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It's not burn marks, it's exposed dirt where the force of the test firing has disturbed the rocky substrate they have spread around.  It's easy to imagine the rocks getting moved around well past the visible fiery plume.
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Epoxy burns in LOx, too.
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I think a number of smaller, identical ECLSS systems is better than one big one, just like the many Raptor engines to provide fail safe thrust. There is something to say for having an equal number of dissimilar systems, but there is trade-off in terms of development cost, training to maintain multiple systems, keeping spare parts, etc.

Not really, it doesn't work for HVAC systems.  One big system with many smaller parts

Iím afraid Iím going to have to call you on this one and disagree.  I have been working with fielded mobile ECU systems for over 35 years.  35 years ago what you said was the prevailing engineering solution.  The thought was fewer parts, means fewer parts to fail and better system efficiency requiring less power.  All of this ends up to be totally wrong.

One big ECU system means one very big power surge whenever the system goes from idle to start.  So every time your compressors startup or your heater startup you are immediately at max load.  This means that your power source must be sized for this max surge load.  This means your power source has to be way over sized for your average load.  In addition, maximum efficiency is only obtained if you have to dissipate your maximum heat load or conversely need to generate your maximum heat.  In the real world, these systems have to operate usually vary from 30% to 100% of their max loads.  This means the system is rarely ever running at its maximum efficiency nor are your power sources operating at their maximum efficiencies.

With just one system you had a single point of failure.  As these systems are critical, this means that the whole system fails if they fail.  So the next prevailing engineering solution was to produce a 100% redundant system.  When one system failed you moved over to your backup.  This also followed with your power generation system.  All of this greatly increased the cost and physical size of the systems.

The most recent engineering solution is for multiple smaller systems.  These systems are not even necessarily sized identically.  These multiple systems are turned on and off as needed but never simultaneously.  This reduces the surge loads by an incredible amount.  Quite often you can reduce the peak power loads easily by over 50%.  The system may decide that it is running at 20% of load and start the system designed to handle 20% load at max efficiency.  If the load increases to 30% it then shuts down the 20% load system and starts a load system optimized for 30%.  If the load increases to 40% it would then start an additional system designed for 10% load with a total now being 40%.  When the load hits 50% the 10% load is shut down in the 20% load comes up.  At 60% the 20% load is turned back on.  This type of game continues all the way up to 100% load.  Not only does this provide for much greater efficiencies but also produces a system much more reliable through graceful redundancy if one of the systems does fail.  To provide redundancy at 100% you just need to provide one additional system at your largest sub system load.  And that would only be necessary if you knew your system was going to be running at 100%.  For example, if you knew your system needed to be designed for 100 bodies but at 1st was only going be running for 10 to 20 initially you could build a smaller system knowing that you would eventually build up to the larger system later.

This type of system is optimized for near maximum efficiencies and maximum redundancy but not for the minimum part count for spare parts.  If this is the more important option than the systems usually would be identical each one at letís say 20% of max load.  This would allow you to have a minimum number of spare parts and if necessary could cannibalize from one system to the other.

Not only are systems like this much more common in mobile systems but Iím seeing similar type systems being installed in buildings.  Even on systems that are going to run at near max load all the time i.e. server farms they are still going with multiple redundant systems.  This is still the more reliable efficient system.
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Regarding high temp auto-pressurization: 
How thick does a layer of epoxy have to be to prevent reaction to LOx?  Is a linerless tank simply lined with extra epoxy from the molding process?
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General Discussion / Re: 2017 US Eclipse thread
« Last post by jimvela on Today at 02:57 AM »
Trip is still on for my little group from the Tinkermill.org makerspace.
It was stunning to me how many of my new colleagues from LASP are going north, and a large number of my old Ball teammates as well.  Not surprising, we in science and industry LIVE for this kind of stuff.

My group is planning to go to dispersed camping in forest land ESE of Casper, West of Glendo.
If you'd previously reached out to me as an NSF'er looking for a possible overnight, PM me.
It'll be an adventure as I may be well out of cell range, but may be able to get coords out via APRS or improvised LTE connection. (Sadly, no satcom- [hangs head in shame]  ;) )

For folks going north from Colorado, CDOT and CSP (as well as their Wyoming counterparts) are advising that traffic will be absolutely unreal.  The upper end of the crazy traffic projections have us doubling the human population of Wyoming on the 21st. (!!)  It's strongly advised to go up before Monday or ridiculously early on Monday.

Large swaths of the US interstate system are going to be restricted to oversize or special needs cargo.  Many locations are treating this as a major holiday/tourist event (it is), so there will be many road restrictions.  Check in advance and be well prepared to shelter in place if traffic grinds to a halt where you are.

Please everyone tell all those in your host state wherever you visit how much you appreciate your hospitality.
I've been visiting Wyoming for years even as a Colorado kid, and the people up there are wonderful. 

Be safe, everyone, and enjoy the show!

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Space Policy Discussion / Re: Is Commercial Crew Dangerous?
« Last post by yg1968 on Today at 02:44 AM »
NASA said that under commercial crew SAAs, it had insight but not oversight. So that was the excuse for Congress and NASA to mandate FAR for CCtCap.

Now that NASA has oversight under FAR, the delays and the cost of commercial crew have increased.

I am not advocating that NASA should have no oversight but it appears to be excessive under CCtCap. Hopefully, it will diminish once certification has been acheived.

The companies didnt have to take the money

The companies will do whatever NASA asks. But that doesn't mean that this was the best model to use. You often hear that NASA should follow the COTS model for new commercial programs but you rarely hear that NASA should follow the follow the commercial crew model for new programs. There was a lot of political interference under the commercial crew program which lead to a FAR/more cumbersome oversight program under CCtCap. In any event, it's water under the bridge now. But I am starting to think that the COTS model will not be replicated in the future. Hopefully, it's not too late for commercial habitats (Nexstep) to avoid the same problems that commercial crew experienced. 
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Can't resist posting this:

Quote
Sound suppression rain birds activate as #Falcon9 lifts off. This is my favorite shot from #CRS12! 🚀

full gallery: http://photos.tmahlmann.com/Rockets/SpaceX/SpaceX-CRS-12/

https://twitter.com/trevormahlmann/status/897971788965195776
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That's an excellent video and it brings back memories, good and bad :'( . In any case, the first thing I noticed is that the first couple of missions staged almost a minute later!
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If anyone thinks that NK hasn't been getting help, I've got two words. Fake news.

Where there's smoke, there's rocket engines...
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Parking orbit achieved and initial Briz M phase complete, according to Anatoly Zak.  Now in the many-hour Briz M climb to insertion orbit.  https://twitter.com/RussianSpaceWeb

 - Ed Kyle
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