totm nov 2023 SpaceX Discussion Thread

[kerbiloid]

I hardly can imagine the 100+ pax zero-g spaceplane's stewardesses with carts of food and drinks.

But I can easily imagine 100+ old-style vomit bags in zero-g.

So, unlikely the space lines are a near future.

Edited June 21, 2020 by kerbiloid

[wumpus]

On 6/20/2020 at 2:33 PM, CatastrophicFailure said:

IIRC, Musk said a while back that Starship would have enough thrust itself to abort from Superheavy off the pad, they’d just light the vacuum Raptors, too. There would be a loss of efficiency but that’s not really a concern at that point. I assume the design is such that the engines could tolerate the underexpansion, at least for a time. This would happen in a fraction of a second, too. 
 

Seems to be two different trains running here, RE: aborts and safety. Are we talking astronaut-level safety or Joe Schmoe-level safety? I believe the LOCV risk for Dragon 2 is said to be 1:270. It’s worth mentioning that Starship as a system could simply demonstrate this level of safety by flying/returning 270 times in a row without incident. This would be a long pole for any other rocket, but SS could possibly do this within a single year.

Add in a decade or so of operations, and you could possibly see 1:thousands reliability demonstrated before passenger ops become a thing. 

It is really weird that a second stage would  not only have TWR>1, but TWR>1 while dealing with suboptimal nozzles.  Of course the Mars edition will need a TWR>~1/3 just to lift off Mars, but that is a special case (and the MoonShip needs even less), but even a TWR of 1/3 seems high for a second stage.

Astronaut-level safety seems to imply some sort of LES, unless they are really willing to limit themselves to Shuttle-level safety (I can't imagine NASA going along with that).  SpaceX *might* quickly prove astronaut-level safety if they can reasonably prove that the Starship *usually* lands and that it can do so even if the vacuum engines fail (so it could abort to land in case of either stage failing, but not both [assuming the vacuum engine can get the thing free, which sounds weird to me]).  They'd have a lot harder time getting passengers to Mars if they lose an astronaut crew...

[mikegarrison]

On 6/20/2020 at 11:33 AM, CatastrophicFailure said:

Starship as a system could simply demonstrate this level of safety by flying/returning 270 times in a row without incident. This would be a long pole for any other rocket, but SS could possibly do this within a single year.

Don't count your launches until they actually launch....

[tater]

Even if they met their aspirational cost per flight immediately, 270 flights would cost between a half a billion and a billion +.

(not that is see them flying that often)

Edited June 21, 2020 by tater

[StrandedonEarth]

5 minutes ago, tater said:

Even if they met their aspirational cost per flight immediately, 270 flights would cost between a half a billion and a billion +.

(not that is see them flying that often)

That's a lot of Starlinks. Also a bunch of Lunaship tanker flights

[zolotiyeruki]

30 minutes ago, tater said:

Even if they met their aspirational cost per flight immediately, 270 flights would cost between a half a billion and a billion +.

(not that is see them flying that often)

Still cheaper than a single SLS launch...

[SOXBLOX]

3 hours ago, zolotiyeruki said:

Still cheaper than a single SLS launch...

Sure. Who's paying for it, though? SLS is government funded. As SpaceX fans are so fond of pointing out, Starship isn't.

Edited June 22, 2020 by SOXBLOX

[CatastrophicFailure]

4 hours ago, wumpus said:

It is really weird that a second stage would  not only have TWR>1, but TWR>1 while dealing with suboptimal nozzles.  Of course the Mars edition will need a TWR>~1/3 just to lift off Mars, but that is a special case (and the MoonShip needs even less), but even a TWR of 1/3 seems high for a second stage.

Well, if they’re ever going to do P2P, Starship will have to have a TWR greater than 1. IIRC in normal operation Starship would only use the vacuum engines during ascent, the sea level engines would be used for landing. 

[tater]

 

[CatastrophicFailure]

4 hours ago, tater said:

Even if they met their aspirational cost per flight immediately, 270 flights would cost between a half a billion and a billion +.

(not that is see them flying that often)

Mostly paid for by someone else, or in pursuit of something else (like Starlink). Even if it takes several years, just by its MO for existing, SSSH could hit a number like that far sooner than anything else on the books. As you’ve said yourself, if they can make it work it will be nothing short of paradigm changing. 

[tater]

7 minutes ago, CatastrophicFailure said:

Mostly paid for by someone else, or in pursuit of something else (like Starlink). Even if it takes several years, just by its MO for existing, SSSH could hit a number like that far sooner than anything else on the books. As you’ve said yourself, if they can make it work it will be nothing short of paradigm changing. 

I just don't see them flying once every 36 hours for a year.

[SOXBLOX]

Once every 36 hours seems to vastly underestimate the engineering difficulties inherent in this project. Also, SS needs infrastructure. That requires some serious Ka-ching!

[kerbiloid]

Spoiler

If the gas storages of the world overfill like the oil ones, the Starship can fly even more often, to burn the excessive NGC, lol.

So, maybe Starlink is too small for Starship.
Maybe then an O'Neil cylinder.

 

[tater]

 

[RCgothic]

9 hours ago, tater said:

Even if they met their aspirational cost per flight immediately, 270 flights would cost between a half a billion and a billion +.

(not that is see them flying that often)

270 flights without a failure would only prove LOC risk to a 63% confidence level.

To be 95% sure you have a craft capable of 1/270 LOC you need 810 flights. And is being 95% sure enough?

1/270 is a 99.62% success rate. To be 99.62% sure you have a craft capable of a 99.62% success rate, that's 1510 flights.

Edited June 22, 2020 by RCgothic

[mikegarrison]

23 minutes ago, RCgothic said:

270 flights without a failure would only prove LOC risk to a 63% confidence level.

To be 95% sure you have a craft capable of 1/270 LOC you need 810 flights. And is being 95% sure enough?

1/270 is a 99.62% success rate. To be 99.62% sure you have a craft capable of a 99.62% success rate, that's 1510 flights.

If it's truly random and statistical, you could have a failure on the very first flight and yet the 1/270 chance could still be true.

For that matter you could have a failure on the first 10 flights and the 1/270 chance could still be true, but the odds of that actually happening if the true chance is 1/270 are about 5x10^-23%. Still, in theory, it could happen. Randomness.

Anyway, in practice things like a 1/270 chance of loss of vehicle are not generally demonstrated by actual launches but are instead calculated.

[RCgothic]

48 minutes ago, mikegarrison said:

If it's truly random and statistical, you could have a failure on the very first flight and yet the 1/270 chance could still be true.

For that matter you could have a failure on the first 10 flights and the 1/270 chance could still be true, but the odds of that actually happening if the true chance is 1/270 are about 5x10^-23%. Still, in theory, it could happen. Randomness.

Anyway, in practice things like a 1/270 chance of loss of vehicle are not generally demonstrated by actual launches but are instead calculated.

True. There was an assertion up-thread that Starship could fly often enough to demonstrate its reliability empirically. But more than 270 flights would be required in that instance.

The number of flights required to demonstrate the reliability would almost certainly get into "expected failures" territory, in which case you need even more flights or even better reliability.

To fly 1500 flights and expect to complete that test program with only 0.1 expected failure, you need LOV to be better than 1 in 15000 flights.

Getting into early airliner territory there!

[RealKerbal3x]

Cool drive-by video of the whole SpaceX Boca Chica site:

 

[Lukaszenko]

8 hours ago, SOXBLOX said:

Sure. Who's paying for it, though? SLS is government funded. As SpaceX fans are so fond of pointing out, Starship isn't.

Profit from Starlink? Even if not, it's not THAT much money. Isn't it around what Falcon Heavy cost to develop?

[tater]

 

[Hannu2]

17 hours ago, kerbiloid said:

But I can easily imagine 100+ old-style vomit bags in zero-g.

So, unlikely the space lines are a near future.

That may be interested situation, when 100 begin vomiting without experience how to use vomit bag in zero-g. I hope they take corrosive stomach acids into account when choose stainless steel type (fortunately many of them can handle mild acids pretty well). I would not like to be there (actually I would very probably vomit, my stomach is quite sensitive for even moderate g-forces in amusement parks).

 

[sh1pman]

11 hours ago, tater said:

I just don't see them flying once every 36 hours for a year.

Elon said that one Starship can theoretically launch every 8 hours, so 36 hours should be doable. Eventually. With enough people, facilities, payloads, etc...

[tater]

5 minutes ago, sh1pman said:

Elon said that one Starship can theoretically launch every 8 hours, so 36 hours should be doable. Eventually. With enough people, facilities, payloads, etc...

I'm not arguing that they haven't said that sort of thing. I'm doubting I'll be watching SS launches on YT every other day any time soon.

[sh1pman]

1 minute ago, tater said:

I'm not arguing that they haven't said that sort of thing. I'm doubting I'll be watching SS launches on YT every other day any time soon.

I'll bookmark this post, let's see how many years it will take them to reach that rate. 

[SOXBLOX]

8 minutes ago, sh1pman said:

I'll bookmark this post, let's see how many years it will take them to reach that rate. 

I'll bet seven years.