SpaceX Falcon Heavy Discussion (Thread 6)

[Jdeshetler]

Falcon Heavy - Possible variants comparisons.

https://twitter.com/elonmusk/status/963095860060934144

"Under consideration. We’ve already stretched the upper stage once. Easiest part of the rocket to change. Fairing 2, flying soon, also has a slightly larger diameter. Could make fairing much longer if need be & will if BFR takes longer than expected."

[spacenut]

How much longer and wider would a larger fairing be?  IF, there was/is a need?  And or how much of a stretch could FH upper stage take, again if needed?  This makes sense if they needed to compete with SLS. 

Also, as seldom as FH will probably fly in the near future, would they consider using F9 stages that have launched 5 or 10 times and expend them as a center core? 

Maybe this is not the place, but what if they only installed 5 or 7 engines on the center core running full thrust and expended it?  I'm thinking without 2 or 4 engines, legs, and grid fins, could this increase payload? 

Just wondering what the absolute maximum payload to various orbits with minimum modifications?

[John Alan]

Just sitting here looking at the pictures up above and looking over specs widely available online [1]...
(and I am rounding down for simple math here, and using expend all $150m price)
Current configuration... 63 metric tons to LEO at ~100+ tons S2 prop
33% prop cap stretch... 33 metric tons more S2 prop (133) and 30 metric ton payload to LEO
50% prop cap stretch... 50 metric tons more S2 prop (150) and 13 metric ton payload to LEO

All three have a place depending on where the payload is going and how much it weighs... 

On edit...
Heck there is a possible 60% stretch... 3 metric tons to LEO and 60 metric tons of prop to take it somewhere else..
But that's a ~7.5 meter stretch... will it fly ok?... 
(later edit... with special short fairing, I bet it would fly fine... IMHO)

[1] one of several references... https://en.wikipedia.org/wiki/Falcon_9_Full_Thrust#Vehicle_specifications

[cppetrie]

How much longer and wider would a larger fairing be?  IF, there was/is a need?  And or how much of a stretch could FH upper stage take, again if needed?  This makes sense if they needed to compete with SLS. 

Also, as seldom as FH will probably fly in the near future, would they consider using F9 stages that have launched 5 or 10 times and expend them as a center core? 

Maybe this is not the place, but what if they only installed 5 or 7 engines on the center core running full thrust and expended it?  I'm thinking without 2 or 4 engines, legs, and grid fins, could this increase payload? 

Just wondering what the absolute maximum payload to various orbits with minimum modifications?

Center cores are custom and can’t be converted from single stick versions. Side boosters and single stick are convertible with small amount of work. Per Elon post launch conference.

[GWH]

$95 million for 10% less than max payload with both cores landing on ASDS. Cost per kg to GTO at an estimated payload of 24 tonnes: $3950/kg.
$62 million for 8 tonnes to GTO as quoted in the recent Nasaspaceflight article: $7750/kg.
The latter is 20% less than Ariane 6 or Vulcan ACES, and the former is less than half. Crazy. Try and compare it to the SLS and its an order of magnitude cheaper...

[alang]

If the second stage was stretched then wouldn't that make the centre core more recoverable since it would be staging earlier?

[vanoord]

How much longer and wider would a larger fairing be?  IF, there was/is a need? 

It may be that the X-37B was a tighter fit than they wanted, so making Fairing 2 a few inches greater in diameter might give them the clearance they want.

The implication from Elon's tweet was - I think - that the increase in size was not massive.

[M.E.T.]

Just sitting here looking at the pictures up above and looking over specs widely available online [1]...
(and I am rounding down for simple math here, and using expend all $150m price)
Current configuration... 63 metric tons to LEO at ~100+ tons S2 prop
33% prop cap stretch... 33 metric tons more S2 prop (133) and 30 metric ton payload to LEO
50% prop cap stretch... 50 metric tons more S2 prop (150) and 13 metric ton payload to LEO

All three have a place depending on where the payload is going and how much it weighs... 

On edit...
Heck there is a possible 60% stretch... 3 metric tons to LEO and 60 metric tons of prop to take it somewhere else..
But that's a ~7.5 meter stretch... will it fly ok?... 
(later edit... with special short fairing, I bet it would fly fine... IMHO)

[1] one of several references... https://en.wikipedia.org/wiki/Falcon_9_Full_Thrust#Vehicle_specifications

I am now quite confused. Why is your payload decreasing as the 2nd stage increases in size? Are you suggesting that the stretched second stage eats into the space normally encapsulated by the fairing? My assumption was that as the 2nd stage stretches the rocket's overall length simply increases, without encroaching into any fairing space.

Surely the payload should increase as the 2nd stage propellant mass grows? What am I missing?

[speedevil]

I am now quite confused. Why is your payload decreasing as the 2nd stage increases in size? Are you suggesting that the stretched second stage eats into the space normally encapsulated by the fairing? My assumption was that as the 2nd stage stretches the rocket's overall length simply increases, without encroaching into any fairing space.

Surely the payload should increase as the 2nd stage propellant mass grows? What am I missing?

The assumption seems to be that the desired end-state is total S2 mass in LEO, with the S2+payload remaining at a constant mass.

This seems unlikely, and is missing the column for extra fuel delivered to S2 that might make this somewhat interesting, and also that you can launch more to LEO if you have more fuel, as S1 velocity is only weakly affected by S2 mass.

[M.E.T.]

I am now quite confused. Why is your payload decreasing as the 2nd stage increases in size? Are you suggesting that the stretched second stage eats into the space normally encapsulated by the fairing? My assumption was that as the 2nd stage stretches the rocket's overall length simply increases, without encroaching into any fairing space.

Surely the payload should increase as the 2nd stage propellant mass grows? What am I missing?

The assumption seems to be that the desired end-state is total S2 mass in LEO, with the S2+payload remaining at a constant mass.

This seems unlikely, and is missing the column for extra fuel delivered to S2 that might make this somewhat interesting, and also that you can launch more to LEO if you have more fuel, as S1 velocity is only weakly affected by S2 mass.

I see. What would be the point of increasing S2 size if it reduces your payload capacity?

[Robotbeat]

A longer upper stage INCREASES payload to high energy orbits like direct GEO and direct to Jupiter. With just a stretched upper stage (and possibly a small kick stage on top), FH should be capable of sending Europa Clipper (baselines 4200kg) direct to Jupiter instead of having to use SLS.

[GWH]

Moving this discussion on FH pricing here since it has nothing to do with the demo flight:

That means a centre core costs only $5M to make. $95M for 0.9*26.7 = 24.03 t is $3,953/kg, which is the cheapest option.

No Legs, no Iconel Heat shield.. No Grid fins..
All of which would not only save cost but also reduce mass on core, which is much bigger benefit than on the boosters.  Also, what's the cost of deep ocean drone ship recovery for what would be a very very toasty core? You have to wonder how many times they figured they could re-use the core to start with.. if only a few times.. then maybe the new numbers make sense.

This isn't the right take away.
From Elon's twitter post if a center core expendable is $95M which is slightly more than an expendable F9 then that means an expendable F9 is about the $90M. That makes perfect sense, since an expendable F9 is roughly the same capacity as the posted price for a recoverable FH. Same capacity - same price. That means throwing away a F9 adds about $30M to its price.

So if an expendable F9 is $90M how is it only $5M more to fly reusable side boosters on an expendable core? That doesn't make sense to current pricing for full recovery FH @ $90M. Then why does a fully expenable FH cost $150M.

Keep in mind posted prices to date have only been for recoverable Falcons on their first flight. The price point has stayed relatively static, with more and more being recoverable as performance increases. So its logical that a fully expendable F9 costs more now that it is more capable.

But with Block V enabling rapid reuse it should be expected that all Falcons are reused unless a customer pays more to insist on first flight OR expendable.
This quote from the recent NSF article provides insight as to what the reuse price will be:

...once Falcon Heavy flies in its fully reusable configuration – essentially lowering its price to just $62 million dollars or the price of a regular, brand new Falcon 9.

Ok $62M for a 3 core + fairing reused and recoverable payload. Now take that $30M adder to throw away a Falcon core and you end up pretty well at $95M for center core expendable. Throw the two side cores away: $150M.

The key thing here isn't to focus on today's pricing, consider it a temporary price point while SpaceX wasn't sure if they could recover cores or refly at a low cost. A rough estimate for reusing block V Falcon 9 is probably $42-45M if similar discounts are applied.

[speedevil]

I see. What would be the point of increasing S2 size if it reduces your payload capacity?

None, because in real life the assumptions above are not true.
Increasing the second stage mass modestly - and here 'modestly' is much under doubling it - has little effect on the staging velocity at booster separation - some 3km/s, because at this point, the whole stacks mass is many times the whole mass of S2.
It reduces significantly the velocity increase until core burnout.

In order to get a payload of 63 tons to orbit, the second stage +payload burnout mass will be 68 tons or so.

With an ISP of 348, and 111 tons of fuel, this means 3200m/s.

Doubling the mass of S2 has minimal effect on velocity before BECO, and approximately halves velocity gain after, taking velocity at BECO down by perhaps 800m/s.

We then need to ask what amount of payload we have from S2 with delta-v of 3200+800, and an initial mass of 290 tons.

The total mass ends up as 89 tons, or some 85 ton payload.

(this is very rough).

[John Alan]

Just sitting here looking at the pictures up above and looking over specs widely available online [1]...
(and I am rounding down for simple math here, and using expend all $150m price)
Current configuration... 63 metric tons to LEO at ~100+ tons S2 prop
33% prop cap stretch... 33 metric tons more S2 prop (133) and 30 metric ton payload to LEO
50% prop cap stretch... 50 metric tons more S2 prop (150) and 13 metric ton payload to LEO

All three have a place depending on where the payload is going and how much it weighs... 

On edit...
Heck there is a possible 60% stretch... 3 metric tons to LEO and 60 metric tons of prop to take it somewhere else..
But that's a ~7.5 meter stretch... will it fly ok?... 
(later edit... with special short fairing, I bet it would fly fine... IMHO)

[1] one of several references... https://en.wikipedia.org/wiki/Falcon_9_Full_Thrust#Vehicle_specifications

I am now quite confused. Why is your payload decreasing as the 2nd stage increases in size? Are you suggesting that the stretched second stage eats into the space normally encapsulated by the fairing? My assumption was that as the 2nd stage stretches the rocket's overall length simply increases, without encroaching into any fairing space.

Surely the payload should increase as the 2nd stage propellant mass grows? What am I missing?

My intent and way to read that is 30 metric tons payload to LEO with 33 metric tons of prop still left to take it onward...
OR 50 left on 13 payload... to take it way far away if need be... 
I was thinking GEO or beyond in a broad sense... parking orbit and how much left in the gas tank...
And no... the rocket was getting longer... S2 tank stretch of the sidewalls...
The 60% stretch could chuck a 3 metric ton probe to beyond Pluto with a lot of speed...
I hope this clarifies things a bit... 

[speedevil]

My intent and way to read that is 30 metric tons payload to LEO with 33 metric tons of prop still left to take it onward...
OR 50 left on 13 payload... to take it way far away if need be... 
I was thinking GEO or beyond in a broad sense... parking orbit and how much left in the gas tank...
And no... the rocket was getting longer... S2 tank stretch of the sidewalls...
The 60% stretch could chuck a 3 metric ton probe to beyond Pluto with a lot of speed...
I hope this clarifies things a bit... 

The second stage + payload mass is not fixed.
Yes, in the limiting case you put a 3 ton payload on a 60% stretch stage do you get a probe going very fast.
But, if you put a 60 ton payload on that same stage, it goes well beyond LEO.

[Coastal Ron]

How much longer and wider would a larger fairing be?  IF, there was/is a need? 

It may be that the X-37B was a tighter fit than they wanted, so making Fairing 2 a few inches greater in diameter might give them the clearance they want.

The implication from Elon's tweet was - I think - that the increase in size was not massive.

The internal diameter of the Falcon 9 payload fairing is already slightly larger than the Atlas V and Delta IV payload fairings (4.6m vs 4.57m), so I don't think the fit was too tight since the X-37B would have been designed to fit those launchers.

[John Alan]

The above postings were me thinking out loud what sort of stretch was within doable range...
SpaceX says FH (w/ normal S2) will put 63 metric tons to LEO (all expended), price $150m per EM... ok great...
And yes... I do agree that stretching S2 will improve that 63 number...

My questions are more...
...what sort of % stretch would suit all FH operations better?
(every need... Heavy to LEO...Medium to GEO-1800 or better...Light to Mars and beyond)
...do you go long, and maybe only partial S2 load prop for some payloads and destinations?
(playing with the rocket equation... does partial fills sometime make sense?)
I really only see them maybe cataloging two lengths... the current certified S2 and one longer one...

And if your going to sometimes expend the center core for a $95m price point...
...Would it make sense to just put 5 engines on that core?
Cap prop lines and not install 4 M1D's in the outer ring...install just cover plates on every other one...
Run those 5 at 100% thrust all the way thru MECO on depletion, instead of this center throttled profile stuff...
Throttle Boosters for Max-Q and as needed for 5G limiting to payload... till BECO
Saves cost of 4 engines... helps a bit on empty mass... hurts on gravity losses only a little...

THAT is the kind of questions I got running thru my head... 

[Stan-1967]

How much longer and wider would a larger fairing be?  IF, there was/is a need? 

It may be that the X-37B was a tighter fit than they wanted, so making Fairing 2 a few inches greater in diameter might give them the clearance they want.

The implication from Elon's tweet was - I think - that the increase in size was not massive.

I am guessing the need might have to do with optimizing the use of FH for delivery of Starlink satellites.  Other threads have suggested the existing fairing is volume limited for delivering the maximum number of satellites per FH launch.

[Jim]

How much longer and wider would a larger fairing be?  IF, there was/is a need? 

It may be that the X-37B was a tighter fit than they wanted, so making Fairing 2 a few inches greater in diameter might give them the clearance they want.

The implication from Elon's tweet was - I think - that the increase in size was not massive.

I am guessing the need might have to do with optimizing the use of FH for delivery of Starlink satellites.  Other threads have suggested the existing fairing is volume limited for delivering the maximum number of satellites per FH launch.

no, it is as vanoord said

[MKremer]

S2 would  never  be under-filled regardless of size.