Author Topic: Abort options for Starship and Starship/SuperHeavy  (Read 252115 times)

Offline Barley

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Re: Abort options for Starship and Starship/SuperHeavy
« Reply #920 on: 05/29/2023 01:41 pm »
What is worst case scenario for the starship stack on ascend?
There is no such thing as a worst case, it can always be worse.  A hole in and collapse of a StarShip (second stage) methane tank is worse than a Super Heavy (first stage) failure you give as a worse case.
Airliner analogy to this is wing could fall off. Is it deadly? yes if you are not f15. Is in frequent? No.
If you add probability to equation worst case start to appear as the severity*probability entity
Once you're using probabilities you should be open to cases were the probability is so low you don't have to deal with them, and the likelihood that the best way to deal with some issues is to address the probability rather than the severity.  It's a framework that allows "make the system so reliable it doesn't need an escape system" rather than "It must have an escape system".  At the very least it means you need the probabilities to justify an escape system.

Of course you need to assess the probabilities, but SS could make it possible to acquire enough empirical data to be significantly safer than the calculated bounds for prior systems.

Offline Robotbeat

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Re: Abort options for Starship and Starship/SuperHeavy
« Reply #921 on: 05/29/2023 09:46 pm »
I would imagine that’s the framework you’d always want to use.

You do need to be careful about how you assign probabilities, though. I really think that a lot of shuttle analyses far too optimistic. where possible, use empirical data to determine probabilities. And where not possible, use analysis and conservative assumptions.

Shuttle shouldn’t have had crew on it for the first several dozen launches. They only put ejection seats on the first few flights and then immediately removed them. If you want to put crew on early flights, you should have to use a launch abort system. But if you are willing to launch the thing 100 flights or 1000 flights, then a launch abort system may not be required. There’s no point in requiring a launch abort system if you can get equivalent safety through some other method… PROVIDED you’re relying primarily on empirically proven safety, not hyper-optimistic analysis.

In fact, I will go further. Launch abort adds risk to a mission. If your ascent is 99.9% survivable without it, then a separate high thrust launch abort system will likely reduce safety.
« Last Edit: 05/29/2023 10:01 pm by Robotbeat »
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Online TheRadicalModerate

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Re: Abort options for Starship and Starship/SuperHeavy
« Reply #922 on: 05/29/2023 10:21 pm »
What is worst case scenario for the starship stack on ascend?
There is no such thing as a worst case, it can always be worse.  A hole in and collapse of a StarShip (second stage) methane tank is worse than a Super Heavy (first stage) failure you give as a worse case.
Airliner analogy to this is wing could fall off. Is it deadly? yes if you are not f15. Is in frequent? No.
If you add probability to equation worst case start to appear as the severity*probability entity

All launches have one of four outcomes:

1) Success.
2) Loss of mission and payload.
3) Loss of mission (payload survives abort).
4) Loss of crew.

If you're constructing a failure tree, which type of outcome is obvious for the scenario against which you're running the tree.

What you're thinking of as "severity" is really better framed as, "How many downstream outcomes are failures if this particular component fails?"  But that's a property that only emerges as you run through the tree.  What you're really looking for is the probability that a particular chain of failures leads to a bad outcome.  To figure that out, you need to know the probability of failure of all the components along the path to the outcome.

So when you ask, "What's the worst case outcome on ascent?" the answer is obvious:  the crew dies.  The real question is, "What's the condition that's most likely to kill the crew?"  On ascent, that's almost always when the vehicle blows up on the pad.  There are several reasons for that:

1) Most systems fail at startup, and most components start up on the pad.  So it has one of the highest rates of catastrophic failure.

2) Because of shockwaves reflected off the ground, the severity of overpressure on crew-critical areas is greatest.

3) Separating and accelerating away from an exploding vehicle is most difficult when the whole stack is static, and you have maximal gravity losses.

Re: Abort options for Starship and Starship/SuperHeavy
« Reply #923 on: 05/30/2023 12:41 am »
To match motorcycles you can have 30 fatalities per 100 million miles travelled. So around 4000 orbits. Or 250 days in orbit continuously.

Or a fatality every 10 days.

That seems achievable.

I was wondering what the fatality rate was at the dawn of commercial aviation. I don't think life is as cheap now as it was then, but I think it's still a useful comparison point.

Finding the stats is actually a little tricky, but seems there were 40-odd crashes a year in the late 1940s, at a time when about a million passengers were being carried a year on planes with a capacity of ~20 people.

Overall that's a crash/flight rate of .1%, or 1000 micromorts per flight.

Turns out that's a bit below the micromorts for climbing Matterhorn, so 1000 micromort/launch feels about right for the threshold of mass economic activity.
« Last Edit: 05/30/2023 12:42 am by andyljones »

Offline MichaelBlackbourn

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Re: Abort options for Starship and Starship/SuperHeavy
« Reply #924 on: 05/30/2023 01:29 am »
That’s twice as safe as wingsuits!

Offline Lee Jay

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Re: Abort options for Starship and Starship/SuperHeavy
« Reply #925 on: 05/30/2023 01:52 am »
I was wondering what the fatality rate was at the dawn of commercial aviation. I don't think life is as cheap now as it was then, but I think it's still a useful comparison point.

Finding the stats is actually a little tricky, but seems there were 40-odd crashes a year in the late 1940s, at a time when about a million passengers were being carried a year on planes with a capacity of ~20 people.

No, you've made two errors.

First, that's 40-ish crashes per year *globally* but you combined that with domestic only passengers carried.  Second, the million passengers you quoted was per *month*, not per year.

Together, those errors made your calculation wrong by a factor of about 25.

Offline chopsticks

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Re: Abort options for Starship and Starship/SuperHeavy
« Reply #926 on: 05/30/2023 05:05 am »
While comparing Starship to airplanes is useful in some aspects, I think that trying to expect the same safety rating is simply untenable and frankly unrealistic. Passenger air travel is statistically the safest way of any kind of travel, period. There is no way that a rocket is ever going to be that safe, it's just not going to happen. Not just with Starship, with or without an abort system, but with any sort of space travel. It's just inherently more unsafe in a myriad of ways. You can't get around this. In a spacecraft you have a few centimeters of material separating you from certain death, while having to rely on life support systems to keep you breathing and not burning or freezing, plus adequate TPS to keep you from becoming plasma on the back home. And that's before you trying figure how you're going land your craft in one piece.

When it comes to ranking safety for paying passengers, we really don't have a lot of options for comparison.

There's air travel, rail, bus, taxi, ship/boat/ferry, what else might I be missing? I'm not including personal vehicles or motorcycles since you are in control or your own safety (for the most part anyway), just on ways the general public can pay a fare to get from one point to another via a paid service. All terrestrial modes of transit are quite safe comparatively speaking, so with rocket travel we are really in uncharted territory if we're talking about the paying public.

Personally, I think it should be treated on its own merits with a higher risk tolerance. There are just way more things to go wrong on a space vehicle, and this should be considered and accepted before purchasing your fare. Whether this is Starship with or without an abort mode, or any other future human space vehicle in the pipeline.

I don't think it helps that SpaceX and Elon Musk often make comments like "imagine if you had to throw away a 747 after every flight". In this case, in my opinion, people subconsciously start equating rockets to airplanes when really it's a pretty apples to oranges comparison. I think some of this comparison has leaked over here, and I'm not sure how helpful it is. Just my 2 cents.

Offline Robotbeat

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Re: Abort options for Starship and Starship/SuperHeavy
« Reply #927 on: 05/30/2023 05:44 am »
The goal is to improve the cadence and reliability to the point that the comparison IS fairly valid.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline CJ

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Re: Abort options for Starship and Starship/SuperHeavy
« Reply #928 on: 05/30/2023 07:52 am »
If a Starship is damaged and/or having control issues, landing back at the launch site on the chopsticks might not be feasible. One abort option that IMHO would be worth looking onto is a water landing, and also a land-landing mode.

As I recall, Elon mentioned the "bouncy castle" approach for a landing option a couple of years ago; my guess is it would be a large inflatable rectangle with blow-out panels, to allow a horizontal landing. That IMHO, if feasible, would be a good emergency option at the launch site (assuming it could be inflated very quickly, so only inflated in case of need). 

The second abort option *might* be a water landing. I suspect SpaceX might be thinking along these lines, and that might be one of the reasons why the test flight plan was for no landing burn off Hawaii; in part to see what a horizontal water landing (more likely at a very shallow angle to the water, not flat) does to a Starship. It it turns out that the damage and impact G forces are within a range that might make it plausible that a crew  would survive, then that's an emergency abort option if RTLS or a landing burn isn't possible (such as due to engine damage).

Would anyone happen to know the approximate speed of decent on the Starship hops just prior to the landing burn ignition?


Offline Corey Mandler

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Re: Abort options for Starship and Starship/SuperHeavy
« Reply #929 on: 05/30/2023 10:43 am »
When will Starship fly a million times? It’ll take longer than that to prove 1 in a million reliability, but at least it becomes numerically possible.
If it takes giving each flip and burn engine it's own header tanks, it will be done to get the reliability needed.
well that might be the answer to all our flippin problems

Offline chopsticks

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Re: Abort options for Starship and Starship/SuperHeavy
« Reply #930 on: 05/30/2023 12:34 pm »
The goal is to improve the cadence and reliability to the point that the comparison IS fairly valid.

Sure, but my point is that that goal is unrealistic.

Offline woods170

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Re: Abort options for Starship and Starship/SuperHeavy
« Reply #931 on: 05/30/2023 01:04 pm »
The goal is to improve the cadence and reliability to the point that the comparison IS fairly valid.

Sure, but my point is that that goal is unrealistic.

You forgot "IMO".

Offline Lee Jay

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Re: Abort options for Starship and Starship/SuperHeavy
« Reply #932 on: 05/30/2023 01:35 pm »
The goal is to improve the cadence and reliability to the point that the comparison IS fairly valid.

Sure, but my point is that that goal is unrealistic.

Right.  With hard work and a lot of flights, that might be able to take us from 5 orders or magnitude worse than an airliner down to 4 orders of magnitude worse.  But not 1 or 0.

Offline Lee Jay

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Re: Abort options for Starship and Starship/SuperHeavy
« Reply #933 on: 05/30/2023 01:43 pm »
I don't think it helps that SpaceX and Elon Musk often make comments like "imagine if you had to throw away a 747 after every flight". In this case, in my opinion, people subconsciously start equating rockets to airplanes when really it's a pretty apples to oranges comparison. I think some of this comparison has leaked over here, and I'm not sure how helpful it is. Just my 2 cents.

It's not subconsciously.  SpaceX put out this video.  What does this look like to you?  To me, it looks like going to an airport, getting on a train to a terminal, walking out a jetway to get on an airliner, and flying to your destination.  It's this sort of nonsense that leads people to think of Starship as an airliner - because SpaceX explicitly said so.  It's the same sort of thing thing that leads people to think Tesla's can drive themselves - the name of the service, "full self driving", which it isn't.

If you're going to claim the same conops as an airliner, it needs to be as safe as an airliner, which you correctly state is unrealistic.

"Starship will be capable of taking people from any city to any other city on Earth in under one hour."

Offline chopsticks

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Re: Abort options for Starship and Starship/SuperHeavy
« Reply #934 on: 05/30/2023 02:16 pm »
The goal is to improve the cadence and reliability to the point that the comparison IS fairly valid.

Sure, but my point is that that goal is unrealistic.

You forgot "IMO".

No I didn't. I'm sorry, but if you believe that rocket travel/space travel can become as safe or routine as commercial air travel, I don't know what to tell you. It's orders of magnitude more complex and way more things to go wrong with far fewer redundancies.

Offline chopsticks

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Re: Abort options for Starship and Starship/SuperHeavy
« Reply #935 on: 05/30/2023 02:18 pm »
I don't think it helps that SpaceX and Elon Musk often make comments like "imagine if you had to throw away a 747 after every flight". In this case, in my opinion, people subconsciously start equating rockets to airplanes when really it's a pretty apples to oranges comparison. I think some of this comparison has leaked over here, and I'm not sure how helpful it is. Just my 2 cents.

It's not subconsciously.  SpaceX put out this video.  What does this look like to you?  To me, it looks like going to an airport, getting on a train to a terminal, walking out a jetway to get on an airliner, and flying to your destination.  It's this sort of nonsense that leads people to think of Starship as an airliner - because SpaceX explicitly said so.  It's the same sort of thing thing that leads people to think Tesla's can drive themselves - the name of the service, "full self driving", which it isn't.

If you're going to claim the same conops as an airliner, it needs to be as safe as an airliner, which you correctly state is unrealistic.

"Starship will be capable of taking people from any city to any other city on Earth in under one hour."

I wonder if SpaceX / Elon Musk would still stand by this video? It's pretty old by now.

Offline JamesH65

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Re: Abort options for Starship and Starship/SuperHeavy
« Reply #936 on: 05/30/2023 03:09 pm »
The goal is to improve the cadence and reliability to the point that the comparison IS fairly valid.

Sure, but my point is that that goal is unrealistic.

You forgot "IMO".

No I didn't. I'm sorry, but if you believe that rocket travel/space travel can become as safe or routine as commercial air travel, I don't know what to tell you. It's orders of magnitude more complex and way more things to go wrong with far fewer redundancies.

I see this more complex claim a lot. With very little to explain why.

So, why is it more complex? Why is it orders of magnitude more complex?

For example, rocket engines probably have fewer moving parts, but run at higher temperatures, that a modern turbofan. There's a trade off there, but as material technology improves, rocket engines could become just as reliable as jet engines. Is there some fundamental law of physics that means a rocket engine (effectively a well controlled deflagration, just like, for examples, an ICE) cannot be made as reliable as a modern jet engine? How do you get to orders of magnitude complexity more than airliners?
« Last Edit: 05/30/2023 03:11 pm by JamesH65 »

Online volker2020

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Re: Abort options for Starship and Starship/SuperHeavy
« Reply #937 on: 05/30/2023 03:21 pm »
The goal is to improve the cadence and reliability to the point that the comparison IS fairly valid.

Sure, but my point is that that goal is unrealistic.

You forgot "IMO".

No I didn't. I'm sorry, but if you believe that rocket travel/space travel can become as safe or routine as commercial air travel, I don't know what to tell you. It's orders of magnitude more complex and way more things to go wrong with far fewer redundancies.

Sorry, you have to be a little bit more specific. Steam Engines did break a lot more often than modern trains, but they have been much simpler. The first generation of aircraft had been much less reliable, even though they have been simpler.

Rockets are high energy events and look surely quite scary, but for a statement like yours you have to detail, which error paths can not be migrated.
Sure a rupture of the hull is game over. But what makes you think, that a rupture has to happen at some point. What makes you certain, that given close inspections it is impossible to develop a rocket that will not rupture. Without going into detail, sorry, it is only IMHO.

Offline Robotbeat

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Re: Abort options for Starship and Starship/SuperHeavy
« Reply #938 on: 05/30/2023 03:28 pm »
The goal is to improve the cadence and reliability to the point that the comparison IS fairly valid.

Sure, but my point is that that goal is unrealistic.

Right.  With hard work and a lot of flights, that might be able to take us from 5 orders or magnitude worse than an airliner down to 4 orders of magnitude worse.  But not 1 or 0.
I think 1-2 is feasible.

To get to the same safety as airliners for long haul flight, Starship needs to get to one in a million survivability. Falcon is around 1:200-250 right now. It could conceivably get to 1:1000 before retiring (this is plausible given how reliable Merlin has been in the last 100-120 flights). Starship would need to get to 1:10,000 to get within 2 orders of magnitude (about on par with general aviation), or an order of magnitude better than Falcon 9 could conceivably be, and that’s doable if it gets to multiple launches per day on average. If it gets to one flight per hour on average, it could get to 1:100,000, or within an order of magnitude of airliners & better than general aviation (private jets, chartered flights, private aircraft in general).

I think 1:10,000 is actually very plausible in the long term. They need ~2,000 flights just to put up the full Starlink constellation at full weight, so after 5 recycles of that constellation, they could get there (of course, that means no unsurvivable failures…). 1:10,000 is plenty good enough for air freight and even good enough for chartered Earth to Earth flights. That could further increase the flightrate to enough to get to within an order of magnitude of airliner safety.
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To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline chopsticks

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Re: Abort options for Starship and Starship/SuperHeavy
« Reply #939 on: 05/30/2023 03:33 pm »
The goal is to improve the cadence and reliability to the point that the comparison IS fairly valid.

Sure, but my point is that that goal is unrealistic.

You forgot "IMO".

No I didn't. I'm sorry, but if you believe that rocket travel/space travel can become as safe or routine as commercial air travel, I don't know what to tell you. It's orders of magnitude more complex and way more things to go wrong with far fewer redundancies.

I see this more complex claim a lot. With very little to explain why.

So, why is it more complex? Why is it orders of magnitude more complex?

For example, rocket engines probably have fewer moving parts, but run at higher temperatures, that a modern turbofan. There's a trade off there, but as material technology improves, rocket engines could become just as reliable as jet engines. Is there some fundamental law of physics that means a rocket engine (effectively a well controlled deflagration, just like, for examples, an ICE) cannot be made as reliable as a modern jet engine? How do you get to orders of magnitude complexity more than airliners?

I already mentioned a few of them without even mentioning rocket engines (that's just one piece of the puzzle): "In a spacecraft you have a few centimeters of material separating you from certain death, while having to rely on life support systems to keep you breathing and not burning or freezing, plus adequate TPS to keep you from becoming plasma on the back home. And that's before you trying figure how you're going land your craft in one piece."

Those are all things that no other method of transport has to deal with. More things to go wrong, etc. In regards to rocket engines, there has been debate about this here already and I think in general the concesus is that rocket engines are a bit more complex all things considered. But you can argue both ways reasonably well I think.

An airliner for example has the advantage of diving down to a low enough altitude if it loses pressurisation. If it loses an engine during flight, it can usually still fly to an airport to land. If it loses both engines, it's bad, but even then airliners have glided to a safe landing. In contrast, with human spaceflight, everything has to go right or else the crew dies (broadly speaking). There's a reason why people say "space is hard". And this is the reason why we have abort systems - rockets are dangerous and space is hard. Starship with no abort system is essentially betting on success. We'll see how it pans out.


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