Author Topic: Precursor to Starship  (Read 7687 times)

Offline redneck

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Precursor to Starship
« on: 06/03/2023 09:32 am »
I posted this elsewhere and am curious as to the previous discussions of this.  It is too obvious to have been missed by these forums. My search has been deficient in locating previous threads on the subject. Where has this been discussed previously??

Looking back, not forward.
1. The Falcon9 development cost is said to have been under $1B including Merlin, Falcon1, and upper stage.
2. The Raptor based Starship architecture is said to be cheaper per launch than the Falcon9.
2.5 Raptor and methane turnaround time is expected to be under one day.
3. A Raptor based drop in replacement for the Falcon9 booster should have cost less time and money than the Falcon9 to develop given the development history of SpaceX.
4, Raptor with much higher Isp and more than double the thrust of Merlin would have that replacement viable with 5 engines.
5. The performance advantage of the replacement would allow RTLS on every mission.
6. That leads to daily flight per booster opportunities at a booster compared cost or <1/6 of Falcon9 if point 2 is correct given <1/6 as many engines as SH.
7. The development flights of two years ago only with Falcon standard landing procedures could have had a vehicle in operational service at least a year ago.
8. Assuming most of the above is a fair take, Raptor based Falcon9 boosters could be flying daily revenue flights today at a fraction of the cost of the current Falcon9.
9. There would be a flight experienced body of knowledge right now pertaining to operational strengths and weaknesses of the methane based vehicle. This would extend to high cadence operational flight crews.
10. This concept is if these decisions had been take years ago and is likely not reasonable going forward.
11. There is very little reason to believe that this would have been a multi year and multi billion dollar detour.

Offline Jim

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Re: Precursor to Starship
« Reply #1 on: 06/03/2023 02:51 pm »

4, Raptor with much higher Isp and more than double the thrust of Merlin would have that replacement viable with 5 engines.


No.
A.  Raptor would be too high of thrust for F9 second stage. 
b.  Raptor thrust would be too high for landing the first stage.  (the Merlin as is can't throttle down low enough to allow hovering, hence the "hover slam".
c.  tank sizes would have to increase, changing all the infrastructure.  (first stage may no longer be road transportable)

Offline Jim

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Re: Precursor to Starship
« Reply #2 on: 06/03/2023 02:51 pm »

11. There is very little reason to believe that this would have been a multi year and multi billion dollar detour.

there is very much so

the idea fails at every point.
« Last Edit: 06/03/2023 02:53 pm by Jim »

Offline mandrewa

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Re: Precursor to Starship
« Reply #3 on: 06/03/2023 03:16 pm »
I posted this elsewhere and am curious as to the previous discussions of this.  It is too obvious to have been missed by these forums. My search has been deficient in locating previous threads on the subject. Where has this been discussed previously??

Looking back, not forward.
1. The Falcon9 development cost is said to have been under $1B including Merlin, Falcon1, and upper stage.
2. The Raptor based Starship architecture is said to be cheaper per launch than the Falcon9.
2.5 Raptor and methane turnaround time is expected to be under one day.
3. A Raptor based drop in replacement for the Falcon9 booster should have cost less time and money than the Falcon9 to develop given the development history of SpaceX.
4, Raptor with much higher Isp and more than double the thrust of Merlin would have that replacement viable with 5 engines.
5. The performance advantage of the replacement would allow RTLS on every mission.
6. That leads to daily flight per booster opportunities at a booster compared cost or <1/6 of Falcon9 if point 2 is correct given <1/6 as many engines as SH.
7. The development flights of two years ago only with Falcon standard landing procedures could have had a vehicle in operational service at least a year ago.
8. Assuming most of the above is a fair take, Raptor based Falcon9 boosters could be flying daily revenue flights today at a fraction of the cost of the current Falcon9.
9. There would be a flight experienced body of knowledge right now pertaining to operational strengths and weaknesses of the methane based vehicle. This would extend to high cadence operational flight crews.
10. This concept is if these decisions had been take years ago and is likely not reasonable going forward.
11. There is very little reason to believe that this would have been a multi year and multi billion dollar detour.


There's a lot to discuss here, but I'll focus on your assertion that "The Raptor based Starship architecture is said to be cheaper per launch than the Falcon9."

Elon Musk is talking about the aspirational, marginal cost of a Starship launch.  First of all, marginal cost does not include development costs.  Marginal cost treats everything that came before as a sunk cost, and asks what it costs to do one more launch.  We can gradually work down the marginal cost by making every step of whatever goes into that more efficient.

And that gets us to what aspirational means.  Aspirational means, in this context, what happens if you push things to the limit.  It's not what is just around the corner.  It is not what is happening now.

It's where you can get if you spend many years pursuing a course.

Elon Musk is fond of saying something like, "If success is not of the possible outcomes, you shouldn't be pursuing it."  And that is a profound point.  People do miss this.

So if you go back to a certain point in time, Elon Musk was making aspirational, marginal cost statements about the Falcon 9.  And then he dropped that completely and switched to the Starship.

Why?  Because it had become apparent that even with the most aspirational, marginal cost assertion that Elon Musk could persuade himself might be true about an improved Falcon 9, it just wasn't going to be sufficient to get people to Mars.

So to get back to what you are saying.  You are mixing things up here.  Your confusing an assertion about the future with the present.


Offline StarshipTrooper

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Re: Precursor to Starship
« Reply #4 on: 06/03/2023 03:21 pm »
Elon thinking:
Would a starship precursor help reach Mars sooner?

No.

I'm very confident that success is within the set of possible outcomes.  Elon Musk

Offline redneck

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Re: Precursor to Starship
« Reply #5 on: 06/03/2023 06:19 pm »

4, Raptor with much higher Isp and more than double the thrust of Merlin would have that replacement viable with 5 engines.


No.
A.  Raptor would be too high of thrust for F9 second stage. 
b.  Raptor thrust would be too high for landing the first stage.  (the Merlin as is can't throttle down low enough to allow hovering, hence the "hover slam".
c.  tank sizes would have to increase, changing all the infrastructure.  (first stage may no longer be road transportable)

A. the stock Falcon9 upper stage would be used. I never suggested Raptor for the second.
B. SpaceX has perfected the hover slam and certainly has the expertise to do the same with another engine.
C. Tank sizes could remain the same as the Isp advantage would negate the requirement for larger tank. Large would be a nice to have rather than necessity. Glow would be less and acceleration higher. Still road transportable.

Offline redneck

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Re: Precursor to Starship
« Reply #6 on: 06/03/2023 06:22 pm »

11. There is very little reason to believe that this would have been a multi year and multi billion dollar detour.

there is very much so

the idea fails at every point.

Since Raptor is charged off to the Starship project, and the stock Falcon9 upper stage would be used, you will need to explain why the booster structure would be such a problem.

Offline redneck

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Re: Precursor to Starship
« Reply #7 on: 06/03/2023 06:28 pm »


""So to get back to what you are saying.  You are mixing things up here.  Your confusing an assertion about the future with the present.""


Fair enough. If Elon and company believe that Starship will be so cheap to operate, It seems that a much simpler and smaller vehicle based on know flight dynamics would also be cheaper. Not to mention much faster into revenue service.

Online spacenut

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Re: Precursor to Starship
« Reply #8 on: 06/03/2023 06:30 pm »
Smaller rockets can't get the mass to orbit, much less Mars as efficient as larger rockets. 

Offline Jim

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Re: Precursor to Starship
« Reply #9 on: 06/03/2023 06:30 pm »

11. There is very little reason to believe that this would have been a multi year and multi billion dollar detour.

there is very much so

the idea fails at every point.

Since Raptor is charged off to the Starship project, and the stock Falcon9 upper stage would be used, you will need to explain why the booster structure would be such a problem.

It removes the commonality between the stages and that is one of largest cost reducing factors.

Offline redneck

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Re: Precursor to Starship
« Reply #10 on: 06/03/2023 06:31 pm »
Elon thinking:
Would a starship precursor help reach Mars sooner?

No.

Unless it would have walked point on some of the problems with the larger vehicle. Somewhat as the problems with Falcon1 prevented the same problems with Falcon9.

I'm sure something of this nature has been discussed before. Does anyone know where and when?

Offline redneck

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Re: Precursor to Starship
« Reply #11 on: 06/03/2023 06:33 pm »
Smaller rockets can't get the mass to orbit, much less Mars as efficient as larger rockets.

Falcon9 seems to be getting plenty of mass to orbit.

Offline EspenU

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Re: Precursor to Starship
« Reply #12 on: 06/03/2023 06:36 pm »



4, Raptor with much higher Isp and more than double the thrust of Merlin would have that replacement viable with 5 engines.


No.
A.  Raptor would be too high of thrust for F9 second stage. 
b.  Raptor thrust would be too high for landing the first stage.  (the Merlin as is can't throttle down low enough to allow hovering, hence the "hover slam".
c.  tank sizes would have to increase, changing all the infrastructure.  (first stage may no longer be road transportable)
C. Tank sizes could remain the same as the Isp advantage would negate the requirement for larger tank. Large would be a nice to have rather than necessity. Glow would be less and acceleration higher. Still road transportable.

Don't know about the overall tank size, but the Merlin and Raptor mixture ratios are different, so the tank sizes would at least have to change internally.

In addition the fuel is now cryogenic, which would again require changes.

You also loose a lot of commonality between the stages, which will affect operations.

Offline redneck

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Re: Precursor to Starship
« Reply #13 on: 06/03/2023 06:37 pm »

11. There is very little reason to believe that this would have been a multi year and multi billion dollar detour.

there is very much so

the idea fails at every point.

Since Raptor is charged off to the Starship project, and the stock Falcon9 upper stage would be used, you will need to explain why the booster structure would be such a problem.

It removes the commonality between the stages and that is one of largest cost reducing factors.

Same engines and structural method as Starship. Same size as Falcon9. My Ford trucks have little commonality with my Chevrolet trucks and really doesn't matter for vehicles in continuous use.

Offline redneck

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Re: Precursor to Starship
« Reply #14 on: 06/03/2023 06:40 pm »



4, Raptor with much higher Isp and more than double the thrust of Merlin would have that replacement viable with 5 engines.


No.
A.  Raptor would be too high of thrust for F9 second stage. 
b.  Raptor thrust would be too high for landing the first stage.  (the Merlin as is can't throttle down low enough to allow hovering, hence the "hover slam".
c.  tank sizes would have to increase, changing all the infrastructure.  (first stage may no longer be road transportable)
C. Tank sizes could remain the same as the Isp advantage would negate the requirement for larger tank. Large would be a nice to have rather than necessity. Glow would be less and acceleration higher. Still road transportable.

Don't know about the overall tank size, but the Merlin and Raptor mixture ratios are different, so the tank sizes would at least have to change internally.

In addition the fuel is now cryogenic, which would again require changes.

You also loose a lot of commonality between the stages, which will affect operations.

Mixture ratios being different would require one tank to grow and the other to shrink. Another ring on one and lose a ring on the other. Many vehicles operate with different propellants in different stages.

Offline Jim

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Re: Precursor to Starship
« Reply #15 on: 06/03/2023 06:42 pm »

4, Raptor with much higher Isp and more than double the thrust of Merlin would have that replacement viable with 5 engines.


No.
A.  Raptor would be too high of thrust for F9 second stage. 
b.  Raptor thrust would be too high for landing the first stage.  (the Merlin as is can't throttle down low enough to allow hovering, hence the "hover slam".
c.  tank sizes would have to increase, changing all the infrastructure.  (first stage may no longer be road transportable)

A. the stock Falcon9 upper stage would be used. I never suggested Raptor for the second.
B. SpaceX has perfected the hover slam and certainly has the expertise to do the same with another engine.
C. Tank sizes could remain the same as the Isp advantage would negate the requirement for larger tank. Large would be a nice to have rather than necessity. Glow would be less and acceleration higher. Still road transportable.

A.  Stock second stage means mixed commodities at the pad and different GSE and requirements = more costs
mixed commodities mean different loading requirements = this will change the countdown sequence and cause problems with

b.  It is too high of high thrust for the hover slam. 

c.  Wrong.  If that were true, then why not go LH2 and even a greater increase ISP.  A larger tank is a necessity.   the ISP difference only affect the mass, it is not enough to make up for the difference in volume(energy density).  ISP is the difference in energy per mass unit.   Methane is about the twice the volume for the same mass of RP-1

Look at Atlas V vs Delta IV (same capability different propellant volume)
« Last Edit: 06/03/2023 06:54 pm by Jim »

Offline Jim

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Re: Precursor to Starship
« Reply #16 on: 06/03/2023 06:44 pm »

Mixture ratios being different would require one tank to grow and the other to shrink. Another ring on one and lose a ring on the other. .

wrong.

That doesn't work and still have the same lift capability.
Intuitively, that means there is less oxygen to burn and hence less total impulse.

Many vehicles operate with different propellants in different stages.

And they are not low cost

« Last Edit: 06/03/2023 06:47 pm by Jim »

Offline redneck

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Re: Precursor to Starship
« Reply #17 on: 06/03/2023 06:48 pm »


c.  Wrong.  If that were true, then why not go LH2 and even a greater increase ISP.  A larger tank is a necessity.   the ISP difference only affect the mass, it is not enough to make up for the difference in volume(energy density).

Look at Atlas V vs Delta IV (same capability different propellant volume)

Because we are discussing using an engine that SpaceX has in hand. If you will do the numbers, you will find that the 60 seconds difference in sea level Isp of Raptor against Merlin, more than makes up for having roughly 10% less propellant.

Offline mandrewa

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Re: Precursor to Starship
« Reply #18 on: 06/03/2023 07:01 pm »
Elon thinking:
Would a starship precursor help reach Mars sooner?

No.

Unless it would have walked point on some of the problems with the larger vehicle. Somewhat as the problems with Falcon1 prevented the same problems with Falcon9.

I'm sure something of this nature has been discussed before. Does anyone know where and when?

The Raptor engine was originally intended for the second stage of the Falcon 9.  It was a much smaller engine at that point and it ran on hydrogen and oxygen, not methane and oxygen.


So it's not like SpaceX didn't realize this possibility -- for a while they were actually doing it.


A second stage engine fueled by hydrogen would have been part of the natural evolution of the Falcon 9 if they were trying to maximize mass to orbit, but that's not necessarily the case.  I'm pretty sure Elon measures things more by dollar per kilogram to orbit than maximum mass to orbit, and in that respect, as Jim points out above, it's not at all obvious that a Falcon 9 with the second stage fueled by hydrogen would be cheaper.  Or if it was eventually cheaper, it might take a long time to get there.

Look, Starship will hopefully win on both of the metrics that count in the near future:

(a) dollars per kg to LEO; and

(b) making missions to Mars practical and feasible.

The Falcon 9 has been incredibly successful, and I expect SpaceX will still be doing Falcon 9 missions five years from now.

But SpaceX does not have a limitless amount of money.  They are investing in Starship and baring disaster I don't believe they will try to improve the Falcon 9 any further.

Offline Jim

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Re: Precursor to Starship
« Reply #19 on: 06/03/2023 07:11 pm »

Because we are discussing using an engine that SpaceX has in hand. If you will do the numbers, you will find that the 60 seconds difference in sea level Isp of Raptor against Merlin, more than makes up for having roughly 10% less propellant.

that is wrong. Need to make up for a difference of 50% or more in less volume and not 10% less mass.
Density
RP-1  8011020  g/L
Methane 422.8 g/L

and it is more like 45 seconds ISP difference but the 15 is not going to matter

Merlin 282 sec
Raptor 327 sec

10 kg of RP-1 is the same as 8.6 kg of Methane ISP wise

But 10 kg of RP-1 requires a tank of  9.8 liters but 8.6 kg of methane requires 20.3 liter tank
« Last Edit: 06/03/2023 07:13 pm by Jim »

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