SpaceX v1.2 (FT) Core Discussion - Block 3, 4, and 5

[scaesare]

Thought I'd re-post this Q in case it got lost...

@Grendal, you mentioned the Merlin engines were making 240K lbs. of thrust currently, and that figure is expected to increase with Block 5 designs. (I've seen estimates of another 7-8%)

I'm trying to reconcile that thrust number with the Wikipedia page on F9 FT which says 1.71mil lbs. thrust total. Those numbers don't jive.

Possibilities:

- The Merlins are detuned on the F9
- Wikipedia is incorrect on the F9 thrust # (although I note that ~1.7mil lbs. thrust would seem to match the ~5 mil lbs. number mentioned for FH w/ 3 cores)
- Other??

Thanks as always for the wealth of info you bring to the forum... just trying to understand what the actual capabilities are.

Thanks.

 

[Electroman]

I'm trying to reconcile that thrust number with the Wikipedia page on F9 FT which says 1.71mil lbs. thrust total. Those numbers don't jive.

I am guessing the combined thrust may not be a question of just adding the thrust of each of the 9 engines. There might be other factors at play that reduces the combined thrust.

it may not be like connecting three 1.5 V batteries in series and to get 4.5v

 

[Cosmacelf]

I am guessing the combined thrust may not be a question of just adding the thrust of each of the 9 engines. There might be other factors at play that reduces the combined thrust.

it may not be like connecting three 1.5 V batteries in series and to get 4.5v

Certainly in the first FH launch, not all engines were firing at full thrust all the time. There was a lot of ramping up and down going on. I would bet that the FH can’t run all engines at full thrust, at least not yet.

 

[ggr]

Certainly in the first FH launch, not all engines were firing at full thrust all the time. There was a lot of ramping up and down going on. I would bet that the FH can’t run all engines at full thrust, at least not yet.

The center booster does all the throttling for the FH. Some throttling is always necessary to meet Max Q limitations around the supersonic transition. This is intentional so that it has fuel left after the side boosters let go.

 

[Grendal]

The center booster does all the throttling for the FH. Some throttling is always necessary to meet Max Q limitations around the supersonic transition. This is intentional so that it has fuel left after the side boosters let go.

Jon Insprucker specifically says at different times during the launch that the side boosters throttle up and down.

 

[ggr]

Jon Insprucker specifically says at different times during the launch that the side boosters throttle up and down.

Interesting. I was going by the original plan. Well, the second original plan ;-). Originally they were going to use fuel from the side boosters to refill the center one, but the piping got too complicated apparently. Still, at takeoff you can see the flame from the center is smaller than the sides; not really visible in the video you posted, but clear in some of the others. Otherwise it wouldn't have had extra fuel after separation.

 

[scaesare]

Certainly in the first FH launch, not all engines were firing at full thrust all the time. There was a lot of ramping up and down going on. I would bet that the FH can’t run all engines at full thrust, at least not yet.

Hmm.. so on the Wikipedia Falcon 9 Full Thrust page it says:

"In 2015, SpaceX made a number of modifications to the existing Falcon 9 v1.1. The new rocket was known internally as Falcon 9 Full Thrust,[16] and is also known as Falcon 9 v1.2, Enhanced Falcon 9, Full-Performance Falcon 9,[12] and Falcon 9 Upgrade.[17]"


On the Merlin 1D page it says:

"In May 2016, SpaceX announced plans to further upgrade the Merlin 1D by increasing vacuum thrust to 914 kN (205,000 lbf) and sea-level thrust to 845 kN (190,000 lbf); "



It just so happens that 190K lbs x 9 =1.71mil lbs.

On that same F9-FT Wikipedia page it says regarding Block 5 improvements:

"For increased payload:

• 7–8% more thrust by uprating the engines"

190K * 108% = 205K lbs thrust.

The Block 5 improvement listings do not call out structural upgrades, as the other Blocks did. That implies the structure can already take more thrust, but they are waiting on the engines.

So I guess the question becomes: Do the Merlin 1D's really currently produce 240Klbs thrust? If so, is that simply not done because it hasn't been validated that the core can take it? The term that they will "uprate" the engines does imply that they are physically capable of making more... but how much more?

 

[ggr]

Hmm.. so on the Wikipedia Falcon 9 Full Thrust page it says:

"In 2015, SpaceX made a number of modifications to the existing Falcon 9 v1.1. The new rocket was known internally as Falcon 9 Full Thrust,[16] and is also known as Falcon 9 v1.2, Enhanced Falcon 9, Full-Performance Falcon 9,[12] and Falcon 9 Upgrade.[17]"


On the Merlin 1D page it says:

"In May 2016, SpaceX announced plans to further upgrade the Merlin 1D by increasing vacuum thrust to 914 kN (205,000 lbf) and sea-level thrust to 845 kN (190,000 lbf); "



It just so happens that 190K lbs x 9 =1.71mil lbs.

On that same F9-FT Wikipedia page it says regarding Block 5 improvements:

"For increased payload:

• 7–8% more thrust by uprating the engines"

190K * 108% = 205K lbs thrust.

The Block 5 improvement listings do not call out structural upgrades, as the other Blocks did. That implies the structure can already take more thrust, but they are waiting on the engines.

So I guess the question becomes: Do the Merlin 1D's really currently produce 240Klbs thrust? If so, is that simply not done because it hasn't been validated that the core can take it? The term that they will "uprate" the engines does imply that they are physically capable of making more... but how much more?

If you want an engine to last, you don't run it at redline all the time. They want to reuse them now.

 

[mongo]

Interesting. I was going by the original plan. Well, the second original plan ;-). Originally they were going to use fuel from the side boosters to refill the center one, but the piping got too complicated apparently. Still, at takeoff you can see the flame from the center is smaller than the sides; not really visible in the video you posted, but clear in some of the others. Otherwise it wouldn't have had extra fuel after separation.

Especially with the light load, FH may have hit the lower limit of the center core throttling range and then needed to reduce thrust on the boosters for Max-Q adjustment.

 

[scaesare]

If you want an engine to last, you don't run it at redline all the time. They want to reuse them now.

Makes sense. Perhaps the published spec is nominal as opposed to max.

 

[Grendal]

The Block 5 core, B1046, is currently on the test stand in McGregor. It is scheduled for the Bangbadhu launch. Indications are that it will launch out of LC-39A. It's a fairly light satellite to ensure everything goes well with this first B5. I expect to see it relaunched relatively quickly.

 

[ItsNotAboutTheMoney]

The Block 5 core, B1046, is currently on the test stand in McGregor. It is scheduled for the Bangbadhu launch. Indications are that it will launch out of LC-39A. It's a fairly light satellite to ensure everything goes well with this first B5. I expect to see it relaunched relatively quickly.

It's not the relaunch that matters. It's the rerelaunch.

 

[Grendal]

It's not the relaunch that matters. It's the rerelaunch.

I expect that to happen fairly quick as well. Though I do expect SpaceX to spend more time examining this booster after every launch than future B5 boosters. The company needs to determine if the wear and tear they expect to see matches with what actually happens.

10 launches before refurbishment is the likely goal. 100 launches for the booster. That will set a very high bar for the competition to try to meet.

 

[Bobfitz1]

The Block 5 core, B1046, is currently on the test stand in McGregor. It is scheduled for the Bangbadhu launch. Indications are that it will launch out of LC-39A. It's a fairly light satellite to ensure everything goes well with this first B5. I expect to see it relaunched relatively quickly.

How far into this year is Bangbadhu launch going to be?

 

[Bobfitz1]

10 launches before refurbishment is the likely goal. 100 launches for the booster. That will set a very high bar for the competition to try to meet.

@Grendal you are the master of understatement as well as rocketry!

 

[Grendal]

How far into this year is Bangbadhu launch going to be?

Next month with no weird delays. After the next Iridium launch, I believe. The schedule seems to be adjusting based on payloads being ready.

Edit: looks like a tentative April 5th out of the Cape. After the CRS launch.

 

[Grendal]

SpaceX is cranking out the Block 5 boosters. The second one (B1047) was seen leaving the Hawthorne factory for Texas two days ago.

I'm pretty sure that was one month from B1046 leaving the factory.

If they keep this pace up then they'll have 9 more boosters made this year. Counting at least one Falcon Heavy, that still leaves 8 Falcon 9s for continuous use. Since these boosters will very rarely be expended then you can see why SpaceX is going to need to focus on BFR by next year. The reality is, if they do hold up to the expected reuse parameters, then SpaceX will have a stable of 3 F9s per launch site and 1 FH always ready to go by the first couple months of next year. That's about all the company will need for the next couple years. If it goes as expected then that translates to 100 launches (90 F9 and 10 FH) before the company needs to refurbish a rocket.

 

[Bobfitz1]

SpaceX is cranking out the Block 5 boosters. The second one (B1047) was seen leaving the Hawthorne factory for Texas two days ago. I'm pretty sure that was one month from B1046 leaving the factory.
The reality is, if they do hold up to the expected reuse parameters, then SpaceX will have a stable of 3 F9s per launch site and 1 FH always ready to go by the first couple months of next year. That's about all the company will need for the next couple years. If it goes as expected then that translates to 100 launches (90 F9 and 10 FH) before the company needs to refurbish a rocket.

Does your launch estimate for next couple of years include the number of Starlink launches needed for the phase 1 4K satellites?

 

[Grendal]

Does your launch estimate for next couple of years include the number of Starlink launches needed for the phase 1 4K satellites?

Good question. No. I was thinking purely in terms of commercial launches. 45 to 50 a year is an impressive cadence. SpaceX currently has about 70 launches on their manifest and about a third of those are for years in the future. So that does leave plenty of possible Starlink launches when SpaceX gets around to doing them. The company will also be trying to get the Boca Chica launch site up and running for BFR testing. I expect that they will also have that ready for F9 launches and that is where I expect the bulk of the Starlink launches to happen. That launch site will probably much easier to use since it won't be a constant negotiation for getting a launch done.

I don't expect the F9 boosters to stop production. I just expect that it will slow as SpaceX moves manufacturing personnel over to BFR manufacturing. Say 60% of the people working on F9 will switch to BFR. So you'll get a new F9 booster every three months instead of one. SpaceX will reach the point where reused boosters will be the normal launch and a new one will be the one we're excited about.

 

[ecarfan]

if they do hold up to the expected reuse parameters, then SpaceX will have a stable of 3 F9s per launch site and 1 FH always ready to go by the first couple months of next year. That's about all the company will need for the next couple years. If it goes as expected then that translates to 100 launches (90 F9 and 10 FH) before the company needs to refurbish a rocket.

Nice analysis. SpaceX is going to be a launching machine! That F9 production rate is certainly going to free up people to transition to the BFR project in a big way next year.