SpaceX Falcon Heavy Discussion (Thread 6)

[TrueBlueWitt]

So would a stretched centre core actually be better? Yes, probably it would. However, it's challenging logistically - I suspect Stage 1 is as long as is feasible to transport by road. The longer it gets, the greater the radius of the arc needed to take corners, so the wider the roads to be: at some point there is no route available to get from the factory to McGregor or the launch site that is wide enough/with high enough radius corners. It can't be transported in bits since the entire wall of the stage is a single welded unit, it's not two separate tanks.

The available space at the factory also constrains the maximum length. You can't build a stage that's longer than the longest dimension of the building, and you might have to completely reorganize the space to make a larger core-assembly area.

I think that's why discussion has focused on stretching the second stage. It's not ideal but it's relatively easy to do without disrupting the whole operation. As I understand it, first and second stages are assembled on the same line - so a new stage length somewhere between the current S1 and S2 could be accommodated.

Speculating:

If SpaceX do go for a third stage, rather than stretch S2, the easiest thing to produce and handle would be yet another kerolox stage with an MVac engine. No new propellants or designs required, although some insulation work would still be necessary to extend the stage's lifetime a bit more. The main reason for staging, after all, is to drop the mass of the empty tanks: switching to a higher-Isp engine is a bonus. Adding a second second stage is probably too much fuel and mass, but otherwise it's just a shortened S2.

Elon himself said that stretching S2 was possible and easiest path to more performance.  Would work even with Falcon 9 after all the thrust upgrades. plus helps recovery as less prop needed.

[Joffan]

The common diameter of S1 and S2 is also probably why a stretch, rather than a fat S2, would be the preferred option. Unless they could just knock something up by the launchpad from sheets of stainless steel.

[Barley]

There may well be limits to the degree of throttling possible (so some throttling might still be needed on the side boosters) but the point remains.

Could they deep throttle by turning off some of the center engines?

[Slarty1080]

There may well be limits to the degree of throttling possible (so some throttling might still be needed on the side boosters) but the point remains.

Could they deep throttle by turning off some of the center engines?

I hadn't thought of that! Yes if some engines were shut down and others throttled it should be possible to use the core stage for the entirety of the throttling requirement for the whole stack for the entirety of the flight.

So do they do this already? If not what is the flaw in this argument?

[cppetrie]

There may well be limits to the degree of throttling possible (so some throttling might still be needed on the side boosters) but the point remains.

Could they deep throttle by turning off some of the center engines?

I hadn't thought of that! Yes if some engines were shut down and others throttled it should be possible to use the core stage for the entirety of the throttling requirement for the whole stack for the entirety of the flight.

So do they do this already? If not what is the flaw in this argument?

Because only 3 of the engines are restartable and the center core already ran out of TEA/TEB last time.

[Roy_H]

There may well be limits to the degree of throttling possible (so some throttling might still be needed on the side boosters) but the point remains.

Could they deep throttle by turning off some of the center engines?

I was asking the same question some time back and it was really nice to get a response from a real rocket engineer (can't remember name) who explained how surprisingly little is gained by turning engines off vs deep throttling. Basically all engines are needed for lift off and shortly after the core engines are throttled to save fuel while outer ones remain on full. This gives maximum fuel in core at side booster separation.

[Slarty1080]

There may well be limits to the degree of throttling possible (so some throttling might still be needed on the side boosters) but the point remains.

Could they deep throttle by turning off some of the center engines?

I hadn't thought of that! Yes if some engines were shut down and others throttled it should be possible to use the core stage for the entirety of the throttling requirement for the whole stack for the entirety of the flight.

So do they do this already? If not what is the flaw in this argument?

Because only 3 of the engines are restartable and the center core already ran out of TEA/TEB last time.

Three engines should be enough. That would cut thrust by a third on the centre stage and throttling down the other 6 engines would reduce thrust even further. Even if that wasn’t enough the propellant saving in the central stage should still be significant and any further throttling could be achieved by using the side boosters.

As for TEA/TEB they clearly need to (and will) carry more. Presumably they had some difficulty in deciding how much was needed, or knew but cut the margin too close to the bone, but either way they must have some way to calculate how much to carry. As such they should be able to calculate how much more to carry for an additional engine fire. And if there is doubt carry a little bit extra. Once a core booster has been recovered they will know how much was used and can plan accordingly. So I don't believe that the TEA/TEB requirements present any fundamental problem.

[Slarty1080]

There may well be limits to the degree of throttling possible (so some throttling might still be needed on the side boosters) but the point remains.

Could they deep throttle by turning off some of the center engines?

I was asking the same question some time back and it was really nice to get a response from a real rocket engineer (can't remember name) who explained how surprisingly little is gained by turning engines off vs deep throttling. Basically all engines are needed for lift off and shortly after the core engines are throttled to save fuel while outer ones remain on full. This gives maximum fuel in core at side booster separation.

Thankyou. So the answer is - that's what they already do except there's enough throttlability in the core booster engines to meet the throttle needs of the entire stack so there is no need to turn any engines off.

So if they are already doing this (over throtting the core engines and not throtting the side engines) presumably they will just throttle down further if they have an extra 10% thrust available?

[Hitech]

Has anyone noticed the different engine heat shield configuration on one of the boosters?

[Barley]

Thankyou. So the answer is - that's what they already do except there's enough throttlability in the core booster engines to meet the throttle needs of the entire stack so there is no need to turn any engines off.

So if they are already doing this (over throtting the core engines and not throtting the side engines) presumably they will just throttle down further if they have an extra 10% thrust available?

With 10% more thrust per engine, if they only throttle the core engines they'd need to reduce throttle by an extra 27% to get the same total thrust.  So one question is if the throttle has enough range to hit the thrust target without taking extra steps.

[Lars-J]

Has anyone noticed the different engine heat shield configuration on one of the boosters?

Your image is corrupted. What do you see that is different, other than the engine base plate color?

[ugordan]

There may well be limits to the degree of throttling possible (so some throttling might still be needed on the side boosters) but the point remains.

Could they deep throttle by turning off some of the center engines?

I hadn't thought of that! Yes if some engines were shut down and others throttled it should be possible to use the core stage for the entirety of the throttling requirement for the whole stack for the entirety of the flight.

So do they do this already? If not what is the flaw in this argument?

Because only 3 of the engines are restartable and the center core already ran out of TEA/TEB last time.

Also, turning off engines deliberately and then having to relight them again on ascent introduces an element of risk to the primary mission.

[niwax]

There may well be limits to the degree of throttling possible (so some throttling might still be needed on the side boosters) but the point remains.

Could they deep throttle by turning off some of the center engines?

I hadn't thought of that! Yes if some engines were shut down and others throttled it should be possible to use the core stage for the entirety of the throttling requirement for the whole stack for the entirety of the flight.

So do they do this already? If not what is the flaw in this argument?

Because only 3 of the engines are restartable and the center core already ran out of TEA/TEB last time.

Also, turning off engines deliberately and then having to relight them again on ascent introduces an element of risk to the primary mission.

I think the question is more about how many more differences you want to have to a regular F9. If you want to go further with optimization, the core that goes to full thrust later could have slight nozzle extensions on a few engines. Obviously that's a very high cost for little performance gain, though.

[SDSmith]

Has anyone noticed the different engine heat shield configuration on one of the boosters?

It looks the same to me. I say it is just the lighting is slightly different.

[Wolfram66]

Has anyone noticed the different engine heat shield configuration on one of the boosters?

It looks the same to me. I say it is just the lighting is slightly different.

the engine boots on the left are grey/silver the engine boots on right booster are black.
probably that the right booster is the center core and would be for high energy entry protection

[Hitech]

The other outer booster is also black, Looking closely the light colored one is metal the other look like a composite or rubber material. below is the full picture.

[Stefan.Christoff.19]

In the past they put the number of the core under the leg arch. Given the number of good pictures we've seen with the FH has anyone seen any core identification?

[docmordrid]

In the past they put the number of the core under the leg arch. Given the number of good pictures we've seen with the FH has anyone seen any core identification?

From the mission updates thread,

UPDATE ONLY THREAD.
>
NET April 11, 2019 at 18:36 EDT (22:36 UTC) on Falcon Heavy to GTO from LC-39A.  Side boosters 1052.1 and 1053.1 with center booster 1055.1.  Side boosters are expected to land back at LZ-1, center booster is expected to land on ASDS.
>

[Alexphysics]

In the past they put the number of the core under the leg arch. Given the number of good pictures we've seen with the FH has anyone seen any core identification?

Core numbers can be seen now with B5 under the grid fins, last few B4 boosters also had their number there apart from the ones they put on the octaweb. This picture from Trevor Mahlmann confirms that the three boosters are B1052, B1055 and B1053.

https://twitter.com/TrevorMahlmann/status/1116381567520210947

[Tomness]

1 44186U 19021A   19102.02912470 -.00000769  00000-0  00000+0 0  9996
2 44186  22.9623  12.6558 8697825 179.4741  18.6070  0.74408419    03

327 km Perigee
89815 km Apogee
22.96 degrees inclination

Using https://gtocalc.github.io/, the delta-v to GTO is about 1,508 m/s.

I wonder with that kinda of insertion if they have any future Falcon 9 customers that have back up option for FH for FH recovery prices. Only issue would be schedule with only 1 launch pad that can handle FH.