SpaceX Falcon Heavy Discussion (Thread 6)

[matthewkantar]

LouScheffer posted a very accurate guess over a year ago, good maths!

Performance prediction for Arabsat 6:  If the figures for Mars throw weight are correct, or even close, then FH recoverable can stage at a much higher speed than even F9 expendable, at least 500 m/s more if they press all the performance buttons.  Let's assume the mass is the same as Intelsat at 6700 kg.  Then the question is how conservative/aggressive SpaceX wants to be.

The first FH mission staged at the same speed as Intelsat expendable.  So they could clearly do this again.  The result would be a similar orbit, since the second stage is unchanged:  Add 2550 m/s from LEO, to get 43K x 28.85^o, 1729 m/s to go.

More aggressive:  they add +150 m/s to staging, to get  56K x 25^o, 1640 m/s to go.

Still more aggressive:  add +300 to staging, to get 78K x 24.5^o, 1550 m/s to go.

Almost pull the stops out:  add +450 to staging, to get 90K x 21.82^o, 1497 m/s to go.  Clearly reaching diminishing returns here.

My guess is that SpaceX will be more aggressive, but not too much.  Perhaps +225 m/s at staging (2860 m/s), final orbit of 62K x 24^o, 1600 m/s to go.

[jketch]

They ended up flying a fairly aggressive flight profile given that it's the first flight of B5 FH. Velocity at staging was 2980 m/s, 345 m/s faster than the test flight.

[Tangado]

At the coverage of the FH you saw for couple frames some wierd cameraviews, can anyone tell me what this may be? To me it could be the inner of the upper stage?

[The Vorlon]

Your looking down the stage 2 LOX tank

[Tangado]

I guess they showed it by accident, i would love to see more coverage of the inner of the LOX tank, but guessing that this is some sort of classified intel is it?

[tyrred]

They used to show lots of snippets of the upper stage interiors. Not the secret Intel you're looking for.

[theinternetftw]

Some old video footage of back when they showed it intentionally here:

https://twitter.com/sivarajkumar237/status/1116479929388941312

Now they time the globe visualization such that it covers for when that camera's being downlinked in the single channel video feed.

[frog]

Yesterday I learned that Launch Photography is Harder than it looks.   Here a couple from Playalinda Beach

[Robotbeat]

Has anyone looked at a 36 engine or 45 engine 4 or 5 core Falcon Superheavy?

Stretching S2 on current is much more bang for buck. S2 really the limiting factor.

More boosters helps a lot more than a bigger upper stage, but would require serious changes to the center core and especially to the ground infrastructure.

A larger upper stage would mainly help when recovering the boosters. For expendable max payload, especially to very high energies, it doesn't help so much. A 3rd or kick stage is probably better value for the money there.

Actually, that's backwards. The stretched stage helps more for high energy payloads than LEO payloads.

[MATTBLAK]

If the upper stage were to be stretched: could we expect a, say; 20 or 30% percent stretch for more propellant? And is there any more margin for Merlin 1D vacuum thrust upgrades?

[envy887]

Has anyone looked at a 36 engine or 45 engine 4 or 5 core Falcon Superheavy?

Stretching S2 on current is much more bang for buck. S2 really the limiting factor.

More boosters helps a lot more than a bigger upper stage, but would require serious changes to the center core and especially to the ground infrastructure.

A larger upper stage would mainly help when recovering the boosters. For expendable max payload, especially to very high energies, it doesn't help so much. A 3rd or kick stage is probably better value for the money there.

Actually, that's backwards. The stretched stage helps more for high energy payloads than LEO payloads.

Do you have a model that suggest that? Because the Silverbird model suggests otherwise. Like all models, it makes a lot of simplifying assumptions, but I don't think this effect is going to change much with a different model. Stretching the stage adds dry mass, and dry mass hurts more the further you throw it.

Using the assumptions below, and adding 500 kg dry mass and 30,000 kg prop to the upper stage, it shows 3% more payload to LEO, 2.2% more to TLI, and 1.6% more to TMI for the stretched stage compared to the standard stage. The returns of stretching the stage are small for a full expendable, and they get smaller as the final energy increases.

[rakaydos]

Has anyone looked at a 36 engine or 45 engine 4 or 5 core Falcon Superheavy?

Stretching S2 on current is much more bang for buck. S2 really the limiting factor.

More boosters helps a lot more than a bigger upper stage, but would require serious changes to the center core and especially to the ground infrastructure.

A larger upper stage would mainly help when recovering the boosters. For expendable max payload, especially to very high energies, it doesn't help so much. A 3rd or kick stage is probably better value for the money there.

Actually, that's backwards. The stretched stage helps more for high energy payloads than LEO payloads.

Do you have a model that suggest that? Because the Silverbird model suggests otherwise. Like all models, it makes a lot of simplifying assumptions, but I don't think this effect is going to change much with a different model. Stretching the stage adds dry mass, and dry mass hurts more the further you throw it.

Using the assumptions below, and adding 500 kg dry mass and 30,000 kg prop to the upper stage, it shows 3% more payload to LEO, 2.2% more to TLI, and 1.6% more to TMI for the stretched stage compared to the standard stage. The returns of stretching the stage are small for a full expendable, and they get smaller as the final energy increases.

As I understood it, the FH uses an upper stage which was oversized for F9 (in order to stage earlier for RTLS) but is undersized for FH using FT and block 5 merlins. The upperstage is too light, making the center core reserve extra fuel for the entry burn, cutting into total lift capability. With more fuel in the upperstage, the center core is moving slower, which means it can use more fuel on pushing and less on slowing. (a fraction of the speed lost by the heavier stage, but the extra fuel also improves the upper stage's mass ratio, improving DV to make up for the core's loss.)

[envy887]

Has anyone looked at a 36 engine or 45 engine 4 or 5 core Falcon Superheavy?

Stretching S2 on current is much more bang for buck. S2 really the limiting factor.

More boosters helps a lot more than a bigger upper stage, but would require serious changes to the center core and especially to the ground infrastructure.

A larger upper stage would mainly help when recovering the boosters. For expendable max payload, especially to very high energies, it doesn't help so much. A 3rd or kick stage is probably better value for the money there.

Actually, that's backwards. The stretched stage helps more for high energy payloads than LEO payloads.

Do you have a model that suggest that? Because the Silverbird model suggests otherwise. Like all models, it makes a lot of simplifying assumptions, but I don't think this effect is going to change much with a different model. Stretching the stage adds dry mass, and dry mass hurts more the further you throw it.

Using the assumptions below, and adding 500 kg dry mass and 30,000 kg prop to the upper stage, it shows 3% more payload to LEO, 2.2% more to TLI, and 1.6% more to TMI for the stretched stage compared to the standard stage. The returns of stretching the stage are small for a full expendable, and they get smaller as the final energy increases.

As I understood it, the FH uses an upper stage which was oversized for F9 (in order to stage earlier for RTLS) but is undersized for FH using FT and block 5 merlins. The upperstage is too light, making the center core reserve extra fuel for the entry burn, cutting into total lift capability. With more fuel in the upperstage, the center core is moving slower, which means it can use more fuel on pushing and less on slowing. (a fraction of the speed lost by the heavier stage, but the extra fuel also improves the upper stage's mass ratio, improving DV to make up for the core's loss.)

Yes, it helps increase payload. But the increase is smaller (as a percentage of payload) for higher energies due to the higher final dry mass of the stage.

[rakaydos]

Has anyone looked at a 36 engine or 45 engine 4 or 5 core Falcon Superheavy?

Stretching S2 on current is much more bang for buck. S2 really the limiting factor.

More boosters helps a lot more than a bigger upper stage, but would require serious changes to the center core and especially to the ground infrastructure.

A larger upper stage would mainly help when recovering the boosters. For expendable max payload, especially to very high energies, it doesn't help so much. A 3rd or kick stage is probably better value for the money there.

Actually, that's backwards. The stretched stage helps more for high energy payloads than LEO payloads.

Do you have a model that suggest that? Because the Silverbird model suggests otherwise. Like all models, it makes a lot of simplifying assumptions, but I don't think this effect is going to change much with a different model. Stretching the stage adds dry mass, and dry mass hurts more the further you throw it.

Using the assumptions below, and adding 500 kg dry mass and 30,000 kg prop to the upper stage, it shows 3% more payload to LEO, 2.2% more to TLI, and 1.6% more to TMI for the stretched stage compared to the standard stage. The returns of stretching the stage are small for a full expendable, and they get smaller as the final energy increases.

As I understood it, the FH uses an upper stage which was oversized for F9 (in order to stage earlier for RTLS) but is undersized for FH using FT and block 5 merlins. The upperstage is too light, making the center core reserve extra fuel for the entry burn, cutting into total lift capability. With more fuel in the upperstage, the center core is moving slower, which means it can use more fuel on pushing and less on slowing. (a fraction of the speed lost by the heavier stage, but the extra fuel also improves the upper stage's mass ratio, improving DV to make up for the core's loss.)

Yes, it helps increase payload. But the increase is smaller (as a percentage of payload) for higher energies due to the higher final dry mass of the stage.

That seems backward. For a given engine+payload, extending the fuel tank improves the mass ratio (adding a small amount of tank-perimiter material, and all the fuel that fits in the cross section added), improving DV. it only becomes an issue when you start cutting into the booster's lift capability, but FH is much better endowed there than F9.

[su27k]

So has anyone calculated how much performance improvement FH expendable can get by adding a shortened S2 as 3rd stage, as woods170 suggested in the other thread?

I gave it a try on http://silverbirdastronautics.com/LVperform.html, by using a 3rd stage half as big as 2nd stage (the numbers actually doesn't seem sensitive to the exact size), the increase is not that big, TLI payload only increased by 3 tons or so.

[M.E.T.]

Of course, until Starship arrives, any size increase to the upper stage just increases the cost of the part of the rocket that gets expended.

Heavy investment in improving upper stage performance is probably to be avoided until said stage can be recovered - which will never be the case for the Falcon family, now that bouncy castle has been abandoned.

Better to save it for Starship.

[kevinof]

Tend to agree - if you assume SS will work and will be on the scene in 3/4 years, then if Heavy will fill most of their customer needs until then, why invest in changes to it? Might be some business you lose because of the lack of a more powerful S2 (or even an S3) but is it really worth the investment?

Of course, until Starship arrives, any size increase to the upper stage just increases the cost of the part of the rocket that gets expended.

Heavy investment in improving upper stage performance is probably to be avoided until said stage can be recovered - which will never be the case for the Falcon family, now that bouncy castle has been abandoned.

Better to save it for Starship.

[spacenut]

I know rockets aren't legos.  However, what if NASA wanted to put a Delta IV heavy upper stage on a FH instead of the existing stage?  What kind of payload would that be to LEO? to TLI?  Say a stretched Delta IV heavy upper stage with say two or four RL-10 engines. 

[Tonioroffo]

They ended up flying a fairly aggressive flight profile given that it's the first flight of B5 FH. Velocity at staging was 2980 m/s, 345 m/s faster than the test flight.

My heart skipped a beat at BECO, watching the movement between boosters and core while they were still connected - but sep went perfectly well.

[TrueBlueWitt]

So has anyone calculated how much performance improvement FH expendable can get by adding a shortened S2 as 3rd stage, as woods170 suggested in the other thread?

I gave it a try on http://silverbirdastronautics.com/LVperform.html, by using a 3rd stage half as big as 2nd stage (the numbers actually doesn't seem sensitive to the exact size), the increase is not that big, TLI payload only increased by 3 tons or so.

Not surprising as you're carrying two Mvac worth of mass and tank domes/bulkheads uphill instead of one..
Also adds way more $$$ throwing away 2 Mvac instead of 1.. Just don't see how that case ever closes.

Betting much better bang for buck stretching S2, as adding a meter or two to the tank walls takes very little cost/added mass. 

Only significant cost is modifying the TE.