totm nov 2023 SpaceX Discussion Thread

[sh1pman]

1 minute ago, tater said:

Yeah, but it's also pretty cool to see. It looks like the total world expenditure on space is about 0.005% of gross world product. Seems like a small price to pay for something as cool as it is.

Not only is it cool, but we will run out of resources here eventually. Sun will fry the Earth in a few hundred million years. Sooner or later humanity (if it doesn’t destroy itself) will have to find a new home. Obviously not on the Moon, but it’s a nice first step.

[CBase]

1 hour ago, sevenperforce said:

Usually, you cannot safely fire a vacuum engine at sea level, because the overexpansion of the flow will lead to it being "pinched" by atmospheric pressure and separating inside the nozzle. This flow separation is chaotic and so it can produce different forces on different parts of the engine bell. With the amount of force in a rocket engine, even a tiny bit of misalignment on the force vectors will easily rip the thin bell apart.

Thanks, this is a damn good reason. Makes throttling even worse, which is kind of critical to landing, even when you neglect the gimbal problems.

The dual-bell noozle sounds interesting, but as he is rushing for time it is no surprise that it is not in the current design.

 

1 hour ago, sevenperforce said:

This thrust is important for other reasons, too. The Starship needs a LOT of thrust at staging so the three SL Raptors will actually fire with the vacuum Raptors after Superheavy separation until their added thrust is no longer needed. Swapping the three SL raptors out for a single vacuum Raptor would lower thrust at staging by 31% while only providing a negligible drop in wet or dry mass, with noticeably higher gravity drag losses due to the loss of T/W ratio.

This is actually a claim that I don't understand, if the stage altitude is not way lower than for Falcon 9. Currently the Merlin 1D Vacuum has 934kN for roughly 100 t second stage or 9.3kN/t TWR and seperates around 80km altitude.

A starship with 4 Raptor Vac engines would have 4x 3500kN for 2400t which is only 5.8kN/t TWR, but you get a much better ISP in return for the gravity loss with longer burns.

[kerbiloid]

Just now, sh1pman said:

Not only is it cool, but we will run out of resources here eventually. Sun will fry the Earth in a few hundred million years. Sooner or later humanity (if it doesn’t destroy itself) will have to find a new home. Obviously not on the Moon, but it’s a nice first step.

We must start storing instant noodles right now, like the Starship building.
Both will be relevant a million years later.

[sevenperforce]

6 minutes ago, ThatGuyWithALongUsername said:

DearMoon, for example, doesn't even require any orbital refueling, so all they need is the crewed Starship and they can send it on like a dozen trips around the moon before anyone goes anywhere in possibly less than a year.

While I agree with most of your rant (lol), they do need orbit refueling for #DearMoon. They just don't need elliptical orbital refueling.

[Wjolcz]

1 hour ago, magnemoe said:

They are pretty expensive to operate. 
yes an starship base will be cheaper as its not a warship and operation is less complex, it will still be an massive vessel.

Don't build a ship then. Make it an oil rig-like structure instead:

Edited September 30, 2019 by Wjolcz

[adsii1970]

Just now, Wjolcz said:

Don't build a ship then. Make it an oil rig-like structure instead:

[snip]

That's how I build large ships - I launch the parts into orbit and assemble it there. I've tried doing that using a fleet of shuttles - to discover the space shuttle is extremely inefficient. It's like using a small pickup truck, say a Ford Ranger, when you need a big box uHaul!

But otherwise, a Saturn-style lifter can actually lift a lot into a LKO, where the parts can be assembled to make a large vehicle fairly easy.

[sh1pman]

1 minute ago, kerbiloid said:

We must start storing instant noodles right now, like the Starship building.
Both will be relevant a million years later.

A million years later we can have the entire galaxy populated. It’s a nice insurance for planetary crises, however unlikely they may be.

Who knows, maybe some other evil alien civilization has already started colonizing Milky Way, and we need to start now to have a fighting chance against them.

[ThatGuyWithALongUsername]

8 minutes ago, sevenperforce said:

While I agree with most of your rant (lol), they do need orbit refueling for #DearMoon. They just don't need elliptical orbital refueling.

Thanks for tolerating my perhaps overly optimistic rant. As for your comment:

 

oh, ok

 

(still kinda odd that it isn't mentioned on the mission diagram on the website, but I'm assuming someone ran the numbers)

Edited September 30, 2019 by ThatGuyWithALongUsername

[Wjolcz]

3 minutes ago, adsii1970 said:

That's how I build large ships - I launch the parts into orbit and assemble it there. I've tried doing that using a fleet of shuttles - to discover the space shuttle is extremely inefficient. It's like using a small pickup truck, say a Ford Ranger, when you need a big box uHaul!

But otherwise, a Saturn-style lifter can actually lift a lot into a LKO, where the parts can be assembled to make a large vehicle fairly easy.

I'm not sure I understand? I was talking about the launch pad being a ship vs it being an oil rig.

Unless I completely misunderstood @magnemoe's post which might br the case too.

[adsii1970]

2 minutes ago, Wjolcz said:

I'm not sure I understand? I was talking about the launch pad being a ship vs it being an oil rig.

Some rigs are assembled in stages in a staging area, then moved out into position. Just like any sort of "starship" we'll need to assemble in orbit. Low orbit is a staging area. That's what I thought you were referring to...

 

[sevenperforce]

7 minutes ago, CBase said:

Thanks, this is a damn good reason. Makes throttling even worse, which is kind of critical to landing, even when you neglect the gimbal problems.

The dual-bell noozle sounds interesting, but as he is rushing for time it is no surprise that it is not in the current design.

I'm not sure that it's "not in the current design" as much as it has simply not been made. They haven't built any vacuum Raptors yet.

Here's where Elon explains...

 

7 minutes ago, CBase said:

This is actually a claim that I don't understand, if the stage altitude is not way lower than for Falcon 9. Currently the Merlin 1D Vacuum has 934kN for roughly 100 t second stage or 9.3kN/t TWR and seperates around 80km altitude.

A starship with 4 Raptor Vac engines would have 4x 3500kN for 2400t which is only 5.8kN/t TWR, but you get a much better ISP in return for the gravity loss with longer burns.

Current Starship design shown the other night is three RVacs. Burning those by themselves would be a T/W ratio of a measly 2.43 m/s², which is simply not workable. A single-engine Centaur has a far higher T/W ratio and it is famously underpowered and needs an inefficient lofted trajectory.

[CatastrophicFailure]

20 minutes ago, ThatGuyWithALongUsername said:

Well... here's what I think about all this. Warning, overall opinion on the system as a whole below:

 

Still no likes so...

Spoiler

 

[sevenperforce]

8 minutes ago, ThatGuyWithALongUsername said:

16 minutes ago, sevenperforce said:

While I agree with most of your rant (lol), they do need orbit refueling for #DearMoon. They just don't need elliptical orbital refueling.

oh, ok

(still kinda odd that it isn't mentioned on the mission diagram on the website, but I'm assuming someone ran the numbers)

They left it out. You need 2,730 m/s out of LEO to get a lunar flyby. I don't know how much the crewed version of Starship will mass, but even if there was literally no crew cabin at all, an empty Starship can reach orbit with about 100 tonnes of propellant remaining. That only gives you 2,260 m/s. 

^{(380 s isp, 220 tonnes wet mass, 120 tonnes dry mass)}

And that's with no cabin, no passengers, no consumables, and no landing propellant.

Unrelated: ripped the gif showing the Starship lunar landing with self-adjusting landing legs.

[Wjolcz]

On the SS LES topic: what happens to the 2nd stage when the 1st stage fails? Has anything like this ever happened? IIRC the last two F9 failures involved the second stage being faulty. To me it seems kind of logical that if the first stage goes boom boom the stage falls apart and the smaller bits slow down much faster than the second heavier stage. Unless the bits get sucked up into the lower pressure zone behind the ship, but even then if the engine spool time is super fast those might get deflected or obliterated before they reach the upper stage.

If an engine fails the flak jackets should stop the shrapnels and the stage would simply lose power.

The worst case scenario that (I think) can happen is when the fuel tank raptures and releases all the pressure. But even then it would first spread and then ignite. How hot is the CH4 and Ox reaction? Since SS is made out of steel (with chilly fuel in it) and the engine nozzles are, well, heat resistand engine nozzles they should be fine, no? Besides, isn't the CH4 stored in relatively low pressure?

Edit: even worse worst case scenario: the whole thing violently turns to the side and snaps in half. Result: complete failure and disintegration. That's something even airliners aren't built for.

 

Do keep in mind I'm obviously not a rocket scientist, but there seems to be a lot of ways to prevent damage to the second stafe when the first one fails.

Edit 2: OK, now I remembered Antares. The second stage seemed fine for the most part, so maybe SS could ditch all the heavy fuel and then use SL Raptors and fuel from the header tanks as LES? That would probably take too much time to do though.

Edited September 30, 2019 by Wjolcz

[mikegarrison]

25 minutes ago, ThatGuyWithALongUsername said:

The thing is, this is the first vehicle ever designed from the ground up to be rapidly reusable. Yes, I know the space shuttle existed, but it wasn't rapidly reusable, even if it was supposed to be. With Starship, you can just double-check the engines and heat shield, refuel it, and relaunch. If they can't do that, Starship is a failure. so, if we're assuming that Starship is far enough into development to launch people, then we have to assume it was successful at this.

Here's the thing: launching Starship is quick and inexpensive, so they can test it many, many more times than a regular rocket. Elon mentioned in the presentation that the system is capable of multiple fights to orbit PER DAY. They also said they would be basically trying to churn out a bunch of Starships while testing.

The other question of course is cost. This is a lot of flights. But that's of course the other place where rapid reuse comes in handy: costs. Costs will be much, much smaller than what we're used to. This is why they need a lot of money for this- not just the development cost, the cost of hundreds f test flights. But fortunately, they have a payload for most of these test flights: Starlink, as well as other commercial missions. So cost will not stop them from doing hundreds of lights, in fact, doing hundreds of flights will stop the cost from stopping them, if that makes any sense.

Some huge issues here.

1) The space shuttle was designed for "rapid reusability". The fact that it wasn't as rapid as they hoped does not negate what the design intent was. And Starship has never once even been used, much less reused, so going by the intent is counting your chickens before they have hatched. (It's also worth noting that Falcon 9 still has not turned around a booster faster than the fastest space shuttle turnaround, so just assuming Starship will do so is a big leap.)

2) Elon says a lot of stuff that I think is crazy. Flying multiple orbital missions per day with the same starship is one of them.

3) You are fundamentally misunderstanding the costs. Flying more missions does not decrease costs. It only increases costs. Even if costs/flight go down, total costs will go up as there are more flights. *Profits* can be increased with volume, but costs go up with volume. And starship needs paying payloads to get those profits. I'm not sure if I count Starlink as a paying payload -- that totally depends on whether Starlink gets customers or not. So starship is depending on there being a huge market for delivery to orbit.

This whole thing reminds me a lot of the 747. Not only were the first 747s built while Boeing was still constructing the factory around them, but they were very big and very costly compared to other planes of the era. If Boeing had been wrong about the demand for international air travel, then the 747 would have dragged the entire company down with it. But to a large extent (pun intended), the 747 actually created its own market.

Starship has the potential to create its own market and be the game-changer that the 747 was. We'll see what actually happens.

[Ultimate Steve]

On Starship LES, there is plenty of room between the raptor bells for emergency single use solid rocket boosters or also more raptors.

[Wjolcz]

7 minutes ago, Ultimate Steve said:

On Starship LES, there is plenty of room between the raptor bells for emergency single use solid rocket boosters or also more raptors.

Yes, I think the 7 Raptors version would be a better choice for P2P. They wouldn't need vacuum engines anyway.

[ThatGuyWithALongUsername]

1 hour ago, mikegarrison said:

Some huge issues here.

1) The space shuttle was designed for "rapid reusability". The fact that it wasn't as rapid as they hoped does not negate what the design intent was. And Starship has never once even been used, much less reused, so going by the intent is counting your chickens before they have hatched. (It's also worth noting that Falcon 9 still has not turned around a booster faster than the fastest space shuttle turnaround, so just assuming Starship will do so is a big leap.)

2) Elon says a lot of stuff that I think is crazy. Flying multiple orbital missions per day with the same starship is one of them.

3) You are fundamentally misunderstanding the costs. Flying more missions does not decrease costs. It only increases costs. Even if costs/flight go down, total costs will go up as there are more flights. *Profits* can be increased with volume, but costs go up with volume. And starship needs paying payloads to get those profits. I'm not sure if I count Starlink as a paying payload -- that totally depends on whether Starlink gets customers or not. So starship is depending on there being a huge market for delivery to orbit.

This whole thing reminds me a lot of the 747. Not only were the first 747s built while Boeing was still constructing the factory around them, but they were very big and very costly compared to other planes of the era. If Boeing had been wrong about the demand for international air travel, then the 747 would have dragged the entire company down with it. But to a large extent (pun intended), the 747 actually created its own market.

Starship has the potential to create its own market and be the game-changer that the 747 was. We'll see what actually happens.

That's kinda what I was saying though about the riskiness and the Boeing comparison- I agree, we will have to see whether they're successful at this.

And yeah I guess I did discredit the shuttle a bit, but just because it wasn't successful doesn't mean that something else can't be. With Shuttle, it *was* designed for this capability from the round up, but it didn't really get the chance to be developed with it available immediately, like Starship might. Or might not. And that might not really even be true. I guess it depends on how you look at it. Anyway, the point was supposed to be that the shuttle as still developed very differently from Starship, in either case, so comparing them is still difficult.

And I didn't mean that more flights cost less, obviously, but the capability to have more flights means you have less to do between flights- in order to do rapid reuse, you have to pretty much only be paying fuel fuel and quick inspections (the quicker the inspection, generally the cheaper). So, yeah, more flights doesn't mean lower costs, but rapid reuse does.

As for Starlink, honestly the only way I can see global high-bandwidth internet not being successful is if someone beats them to it or they charge too much. For people in rural areas, this is one of the only real options, so there's certainly demand.

 

And everything Elon says is crazy. He just tries really hard to make them true. Realizing what he's saying is crazy doesn't stop him, it just slows him down a few years, lol. At least that's how it's gone so far.

Psssh. Landing rockets on a barge. That's ridiculous.

Edited September 30, 2019 by ThatGuyWithALongUsername

[Wjolcz]

15 minutes ago, ThatGuyWithALongUsername said:

Psssh. Landing rockets on a barge. That's ridiculous.

+1 it still is.

I agree that he says a lot of questionable things but at the same time his company is the only one to deliver payloads to orbit, land the first stage and reuse it a couple of times. I don't think he and the whole SpaceX team will succeed in realising all those crazy projects but I sure do want them to.

Edited September 30, 2019 by Wjolcz

[Rakaydos]

1 hour ago, sevenperforce said:

 

I would still imagine that having positive T/W is important so that you can actually separate from Superheavy. What if Superheavy catches on fire but remains standing?

Shelter In Place behind your fireproof steel hull, start draining fuel to get above TWR=1 as a precautionary measure, and let Pad Emergency Services handle the problem.

[mikegarrison]

6 minutes ago, Rakaydos said:

Shelter In Place behind your fireproof steel hull, start draining fuel to get above TWR=1 as a precautionary measure, and let Pad Emergency Services handle the problem.

"draining fuel" with a fire going on just below you? I'm thinking this is not a good plan.

[Jacke]

52 minutes ago, Rakaydos said:

Shelter In Place behind your fireproof steel hull, start draining fuel to get above TWR=1 as a precautionary measure, and let Pad Emergency Services handle the problem.

...and this also doesn't handle the catestrophic failure of the 1st stage.  Saturn 5 had 3 wires going all the way from the bottom up to the Instrument Unit.  If a line broke before 1st staging, that triggered the LES.  Without a similar LES, that's a major fault case not handled.

[Castille7]

4 hours ago, Wjolcz said:

Don't build a ship then. Make it an oil rig-like structure instead:

I made something similar when building bridges. I also built one of these Jackets with a Helipad on top but wasn't able to set in place at the Island where I wanted to. I plan to make more attempts in the future.

[magnemoe]

4 hours ago, sevenperforce said:

This is also particularly likely if they put the LOX tank at the top rather than the bottom. I can't recall the exact configuration, but if the LOX tank is at the top then you have a massive barrier between you and anything explodey. Granted, LOX is awful, awful stuff, but there's no way to make it detonate under those circumstances.

I would still imagine that having positive T/W is important so that you can actually separate from Superheavy. What if Superheavy catches on fire but remains standing?

Yes, LOX on top is standard, as you say it also act as an barrier. Guess they also add an plate on top of the superheavy as an weather cover to protect the separation mechanism and other systems on top. 
However that is another part who might fail and both falcon 9 losses was to upper stage fail.
i still feel that the requirements NASA has for an abort system is a bit overkill. 
 

[Nothalogh]

2 minutes ago, magnemoe said:

the requirements NASA has for an abort system is a bit overkill.

Especially in light of their adoption of the STS as they did.