totm nov 2023 SpaceX Discussion Thread

[Green Baron]

I don't think it is fraud. Just ... overenthusiastic.

It is absolutely ok if a guy like Musk, Branson and the many other utter their dreams and ideas even if they are beyond current capabilities. One just shouldn't run after every guru who promises a new world. Wait until they show up with a realistic plan, best a technology demonstrator, and others jump the train to develop all that is necessary.

Edit (once again): look, they have made that marvellous F9 rocket, so the basic capabilities are there. It is just that technology cannot be scaled indefinitely without sideeffects, in this case vibration, aerodynamics, and so on. Every material has its limits.

Edited October 2, 2017 by Green Baron

[aluc24]

1 minute ago, Green Baron said:

I don't think it is fraud. Just ... overenthusiastic.

It is absolutely ok if a guy like Musk, Branson and the many other utter their dreams and ideas even if they are beyond current capabilities. One just shouldn't run after every guru who promises a new world. Wait until they show up with a realistic plan, best a technology demonstrator, and others jump the train to develop all that is necessary.

Yes, but these are not just talks, they are shutting down F9 and FH production lines to fund this thing, as many in this topic have pointed out before. That means they think they can pull this off. Which doesn't make any sense for me.

[Green Baron]

4 minutes ago, aluc24 said:

Yes, but these are not just talks, they are shutting down F9 and FH production lines to fund this thing, as many in this topic have pointed out before. That means they think they can pull this off. Which doesn't make any sense for me.

Yes, and that is why, if they succeed it will be 10-20 years later than 2024. You all may triumph over me if they show up with ready BFR to support astronauts for a Mars shot and return(!) before 2025.

Edit: and the rocket isn't all it takes !

Edited October 2, 2017 by Green Baron

[aluc24]

Just now, Green Baron said:

Yes, and that is why, if they succeed it will be 10-20 years later than 2024 if there is something. You all may triumph over me if they show up with ready BFR to support astronauts for a Mars shot and return(!) before 2024.

So again, I don't understand why they officially state these unrealistic timeframes. They must know it's impossible to pull off in 7 years, and not making the quota will hurt the company's reputation, among other things. Shouldn't a company of this scale be able to manage it's expectations in a realistic way?

[Nibb31]

2 hours ago, Nefrums said:

About the supposedly reusable heat shield on the BFR ship, are there any examples of heat shields that have been reused without extensive refurbishment today?

No, and there aren't many of examples of heat shields that have been reused, period. CRS-11 reused the same Dragon as CRS-4, but a lot of systems, including the heatshield, were replaced.

There is actually a lot of unproven technology in the BFR program, and all of these technologies have to work as designed. A non-exhaustive list:

• Low maintenance reusable heatshield
• Orbital cryo propellant refilling
• 6 month ECLSS (for 100 passengers)
• Composite tankage (with common bulkhead and internal header tanks)
• Cradle landing
• Flip-over manoeuver and propulsive landing
• Vacuum nozzles that can survive reentry and hypersonic flow
• Mars ISRU

And then there is the entire economical, legal, and political environment to deal with.

While a lot of this works on paper, we all know that the actual engineering is much more complicated. Things like SpaceX upper stage reuse, Falcon Heavy, or propulsive landing with Dragon 2 also seemed easy on paper, but proved more complicated once they were confronted with reality. Even F9 1st stage reuse, although technically proven, now has to prove to be economically viable, which is a whole different set of problems.

The challenges are just as significant as the milestones that the Apollo program had identified for Moon shot to become possible: multiple day ECLSS, EVA, rendez-vous, docking, navigation, etc... These were all possible on paper, but required the Gemini program to develop the techniques, discover the pitfalls and workarounds, and prove that they were practical. Gemini was a significant effort that had to run in parallel with the Apollo development effort.

If only one of the technologies required for BFR turns out to be a dead end, then the whole fundamental architecture is screwed.

Edited October 2, 2017 by Nibb31

[Green Baron]

6 minutes ago, aluc24 said:

So again, I don't understand why they officially state these unrealistic timeframes. They must know it's impossible to pull off in 7 years, and not making the quota will hurt the company's reputation, among other things. Shouldn't a company of this scale be able to manage it's expectations in a realistic way?

I don't know why and i only know that a company should not give up its cash cow or it'll go bankrupt if no other sources for money exist.

Why did Musk say the FH will fly 2013 ? It won't fly 2017 apparently. Why did he say "you can fly" (to Mars) when he presented the ITS ? The ITS won't exist and nobody can fly nowhere right know, except with foreign aid to the ISS.

There is nothing substantial in an announcement or in an announcement of an announcement. When dealing with visionaries one musk err must wait for facts. Facts.

:-)

[aluc24]

1 minute ago, Green Baron said:

I don't know why and i only know that a company should not give up its cash cow or it'll go bankrupt if no other sources for money exist.

Why did Musk say the FH will fly 2013 ? It won't fly 2017 apparently. Why did he say "you can fly" (to Mars) when he presented the ITS ? The ITS won't exist and nobody can fly nowhere right know, except with foreign aid to the ISS.

There is nothing substantial in an announcement or in an announcement of an announcement. When dealing with visionaries one musk err must wait for facts. Facts.

:-)

I couldn't agree more. Indeed, this is very puzzling. Hopefully some other members of this forum have some ideas as to why SpaceX keeps making these unrealistic promises.

[Green Baron]

One last word: i tried to follow Musk's presentation in Australia last Friday. I switched of after 3-4 minutes because the babble wasn't worth my limited bandwidth (am on satellite). Apparently some intended plans were told out after i switched off and that started the above discussion.

[Nibb31]

4 minutes ago, aluc24 said:

I couldn't agree more. Indeed, this is very puzzling. Hopefully some other members of this forum have some ideas as to why SpaceX keeps making these unrealistic promises.

SpaceX is composed in majority of a young, enthusiastic, overworked, and underpaid workforce. I suspect the overoptimistic timelines and Mars plans has more to do with keeping them motivated.

[aluc24]

28 minutes ago, Nibb31 said:

SpaceX is composed in majority of a young, enthusiastic, overworked, and underpaid workforce. I suspect the overoptimistic timelines and Mars plans has more to do with keeping them motivated.

I didn't know they were underpaid... But in any case, these guys are likely much more knowledgeable about rocket science than we are. It is highly unlikely that they would be naive enough to believe these timelines.

[HebaruSan]

13 minutes ago, aluc24 said:

I didn't know they were underpaid... But in any case, these guys are likely much more knowledgeable about rocket science than we are. It is highly unlikely that they would be naive enough to believe these timelines.

A lot depends on the audience.

When making promises to customers or to attract business,  forecasts should be accurate, so that what you say is what happens. Often this means only committing to things you have done before, since you know exactly how much time and money is required.

When speaking to investors or the public or your workforce, it's more important to say what you want to be doing and where you intend to take the company. But since you haven't done it before, you can't know how much time and money is required. So you have a choice: Do you try to guess as accurately as possible, or do you err more towards optimism? If you go with the most reasonable guess, your workers will feel that not much is being asked of them; you might find that even this timeline will slip. On the other hand, low-balling such estimates makes you look bold, and says to your investors that you're going to squeeze as much productivity as possible out of your employees to get there as quickly as possible.

All businesses do it (we can all probably think of examples from our own lives). Elon Musk just takes it to an extreme and has become somewhat notorious for it.

[aluc24]

1 minute ago, HebaruSan said:

A lot depends on the audience.

When making promises to customers or to attract business,  forecasts should be accurate, so that what you say is what happens. Often this means only committing to things you have done before, since you know exactly how much time and money is required.

When speaking to investors or the public or your workforce, it's more important to say what you want to be doing and where you intend to take the company. But since you haven't done it before, you can't know how much time and money is required. So you have a choice: Do you try to guess as accurately as possible, or do you err more towards optimism? If you go with the most reasonable guess, your workers will feel that not much is being asked of them; you might find that even this timeline will slip. On the other hand, low-balling such estimates makes you look bold, and says to your investors that you're going to squeeze as much productivity as possible out of your employees to get there as quickly as possible.

All businesses do it (we can all probably think of examples from our own lives). Elon Musk just takes it to an extreme and has become somewhat notorious for it.

That's a really interesting approach to it, I haven't thought about it that way. Makes a lot of sense. Maybe that is what he's actually trying to accomplish here. I just hope this bold strategy won't become the downfall of SpaceX.

[tater]

The point to point travel idea is notional, and is pretty much exactly what was talked about by Douglas aviation (Phil Bono) in the mid 1960s. I don't consider it serious from a civilian point of view, the regulatory hurdles are overwhelming. The military, OTOH...

The 2024(?) Mars aspect is certainly very optimistic, and we know what Musk timeframes can be. That said, the idea that they could have a vehicle flying by 2020-2024 is not at all impossible, IMO. This is exactly the timeframe in which BO should be flying NG, and BO has similar reuse aspirations.

I don't see any downfall here. F9 will soon be mature (block 5 or whatever they call the end version), and every reflown booster is 10s of millions in their pocket. They need to move on to the next step, and Falcon wasn't designed for reuse from the start, they need a blank slate design.

 

[sevenperforce]

21 hours ago, Northstar1989 said:

Now if only SQUAD would get that memo!  I'm sick and tired of designing 100% reusable spaceplanes in stock, sometimes to find out they are actually MORE expensive than expendable rockets (with SRB first stages and optimized ascent-curves) simply because of fuel-costs...

Yes, I know that RealFuels fixes the problem- but it also introduces realistic ISP's and TWR's that are much too powerful for stock, and then I end up using RSS 64K, and then re-entry heating becomes a major problem and all my launches take longer (which has become a real problem lately on my failing laptop...)

Solution: Put an ISRU rig a few dozen meters away from the runway with a Klaw sticking out of one side. Build your plane with bingo fuel, roll over and jam yourself into the Klaw, then fuel up.

[sevenperforce]

One thing I'd like to see would be an analysis of whether the Mars architecture could still work if Martian ISRU was limited to LOX production. LOX can be cracked out of the Martian atmosphere without drilling, digging, or any sort of soil processing; just open the window, pump in CO₂, and start cracking via solid oxide electrolysis. It can be tested extensively on Earth, unlike full CH₄+CO₂ production, and it has far fewer failure modes.

My thought: instead of fueling up two cargo BFRs in 2022, you'd fuel up a single cargo BFR plus a single tanker, both in elliptic Earth orbit. The tanker's fuel tank would be full, but its oxidizer tank would only be about halfway full. Once you reached the transfer window, the two ships would depart together for Mars.

Once in transit, the tanker would transfer a portion of its fuel to the cargo BFR. The cargo ship would adjust its trajectory for Martian EDL, while the tanker would raise its trajectory slightly in order to aerocapture rather than fully entering.

The tanker comes in high, aerocaptures, and circularizes in Martian orbit, bingo on LOX but still carrying a respectable amount of fuel. The cargo ship lands and begins cracking atmospheric CO2 into LOX. Once the LOX tanks are full (and once soil samples, etc. have been collected), the cargo ship takes off and enters orbit. It rendezvouses with the tanker and gives the tanker enough LOX to make the trip home, while the tanker gives the cargo ship enough fuel to make the trip home. They both return together.

[tater]

I'd add, regarding the replacement of Falcon, that they will build up a stock of F9 stuff, then reuse boosters. We've had the conversation here before about booster reuse---with only so many launches available per year, and boosters that can be reused, how many would SX actually need? People then talk about new, planned satellite constellations that require loads of launches. OK, but if you can reuse a booster somewhere between 10 and 100 times, and there are perhaps a few 10s of launches per year, the SX already has several years worth of F9s laying around right now. If all the old blocks become expendables, then the block 5s will become the reuse vehicles. The fairing reuse is much the same. They are apparently close to this capability, and this means that they make a few sets of fairings, then turn the carbon fiber people loose on BFR.

From a business standpoint this makes total sense to me---that they would use their stage 2 people to keep making second stages, and the booster people move on. If BFR takes longer than expected, they make some more F9s. They have a factory that needs to keep busy 100% of the time, and with reusable rockets, all those people are not needed 100% of the time. This keeps their payroll flat (and retains their employees), while making the next vehicle.

@sevenperforce, the orbital vehicle could also disperse a constellation of commsats.

NASA would be all in for cooperation on a huge vehicle to Mars, just as they were for Red Dragon. Any aspirations for Mars from NASA depend on landing large vehicles there.

[tater]

 

 

Edited October 2, 2017 by tater

[tater]

 

 

[sevenperforce]

So I built a 5-meter BFR upper stage in KSP using stock parts and Tweakscale, and for the life of me I cannot get anything even remotely approaching aerodynamic stability on re-entry or landing.

[magnemoe]

53 minutes ago, sevenperforce said:

So I built a 5-meter BFR upper stage in KSP using stock parts and Tweakscale, and for the life of me I cannot get anything even remotely approaching aerodynamic stability on re-entry or landing.

The weird part is that they go in with nose bottom rather than the more obvious space shuttle approach. at 10km and 3Km/s you rotate and put nose up, this take you down to 5 km and it then climb to 10 km while dropping to 1 km /s you then turn bottom first and start the braking burn at 3 km. 
can it be that the rear generates too much drag?  

[sevenperforce]

57 minutes ago, magnemoe said:

The weird part is that they go in with nose bottom rather than the more obvious space shuttle approach. at 10km and 3Km/s you rotate and put nose up, this take you down to 5 km and it then climb to 10 km while dropping to 1 km /s you then turn bottom first and start the braking burn at 3 km. 
can it be that the rear generates too much drag?  

That was for Mars entry; I don't know what Earth entry looks like.

Those deltas at the back cause a pretty dramatic shuttlecock effect throughout the flight envelope. Also, in tests, my version kept wanting to rotate back around to where the wings were at the back, as if it was flying upside down. I don't see how split flaps could give anywhere near the required amount of control authority, especially for that big flip.

[tater]

2 hours ago, sevenperforce said:

So I built a 5-meter BFR upper stage in KSP using stock parts and Tweakscale, and for the life of me I cannot get anything even remotely approaching aerodynamic stability on re-entry or landing.

Forgetting that KSP is not useful as a simulator in this regard, where KSP puts the propellant mass is likely the issue. Remember that the landing tanks are separate, and at the bottom, center.

[Guest]

2 hours ago, sevenperforce said:

So I built a 5-meter BFR upper stage in KSP using stock parts and Tweakscale, and for the life of me I cannot get anything even remotely approaching aerodynamic stability on re-entry or landing.

9 minutes ago, tater said:

Forgetting that KSP is not useful as a simulator in this regard, where KSP puts the propellant mass is likely the issue. Remember that the landing tanks are separate, and at the bottom, center.

If you're using RO/RSS with FAR to "simulate" the BFR just clip the landing tanks into the bottom tank, then reduce propellant usage on the bottom tank to match the reduction in volume caused by the inner tanks. If everything is in the right place you'll get an "okay" approximation of how BFR should fly. Stock KSP really shouldn't be considered a proper sim in this regard. At all. Ever.

 

[sevenperforce]

23 minutes ago, tater said:

Forgetting that KSP is not useful as a simulator in this regard, where KSP puts the propellant mass is likely the issue. Remember that the landing tanks are separate, and at the bottom, center.

I had a separate landing tank blocked off at the bottom to simulate this exactly.

[sh1pman]

Elon selling houses on Jupiter with solar power. Obvious fraud! Everybody knows that Jupiter is too far from the Sun to have any useful solar power generation potential!