Author Topic: Griffin speech - Why one STS derived launch system would not work for Constellation  (Read 91610 times)

Offline yinzer

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ISS can still be very instructive.

Your typical Shuttle assembly flight requires turning around the orbiter, producing a more or less unique 20 ton chunk of aerospace hardware, training a crew in how to install that hardware via EVA, configure it, and troubleshoot it, and then carrying off a two-week mission.  Your typical Progress flight involves building the 10th consecutive copy of a 4000kg spacecraft, filling it with a bunch of fuel, air, and food, carrying out the 100th consecutive launch of a medium-lift LV, an automated docking to a space station, then some valve reconfiguration.  The interfaces, procedures, and hardware in the latter case are just much, much, simpler.

Depending on your EELV lunar architecture, the majority of the flights should be at least as simple as a Progress, albeit with larger propellant tanks.
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Offline jongoff

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William,
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We're not ignoring the other 20mT launchers, they're just not germaine to  the discussion. Assuming VSE continues to be an all-US endeavor, it makes sense to rule out non-US launchers. In another thread (God knows which one), there was a discussion of world wide launch capacity that looked at what you could do with EELVs, Ariane V, H2, Proton, etc.

But are they really "not germane"?  I think you're still assuming things like a government-run propellant depot.  Why?  It would make a lot more sense for the propellant depot to be privately run, and one of the reasons is precisely so it decouples the propellant purchase from how exactly it gets there in the first place.  Some of it would be launched by US providers, but it doesn't have to be.  After all, nobody seems to have a problem with some of Ares I coming from Sweden, or some of Atlas V or Delta-IV coming from Japan.  In fact a propellant depot would be even better than those examples, because if you're buying from anyone who can deliver their tanker to some prespecified trajectory near your station, then you aren't beholden to any one particular supplier.  Putin wants to be annoying, his loss--we'll buy Ukrainian, or Chinese, or Indian, or Californian....

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By the way, IIRC some parts of ISS were lugged up by Proton, and wasn't the Russian airlock lugged up by a Soyuz (the rocket, not the capsule)?

I don't know about the Soyuz part, but yes, some of the Russian stuff was launched by Proton. And it's also been the stuff that's been up the longest.   Almost all of the real delay in construction has been due to the Shuttle, not Proton.  And a lot of the delay from Proton was actually delay on the Russian side for getting their modules together because they were so tight on cash.  If someone were to do station over again, but this time with EELVs being in existence, but still with the 20 ton limitation, I bet it would go together far smoother.  Blaming station's woes on 20 ton chunks I think is learning the wrong lessons from history.

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As far as ISS not being 5 parts propellant 1 part hardware, what difference does it really make? You still have to get the pieces and parts to one spot in LEO and make them work together, whether its berthing bits of ISS together and hooking up electricals or docking tankers to a fuel depot and pumping fuel/oxydizer. ISS is the only example we have of orbital assembly, unless you want to count Mir.

I think that his point actually makes a lot of difference.  At least based on mankind's experience with non-cryogenic propellant transfer, it's really not that big of a deal.  It's only a few minor steps beyond just a simple docking/berthing.  There's no need for space-walks, or months worth of specialized training for each and every propellant transfer mission.  It's a totally different situation.  Cryogenic transfer will add a couple of steps, but a 1 million pound vehicle that's 90% propellants and only 4-5 big chunks is going to be tons easier than a 1 million pound vehicle that's 50 hardware pieces that have to be permanently integrated.

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It'd be a lot easier to embrace the EELV architecture if the EELV flight rate were already high. Remember that's the same sales tool was used to promote STS. EELV proponents are certain it can be brought to a high flight rate, but then most people believe the thing we believe in will work the way we hope. What if it doesn't?

It is fair to question how high the flight rate capability of the EELV fleet really is.  But doesn't the same apply to DIRECT?  I'm just as skeptical of getting more than 8 flights per year of DIRECT off per year as I am of getting more than 20 EELV flights in a year.  Moreso in fact.

~Jon

Offline jongoff

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yinzer - 24/1/2008  2:50 PM

ISS can still be very instructive.

Your typical Shuttle assembly flight requires turning around the orbiter, producing a more or less unique 20 ton chunk of aerospace hardware, training a crew in how to install that hardware via EVA, configure it, and troubleshoot it, and then carrying off a two-week mission.  Your typical Progress flight involves building the 10th consecutive copy of a 4000kg spacecraft, filling it with a bunch of fuel, air, and food, carrying out the 100th consecutive launch of a medium-lift LV, an automated docking to a space station, then some valve reconfiguration.  The interfaces, procedures, and hardware in the latter case are just much, much, simpler.

Depending on your EELV lunar architecture, the majority of the flights should be at least as simple as a Progress, albeit with larger propellant tanks.

Thanks yinzer, couldn't have said it better myself!

~Jon

Offline clongton

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Someone said a while back that the VSE provided a direction to go in but did not specify "heavy lift" to be utilized. Here is the appropriate portion of the 2005 Authorization Act that set the VSE in motion and made it law:

"The Administrator shall, to the fullest extent possible consistent with a
successful development program, use the personnel, capabilities, assets, and
infrastructure of the Space Shuttle program in developing the Crew Exploration
Vehicle, Crew Launch Vehicle, and a heavy-lift launch vehicle." (emphasis mine).

NASA is required by law to build a heavy lift launch vehicle to use in execution of the VSE.
Notice that it required the "use the personnel, capabilities, assets, and
infrastructure of the Space Shuttle program" to build it. A Shuttle-Derived launch vehicle was mandated by this authorization act.

I'm not bringing this up to justify STS vs EELV; only to point out what NASA was directed by Congress to do. This comes directly from Dr Griffin's speech.
Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine

Offline mike robel

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Former Congressman Lou Frey has a saying "When you start having to explain, you are in trouble."  (or something close to that.

One may well infer that Ares I/V are in trouble given that Griffin is 'splainen.

Offline yinzer

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I think your reading is off.  NASA is required by law to use elements from the space shuttle program to the maximum extent possible consistent with a successful development program.

Furthermore, the authorization does not get created out of thin air.  It's the result of collaboration between NASA, the president, and congress.  They frequently get amended and updated.  After O'Keefe retired, Griffin came in with his existing architecture including the Stick and a SDHLV.  Hence, this is what got authorized.
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Offline clongton

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yinzer - 24/1/2008  7:02 PM

I think your reading is off.  NASA is required by law to use elements from the space shuttle program to the maximum extent possible consistent with a successful development program.

Furthermore, the authorization does not get created out of thin air.  It's the result of collaboration between NASA, the president, and congress.  They frequently get amended and updated.  After O'Keefe retired, Griffin came in with his existing architecture including the Stick and a SDHLV.  Hence, this is what got authorized.
Regardless of the time frame, the end result is that Congress mandated an STS solution, and a heavy lift based on that. You are correct. Congress did not say to build the Ares - that was Griffin's answer to how to implement what Congress mandated.  But any one of the STS solutions in the ESAS, or any other STS-based solution for that matter, regardless of how it looked, would comply with the law. Whether Griffin presented Ares to Congress before or after the passing of the Act is essentially irrelevant at this point. By whatever means, and in whatever time frame, he got the Congress to codify the STS solution in the form of a law. To switch to an EELV solution at this juncture would require amending the law. That is not impossible, but would be difficult. At this point in time, for better or worse, it is what it is. And I believe that Dr Griffin was specifically making a point of that, which is why he quoted that section of the Authorization Act. Whether you or I agree or disagree, he was stating his interpretation of the law in explaining the how and why of his VSE implementation policy and architecture.

Like I said. I'm not pointing out any merits of one system over the other, because quite frankly, either system is capable of the job, each in its own way and each with its own unique set of pros and cons. I am just pointing out what is actually stated in the Authorization Act and Dr Griffin's interpretation of it.
Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine

Offline Lee Jay

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yinzer - 24/1/2008  5:02 PM
I think your reading is off.  NASA is required by law to use elements from the space shuttle program to the maximum extent possible consistent with a successful development program.

So, since Constellation is using only the SRB casings, the tank material and the tank foam from STS, rather than using STS elements "to the maximum extent possible", NASA is in violation of the law.  Is that what you are saying?

Offline khallow

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William Barton - 24/1/2008  1:31 PM

As for using a single EELV to put up ISS in a year, I certainly have not suggested that. As far as I know, the manufacturing infrastructure couldn't produce 25 Delta IVH's in a year. And how many have been flown since the beginning of the program? Two? Besides which, having a rocket that can lug 20mT to LEO doesn't build a space station. One of the handy things about Shuttle is, you don't need a space tug because it is a space tug.

I'm sorry. I thought when you said infrastructure to support 25 launches per year, you meant it. Manufacture is part of the launch support infrastructure. But at a glance, one can always expand infrastructure if the money is there. At 25 launches a year, it would be.

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William Barton - 24/1/2008  1:42 PM

It'd be a lot easier to embrace the EELV architecture if the EELV flight rate were already high. Remember that's the same sales tool was used to promote STS. EELV proponents are certain it can be brought to a high flight rate, but then most people believe the thing we believe in will work the way we hope. What if it doesn't?

There's a difference. EELV launches now and doesn't require a high flight rate to be economical to NASA.
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Offline kraisee

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Jon and everyone - IMHO, you are all missing a vital point:   The DIRECT plan hopes to *include* any and all domestic and foreign launch assets to improve the overall architecture - on the single condition that they are cheaper for NASA to use than Jupiter.


Approximately 50% of the Lunar architecture lift requirements are propellant.  This doesn't require the additional cost inherent in all human-rated launch systems, and is also completely open to any foreign partner to take real practical part in supporting the missions.

We need to lift some 400 Tons (about 16 Delta-IV Heavy's worth), or more, of propellant every year to accomplish just the baseline Lunar mission projections of the VSE.

It does not *have* to be launched by Jupiter's.   If there is a cheaper alternative in the commercial market I say lets damn well use it!   If there are foreign partner(s) willing to put their money into the program and launch some, or all, of that propellant then that is an extremely worthwhile contribution they can make and it should earn those partners seats and payload mass for experiments on all of the missions which they contribute towards.

If a nation wants a seat, but doesn't have its own launch assets to do the job, it can pay any "commercial" operation to launch sufficient propellant on their behalf.   This sort of demand will help the international commercial launch market considerably.

But best of all, IMHO, is both cheap domestic and foreign assets used to supply all this essential mass ultimately reduces the baseline costs to NASA - and that translates directly into NASA's normal budget being able to pay for even *MORE* missions every year.


*If* the commercial operations (EELV, Space-X, whoever) can really reduce the cost of launching 400-Tons of propellant each year by 20% compared to Jupiter, then those savings go back into NASA's budget to pay for extra spacecraft and missions.   That works to everyone's advantage.

Better still, *if* all of the Lunar propellant is launched by foreign partners every year, then NASA wouldn't have to pay *anything* for it.   By removing the propellant cost, NASA's budget can then be dedicated to just launching the spacecraft.   At that point, NASA's exact same budget would be enough to pay for many *MORE* missions (8 full Lunar crewed missions per year is quite achievable) - assuming the foreign partners can keep up with propellant demand.


The basic architecture we have proposed creates the means for NASA to start the process entirely itself.   But it immediately lends itself to utilizing and and all commercial/foreign assets available to reduce NASA's costs for each mission.   Simply by reducing the cost of propellant lifting, we get any more missions.


We need to give up this "it must be all EELV" and "it must be all Jupiter" arguing.   It needs to be a NASA approved foundation to get the system operational and to make sure that a complete infrastructure exists if the other options do not mature as hoped - but it need to be designed to be extensible - utilizing any and *ALL* cost-reducing assets in the arsenal.

Like many things, we are much stronger together than apart and we need to give up the "us vs. them" mentality entirely if we are to get the best architecture of all.

Ross.
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Offline Jeff Bingham

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yinzer - 24/1/2008  7:02 PM

I think your reading is off.  NASA is required by law to use elements from the space shuttle program to the maximum extent possible consistent with a successful development program.

Furthermore, the authorization does not get created out of thin air.  It's the result of collaboration between NASA, the president, and congress.  They frequently get amended and updated.  After O'Keefe retired, Griffin came in with his existing architecture including the Stick and a SDHLV.  Hence, this is what got authorized.

Actually, look back at the legislative history and you'll see that the relevant language on SDLV was written in the May-June time frame of 2005 (the bill, S. 1281, was introduced on June 21, 2005; section 302(a) contained the relevant language, which was only slightly modified as the bill went through the Senate and conference with the House), and thus predated the ESAS final outcome in September of that year. It might even be argued that Mike and NASA saw the SDLV writing on the wall and that helped nudge them in the direction of an SDLV approach. It is argued here, of course, by some, that they have veered away from that in significant ways with Ares, and to the extent that's true, it might well prompt the Congress to consider redirecting that effort in the course of drafting a NASA reauthorization bill this year, which is currently under discussion. (the 2005 bill only included authorization funding levels for FY 2007 and 2008, so new legislation is needed to formally authorize funding levels for FY 2009 and possibly 2010.)
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Offline Smatcha

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tankmodeler - 24/1/2008  12:50 PM

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SMetch - 24/1/2008  2:02 PM
Paul, no disrespect but I have been to the 9th floor and let me assure you that even when we are blessed with comparatively open mind leadership it’s the exact opposite of the “It’s a Small World” ride at Disneyland.
Wow, you sound more cynical then I am & I teach grad level cynicism courses here at work!  :)

Seriously, no disrespect taken at all and I am more than willing to belive you are correct in this assessment. However, such an open letter as Ross has written really isn't for the NASA HQ staff anyway. It's for Congress and the press and should be posted to any press outlets you can think that might be interested. It is the press who really don't need an incentive to go looking for interpersonal dirt that may or may not exist to spice up a story. Get it out to Congress and let them see if they can get a response out of the NASA Administration that jives with the letter & the speach.

That's where the hope lies. Not, really, with senior NASA HQ, whose ability to remove their rectally emplaced craniums I am seriously in doubt of. At least not without Congress' help.

Paul

LOL , yes that is the best place for the letter.  Mike is beyond hope at this point.  
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Offline Smatcha

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david-moon - 24/1/2008  12:17 PM

Ross, that's an excellent open letter, very well written.  I just have one suggestion, concerning this paragraph:

While I have previously been a vocal and sometimes bitter critic of both Dr. Griffin and .... While there has been vitriol aplenty, I actually find I support NASA's Administrator far more than I oppose him.

The natural reaction of anyone inside NASA to this would be "who are you and why should I care whether you support or oppose my plans."  That reaction might even stop some from reading the rest of the letter, which would be unfortunate.

I suggest that you edit down the discussion of your personal history and just focus on your point about two separate launch vehicles versus one launch vehicle with two configurations.  I would limit the personal stuff to at most an apology for any intemperate comments you may have made in the past.  Actually as far as I can remember, the intemperate vitriol on these forums came from other fans of DIRECT, not from you.

I don’t know why anyone continues to believe that if we just find the right way to sugar coat this for Mike then he will finally come around.  You obviously don’t know Mike.  The very fact that you disagree with him or dare suggest something he hasn’t endorsed or dare to not practically echo what he just told you is more than enough to get you kicked out of his office if he happens to be in good mood that day.

What is so hard to understand about this?

“I’m a people person I’m good with people what is wrong with you people” :)
From Office Space

Now that you have heard my more honest approach towards Mike let’s try the fuzzy bunny method and see what happens.

“Mike, pretty please with sugar on top may I ask for your forgiveness in advance at daring to suggest that maybe just maybe I could ask your indulgence in looking at my exceedingly feeble attempt at even remotely approaching your greatness with this little inferior idea when measured against your god like intelligence by daring to suggest we use something along the lines of……………………….I’m so afraid to say it something like…………………DIRECT.”

You will get the same result from Mike regardless of how you case it.

I would say ditch the apology altogether since the audience isn’t Mike or anyone that actually believes he has a clue as to what he is doing but people looking for a way out of this mess.

You are right though its time to forget about Mike and focus on the solutions not the problem.

“Do we want to go to the moon or not?”
John C. Houbolt - November 15, 1961
Question posed in Letter to Dr. Robert C. Seamans Jr, NASA Associate Administrator

Ralph Ellison “I was never more hated than when I tried to be honest”




Offline jongoff

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Ross,
I guess my fundamental fear is that when the chips come down, if NASA owns its own launch vehicle, it's going to end up mostly finding ways to compete with commercial launchers.  I'm not saying this because I think that you're arguing in bad faith, or that the people in NASA are intentionally "out to get" the commercial guys.  It's just that we're already seeing signs of it.  In an effort to show how great DIRECT can be, you guys are dreaming up all sorts of missions for it, many of which could be done with EELVs or other commercial launchers.  I'm just worried that when push comes to shove, the commercial side of things is going to continue to get screwed in favor of parochial interests in Florida, Louisiana, Alabama, and Utah.  

If NASA builds DIRECT, but then ends up getting its budget cut due to the worsening economic situation, do you really think that they're going to cut into those shuttle jobs first?  No, they'll say "well, we need to maintain this infrastructure, and if we're going to maintain it we may as well use it.  And if we do the accounting just right, our vehicle is cheaper per kg anyway.  Oh, and if we make certain assumptions about docking reliability....sorry guys, propellant depots are a great idea, but Jupiter is obviously the most cost effective way of servicing it."

Maybe if there were a law on the books that forbade NASA from using any propellants outside of LEO that weren't launched to LEO on a commercial vehicle...

But realistically, while I think that Jupiter might leave enough money for a propellant depot, that there's still going to be a huge temptation to massively distort the market in favor of the NASA-centric launcher, in spite of your best intentions.

~Jon

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William Barton - 24/1/2008  11:42 AM
As far as ISS not being 5 parts propellant 1 part hardware, what difference does it really make? You still have to get the pieces and parts to one spot in LEO and make them work together, whether its berthing bits of ISS together and hooking up electricals or docking tankers to a fuel depot and pumping fuel/oxydizer. ISS is the only example we have of orbital assembly, unless you want to count Mir.
The difference it really makes is first, you are NOT limited to 20-ton launchers for propellant. If a 10-ton or 5-ton works out cheaper or is politically more convenient over a range of launches, then by all means use it. Just a possibility, but a basic Dragon 9 is likely to be pretty cheap per pound delivered..
And ISS and Mir are not the only examples of orbital assembly. There was a certain alternative to Apollo program that sucessfully docked manned capsules and propulsion stages together, and had laid the entire path to lunar surface out using ~10 mT or smaller launchers at some point in history. Just because Apollo approach won out thanks to congressional wallets being wide open, does not mean that the alternative would not have worked.
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Offline kraisee

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Jon, I disagree.

From where I sit, Congress has made it profoundly clear that it intends to protect the existing workforce as its first and overriding priority.

All other decisions, even the idea of any exploration mission at all, seem based with that in mind.

Given that, they know as well as anyone that cutting NASA's budget would impact that political goal negatively.   While they seem disinclined to give NASA extra cash, they are showing strong bi-partisan support of NASA's current funding level, and unless there is a complete economic collapse (in which case the whole program will be closed anyway), I don't see their current support level wavering much over the next decade or two.

Even in the situation of an unlikely funding cut - EELV still isn't the answer.   Even the first mission every year is no less expensive with EELV than it is with Jupiter.   And even Ares isn't actually very far behind at that flight rate.

Yet I can't believe that anyone wants NASA to operate a new program with just one flight per year (except perhaps Ed! :) ).   That is too obviously wasteful, and the public wouldn't stand for any stripped-down ~$6bn program only flying once per year.

The minute you get to two missions per year, the EELV's begin losing significant ground in terms of operational cost - $600m in favour of the 2-launch solutions for every subsequent mission is a pretty big gap any way you cut it.

These are two daunting issues which are facing the EELV options - and that is even if they could get the law overturned somehow - which I personally doubt - STS has a lot of political support and a lot of lobbyists.


Irrelevant of launch system though, if NASA's Constellation budget were to be cut from ~$8bn per year to less than $5bn, we simply aren't going anywhere at all.   You couldn't pay for CEV and LSAM with that - let alone any launch vehicles at all.   A $3bn cut to Constellation's budget would effectively close all the doors equally.


I also strongly doubt that NASA would reject the opportunity to fly more missions just to boost their LV flight rate.   For a start they don't have to because they can get BOTH.

The number of Jupiter's doesn't change with the assistance of foreign assets - there will still be 8 Jupiter launches each year.   NASA still gets the value out of the system either way.   The only difference is that four of them will no longer carry propellant - they will carry additional spacecraft  instead.   That way we get 8 missions per year for the same cost as 4 done entirely with Jupiter.   The launch rate and cost at KSC doesn't change - but the size and scope of what we can actually do *doubles*.   We get a much larger infrastructure as a by-product of international assistance.   But we aren't reliant upon that for success either.

WRT domestic propellant supplies, I think NASA would pick the cheapest solution for precisely the the same reasoning.   If they can add an extra mission every year by using a cheaper supplier, I think they will.   But the EELV's and any other competitor are going to have to make sure they really are the cheaper solution.

Right now, Jupiter is looking damn good value for money when compared to any existing EELV solutions.   Make no mistake, when you delete the Orbiter from the Shuttle, the rest of the Stack has had 25 years of continual cost-cutting measures applied to it  - today it is VERY competitive compared to any other launch system in the US.

Something is going to have to change if they want to compete.   Certainly NASA should never be forced to use more costly solutions just to prop-up a market, so any commercial solution is going to have to make sure it is legitimately cheaper.

I personally think the current EELV's are overpriced when compared to Ariane and Proton.   They don't get many, if any, international launch contracts these days simply because the "commercial" world has cheaper alternatives.   But I hope companies like Space-X entering the US marketplace, if they can keep to their claimed low pricing, will force the necessary changes throughout the domestic launch market by creating serious competition.   A truly "competitive" and "commercial" environment would benefit NASA, the DoD and the commercial sector.   Whoever can make the best value systems should be the ones to win and I will strongly cheer any solutions which can beat Jupiter.

Ross.
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kraisee - 24/1/2008  9:03 PM

Jon, I disagree.

From where I sit, Congress has made it profoundly clear that it intends to protect the existing workforce as its first and overriding priority.
Has Congress also made id profoundly clear that they WANT this workforce be building and operating yet another launch vehicle, or would something else work as well ?
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Ross, I would drop the appology, Griffin has to walk for DIRECT, and Turkeys simply don't vote for xmas.  Your audience is all the wavers at NASA who sense the need for change, and you should address your letter to all at NASA.  If change comes, it will come from within.  Inclusion of these people is the right way. Merely being "right" does not win the day with anyone but Spock (and I dont mean Griffin).  

Also, the two points you need to address head on :
1) ISS mission being too costly for DIRECT compared to ARES-1
2) Mars Boiloff ( ... is NASA really going to spend an extra 16Billion to avoid a technology challenge ?)

Offline William Barton

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khallow - 24/1/2008  9:49 PM

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William Barton - 24/1/2008  1:31 PM

As for using a single EELV to put up ISS in a year, I certainly have not suggested that. As far as I know, the manufacturing infrastructure couldn't produce 25 Delta IVH's in a year. And how many have been flown since the beginning of the program? Two? Besides which, having a rocket that can lug 20mT to LEO doesn't build a space station. One of the handy things about Shuttle is, you don't need a space tug because it is a space tug.

I'm sorry. I thought when you said infrastructure to support 25 launches per year, you meant it. Manufacture is part of the launch support infrastructure. But at a glance, one can always expand infrastructure if the money is there. At 25 launches a year, it would be.

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William Barton - 24/1/2008  1:42 PM

It'd be a lot easier to embrace the EELV architecture if the EELV flight rate were already high. Remember that's the same sales tool was used to promote STS. EELV proponents are certain it can be brought to a high flight rate, but then most people believe the thing we believe in will work the way we hope. What if it doesn't?

There's a difference. EELV launches now and doesn't require a high flight rate to be economical to NASA.

I meant 25 launches of the single-CBT EELV variants. Delta IVH counts as 3 "launches." My understanding is, the balls-to-the-wall production capacity for each EELV type is somewhere between 20 and 40 CBTs per type. Realistically, I think 25 launches of any sort us EELV per year would max out the existing infrastructure. My point was, even if you could manage that many launches, you'd be hard pressed to manage them into a single program. It's the same with STS. The ground infrastructure could theoretically support 17 launches per year, but the practical maximum seems to be in the 9 - 12 range. I think DIRECT will face the same issue.

Offline William Barton

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savuporo - 25/1/2008  12:38 AM

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William Barton - 24/1/2008  11:42 AM
As far as ISS not being 5 parts propellant 1 part hardware, what difference does it really make? You still have to get the pieces and parts to one spot in LEO and make them work together, whether its berthing bits of ISS together and hooking up electricals or docking tankers to a fuel depot and pumping fuel/oxydizer. ISS is the only example we have of orbital assembly, unless you want to count Mir.
The difference it really makes is first, you are NOT limited to 20-ton launchers for propellant. If a 10-ton or 5-ton works out cheaper or is politically more convenient over a range of launches, then by all means use it. Just a possibility, but a basic Dragon 9 is likely to be pretty cheap per pound delivered..
And ISS and Mir are not the only examples of orbital assembly. There was a certain alternative to Apollo program that sucessfully docked manned capsules and propulsion stages together, and had laid the entire path to lunar surface out using ~10 mT or smaller launchers at some point in history. Just because Apollo approach won out thanks to congressional wallets being wide open, does not mean that the alternative would not have worked.

It's not a matter of whether one architecture or another would _work_ in any eventuality, it's a matter of practicality. It's easy to say, we could launch the fuel in 5mT lots, if those launchers are more economical, but the number of launch and rendezvous events goes up as the payload goes down. It's easy to imagine successfully operating hundreds of LV per year to the same point in space, flying rendezvous and making fuel transfers, because we have the model of the air travel infrastructure to work from. It's easy to ignore the fact that that infrastructure was put into place incrementally over the course of decades. If you had to build that infrastructure from scratch in today's economy, and get it up and running in five years, it would be all but imposisble. A single metropilitan jetport costs around $40bln to construct. How many would you need?

I'm sure you've read "The Mars Project." It was easy for Von Braun to assume his hypothetical ferry rockets could managed 950 flights in under a year. History tells us he was being a little optimistic. Pulling off a Moon/Mars program with EELVs might be possible, but it's fraught with unknowns, because we've never done anything like it before, and the only similar project executed (ISS) turned out less well than we hoped (although not as hard as some early critics claimed).

And it's really easy to imagine a Moon program based on Gemini/Titan. A few years back I published an alternate history story called "Harvest Moon" (in Asimov's Science Fiction) that did just that, portraying a giant moonbase set up by the US in 1965. But as so many people here like to say, it's not real engineering. The real issue is, we have a heavy-lift infrastructure now (STS), and the easiest way to preserve that is by converting it to a new HLV infrastructure (such as Ares V or DIRECT). If we discard it, then it will be gone, and building it anew will probably be impossible. Remember, STS was built on the skeleton of Apollo. It didn't have to pay for VAB or the launch pads, crawlers, the Michoud facility, etc. So in reality, what DIRECT and ESAS try to do is keep the Apollo infrastructure alive for another generation, because once it's lost, it's probably lost forever. EELV might work. But if it doesn't, then the HLV infrastructure is still lost.

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