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Liquid Vs. Solid Rocket Propellants


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Initial post: Jan 27, 2010, 2:04:14 PM PST
Last edited by the author on Jan 27, 2010, 2:05:31 PM PST
The debate and research continue. Most say that solid fuel is the best, but loses some of the advantages of liquid fuel. Here are a sampling of articles on this topic:

http://www.centennialofflight.gov/essay/SPACEFLIGHT/solids/SP13.htm
(A government essay on liquid versus solid rocket fuels, and which country uses what.)

http://www.braeunig.us/space/propel.htm
(A discussion and list of ROCKET PROPELLANTS)

http://moncom.net/moncomrocketrymsgs.asp?topictoview=2
(An amateur rocketry site, with a Q&A discussing HOMEMADE SOLID ROCKET FUEL.)

You might also want to check out a book here on Amazon, the 2009 edition of "Future Spacecraft Propulsion Systems ..." by Czysz and Bruno.

Let the discussion begin!

In reply to an earlier post on Jan 27, 2010, 11:58:02 PM PST
Ronald Craig says:
Wrong forum: move to Science.

Posted on Jul 17, 2010, 6:48:44 AM PDT
Last edited by the author on Jul 17, 2010, 6:50:00 AM PDT
http://io9.com/5401436/the-best-sub+light-propulsion-system-this-side-of-luyten-726+8b/

Ion Thrusters running on xenon for Generation Ships?

In reply to an earlier post on Jul 17, 2010, 7:54:32 AM PDT
M. Helsdon says:
"Ion Thrusters running on xenon for Generation Ships?"

Ion thrusters aren't "Liquid" or "Solid Rocket Propellants".

The main difference between liquid and solid rockets is that a solid rocket cannot be shut down -- until it has exhausted its fuel supply. This means you cannot use a solid rocket to make small course changes which is why they are generally used for missiles or as booster rockets to augment the lift capability of a liquid rocket.

An ion 'rocket' accelerating ions and still need a propellant. The main problem with an ion thruster for an interstellar ship is that the thrust is very low even though it can continue 'firing' for long periods of time.

In reply to an earlier post on Jul 17, 2010, 7:21:53 PM PDT
Ronald Craig says:
"Ion thrusters aren't 'Liquid' or 'Solid Rocket Propellants'."

Details, man, just details! Who are YOU to let details stand in the way of unrestricted truth-seeking SPECULATION?!

:D

Posted on Jul 18, 2010, 3:05:07 PM PDT
One of the best books I ever read was Apollo (I have the original 1989 version with a different cover). It's available for the Kindle also, but I don't know if that has the 16 pages of photos that are in the middle of the book.

In one section of the book, they relate the testing of the Saturn V F-1 Rocket engines. The F-1's were prone to combustion instability, which would run away and cause a catastrophic explosion with no warning. One engine test would run along fine, no problems. Next test... running fine then "BOOM".

Since they were so unpredictable, one of the engineers came up with the idea of placing a bomb in the combustion chamber to trigger an explosion so they could test at will whether they had really solved the problem. They had to fiddle constantly with various things like impingement angles of the propellant and sizes of nozzle openings before they had it solved. It was really more of an art than science.

From the book (p. 180)-> "The bombs would explode, the pressure in the combustion chamber would skyrocket -- and then the engine would be running smoothly again, not just within the 400 millisecond goal the team had set for itself, but within 100 milliseconds." The adjustments only cut the efficiency of the F-1 by a few percent.

I highly recommend the book if you are interested in the real details behind the whole Apollo program.

Posted on Jul 19, 2010, 6:22:26 AM PDT
Bob -

Very interesting. But I'm not an engineer. Could you please explain how a planned-explosion in the cumbustion chamber solved the F-1s "combustion instability"?

In reply to an earlier post on Jul 19, 2010, 1:11:59 PM PDT
M. Helsdon says:
"Could you please explain how a planned-explosion in the cumbustion chamber solved the F-1s "combustion instability"?"

Bob explains that they had 'the idea of placing a bomb in the combustion chamber to trigger an explosion so they could test at will whether they had really solved the problem.'

By creating a controlled detonation they could emulate the combustion disturbance; one of the worst problems in engineering is an intermittent fault, which won't occur as and when desired, making it very difficult to test. The 'bomb' allowed the event to occur at will, permitting it to be analyzed and investigated. The 'bomb' was actually a fairly small explosive charge.

The F-1 engines continued to suffer from problems all the way through to Apollo 17 because of 'pogo' problems creating combustion instability in the engines. Pogo was gradually reduced by fiddling with the engine settings.

Posted on Jul 19, 2010, 9:36:58 PM PDT
Marilyn,

Martin explained it very well. Intermittent problems are amongst the hardest to solve.

It's like if your PC does something weird, and you have the tech guy come to look at it. Of course, at that time, your PC works fine, so he can't figure out what went wrong. Then you finally do something and it goes wrong, but doing the exact same thing again doesn't cause a failure. So what causes it and how do you fix it? The only way is to be able to figure it out is to be able to make it fail on demand, so that you can try different fixes.

I used to launch large Internet campaigns, and flash stuff that I got from our ad agency used to drive me crazy, since it would do some intermittent strange things on various browsers.

Posted on Jul 19, 2010, 9:47:00 PM PDT
Last edited by the author on Jul 19, 2010, 9:50:06 PM PDT
Martin,

They actually fixed the pogo problem (Marilyn, pogo feels like if your car chugs forward/back as you drive due to a bad engine).

They had an explanation of the fix in the book, Apollo:
(P. 313)-> "Slowly, each of Apollo 6's malfunctions yielded an explanation. The pogo effect had occurred because the natural vibration of the thrust chambers of the F-1 engines, approx. 5.5 herz, was too close to the structural vibration of the vehicle as a whole, which peaked at about 5.25 herz. A system of 'shock absorbers' was installed to de-tune the engine frequencies...so that they would never again get in synch with the structural frequencies." The book also mentioned that pogo had occurred on the Titan that flew the Gemini craft, so it wasn't unique to the F-1/Saturn V.

Posted on Jul 19, 2010, 10:04:25 PM PDT
Marilyn,

Here's something else to consider on very large launchers (this I also learned from the aforementioned book). The Saturn V generated 7,500 lbs. of thrust. The 5 engines came on at slightly staggered intervals to reduce the giant shock pressure of all 5 coming to full power at once. The 4 hold-down arms had to release the rocket simultaneously, but that ALSO would generate a giant shock through the frame. So the Saturn V was tethered to the hold down arms with soft steel bolts, 1 inch in diameter. The bolts protruded into bell-shaped sockets and were extruded through the sockets as the Saturn lifted off, thus giving it a more 'gentle' release than just letting go. It's amazing what the engineers did.

I used to have a huge model Saturn V that I put together as a kid, unfortunately trashed by an over-zealous clean-up mom while I was at college. (Along with my NCC-1701 with the light up bulb on the top!!!!) Sigh..I guess it was for the best.

Posted on Jul 19, 2010, 10:30:26 PM PDT
Yog-Sothoth says:
The Apollo program was real big at my house in the 1960's - my father was one of several technicians at the Douglas Aircraft (later McDonnel-Douglas) test facility near Scramento. He was an inspector of the fuel/oxidizer systems of the S-IVB third stage, which used the J-2 engine. They had several similar problems with the J-2, but I never really caught on to how they resolved those issues. I do remember a late spring (May/June?) day in 1967 when S-IVB #503 exploded on the test stand, nearly a quarter-million pounds of LOX and liquid hydrogen (total). I was in school (7th grade) about 15 miles from the facility. The shockwave cracked, but did not shatter the windows in the classroom. We thought the Russians had finally dropped "the big one". Yeah, we did the whole "duck and cover" thing.

Cool mushroom cloud, tho.

In reply to an earlier post on Jul 19, 2010, 11:51:11 PM PDT
Last edited by the author on Jul 20, 2010, 12:47:24 AM PDT
M. Helsdon says:
Bob,

"They actually fixed the pogo problem"

The pogo problem was a constant throughout the program; its worst effects were fixed relatively early, but it continued to be an issue throughout Apollo.

Pogo in the F-1 was virtually suppressed and there was never an engine failure, though Apollo 6 suffered severe first stage pogo.

The J-2 second stage rockets had a worse history, with an engine failure in Apollo 13, significant difficulties in Apollo 6 and nearly caused structural damage in Apollo 12.

In reply to an earlier post on Jul 20, 2010, 6:15:28 AM PDT
Last edited by the author on Jul 20, 2010, 6:16:00 AM PDT
EdM says:
Marilyn Martin - There you go again. A fool's game of false facts ["Most say that ..."] and inadequate technical knowledge [below, "But I'm not an engineer"; you will still not be an engineer when/if someone explains...].

Each is better in specific, different situations, and you never mentioned the intended use. Nor considered that for in atmosphere use, use of jets over rockets saves carrying oxidizer, for less weight and complexity.

It's all a tradeoff, or why would the SS use both solid propellant boosters and liquid propellant main rockets? See, e.g., a short version:

http://science.jrank.org/pages/6324/Space-Shuttle-Propulsion-systems.html

Bear in mind that your questions reveal much about yourself ...

In reply to an earlier post on Jul 20, 2010, 6:35:51 AM PDT
Bob -

Thanks for educating me! That was all very interesting. Engineers do come up with some innovative solutions. I remember watching a close-up video of a Saturn taking off, and all the soft-bolts being flung aside during lift-off. I remember thinking "Is that supposed to be happening?"

Horrors! You lost your Classic NCC-1701? That would be worth a pretty penny today. That big auction last year of "Star Trek" models, costumes, mock-ups, etc., was quite a hit. I think the entire Classic Bridge went for something like $25 thousand. (Some fortunate Trekker is in his basement every weekend, playing Captain Kirk!)

Posted on Jul 20, 2010, 11:32:33 AM PDT
Marilyn,

You're welcome! I have a buddy who runs Star Trek conventions. He liked it so much that he gave up a lucrative medical practice to do that!! About 10 years ago he gave me 20 very nerdy tee-shirts with photos of the various Star Trek casts and crews. I am too embarrassed, or have too much good sense, to ever wear them!

Posted on Jul 20, 2010, 11:47:47 AM PDT
LBOM,

Awesome!! (As long as no one got hurt.)

Posted on Jul 20, 2010, 12:28:08 PM PDT
Hi Bob!

Too bad Paramount Studios dropped most of the "Star Trek" franchise, and turned the re-boot over to a "Lost" fanboy refugee. I think Fox Studios is the only Hollywood Studio still actively involved with intelligent Science Fiction.

You could probably sell those t-shirts on E-bay. As they would say on my Monday night History Channel line-up of Pickers and Pawn Stars, "Star Trek memorabilia is VERY collectible". (One of the best t-shirts I saw on a teen boy was from the "Star Wars" franchise: Sith Happens.)

Posted on Jul 20, 2010, 8:22:18 PM PDT
Hey, I like that one...Sith Happens.

One of my favorite scenes was when the Trekkers confront the Star Wars fans in the movie "Fanboys".

In reply to an earlier post on Jul 20, 2010, 10:32:02 PM PDT
Ronald Craig says:
"Lost" fanboy refugee?

What an utterly original and bizarre way to refer to Abrams.

Posted on Jul 28, 2010, 9:53:13 AM PDT
http://www.projectrho.com/rocket/rocket3c2.html

Updated 12/2009 - ATOMIC ROCKETS - ENGINE LIST

In reply to an earlier post on Jul 28, 2010, 9:58:36 AM PDT
M. Helsdon says:
"http://www.projectrho.com/rocket/rocket3c2.html"

You were pointed to that website about six months ago on another thread when we were trying to explain specific impulse to you.

Posted on Jul 28, 2010, 10:50:30 AM PDT
http://www.astronautix.com/props/index.htm

LIST OF SPACECRAFT PROPELLANTS. (A curious Electric/Teflon Bar propellant is being developed by Aerojet, but I couldn't find any research data on their site: http://www.aerojet.com/ )

Posted on Jul 28, 2010, 6:41:52 PM PDT
Marilyn,

The electric/teflon is an ion drive. See-> http://www.astronautix.com/props/eleeflon.htm

Basically, you can take almost anything for an ion drive, I think. You strip off an electron so that the atom is now positive, and then use an electric field to push the atom out the back, thus providing a forward thrust.

Heavy atoms are better, since they provide a nice push. I don't know if Teflon is better than Xenon that you normally hear about for an Ion drive, but sure, why not? Maybe it takes less energy to strip off the electrons.

Remember, Ion drives provide very very tiny thrust over long periods. Good for deep space missions.

In reply to an earlier post on Jul 28, 2010, 10:51:45 PM PDT
Ronald Craig says:
"You were pointed to that website about six months ago on another thread when we were trying to explain specific impulse to you."

LOL. The farce that writes itself. :D
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Discussion in:  Science Fiction forum
Participants:  10
Total posts:  50
Initial post:  Jan 27, 2010
Latest post:  Dec 30, 2012

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