fact that all of that Titan II footage is in a sea level atmosphere. The turbine exhaust duct in also located between the two engine nozzles. It's possible that the turbine exhaust's interaction with the main plume may be contributing to the brighter zone that you're noticing. This is again not applicable to Apollo as the LM's engines were pressure-fed and didn't use turbopumps.
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raven
Jupiter
That ain't Earth, kiddies.
Posts: 509
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Post by raven on Nov 8, 2011 19:03:45 GMT -4
According to Astronautix, gods that's an awesome sight to just read, the initial run of Delta II had surplus LM descent stage engines as the second stage.
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Post by Apollo Gnomon on Nov 11, 2011 11:56:56 GMT -4
I have a nit to pick with the OP video.
Regarding the image of steam coming from a kettle: the invisible portion is, as stated in the video, gaseous water. The visible portion is NOT, as stated, due to "other gasses." That's liquid water, very small droplets. The gas condenses as it cools and returns to liquid phase, but the droplets of liquid are so small that they are just floating around in the air. If you observe a plume of "steam" you might note that the cloud eventually disperses from the moisture-saturated area and evaporates.
This might seem like picking at an irrelevancy, but the steam image was presented in support of another argument, that the visible exhaust plume is due to "other gasses" in the atmosphere burning. I'm pretty sure the flame temperature of rocket exhaust is too low for that.
The visible exhaust plume is not adequately explained in your response video. The handwaving of jw should not be met with other handwaving but with specifics, details, equations and charts.
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