Author Topic: NASA Study Shows Cheaper Alternatives to SLS  (Read 79065 times)

Offline muomega0

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Re: NASA Study Shows Cheaper Alternatives to SLS
« Reply #400 on: 11/29/2011 01:44 PM »
Thus the process of boiling the LH2 is absorbing 500 W (0.0012 kg/s * 428,000 J/Kg)

I would have to agree that if someone proposed using a 1:1000 cryocooler, then it makes the design a wee bit more challenging- not impossible but more challenging.

The current state of the art for Space Solar panels is 91W/kg so for a 500kW array (enough power to fully power the cryo cooler at 1:1000) it would weigh ~5.5MT. For a 100MT propellant depot 5.5MT is only 5% of the total weight and half of the depot dry weight making the depot dry weight about 10-12MT.


Lost of Garbage In, Lots of Garbage Out.
----

"its never flown before"

IOW, if the TRL of technology is never raised, then the status quo is what you get.  This is not *research*, which would help even more, but simply flying technology to obtain a higher TRL,*IF* it helps the architecture.

Oh well back to reality tv, how much money did SLS get this year, and was anyone voted off the island?!


Ok, GIGO.

In considering a cryo cooler using 500kW of power you also need 500kW of heat rejection or about 50MT of a system to do this. Heat rejection is why the ISS solar power and heat rejection combined system weighs so much for the power it produces. The heat rejection portion of the system is what will make a ZBO system based on a cryo cooler for a LEO depot not feasible, at least in the next 20 years. But using cryo coolers for deep space depots is feasible since they would need 1/10 the power or about 50kW and 1/10 the heat rejection to be able to achieve ZBO, a must for efficient storage for a Mars mission or even a good to have for a L1/L2 depot.

--- Only 500 kWe, why not 12.4 MWe?!
 
Why did you start with 500 kWe, when you could have started with a bare LH2 tank in space, requiring 12.4 MWe of power plus the heat rejection system?  The calculation, by the ‘old atlas guy’ estimation would then be: 1373 W/m^2 –solar constant * 0.2 abs * 45 m^2 * 1000:1 = 12.4 MWe, without including any earth ir and albedo!
 
Again, the 500 KWe is complete garbage, which is quite a disappointing assessment from ‘ an old Atlas guy’.   Ironically,   a similar ‘argument’ was made to eliminate ZBO systems from any consideration during Constellation- yet another ‘thumb on the scale’ approach.

So the good news is ZBO in a dedicated depot is achievable in LEO with about 10 KWe of power and is by far the cheaper approach (billions) than the refueling stages relying passive TCS rather than an active.

This will be shown later.  Stay tuned... :)

--- NASA has two big $$$ problems

1. Choosing depot centric over SLS HLV reduces NASAs cost by the 10s of billions over 20 years.

2. The permanent depot saves billions over 20 years versus refueling stages.

--- 0.1%/day boiloff is *Lousy* and limits operations and drives costs
 
0.1%/day is *Lousy* - it limits LEO operations of a refueling stage to ~ 180 days and throws away hardware that could last for over a decade.  To state otherwise, needs, well proof:
 

LEO operations are limited to ~180 days is a more more reasonable estimate assuming 0.1%/day
because the the LH2 tank is much larger than the LOX tank, even at 5:1 ratio!  Now it must increase 20% just to achieve 180 days (which increases the boiloff rate!).


---  Why does the passive system alone not work?

Its rather simple.  Weight needs to be added to reduce the passive heat load to the shields for the depot (or tank walls for the refueling stages).

But when weight is added to the upper stage, it reduces mass fraction, killing overall architecture costs and performance, increasing mass to orbit requirements.

To justify the refueling stage approach, an "acceptable" boiloff percentage is arbitrarily defined to justify the hardware approach. ::)

Some simple calculations can show this. 

Stay tuned for more details.... :)


--- Advantages of a dedicated depot

Read the last page of the leaked NASA study, "Depots vs Refueling".
Internal NASA Studies Show Cheaper and Faster Alternatives to The Space Launch System

The study shows that costs can be substantially cheaper and risk significantly lower with a depot versus refueling, the exact opposite of  unsubstantiated claims.

Depot Study:
* Most expensive hardware/capability can be located on the depot to be re-used over and over again rather than expended every flight
* The expendable CPS and delivery tankers can be made as dumb/cheap as possible
* Mass of the CPS that has to be pushed through thousands of m/s and delta-V can be reduced
* All of the important and costly avionic/software/IVHM can be on the depot
* The prox-ops and rendezvous and docking systems can be on the depot, rather than the CPS
* The depot could do the last prox-ops maneuvers and even berth the tanker/CPS with an RMS
* Relieves CPS of need for active boil-off control for cis-lunar missions (...)
* Reduces risk to CPS from MMOD by reducing time in orbit prior to departure
* Reduces number of rendezvous events required to fuel CPS from many to ONE, reducing risk of collision or propellant transfer rate
* Reduces risk of LOM by decoupling propellant delivery flights FROM delivery of mission elements

Edit:  Added Links
« Last Edit: 05/19/2012 11:46 AM by muomega0 »

Offline JohnFornaro

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Re: NASA Study Shows Cheaper Alternatives to SLS
« Reply #401 on: 11/29/2011 05:06 PM »
Note however John F's observation and inconsistency between two papers:

Just a nit, but:  John F is the monicker of some other person who posts on this forum.  I believe that you are mentioning my previous questioning of the 0.1% boil-off meme?  It would be nice if you'd fix this, if appropriate.

Quote
Now most have assumed that the LO2 in the caption was really a typo.  So anyone want to comment on famous 0.1%/day figure 9?

What?  I have never heard of this!  I'm really fed up with these "typos".  On another thread some guy posted a calculation based on one meter.  Others commented that he really meant one centimeter.

Apparently, we are not entitled to published papers being free of typos in the most important places.  I don't believe that it's a typo.  There is no discussion in the ULA paper of hydrogen boil-off rates, and little discussion beyond the schematic notion of using O2 to ameliorate H2 boiloff.  If the published data is so completely error prone, then it is no wonder that Congress has difficulty in appropriations based on rational bases.

Of course, I would appreciate other papers on this important issue.
Sometimes I just flat out don't get it.

Online oldAtlas_Eguy

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Re: NASA Study Shows Cheaper Alternatives to SLS
« Reply #402 on: 11/29/2011 06:58 PM »
Some of the discussions related to energy input into the system (Sun, Earth as heat radiation sources) and the passive thermal shielding limiting the thermal energy reaching the inside of the tank, made me realize the boiloff is actually related to the energy IN not to the amount of propellant. A 100MT tank only partially full say 10MT would boiloff nearly the same amount of propellant in a day measured in kg that a full tank of 100MT of propellant would (basic thermodynamics Energy IN = Energy OUT). So the boiloff rates expressed in % of the propellant weight has no real meaning except in a quick evaluation of systems all with the same size tank that is full of prop of the same type of prop!

The % boiloff rates being thrown around do not specify the tank sizes (volume or surface area) or the amount of prop in the tank, without which the numbers have little meaning from an engineering standpoint.

muomega0 you are correct a lot of the info based on % boiloff is just so much GIGO, which unfortunately includes my own estimates and conclusions presented based on % boiloff.

Offline muomega0

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Re: NASA Study Shows Cheaper Alternatives to SLS
« Reply #403 on: 11/29/2011 07:23 PM »
Note however John F's observation and inconsistency between two papers:

Just a nit, but:  John F is the monicker of some other person who posts on this forum.  I believe that you are mentioning my previous questioning of the 0.1% boil-off meme?  It would be nice if you'd fix this, if appropriate.

Quote
Now most have assumed that the LO2 in the caption was really a typo.  So anyone want to comment on famous 0.1%/day figure 9?

What?  I have never heard of this!  I'm really fed up with these "typos".  On another thread some guy posted a calculation based on one meter.  Others commented that he really meant one centimeter.

Apparently, we are not entitled to published papers being free of typos in the most important places.  I don't believe that it's a typo.  There is no discussion in the ULA paper of hydrogen boil-off rates, and little discussion beyond the schematic notion of using O2 to ameliorate H2 boiloff.  If the published data is so completely error prone, then it is no wonder that Congress has difficulty in appropriations based on rational bases.

Of course, I would appreciate other papers on this important issue.

The name will be edited.

--
In a way the question is already answered. 

Assume that the LOX tank has no net heat load on its surface from the environment.  In this case, the LH2 boiloff will simply be subcooling the LOX, so no boiloff.

So now assume 0.1% boiloff of LH2, calculate how much cooling can be provided at 90K, and magically spread this heat over the surface of the LOX tank to determine the allowable environmental limit on the LOX tank.  One will now have subtract, however, that amount be used for power, attitude control, reboost, *if* that is the operational mode being used.  Sure is quite a bit of work to do.

The issue returns now to weight and cost.  One can always add more passive thermal control to cut heat gain from the environment, but it weighs more.   To magically spread the cooling gas to all sides of the tank takes more tubing and conduction paths, but this *may* increase heat gain from the environment.

So *only* knowing the boiloff is not the complete answer, one needs the mass fraction of the refueling stage also, as well as the tank sizes, etc.

But if one never studies options not on the table, then only local minimums will be found.

Not a precise answer, so stay tuned :)

Offline Xplor

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Re: NASA Study Shows Cheaper Alternatives to SLS
« Reply #404 on: 11/30/2011 01:40 AM »
 
So now assume 0.1% boiloff of LH2, calculate how much cooling can be provided at 90K, and magically spread this heat over the surface of the LOX tank to determine the allowable environmental limit on the LOX tank.  One will now have subtract, however, that amount be used for power, attitude control, reboost, *if* that is the operational mode being used.  Sure is quite a bit of work to do.
How do you propose to spread your active cooling into the LO2 tank? 
Why does it take magic to spread hydrogen vapor cooling over the LOX tank

The issue returns now to weight and cost.  One can always add more passive thermal control to cut heat gain from the environment, but it weighs more.   To magically spread the cooling gas to all sides of the tank takes more tubing and conduction paths, but this *may* increase heat gain from the environment.

Do you have any information to back up this claim?  Do you suggest a bare tank (no MLI) with active cooling is lighter than a tank with 3 layers of MLI or 40 or 200? Do you suggest that adding 10 kw of power, power conditioning unit, cryo cooler and radiator are cheaper than a Joule Thompson orifice and 100 feet of 3/8” tubing?   

The real question is: what is the appropriate balance between passive and active cooling?  The answer is application specific.
« Last Edit: 11/30/2011 02:33 AM by Xplor »

Offline Robotbeat

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Re: NASA Study Shows Cheaper Alternatives to SLS
« Reply #405 on: 11/30/2011 04:34 AM »
Passive insulation probably does have less mass for quite a while before active cooling becomes less massive for incrementally lower boiloff.

Any active system will want a heck of a good passive insulation system. No one who thinks that scrimping on passive insulation makes sense would be let anywhere near the design of the depot.
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Offline muomega0

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Re: NASA Study Shows Cheaper Alternatives to SLS
« Reply #406 on: 11/30/2011 06:21 PM »

How do you propose to spread your active cooling into the LO2 tank? 



The concept is very simple, but the active cooling loops, nor open circuit LH2 Boiloff tubing/pipes do not need to enter the tanks.

A shield has tubes/pipes attached to it and the shield is maintained at the desired temperature.   The shield could be the outer tank wall, or could be only radiating to the tank wall (i.e. no or very small conduction paths).

Lets try a gas cooling (not a heat pipe) example:  If the room temperature is below freezing, say 30F, and the freezer with ice is unplugged, the ice will not melt.  Assuming there is no conduction path to the ice (or other stored energy), it can only radiate to an already cold state.  Or if the freezer walls are maintained below freezing, the radiating only ice will not melt.

Quote
Why does it take magic to spread hydrogen vapor cooling over the LOX tank

If one adds weight, no magic involved.

Assume a single straight tube (not a heat pipe) runs vertically up the vacuum jacket tank wall at one circumferential position.  As the gas flows straight up, it will be warmed, and it will have to rely on conduction to cool the "other side" 180 degrees away--IOW a gradient will exist on the wall/shield, axially and radially, unless the conduction is infinite.  Now this would be the lightest design(?).

One could add more straight tubes in parallel, or "wind" the tubing around the tank/shield, but of course the goal is to minimize the weight.  Its not *alot* of weight, but it can add up.  Try it!  If the million plus welds on Apollo where increased by a very small fraction, it would not lift off the ground.

Of course, the attached tubing (or heat pipes) must sustain launch loads, etc.   Please do not think this is a trivial task, it is not, and the NASA community fortunately has many dedicated experts that somehow make it *look* easy.

Quote
Do you have any information to back up this claim?  Do you suggest a bare tank (no MLI) with active cooling is lighter than a tank with 3 layers of MLI or 40 or 200? Do you suggest that adding 10 kw of power, power conditioning unit, cryo cooler and radiator are cheaper than a Joule Thompson orifice and 100 feet of 3/8” tubing?   

The real question is: what is the appropriate balance between passive and active cooling?  The answer is application specific.

Not trying to duck the question, but can you demonstrate that the 10 kWe is wrong?  If not, how much effort would it take to simply do a BOE analysis to see that the estimate is in the ball park?

Again, one must consider the entire architecture when conducting a trade study, and with the SLS HLV only approach, this is not being done.

Optimizing a transfer stage that must launch within a few hours of LEO deployment is quite a bit different than assembling say 100,000 kg of propellant (in LEO or L2), then transferring this propellant to its eventual payload.

What is so interesting about all the debate on the 10 KWe of power is that EVERYONE has all the info they need to do the calculations themselves, or reverse engineer the values, with just a bit of work.  Just read the ULA papers and try it!  Find out for yourself!  Not the detailed calculations and design, but sound, BOE, first order approximations.

So the good news is that ZBO is achievable in LEO with about 10 kWe of power with a dedicated depot (not a refueling stage) and the cost savings is in the billions of dollars over 20 years over refueling stages.

This *rather bold statement* of course needs to be demonstrated and peer reviewed, rather than to just blankly accept--would anyone  expect anything less. ::)

But after watching mass fractions drop into the 0.7 range, and *acceptable* boiloff  being defined as 0.1%/day resulting in 70 tons of boiloff requiring one additional flight for Ares V DRM 5 missions, and then having LH2 tanks stretched 20% just to reach ~180 days without additional launches, many, many others start to question if launch costs can be reduced further than the status quo that wants to 'explore for a few days and sooner'

Not a precise answer....Stay tuned :)

Offline muomega0

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Re: NASA Study Shows Cheaper Alternatives to SLS
« Reply #407 on: 12/01/2011 09:47 PM »
Passive insulation probably does have less mass for quite a while before active cooling becomes less massive for incrementally lower boiloff.

Any active system will want a heck of a good passive insulation system. No one who thinks that scrimping on passive insulation makes sense would be let anywhere near the design of the depot.

Great comment!  Thank You!

Let's pose it as a question:

So how many MLI layers are needed around the 90K cylindrical shield to make an 10 kWe Active System viable?

The answer, is well, quite amazingly, zero :)  Does this count as scrimping?

Depot Size Assumptions

-  Active System can fail, 180 days contingency with 0.1% boiloff/day
-  5:1 LOX:LH2
-  LH2 boiloff maintains LOX to zero
-  LH2 Tank Size increased by 20% for 180 day contingency
-  20m Length, 5m diameter 90 K Shield surrounds two tanks
-  ~100,000 kg of prop
        15 ft (~ 4.5 m) diameter by 31 ft (~10 m) long tank holds:
              140 mT of LOX *or* 15 mT of LH2   (9.3:1 ratio)
        so scale the lengths accordingly

Cylindrical 90 K Shield, Solar Flux Only

- 10kWe for the LOX refrigeration system.  That’s 500 W total at 90K.
- Projected area of the two tanks is 20 x 5 = 100 m^2
- cyl. surface faces the sun = 314 m^2 (ignore top/bottom for now)
- Absorbed Flux:  1373 W/m2 * 0.2 abs = 274.6 W/m2
- Allowable heat load on the 90 K shield   500W/100 m^2 = 5W/m^2

==>  Incorrectly calculated, 55 layers of MLI are needed in between the solar flux and the tank wall as the first approximation (274.6/5+1)

What if the shield was conical and not a simple cylindrical wrap?

- ULA/KSC concept (deployable, conical shield)
- The projected area would increase by the cone angle
- The inner part of sun shield and the outer part of the 90 K shield would have view factors to deep space and to themselves

==> The number of layers of can be reduced by the cylindrical area/projected area ratio, so 55 layers becomes 55 * 100/314 = 19 layers * 10 degree area increase on solar flux (*1.7)   so 33 layers (an approximation)

So with just a few minutes of BOE estimation, one can see, incorrectly, that a 4 layer conical sunshield and 29 layers of cylindrical MLI is a starting point for solar only heat flux in the design of the passive system for the active 90 K refrigeration system requiring 10 kWe.

Issues?   Did not include earth ir and albedo, no conduction paths.   Top and bottom surfaces not included.  No temperature gradient, the shield is not a lumped temperature.

The Passive Design for an Active System

Recall that the net heating on the cylindrical shield (5m x 20 m) must be less than 500 W.

So with a 4 layer conical MLI shield--ULA concept and ZERO MLI layers on the 5m x 20m cylindrical shield at 90 K, the total average shield heat load over the orbit is less than 500W!   (300 km, beta=0, nominal albedo and earth IR.  The model is simply a 10 deg cone (4 MLI layers)  and a cylinder maintained at 90 K, 5 m OD by 20m long, with axial and circumferential gradients.)

The system would require a radiator to dump this heat however, along with power and solar arrays and a refrigeration system--things that really do not package well on a transfer stage and were not modeled.  BTW, the solar arrays could also act as a sun shield.

Adding passive cylindrical wrap insulation from ZERO layers will only help reduce the 10 KWe 90K power consumption, and does not hurt transfer stage mass fraction and hence mass to orbit.

The Passive MLI design is independently driven by the % boiloff required for contingency.

What about the LH2 tank?  Stay tuned.

What does this mean?

- It means that one of the major cost drivers of exploration (boiloff) can be solved with a LEO depot – Billions of dollars over 20 years.

- With a depot, the size of the LV can be reduced from 100+ metric tonnes, to ~20 to 30 tonnes—tens of billions of dollars over 20 years

Anyway to get this option on the table?

Offline JohnFornaro

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Re: NASA Study Shows Cheaper Alternatives to SLS
« Reply #408 on: 12/02/2011 12:57 PM »
Quote from: muomega
Issues?   Did not include earth ir and albedo, no conduction paths.

As to Earth IR, the conical ULA proposal attempts to solve this by the 80m 80 feet [Edit: Per Fig. 9 of the ULA paper, "A Practical, Affordable Cryogenic Propellant Depot"] cone length, and they also account some for the reflection path of IR back to the tank.  They don't talk about conduction paths all that much.

I'm gonna have to study your argument more, since I'm not the math guy.

Edit:  Uhhh.... line of reasoning?  Not an argument exactly, I guess.
« Last Edit: 12/02/2011 03:06 PM by JohnFornaro »
Sometimes I just flat out don't get it.

Offline muomega0

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Re: NASA Study Shows Cheaper Alternatives to SLS
« Reply #409 on: 12/02/2011 02:15 PM »
Quote from: muomega
Issues?   Did not include earth ir and albedo, no conduction paths.

As to Earth IR, the conical ULA proposal attempts to solve this by the 80m cone length, and they also account some for the reflection path of IR back to the tank.  They don't talk about conduction paths all that much.

I'm gonna have to study your argument more, since I'm not the math guy.

There is no argument- its data and what the data means if its correct.

But why did you select, out of context if i may add, the "issues" with the BOE calculations, which are fully accounted for in the numerical results?
and why did you change the 20m cone to a 80 m cone length?   Where you trying to reduce the power level further?

The ZERO MLI results are based on a detailed model that allows a temperatire gradient on the 4 layer MLI conical sun shield.  The numerical model with zero MLI layers on the cylindrical shield results in (significantly) less than 10 kWe required to cool the 90K shield and includes the nominal earth's thermal environment: solar, albedo, earth IR. 

---
As for the math:

The first two results are simply approximations, and only solar flux was included.

They first two BOE calculations were provided to show
 - that its not 1000s of layers of MLI, which would be a nonstarter
 - that passively, its a tough job, especially without the cone!
 - so why not try a different approach!

Results were omitted in the BOE estimates that include earth ir and albedo. Albedo and IR are quite easy to add.  Take 90 degrees before noon: the albedo is zero!  Now the earth ir is 234 W/m^2  * 100 m^2  (same projected area * increase in cone angle 1.7)  * 0.8 emissivity * VF to earth, which depends on altitude.  Of course in the eclipse for low earth orbits, its all earth IR.

In the first two approximations, an approximation is made that the heat flux is reduced by 1/(n+1) layers.  http://en.wikipedia.org/wiki/Multi-layer_insulation.

More exact analytical formulas exist for concentric cylinders, and cylinders inside cones.    However, the results are still only estimates, as a significant temperature gradient develops across the conical shield, eventually one ends up running one of the numerous thermal radiation analysis programs available.
« Last Edit: 12/02/2011 02:24 PM by muomega0 »

Offline JohnFornaro

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Re: NASA Study Shows Cheaper Alternatives to SLS
« Reply #410 on: 12/02/2011 03:32 PM »
But why did you select, out of context if i may add, the "issues" with the BOE calculations, which are fully accounted for in the numerical results?
and why did you change the 20m cone to a 80 m cone length?   Where you trying to reduce the power level further?

First, the idea of "out of context".  I don't take things out of context in order to mislead, if that's where you're headed with that remark.  Second, there's no practical reason to bloat bandwidth by re-quoting your entire comment, when the only thing I wanted to briefly comment about was the cone length and albedo IR.  Third, my observation is simply not out of any context, that I can tell.  You gave a series of calculations, which could be characterized as a line of reasoning, which itself can be taken to mean an argument, and then asked the question "Issues?" as if to ask; Are there any issues which your argument has overlooked?  You answer the question yourself.  I simply observe that ULA appears to have considered Earth albedo IR to some extent, and that the cone is longer than the tank in order to address albedo IR.

Fourth, and most importantly, I erred in saying 80m when the shield is only 80 feet!  Therefore, there is no ulterior intent or purpose behind my remarks; I'm kind of sensitive about that issue.  Now it may be said that I should read more carefully, and not mix units, while simultaneously saying that ULA is free to mix units.  Personal favorite from the paper:

Quote
The proposed depot is composed of a 180" cryogenic tank which can be launched inside of existing 5m fairings.

What I'm trying to do is understand what you're saying, and get a better handle on the issues surrounding boiloff and all.

Savvy?
Sometimes I just flat out don't get it.

Offline muomega0

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Re: NASA Study Shows Cheaper Alternatives to SLS
« Reply #411 on: 12/02/2011 05:32 PM »
It was trivial to do this analysis, and it could save billions--which is both good news and bad news. ::)

But all that is repeated, "over and over", is, in effect:  "A wide number of HLV only architectures have been studied by NASA....

Now where is that report.....

-----

You may be missing a subtle, but very important point:

The calculations show (substantially) less than 10 kWe for the 90K shield, yet ZERO MLI is wrapped around the cylindrical shield, the shield length is at a minimum to shade earth IR and albedo (its equal to the two tank lengths), and its 100,000 kg of prop.    :)

In other words, there is still lots of design options and margin available for all the gotchas.  (increase the shield length, add MLI, shrink the tank size, better coatings, different operational modes, solar array shadowing, improved cryocooler performance).  Further, if the solar array tears, or the gimbals lock up, or the pump sticks, or the radiator fails to deploy, and are waiting on repairs from some highly trained crew, one still has 180 days contingency (or more since more passive weight could be added since its NOT a transfer stage) for the next mission.

What's not to like?

Offline RanulfC

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Re: NASA Study Shows Cheaper Alternatives to SLS
« Reply #412 on: 12/02/2011 07:15 PM »
By no means is ISP the only, or even most important parameter.

And this, ladies and gents, is how debate should take place, particularly in the halls of Congress.  Directly discuss the issues at hand, acknowledge inadequacies where they exist, and hone in to a better understanding of the other side, and work cooperatively towards finding the best solution to the problem at hand.
True John, but lest we forget it's so much more FUN calling your opponent a "Commie-Pooty-Head" than actually discussing the facts and working towards a coopertive compromise :)

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Offline JohnFornaro

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Re: NASA Study Shows Cheaper Alternatives to SLS
« Reply #413 on: 12/02/2011 07:25 PM »
Quote
In other words, there is still lots of design options and margin available for all the gotchas. ... What's not to like?

Well, other than now the info is in the public domain, they can't wrap it in secrecy, put a multi-B dollar amount on it, solve some problems in the wrong order while ignoring others that are more crucially solved earlier, claim that some published data is a typo while insisting on the truth of other non-vetted data, hornswoggle a pol or two with a few grand of campaign contributions, seal a contract which gives them a monopoly for a decade before they have to actually do anything, and a few more things besides; I can't think of anything not to like either.
Sometimes I just flat out don't get it.

Offline RanulfC

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Re: NASA Study Shows Cheaper Alternatives to SLS
« Reply #414 on: 12/02/2011 07:28 PM »
What's not to like?
Well we can START with it conflicts with my pre-conceived and decided notions and go from there if you wish :)

However I'd note that's what STARTED this whole "controversy" in the first place....

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline deltaV

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Re: NASA Study Shows Cheaper Alternatives to SLS
« Reply #415 on: 12/26/2011 09:46 PM »
The propellant depot architecture that started this thread was designed for visiting near earth asteroids (NEAs) or the moon. In my opinion the obvious next goal after visiting a NEA is to visit a moon of Mars. How could this architecture be adapted to send a man to a Martian moon? A multi-year mission to a Martian moon would presumably require more propulsion than a single 300 mt (wet) CPS can provide.

One possible approach would be to fasten 3 CPS stages together in orbit side by side in a manner similar to the first stages of various modern "heavy" launch vehicles. (The CPSs would have to be designed for this, but that's why it makes sense to think about this now!) The outer two CPSs would be used for the earth departure burn and the inner one would be used for the burns arriving and departing the Mars system. An advantage of this approach is it's quite simple. A drawback is the huge scale of hardware required: three 300 mt CPSs, three 300 mt depots to fill the CPSs, and 18+ Falcon Heavies worth of propellant to fill the depots.

Another possibility is to use a single CPS, but fill it from a depot at EML-1 or EML-2 instead of LEO. If you're pessimistic about how the propellant gets to EML-n this approach is if anything a bit worse than the previous approach as it adds complexity and a few hundred m/s delta vee for no gain. On the other hand if someone comes up with a clever and cheap way to get propellant to EML-n this could reduce launch cost substantially. One plausible possibility is a solar-electric propellant tanker, but the market might come up with something better.

Offline deltaV

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Re: NASA Study Shows Cheaper Alternatives to SLS
« Reply #416 on: 01/28/2012 07:22 PM »
I just noticed that the presentation which started this thread
http://www.spaceref.com/news/viewnews.html?id=1577
uses very similar graphics to a Georgia Tech / National Institute of Aerospace presentation of a similar architecture reported in a different thread:
http://nasawatch.com/archives/2011/03/using-commercia.html
http://www.nasawatch.com/images/F9PropDepot.pdf
. For example the picture of the blue and green EDS and depot in the mission diagrams look identical. Does anyone know if the two presentations have authors in common?

« Last Edit: 01/28/2012 07:31 PM by deltaV »

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