Author Topic: SpaceX F9 Block 5 payload capability  (Read 12575 times)

Offline MP99

Re: SpaceX F9 Block 5 payload capability
« Reply #20 on: 09/05/2022 08:10 pm »

About payload capacity, since this is the purpose for the thread.  I find it amazing that one vehicle can win such a wide range of payloads.  As we have seen the F9 can be a beast to LEO and yet still has flights for payloads under a few thousand kilos.

I wonder how much of the cost of those low-mass launches is the Merlin that's expended on the upper stage. The MVac is much harder to make than the SL version.

I wonder if eventually they might fit an older SL Merlin on F9US with very low mass payloads instead?

The new SL engine added to the rotation would be cheaper to make, and could serve multiple launches.

Cheers, Martin
« Last Edit: 10/06/2022 07:15 am by zubenelgenubi »

Offline alugobi

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Re: SpaceX F9 Block 5 payload capability
« Reply #21 on: 09/05/2022 08:32 pm »
MP99, good posting.  You could improve it by losing the Tapatalk spam. 

Offline Coastal Ron

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Re: SpaceX F9 Block 5 payload capability
« Reply #22 on: 09/05/2022 08:46 pm »
About payload capacity, since this is the purpose for the thread.  I find it amazing that one vehicle can win such a wide range of payloads.  As we have seen the F9 can be a beast to LEO and yet still has flights for payloads under a few thousand kilos.
I wonder how much of the cost of those low-mass launches is the Merlin that's expended on the upper stage. The MVac is much harder to make than the SL version.

Why do you think the Merlin Vacuum is "much harder to make"? Do you mean it costs more? Or that it takes more labor? Or what?

Quote
I wonder if eventually they might fit an older SL Merlin on F9US with very low mass payloads instead?

Vacuum rocket engines work differently than sea level ones, so even if the expansion ratio of the nozzle wasn't an issue (it is), then a sea level Merlin engine likely would fail while trying to operate in space.

Plus, if this were at all a possibility, then SpaceX likely would have tried it already...  ;)

Quote
The new SL engine added to the rotation would be cheaper to make, and could serve multiple launches.

You seem to assume that a Merlin Vacuum costs significantly more than a sea level Merlin 1D. Where is this assumption coming from, because in some aspects the Merlin Vacuum is a more simple engine.
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Offline rpapo

Re: SpaceX F9 Block 5 payload capability
« Reply #23 on: 09/06/2022 11:47 am »
Why do you think the Merlin Vacuum is "much harder to make"? Do you mean it costs more? Or that it takes more labor? Or what?
Not that I agree with the notion that the MVac must be much more expensive than the standard Merlin, but IIRC, from the early teething issues (Cassiope, etc), it would seem to me that though there are vacuum-specific issues, there are or were also issues related to radiative heat dissipation to space.  That is, some things were freezing.

So, even if the motor is only used once, it still requires more special treatment than simply giving it a bigger nozzle.  Whether that requires a lot more money is another question entirely.
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Offline Robotbeat

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Re: SpaceX F9 Block 5 payload capability
« Reply #24 on: 09/06/2022 01:50 pm »
I actually agree MVac probably is significantly more expensive than the sea level version. Its an underrated part of Falcon 9s success.
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Offline wannamoonbase

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Re: SpaceX F9 Block 5 payload capability
« Reply #25 on: 09/06/2022 02:34 pm »
I actually agree MVac probably is significantly more expensive than the sea level version. Its an underrated part of Falcon 9s success.

I love that the MVac is such a beast for thrust compared to other US. 

Also very impressive that they can control it so precisely.  I always love seeing the 1-2 second burns of the US and then nail it. 

Seems the MVac thrust is like filling a coffee cup with a firehose and nailing it!
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Offline Coastal Ron

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Re: SpaceX F9 Block 5 payload capability
« Reply #26 on: 09/06/2022 02:40 pm »
I actually agree MVac probably is significantly more expensive than the sea level version. Its an underrated part of Falcon 9s success.

The Merlin Vacuum is built to do the job that SpaceX requires, which was really the point I making in response to the other poster. There is no evidence that SpaceX is unhappy with the Merlin Vacuum, and it has a stellar record.

There is no reason to make any changes at this point, especially considering that Starship is supposed to replace Falcon 9/H not too far in the future, so SpaceX would gain nothing by making changes to a reliable engine.
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Online Stan-1967

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Re: SpaceX F9 Block 5 payload capability
« Reply #27 on: 09/06/2022 06:11 pm »

I wonder how much of the cost of those low-mass launches is the Merlin that's expended on the upper stage. The MVac is much harder to make than the SL version.

I wonder if eventually they might fit an older SL Merlin on F9US with very low mass payloads instead?

The new SL engine added to the rotation would be cheaper to make, and could serve multiple launches.

Cheers, Martin

I don't think the showstopper issues with this idea are that Merlin 1-D can't operate effectively in a vacuum, it already does that when it does boostback & entry burns.  Long loiter times between restarts is a different issue, but much of the thermal management work has been done for the existing Falcon 9 S2.

I think the showstopper is that there is no market for this.  This configuration would not enable serving new launches.  I think your primary error is in that speculative assumption.

 You are basically pushing the performance of F9 back towards V1.0 days with Merlin 1-C, so what are the implications of this?  What do you lose with an F9 when you cut performance of the upper stage to something of similar thrust, but around 10% lower ISP ( 311s)

1.  Launch +45 Starlink satellites with a down range landing  ( this is the bulk of F9's manifest)  At best you may get half of that mass to LEO, & maybe have to expend the booster
2.  Launch rideshares with accompanying Starlinks.  Might have to choose between expending the booster, or removing Starlinks from Transporter missions.
3.  CRS missions won't benefit from it.  Re-use may also be non-viable
4.  Not viable for crewed missions.  Period.  Never going to re-qualify this mod for crewed flight.
5 What is left?  GTO, other high energy missions?  Out of the question for this lower performance configuration.

Looking back at the capability development of F9, it is all intertwined between upgraded Merlin 1-D's & MVac working together.  The combined performance closed the gap for creating the margins for booster re-use on most all mission up to 5 tons to GTO.  Without that efficient MVac carrying payloads to obit, the booster wouldn't have the margins to be re-used because it would have to make up the shortfall in DV that the upper stage lacks with a boilerplate Merlin 1D. 

All the above is what made a subscale Raptor powered S2 such fun to speculate about a few years ago.  That would at least move the needle forward on re-use & performance. 

« Last Edit: 10/06/2022 07:15 am by zubenelgenubi »

Online Exastro

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Re: SpaceX F9 Block 5 payload capability
« Reply #28 on: 09/08/2022 03:23 am »
I wonder how much of the cost of those low-mass launches is the Merlin that's expended on the upper stage. The MVac is much harder to make than the SL version.

I wonder if eventually they might fit an older SL Merlin on F9US with very low mass payloads instead?

The new SL engine added to the rotation would be cheaper to make, and could serve multiple launches.

Cheers, Martin


I think your idea has merit, at least in principle.  We think we know that an M1D costs SpaceX well under $1M to build, IIRC.  It stands to reason that the vacuum version would be more expensive than the sea-level version for several reasons:

* It's a lower-volume product (though likely built with a lot of the same parts)

* It's single-point loss-of-mission critical, whereas F9 has demonstrated that it can suffer a sea-level engine failure and still complete its mission

* It needs to be able to restart after spending hours in orbit, including several day-night cycles

* It's potentially competing against well-used sea-level engines, so (as you point out) the real cost difference is likely larger than the difference in manufacturing cost.

As you say, using a sea-level engine on the upper stage could allow F9 to compete for less demanding launches.  I don't think anybody who knows for sure why it isn't implemented would be allowed to say.  At a guess, the size of the small-payload-to-low-orbit market is just too small to justify the NRE cost and the added cost of keeping another version of the upper stage in production.
« Last Edit: 09/08/2022 03:26 am by Exastro »

Offline kevin-rf

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Re: SpaceX F9 Block 5 payload capability
« Reply #29 on: 09/08/2022 11:10 am »
With reuse, is it still a lower volume product?  I would argue with the current flight rate,  between the two volume is currently on par. They will need,  what 60ish vac engines this year?  That's 6 or 7 new first stages worth of engines.
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Offline spacenut

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Re: SpaceX F9 Block 5 payload capability
« Reply #30 on: 09/08/2022 12:01 pm »
From what I understand the Merlin Vac uses all the same parts as a Merlin 1D, except the extended nozzle to make it a vacuum engine.  Probably has some tweeking here or there.  However, it shouldn't be much more expensive than the regular Merlin since it is made on the same assembly line.  If Merlin is $1 million each, maybe Merlin Vac is $1.2 million each.  Not a showstopper. 

Also, if they are launching 50-60 rockets this year and about 100 next year.  They will be manufacturing a lot of engines, even if most launches are on used rockets.  They will still have to make a couple of new boosters next year plus all the second stages.  Some of those launches will probably be Starships.  How many we don't yet know. 

I think SpaceX has tweeked F9 about as much as they can short of making the upper stage reusable, but that cuts the payload probably in half.  A million+ to expend a second stage engine vs loosing 10 tons of payload to make it reusable.  With a paying customer this doesn't make sense yet. 

Offline r8ix

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Re: SpaceX F9 Block 5 payload capability
« Reply #31 on: 09/08/2022 04:20 pm »
Well, as average booster life hits 9 flights, MVac will have a higher production rate than M1D. It's already around 1/3 of total engines, I think, but might be 1/2 or possibly more of current production...

Offline MP99

Re: SpaceX F9 Block 5 payload capability
« Reply #32 on: 09/11/2022 08:48 pm »
As you say, using a sea-level engine on the upper stage could allow F9 to compete for less demanding launches.  I don't think anybody who knows for sure why it isn't implemented would be allowed to say.  At a guess, the size of the small-payload-to-low-orbit market is just too small to justify the NRE cost and the added cost of keeping another version of the upper stage in production.

TBH, I thought there were a small number of flights which were relatively light and to easy orbits, EG SSO. Not sure about the MEO ones, like GPS.

OTOH, looking at the list of RTLS launches in the last couple of years, those seem to actually be hen's teeth.

On the subject of Mvac production, I thought I had read that the SL were produced one per day, and the vac once per week. But I've not been able to back that up.

One final thought - would mini Starlink v2 be volume limited if they have to fall back to F9 launches? Still probably cheaper to convert those to RTLS instead of a weird US config.

Cheers, Martin
« Last Edit: 09/11/2022 08:50 pm by MP99 »

Offline MP99

Re: SpaceX F9 Block 5 payload capability
« Reply #33 on: 09/11/2022 08:53 pm »
MP99, good posting.  You could improve it by losing the Tapatalk spam.
Would love to.

I have always configed this away in the past, but I think they may have removed the setting for that at some point.
« Last Edit: 10/06/2022 07:16 am by zubenelgenubi »

Offline alugobi

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Re: SpaceX F9 Block 5 payload capability
« Reply #34 on: 09/11/2022 09:14 pm »
MP99, good posting.  You could improve it by losing the Tapatalk spam.
Would love to.

I have always configed this away in the past, but I think they may have removed the setting for that at some point.
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« Last Edit: 10/06/2022 07:16 am by zubenelgenubi »

Offline virtuallynathan

Re: SpaceX F9 Block 5 payload capability
« Reply #35 on: 09/12/2022 07:26 pm »
Staging the fairing significantly earlier, taking less time after stage sep to ignite the second stage. Better understanding of propellant residuals, more aggressive hoverslam.

SpaceX also has used Starlink missions to experiment with the timing between first-stage separation and second-stage engine ignition. Separating the first stage and immediately lighting the second is better from a second-stage performance perspective, but the plume then hits the first-stage interstage components, increasing wear. Were looking at how you light the engine the earliest, but not damage components in the first stage, Jensen says.
So far, SpaceX has worked down to a 1,000-in. separation by decreasing the time between first-stage separation and second-stage ignition in increments of 0.25 sec.
Similarly, Starlink missions provide SpaceX a testbed for fairing separation timing. Customers typically have strict requirements on when the fairing is deployed to prevent rarified atmospheric particles in the fringe of space from heating the payload.
On Starlink missions, we incrementally started deploying the fairing earlier and allowing higher and higher heating, Edwards says. Now were at the point where its more than 10 times the heating that is typically allowed on an external customer mission.

Offline whitelancer64

Re: SpaceX F9 Block 5 payload capability
« Reply #36 on: 09/12/2022 08:27 pm »
Staging the fairing significantly earlier, taking less time after stage sep to ignite the second stage. Better understanding of propellant residuals, more aggressive hoverslam.

SpaceX also has used Starlink missions to experiment with the timing between first-stage separation and second-stage engine ignition. Separating the first stage and immediately lighting the second is better from a second-stage performance perspective, but the plume then hits the first-stage interstage components, increasing wear. Were looking at how you light the engine the earliest, but not damage components in the first stage, Jensen says.
So far, SpaceX has worked down to a 1,000-in. separation by decreasing the time between first-stage separation and second-stage ignition in increments of 0.25 sec.
Similarly, Starlink missions provide SpaceX a testbed for fairing separation timing. Customers typically have strict requirements on when the fairing is deployed to prevent rarified atmospheric particles in the fringe of space from heating the payload.
On Starlink missions, we incrementally started deploying the fairing earlier and allowing higher and higher heating, Edwards says. Now were at the point where its more than 10 times the heating that is typically allowed on an external customer mission.

Wow. That's very close.

1,000 inches is 83 ft. 4 in, or 25.4 meters

That's roughly 2/3 the length of the first stage.
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Offline MP99

Re: SpaceX F9 Block 5 payload capability
« Reply #37 on: 09/21/2022 10:00 am »


MP99, good posting.  You could improve it by losing the Tapatalk spam.
Would love to.

I have always configed this away in the past, but I think they may have removed the setting for that at some point.

Sent from my 21091116UG using Tapatalk


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That's a relief. Thanks!

Cheers, Martin


Offline Bob Shaw

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Re: SpaceX F9 Block 5 payload capability
« Reply #38 on: 09/21/2022 10:32 am »
Has anyone ever looked at a lengthened second stage or adding a third stage? Greater hardware cost, but perhaps a saving on expended boosters.

Offline wannamoonbase

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Re: SpaceX F9 Block 5 payload capability
« Reply #39 on: 09/21/2022 02:21 pm »
Has anyone ever looked at a lengthened second stage or adding a third stage? Greater hardware cost, but perhaps a saving on expended boosters.

Years ago, I recall Elon saying that best path to performance increase with F9 would be a minor stretch of the US.

I think that was in reference to the booster design being fixed, so probably around the time of the Block 5 introduction.

I don't know that they have done anything to extend the US since he said that.  One would think even a few inches could have a significant impact with a few more seconds of burn time for that MVac beast pushing max G's.

Regarding the tinkering with the timing of US engine start and fairing separation, that's a benefit of a high flight rate with reusable hardware.

Does anyone know if they have done anything to increase the separation speed to reduce the time to get to that 1000 inch spacing?
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