Author Topic: Falcon 9 additional performance (12 tons)  (Read 70764 times)

Offline Analyst

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Re: Falcon 9 additional performance (12 tons)
« Reply #80 on: 02/20/2009 05:58 pm »

That's the spirit! It's detailed analyses like these what really contributes to this thread, as opposed to empty speculation.

Well, I guess the matter is settled, then.

Noone does prevent you from calculating. Sometimes things are so way off, you don't need to calculate exactly to see something is wrong.

It is like adding two three digit numbers and getting a five digit number. You should know you have messed up without calculating again.

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Offline William Barton

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Re: Falcon 9 additional performance (12 tons)
« Reply #81 on: 02/20/2009 05:59 pm »
[
 Looking at Spacex's prices, going from 3500kg to 5000kg gto is about a 60% jump in price,

that is because they can't reuse the upperstage

I though re-use was not accounted in the stated price list?

Offline ugordan

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Re: Falcon 9 additional performance (12 tons)
« Reply #82 on: 02/20/2009 06:08 pm »
Noone does prevent you from calculating. Sometimes things are so way off, you don't need to calculate exactly to see something is wrong.

I don't have the proper tools and stage data to do a valid and accurate analysis past the excel sheet delta-V calculations ignoring trajectory shapes, drag and importance of T/W related to gravity losses so, yes I am skeptical of any claims the numbers are unworkable. Especially arm-waving arguments comparing launch vehicle A with launch vehicle B.

I have said this several times now - I don't hold any value to arm-waving arguments like the above. This isn't about being wrong an order of magnitude or two, and you know it. The Zenit was brought up over and over again in many threads and just because it has currently the most powerful and efficient kerolox 1st stage engine doesn't make it a yardstick for comparing the entire system performance. As jongoff stated, there are several reasons why the stated F9 numbers might turn out not so "magical" in the end.
« Last Edit: 02/20/2009 06:09 pm by ugordan »

Offline ugordan

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Re: Falcon 9 additional performance (12 tons)
« Reply #83 on: 02/20/2009 06:12 pm »
that is because they can't reuse the upperstage

I though re-use was not accounted in the stated price list?

The current price is not accounting possible reuse AFAIK, but you're effectively paying for denying them any chance of 2nd stage recovery as I understand it - using up all available propellant in the launch.

Offline mlorrey

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Re: Falcon 9 additional performance (12 tons)
« Reply #84 on: 02/20/2009 06:23 pm »
Given that SeaLaunch's original capacity to GTO was 5 tons, launched on a Saturn class, 3 stage vehicle sitting on the Equator, its hard to imagine that a 2 stage vehicle with lower ISP, launched from Florida, would provide 4.5 tons to GTO. These numbers just don't make sense.



Its about the mass ratio of the vehicle. Saturn class vehicles did not get structural strength from pressurization of the fuel tanks, and the upper stage's LH2 fuel mandating much larger such tanks. However I think you are comparing apples and oranges.

The Saturn IB was a two stage vehicle with a empty weight of 54500 lb. The first stage was an RP-1/LOX fuelled stage, the second stage was LH2/LOX S-IVB stage common to the Saturn V launcher. Its payload was 18.6 metric tons, not 5 tons, to a 185 mile orbit with 28 degree inclination. A 5 ton payload vehicle is not a Saturn-class launcher.
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Offline Danderman

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Re: Falcon 9 additional performance (12 tons)
« Reply #85 on: 02/20/2009 06:28 pm »
The Saturn IB was a two stage vehicle with a empty weight of 54500 lb. The first stage was an RP-1/LOX fuelled stage, the second stage was LH2/LOX S-IVB stage common to the Saturn V launcher. Its payload was 18.6 metric tons, not 5 tons, to a 185 mile orbit with 28 degree inclination. A 5 ton payload vehicle is not a Saturn-class launcher.

Ooops, I was  not comparing the Saturn IB with F9, but rather simply stating that the Zenit 2 was/is a Saturn class LV, with its 13.5 metric ton payload (Saturn I was about 10 tons IIRC).


Offline Danderman

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Re: Falcon 9 additional performance (12 tons)
« Reply #86 on: 02/20/2009 06:29 pm »
That's the spirit! It's detailed analyses like these what really contributes to this thread, as opposed to empty speculation.

Well, I guess the matter is settled, then.

Incredible claims require incredible proof.

Offline ugordan

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Re: Falcon 9 additional performance (12 tons)
« Reply #87 on: 02/20/2009 06:45 pm »
Incredible claims require incredible proof.

Right about now I have to ask: what was the point of this thread, then? Obviously, no proof is possible until F9 Block 2 flies a couple of times so all this is moot.

Offline jongoff

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Re: Falcon 9 additional performance (12 tons)
« Reply #88 on: 02/20/2009 07:07 pm »
Here's a comparable LV, do they hold up using Ed's formulas?


Zenit-2: (data from Astronautix.com)

Stage 1
Gross Mass:  ~354 tonnes
Propellant Mass:  ~325 tonnes (mass fraction = 92%)
Thrust:  835 tonnes S/L, (doesn't give) tonnes vacuum
ISP:  309 sec S/L, 337 sec  vacuum

Stage 2
Gross Mass:  ~90 tonnes
Propellant Mass:  ~81 tonnes (mass fraction = 90%)
Thrust:  93 tonnes vacuum
ISP:  ~349 sec vacuum

Payload:  13.5 tonnes (to 51.6 degrees)
Delta-V:  9150-9200 m/s plus 200 m/s
Gross Liftoff Weight:  459 tonnes

One thing to note is that the Falcon IX is shooting for a much better upper stage mass fraction than Zenit 2 (IIRC they're shooting for ~95% propellant fraction).  If the Zenit 2 had a 95% propellant fraction on their upper stage (4.25ton upper stage dry weight), with the same propellant loading and engine performance, it would free up another 4.75 tonnes of cargo to the same orbit.

I think a lot of your misgivings are because SpaceX really is gunning for a very aggressive mass ratio.  That's what you should be questioning.  It looks pretty clear that if they can meet those numbers that there's nothing "magic" at all about the vehicle's performance numbers.

~Jon

Offline William Barton

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Re: Falcon 9 additional performance (12 tons)
« Reply #89 on: 02/20/2009 07:35 pm »
that is because they can't reuse the upperstage

I though re-use was not accounted in the stated price list?

The current price is not accounting possible reuse AFAIK, but you're effectively paying for denying them any chance of 2nd stage recovery as I understand it - using up all available propellant in the launch.

That was my question: if possible reuse is not accounted in the price, then that can't be the reason for the price difference. On the other hand, it's possible they are simply not accounting it in the profit margin. And I can't think of any other good reason for the price difference, other than, as someone suggested, bigger tanks required (but doesn't that seem like a semi-new rocket that ought to be called Falcon 9e?).

Offline wannamoonbase

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Re: Falcon 9 additional performance (12 tons)
« Reply #90 on: 02/20/2009 08:03 pm »
I will eat my hat and post pictures of it the day someone reuses an ELV 2nd stage.

Jon makes a good point that mass fraction is the end variable to evaluate.  Not unlike the DIRECT teams EDS mass fraction that is questioned by some.

I do wish SpaceX well but I'll have to see it work before I believe it.
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Offline A_M_Swallow

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Re: Falcon 9 additional performance (12 tons)
« Reply #91 on: 02/20/2009 09:27 pm »
I will eat my hat and post pictures of it the day someone reuses an ELV 2nd stage.

Half of the second stages could be refuelled and used as Earth departure stages.  They will need a restartable engine and to fly to a propellant depot.

Offline jongoff

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Re: Falcon 9 additional performance (12 tons)
« Reply #92 on: 02/20/2009 09:47 pm »
I will eat my hat and post pictures of it the day someone reuses an ELV 2nd stage.

Of course, to be a useful promise, it needs to be physically realistic (if somewhat outlandish).  My usual statement is something like "If Ares-1 ever a) flies, and b) flies succesfully 100x without losing a single mission, I'll print this post out, cover it in wasabi sauce, and eat it". 

But I take it you don't think an ELV upper stage can be reused.  Question, if something is intentionally designed as an RLV, does that not count? ;-)

Quote
Jon makes a good point that mass fraction is the end variable to evaluate.  Not unlike the DIRECT teams EDS mass fraction that is questioned by some.

I do wish SpaceX well but I'll have to see it work before I believe it.

FWIW, the Falcon 1 upper stage almost meets the mass fraction requirements needed to make the "magic" Falcon 9 numbers work.  And it uses a pressure-fed engine.  Not saying that a ~95% propellant fraction is easy, just saying it isn't impossible either. 

~Jon

Offline Jim

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Re: Falcon 9 additional performance (12 tons)
« Reply #93 on: 02/20/2009 09:50 pm »
I will eat my hat and post pictures of it the day someone reuses an ELV 2nd stage.

Half of the second stages could be refuelled and used as Earth departure stages.  They will need a restartable engine and to fly to a propellant depot.

These comments don't add to this thread. 
There are no propellant depots and spacex is not planning any refueling. 
Stay with in the context of the discussion.

Offline edkyle99

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Re: Falcon 9 additional performance (12 tons)
« Reply #94 on: 02/20/2009 10:17 pm »
Given that SeaLaunch's original capacity to GTO was 5 tons, launched on a Saturn class, 3 stage vehicle sitting on the Equator, its hard to imagine that a 2 stage vehicle with lower ISP, launched from Florida, would provide 4.5 tons to GTO. These numbers just don't make sense.


Its about the mass ratio of the vehicle.

PRECISELY!  Zenit might be considered a heavy NASCAR racer.  Falcon 9, by comparison, would be a lightweight Formula 1 race car. 

The Zenit first stage was originally designed to be a strap-on booster for Energia, so it likely had robust margin built into the design.  Both Zenit stages use separate tanks - and the second stage uses a torodial tank around the engine.  Zenit is built from aluminum, presumably aircraft grade aluminum.  The rocket has aluminum interstages and an aluminum thrust section, to the best of my knowledge.   

Falcon 9 is built from Aluminum-Lithium and carbon composites.  It has common bulkhead tanks.  While one RD-180 weighs 5.4 tonnes, nine Merlin 1C engines only weigh 4.22 tonnes all together - and produce more thrust.  When SpaceX lifted the Falcon 9 "run tank" onto the test stand in Texas, the company's web site said that the tanks and engine section (minus engines) weighed only 4.1 tonnes combined during the lift.  I'm still not sure I believe that number, but regardless it hints that the thing really is light. 

This is the revolutionary evolution that Falcon 9 seems to represent.  Using the latest materials and the lightest weight structural design methods, SpaceX is aiming to do things with a two-stage kerosene rocket that no one else has done since the Space Age began. 

If the company pulls it off, and it is an "if", it will be the equivalent of the emergence of lightweight aluminum monoplanes just before World War II.  They had engines and wings like their predecessors, but they weighed less while being stronger, and were faster than anything that had flown before.  Each piece of the puzzle was an evolutionary change, but when the puzzle was assembled, a revolution happened.

 - Ed Kyle

Offline ugordan

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Re: Falcon 9 additional performance (12 tons)
« Reply #95 on: 02/20/2009 10:19 pm »
FWIW, I just noticed Falcon 9 User's Guide appeared on the SpaceX site.

It has a few detailed performance graphs and tables. I didn't get a chance to check it out yet, but looks like it will give you all something juicier to rip apart than a few vague payload figures.

Quote
The initial flights of the Falcon 9, currently planned in 2009 and 2010, use the Falcon 9 Block 1.
Beginning in late 2010/early 2011, SpaceX will begin launching the Falcon 9 Block 2. Block 2
features increased engine thrust, decreased launch vehicle dry mass, and increased propellant
load
‐ combined with lessons learned from the flights of the Falcon 9 Block 1. This results in
increased mass‐to‐orbit performance for the Falcon 9 Block 2 when compared with Block 1
performance.

What I really don't like about their sample flight timeline is the fact stage separation occurs 2 seconds after MECO. Lessons learned?
« Last Edit: 02/20/2009 10:46 pm by ugordan »

Offline jongoff

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Re: Falcon 9 additional performance (12 tons)
« Reply #96 on: 02/20/2009 10:31 pm »
I will eat my hat and post pictures of it the day someone reuses an ELV 2nd stage.

Half of the second stages could be refuelled and used as Earth departure stages.  They will need a restartable engine and to fly to a propellant depot.

To be fair to wannamoonbase, I think he was talking about reentry, recovery, and relaunch of an ELV 2nd stage.  I agree that derivatives of some existing ELV stages could provide pretty good foundations for a reusable in-space stage, but they would be derivatives.  Most of the existing upper stages are restartable, and wouldn't need *that* many changes, but it isn't exactly trivial to add a bunch of unproven systems to an expensive upper stage.

Plus, until a depot is either in operations, or at least in construction, or at least some demonstrated way of tanking up in LEO, I doubt there's going to be a lot of justification for someone like ULA or SpaceX to make changes like those.

Patience Grasshopper.  ;-)

~Jon

Offline Danderman

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Re: Falcon 9 additional performance (12 tons)
« Reply #97 on: 02/20/2009 10:55 pm »
OK, let's look at the specific case of a Block II F9 upper stage, launched to GTO, at the time when it enters a transitional low LEO orbit (200 X 200 km). I don't know if SpaceX will use a parking orbit, but if they don't, there would be an equivalent delta-V to work from.

Since we know the low LEO performance of the Block II F9, 12,500 kg, we know the payload mass (4,500 kg), we can estimate the dry mass of the stage at about 3000 kg (yes, this ignores the maybe 300 - 500 kg for the launch adapter, but let's not work about that for now), which leaves us with a prop load - at that moment of about 5 tons, from which to attain GTO (12,500 kg = 4,500 kg + 3,000 kg + 5,000 kg, I hope). To get from a 27 or 28 degree LEO orbit at 200 km to GTO, the vehicle must generate about 2500 m/s. This does not produce ANY lowering of the inclination, though, which is not good.

I don't know about your universe, but in the universe where my set of the laws of physics live, F9 doesn't make it to GTO. Or else I made a math error.

I would happy if someone could demonstrate on paper that the F9 BK II really sends 4,500 kg to GTO, I don't need to wait to see the vehicle flying, I just would like to see the numbers, and I will accept that SpaceX can produce a 95% mass ratio as a given.




Offline Danderman

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Re: Falcon 9 additional performance (12 tons)
« Reply #98 on: 02/20/2009 11:12 pm »
Stage 2
Gross Mass:  ~46 tonnes
Propellant Mass:  ~43 tonnes
Thrust:  48.99 tonnes vacuum
ISP:  ~340 sec vacuum

I just read the F9 User manual that the 2nd stage burns for 345 seconds. With an ISP of 340 and a thrust of 49 tons, that means that the propellant *consumed* during the burn must be > 49 tons. Since your gross mass for the stage is 46 tons, something is off here.

Not to mention setting aside some 500 kg for residual prop.


Offline ugordan

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Re: Falcon 9 additional performance (12 tons)
« Reply #99 on: 02/20/2009 11:16 pm »
I just read the F9 User manual that the 2nd stage burns for 345 seconds. With an ISP of 340 and a thrust of 49 tons, that means that the propellant *consumed* during the burn must be > 49 tons. Since your gross mass for the stage is 46 tons, something is off here.

Yes, your assumption that the engine runs at full throttle the whole time is off.

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