Author Topic: Fill Hypergolic Tank in LEO, Transfer it to EML for Rendezvous  (Read 26897 times)

Offline Warren Platts

It's a train wreck waiting to happen because it shoehorns you into to an exploration architecture that going to be exploring for ISRU propellant that it cannot use.

Why use hypergolics? It's low Isp, it's heavy, it's toxic, it cannot be made from readily available lunar mineral resources.

Boiloff is a nonissue. Boiloff will be used for station keeping in orbit, and for fuel cells during the lunar night.

Sorry to be the bearer of bad news, but this idea will never fly.
Depots filled with propellants manufactured off Earth will definitely fly.  One day.  In the 22nd century.
Sadly, you have a point: given the current level of pervasive disfunctionality, the likelihood that hare-brained ideas like using a hypergolic architecture for lunar exploration will get through the filter of rationality and set back progress by a century has become a realistic possibility.

Quote
On the other hand, the FY2012 budget could fund construction of a hypergolic depot that would be filled with propellant manufactured on Earth.
It could also fund a cryogenic depot.

"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."--Leonardo Da Vinci

Offline Warren Platts

A 1MW SEP tug could move hundreds of tons of propellant from LEO to EML1/2/LLO
The turnaround time is too slow. A 1MW SEP cannot supply  propellant requirements for even a first generation lunar base. For example, if we take the one published lunar architecture out there that's been designed by actual engineers (Zegler et al., AIAA 2009-6567), by year 3, a 1st generation lunar base could be expected to go through close to 300 tons of propellant per year. A 1MW SEP can only deliver on the order of a few 10's of tons of propellant--every 7 months--if the VASIMRTM studies put out by Ad Astra are accurate.
...
If you allow more time for turnaround (like a year or more), then you can have much, much more payload. Not good for time-sensitive payloads, but great for propellant. That's the thing about SEP: having a much longer turnaround gives you much more performance (since you are able to put proportionally more energy into the same amount of propellant), whereas a longer turnaround past a certain point for chemical is not helpful, since the energy you can put into the propellant is fixed.
Great. And so how many modules of fuel tanks will have to be assembled in LEO to hold all this propellant? And how big/how many will the L2 depot have to be? This is the proplem: you guys will take a well-thought out plan like that proposed by the ULA engineers that have thought of everything. But then you'll obsess over one little detail that you think can be improved. So by solving one nonproblem, boiloff, you cause a whole slough of problems that cascade back through the architecture, and where it stops nobody knows.
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."--Leonardo Da Vinci

Offline Warren Platts

A 1MW SEP tug could move hundreds of tons of propellant from LEO to EML1/2/LLO
The turnaround time is too slow. A 1MW SEP cannot supply  propellant requirements for even a first generation lunar base. For example, if we take the one published lunar architecture out there that's been designed by actual engineers (Zegler et al., AIAA 2009-6567), by year 3, a 1st generation lunar base could be expected to go through close to 300 tons of propellant per year. A 1MW SEP can only deliver on the order of a few 10's of tons of propellant--every 7 months--if the VASIMRTM studies put out by Ad Astra are accurate.

Using the figures in Ad Astra's new paper
http://www.adastrarocket.com/VASIMR_for_flexible_space_exploration.pdf
A Survey of Missions using VASIMRŽ for Flexible Space Exploration
April 2010
JSC-65825

A 500 kW VASIMR can deliver 14 mT of payload about every 6 months (or approx 28 mT per year) to low lunar orbit.

300 mT / 28 = 10.7 tugs

So the Moon base can be supplied by launching 21 EELV year.
Thank you, Mr. Swallow, for putting numbers to the absurdity of using SEP space tugs as tankers. The ACES-71 tankers can deliver 29 tons to the L2 depot, so the needs could be provided by 10-11 EELV's.
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."--Leonardo Da Vinci

Offline Robotbeat

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A 1MW SEP tug could move hundreds of tons of propellant from LEO to EML1/2/LLO
The turnaround time is too slow. A 1MW SEP cannot supply  propellant requirements for even a first generation lunar base. For example, if we take the one published lunar architecture out there that's been designed by actual engineers (Zegler et al., AIAA 2009-6567), by year 3, a 1st generation lunar base could be expected to go through close to 300 tons of propellant per year. A 1MW SEP can only deliver on the order of a few 10's of tons of propellant--every 7 months--if the VASIMRTM studies put out by Ad Astra are accurate.
...
If you allow more time for turnaround (like a year or more), then you can have much, much more payload. Not good for time-sensitive payloads, but great for propellant. That's the thing about SEP: having a much longer turnaround gives you much more performance (since you are able to put proportionally more energy into the same amount of propellant), whereas a longer turnaround past a certain point for chemical is not helpful, since the energy you can put into the propellant is fixed.
Great. And so how many modules of fuel tanks will have to be assembled in LEO to hold all this propellant? And how big/how many will the L2 depot have to be? This is the proplem: you guys will take a well-thought out plan like that proposed by the ULA engineers that have thought of everything. But then you'll obsess over one little detail that you think can be improved. So by solving one nonproblem, boiloff, you cause a whole slough of problems that cascade back through the architecture, and where it stops nobody knows.
What the heck are you talking about? I'm just showing how prop depots work and how you can turn a multi-hundred-ton LEO depot into an EML2 depot just by hauling the whole depot there with a SEP tug.

A multihundred ton depot could be launched (empty) on an EELV. It would be refueled... hopefully by RLV tankers.

EDIT: I wasn't "attacking" the ULA Moon architecture.
« Last Edit: 06/10/2010 09:22 PM by Robotbeat »
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Offline sdsds

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On the other hand, the FY2012 budget could fund construction of a hypergolic depot that would be filled with propellant manufactured on Earth.

It could also fund a cryogenic depot.

Really?  Construction of something like that sounds like something NASA could have in its 2012 budget?  When would it have gone through PDR?  In 2012 NASA could (and should) fund an umbrella shade for a Centaur flight, rather than forcing ULA to fund that themselves.  And NASA could (and should) fund some design work for a small prototype cryogenic depot that might be constructed as soon as 2014 and flown in 2015.  Based on the results of operating that prototype, NASA might design in 2016/2017, construct in 2018/2019, and fly in 2020 a full scale cryogenic depot.  That gets you an empty depot in LEO ready to receive propellants by 2021.  Maybe.

By then, a hypergolic depot could have been designed, manufactured, flown to LEO, filled, and flown to EML1 or EML2 using an existing cryogenic upper stage for the departure burn.
« Last Edit: 06/10/2010 09:22 PM by sdsds »
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Offline Warren Platts

If you have a three year time and only 20 tons of electric thruster propellant and no more than 22 tons of tug dry mass:
...
payloadm=(20.3+22-1.0779*(20.3+2))/(1.0779-1) =  234 tons of payload

you could get hundreds of tons to EML2, but with the tug still able to just barely fit on a Delta IV heavy).
Three years? To go to the freakin Moon?!? You've got to be kidding! Now that is one Inflexible Path. Hope your plans 3 years down the road are right on--that you won't need more or less than 243 tons. Also, hopefully your VASIMR won't break after 3  years of constant action--otherwise, those astronauts stranded on the Moon as a result are going to be SOL. And you'd probably want a heavy lift vehicle with gigantic farings to hold the tanks you'll need.
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Offline Robotbeat

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If you have a three year time and only 20 tons of electric thruster propellant and no more than 22 tons of tug dry mass:
...
payloadm=(20.3+22-1.0779*(20.3+2))/(1.0779-1) =  234 tons of payload

you could get hundreds of tons to EML2, but with the tug still able to just barely fit on a Delta IV heavy).
Three years? To go to the freakin Moon?!? You've got to be kidding! Now that is one Inflexible Path. Hope your plans 3 years down the road are right on--that you won't need more or less than 243 tons. Also, hopefully your VASIMR won't break after 3  years of constant action--otherwise, those astronauts stranded on the Moon as a result are going to be SOL. And you'd probably want a heavy lift vehicle with gigantic farings to hold the tanks you'll need.
You clearly need to calm down (and stop insulting everyone that you think might disagree with your narrow architectural opinions). We are talking about logistics possibilities for propellant. We have had multiple SEP spacecraft operating for that length of time already. We are obviously not going to be launch astronauts on these sort of slow-boat trajectories.

EDIT:And multihundred-ton depot tanks could fit on an EELV, no HLV required.
« Last Edit: 06/10/2010 09:26 PM by Robotbeat »
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Offline Warren Platts

On the other hand, the FY2012 budget could fund construction of a hypergolic depot that would be filled with propellant manufactured on Earth.

It could also fund a cryogenic depot.

Really?  Construction of something like that sounds like something NASA could have in its 2012 budget?  When would it have gone through PDR?  In 2012 NASA could (and should) fund an umbrella shade for a Centaur flight, rather than forcing ULA to fund that themselves.  And NASA could (and should) fund some design work for a small prototype cryogenic depot that might be constructed as soon as 2014 and flown in 2015.  Based on the results of operating that prototype, NASA might design in 2016/2017, construct in 2018/2019, and fly in 2020 a full scale cryogenic depot.  That gets you an empty depot in LEO ready to receive propellants by 2021.  Maybe.
An Orbital-Express-scale system capable of boosting a satellite to GEO or something could be done in a year or two. If the ULA plan had been adopted to replace CxP, they would be landing on the Moon by 2020; if you'll bother to read the paper, you'll see they have full-scale depots in LEO 11 months before first crewed landing.

Quote
By then, a hypergolic depot could have been designed, manufactured, flown to LEO, filled, and flown to EML1 or EML2 using an existing cryogenic upper stage for the departure burn.
This would be a needless duplication of effort that would only be prematurely retired anyway. First of all, there is no need for a full-scale depot in L2 until there is an actual plan to put the depot to some good use. Also, even you are calling for "cryogenic upper stages". So you're doubling the infrastructure you're going to need by having two sets of propellants.

And for what?

You still haven't explained what's the point of using hypergolics in the first place.
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."--Leonardo Da Vinci

Offline Robotbeat

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Benefits of hypergolics is a more reliable and simpler ignition system plus no cryogenic handling issues (still have to keep them from freezing, though). Also, they've been used for decades and are well understood for long-duration missions. We already use orbital refueling with hypergolics on the ISS on the Russian segment (something the Russians have been doing for decades with their space stations). They have a much higher density than hydrolox, over three times denser, which means a tank which can hold 1 ton of hydrolox propellant could hold 3 tons of hypergolic propellant (though obviously there are a few other details) and a similarly-sized pump can pump more hypergolics than hydrolox and also less pressurant is needed for pressure-fed hypergolics than some kind of pressure-fed hydrolox (if any such thing exists).

There are drawbacks, as well: Lower Isp, more difficult to produce via ISRU (though not impossible), toxicity.
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Offline sdsds

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You still haven't explained what's the point of using hypergolics in the first place.

I thought that was clear.  The propellant would be used for propulsion on missions out-bound from the depot.  Robotbeat provides a good explanation of the benefits of hypergolics.  Primarily:  hypergolic propulsion systems are known to work with high reliability even after long in-space storage.

No mission has soft-landed on the Moon using other than hypergolic propellant.  No mission has ascended from the Moon using other than hypergolic propellant.  No hydrolox system has provided propulsion more than twelve hours after it left the ground.  Some people only want to attempt what has never been done before.  Other people want to succeed.
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Offline A_M_Swallow

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A 1MW SEP tug could move hundreds of tons of propellant from LEO to EML1/2/LLO
The turnaround time is too slow. A 1MW SEP cannot supply  propellant requirements for even a first generation lunar base. For example, if we take the one published lunar architecture out there that's been designed by actual engineers (Zegler et al., AIAA 2009-6567), by year 3, a 1st generation lunar base could be expected to go through close to 300 tons of propellant per year. A 1MW SEP can only deliver on the order of a few 10's of tons of propellant--every 7 months--if the VASIMRTM studies put out by Ad Astra are accurate.

Using the figures in Ad Astra's new paper
http://www.adastrarocket.com/VASIMR_for_flexible_space_exploration.pdf
A Survey of Missions using VASIMRŽ for Flexible Space Exploration
April 2010
JSC-65825

A 500 kW VASIMR can deliver 14 mT of payload about every 6 months (or approx 28 mT per year) to low lunar orbit.

300 mT / 28 = 10.7 tugs

So the Moon base can be supplied by launching 21 EELV year.
Thank you, Mr. Swallow, for putting numbers to the absurdity of using SEP space tugs as tankers. The ACES-71 tankers can deliver 29 tons to the L2 depot, so the needs could be provided by 10-11 EELV's.

Current EELV can only get a maximum of 30 mT to LEO, you are going to need fuel from LEO to low lunar orbit.

Offline Warren Platts

You still haven't explained what's the point of using hypergolics in the first place.

I thought that was clear.
IT's not at all clear. That's why I asked.

Quote from: sdsds
The propellant would be used for propulsion on missions out-bound from the depot.  Robotbeat provides a good explanation of the benefits of hypergolics.  Primarily:  hypergolic propulsion systems are known to work with high reliability even after long in-space storage.
Another non-problem that does not need to be fixed. The 50-year old RL-10 LH2/LO2 motor has a long track record of proven reliability.

Quote from: sdsds
No mission has soft-landed on the Moon using other than hypergolic propellant.  No mission has ascended from the Moon using other than hypergolic propellant.  No hydrolox system has provided propulsion more than twelve hours after it left the ground.  Some people only want to attempt what has never been done before.  Other people want to succeed.
OK, let me get this straight. It is your claim that the engineers at United Launch Alliance must not want to succeed because what they propose is quite different from your hypergolic idea. You should go work for ULA--their engineers are badly in need of your help!  :o

Quote from: A_M_Swallow
Current EELV can only get a maximum of 30 mT to LEO, you are going to need fuel from LEO to low lunar orbit.
OK, good point. There's no need to speculate further: according to table 5 (p. 22) of Zegler et al. (2009), the plan calls for 6 tanker launches to L2 and 16 tanker launches to LEO. Total cost is probably going to be on the order of $4 billion USD. If Ad Astra can beat that, then more power to them. If they can't beat that, then they shouldn't get the contract. The problem of transport is at least an open question that requires detailed trade studies to answer.

Meanwhile, the choice between SEP versus chemical propulsion is rather beside the point for the topic of this thread, which is whether the lunar landing architecture should rely on weak hypergolic engines or the beefy RL-10. Under no reasonable trade scenario would it be worthwhile to build a lunar architecture using hypergolics rather than LH2/LO2.
« Last Edit: 06/11/2010 12:44 AM by Warren Platts »
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Offline mmeijeri

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Meanwhile, the choice between SEP versus chemical propulsion is rather beside the point for the topic of this thread, which is whether the lunar landing architecture should rely on weak hypergolic engines or the beefy RL-10. Under no reasonable trade scenario would it be worthwhile to build a lunar architecture using hypergolics rather than LH2/LO2.

Warren, I suggest you lose the abrasive tone, it's not helping. We're on the same side here. We have all seen the ULA architecture and we all like it. We all understand the importance of propellant transfer and the lure of LOX/LH2. The point of using hypergolics is to get the essence of the ULA proposal (which is in line with lots of earlier proposals by the way), but to do it faster, more cheaply and with less risk as I explained to you in another thread.

Sometimes less is more. If we start using existing systems and components (EELVs, AJ-10, RL-10, Centaur, hypergolic propellant transfer) now, then more of us here will live to see manned exploration, cheap lift and commercial development of space. The whole idea about hypergolics is where to start, not where you would want to end up eventually. The history of NASA exploration has been one of overreach and cancellation (Apollo, STS, SEI, SLI, Constellation). Going back to the incrementalism of the early rocket pioneers, current New Space pioneers and ironically the incrementalism of Craig Steidle is what we need to succeed.
« Last Edit: 06/11/2010 01:25 AM by mmeijeri »
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Offline A_M_Swallow

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Meanwhile, the choice between SEP versus chemical propulsion is rather beside the point for the topic of this thread, which is whether the lunar landing architecture should rely on weak hypergolic engines or the beefy RL-10. Under no reasonable trade scenario would it be worthwhile to build a lunar architecture using hypergolics rather than LH2/LO2.

Hydrogen boil-off exists.  With a 1% per day boil-off rate attempting liftoff on day 101 is likely to be difficult.

Boil-off effects the Earth launch tankers, LEO propellant depot, cis-lunar tanker, EML depot, manned transfer vehicle, lunar lander and ascent stage waiting for 6 months.

Offline Warren Platts

1. Hydrogen boil-off exists.  With a 1% per day boil-off rate attempting liftoff on day 101 is likely to be difficult.

2. Boil-off effects the Earth launch tankers, LEO propellant depot, cis-lunar tanker, EML depot, manned transfer vehicle, lunar lander and ascent stage waiting for 6 months.

1. According to my spreadsheet, if you start off at day 1 with 100%, with 1% loss per day, by day 101, you still have 36.6% left. Also, where did you get the 1% loss per day figure?

2. I think the white papers estimate the boiloff rate for EML depots to be on the order of a few percent per year. This would barely cover the stationkeeping requirements, if that. As for the Moon's surface, some boiloff is necessary for fuel cells. If boiloff exceeds demand from fuel cells, then boiloff could be mitigated with mylar sunshades. Also storing LH2 within abandoned lander tanks inside permashaded lunar craters would radically slow down boiloff. And once ISRU water cracking go going, you would be producing LH2 faster than it could boiloff.

In sum, boiloff is manageable, and is indeed useful. It is certainly no showstopper and is not a good enough reason to forgo LH2/LO2 architecture in favor hypergolics.
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Offline mmeijeri

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1. According to my spreadsheet, if you start off at day 1 with 100%, with 1% loss per day, by day 101, you still have 36.6% left. Also, where did you get the 1% loss per day figure?

1% is of the original mass, it's not an exponential decay. It is determined by solar heat flux, insulation, heat of vaporisation, density and the geometry of your depot.

Quote
In sum, boiloff is manageable, and is indeed useful.

You have not demonstrated that since you started from a false assumption. The ULA architecture makes intelligent use of the boil-off in LEO and intelligent use of the superior thermal environment at L2. They believe a month in LEO with acceptable losses is feasible in the near term, but they have yet to demonstrate it, so there is still uncertainty associated with it. And even so, that still puts schedule pressure on the LEO to L1/L2 transport infrastructure.

Another interesting thing to look at is how things work for mild cryogens. ULA are the world's experts on cryogenic fluid handling in microgravity, so it makes sense for them to focus on liquid hydrogen. It is part of their competitive advantage and LH2 has a very high heat of vaporisation. This leads them to mixed fluid depots which use the boil-off of LH2 to cool the LOX and very low orbits for the depot which makes them slightly cheaper to reach for launch vehicles and allows the boil-off to be put to good use by compensating for the higher drag. But oxygen is much denser and thus easier to insulate and it catches less solar heat flux. Active cooling is also much more feasible for mild cryogens than for liquid hydrogen.

Quote
It is certainly no showstopper and is not a good enough reason to forgo LH2/LO2 architecture in favor hypergolics.

No one claimed otherwise. But the benefits of LOX/LH2 are not worth delaying everything until it is operational. That's the crucial point you seem to be missing. We can always upgrade to LOX/LH2 later and we can even have development of that proceed in parallel, just not in series.

Look, you do not need to recite the virtues of the ULA architecture to us, we're all familiar with it. It's also not the last word on such architectures and the idea has been around for a long time and some of us have been studying it for a long time. Are you familiar with OASIS and its use of propellant transfer? It is even more advanced than the ULA architecture. You may want to look into it if you haven't done so already.

ULA's plan is not the only way and not necessarily the best way. It's important to get this right, so we mustn't succumb to tunnel vision. Are you even aware of all the alternatives? Since we have similar goals it might make sense to try to collaborate instead of assuming you have all the answers and need to lecture us.
« Last Edit: 06/11/2010 03:32 AM by mmeijeri »
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Offline Warren Platts

1. Warren, I suggest you lose the abrasive tone, it's not helping.
2. We're on the same side here. We have all seen the ULA architecture and we all like it. We all understand the importance of propellant transfer and the lure of LOX/LH2.
3.The point of using hypergolics is to get the essence of the ULA proposal (which is in line with lots of earlier proposals by the way), but to do it
3.1 faster,
3.2 more cheaply and
3.3 with less risk as I explained to you in another thread.
1. Sorry, but when a guy like sdsds insinuates that a guy like Frank Zegler doesn't want the American HSF program to succeed, I find that rather grating. What bugs me is this constant willingness to question authority. When it comes to politics, I am a total anarchist. But when it comes to science and engineering, I tend to defer to the experts. If I disagree with the experts, then I back up my counterargument with citations to other experts, along with detailed calculations of my own. I see neither citations to other work here nor calculations to back up what is being asserted here in this thread and elsewhere with respect to purported shortcomings in the ULA proposal.
2. OK....
3. I'm not sure you've quite grokked the essence of the ULA proposal. The Zegler et al. paper bears rereading quite well. I recommend it. It is not merely a particular proposal, but is in fact an applied philosophy on the proper way to do space travel. The essence of the ULA proposal is spelled out on the first page:

Quote
"The guiding philosophy that we have followed in developing the proposed sustainable exploration
architecture is to use the least number of distinct elements. This meant not only all-up vehicles but the least
number of main engines, avionics systems, fluids systems, ECLSS systems, etc. By keeping the many
elements as common as possible development is foreshortened and costs suppressed. Recognizing that each
vehicle has unique functions it had to perform in addition to functions it shared with all other elements
flexibility and modularity had to be built in." (Zegler et al. "A Commercially Based Lunar Architecture, AIAA 2009-6567)

So from the very get go, by proposing to mix in hypergolics, you are not getting at the essence of the ULA plan, but in fact you are running away from it. Speed is good, but not when it comes at the expense of sustainability, affordability, and ROI for the American taxpayer. Moreover, you guys are offering nothing but assertions to back up your idea that your alternative idea is:

3.1. Faster: why exactly do you think hypergolics are going to be faster? (And we both know faster doesn't mean in terms of delta v--that's for sure!) The TRL for cryogenic propellant depots is high. Experiments have been carried out. Designs down to the last bolt exist. All that awaits is funding. Why send up a hypergolic depot anyway? There is no spacecraft that exists for the hypergolic propellant to power. So to be faster, you've got to design a hypergolic spacecraft to use it. There is no reason to think a hypergolic spacecraft can be developed any faster than a spacecraft powered by RL-10's.

3.2. More cheaply: this is a red herring for sure. By unnecessary duplication of effort and increased complication is a sure-fire recipe for out of control cost spirals. In other words, you'll have to fund two development programs, instead of one, and you will have to fund to two separate support contracts. Now, I may be wrong in my reasoning, but if so, you need to prove that with actual numbers.

3.3. Less risk: As the ULA paper says:

Quote
Despite the best engineering design and analysis activities it is amply clear that even highly vetted designs such as the Space Shuttle can fail catastrophically. Probabilistic analyses are spectacularly flawed in that they make sweeping assumptions about failure modes and the means to prevent them. Nature relentlessly renders these complex analyses moot when we find another hidden failure mode via flight experience. Ground testing can assure a baseline level of confidence but only extensive flight experience can truly generate a safe vehicle with high confidence in its overall reliability.

The RL-10 motor is among the most flight tested motors in the world. So as for risk, there is no way a hypergolic spacecraft is going to deliver less risk than an RL-10. Moreover, a single RL-10 is powerful enough to land a DTAL crewed lander. Since the design calls for 4 such engines in a lander, that results in quadrupally redundant engine-out capability. I don't think a hypergolic lander can deliver such engine-out capability. I may be wrong, but I want to see numbers before I change my mind.

Quote from: mmeijeri
4. Sometimes less is more.
5. If we start using existing systems and components (EELVs, AJ-10, RL-10, Centaur, hypergolic propellant transfer) now, then more of us here will live to see manned exploration, cheap lift and commercial development of space.
6. The whole idea about hypergolics is where to start, not where you would want to end up eventually.
7. The history of NASA exploration has been one of overreach and cancellation (Apollo, STS, SEI, SLI, Constellation).
8. Going back to the incrementalism of the early rocket pioneers, current New Space pioneers and ironically the incrementalism of Craig Steidle is what we need to succeed.
4. No kidding. Unfortunately, you're proposing more (hypergolics and hydrolox) and calling it less. That's why I call your reasoning backwards. Not to be abrasive, but because literally, the arrows of implication in your arguments point in the opposite of the correct direction.

5. I see this argument all the time: If only NASA will do __________________, then at least I will be able to die happy; therefore, NASA should do _____________________. This is not a valid argument because it ignores the fundamental premise that the American taxpayer does not care whether you or I die unhappy. Furthermore, it leads to less than optimal decisions because it tends to sacrifice long-term afforadability and sustainability--and is thus unethical because it sacrifices the long-term benefits of future generations for short-term selfish gratification. (And such jejune versions of happiness that depend on space-as-edutainment are bound to lead to more ennui than happiness anyway, and are better off being relinquished.)

6. More backwards logic again. I don't mean to be abrasive, I'm merely pointing out the truth that the arrow of implication is drawn in the wrong direction. The ends should dictate the means. You put the means first, and it's bound to screw up where you're going to end up.

7. Overreach is exactly what a sensible and sustainable mission to establish a permanent presense on the Moon seeks to avoid--in sharp contrast to pie-in-the-sky Missions to Mars.

8. Incrementalism is the very heart of the ULA philosophy. That's just a simple fact of life. It's what they do. It's their bread and butter. What is not incrementalism is the addition of an unnecessary excrescence to a streamlined and sensible lunar architecture.
« Last Edit: 06/11/2010 03:41 AM by Warren Platts »
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."--Leonardo Da Vinci

Offline mmeijeri

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1. Sorry, but when a guy like sdsds insinuates that a guy like Frank Zegler doesn't want the American HSF program to succeed, I find that rather grating.

Huh, where did he do that? Are you sure you aren't putting words into his mouth?

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What bugs me is this constant willingness to question authority. When it comes to politics, I am a total anarchist. But when it comes to science and engineering, I tend to defer to the experts.

HA! That's precisely the wrong attitude, always question everything. Including one's own ideas obviously. Fanboyism is not the solution.

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If I disagree with the experts, then I back up my counterargument with citations to other experts, along with detailed calculations of my own. I see neither citations to other work here nor calculations to back up what is being asserted here in this thread and elsewhere with respect to purported shortcomings in the ULA proposal.

That doesn't mean those calculations don't exist. And I don't think ULA have shared the details of their calculations.

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3. I'm not sure you've quite grokked the essence of the ULA proposal.

What can I say, I believe I have. I think ULA understands the importance of simplicity, but I'm not sure they understand the full importance of incrementalism. And they also understand the principle of competitive advantage and they are a company with a profit motive.

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So from the very get go, by proposing to mix in hypergolics, you are not getting at the essence of the ULA plan, but in fact you are running away from it.

Not at all, I'm removing complexity by combining the lander with the depot. I think they still propose hypergolic landing thrusters (the vertical ones). They did in earlier incarnations of their proposal.

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Speed is good, but not when it comes at the expense of sustainability, affordability, and ROI for the American taxpayer. Moreover, you guys are offering nothing but assertions to back up your idea that your alternative idea is:

Warren, I find this statement insulting. For the past year I have been constantly arguing for this, backing it up with details and calculations, spending most of my waking hours studying manned spaceflight. You just barge in and act as if you are some kind of authority. Just because you have read a ULA paper does not make you an expert. Sustainability, affordability, and ROI for the American taxpayer are precisely what I'm trying to optimise because I want to see economic development of space.

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Why send up a hypergolic depot anyway? There is no spacecraft that exists for the hypergolic propellant to power. So to be faster, you've got to design a hypergolic spacecraft to use it. There is no reason to think a hypergolic spacecraft can be developed any faster than a spacecraft powered by RL-10's.

Of course there is, pretty much all spacecraft use hypergolics. Building a hypergolic spacecraft does not require new technology, using LOX/LH2 does. Before you start lecturing others you may want to learn some of the basics. If you use in-flight refueling as a simpler precursor to full depots, then you can avoid having to build a fully fledged depot initially.

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3.2. More cheaply: this is a red herring for sure. By unnecessary duplication of effort and increased complication is a sure-fire recipe for out of control cost spirals. In other words, you'll have to fund two development programs, instead of one, and you will have to fund to two separate support contracts. Now, I may be wrong in my reasoning, but if so, you need to prove that with actual numbers.

The noncryogenic one would be cheaper than the cryogenic one and that's what I was saying, not that two would be cheaper than one.

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The RL-10 motor is among the most flight tested motors in the world. So as for risk, there is no way a hypergolic spacecraft is going to deliver less risk than an RL-10. Moreover, a single RL-10 is powerful enough to land a DTAL crewed lander. Since the design calls for 4 such engines in a lander, that results in quadrupally redundant engine-out capability. I don't think a hypergolic lander can deliver such engine-out capability. I may be wrong, but I want to see numbers before I change my mind.

By risk I meant development risk, not operational risk. RL-10 is an excellent engine, and part of what we are proposing here, just not for the lander - at least not initially. But yes, hypergolics do in fact have certain safety advantages, though that is not the deciding factor. It was one of the main considerations for Apollo however: the LM engines were pressure fed, hypergolic and non-gimbaled to keep them as simple and thus as safe as possible.

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4. No kidding. Unfortunately, you're proposing more (hypergolics and hydrolox) and calling it less. That's why I call your reasoning backwards. Not to be abrasive, but because literally, the arrows of implication in your arguments point in the opposite of the correct direction.

You apparently don't understand incrementalism. The individual steps are smaller (less), which is all that matters. A storable lander is simpler (less new technology) than a cryogenic lander. A pressure fed engine is simpler than a pump-fed engine. An unmanned lander is simpler than a manned lander. An orbital precursor is simpler than a full lander etc.

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5. I see this argument all the time: If only NASA will do __________________, then at least I will be able to die happy; therefore, NASA should do _____________________. This is not a valid argument because it ignores the fundamental premise that the American taxpayer does not care whether you or I die unhappy. Furthermore, it leads to less than optimal decisions because it tends to sacrifice long-term afforadability and sustainability--and is thus unethical because it sacrifices the long-term benefits of future generations for short-term selfish gratification. (And such jejune versions of happiness that depend on space-as-edutainment are bound to lead to more ennui than happiness anyway, and are better off being reliquished.)

Tell me, what is your rationale then? And mine applies as much to the ULA architecture as to hypergolic precursors.

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6. More backwards logic again. I don't mean to be abrasive, I'm merely pointing out the truth that the arrow of implication is drawn in the wrong direction. The ends should dictate the means. You put the means first, and it's bound to screw up where you're going to end up.

You misunderstand. The whole idea of the incremental approach is to find an optimised path (as measured by cost, risk, time) towards both exploration and economic development of LEO. Both the path and the end goal deserve optimisation.

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7. Overreach is exactly what a sensible and sustainable mission to establish a permanent presense on the Moon seeks to avoid.

Have you read the OASIS proposal? Tell me why it didn't happen. They wanted to make things sustainable and came up with a very good architecture. It still didn't happen.

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8. Incrementalism is the very heart of the ULA philosophy. That's just a simple fact of life. It's what they do. It's their bread and butter. What is not incrementalism is the addition of an unnecessary excrescence to a streamlined and sensible proposal.

You seem unable to listen which is a pity.
« Last Edit: 06/11/2010 04:37 AM by mmeijeri »
We will be vic-toooooo-ri-ous!!!

Offline Warren Platts

1. According to my spreadsheet, if you start off at day 1 with 100%, with 1% loss per day, by day 101, you still have 36.6% left. Also, where did you get the 1% loss per day figure?

1% is of the original mass, it's not an exponential decay. It is determined by solar heat flux, insulation, heat of vaporisation, density and the geometry of your depot.
Um. A_M_Swallow said 1% per day; that means 1% per day. But I see your point that boiloff rate is roughly independent of mass of propellant. That said, it's even more clear that the 1% figure was pulled out of a hat.

Quote from: mmeijeri
Quote from: Warren Platts
In sum, boiloff is manageable, and is indeed useful.
You have not demonstrated that since you started from a false assumption.
The false assumption is irrelevant because the point about managability and usefulness comes from ULA.

Quote from: mmeijeri
The ULA architecture makes intelligent use of the boil-off in LEO and intelligent use of the superior thermal environment at L2. They believe a month in LEO with acceptable losses is feasible in the near term, but they have yet to demonstrate it, so there is still uncertainty associated with it. And even so, that still puts schedule pressure on the LEO to L1/L2 transport infrastructure.
So? The answer is don't send up propellant to a LEO depot unless you've already got a customer lined up who's going to take delivery at a reasonable time in the future.

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Another interesting thing to look at is how things work for mild cryogens. ULA are the world's experts on cryogenic fluid handling in microgravity, so it makes sense for them to focus on liquid hydrogen. It is part of their competitive advantage and LH2 has a very high heat of vaporisation. This leads them to mixed fluid depots which use the boil-off of LH2 to cool the LOX and very low orbits for the depot which makes them slightly cheaper to reach for launch vehicles and allows the boil-off to be put to good use by compensating for the higher drag. But oxygen is much denser and thus easier to insulate and it catches less solar heat flux. Active cooling is also much more feasible for mild cryogens than for liquid hydrogen.

Yes, this is interesting. Another interesting fact is that the latest radar data implies that there are relatively pure water ice deposits on the Moon that are at least 2 meters thick. A fun exercise is to calculate the number of cubic meters per year that would have to be excavated to completely supply the propellant needs of a 1st generation lunar base.

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Quote from: Waren
It is certainly no showstopper and is not a good enough reason to forgo LH2/LO2 architecture in favor hypergolics.
No one claimed otherwise. But the benefits of LOX/LH2 are not worth delaying everything until it is operational. That's the crucial point you seem to be missing. We can always upgrade to LOX/LH2 later and we can even have development of that proceed in parallel, just not in series.
The crucial point you seem to be missing is that the benefits of LOX/LH2 are not delaying anything. You're manufacturing a solution to a problem that absolutely does not exist.

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Look, you do not need to recite the virtues of the ULA architecture to us, we're all familiar with it. It's also not the last word on such architectures and the idea has been around for a long time and some of us have been studying it for a long time. Are you familiar with OASIS and its use of propellant transfer? It is even more advanced than the ULA architecture. You may want to look into it if you haven't done so already.

ULA's plan is not the only way and not necessarily the best way. It's important to get this right, so we mustn't succumb to tunnel vision. Are you even aware of all the alternatives? Since we have similar goals it might make sense to try to collaborate instead of assuming you have all the answers and need to lecture us.

Actually, the ULA proposal is the last word, literally. It represents the latest state of the art. If there are any flaws in the proposal, then please feel free to point them out. So far you haven't pointed out any. The problem of RL-10 powered spacecraft being harder to develop than hypergolic spacecraft is nonexistant. You have also pointed to boiloff. This is one con that attaches to LH2. Against this has to be weighed the pros: high Isp, universal application to all parts of the architecture, and most of all from my perspective as an economic geologist, it is available from easily accessible mineral deposits on the Moon. You want cheap lift, the most likely place to get this is going to be the Moon first, Earth second. But it's going to depend on using readily available lunar materials. This means LH2/LO2--not methane, not hydrazine or whatever. I've spent a lot of time studying this piece of the puzzle. If you want to collaborate, I'm all for it, but you've got to take seriously all aspects of the big picture, and that includes lunar ISRU. These latest findings that are only about 3 months old entail that lunar ISRU is going to be far easier than has ever been contemplated. The significance of this fact has yet to sink into all but a very few people on this forum. These ice fields are exciting in themselves and should be pursued to the full extent. Rather than OASIS, you should be looking at Chadrayaan and LUNOX.
« Last Edit: 06/11/2010 04:52 AM by Warren Platts »
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."--Leonardo Da Vinci

Offline Bill White

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@Warren Platts

How do you intend to persuade NASA and Congress to see things your way?
« Last Edit: 06/11/2010 04:42 AM by Bill White »
EML architectures should be seen as ratchet opportunities

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