totm nov 2023 SpaceX Discussion Thread

[PB666]

21 hours ago, wumpus said:

Except that plenty of parts of BFR and SLS are well known, allowing a certain amount of comparison:

We know the original flight characteristics of the SLS engines because they've flow before (mostly in the shuttle).  Granted, after sufficient senatorial meddling the rocket already has changed significantly and will likely continue to mutate until (or if) it flies.

The BFR's Raptor engine has undergone plenty of testing and has become a known thing.  The lower stage of the BRF is largely a scaled up Falcon 9 lower stage and is known within "Kerbal levels".  Unfortunately the upper stage (fairing, and any third stages) are completely unknown and would remain untested and malleable even if Elon Musk gave everyone access to the engineering data.

So you can argue a lot about each rocket.  Unfortunately the things you can't calculate accurate information about are things like "tonnage to orbit" and "cost of said tonnage", which makes most of the discussion here pointless (except to argue that Rocket labs can likely deliver raw payload cheaper to orbit cheaper (per kg) than SLS.  Because that simply isn't a SLS design goal).

This is so much bunk. This is the reason that shuttle bashers (Armchair astrophysicists) stand on their high horses and make proclamations about how so much better other systems are . . . . systems that have never been produced.

As BO clearly demosntrated the other day, they completely redesigned the propulsion system of the second stage of their proposed rocket. This can happen with either BFR or SLS. Its not flyable until its ready to fly, and until that point it vaporware.

The first V1 rockets flew up in the air and cavitated, so those days to the present production of spacecraft for their functions has been extensively modified from what they tell the public (i.e. dreamy-eyed denizens of KSP Science and spaceflight forum).

Shuttle bashers and Mars dreamers have one thing in common . . .they compare fictitious space flight systems with operational (past-operational) systems as if the are equivalent. A fictitious system is not a valid perspective.

[DAL59]

26 minutes ago, PB666 said:

about how so much better other systems are . . . . systems that have never been produced.

[PB666]

36 minutes ago, DAL59 said:

Irrelevant as usual

[Rakaydos]

1 hour ago, PB666 said:

This is so much bunk. This is the reason that shuttle bashers (Armchair astrophysicists) stand on their high horses and make proclamations about how so much better other systems are . . . . systems that have never been produced.

As BO clearly demosntrated the other day, they completely redesigned the propulsion system of the second stage of their proposed rocket. This can happen with either BFR or SLS. Its not flyable until its ready to fly, and until that point it vaporware.

The first V1 rockets flew up in the air and cavitated, so those days to the present production of spacecraft for their functions has been extensively modified from what they tell the public (i.e. dreamy-eyed denizens of KSP Science and spaceflight forum).

Shuttle bashers and Mars dreamers have one thing in common . . .they compare fictitious space flight systems with operational (past-operational) systems as if the are equivalent. A fictitious system is not a valid perspective.

V2 rocket. The V1 was a ramjet.

[PB666]

True actually Aggregat 4 , but both V1 and V2 has production problems that had to be circumvented with new technologies.

[tater]

1 hour ago, PB666 said:

It’s all wrapped up in demand. Who really wants something 62 tons in LEO

No one wants 60 tons in LEO. 

People need to stop thinking FH is about putting 60 tons in LEO. It’s about normal payloads thrown farther.

Also, as @sevenperforce has said several times, that’s the value for a fully expended FH. SpaceX doesn’t want to throw 3 block 5 boosters away at a time. Think fully recovered booster payloads, and/or direct to GEO, or on GTO trajectories.

[NSEP]

3 hours ago, tater said:

Also, as @sevenperforce has said several times, that’s the value for a fully expended FH. SpaceX doesn’t want to throw 3 block 5 boosters away at a time. Think fully recovered booster payloads, and/or direct to GEO, or on GTO trajectories.

The FH can only send 34t into LEO using reusabillity, some even estimate 26t. Many people seem to forget those things.

[tater]

If you had to ask me what the biggest thing (mass) to ever plausibly be launched by FH might be, I'd tend to think an extended fairing with a B330 under it.

Edited April 7, 2018 by tater

[PB666]

3 hours ago, tater said:

No one wants 60 tons in LEO. 

People need to stop thinking FH is about putting 60 tons in LEO. It’s about normal payloads thrown farther.

Also, as @sevenperforce has said several times, that’s the value for a fully expended FH. SpaceX doesn’t want to throw 3 block 5 boosters away at a time. Think fully recovered booster payloads, and/or direct to GEO, or on GTO trajectories.

As i said it was dubious, remember, but my point was SpaceX said they could do it, this is misleading if the intent really is to increase weight to GTO. You guys placed this as  fit into fairing issue.. What i say its not a fairing issue, SpaceX does not want to get into dealing with full crylox systems. Based on that they really are not interested in delivering anything 62 t to LEO. . . . . . . .this is more about fuzzy stats from unproven configurations of spacecraft, not about what I think they should do. . . . .its about what they said they can do but that everyone knows is unlikely to ever be done. You cannot really rely on this kind of company publicity. 

Again we are having a debate about what is proven and what is not. Why we are debating this issue is that those that support the unproven stats really dont get that the stats are untenable. Its the same thing as SLS EM-1 sitting on the launch pad dec 14th 2019 and NASA and the fed canceling the program, and then arguing for years whether it would have been a great program. Up until the day SLS puts men intonspace its nothing more than unproven stats and a big hole which public money gets thrown into. For spaceX its only a little white lie. 

[tater]

13 minutes ago, PB666 said:

As i said it was dubious, remember, but my point was SpaceX said they could do it, this is misleading if the intent really is to increase weight to GTO. You guys placed this as  fit into fairing issue.. What i say its not a fairing issue, SpaceX does not want to get into dealing with full crylox systems. Based on that they really are not interested in delivering anything 62 t to LEO. . . . . . . .this is more about fuzzy stats from unproven configurations of spacecraft, not about what I think they should do. . . . .its about what they said they can do but that everyone knows is unlikely to ever be done. You cannot really rely on this kind of company publicity. 

No, it's about the way people talk about launch vehicles. You can see the same figures quoted for Saturn V to LEO, etc. We also talk about SLS block 1 putting 70 tons in LEO, and the 1b putting 105 tons to LEO. That vehicle is not optimized for LEO, either. These numbers merely function as a ballpark comparison of capabilities, nothing more.

You are right that SpaceX is not going to do hydrolox upper stages. I used them as an example because the 5m DCSS is about as physically large as you could hope to fit on F9 S2, and it is half the "mass to LEO."

I think we can rely on it being roughly accurate, and it serves as a comparison vs other LVs at a gross level. They are not misleading anyone, as the people that have skin in the game (customers) understand what the figure means. People who mistake the figure for the notion that you can actually fit 60+ tons under the fairing... meh, their opinion won't be used to send any real payloads anywhere, anyway.

 

Quote

Again we are having a debate about what is proven and what is not. Why we are debating this issue is that those that support the unproven stats really dont get that the stats are untenable. Its the same thing as SLS EM-1 sitting on the launch pad dec 14th 2019 and NASA and the fed canceling the program, and then arguing for years whether it would have been a great program. Up until the day SLS puts men intonspace its nothing more than unproven stats and a big hole which public money gets thrown into. For spaceX its only a little white lie. 

Current modelling is quite capable of accurately determining what actual flights will look like. Heck, this was true 50 years ago---barring a failure, rockets fly as designed.

 

Edited April 7, 2018 by tater

[PB666]

15 minutes ago, tater said:

No, it's about the way people talk about launch vehicles. You can see the same figures quoted for Saturn V to LEO, etc. We also talk about SLS block 1 putting 70 tons in LEO, and the 1b putting 105 tons to LEO. That vehicle is not optimized for LEO, either. These numbers merely function as a ballpark comparison of capabilities, nothing more.

You are right that SpaceX is not going to do hydrolox upper stages. I used them as an example because the 5m DCSS is about as physically large as you could hope to fit on F9 S2, and it is half the "mass to LEO."

I think we can rely on it being roughly accurate, and it serves as a comparison vs other LVs at a gross level. They are not misleading anyone, as the people that have skin in the game (customers) understand what the figure means. People who mistake the figure for the notion that you can actually fit 60+ tons under the fairing... meh, their opinion won't be used to send any real payloads anywhere, anyway.

 

Current modelling is quite capable of accurately determining what actual flights will look like. Heck, this was true 50 years ago---barring a failure, rockets fly as designed.

 

Then that's why we are arguing vaporware all the time and its acceptable to do this, it creates an open standard. Aside from that Saturn V with its many stages could roughly approximate an LEO on an abort mode. I would very seriously doubt that SpaceX could haul 62 tons into LEO, other than as part of fuel in its second stage. If you can show me some kind of evidence to the contrary I would be happy to change my opinion. I took their telemetry from the FH launch and looked many ways at it. If we estimate second stage mass with payload of 110 t, and we added 62t of payload on top of that then at 172 tons the acceleration of S2 at engine fire is something like 7 m/s * 110/172 = 4.4 m/s that's less than 1/2g of acceleration.

Again this is with block 3 and block 4. There is a claim that block 5 has more power and more dV which if true changes that but my stats on engine performance come from February of this year. Just the very fact of placing 62t on top of the second stage would require some sort of S2 and S1 redesign. 

62t to LEO is nothing more than a half dressed woman in lingerie trying to sell Mercurys.

[sevenperforce]

1 hour ago, PB666 said:

Then that's why we are arguing vaporware all the time and its acceptable to do this, it creates an open standard. Aside from that Saturn V with its many stages could roughly approximate an LEO on an abort mode. I would very seriously doubt that SpaceX could haul 62 tons into LEO, other than as part of fuel in its second stage. If you can show me some kind of evidence to the contrary I would be happy to change my opinion. I took their telemetry from the FH launch and looked many ways at it. If we estimate second stage mass with payload of 110 t, and we added 62t of payload on top of that then at 172 tons the acceleration of S2 at engine fire is something like 7 m/s * 110/172 = 4.4 m/s that's less than 1/2g of acceleration.

Again this is with block 3 and block 4. There is a claim that block 5 has more power and more dV which if true changes that but my stats on engine performance come from February of this year. Just the very fact of placing 62t on top of the second stage would require some sort of S2 and S1 redesign. 

62t to LEO is nothing more than a half dressed woman in lingerie trying to sell Mercurys.

Nonsense. Half a gee of acceleration at separation is not problematic with a sufficiently lofted trajectory.

[tater]

I’ve never said that they could put 60’tons on top, I’m not sure what the disagreement is. All I have ever said is that the 60-whatever tons to LEO is whatever is in a nominal orbit after launch, most of which would be stage 2 kerlox.

1 minute ago, sevenperforce said:

Nonsense. Half a gee of acceleration at separation is not problematic with a sufficiently lofted trajectory.

Indeed. Doesn’t centaur only have like a 0.3 twr during circularization burns?

[DAL59]

12 hours ago, PB666 said:

Shuttle bashers and Mars dreamers have one thing in common . . .they compare fictitious space flight systems with operational (past-operational) systems as if the are equivalent. A fictitious system is not a valid perspective.

Yes it is.  If you can't compare something with something that doesn't exist, you cant improve it.  Just because Avatar 2 hasn't been released yet, we can speculate that it will be better than the emoji movie.    

11 hours ago, PB666 said:

Irrelevant as usual

?

[DAL59]

 

[CatastrophicFailure]

Seeing how much that thing actually wiggles around on the high-speed makes me feel a lot better about my own docking attempts. 

[PB666]

8 hours ago, DAL59 said:

Yes it is.  If you can't compare something with something that doesn't exist, you cant improve it.  Just because Avatar 2 hasn't been released yet, we can speculate that it will be better than the emoji movie.    

?

What impeccable logic! Lets compare something that exists with something that doesn't exist. Im going to compare Star Treks Voyager with NASA's voyager. Obviously the star trek voyager wins the TV ratings contest, the mileage contest goes to the real one.

Engineering is both a theoretical and empirical science. Most of the structural properties are based on observations. Steel is not a natural compound, its manmade (charcoal and iron slag). The same is true with brass and the aluminum alloy that spacecraft are made out of. If you want to know how an engineered systems performs you have to build it. NASA has testing grounds, SpaceX has testing grounds.

_______ thinks testing is superfluous, just dream, build and it will fly . . .thats good enough.

[PB666]

14 hours ago, tater said:

I’ve never said that they could put 60’tons on top, I’m not sure what the disagreement is. All I have ever said is that the 60-whatever tons to LEO is whatever is in a nominal orbit after launch, most of which would be stage 2 kerlox.

Indeed. Doesn’t centaur only have like a 0.3 twr during circularization burns?

if they cannot put 60t of weight on top than you have to put an asterisks by the claim of 62t to orbit, otherwise DAL59 or someone of that thinking is going to twist that into a belief that they actually can push a PL (say H2/O2 . . .or .. .unobtainium) into LEO. This is actually a double asterisks because it likely a claim based on B5 performance, a rocket that has not flown. As I said if the increased the performance of the engines, including M1D vacuum engine, then (see below at worst case scenario a 13% increase in engine performance converts no gain in horizontal velocity into a 50% gain of velocity relative to a flat trajectory along an isoquant).

Remember, I made the claim in the beginning that there were fuzzy stats . . fuzzy factoids. That claim of 62t to orbit is clearly a fuzzy fact even by your own statements.

Secondarily, if you are pushing S1 trajectory to 2.5Mm above the earth simply to give S2 long enough time to circularize then its no longer 62t to LEO, its something else to something else. 

Lets go backward with the facts.

If you are 99/100% to orbit (tangential component of velocity) you only need what. 0.02TWR on mostly a flat trajectory (just to hold isoquant, 100% cosine loss). With a cosine loss of 0.5 you need 0.023TWR (adjust TWR to reflect gravity at altitude)
98/100% 0.0396TWR, 0.045TWR 50% loss
90/100%  0.19%TWR, 0.219
80/100%  0.36%TWR, 0.414 (this is what 62t to orbit w
60/100%  0.64%TWR  <------ 5000 m/s, 0.736TWR for 50% cosine loss  (This is approximately what M1D on last FH launch delivered at its start up burn. The craft was losing some but not a horrific amount of vertical velocity.
40/100%  0.84%TWR  <------ 3120 m/s, 0.966TWR for 50% cosine loss     

Just going by this the S1/S2 separation would have had to occur going 2000 m/s faster than FH#1 S1/S2 sep. Cosine losses mean that thrust is given to gravity and not into kinetic energy (whether it be height or hoovering). If you are significantly giving thrust to gravity then you have inadequate thrust to make it to desired orbit, If you devote sufficient enough S1 thrust to generation of apoapsis, the it translates to a loss of horizontal velocity in the S2 which means a greater amount of cosine losses.  

If you are playing with TWR significantly below the tabulated values then your rocket engine will have significant cosine loses. Centaur used hydrolox, which has ISP in the 460 range, they can afford some cosine losses. But what we are talking about is a strict 200 km LEO orbit, not some elliptoid shaped thing.

While this may seem trivial, the ability to convert thrust into energy is dependent on speed. (Why I keep reposting the physics basics over and over again). E = F * d. The faster you travel they greater distance that is covered when force is applied. Ideally if you want to go interplanetary with a massive amount of weight, the best place to make that push is from as low an orbit as possible in which the loss of energy due to drag is less than the loss of energy due to loss of orbital velocity of a higher orbit. You can of course kick out of an elliptical orbit, but our metric here is not that, the metric is what mass was delivered to that ideal LEO. The logic for this is this; lets assume that orbital boost is based on a ~325 ISP system. Your payload is a 460 ISP system, it makes less sense to put the PL into an elliptoid orbit rather than handing more PL mass to so that the more efficient PL can kick to higher orbit. The Centaur _HAS_ ISP of 460, so that its ellipsoid is only a partial loss of energy if it pushes out from the ellipsoid . . and its still better off than M1D because it had higher ISP during the circularization part of its burn. M1D to achieve its claim needs to efficiently place that 62t in an LEO orbit so that the vehicles unobtainium based fuel system can send it to its interplanetary destination.

Why would anyone want a 62t payload . . . . one particular reason is to used that PLs propulsion system to drive out an interplanetary orbit. Conserving the fuel for one earth orbit and a burn outward (assuming that the launch occurred from an optimal launch to inclination) then a powerful enough second stage to push to LEO and hold at LEO just long enough to intercept the outbound burn point, followed by a transfer burn (as part of the PL 62t).

 

 

 

[tater]

@DAL59, that reddit link autoplays on my machine. It's pretty annoying.

[tater]

37 minutes ago, PB666 said:

Remember, I made the claim in the beginning that there were fuzzy stats . . fuzzy factoids. That claim of 62t to orbit is clearly a fuzzy fact even by your own statements.

Except that all launch vehicles have this similarly fuzzy stat listed. Check out the wiki pages. Or the providers.

On ULA's own page for Atlas V: "Lift Capability to LEO 41,570 lbs | 18,850 kg." The largest actual payload they have flown is the USN MUOS at 15,000lbs. (and that was a 551, so as big as Atlas V gets (the 552 has a different US, and does 20 tons).

Arianespace has "over 20 metric tons" listed as payload to LEO for Ariane 5 on their page.

ALL providers use these fuzzy figures (ISRO is a lot more specific, actually, PSLV only lists payload to SSPO and "sub GTO"). People just need to realize that the payload to LEO figure includes excess capacity in the upper stage for sending a normal sized payload someplace else.

In short, the payload to LEO figure is just a ballpark that is only useful for comparing two or more LVs with each other in relative terms. Specific needs anywhere near the upper limits of these payload to LEO values require that people "do the math" to see what is actually possible assuming they want a payload, and not just excess propellant in an upper stage.

Edited April 8, 2018 by tater

[PB666]

3 minutes ago, tater said:

Except that all launch vehicles have this similarly fuzzy stat listed. Check out the wiki pages. Or the providers.

On ULA's own page for Atlas V: "Lift Capability to LEO 41,570 lbs | 18,850 kg." The largest actual payload they have flown is the USN MUOS at 15,000lbs. (and that was a 551, so as big as Atlas V gets (the 552 has a different US, and does 20 tons).

Arianespace has "over 20 metric tons" listed as payload to LEO for Ariane 5 on their page.

ALL providers use these fuzzy figures (ISRO is a lot more specific, actually, PSLV only lists payload to SSPO and "sub GTO"). People just need to realize that the payload to LEO figure includes excess capacity in the upper stage for sending a normal sized payload someplace else.

In short, the payload to LEO figure is just a ballpark that is only useful for comparing two or more LVs with each other in relative terms. Specific needs anywhere near the upper limits of these payload to LEO values require that people "do the math" to see what is actually possible assuming they want a payload, and not just excess propellant in an upper stage.

No doubt, ULA has alot of fuzzy stat rockets themselves, i think i have mentioned that before in critique. Go back to the thread about RL10b-2 in which i was complaining about the high cosine losses. But this was a SpaceX thread and i was focusing on their claims. While i have not commented on their stats on their livery, i have a mental note on some of the fluffiness and untested systems of their livery.

Not too long after that ULA claims they are going to use RL10c-'x' for the exact reason of my critique, they sacrifices 15 ISP unit to provide space for 4 engines with 3.8 times the thrust that one b2 could provide. 

But i am glad you brought the point, but there is one difference, ULA basically solves all of the problems with virtually any sized payloads by using the somewhat inefficient RS25-E/F as second stage engine. They have, with a more efficient cost per thrust unit, a substitute for any payload you can imagine. 

 

[tater]

That reddit post is really annoying, since I have to hear that awful music, from that awful movie. I'll keep making new posts til it's on the next page. Ugh.

 

[PB666]

2 hours ago, tater said:

That reddit post is really annoying, since I have to hear that awful music, from that awful movie. I'll keep making new posts til it's on the next page. Ugh.

 

Dal could edit the link to make it a std hyperlink, i generally dont click on those links. 

Well the F9 comes very close to the stated PL to LEO

[tater]

I think it's a matter of fitting it on top, mostly. Also, their quoted figures (SpaceX website) are exclusively for expended vehicles. Reuse takes a substantial hit.

[PB666]

19 minutes ago, tater said:

I think it's a matter of fitting it on top, mostly. Also, their quoted figures (SpaceX website) are exclusively for expended vehicles. Reuse takes a substantial hit.

I have been using 90% of S1 fuel till S1/S2 sep. I expect one of the things block 5 will attempt to do is to get that number up.