totm nov 2023 SpaceX Discussion Thread

[NSEP]

Any news on the BFR? Haven't head that name in a while.

If all goes well, the first BFR will be built in April-July this year. Im more exited for that than Falcon Heavy to be honest.

[sh1pman]

13 minutes ago, NSEP said:

Any news on the BFR? Haven't head that name in a while.

If all goes well, the first BFR will be built in April-July this year. Im more exited for that than Falcon Heavy to be honest.

This year? I don’t think so. I expect them to get Raptor to full strength this year though. MAYBE they’ll finish the carbon fuel tank that doesn’t explode. 

[Ultimate Steve]

AFAIK the plan was to begin construction in Q2 this year of the first test article.

[sh1pman]

Just now, Ultimate Steve said:

AFAIK the plan was to begin construction in Q2 this year of the first test article.

You know how it always is with SpaceX. Aspirational goals and all that.

[NSEP]

I hope Elon says something about BFR after the FH madness is over.

I think this is going to be another one of those harder than we thought moments. From what a tried in KSP, you need some pretty powerfull RCS to do a BFR landing flip d:

[CatastrophicFailure]

14 minutes ago, sh1pman said:

This year? I don’t think so. I expect them to get Raptor to full strength this year though. MAYBE they’ll finish the carbon fuel tank that doesn’t explode. 

The test tank they built already only exploded after they deliberately overpressured it to see when it would explode. 

———————————

 

Also, here’s some news I didn’t know, re: Falcon Heavy payloads:

http://www.planetary.org/explore/projects/lightsail-solar-sailing/

Apparently the Planetary Society’s experimental lightsail is going to be hitching a ride on the third paying FH flight, STP-2 for the USAF. Says spring of this year but probably more like fall or winter. 

 

[CastleKSide]

If the test is 100% successful, they won't need to build much hardware for the second flight of FH

[DAL59]

2 hours ago, sh1pman said:

MAYBE they’ll finish the carbon fuel tank that doesn’t explode.

It was supposed to explode.  They were trying to determine at what point it would explode.

[CastleKSide]

21 minutes ago, DAL59 said:

It was supposed to explode.  They were trying to determine at what point it would explode.

I just hope we don't have to say this about the FH....

[cubinator]

2 hours ago, CastleKSide said:

If the test is 100% successful, they won't need to build much hardware for the second flight of FH

Good point. New second stage, 8 grid fins, maybe some landing legs...

[Ultimate Steve]

5 minutes ago, cubinator said:

Good point. New second stage, 8 grid fins, maybe some landing legs...

Wouldn't it be 4 new grid fins? I think the titanium ones on the outer boosters are designed to be used several times. 

[cubinator]

8 minutes ago, Ultimate Steve said:

Wouldn't it be 4 new grid fins? I think the titanium ones on the outer boosters are designed to be used several times. 

My bad. I mixed up which boosters have the titanium grid fins. There's quite a few to keep track of, you know.

Edited January 7, 2018 by cubinator

[CatastrophicFailure]

25 minutes ago, CastleKSide said:

I just hope we don't have to say this about the FH....

Well, given that it’s a full-on test flight, determining when or if it explodes is still the point... 

 

 

[Scotius]

Well, configuration-wise currently closest to Falcon Heavy is Delta IV Heavy. And it never failed, so... Let's hope for the best.

[StarStreak2109]

1 hour ago, Scotius said:

Well, configuration-wise currently closest to Falcon Heavy is Delta IV Heavy. And it never failed, so... Let's hope for the best.

With the exception that Delta IV Heavy is "only" 3 RS25s as opposed to 27 Merlins...

[PB666]

17 hours ago, mikegarrison said:

So that basically ends their funding, or what?

 

 

Its not dead, just in a coma.

[NSEP]

3 hours ago, StarStreak2109 said:

With the exception that Delta IV Heavy is "only" 3 RS25s as opposed to 27 Merlins...

SpaceX is not known for having engine failures, unlike the Soviet Union. I think that when the engines are lit, the chance off succes goes up like the rocket itself does.

[tater]

 

[Starman4308]

3 hours ago, StarStreak2109 said:

With the exception that Delta IV Heavy is "only" 3 RS25s as opposed to 27 Merlins...

Technical point of order: that's 3 RS-68 engines, not 3 RS-25s. An RS-25 is an SSME (Space Shuttle Main Engine), AKA "so expensive nobody but Congress would envision using them on an expendable lift vehicle".

I think the chances for the Falcon Heavy are reasonably good. With respect to other first-launches, the Falcon Heavy has an advantage in sharing so much hardware with proven boosters (to the point of literally, physically sharing two boosters!), with the primary disadvantage of using almost as many engines as the N-1, with possible vibration and other issues.

In comparison to the N-1, of course, there are mitigating factors such as the engines being arranged in 3 clusters of 9, instead of 30 engines all driven from the same tanks, plus the fact that they can actually test the whole assembly in a static fire beforehand.

[PB666]

48 minutes ago, Starman4308 said:

Technical point of order: that's 3 RS-68 engines, not 3 RS-25s. An RS-25 is an SSME (Space Shuttle Main Engine), AKA "so expensive nobody but Congress would envision using them on an expendable lift vehicle".

I think the chances for the Falcon Heavy are reasonably good. With respect to other first-launches, the Falcon Heavy has an advantage in sharing so much hardware with proven boosters (to the point of literally, physically sharing two boosters!), with the primary disadvantage of using almost as many engines as the N-1, with possible vibration and other issues.

In comparison to the N-1, of course, there are mitigating factors such as the engines being arranged in 3 clusters of 9, instead of 30 engines all driven from the same tanks, plus the fact that they can actually test the whole assembly in a static fire beforehand.

RS-68 is a hydrolox engine, the problem with hydrolox engines is that unless you have a dedicated first stage system such as the shuttles EFT "big orangee tank" and you are also getting those very high ISP its kind of a problem. I like RS-68A, I think that on the very largest rockets, because its utilization of heat almost ISP as as good at SSME,  but can be packed at higher thrust per meter it really is a necessity in the current global livery of rocket engines.

But we are not there yet, and falcon 9 loses in efficiency and heat conversion with kerosene (Kerosene is still burning even as gas leaves the end of the nozzle . . .and its typically used rich, where as hyrdrolox is typically used lean). All of this may be true, but a less voluminous first stage that is also recyclable without using an SSME is of a definite economic advantage. Even the small RL10b-2, which uses only an expansion cycle is incredibly expensive. At least in my own modeling for RSS and the various engines I see that there will come a day given launch pad restrictions limit further uses in the Merlin engine and Space X will have to begin looking at hyrdrolox first stages, either that or they will have to come up with higher performing Metholox or Kerolox engines.  Space X has made a good choice with the current system, obviously, because its far more recyclable than SFRBs (SFRBS takes months to repack, single fire system, and cannot be re'landed', not to mention higher ISP), because the kerosene is stable at STP, liquid hydrogen is not, because oxygen can be made on site but liquid hydorgen must be shipped remotely.

I suspect that the Falcon 9 can achieve up to 4 more boosters (6 on 1) where each pair throttles down and releases independently of each other. This may allow 250 T to LEO with a more powerful Merlin vacuum engine, but then at that the current space X system would need to look at other propulsion. Though with current foot design 6 would be difficult and 4 engines would fit more with current design. The current BFR design I view as concept only. Again we have to see what the end result of Metholox thruster testing produces. Since Metholox runs a bit rich and hydrolox runs a bit poor one could have a mixture of the two that run at perfect stoichemtric oxygen to fuel ratios and possibly improve the expansion ratio and really take out all of the heat by the end of the nozzle.

 

[Starman4308]

3 minutes ago, PB666 said:

RS-68 is a hydrolox engine, the problem with hydrolox engines is that unless you have a dedicated first stage system such as the shuttles EFT "big orangee tank" and you are also getting those very high ISP its kind of a problem. I like RS-68A, I think that on the very largest rockets, because its utilization of heat almost ISP as as good at SSME,  but can be packed at higher thrust per meter it really is a necessity in the current global livery of rocket engines.

But we are not there yet, and falcon 9 loses in efficiency and heat conversion with kerosene (Kerosene is still burning even as gas leaves the end of the nozzle . . .and its typically used rich, where as hyrdrolox is typically used lean). All of this may be true, but a less voluminous first stage that is also recyclable without using an SSME is of a definite economic advantage. Even the small RL10b-2, which uses only an expansion cycle is incredibly expensive. At least in my own modeling for RSS and the various engines I see that there will come a day given launch pad restrictions limit further uses in the Merlin engine and Space X will have to begin looking at hyrdrolox first stages, either that or they will have to come up with higher performing Metholox or Kerolox engines.  Space X has made a good choice with the current system, obviously, because its far more recyclable than SFRBs (SFRBS takes months to repack, single fire system, and cannot be re'landed', not to mention higher ISP), because the kerosene is stable at STP, liquid hydrogen is not, because oxygen can be made on site but liquid hydorgen must be shipped remotely.

I suspect that the Falcon 9 can achieve up to 4 more boosters (6 on 1) where each pair throttles down and releases independently of each other. This may allow 250 T to LEO with a more powerful Merlin vacuum engine, but then at that the current space X system would need to look at other propulsion. Though with current foot design 6 would be difficult and 4 engines would fit more with current design. The current BFR design I view as concept only. Again we have to see what the end result of Metholox thruster testing produces. Since Metholox runs a bit rich and hydrolox runs a bit poor one could have a mixture of the two that run at perfect stoichemtric oxygen to fuel ratios and possibly improve the expansion ratio and really take out all of the heat by the end of the nozzle.

 

Hydrolox is used fuel-rich, so as to pack the exhaust with as much molecular hydrogen as possible. For hydrocarbons, those are also run fuel-rich so as to minimize the amount of heavy carbon dioxide in the exhaust.

I'm not sure, for that matter, that it's the right direction for reusability. On first stage, specific impulse is often not as important as good thrust-to-weight ratio, so as to minimize the number of expensive* engines used. On the uppers, hydrolox has an issue with being very low-density; while not a large issue with expendable launch vehicles, a physically bulkier upper stage is going to be harder to recover, since you need to shield that much more surface area from reentry heat.

I think SpaceX is going in a good direction with the Raptor methalox engines; methane is still reasonably dense, in much wider supply than specialty RP-1, and doesn't coke as much as RP-1. I'm still.. unconvinced about the BFR, but the Raptor is a good engine.

*While reusability reduces the importance of how expensive and complicated the engines are, you still have to occasionally refurbish them, and replace any operational losses.

 

I'm also uncertain what SpaceX could possibly accomplish with a Falcon Extra-Heavy. The entire reason for making the Falcon Heavy was not necessarily to extend the payload reach of the Falcon 9, but rather to let them extend the reusable payload reach to the heaviest commercial GTO payloads.

There's also a serious limiting factor on how many first-stage cores you pack on: reusing them (which, again, is SpaceX's entire business model). There are two things you can do with a larger first stage: either deliver more delta-V to the same upper+payload, or deliver a heavier upper+payload.

If you want to recover, there's strong diminishing returns on the first, since past a certain point, every m/sec of delta-V provided is another m/sec that the first stage has to cancel out when returning home to avoid getting too crispy on reentry. As such, a larger first stage has strongly diminishing returns on delta-V provided... because you have to cover that m/sec forwards and backwards. Much more productive would be increasing the upper+payload mass, but...

Given a fixed amount of delta-V that the upper stage must cover, there's a fixed payload that you can put atop that upper stage. While a larger upper stage would help alleviate this... why would SpaceX make that upper stage? They can already cover almost any conceivable payload with the Falcon Heavy (nevermind the vastly improved Block 5 Falcon 9). There's no economically convincing reason to build an expanded upper stage, which would furthermore be a distraction from their BFR plans.

[KSK]

Also, my understanding from other, wiser heads on this thread is that the FH payloads are already volume limited rather than mass-limited. That being the case, is there much point in developing a  Falcon Super? It would be spectacular for sure but so would BFR...

[cubinator]

I don't think SpaceX intends to make any more large Falcon rockets. They want to use Falcon 9 and Falcon Heavy to fund development of BFR.

[PB666]

39 minutes ago, Starman4308 said:

let them extend the reusable payload reach to the heaviest commercial GTO payloads.

There's also a serious limiting factor on how many first-stage cores you pack on: reusing them (which, again, is SpaceX's entire business model). There are two things you can do with a larger first stage: either deliver more delta-V to the same upper+payload, or deliver a heavier upper+payload.

If you want to recover, there's strong diminishing returns on the first, since past a certain point, every m/sec of delta-V provided is another m/sec that the first stage has to cancel out when returning home to avoid getting too crispy on reentry. As such, a larger first stage has strongly diminishing returns on delta-V provided... because you have to cover that m/sec forwards and backwards. Much more productive would be increasing the upper+payload mass, but...

Given a fixed amount of delta-V that the upper stage must cover, there's a fixed payload that you can put atop that upper stage. While a larger upper stage would help alleviate this... why would SpaceX make that upper stage? They can already cover almost any conceivable payload with the Falcon Heavy (nevermind the vastly improved Block 5 Falcon 9). There's no economically convincing reason to build an expanded upper stage, which would furthermore be a distraction from their BFR plans.

Yes but for the first stage less fuel is required to return to the site, which virtually means the core keeps more fuel. I do believe and I see that Space X is increasing the size of its grid fins, So it might be possible for them to reach faster begin recover speed. The more early stages the more fuel can be 'virtually' transferred to the core, which means the more the core can have to transfer up and burn back. But I see another potential, if they improve the reentry, at higher speeds the reentry angle is lower, which mean you have more upper atmosphere to break, so provided the atmosphere does not tear up  your engines, you can use more breaking force. Aside from that if you have 4 boosters and a central core let the core burn out and crash. You only lost a quarter of the cost of the first stage, you are still way ahead of your competitors.

The problem is that payloads cannot be infinitely divided. So if you have a bulk that must be of a certain weight and volume. Also we need to remember that more complex first stages (i.e. that commit airflow) can also stabilize wider and more complex payloads under when (V^2)*P is over a certain level. So that in early flight the more side engines the rocket has, the more stable the payload will be, the lower the CoG, also.
I must admit really complex lower stages are a managment problem, particularly on the recycling side, and its often better to simplify the first stage, but OTOH if you have a complex payload, you might have to do it.

SpaceX's limitation on Payload lie in the second, which can have variants. But Payloads can provide their own fairing for bulkiest payloads, so that's not particularly a limitation.

The reason to improve the upper stage is almost package rocket science. The size of the upper stage is best tuned to be intermediate in magnitude between the first and final stage. If we handwavingly argue that the PL is a final stage with equal dV as the first stage, then the second stage should roughly produce that intermediate. To simplify the argument of the FS produces an initial  thrust of 64 and the PL produces a thrust of 1, the FH upper stage should produce a thrust of 8. So FH has thirty engines the upper stage should roughly have 2 to 4 engines (3 is best). And roughly 4 times as much fuel (since the core will lift it higher and faster upon separation). There are reasons that you might not want to do this, but there are obvious reasons why you do.

[Starman4308]

3 minutes ago, PB666 said:

Yes but for the first stage less fuel is required to return to the site, which virtually means the core keeps more fuel. I do believe and I see that Space X is increasing the size of its grid fins, So it might be possible for them to reach faster begin recover speed. The more early stages the more fuel can be 'virtually' transferred to the core, which means the more the core can have to transfer up and burn back. But I see another potential, if they improve the reentry, at higher speeds the reentry angle is lower, which mean you have more upper atmosphere to break, so provided the atmosphere does not tear up  your engines, you can use more breaking force. Aside from that if you have 4 boosters and a central core let the core burn out and crash. You only lost a quarter of the cost of the first stage, you are still way ahead of your competitors.

The problem is that payloads cannot be infinitely divided. So if you have a bulk that must be of a certain weight and volume. Also we need to remember that more complex first stages (i.e. that commit airflow) can also stabilize wider and more complex payloads under when (V^2)*P is over a certain level. So that in early flight the more side engines the rocket has, the more stable the payload will be, the lower the CoG, also.
I must admit really complex lower stages are a managment problem, particularly on the recycling side, and its often better to simplify the first stage, but OTOH if you have a complex payload, you might have to do it.

SpaceX's limitation on Payload lie in the second, which can have variants. But Payloads can provide their own fairing for bulkiest payloads, so that's not particularly a limitation.

The reason to improve the upper stage is almost package rocket science. The size of the upper stage is best tuned to be intermediate in magnitude between the first and final stage. If we handwavingly argue that the PL is a final stage with equal dV as the first stage, then the second stage should roughly produce that intermediate. To simplify the argument of the FS produces an initial  thrust of 64 and the PL produces a thrust of 1, the FH upper stage should produce a thrust of 8. So FH has thirty engines the upper stage should roughly have 2 to 4 engines (3 is best). And roughly 4 times as much fuel (since the core will lift it higher and faster upon separation). There are reasons that you might not want to do this, but there are obvious reasons why you do.

First: why is a low CoG preferable again? I'm under the impression a low CoG would make it less aerodynamically stable, not more stable.

Second: what complex payloads? Maybe a handful for NASA/ESA, but hardly worth the cost of developing a Falcon Super for. It'd probably be cheaper to use a FH in expendable or partially-expendable mode than to once again go through the enormous cost of developing a new rocket for those very few payloads. While SpaceX has ambitious plans of its own... those ambitious plans are planned to go up on the vastly more capable BFR.

Third: I'm pretty sure aerodynamics and structural integrity are more complicated than "moar booster and moar fairing". If it was simple, SpaceX would just build a bigger fairing.

Sure, you can further develop the Falcon 9 platform, but... why? The conventional commercial payloads that are your bread and butter are already handled by the Falcon 9/Falcon Heavy. Almost all scientific payloads can be handled by the F9/FH. Occasional super-heavy payloads can be handled by an expendable-configuration FH, and there's no funded plan for a lot of super-heavy payloads.

While Musk still has his grand plans for scaling up, the Falcon 9 isn't the right platform for that. You still use an expendable upper, you're talking an additional 18 first-stage engines (and thus points of vibration and catastrophic failure) per core, payloads are still limited in volume by a 5-meter fairing, and a lot of miscellaneous hardware is tuned to relatively small payloads in a 5-meter fairing. Payload adapters, the horizontal assembly building (where now you have to have one booster atop another), all that is geared to the current size of the Falcon 9/Falcon Heavy.

By the time you finish reengineering the Falcon platform into a true SHLV, the final production process will probably not look a lot like the original F9/FH production pipeline... and you still don't have payloads for it. It'd be the private-enterprise version of the SLS boondoggle.