totm nov 2023 SpaceX Discussion Thread

[mikegarrison]

45 minutes ago, darthgently said:

Aside from humor and aesthetics, and sticking to engineering, what is the issue with "too pointy"?   Will it heat more on ascent and descent?  Honest question

You want blunt shapes when re-entering the atmosphere at reasonable decelerations. Pointy works better, actually, for objects like nuclear warheads that can take much more g-load and temperature than human beings. But when balancing heat and g-loading for something in the range that humans can survive, blunt is better.

Edited April 9, 2023 by mikegarrison

[darthgently]

Ok. So maybe human rated Starship with need less pointy.  Thanks for the reality check

[tater]

A 10m stretch of SS would add ~450t of props, leaving the cargo/crew volume the same. It would add ~8.7t dry mass to the vehicle. The 3 additional engines add ~4.5t.

Back in January, I assumed an 80t HLS with 10t cargo.

With a stretched HLS, we're at 93t, and 103t with 10t cargo. ~1640t props.

HLS gets delivered to LEO with ~300t residual props I would think. Fully tanked up it would have 10,638 m/s of dv (at 378s I_sp )

A propulsive round trip to the lunar surface from LEO is 10,400 m/s.

Commercial crew to LEO in a less annoying orbit than ISS (faster rendezvous). Crew leaves their cramped quarters after a few hours en route for their suburban-house sized lander. Enjoys their trip to the Moon, and subsequent stay in comfort. Returns to LEO, docks with crew taxi. Is home in a couple hours. Repeat.

Edited April 10, 2023 by tater

[tater]

"Another 10m or so" is 5.46 rings. Rings are not partial, so maybe add 6 rings. 10.98m. That would add ~480-510t props (note that all the added props estimates includes the domes, so I am probably under estimating).

Then with 80t HLS and 10t cargo we'd go to 94t dry, plus 10t cargo, and 1700t props. 10,753 m/s.

Note also that I didn't bother leaving the cargo on the Moon, so that's with returning 10t of rocks

Edited April 9, 2023 by tater

[tater]

 

 

[CatastrophicFailure]

6 hours ago, mikegarrison said:

You want blunt shapes when re-entering the atmosphere at reasonable decelerations. Pointy works better, actually, for objects like nuclear warheads that can take much more g-load and temperature than human beings. But when balancing heat and g-loading for something in the range that humans can survive, blunt is better.

I’m wondering if a blunter shape would simplify the engineering for that chomper cargo bay, myself. 

[magnemoe]

6 hours ago, darthgently said:

Ok. So maybe human rated Starship with need less pointy.  Thanks for the reality check

I see this as little likely.  Think you want to keep something like this the same as it affect reentry heating a lot.  Human rated might have different flaps as the crew module will add front weight. They could compensate by moving the methane tank doing into the main tanks. 

[darthgently]

1 hour ago, magnemoe said:

I see this as little likely.  Think you want to keep something like this the same as it affect reentry heating a lot.  Human rated might have different flaps as the crew module will add front weight. They could compensate by moving the methane tank doing into the main tanks. 

Maybe a later iteration with blunter nose for all Starships to accommodate the human rated version then.  Given Musk now thinks it is too pointy and all.  The design is still in the proto phase until it goes into production, to be blunt (pun intended). 

Pointy is fine for an orbital test, for now.

Still, I do recall something about the taller nose being better able to accommodate the header tanks up there so SpaceX may have a plan b for that issue

[tomf]

It's re-entering in a belly down attitude rather than nose first though, so I would expect the pointyness to have much less effect. The plasma flow around a tip would probably be complicated, but not the same as a capsule style.

[zolotiyeruki]

A blunter nose also shifts the center of pressure slightly aft during the belly flop. May be a bit easier to fabricate as well.

[mikegarrison]

1 hour ago, tomf said:

It's re-entering in a belly down attitude rather than nose first though, so I would expect the pointyness to have much less effect. The plasma flow around a tip would probably be complicated, but not the same as a capsule style.

I am not an expert on re-entry, but I think that a pointy nose would act something like a stress concentrator (both for the structure and the plasma flow). If you look at all the spaceplanes, they all have blunt noses.

Edited April 9, 2023 by mikegarrison

[Meecrob]

I think @tomf is trying to say that Starship is not re-entering nose first, but rather with a healthy angle of attack so the body will be doing much of the work of keeping the plasma flow away from the rest of the structure.

[mikegarrison]

18 minutes ago, Meecrob said:

I think @tomf is trying to say that Starship is not re-entering nose first, but rather with a healthy angle of attack so the body will be doing much of the work of keeping the plasma flow away from the rest of the structure.

Thank you, but I knew that.

The point of blunt re-entry is two-fold. One is to increase drag, but the other is to set up a normal shock as  far as possible away from the re-entry vehicle. Any pointy bits (even sideways) bring the shock (and thus the plasma) closer to the vehicle. At least, I think they do. This is an aerodynamic regime I haven't personally studied much in.

[sevenperforce]

On 4/9/2023 at 7:20 AM, darthgently said:

Aside from humor and aesthetics, and sticking to engineering, what is the issue with "too pointy"?   Will it heat more on ascent and descent?  Honest question

Just unnecessary added mass.

That sharper ogive isn't necessary from an aerodynamic perspective. A blunter nose would work just as well, and a blunter nose would weigh slightly less.

17 hours ago, mikegarrison said:

Thank you, but I knew that.

The point of blunt re-entry is two-fold. One is to increase drag, but the other is to set up a normal shock as  far as possible away from the re-entry vehicle. Any pointy bits (even sideways) bring the shock (and thus the plasma) closer to the vehicle. At least, I think they do. This is an aerodynamic regime I haven't personally studied much in.

Agreed. The nose will probably experience slightly more aggressive re-entry heating than it otherwise would, because it has a lower radius of curvature at the tip.

[Meecrob]

21 hours ago, mikegarrison said:

Thank you, but I knew that.

The point of blunt re-entry is two-fold. One is to increase drag, but the other is to set up a normal shock as  far as possible away from the re-entry vehicle. Any pointy bits (even sideways) bring the shock (and thus the plasma) closer to the vehicle. At least, I think they do. This is an aerodynamic regime I haven't personally studied much in.

My bad, I was hesitant to reply, since I know you are very knowledgeable, I thought you misread it is all.

 

Edit: or I had misread.

Edited April 10, 2023 by Meecrob

[tater]

 

 

[tater]

(a slight alteration of one they already had posted)

 

(video)

[mikegarrison]

2 hours ago, Meecrob said:

My bad, I was hesitant to reply, since I know you are very knowledgeable, I thought you misread it is all.

No, don't worry. I realized I hadn't given enough detail in my first post.

[magnemoe]

On 4/9/2023 at 4:35 PM, tater said:

A 10m stretch of SS would add ~450t of props, leaving the cargo/crew volume the same. It would add ~8.7t dry mass to the vehicle. The 3 additional engines add ~4.5t.

Back in January, I assumed an 80t HLS with 10t cargo.

With a stretched HLS, we're at 93t, and 103t with 10t cargo. ~1640t props.

HLS gets delivered to LEO with ~300t residual props I would think. Fully tanked up it would have 10,638 m/s of dv (at 378s I_sp )

A propulsive round trip to the lunar surface from LEO is 10,400 m/s.

Commercial crew to LEO in a less annoying orbit than ISS (faster rendezvous). Crew leaves their cramped quarters after a few hours en route for their suburban-house sized lander. Enjoys their trip to the Moon, and subsequent stay in comfort. Returns to LEO, docks with crew taxi. Is home in a couple hours. Repeat.

Two things, moonship does not need a crew model the size of the Mars liner ship in initial presentation. Even less if resupplied by Orion as an 4 man crew is maximum.  
Starship is very overbuild for this mission profile.  But its an lander SpaceX is pushing, everything else NASA has to pay for development. 

I agree with your idea  at an later stage there we have an moon base. But not at this phase.

Operating out of moon orbit you don't need aerobraking stuff on your lander, you might build the crew quarters of lighter material than steel who also help with secondary radiation. 
You aerobrake the unmanned tanker, if you loose that its an financial loss only assuming you have spares who SpaceX plan for as they have an production line setup.  
And we all know SpaceX like learning while doing stuff other people pay for. 

And they would use another moonship as the lunar space station as it would double as an fuel depot and is fueled could probably do an rescue mission if fueled and has an tanker as backup. 

[AtomicTech]

2 hours ago, tater said:

 

 

I'd reckon that we're looking at a launch probably next month; Elon-time has got me worn out.

[tater]

35 minutes ago, magnemoe said:

Two things, moonship does not need a crew model the size of the Mars liner ship in initial presentation. Even less if resupplied by Orion as an 4 man crew is maximum.  
Starship is very overbuild for this mission profile.  But its an lander SpaceX is pushing, everything else NASA has to pay for development. 

"Overbuilt" is meaningless. They are building what they are building, getting paid by NASA is gravy.

NASA is not paying for dev in the old-fashioned way—they bought an uncrewed test mission, and a crewed test mission for $2.9B, all-in. Fixed price.

 

35 minutes ago, magnemoe said:

I agree with your idea  at an later stage there we have an moon base. But not at this phase.

Operating out of moon orbit you don't need aerobraking stuff on your lander, you might build the crew quarters of lighter material than steel who also help with secondary radiation. 
You aerobrake the unmanned tanker, if you loose that its an financial loss only assuming you have spares who SpaceX plan for as they have an production line setup.  
And we all know SpaceX like learning while doing stuff other people pay for. 

My stretched numbers above don't require aerobraking. A stretched LSS can fly round trip from LEO with no Earth entry at all, just engine burns. A stretched LSS merely existing completely obviates SLS/Orion as part of Artemis. I also did not assume thinner steel—which they certainly could do with LSS as it only needs to survive launch stress. The hull mass could possibly drop by 25% (4mm to 3mm steel). Actually, I think they might already be down to 3.6mm by default, so my dry mass might be 10% too high.

 

35 minutes ago, magnemoe said:

And they would use another moonship as the lunar space station as it would double as an fuel depot and is fueled could probably do an rescue mission if fueled and has an tanker as backup. 

Gateway is entirely pointless if they stretch Starship.

[cubinator]

3 hours ago, tater said:

 

 

3:04 look at the Earth, they are going to Venus

[tater]

launch tonight slipped to tomorrow

 

[tater]

 

[StrandedonEarth]

*Military cadence*

“Falcon Heavy on the crawlerways!

/ Massive stuff getting launched in days!”