Author Topic: Reusable Falcon for propellant depot.  (Read 29205 times)

Online meekGee

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Re: Reusable Falcon for propellant depot.
« Reply #20 on: 12/02/2012 07:49 pm »
A question to those who know:

In Earth orbit - what is the benefit of long term propellant storage?

When you have the capability to launch often, why wouldn't you pre-launch the propellant in the month preceding the mission?

And if you do that, why not keep the propellant in "extended cab" second stages, fuel from them into the BEO vehicle, and then return them afterwards?


I think this is the most basic reason: If your mission involves N launches and the chance of failure is F, you want to avoid this meaning chance of the mission failing is multiplied (FN) because one launch lost means all your other launches were wasted.

This means it is nice to have the fuel up there well in advance with time to schedule another fuel flight or two if necessary. Someone else here could give you a good estimate for scheduling a replacement flight but I think it is quite a while. Also if your later launches are delayed you don't want to have wasted your earlier fuel flights.

With a high flight rate I think a depot would become more natural, with fuel not dedicated to any specific mission.

The way I see it, if you're launching only once a month or so, then fuel planning is in the order of 1 year, and then propellant boil off is an issue, and then it pays to invest in a larger tank (better volume/surface) with added features like insulation.  So a fuel depot makes sense in that case.

But if you can launch often, you launch N (or even N+1) tankers on the few weeks leading up to your BEO mission, and basically save yourself the extra hardware, the extra fuel transfers, etc.  Actually, you don't even need N+1, since you know in advance whether your tankers made it to orbit.

And even suppose the BEO launch is delayed, and you have some boil-off - all is not lost - you'll launch that +1 tanker to make up for it if necessary.

So in Elon-world, with a frequent flight rate and rapid reuse, I just don't see it making sense.
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Offline joek

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Re: Reusable Falcon for propellant depot.
« Reply #21 on: 12/02/2012 07:52 pm »
Some discussion of mission vs. launch reliability for a depot architecture in the thread Human Space Exploration Architecture Using Commercial Launch/Propellant Depots; see Section III Commercial Launch/Depot Cost and Safety (pg. 7) of the paper which is the basis of that thread; in particular Table 1 and Figure 9.

Online meekGee

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Re: Reusable Falcon for propellant depot.
« Reply #22 on: 12/02/2012 08:55 pm »
Well, the paper assumes implicitly (under reliability) that it is the only architecture that accommodate failure of refueling vehicles - but that's not true.

It also assumes boil-off is the overriding issue, which is probably true for Hydrogen and one-year storage, but is less of an issue for heavier fuel and one-month storage.

Here's a comparison table showing three options. 
DEPOT - one dedicated super-tanker with a cryo-cooler
TANKER - "extended-cab" short duration storage in the upper stage
TANKER3 - same as TANKER, but we top off one TANKER with two more before returning the empty ones right away.


                     DEPOT     TANKER    TANKER3
BEO vehicle launches   1         1         1
DEPOT launces          1         0         0
FUEL lanches           N         N         N

Fuel transfers         N         N         N
Largest failure loss   N         1         N/3
Boil-off losses       ~0         ?         ?


Clearly most everything is the same, except TANKER doesn't need to develop and launch the depot, and risk of fuel loss is compartmentalized, since you can only lose on tanker, not one depot.

I think the mega-depot makes sense only in an environment which is very different than what SpaceX is planning, and the idea just doesn't transfer well.

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Offline joek

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Re: Reusable Falcon for propellant depot.
« Reply #23 on: 12/02/2012 09:25 pm »
I think the mega-depot makes sense only in an environment which is very different than what SpaceX is planning, and the idea just doesn't transfer well.
What is SpaceX planning? [edit...] Sorry, not trying to be obtuse, but I don't see anything SpaceX has suggested which fundamentally changes the equation with respect to tankers, depots, etc.
« Last Edit: 12/02/2012 09:33 pm by joek »

Online meekGee

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Re: Reusable Falcon for propellant depot.
« Reply #24 on: 12/02/2012 10:17 pm »
I think the mega-depot makes sense only in an environment which is very different than what SpaceX is planning, and the idea just doesn't transfer well.
What is SpaceX planning? [edit...] Sorry, not trying to be obtuse, but I don't see anything SpaceX has suggested which fundamentally changes the equation with respect to tankers, depots, etc.

Mostly non-hydrogen engines and rapid launch rates - They skew the trade-off away from the large depot.

So, for example, 3 F9Rs can put 9 tankers in orbit within a week. (or for that matter, within a month)

And if you're using 3 tankers to top off 1, then you might be able to get away with less hardware even - all depends on what 2nd stage reusability looks like.
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Offline kch

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Re: Reusable Falcon for propellant depot.
« Reply #25 on: 12/02/2012 11:28 pm »

And even suppose the BEO launch is delayed, and you have some boil-off - all is not lost - you'll launch that (EDIT: Chris here. This post originally had "+1" as its response, but I really find that pointless, so I've edited this automatic replacement in via the censor options. Clever me! Thanks for listening ;) OH, and by the way, we will have "Likes" added when we upgrade the forum soon, so that'll solve that. Thanks again! ;D) tanker to make up for it if necessary.


Looks like AutoIncorrect has been upgraded ("with added recursion!") ... :D

Online meekGee

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Re: Reusable Falcon for propellant depot.
« Reply #26 on: 12/03/2012 12:03 am »
oh wow.  I missed all the excitement....

I'd go back and fix it, but it has a certain poetic beauty to it...

So for the record, I was trying to type that there was a single potential additional launch, by using the additive character whose name should not be mentioned next to the universal digit of unity...

You know, like "additionally, there can be only a single of us", or "also, Neo, you are the integer that is less than two and more than zero".

Process that, filter!  I hope that's obfuscated enough to be deemed clear.
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Offline Jim

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Re: Reusable Falcon for propellant depot.
« Reply #27 on: 12/03/2012 12:04 am »

So, for example, 3 F9Rs can put 9 tankers in orbit within a week. (or for that matter, within a month)


Not in this decade
« Last Edit: 12/03/2012 12:05 am by Jim »

Online meekGee

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Re: Reusable Falcon for propellant depot.
« Reply #28 on: 12/03/2012 12:19 am »

So, for example, 3 F9Rs can put 9 tankers in orbit within a week. (or for that matter, within a month)


Not in this decade

The argument was that under a plan that includes rapid launching of F9Rs, and a non-hydrogen BEO stage, it makes more sense to have those extended-cab upper stages than it does no have a long-duration dedicated propellant depot.

Your opinion of how long it will take SpaceX to get there is unsubstantiated and irrelevant all at the same time.
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Offline Elmar Moelzer

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Re: Reusable Falcon for propellant depot.
« Reply #29 on: 12/03/2012 01:32 am »
Quote
Spacex has yet to demonstrate routine operations for current systems and won't for a substantial amount of time (years) since their designs have not stabilized and can't due to interdepencies.  This is something that shills for Spacex ignore.
Their designs have not stabilized yet, but they do have developed quite a routine. Just think of how quickly they are able restart the countdown after an abort (and fix of the problem). I have yet to see anyone else in the industry do that at that level. Plus, reusability will facilitate routine. With ELVs every launch equals the first testflight of the rocket.
I think that there is potential for them to get routine really quickly.

Offline douglas100

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Re: Reusable Falcon for propellant depot.
« Reply #30 on: 12/03/2012 03:55 pm »
First they've got to find the cause of the anomaly on the previous flight and fix it. Next year should give a better idea of what their real launch rate will amount to.
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Offline Robotbeat

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Re: Reusable Falcon for propellant depot.
« Reply #31 on: 12/03/2012 05:21 pm »
First they've got to find the cause of the anomaly on the previous flight and fix it. Next year should give a better idea of what their real launch rate will amount to.
Or, we'll find out it takes a lot longer for them to ramp up to a real launch rate than they thought.
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Offline Elmar Moelzer

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Re: Reusable Falcon for propellant depot.
« Reply #32 on: 12/03/2012 05:37 pm »
Quote
First they've got to find the cause of the anomaly on the previous flight and fix it.

Sometimes anomalies are just that, anomalies, freak accidents, etc.
With expendable rockets, this is bound to happen. They might never find the actual cause of it.

Offline Robotbeat

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Re: Reusable Falcon for propellant depot.
« Reply #33 on: 12/03/2012 05:47 pm »
Quote
First they've got to find the cause of the anomaly on the previous flight and fix it.

Sometimes anomalies are just that, anomalies, freak accidents, etc.
With expendable rockets, this is bound to happen. They might never find the actual cause of it.
There IS a reason for it. And they probably will discover it.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline Jim

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Re: Reusable Falcon for propellant depot.
« Reply #34 on: 12/03/2012 06:36 pm »
Sometimes anomalies are just that, anomalies, freak accidents, etc.
With expendable rockets, this is bound to happen. They might never find the actual cause of it.

No, they end up always finding the reason.  There have been no unknown reasons for US accidents.  There may be repeats, but the cause is eventually found. 

Online meekGee

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Re: Reusable Falcon for propellant depot.
« Reply #35 on: 12/03/2012 06:56 pm »
Back to the topic - does anyone know the weight of the fueled upper stage+payload, for F9 and for F9H?

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Offline Elmar Moelzer

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Re: Reusable Falcon for propellant depot.
« Reply #36 on: 12/03/2012 07:29 pm »
Quote
There have been no unknown reasons for US accidents.  There may be repeats, but the cause is eventually found.

You are probably right. I am still not ruling out the possibility. After all, the other 9 Merlin engines (8 of which on the first stage) on that flight worked just fine and none of them had a RUD.

Offline cleonard

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Re: Reusable Falcon for propellant depot.
« Reply #37 on: 12/03/2012 08:32 pm »
No, they end up always finding the reason.  There have been no unknown reasons for US accidents.  There may be repeats, but the cause is eventually found. 

That is too strong a conclusion.  The issue is that the hardware was not recovered.  I agree that if the hardware could have been examined then the true cause can be found with some certainty.  Sometimes, depending on the exact condition, even with the hardware it can be almost impossible to determine what exactly happened.

Without the hardware all that can be done is analysis of the video and telemetry data.  That may yield a set of possibilities each with it's own probability.  A determination to the level of a 100% probability may well not be possible.  Engine and system testing can be done to better try and discover exactly what happened.  However, in this case the failure occurred at max-q.  The only way to simulate that with complete fidelity would be launch again.  Repeats with some additional telemetry work, but they can be very expensive. 

Please note, I am not saying that it's impossible that an exact cause can be found in this case.  I certainly have no more insight into the incident than anyone else on the outside.  I'm just saying that even though a cause will be found, the report might say that there are more than one possibility that can not be ruled out.

I hope that the process doesn't take too long and that we hear something.  Not that it matters to any of the parties, but I'd like to know.
« Last Edit: 12/03/2012 08:35 pm by cleonard »

Offline douglas100

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Re: Reusable Falcon for propellant depot.
« Reply #38 on: 12/03/2012 08:48 pm »
First they've got to find the cause of the anomaly on the previous flight and fix it. Next year should give a better idea of what their real launch rate will amount to.
Or, we'll find out it takes a lot longer for them to ramp up to a real launch rate than they thought.

Yep.
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Offline Jim

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Re: Reusable Falcon for propellant depot.
« Reply #39 on: 12/03/2012 09:40 pm »
No, they end up always finding the reason.  There have been no unknown reasons for US accidents.  There may be repeats, but the cause is eventually found. 

That is too strong a conclusion. 


No, that is the case for every US failure.  The cause was always found.

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