SpaceX Falcon Heavy Discussion (Thread 6)

[su27k]

I was looking at edge-case performance of Falcon Heavy and did some math specifically around the quoted Pluto delivery....

Came up with a whopping 81+ tonnes of propellant residuals if launched without payload to use as a space tug.

Really blew my mind. I keep checking my math to see if I missed something.

I'd be very careful when using the Pluto number, this has been discussed several times in the past, it doesn't fit the rest of the performance and it's not clear what kind of trajectory it is using:

https://forum.nasaspaceflight.com/index.php?topic=41019.msg1665304#msg1665304

https://forum.nasaspaceflight.com/index.php?topic=43025.msg1814633#msg1814633

[Negan]

A deep space Dragon capsule with Superdracos added for more maneuverability.  Then for a lunar lander add a stripped Dragon capsule with no heat shield and Superdracos for landing and return to orbit.  Both of these would be launched by a Falcon Heavy.  The almost fully fueled upper stage of a Falcon Heavy would dock at the rear of the stack and launch them to the moon like Saturn V upper stage.  If it takes 3 launches to get the whole stack, maybe two Falcon 9's could launch the Dracon capsule and the lander.  Join, then dock with the upper stage, and you have a lunar program for less than half the cost of an SLS>

Cons: would only allow for flags and footprints unless you pre-landed surface assets. Would be better to have a standard delivery module (using either SuperDracos or meth-gox thrusters) and use that both for delivering surface assets and as the descent module.

Deep space Dragon 2 doesn't need more SuperDracos; it needs more propellant. And you can't put more propellant in the trunk without running prop lines into the capsule, which hoses the current design. Better to put an independent propulsion unit in the trunk. Trouble is engines. SuperDraco is too large and too thrusty; Dracos are not thrusty enough. You could use something like a Rutherford if you could find a way to solve kerolox boil-off.

Couldn't SS deliver a big enough SuperDraco propulsion unit in one shot?

[punder]

So, is this discussion along the lines of what SpaceX might have proposed for the HLS?

I wonder if they submitted two architectures--one F9/FH based and one SS/SH based.

[TripleSeven]

Cons: would only allow for flags and footprints unless you pre-landed surface assets. Would be better to have a standard delivery module (using either SuperDracos or meth-gox thrusters) and use that both for delivering surface assets and as the descent module.

this is what I dont grasp about the current "program".  What NASA wants is a program which can, like Apollo send people to different spots to "explore" (which robots can probably do better but...)...so what I dont understand is why they dont put the "meat" in a surface "habitat" that is sustainable for XX days and then have a smaller go and come lander that simply brings the crew and returns them and the rocks...

[sevenperforce]

I'd be very careful when using the Pluto number, this has been discussed several times in the past, it doesn't fit the rest of the performance and it's not clear what kind of trajectory it is using:

https://forum.nasaspaceflight.com/index.php?topic=41019.msg1665304#msg1665304

https://forum.nasaspaceflight.com/index.php?topic=43025.msg1814633#msg1814633

Yeah, I've seen those threads. I agree it's uncertain, but I'm taking it at face value. Starting from the max payload and reasoning backward doesn't capture the savings of having a lighter mass payload during the end of the core booster burn.

Couldn't SS deliver a big enough SuperDraco propulsion unit in one shot?

Well, yes. But using SS to deliver components to LOP-G is a little like using a semi to deliver a new keyboard when you need to replace your whole computer.

[Negan]

Well, yes. But using SS to deliver components to LOP-G is a little like using a semi to deliver a new keyboard when you need to replace your whole computer.

"A single Starship will expend about $900,00 worth of fuel and oxygen for pressurization to send “at least 100 tons, probably 150 tons to orbit,” Musk said. SpaceX’s cost to operate Starship will be around $2 million per flight, which is “much less than even a tiny rocket,” he added."

https://spacenews.com/elon-musk-space-pitch-day/

Edit: From this statement, I wouldn't be surprised if sending and expendable SS to LEO would be cheaper than any scheme involving doing the same with FH.

[sevenperforce]

Well, yes. But using SS to deliver components to LOP-G is a little like using a semi to deliver a new keyboard when you need to replace your whole computer.

"A single Starship will expend about $900,00 worth of fuel and oxygen for pressurization to send “at least 100 tons, probably 150 tons to orbit,” Musk said. SpaceX’s cost to operate Starship will be around $2 million per flight, which is “much less than even a tiny rocket,” he added."

https://spacenews.com/elon-musk-space-pitch-day/

Edit: From this statement, I wouldn't be surprised if sending and expendable SS to LEO would be cheaper than any scheme involving doing the same with FH.

Flying SS expendable obviates cost savings. But presumably SS can certainly take a full ACES or Centaur V into LEO and drop it off there, to use as a kick stage to send large payloads BLEO.

[Negan]

Well, yes. But using SS to deliver components to LOP-G is a little like using a semi to deliver a new keyboard when you need to replace your whole computer.

"A single Starship will expend about $900,00 worth of fuel and oxygen for pressurization to send “at least 100 tons, probably 150 tons to orbit,” Musk said. SpaceX’s cost to operate Starship will be around $2 million per flight, which is “much less than even a tiny rocket,” he added."

https://spacenews.com/elon-musk-space-pitch-day/

Edit: From this statement, I wouldn't be surprised if sending and expendable SS to LEO would be cheaper than any scheme involving doing the same with FH.

Flying SS expendable obviates cost savings. But presumably SS can certainly take a full ACES or Centaur V into LEO and drop it off there, to use as a kick stage to send large payloads BLEO.

Or a full Falcon S2.

Edit: It could even be a reused one from a prior F9 mission if SS can retrieve it.

Edit: Also IMO it's very likely and expendable SS will still cost SpaceX less or the same as a FH with the center core expended. Even without a lot of cost savings, SS gives you a more mass to orbit and a 9m fairing. Of course the only reason I bring up an expendable SS is because of the skepticism of being able to reuse SS (which I don't share). There's good reason to believe that SpaceX will get SS to orbit and soon. They're not building all those Raptors to sit in a warehouse.

[Zed_Noir]

Cons: would only allow for flags and footprints unless you pre-landed surface assets. Would be better to have a standard delivery module (using either SuperDracos or meth-gox thrusters) and use that both for delivering surface assets and as the descent module.

this is what I dont grasp about the current "program".  What NASA wants is a program which can, like Apollo send people to different spots to "explore" (which robots can probably do better but...)...so what I dont understand is why they dont put the "meat" in a surface "habitat" that is sustainable for XX days and then have a smaller go and come lander that simply brings the crew and returns them and the rocks...

Are you suggesting a planted non-reusable Starship as habitat and logistics depot?

That seems to be the only current concept that is large enough to act as a Lunar base for more than flag & footprint sortie. Presuming the Starship becoming operational before 2023.

Of course if you are using a Starship as a base facility. There is no point in developing a small multi-element lander along with the Lunar toll-booth current version of the Gateway. Just swapped a Starship for each of those roles.

My points above requires resetting the Artemis program with using just the hardware from the Hawthorne folks. Which might be realize quite soon if Congress don't provide enough funding for the non SLS/Orion parts of Artemis before the Hawthorne folks fields their shiny vehicles.

[envy887]

From the new FAA EIS (attached):

2.1.1.2. Falcon Heavy
The Falcon Heavy has a mass of approximately 3.1 million pounds and an overall length of 229 feet.
Falcon Heavy has the ability to lift up 64 tons (141,000 pounds) into low Earth orbit. Merlin engines are
used on both stages of the Falcon Heavy. The propellants are the same as the Falcon 9 (LOX and RP-1).
The Falcon Heavy contains 1,898,000 pounds of LOX and 807,000 pounds of RP-1 in the first stage, and
168,000 pounds of LOX and 64,950 pounds of RP-1 in the second stage. The center and two side
boosters are essentially the same design as the Falcon 9 first stage booster. The Falcon Heavy produces
a total of 5.13 million pounds of thrust at liftoff.

That's 105,665 kg of upper stage propellants.

[dlapine]

From the new FAA EIS (attached):

Did you also see the plans for VI and the mobile service tower?

2.1.1.4. Vertical Integration
SpaceX plans to develop vertical integration capabilities at LC-39A to support commercial launches, NASA launches, and USAF’s National Security Space Launch program. An MST would be constructed on the existing LC-39A pad to support this capability. The MST would consist of a steel trussed tower, a base, and a rail bridge (Figure 2-4). Four transport wheel assemblies located at the corners of the tower would be constructed and used to move the tower 130 feet from an integration to a launch position (Figure 2-5). The tower would have 11 floors and would be approximately 284 feet tall.

Figures 2.5 & 2.6

During tower construction, equipment and build materials would be staged east of the pad deck in the laydown area. Mobile cranes on the east and west of the tower site would be used to construct and assemble the tower. Construction dumpsters would be placed around the area and all materials would be disposed of according to federal and state regulations. Minimal demolition would occur on top of the MST area to allow access to the top of the existing concrete and install new shear walls and foundations. Figure 2-6 shows a general site overview for the proposed staging and laydown operations.

Figure 2.9

Spiffy!

[Nate_Trost]

If SpaceX isn't one of the NSSL winners, I wonder if they stop taking new commercial Falcon Heavy orders and discontinue it after flying out the current manifest.

[wannamoonbase]

If SpaceX isn't one of the NSSL winners, I wonder if they stop taking new commercial Falcon Heavy orders and discontinue it after flying out the current manifest.

I think it would be foolish to stop selling FH until SS/SH are operating and certified/approved for DOD flights. No one knows how long this development will take.

They could always write contracts with options for clients to transfer to the new vehicle. If they want.

[rpapo]

If SpaceX isn't one of the NSSL winners, I wonder if they stop taking new commercial Falcon Heavy orders and discontinue it after flying out the current manifest.

I think it would be foolish to stop selling FH until SS/SH are operating and certified/approved for DOD flights. No one knows how long this development will take.

They could always write contracts with options for clients to transfer to the new vehicle. If they want.

The hard work is done.  They have the design and all the knowledge, tooling and procedures required to build and operate the FH.  And it's tested.  It's not like they need to keep in inventory of FH cores around just in case somebody wants a launch in a month or two.  Though that is one of the things that the SpaceForce really wants: high availability.

So the cost of keeping the FH in the customer catalog should be quite minimal.

[ugordan]

Combining all four missions, the total payload mass should be about 3,734 kilograms, which is well within the gap between the Mars and Pluto capabilities (between 16,800 and 3,500 kilograms).

Pluto capability number listed on SpaceX site is utter nonsense. Unless by "capability" you mean several planetary flybys, Jupiter included. Mars "capability" is highly suspect as well.

[woods170]

Combining all four missions, the total payload mass should be about 3,734 kilograms, which is well within the gap between the Mars and Pluto capabilities (between 16,800 and 3,500 kilograms).

Pluto capability number listed on SpaceX site is utter nonsense. Unless by "capability" you mean several planetary flybys, Jupiter included. Mars "capability" is highly suspect as well.

Pardon me for not immediately believing your assessment.
When you make such a strong statement you would be well advised to back up your claim with hard figures.

[ugordan]

Combining all four missions, the total payload mass should be about 3,734 kilograms, which is well within the gap between the Mars and Pluto capabilities (between 16,800 and 3,500 kilograms).

Pluto capability number listed on SpaceX site is utter nonsense. Unless by "capability" you mean several planetary flybys, Jupiter included. Mars "capability" is highly suspect as well.

Pardon me for not immediately believing your assessment.
When you make such a strong statement you would be well advised to back up your claim with hard figures.

Direct injection to Pluto requires a C3 in excess of 150 (km/s)^2 and that's for a 13 year flight. If you want to cut that down to 9 years, the C3 goes to an excess of 200. Look at the attached NASA LSP performance curve vs. required C3.

If you extrapolate that to 150 and above you will see where the payload mass ends up. Now, you can personally believe that the LSP number is so heavily sandbagged that the payload at 150 C3 is actually not below zero but is, in fact, 3500 kg, but then you could work up back the curve and ask how come a FH could then not throw Europa Clipper directly to Jupiter (if not without a kick stage then certainly with a Star 48) instead of needing an Earth gravity assist trajectory.

There's also that whole exercise from the previous year of seeing if it could launch Orion + and underfueled SM around the Moon and the constraints there worked out to be around 15.5-16 metric tonnes which is consistent with the LSP figure for C3 of around 0. So we have a data point on low C3, we have implicit data for not being able to launch 6000 kg directly to over 80 (km/s)^2 C3 and we have implicit data that the curve is consistent with FH+Star 48 just barely being able to launch Clipper to a L+3 year Earth flyby trajectory. And yet we're supposed to believe that the performance curve does something magical and actually goes back up to 3500 kg at a minimum of 150 C3?

FH is a powerful vehicle as current launchers stand, but it is not magic and the Pluto number does not make any physical sense. There is only so much a kerolox upperstage can do and the lower Isp over hydrolox is not doing it any favors when it comes to really high C3 - which is why Delta IV is included in the graph for reference.

[woods170]

Combining all four missions, the total payload mass should be about 3,734 kilograms, which is well within the gap between the Mars and Pluto capabilities (between 16,800 and 3,500 kilograms).

Pluto capability number listed on SpaceX site is utter nonsense. Unless by "capability" you mean several planetary flybys, Jupiter included. Mars "capability" is highly suspect as well.

Pardon me for not immediately believing your assessment.
When you make such a strong statement you would be well advised to back up your claim with hard figures.

Direct injection to Pluto requires a C3 in excess of 150 (km/s)^2 and that's for a 13 year flight. If you want to cut that down to 9 years, the C3 goes to an excess of 200. Look at the attached NASA LSP performance curve vs. required C3.

If you extrapolate that to 150 and above you will see where the payload mass ends up. Now, you can personally believe that the LSP number is so heavily sandbagged that the payload at 150 C3 is actually not below zero but is, in fact, 3500 kg, but then you could work up back the curve and ask how come a FH could then not throw Europa Clipper directly to Jupiter (if not without a kick stage then certainly with a Star 48) instead of needing an Earth gravity assist trajectory.

There's also that whole exercise from the previous year of seeing if it could launch Orion + and underfueled SM around the Moon and the constraints there worked out to be around 15.5-16 metric tonnes which is consistent with the LSP figure for C3 of around 0. So we have a data point on low C3, we have implicit data for not being able to launch 6000 kg directly to over 80 (km/s)^2 C3 and we have implicit data that the curve is consistent with FH+Star 48 just barely being able to launch Clipper to a L+3 year Earth flyby trajectory. And yet we're supposed to believe that the performance curve does something magical and actually goes back up to 3500 kg at a minimum of 150 C3?

FH is a powerful vehicle as current launchers stand, but it is not magic and the Pluto number does not make any physical sense. There is only so much a kerolox upperstage can do and the lower Isp over hydrolox is not doing it any favors when it comes to really high C3 - which is why Delta IV is included in the graph for reference.

Thank you for  your elaborate response.

Please note: SpaceX doesn't mention what trajectory FH uses to inject 3,500 kg to Pluto. As such, it is probably incorrect for you to assume that SpaceX meant direct injection to Pluto. Nor did SpaceX mention the transit time. So your examples of transit times of 13 years and 9 years are probably not appropriate either.
Now, I challenge you to prove that 3,500 kg to Pluto is absolutely impossible. Personally I think you won't be able to prove that.

[ugordan]

Please note: SpaceX doesn't mention what trajectory FH uses to inject 3,500 kg to Pluto. As such, it is probably incorrect for you to assume that SpaceX meant direct injection to Pluto. Nor did SpaceX mention the transit time. So your examples of transit times of 13 years and 9 years are probably not appropriate either.

That's pretty much what I said in my original post, that such a number can only work if several planetary flybys are executed, Jupiter being a guarantee. As such, the figure is useless for any kind of performance consideration as you can massage even an Atlas V to reach a number like that once you start assuming elaborate and prolonged flyby trajectories and not a direct flight.

Now, I challenge you to prove that 3,500 kg to Pluto is absolutely impossible. Personally I think you won't be able to prove that.

Alright, let's do a quick BOTE calculation. An injection C3 of 150 requires 8.8 km/s of instantaneous delta V over the LEO parking orbit velocity, so we're looking at 16.6 km/s of delta V.
For this exercise we'll:
1) completely ignore all gravity losses and drag
2) treat an expendable FH as a 3 stage vehicle with the strapons being 1st stage and core only lighting up after booster sep, the absolute best case scenario and not attainable with a real FH.
3) We'll take Ed Kyle's estimates for the vehicle :
* boosters 425 t full, 17 t empty, 312 s Isp (again, using the best, vacuum Isp value)
* 2nd stage 112 t full, 4.5 t empty, 348 s Isp

This then works out to the following delta Vs:
1st stage: roughly 2720  m/s
2nd stage: roughly 4365 m/s
3rd stage: roughly 9100 m/s with 3500 kg payload (only stage where I actually factored in the 3500 kg payload mass, fairing was never factored in)

Total accumulated delta V is then 16181 m/s out of the 16600 m/s required for a direct injection.
I leave the final conclusion to the reader considering all the benefits I granted the vehicle in this BOTE calculation like completely negating gravity losses and treating it as a full 3 stage vehicle - which it is not.

Does this show that it's absolutely impossible? For some of you, probably not.

[rakaydos]

it's a ridiculus idea, but what's the C3 for a low energy transfer to the innermost portion of pluto's orbit?


The window will almost never be open, but technically it's an apples to apples comparison.