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Posted by: nprev Oct 6 2007, 02:45 AM

Starting this thread in hopes that we'll all have some detailed insight into the next generation of MSF engineering.

Noble goal, eh? Truth of the matter is that I was just looking at one of the innumerable 'CEV enroute to the moon' artist conceptions, and I realized that the solar arrays as depicted meant that the vehicle almost certainly has to remain in a fixed attitude with respect to the Sun for them to operate at maximum efficiency. IIRC, the Apollos had to spin a bit in order to maintain thermal equilibrium & avoid localized heating and/or freezing.

Am I missing something here in terms of trade-offs? Seems unwieldy at best to have the arrays mounted to a sort of slip-ring assembly (with mast articulation) to maintain solar lock while the main body rotates. Likewise, seems as if an extensive--and in terms of power & volatile requirements/risk, expensive--ECS would be needed to avoid the temperature differential problem if the S/C is intended to maintain a continuous power-positive attitude during transit.

Sure that there's a simple answer I've missed; would very much like to hear it! (Let me guess: LOTS of heat pipes?)

Posted by: ElkGroveDan Oct 6 2007, 03:13 AM

I have a CEV DVD that the PIO at Dryden gave me. It looks like the vehicle and the solar panels retain a constant attitude for the entire trip. Perhaps those kinds of thermal concerns are not an issue with this more modern vehicle.

I'll see if I can figure out how to convert this into something I can share. Interestingly they are suggesting that the vehicle touchdown on return would be at Edwards. That would be way too cool.

Posted by: nprev Oct 6 2007, 03:36 AM

Well, can't bust you by then; I'll be long retired! Cool indeed, though.

All I can think of is that they're planning on a very efficient and extensive heat pipe system, then; probably would need a controllable external radiator with a good amount of surface area as well, unless they're dual-using the solar arrays.

Posted by: dvandorn Oct 6 2007, 07:58 AM

Y'all have painted the Apollo thermal problem with too broad a brush, I'm afraid. The issue wasn't with CSM systems -- the CSM was fitted with radiators that served to keep its internal temperatures within acceptable ranges, even in heat soak / cold soak conditions. The fact that CSMs were able to fly in Earth orbit without any problems without resorting to passive thermal control proves this, as does the fact that CSMs were used as crew ferry vehicles during Skylab, during which time they spent days at a time with roughly the same solar orientation (they had to, Skylab spent a large amount of time in solar inertial attitude so that the ATM could make long-term solar observations).

The thermal issue with Apollo was entirely and solely with the ablative used on the lunar CMs. A different ablative was used on CMs designed for return from the Moon than was used on Skylab CMs, for example. It had better characteristics under the higher heat loads encountered on a lunar entry trajectory than anything else out there. But it had a very nasty tendency to deteriorate when it got too cold.

The lunar CSMs were, during trans-lunar and trans-earth flight, faced with a much more complete blackbody environment on their shadowed sides than is found in orbit around a reflective body such as Earth, or even the Moon. The CSM systems could maintain temps in the CM and SM, no problem, even in that environment and even in cold-soak conditions. But the heat shield needed to be rotated in order to keep it from getting too cold and deteriorating (shredding is a better word).

That's the reason why the extra-long entry blackout was more worrisome than anything else on Apollo 13 -- that spacecraft had used a very badly controlled PTC on its way back to Earth, and by the end the CM and LM were mostly in shadow, with the sun shining mostly down the throat of the SPS engine bell. That heat shield got colder than any other during Apollo, and the great fear was that it would have deteriorated enough to be ineffective during peak heating. Those who knew the risk at the time took every second that blackout lasted longer than normal as additional confirmation that the crew had been incinerated. It was a very emotional moment for those people when contact was finally regained.

-the other Doug

Posted by: nprev Oct 6 2007, 12:02 PM

Aha! I was hoping that MSF sensei oDoug would chime in with authoritative commentary...thanks, man!

I presume that we now have lunar-rated reentry shield materials that are not prone to this effect, then? (Actually, can they just use Shuttle tile material? Not sure what the upper limits are for that.)

Posted by: Jim from NSF.com Oct 6 2007, 03:08 PM

I disagree. There wasn't a difference in the heatshields and the skylab CSM's did have mods for the LEO environment. The PTC was also for the systems in the SM. There was white paint on the CM and heaters were added

Posted by: ElkGroveDan Oct 6 2007, 06:31 PM

Here's a compressed version of the http://smg.photobucket.com/albums/v387/elkgrovedan/?action=view&current=Title_0201.flv. (I have a higher res DVD quality version if anyone is interested)

Posted by: ugordan Oct 6 2007, 06:43 PM

How old is that video? I might be out of loop, but I thought the cryogenic engines used on the cargo LV will be RS-68, not SSMEs as said in the video.

Posted by: ElkGroveDan Oct 6 2007, 07:13 PM

A Dryden PR guy sent it to me back in June. I'll call him Monday and ask if there is anything more current (that's Griffin narrating BTW).

Posted by: dvandorn Oct 7 2007, 03:16 PM

There were some *minor* modifications made to the SMs of Skylab CSMs to add heaters for long periods in solar inertial orientation. But in this case, about the heatshield materials, you're wrong, Jim. The heatshield material used on Skylab CSMs was indeed different than that used on lunar flights. And the *primary* reason for PTC on lunar flights was heatshield thermal control. Look it up. (The ethylene glycol active thermal control system in the CSM was designed to maintain thermal control inside the vehicle throughout translunar and transearth cost, with the understanding that attitudes would be shifted *on occasion* to avoid hot spots. PTC was *only* introduced to address the heatshield thermal regime issue.)

Actually, the largest modifications made to Skylab CSMs had nothing to do with the thermal regime. They had to do with the seals used on the hypergolic fuel systems. Mainline Apollo CSMs (and LMs, for that matter) used a variety of plastic seal materials on the hypergolic fuel systems that fed the various engines. The useful lifetime of an Apollo CSM was measured from the first moment it was fueled. At that point, the seals in the fuel lines began to deteriorate. You could not fly an Apollo CSM or LM more than two months after it was first fueled without tearing it apart and replacing all of the seals. For Skylab, the plastic materials (nylon mostly, IIRC) were replaced by newer materials (metals, in some cases) which resisted the corrosive effects of the hypergolics better, and for longer periods. Unfortunately, they didn't work as seals *quite* as well as the original materials -- the fuel leakage in the Skylab 3 RCS fuel system occurred around one of these new, longer-lasting seals.

But, once again, if you delve deeply into the Skylab historical documents, you'll find that the heatshield materials used were modified to avoid the cold-soak deterioration issue that lunar Apollo heatshields were prone to. The Skylab chronology mentions the subject at least a couple of times.

-the other Doug

Posted by: Jim from NSF.com Oct 8 2007, 12:26 AM

http://history.nasa.gov/SP-4011/

makes no mention of heatshield mods

Posted by: lyford Dec 28 2007, 03:14 AM

http://www.ceqamap.com/search.php?mode=view&action=view&id=1117

PDF for download if you're into this sort of thing. A good overview of the whole program and its development; it also has some nice cutaways and mission profile pics that were new to me.

It also investigagtes "cultural significance" which covers the potential impacts to sites due to the new program, such as the Lunar Landing Research Facility or the Apollo Control Room, which are National Historic Landmarks.

No word on the Lunar Impact Statement - or does that fall under the planetary protection office, which gets a nod on page 373?

Posted by: simonbp Jan 2 2008, 10:10 PM

They'll be RS-68B's, which are a modification of the RS-68 jointly being developed by NASA and the USAF (for Delta IV). Also, the core stage and EDS are 10 meters in diameter (like Saturn V), rather than 8 meters (like the Shuttle tank).

Simon

Posted by: PhilCo126 Jan 15 2008, 10:18 AM

Check out this Orion 1/48 scale model:
http://www.picturetrail.com/gallery/view?p=999&gid=18290999&uid=2335047

Posted by: nprev Jan 19 2008, 05:10 PM

Apparently, a http://ap.google.com/article/ALeqM5gM9u4XKevS9s8S62luONrIPRJD3QD8U8N4VO1 has been discovered with the Ares first stage; the resolution should be interesting.

Posted by: ugordan Jan 19 2008, 05:34 PM

From what I've read on nasaspaceflight.com this issue is a very serious one and untrivial to resolve. Without any dampening applied, the crew would experience longitudinal G force oscillations far beyond anything experienced till now and far above NASA recommendations on human safety. The vibrations would adversely affect both the Orion spacecraft and the cryogenic Ares I second stage, too. Any dampening mechanism would likely add significant weight penalties, even more so if you were to put it between the SRB and second stage (instead of between 2nd stage and Orion) to protect that stage as well.

I never could get my head around the reasoning of making a 5-segment SRB the base of a man-rated vehicle when SRB's are known to provide a very bumpy ride and cannot be shut down. SRB vibrations in itself have been a known issue ever since first solid boosters were developed (there are apparently two vibration modes, each due to different factors) so it's a bit funny no one figured out until now they might be problematic for an inline configuration, especially with the uprated booster. Just like (in retrospect) the shuttle payload configuration looks like a wrong design decision, this too looks to me like a bad choice.

The vibration problem should not affect the Ares V because the vibrations are dampened by "tying" two SRBs through the intertank structure, just as the Shuttle currently works.

Posted by: nprev Jan 19 2008, 06:04 PM

I'm not too surprised, frankly; projectitis is endemic in government nowadays, and large issues seem to be discovered later rather then sooner. Still, despite that cheap shot on my part, at least they realized this seven years before the planned first launch. Based on the problem description, I speculate that they might be looking at an exhaust bell redesign of some sort to minimize the vibes, but this might be too simplistic from what you were saying, Gordan.

In analogy to aircraft, perhaps a stability augmentation system (SAS) would be a good answer, using vanes in the exhaust flow to disrupt the resonance. The problematic flight phase is just the first few minutes of flight; might be worth sacrificing some thrust for vibe dampening.

Posted by: dvandorn Jan 19 2008, 06:27 PM

Problem is, the CEV has been redesigned and made smaller once already, based on performance projections for the Stick. We're now at the raw edge of the Stick's current ability to orbit Orion as currently designed. Any reduction in performance will result in a further redesign that will severely limit the CEV's ability to perform its design mission.

I think we may be looking at the potential for changing over to an Atlas V or a Delta IV (in their Heavy configurations) as the first stage for Orion. Any such decision has to be made *very* soon, though.

-the other Doug

Posted by: nprev Jan 19 2008, 06:42 PM

I like the Delta IV Heavy idea; in fact, I wonder if it would be feasible to cluster additional cores (up to six) for incrementally greater boost capability. Hell, this might make Orion more achievable in the short term, esp. because the IV Heavy is going to be used extensively over the next few years; lots of shake-down (sorry! )/testing will already be in place.

Posted by: ugordan Jan 19 2008, 06:52 PM

I don't think the problem can be adressed by changing engine bells, it has to do with oscillations in booster casing volume, pressure and hence burn speed. It's a process that feeds itself and is a natural characteristic of all solid boosters. An analogy might be pogo in liquid fuelled engines, even though the mechanisms at work are different.

I agree with oDoug in that it would be wise to bite the bullet and consider abandoning the Stick altogether. I'm really pessimistic that will actually happen. Rather, billions of dollars might be spent on fixing this issue that came up in the first place because they wanted to use as much Shuttle technology as possible, but that's going too much into politics here.

There are obvious problems with switching to the Atlas V - it uses Russian engines so it's probably a big no-no. The Delta IV is more expensive and the Heavy variant produces a rather large fireball during ignition which, although it doesn't pose any significant problems to the payload, does look rather discomforting. There are also things like Ares V using components built for Ares I which then can be scratched off the funding for V, i.e. if you were to cancel the Ares I, Ares V development costs would be seen to rise. It looks like it's going to be a pretty expensive booster even now, I hear.

Posted by: nprev Jan 19 2008, 07:13 PM

Argh. If so, there's no conceivable active control system to counteract that. Despite the fireballs, I'm gonna back D4Hx as the best solution at this point (limited as the data is, of course...)

Posted by: Jim from NSF.com Jan 20 2008, 02:00 PM

Not really, only 3 flights in the next ten years

Posted by: Greg Hullender Jan 20 2008, 04:50 PM

Great opportunity for those SpaceX guys to get their Falcon 9 Heavy ready.

--Greg