totm nov 2023 SpaceX Discussion Thread

[magnemoe]

8 minutes ago, tater said:

I'm not seeing LES as a thing. What's the abort scenario on a 777 if a wing falls off?

For crew applications I've always had issues with the BFR/ITS/SS concept. Honestly, if they are still remotely serious about P2P, they need full on "airworthiness" certification.

The stubby legs, too... Yikes.

However starship is not an turbofan passenger plane. its an orbital rocket, they are far more stressed than fighter jets who always has had ejection seats with a few exceptions i assumes. 
And powered landings is also pretty dangerous, probably more so than launches. 
Note that both Falcon 9 fails was in upper stage. 
The legs are not so much of an issue at least not then landing on an pad. 

However P2P is pure scifi. It has lots of issues, first you need to operate an offshore base who is able to service and refuel starships and also bring in passengers with helicopter. 
We have ships like this but they are not able to service ballistic missiles 

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.
Second is the capacity who is to high. Yes if you have an fast but expensive route you need frequent flights or an slower flight is faster at getting you to location. 
This was an major issue for Concorde, They worked if you wanted to go from London to NY, but if you wanted to go from Berlin to Miami an direct flight with an turbofan was faster, less stressfull and cheaper flying business class who is pretty much like the old first class nowday. 
This analysis ignores safety. 

 

[CatastrophicFailure]

49 minutes ago, tater said:

NASA just barged in their SLS Core Stage test article (a large boilerplate thing to rehearse moving it around) to the VAB. I'd be willing to bet that that boilerplate object cost as much as Starship (minus the engines).

Clearly, you underestimate the ability of NASA contractors to siphon money. 

38 minutes ago, tater said:

I'm not seeing LES as a thing. What's the abort scenario on a 777 if a wing falls off?

I’m not entirely sold on the whole P2P thing myself, but one way or another, “a whole ‘nother level of reliability” is a thing that needs to happen if Starship is ever going to be fully successful, whether it flies P2P or not. 

Thing is, until Starship gets going it’s been impossible to even measure that level of reliability in rockets because they all (or nearly all) just get thrown away. So there’s also no incentive to build that level in the first place, since it'd just be a waste. The Atlas V is the pinnacle of reliability, but we’ll probably never know exactly how much so, since it’s likely to be  retired without a single major failure. 

Which, if you stretch the words a bit, is a level of reliability even airliners can’t match. 

Starship may be the first rocket to approach airworthiness-levels of reliability if only because it can, since it’s been made to. 

After all, there was a point in history when a wing falling off your airplane was a perfectly valid concern... 

[sevenperforce]

14 minutes ago, tater said:

I have to say, best "Starship" lunar landing might be:

Use SS to get to lunar orbit (it has the dv for a lunar orbit and return when refilled). Drop off 100t in LLO. Land cargo.

A 100t (wet) lander with a single Vac Raptor could do a round trip from LLO with 37t of cargo (I'm calling the lander 9t dry). You can drop the cargo mass slightly and take the lander all the way back to Gateway (if anyone cares to do that).

Nominally you'd return to SS, which takes the now 9t Lander back to earth.

This makes way, way more sense to me than SS to the lunar surface. Vacuum space vehicles will always make more sense to stay in that environment.

Basically reverse staging. I like it. I have done this exact same thing more times than I can count in KSP. 

[CatastrophicFailure]

9 minutes ago, magnemoe said:

first you need to operate an offshore base who is able to service and refuel starships and also bring in passengers with helicopter

We’ve been building offshore airports to mitigate noise (among other concerns) for a while now. And helicopters? Not at all, you just need an undersea tunnel and high-speed electric trams running in it to move passengers. 

Oddly enough, Musk has some interest in companies that do both. 

[magnemoe]

5 minutes ago, tater said:

I have to say, best "Starship" lunar landing might be:

Use SS to get to lunar orbit (it has the dv for a lunar orbit and return when refilled). Drop off 100t in LLO. Land cargo.

A 100t (wet) lander with a single Vac Raptor could do a round trip from LLO with 37t of cargo (I'm calling the lander 9t dry). You can drop the cargo mass slightly and take the lander all the way back to Gateway (if anyone cares to do that).

This makes way, way more sense to me than SS to the lunar surface. Vacuum space vehicles will always make more sense to stay in that environment.

This, I would even cut back on the cargo quite a bit. You use starship to land the heavy stuff, yes it require lots of refueling missions but you don't do many of them. 
//tilt: an setting there you drop 12 astronauts two rovers and an drill rig is cheaper than putting an small rover on moon.
 

[tater]

1 minute ago, sevenperforce said:

Basically reverse staging. I like it. I have done this exact same thing more times than I can count in KSP. 

Yeah, SS cannot ( I think) do a lunar surface RT. Seems to have ~8900m/s of dv (6900m/s with 100t cargo). The only way to close the math---empty, BTW, no cargo to speak of---is to refill in an elliptical orbit, or add some other refilling step, etc. More complex with cargo.

Instead, you drag a lander to the Moon, land it, then come back to SS, and head home. The lander could possibly be a crew pod even for launch (assuming no LES is a thing), alternately, SS has crew dropped off some other way in LEO, or meets Orion (short term), etc.

37t is a lot of useful cargo to the lunar surface.

3 minutes ago, magnemoe said:

This, I would even cut back on the cargo quite a bit. You use starship to land the heavy stuff, yes it require lots of refueling missions but you don't do many of them. 

First they'd need to show they can even utilize 37t of cargo, lol.

[Rakaydos]

1 hour ago, sevenperforce said:

Elon has always insisted that if there is a problem with Superheavy on ascent, the upper stage can just boost way. But it cannot do that if it cannot pull a gee.

Bullship. You'd be right for a pad abort, but in flight... "You don't have to outrun the bear, you just have to outrun your buddy." The Superheavy will stop accelerating in any conceivable abort scenario, so any Starship acceleration, even sub-G, creates relative acceleration to increase separation distance.

Now for Pad Abort... With dual-nozzels on the vac bells and running at qualification power (110%), Starship only accelerates at around .9g at sea level. Which means that, from a Superheavy height of 68m, it takes a bit over 6 seconds to reach the ground, at an impact speed of 12-13 meters per second. And THATS a simple drag race constant acceration calculation, that doesn't count the starship getting lighter as it burns fuel and oxidizer, nor does it allow for dumping excess fuel through the refueling lines.

[sevenperforce]

23 minutes ago, tater said:

Yeah, SS cannot ( I think) do a lunar surface RT. Seems to have ~8900m/s of dv (6900m/s with 100t cargo). The only way to close the math---empty, BTW, no cargo to speak of---is to refill in an elliptical orbit, or add some other refilling step, etc. More complex with cargo.

Instead, you drag a lander to the Moon, land it, then come back to SS, and head home. The lander could possibly be a crew pod even for launch (assuming no LES is a thing), alternately, SS has crew dropped off some other way in LEO, or meets Orion (short term), etc.

You only need a 64% fuel fraction to make LLO to surface and back on a single-stage with a vacuum Raptor.

1 minute ago, Rakaydos said:

...for Pad Abort... With dual-nozzels on the vac bells and running at qualification power (110%), Starship only accelerates at around .9g at sea level. Which means that, from a Superheavy height of 68m, it takes a bit over 6 seconds to reach the ground, at an impact speed of 12-13 meters per second. And THATS a simple drag race constant acceration calculation, that doesn't count the starship getting lighter as it burns fuel and oxidizer, nor does it allow for dumping excess fuel through the refueling lines.

Descends to the ground at an impact of speed of thirty miles per hour directly into the flaming, exploding, shrapnel-shredding flaming carcass of Superheavy?

More likely that they will add three additional engines for crew and/or fly them without as many props.

[RealKerbal3x]

4 minutes ago, Rakaydos said:

Bullship. You'd be right for a pad abort, but in flight... "You don't have to outrun the bear, you just have to outrun your buddy." The Superheavy will stop accelerating in any conceivable abort scenario, so any Starship acceleration, even sub-G, creates relative acceleration to increase separation distance.

Now for Pad Abort... With dual-nozzels on the vac bells and running at qualification power (110%), Starship only accelerates at around .9g at sea level. Which means that, from a Superheavy height of 68m, it takes a bit over 6 seconds to reach the ground, at an impact speed of 12-13 meters per second. And THATS a simple drag race constant acceration calculation, that doesn't count the starship getting lighter as it burns fuel and oxidizer, nor does it allow for dumping excess fuel through the refueling lines.

I believe someone a while back said that the RVacs could have pyrotechnics to shear off the vacuum nozzle extensions in the event of a pad abort, increasing efficiency.

Edited September 30, 2019 by RealKerbal3x

[sevenperforce]

4 minutes ago, RealKerbal3x said:

I believe someone a while back said that the RVacs could have pyrotechnics to shear off the vacuum nozzle extensions in the event of a pad abort, increasing efficiency.

Scott Manley suggested that and Elon said no, they would go dual-bell instead. No meaningful difference in efficiency between a dual-bell and a SL bell other than added dry mass.

Also wouldn't work because

1. They are regeneratively-cooled nozzle extensions, which means they are plumbed for pumping propellant through for cooling, which means you can't break them
2. They are welded to the skirt of Starship

[RealKerbal3x]

Just now, sevenperforce said:

Scott Manley suggested that and Elon said no, they would go dual-bell instead. No meaningful difference in efficiency between a dual-bell and a SL bell other than added dry mass.

Also wouldn't work because

1. They are regeneratively-cooled nozzle extensions, which means they are plumbed for pumping propellant through for cooling, which means you can't break them
2. They are welded to the skirt of Starship

Thank you for reminding me of those factors, I had failed to consider them

[mikegarrison]

1 hour ago, tater said:

I have to say, best "Starship" lunar landing might be:

Use SS to get to lunar orbit (it has the dv for a lunar orbit and return when refilled). Drop off 100t in LLO. Land cargo.

A 100t (wet) lander with a single Vac Raptor could do a round trip from LLO with 37t of cargo (I'm calling the lander 9t dry). You can drop the cargo mass slightly and take the lander all the way back to Gateway (if anyone cares to do that).

Nominally you'd return to SS, which takes the now 9t Lander back to earth.

This makes way, way more sense to me than SS to the lunar surface. Vacuum space vehicles will always make more sense to stay in that environment.

Tradeoffs all around. As we discussed earlier, keeping things simple is hugely attractive. Not having to have a separate lunar lander saves all sorts of cost and effort and probably increases reliability. Plus, if you are hauling this lunar lander from Earth and back every time, it may easily cost you more (in $$$ and payload mass) than just using the main ship as a lander.

On the other hand, if you had a dedicated lunar lander/ascent vehicle that could be refueled and reused at the moon without bringing it back to Earth, that might be the way to go. However, that probably requires a lot of lunar infrastructure (either in orbit or on a base).

Big picture, though, I'm still not sure why we want to be messing around with the moon much at all. What's there that we need?

[RealKerbal3x]

6 minutes ago, mikegarrison said:

Big picture, though, I'm still not sure why we want to be messing around with the moon much at all. What's there that we need?

The big thing is water ice near the poles, in permanently shadowed craters. That could be converted to to rocket fuel (by splitting the H20 into hydrogen and oxygen) or used as drinking water.

[tater]

7 minutes ago, mikegarrison said:

Big picture, though, I'm still not sure why we want to be messing around with the moon much at all. What's there that we need?

If the engines are hydrolox, then water is propellant. Otherwise... why do we have ISS, lol? It's a thing to do, and is sorta cool.

 

[kerbiloid]

Just now, RealKerbal3x said:

That could be converted to to rocket fuel (by splitting the H20 into hydrogen and oxygen) or used as drinking water.

And why need the fuel and the drinking on the Moon when you can stay here and don't need?

Spoiler

2 minutes ago, tater said:

why do we have ISS, lol? It's a thing to do, and is sorta cool.

 

Because NASA people need some food, too.

 

[RCgothic]

Could be they aren't overly concerned with a SH conflagration. It's so large it's likely to not mix particularly well before ignition, so not a detonation. Stainless steel can survive over a thousand 'C and the blast of six raptors would scatter debris away from Starship pretty effectively. Starship could just translate sideways to an abort pad and by the time it touched down you'd be at about a g due to fuel use.

[sh1pman]

8 minutes ago, mikegarrison said:

What's there that we need?

There can be research stations studying off-world habitation. Testing life support tech and ISRU, etc. Maybe hotels for ultra-rich.

[kerbiloid]

1 minute ago, sh1pman said:

There can be research stations studying off-world habitation

Which part of the off-world habitation except low-G is not available on the Earth?
How many test objects are required to fill the gap between the 1 g and 0 g results?

Edited September 30, 2019 by kerbiloid

[mikegarrison]

3 minutes ago, kerbiloid said:

Which part of the off-world habitation except low-G is not available on the Earth?

Danger. Cost. Exclusivity. Excitement.

Yeah, you can get all those on Earth too, but it only costs about $100,000 to get a guided climb of Everest. Going to the moon is a whole different category of showing off.

Edited September 30, 2019 by mikegarrison

[kerbiloid]

1 minute ago, mikegarrison said:

Yeah, you can get all those on Earth too, but it only costs about $100,000 to get a guided climb of Everest. Going to the moon is a whole different category of showing off.

And where is the "research" in the list?

[sevenperforce]

7 minutes ago, RCgothic said:

Could be they aren't overly concerned with a SH conflagration. It's so large it's likely to not mix particularly well before ignition, so not a detonation. Stainless steel can survive over a thousand 'C and the blast of six raptors would scatter debris away from Starship pretty effectively. Starship could just translate sideways to an abort pad and by the time it touched down you'd be at about a g due to fuel use.

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?

[sh1pman]

Just now, kerbiloid said:

Which part of the off-world habitation except low-G is not available on the Earth?

Vacuum, hazardous moon dust all around, no civilization, heavy radiation, extreme temperatures, 14 Earth-day long days and nights, absence of naturally growing food and most resources. It’s a unique environment that needs conquering and colonizing if we’re serious about becoming a multiplanetary species.

[tater]

1 minute ago, kerbiloid said:

How many test objects are required to fill the gap between the 1 g and 0 g results?

At least 1 would be a good idea

Honestly, the one thing I really like about Musk's newer presentations is that he abandons the existential threat mitigation as the primary mover, and says he wants it just for the inspiration of it. I think humans---actual people, not robots---going out and exploring other worlds is worth doing just because it's cool/inspiring.

Just now, mikegarrison said:

Yeah, you can get all those on Earth too, but it only costs about $100,000 to get a guided climb of Everest. Going to the moon is a whole different category of showing off.

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.

[kerbiloid]

6 minutes ago, sh1pman said:

Vacuum, hazardous moon dust all around, no civilization, heavy radiation, extreme temperatures, 14 Earth-day long days and nights, absence of naturally growing food and most resources.

It's a good Vault-Tek practice to build huge vaults to run psychological experiments, but unlikely can be done without Delta-IX rocket.

4 minutes ago, tater said:

At least 1 would be a good idea

So, 3 Apollo flights + 1 landed Salyut is absolutely enough even to check the results twice.

4 minutes ago, tater said:

I think humans---actual people, not robots---going out and exploring other worlds is worth doing just because it's cool/inspiring.

Starship Troopers are a thing!

Edited September 30, 2019 by kerbiloid

[ThatGuyWithALongUsername]

Quote

Lots of opinions and stuff, especially regarding LES and reliability

For some reason I went on a minor rant on Starship after reading through some of these. Yes, that is a link to a space blog in my signature, and yes, this probably should just go there, but no, I'm lazy and that thing's been dormant for like a year now.

 

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

Starship, whether it will be successful or not, is unlike any other rocket in history. Thus such things like cost, reliability, and flight rate cannot be compared to any other rocket.

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.

So, here's the thing: Even with something more realistic for analyzing test data like 1 flight per weekday, they can test their system and iron out reliability problems hundreds of times in a single year. and this is why it's expected to be reliable- the airline-like reliability would be expected because of airline-like numbers of flights! If a plane only flew, say, 20 times a year, you wouldn't know if it was all that reliable, would you?

This is also why all the other deadlines are so ambitious. Development can go a heck of a lot faster when tests can be done a heck of a lot more often. DearMoon, for example, doesn't even require any orbital refueling, (ok apparently it does but they can test that too) 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.

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.

And of course the argument that Starship is overbuilt for many of the things it does is true, but irrelevant. It doesn't matter how overbuilt it is for the task, it's cheaper and more flexible than anything else. Yes it has fins, but it can still land on the moon for the cost of only like  flights, which isn't that much. Something that is built solely for the moon can't take advantage of this rapid reuse as often, and therefore would have much higher development costs and less flights to offset those, so it isn't as good as it sounds on paper. With Starship, unlike any other launch vehicle ever, it isn't about mass efficiency all the time, but rather operational efficiency/flexibility.

Yes, again, rapid reuse is objectively an utterly insane and crazy goal, and perhaps an unrealistic one, but it's kind of the most important thing that Starship has to do to do, well, anything. Cost, reliability, safety, and ability to do interplanetary missions (tank it up quickly) all depend on Starship's seriously rapid reuse capability. If this does not work, Starship does not work. It's obviously not going to be easy, otherwise it would have been done before, but it is necessary, and Elon wants to get to Mars pretty badly, so they're certainly not going to give up on this any time soon. Either they'll fail hard or they'll change everything in the industry. Not much room in between when you commit to such huge risks like this. But Elon wants to go to Mars, and they need this radical change if hey're going to do so. Will they do it? Well, obviously they're doing a lot of things differently with Starship already, but we can't really know if these differences will be successful. Only time will tell. It's going to be some seriously exciting next few years as we figure out which one that's going to be.

Do I think it will work? Well, I don't know. I certainly hope it does, but it's hard to even talk about "hundreds of launches per year" while sounding realistic in any way. So, we'll see.

So yeah, safety is no problem if anything goes anywhere near planned. We just have to worry about how well reuse works, and if that woks, everything else does too IMO.

 

Edited September 30, 2019 by ThatGuyWithALongUsername