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The Reality of Apollo / Re: Apollo Filters
« Last post by smartcooky on May 22, 2019, 11:56:17 PM »
https://history.nasa.gov/alsj/TM-2005-213610.pdf

Haven't had a chance to go through it all yet so there's probably more info in the rest of it about vacuum cleaners used on Apollo missions.

Thank you for the link to the PDF... that was a fascinating read, especially the documentation at the end showing all the references to dust in the Apollo Mission Reports and Technical Debriefings. I knew dust had been a problem, but didn't really have any idea just how much havoc it created.

This just shows that Gene Cernan wasn't kidding when he said that “dust is the number one concern in returning to the moon.”

This PDF was dated 2005... its amazing to think that even after ~35 years, the actions of the Apollo crew and the data they collected is still being analysed with an eye to the future.
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General Discussion / Re: Oberth Effect?
« Last post by jfb on May 21, 2019, 04:55:06 PM »
IINM, methane and oxygen have similar boiling points, so the tanks can share a common bulkhead, which saves some mass.  But I think the real attraction is that methane can be synthesized on Mars relatively easily. 
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The Apollo 9 CM ("Gumdrop") is in the San Diego Aerospace Museum. It's missing its DSKY, along with a lot of other stuff (looks really sad in there). Maybe Jay knows where it went? :-)

It was even sadder in Jackson, Mich. where it came from.  It's also the only flight CM I've been inside, and it was sad (and smelly) and missing its DSKY then too.
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The Reality of Apollo / Re: Apollo Filters
« Last post by JayUtah on May 21, 2019, 03:13:35 PM »
You'd think the humidity of the cabin air would take care of any electrostatics. The problem had to be mainly the sharp particles.

My impression is that electrostatic effect is what attracted more than expected particles to the suit in the first place during the EVA.  And once on the suit, the jagged edges kept them there.
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General Discussion / Re: Oberth Effect?
« Last post by JayUtah on May 21, 2019, 03:10:29 PM »
Plumbing fittings for liquid hydrogen are hard to engineer.  It's a very tiny molecule, and it likes to sneak past seals.
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General Discussion / Re: Notre Dame Cathedral fire
« Last post by ka9q on May 21, 2019, 03:00:02 PM »
Speaking of I. M. Pei, I believe MIT people refer to one of their buildings as the "Pei Toilet" because of its appearance and designer.
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The Reality of Apollo / Re: Apollo Filters
« Last post by ka9q on May 21, 2019, 02:58:31 PM »
You'd think the humidity of the cabin air would take care of any electrostatics. The problem had to be mainly the sharp particles.
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The Apollo 9 CM ("Gumdrop") is in the San Diego Aerospace Museum. It's missing its DSKY, along with a lot of other stuff (looks really sad in there). Maybe Jay knows where it went? :-)
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General Discussion / Re: Oberth Effect?
« Last post by ka9q on May 21, 2019, 02:49:53 PM »
The reasons are all practical tradeoffs.

Methane/LOX has roughly the same performance as RP-1/LOX, so that's a wash.

Methane is less dense than RP-1, requiring a larger tank, and liquid methane is a cryogenic liquid, unlike RP-1 (but not nearly as cold as LH2). Those are strikes against methane.

Methane doesn't coke (release elemental carbon) as easily at high temperatures. That's an advantage, as it makes it easier to reuse a regeneratively cooled engine. More complex (and efficient) engine cycles (like preburning) may be possible. That's another advantage.

Methane can supposedly be made from raw materials on Mars.

So while methane has had no particular advantages (only disadvantages) until now, you can see why BlueOrigin and SpaceX are interested in it.
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General Discussion / Re: Oberth Effect?
« Last post by bknight on May 21, 2019, 12:04:05 PM »
The effect of the Effect is simple enough; the faster the rocket is going, more delta-V it gets from a kg propellant.o any constructive
This is actually incorrect; you get the same delta-v regardless of the rocket's velocity relative to the observer (ignoring relativistic effects). What Jay said is correct; you get more kinetic energy from each kg of propellant when you're going faster.

Some years ago I worked out the powers and energies for each stage of the Saturn V. It turns out that during much of the third stage burn more mechanical power (force times velocity) is being given to the Apollo spacecraft than the heat power released in the J-2's combustion chamber. This is not "free energy"; that extra energy is coming from the kinetic energy that had been stored in the J-2's propellants before they were burned. That energy was put there by the lower stages of the rocket. So rockets aren't quite as inefficient as they seem early in flight when they're furiously burning propellant and still moving fairly slowly. Only a small fraction of the released energy may be going into the payload but much more is being "invested" into the kinetic energy of the as-yet-unburned propellants, some of which will be recovered later.

The most energy-efficient rocket is one that increases its Isp (effective exhaust velocity) linearly with speed so that its exhaust is always stationary in the inertial frame of the launch site. Of course this would be a much more massive rocket because energy efficiency is usually not the primary consideration in rocket design. Size and weight are more important, which is why a highly energetic propellant like liquid hydrogen is so attractive even though it costs a lot of energy to make.

With Blue Origin and mow SpaceX opting for methane is because it is easier to handle than liquid H2?
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