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SpaceX Vehicles and Missions => SpaceX Reusability => Topic started by: bioelectromechanic on 11/01/2013 06:08 pm

Title: Reusability as abort functionality
Post by: bioelectromechanic on 11/01/2013 06:08 pm
I was thinking a F9R could use it's ability to land to abort a failed launch.
E.g if an F9R suffers an early stage engine loss, or later double engine loss.
What would be needed to be done to allow it to land with a 2nd stage plus payload on top?

My first thought was it needs to vent a huge amount of propellant to avoid overloading the legs during landing.
Title: Re: Reusability as abort functionality
Post by: Kabloona on 11/01/2013 06:21 pm
I was thinking a F9R could use it's ability to land to abort a failed launch.
E.g if an F9R suffers an early stage engine loss, or later double engine loss.
What would be needed to be done to allow it to land with a 2nd stage plus payload on top?

My first thought was it needs to vent a huge amount of propellant to avoid overloading the legs during landing.

Land where? On the ocean? Because it can't return to the launch site at that point. And anyway, an abort for a "failed launch" is going to result in flight termination. That's what the "red button" is for, and the addition of legs isn't going change range safety protocol.
Title: Re: Reusability as abort functionality
Post by: Jason1701 on 11/01/2013 06:26 pm
Jim will say that satellites are not designed to survive the loads that would be encountered during an abort.
Title: Re: Reusability as abort functionality
Post by: Jim on 11/01/2013 06:29 pm
I was thinking a F9R could use it's ability to land to abort a failed launch.
E.g if an F9R suffers an early stage engine loss, or later double engine loss.
What would be needed to be done to allow it to land with a 2nd stage plus payload on top?

My first thought was it needs to vent a huge amount of propellant to avoid overloading the legs during landing.

It is a non starter. It would need stronger legs for the added weight of upperstage, payload and fairing.   Vent is a misnomer.  It has to get rid of the propellant fast and guess what?  It can't get rid of it faster than burning it through the engines.  That includes the upperstage propellant.  And then there is  the spacecraft.  Not to mention the that whole vehicle has to be able to take the new aeroloads from the pitch around maneuver.  That means strengthened interstage and fairing.  Also, there now is a live payload, with toxic and hazardous propellant onboard with no ability to command it if using current conops (typically, there is no electrical or rf interaction between spacecraft and LV except for breakwires, and maybe some occasion discreets )

This would require a whole redesign of the vehicle
Title: Re: Reusability as abort functionality
Post by: Lar on 11/01/2013 07:05 pm
Maybe some large number of years from now aborts like this might actually be possible.

Right now payloads and launch costs are fairly similar... it's rare that one is an order of magnitude more than the other (JWST perhaps being one of those rarities) But consider what it would be like if launch costs are 100 USD/kg ... at that point, payloads are worth so much more than the launch that designing for abort becomes more economical....

Jim's response, just above, lists off a lot of the issues that would need to be dealt with.... what other issues would there be? Developing a list of such issues might be a good exercise.
Title: Re: Reusability as abort functionality
Post by: TrevorMonty on 11/02/2013 10:56 am
The only option is for the 2nd stage to separate and try to land with the payload. I doubt it is viable, as the 2nd stage would need to burn most of its fuel before attempting a landing. Then it would be top heavy, making control difficult if not impossible.

Title: Re: Reusability as abort functionality
Post by: TrevorMonty on 11/02/2013 11:02 am
Just had another thought on this, if payload was a Dragon and it landed separately then maybe it is possible. For all stages to survive the rocket would need to reduce its speed, before separate of the individual stages.
Title: Re: Reusability as abort functionality
Post by: eriblo on 11/02/2013 11:38 am
As previous posters have concluded: Asking a reusable multi-stage LV to perform an intact abort is to ask it to do something which is several times harder than a normal launch - after a failure has already made it impossible for it to do that...  ::)

Saving the payload is already done for crew and might be doable for more fragile satellites, but saving the entire LV is probably only possible/worth it for SSTO (especially space planes).
Title: Re: Reusability as abort functionality
Post by: Avron on 11/02/2013 02:50 pm
As previous posters have concluded: Asking a reusable multi-stage LV to perform an intact abort is to ask it to do something which is several times harder than a normal launch - after a failure has already made it impossible for it to do that...  ::)

Saving the payload is already done for crew and might be doable for more fragile satellites, but saving the entire LV is probably only possible/worth it for SSTO (especially space planes).

I think that the best way to use the existing technology is via  redundancy, If part of the re-usability provides redundancy then it can be used, however, when one has had multiple failures to a point where the redundant streams have failed, its time to press the red button and use the abort system built into say Dragon if applicable. If there is no built in abort system and one has had so many failures that the redundant systems have not been able to cope, one askes the question, does one really want that vehicle flying back on any half baked string..




Title: Re: Reusability as abort functionality
Post by: Ben the Space Brit on 11/02/2013 03:31 pm
When a civil airliner performs an ATLS (Abort to Launch Site) equivalent, the big problem is that it really weighs too much to land safely, so they have to jettison most of the fuel. Similarly, any attempt to modify the core return equipment to allow for a ATLS would require for the vehicle to dump most of its propellent. There are probably several serious safety issues, especially if it is done close to the pad. That amount of RP1/LCH4 and LOX being vented in the air around a hot launch pad and an even hotter exhaust flame? That spells "catastrophic burn-off".

Then there is the question of repositioning the vehicle over the landing pad and carrying out a controlled descent.  This would raise issues about stabilising the now top-heavy stack during translate and hover before descent.

Overall, it's far from impossible but would be a complex process to develop and prove. It certainly isn't a capability that I'd want available from the outset as it would lead to delays and unnecessary expenses.
Title: Re: Reusability as abort functionality
Post by: douglas100 on 11/02/2013 06:44 pm

...Overall, it's far from impossible but would be a complex process to develop and prove. It certainly isn't a capability that I'd want available from the outset as it would lead to delays and unnecessary expenses.

If you're talking specifically about F9R as per the original poster, then I disagree. It is impossible for the current vehicle to recover  a standard payload (not Dragon of course) after launch commit.

As whether it will be developed in a future vehicle, you rightly point out how difficult it would be for a multistage LV. If it were technically possible it would inevitably eat payload margin.

So the first question should be "who wants this capability?"
Title: Re: Reusability as abort functionality
Post by: Heinrich on 11/02/2013 07:34 pm
What about a TAL-style abort? Complete the S1 burn. Due to the engine failure the vehicle can't reach the desired orbit anymore. Do stage separation, and let the second stage do the breaking and landing burns towards a downrange location. (let's hpothetically assume this downrange location is available...)

One drawback I see is that the second stage would be able to land with its engine, but with the payload still on top it will be heavier...
Title: Re: Reusability as abort functionality
Post by: Lars_J on 11/02/2013 07:46 pm
These kinds of intact aborts won't be possible until we have reusable SSTOs.
Title: Re: Reusability as abort functionality
Post by: LouScheffer on 11/02/2013 08:15 pm
If you want intact recovery upon abort, rather than fiddle with the rocket, it might be better to replace the fairing with a giant capsule-ish construction.  If something goes wrong, it separates from the rocket, then descends with heat shields, parachutes, and maybe last-second retrorockets.  If all goes right it splits in half and releases the payload.

Sure it's big and heavy, but if cost to orbit is cheap and the payload is expensive it could easily be worth it.  Also it has no dependence on the rocket, which is already known to have problems if you are trying an abort

Depending on the loads the payload can endure, it might provide protection throughout the launch (as crew capsules do), or just a subset of possible failures.  It almost surely has a better chance at recovery than depending on the rocket, since any case where the rocket is still even partially functional would allow a low-stress separation.
Title: Re: Reusability as abort functionality
Post by: CuddlyRocket on 11/03/2013 06:59 am
The answer is an obvious 'yes' despite the suggestions of the apparently more conservative members of the engineering fraternity. Any rocket that is, or some or all of its parts are, reusable is potentially recoverable (at least in part) in abort scenarios. What is needed is to analyse which scenarios are both achievable - taking into account safety considerations - and economically desirable.

We have to remember that current launch and range safety protocols have been developed under the assumption that once launch is commenced no part of the launcher is going to come back. Once you have LoM, it makes no difference precisely when the launcher or its parts are destroyed, whether deliberately or by catastrophic failure or impact. When the launcher of parts thereof is recoverable it certainly does make a difference; there's valuable equipment at stake! No one is going to be happy if a multi-million dollar piece of equipment is needlessly abandoned or destroyed (except the lawyers, perhaps).

Safety comes first. But some failures are perfectly safe! Lots of launchers have failed without engaging safety protocols (usually because the launcher is by then sufficiently high up and out to sea). Are there failure scenarios that don't require safety action (i.e. blowing up the launcher), or at least not immediate action? I think there are.

There are three main types of failure scenarios: Catastrophic, out of control (usually directional) and under control (usually loss of one or more engines in a multi-engine stage). Catastrophic tends to speak for itself; but even here there is potential for recovery. After all, a manned Dragon is designed to be recoverable under all scenarios, so a cargo Dragon is presumably potentially recoverable as well. And not just the capsule, there's also its cargo. Even if it has to be recovered from the ocean. Satellites are a different matter, as you'd have to design a kind of fairing that contains parachutes and will stay intact for an ocean landing etc; this involves weight penalties unless the launcher is drastically over-powered for the mission. And the satellite might not survive the loading, although it might be repairable (again, current protocols are based on the idea that if the satellite breaks there's no repair opportunity).

If the first stage catastrophically fails, it might be possible to fire the second stage early, thereby potentially recovering it. The question would be when to detach the payload, immediately or after a delay. (For a manned payload, this would almost certainly be immediately.) This might depend on whether the second stage has T/W>1 or not.

An out-of-control failure is basically a catastrophic failure with more time. One consideration is whether the loss of control means the launcher is heading in a dangerous direction or not. If not (for instance it's heading out to sea), the range officer won't need to blow it up!

An in-control failure (for instance loss of four engines on an F9 first stage), gives much more opportunity for recovery. The main problem is burn off of propellant, because it's unlikely that any landing system for a launcher or component will be robust enough to handle much more than the empty weight. If you have control, you can just fly around of course - maybe simply pogoing up and down - though you may be limited for how long you can do this by supplies of attitude control thruster propellant.

I think planning for some of these scenarios is going to happen sooner than some might think. Basically, as soon as it becomes clear that the F9 first stage is recoverable. If there was a launch where four engines failed, SpaceX is going to want to try and recover the first stage (assuming the centre engine isn't one of them!). You'd simply keep the engines firing to burn off the propellant; launch the second stage and then try to land!
Title: Re: Reusability as abort functionality
Post by: KelvinZero on 11/03/2013 10:05 am
So recovery looks pretty difficult if it is not dragon and already designed to land with payload.

This is a bit of a flakey idea, but could the second stage drop the payload say 10 meters over a body of water and then return to shore?
Title: Re: Reusability as abort functionality
Post by: Lee Jay on 11/03/2013 01:18 pm
Isn't this exactly what a Shuttle RTLS was?
Title: Re: Reusability as abort functionality
Post by: douglas100 on 11/03/2013 03:57 pm
The Shuttle didn't dump the payload for RTLS.
Title: Re: Reusability as abort functionality
Post by: douglas100 on 11/03/2013 04:27 pm

...I think planning for some of these scenarios is going to happen sooner than some might think. Basically, as soon as it becomes clear that the F9 first stage is recoverable. If there was a launch where four engines failed, SpaceX is going to want to try and recover the first stage (assuming the centre engine isn't one of them!). You'd simply keep the engines firing to burn off the propellant; launch the second stage and then try to land!

I don't think planning for the kind of failure you cite is worth it. Losing four engines is very unlikely. Instead the effort should go into improving the reliability of the vehicle so aborts become less likely in the first place.

The correct way to go in the event of first stage engine failure is to abort the first stage recovery sequence to recover the margin needed to allow the second stage and payload to achieve orbit.
Title: Re: Reusability as abort functionality
Post by: Lar on 11/03/2013 04:44 pm
The correct way to go in the event of first stage engine failure is to abort the first stage recovery sequence to recover the margin needed to allow the second stage and payload to achieve orbit.

Today. And in the near future too. But if Musk's vision materializes, economics would change. I think it interesting to explore what happens if they do change.   

By analogy we don't typically sacrifice cargo aircraft in order to deliver the cargo, they abort to somewhere and get fixed and try again.  Right now rockets are NOTHING like that. But what if they were? What changes would need to happen?
Title: Re: Reusability as abort functionality
Post by: Silmfeanor on 11/03/2013 05:14 pm
perhaps this should be moved to advanced concepts?
because we are talking about 10+ years here, for sure.
Title: Re: Reusability as abort functionality
Post by: CuddlyRocket on 11/03/2013 05:34 pm
perhaps this should be moved to advanced concepts?
because we are talking about 10+ years here, for sure.

No we're not. Once first stage reusability is demonstrated (which I think will be in the near future), it becomes obvious to ask whether there would be circumstances in which a launcher failure involved LoM but where the first stage is recoverable. If the answer is yes, it's sensible to plan for such situations - the first stage is a piece of equipment costing millions of dollars, even in the rocket industry you don't throw such things away unnecessarily.


...I think planning for some of these scenarios is going to happen sooner than some might think. Basically, as soon as it becomes clear that the F9 first stage is recoverable. If there was a launch where four engines failed, SpaceX is going to want to try and recover the first stage (assuming the centre engine isn't one of them!). You'd simply keep the engines firing to burn off the propellant; launch the second stage and then try to land!

I don't think planning for the kind of failure you cite is worth it. Losing four engines is very unlikely. Instead the effort should go into improving the reliability of the vehicle so aborts become less likely in the first place.

Unlikely things happen! (And there may be other more likely causes of LoM; a four-engine failure was something I came up with off the top of my head.) But it's a question of economics; efforts in improving reliability run into diminishing returns, at some point there is a crossover as to where further resources should be spent. No doubt someone will run the figures. But SpaceX has a Silicon Valley mindset, part of which is the Japanese concept of kaizen or continuous improvement. And the F9 is a research and development vehicle as much as an operational one; best to learn how to do these things before moving on to bigger and more valuable launchers!

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The correct way to go in the event of first stage engine failure is to abort the first stage recovery sequence to recover the margin needed to allow the second stage and payload to achieve orbit.
Really? Or is this another of those items of received wisdom developed in an era of expendable launchers? For example, if it's a cargo Dragon, the first stage could be worth more than the second stage, capsule and cargo combined! Given that the Dragon and cargo are probably recoverable as well, would it not make financial sense to abort the mission; recover the first stage and relaunch the cargo later? (If the payload is a satellite, the opposite might well be true, but horses for courses.)
Title: Re: Reusability as abort functionality
Post by: meekGee on 11/03/2013 06:07 pm
My 2c on this often discussed topic:

For a VTVL system, landing involves much the same systems as launch.  So if the launch is not going to plan, odds are that landing is not going to be possible - even if such an idea was entertained at design time.

On top of that, making it even theoretically possible requires that several systems be beefed up (in particular the legs) and so for that very narrow set of circumstances where such recovery can be entertained, you'd be paying a mass penalty on each and every flight.

So no, IMO this is not a good idea.
Title: Re: Reusability as abort functionality
Post by: Lars_J on 11/03/2013 07:25 pm
Exactly - it is not practical until we have gas-n-go RLV's which launch from their own legs.
Title: Re: Reusability as abort functionality
Post by: llanitedave on 11/03/2013 07:29 pm
perhaps this should be moved to advanced concepts?
because we are talking about 10+ years here, for sure.

No we're not. Once first stage reusability is demonstrated (which I think will be in the near future), it becomes obvious to ask whether there would be circumstances in which a launcher failure involved LoM but where the first stage is recoverable. If the answer is yes, it's sensible to plan for such situations - the first stage is a piece of equipment costing millions of dollars, even in the rocket industry you don't throw such things away unnecessarily.


...I think planning for some of these scenarios is going to happen sooner than some might think. Basically, as soon as it becomes clear that the F9 first stage is recoverable. If there was a launch where four engines failed, SpaceX is going to want to try and recover the first stage (assuming the centre engine isn't one of them!). You'd simply keep the engines firing to burn off the propellant; launch the second stage and then try to land!

I don't think planning for the kind of failure you cite is worth it. Losing four engines is very unlikely. Instead the effort should go into improving the reliability of the vehicle so aborts become less likely in the first place.

Unlikely things happen! (And there may be other more likely causes of LoM; a four-engine failure was something I came up with off the top of my head.) But it's a question of economics; efforts in improving reliability run into diminishing returns, at some point there is a crossover as to where further resources should be spent. No doubt someone will run the figures. But SpaceX has a Silicon Valley mindset, part of which is the Japanese concept of kaizen or continuous improvement. And the F9 is a research and development vehicle as much as an operational one; best to learn how to do these things before moving on to bigger and more valuable launchers!

Quote
The correct way to go in the event of first stage engine failure is to abort the first stage recovery sequence to recover the margin needed to allow the second stage and payload to achieve orbit.
Really? Or is this another of those items of received wisdom developed in an era of expendable launchers? For example, if it's a cargo Dragon, the first stage could be worth more than the second stage, capsule and cargo combined! Given that the Dragon and cargo are probably recoverable as well, would it not make financial sense to abort the mission; recover the first stage and relaunch the cargo later? (If the payload is a satellite, the opposite might well be true, but horses for courses.)

Unlikely things happen, but once life and limb are protected, sometimes its more economical just to eat the loss of the unlikely things and just concentrate on continually making them less likely.
Title: Re: Reusability as abort functionality
Post by: go4mars on 11/03/2013 10:22 pm
(If the payload is a satellite, the opposite might well be true, but horses for courses.)
That's apt cuddly!  Give horses a few days in low gravity, then race them around the circumference.  My kind of future.  Cheers.
Title: Re: Reusability as abort functionality
Post by: douglas100 on 11/04/2013 08:58 am

Really? Or is this another of those items of received wisdom developed in an era of expendable launchers?

Yes, really. And it isn't "received wisdom." It's common sense as opposed to wishful thinking.

F9R in its presently conceived form (even with recovery of both stages) cannot recover the payload in the event of an abort. To put any effort into abort scenarios when you are going to lose the payload is waste of effort. The effort should go into increasing reliability so the possibility of abort is reduced in the first place. (And that makes it more likely you're going to recover the first stage successfully too.)

Payload abort recovery is a capability for a future vehicle. So we are talking about something which should be in advanced concepts.
Title: Re: Reusability as abort functionality
Post by: Jcc on 11/04/2013 10:21 am
Or Skylon.
Title: Re: Reusability as abort functionality
Post by: CraigLieb on 11/04/2013 03:29 pm
Crazy idea number 37:
We seem to assume that a fully-loaded complete stack can't be supported by legs in an abort and CG issues would cause control and tip-over issues. What if there was a specially prepared pit with appropriate fire resistant, padded material (think deep ball pit for the kids play area at pizza joint)?

The pit would have to be deep enough and wide enough to allow a landing vehicle to decend possibly half way up the stack into it and then essentially either rest on the bottom on those legs, or tip to the side somewhat as the legs gave way. The pit would have to have side materials that could support the weight of the stage gently, or mechanisms for gently closing as the stage descends.  This way, legs don't have the whole job to support the recovered vehicle.  This would only be an emergency contingent. I don't know if any stage recoverd in this way would be usable again, maybe just the engines. In addition,  the sides of any pit (in a tip-over) would press against the vehicle 1st stage, and that creates new stresses for which the vehicle isn't designed.  Is that enough to kill the idea?
Title: Re: Reusability as abort functionality
Post by: Lars_J on 11/04/2013 03:37 pm
Are you serious?
Title: Re: Reusability as abort functionality
Post by: AJA on 11/04/2013 03:53 pm
Crazy idea number 37:

LOL.. Entertaining the thought for a second... the "pit" can be the sea. A fully loaded Falcon 9 (either v1.0/ v1.1) - with maximum payload - still has a relative density of (505846 kg+13150 kg)/(pi*((3.7 m/2)^2)*(68.4 m)) ~= 0.7
Title: Re: Reusability as abort functionality
Post by: mlindner on 11/05/2013 12:39 am
Why are we discussing this? This is impossible. A rocket that has a design with legs rated for a full vehicle load won't be making it to orbit with any reasonable payload. Not to mention that after any kind of flight path is flown, returning to launch site becomes impossible because of lack of fuel. Not to mention if a flight path change is attempted while in the atmosphere the vehicle will break up.

Early abort - too heavy
Mid abort - too much dynamic atmospheric pressure from velocity
Late abort - not enough fuel to return
Very late abort (upper stage + payload only) - need heat shield on bottom of stage where the engine is

Can we close this?
Title: Re: Reusability as abort functionality
Post by: CuddlyRocket on 11/05/2013 02:29 am

Really? Or is this another of those items of received wisdom developed in an era of expendable launchers?

Yes, really. And it isn't "received wisdom." It's common sense as opposed to wishful thinking.

Being trained as a scientist, I am wary of arguments based on common sense, as they frequently turn out not to be sensible even if common. I gave an argument why it may not be as sensible in this case as you suppose, which you signally failed to address.

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F9R in its presently conceived form (even with recovery of both stages) cannot recover the payload in the event of an abort.

If the payload is a Dragon of course it can as the Dragon is designed to be recoverable in the event of an abort; hence the upcoming abort tests. (Granted, these are on a manned Dragon, but the cargo Dragon is a variant.)

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To put any effort into abort scenarios when you are going to lose the payload is waste of effort. The effort should go into increasing reliability so the possibility of abort is reduced in the first place. (And that makes it more likely you're going to recover the first stage successfully too.)

Why is it an either/or?

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Payload abort recovery is a capability for a future vehicle. So we are talking about something which should be in advanced concepts.

I don't agree with the first sentence. And are different ways of using existing vehicles really advanced concepts?

Why are we discussing this? This is impossible. A rocket that has a design with legs rated for a full vehicle load won't be making it to orbit with any reasonable payload.

Nobody's suggesting this. Well, at least I'm not - I assumed that landing legs would be designed for a nearly empty vehicle. This does mean you'd have to consider whether burn off of excess propellant is possible.

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Not to mention that after any kind of flight path is flown, returning to launch site becomes impossible because of lack of fuel.

That would mean reusability is impossible, which seems at odds with what SpaceX are attempting.

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Not to mention if a flight path change is attempted while in the atmosphere the vehicle will break up.

Best not do it in the atmosphere then. Or reduce speed sufficiently first.

Look, I'm not saying that recovery in an abort is easy; just that it may not be impossible, and if not impossible then it's worth looking at because millions of dollars could be saved.

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Can we close this?

If you're not interested just don't read the thread! Why propose short-circuiting things for other people who may be?
Title: Re: Reusability as abort functionality
Post by: Lars_J on 11/05/2013 04:15 am

Really? Or is this another of those items of received wisdom developed in an era of expendable launchers?

Yes, really. And it isn't "received wisdom." It's common sense as opposed to wishful thinking.

Being trained as a scientist, I am wary of arguments based on common sense, as they frequently turn out not to be sensible even if common. I gave an argument why it may not be as sensible in this case as you suppose, which you signally failed to address.

I don't know where you "trained as a scientist" - but if you have some wild idea that goes against common sense, you should back it up with some evidence, instead of complaining that it is too easily dismissed. The burden of proof is on *you*. And if you cannot back it up... well, there isn't much science in your approach, now is there?

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Payload abort recovery is a capability for a future vehicle. So we are talking about something which should be in advanced concepts.

I don't agree with the first sentence. And are different ways of using existing vehicles really advanced concepts?

What don't you agree with? The F9R will have very thin margins for being able to recover its stages. Therefore any anomaly that reduces performance (and would cause an abort) would eat into the very thin recovery margin. Do you dispute this?

Why are we discussing this? This is impossible. A rocket that has a design with legs rated for a full vehicle load won't be making it to orbit with any reasonable payload.

Nobody's suggesting this. Well, at least I'm not - I assumed that landing legs would be designed for a nearly empty vehicle. This does mean you'd have to consider whether burn off of excess propellant is possible.

And what do you think the most efficient way of burning off or venting propellant is? As others have pointed out, it is through a burning engine. And virtually all aborts will involved a propulsion failure. This will negatively impact your ability to burn off propellant - Do you see a pattern forming?

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Not to mention if a flight path change is attempted while in the atmosphere the vehicle will break up.

Best not do it in the atmosphere then. Or reduce speed sufficiently first.

It sounds rather easy when you put it that way. But aborts are most likely to be caused by two problems - guidance and propulsion. Neither will make what you suggest very plausible.

Look, I'm not saying that recovery in an abort is easy; just that it may not be impossible, and if not impossible then it's worth looking at because millions of dollars could be saved.

Just because it may be theoretically possible in a very few situations (care to provide any?), does not make it practical or useful. I see from your profile that you are from London. Do you have earthquake insurance? If not, why?

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Can we close this?

If you're not interested just don't read the thread! Why propose short-circuiting things for other people who may be?

He gave four abort scenarios, why did you not respond to them?
Title: Re: Reusability as abort functionality
Post by: meekGee on 11/05/2013 04:27 am

...
Why is it an either/or?
...


Cuddly - I'm all for exploring the envelope.

But you have to address the issue of how a sick rocket is able to perform a maneuver that requires the rocket to be healthy.   There's a very narrow set of circumstances that fits this bill.

Consider:

If you have a GNC issue, definitely no RTLS abort today

If you have a structural issue, definitely no RTLS abort today

If you have a steering actuation issue, no dice.

If you're already moving at a significant speed, but are still heavy, the loads involving RTLS abort are higher than a normal launch (inertia, aero loads etc).

If you're not generating enough thrust to ascend (e.g lost 2 engines), then likely you're descending, and so will crash before you pull of the RTLS abort trick.

...

Sso there's only a very very small set of circumstances in which a rocket is unable to achieve orbit, but is healthy enough to perform RTLS abort.  With a deeper look, since rockets don't have a lot of margin, I suspect that set of circumstances is actually empty. 

Also consider - when things are not going well, you don't always know in real time what the root cause is, so you're not in a good position to make a decision on whether it is possible to RTLS without risking your base.

OTOH - it's just a rocket.   If there's a capsule on top, it can abort safely.  If it's a payload, maybe one day it will be able to abort - but probably the mass is not worth it.  Maybe it will be a per-payload decision.     But the rocket itself?  Let it go.  Not worth it.

----

Here, much shorter:

After a pilot ejects, aircraft are not designed to try to land themselves.  This is not because it is technologically impossible.  It is because there was a reason the pilot ejected, and so the plane is most very likely a goner already.
Title: Re: Reusability as abort functionality
Post by: Elmar Moelzer on 11/05/2013 01:23 pm
Hmm, what about recovering only the second stage with the payload in case of a first stage failure. Obviously not as neat as recovering the entire rocket, but maybe more plausible?
Title: Re: Reusability as abort functionality
Post by: Silmfeanor on 11/05/2013 01:36 pm
Hmm, what about recovering only the second stage with the payload in case of a first stage failure. Obviously not as neat as recovering the entire rocket, but maybe more plausible?

Same objections.
The 2nd stage will need to have legs to carry a partially full 2nd stage and a fueled payload.
It will need control authority sufficient for such a load
it will require advanced on-the-fly analysis on the exact weight of the stage, propellant, current trajectory, position, CoG and much more.
It will can't be too heavy, or the M1Dvac will not be able to land; or too late, since it can't return. The throttleability of the M1Dvac needs to be sufficient for the loads and landing, which it normally would never do ( if we assume a very close to empty 2nd stage landing on something like superdracos as normal).

Then there is the issue of thermo and aero dynamics on the payload shroud. A normal 2nd stage would never land with it attached. Thus control issues are even greater. The shroud needs to be strengthened to go through a new environment ( the abort path ).
The same goes for the payload. New paths, new shocks, new environments, new loads.

The set of cases where the 2nd stage can recover payloads to the ground is 0.

All of this eats into the payload mass, into the cost of the rocket, and adds new failure paths. Combined this makes the economic possibility of such a change not worth it  and might even make the flying of the rocket not worth it. For each mission where you want this to be a possibility, you will have additional requirements for the rocket and the payload provider. All of these cost big bucks. So, you have a 95%+ succes rate, and all your flights cost 20% more because of these requirements in mass and engineer analysis.  This causes you to lower your flight rate, etc etc etc.

This discussion, I think, is useless.
It's a bit like taking the following seriously:

Imagine that 2 M1D's crap out on the same side of a F9R. SpaceX can easily add another rings of 8 M1D's halfway up the stage, above the legs. If the lower engines crap out, just ignite the next ring, so you can complete the mission! That way there'll be improved safety margins!

Sure it is possible. It'll just never happen, because it makes no sense. The discussion in this thread is on the same path. Dragon can be aborted because it is designed to reenter anyway.

Remember, this is NSF. More engineering based on real-life rockets, less " but they should totally design for this because i think it's possible".
Title: Re: Reusability as abort functionality
Post by: bob the martian on 11/07/2013 03:43 pm
I was thinking a F9R could use it's ability to land to abort a failed launch.
E.g if an F9R suffers an early stage engine loss, or later double engine loss.
What would be needed to be done to allow it to land with a 2nd stage plus payload on top?

My first thought was it needs to vent a huge amount of propellant to avoid overloading the legs during landing.

Why would you expect to be able to safely land an entire stack on a stage that's undergone multiple engine failures?  The odds of multiple independent engine failures should be infinitesimally low; if more than one engine shreds itself on the same launch, then you almost have to assume something is systemically wrong with the stage and that it is no longer safe to fly.  Not to mention that if you lose the center engine, you're boned on recovery regardless. 

The best-case scenario is recovering the US.  Hopefully it can make the desired orbit (or close enough) on the remaining engines and deploy the payload normally.  Otherwise, it stages early and jettisons the payload (I don't think it will be able to land with the payload and fairing still attached). 

SpaceX have built in a reasonable amount of redundancy in the F9R, but some scenarios are simply unrecoverable. 

Title: Re: Reusability as abort functionality
Post by: bioelectromechanic on 11/09/2013 08:20 pm
I was thinking a F9R could use it's ability to land to abort a failed launch.
E.g if an F9R suffers an early stage engine loss, or later double engine loss.
What would be needed to be done to allow it to land with a 2nd stage plus payload on top?

My first thought was it needs to vent a huge amount of propellant to avoid overloading the legs during landing.

It is a non starter. It would need stronger legs for the added weight of upperstage, payload and fairing.   Vent is a misnomer.  It has to get rid of the propellant fast and guess what?  It can't get rid of it faster than burning it through the engines.  That includes the upperstage propellant.  And then there is  the spacecraft.  Not to mention the that whole vehicle has to be able to take the new aeroloads from the pitch around maneuver.  That means strengthened interstage and fairing.  Also, there now is a live payload, with toxic and hazardous propellant onboard with no ability to command it if using current conops (typically, there is no electrical or rf interaction between spacecraft and LV except for breakwires, and maybe some occasion discreets )

This would require a whole redesign of the vehicle

What about a water recovery, after stage separation?
There might be value in recovering a stage for fault diagnosis and partial reuse.
Title: Re: Reusability as abort functionality
Post by: Jim on 11/09/2013 08:23 pm


What about a water recovery, after stage separation?
There might be value in recovering a stage for fault diagnosis and partial reuse.

Not if it is not designed for water recovery.  Not all failures are graceful.
Title: Re: Reusability as abort functionality
Post by: garidan on 11/09/2013 09:18 pm
What about a water recovery, after stage separation?
There might be value in recovering a stage for fault diagnosis and partial reuse.
It would be nice, if the failure is such to let it possible, switch off the engines less 2-3 and control the whole rocket to go upward to slow down horizontal velocity end then "land" tail first in the ocean, breaking velocity through its 2-3 engines.
Perhaps (?!) the payload could survive and be recovered, and it's the most valuable piece of the rocket...
Title: Re: Reusability as abort functionality
Post by: Jim on 11/09/2013 09:27 pm

Perhaps (?!) the payload could survive and be recovered, and it's the most valuable piece of the rocket...

Fairings aren't watertight and it would be uncontrolled and hazardous
Title: Re: Reusability as abort functionality
Post by: Avron on 11/09/2013 09:49 pm
Reading back on this thread, the use of "reusability as  abort functionality", I guess can best be described as "hazardous".

Even if the payload made it back in one piece, I would doubt that approaching said aborted vehicle could be done is a safe way. 
Title: Re: Reusability as abort functionality
Post by: Robotbeat on 11/10/2013 01:56 am
...reusability as an abort functionality pretty requires redundant recovery mechanisms. And probably some way to dump the propellant.

...which is to say it's likely not worth it.
Title: Re: Reusability as abort functionality
Post by: mlindner on 11/10/2013 04:07 am
It's interesting how arguments continue even when its been accepted that the thing being argued about is impossible.
Title: Re: Reusability as abort functionality
Post by: llanitedave on 11/10/2013 04:29 pm
Not all failures are graceful.

Nice!
Title: Re: Reusability as abort functionality
Post by: Robotbeat on 11/11/2013 02:07 am
It's interesting how arguments continue even when its been accepted that the thing being argued about is impossible.
...impossible isn't accurate. Someday, reusable launch vehicles /will/ have intact abort capability.
Title: Re: Reusability as abort functionality
Post by: meekGee on 11/11/2013 02:20 am
It's interesting how arguments continue even when its been accepted that the thing being argued about is impossible.
...impossible isn't accurate. Someday, reusable launch vehicles /will/ have intact abort capability.

I'll very certain that they won't.
Payloads - maybe.  Maybe some.
Vehicles? I can't see how or why.
Title: Reusability as abort functionality
Post by: Lars_J on 11/11/2013 03:54 am
It's interesting how arguments continue even when its been accepted that the thing being argued about is impossible.
...impossible isn't accurate. Someday, reusable launch vehicles /will/ have intact abort capability.

I'll very certain that they won't.
Payloads - maybe.  Maybe some.
Vehicles? I can't see how or why.

Sigh... People in this thread keep talking across each other with different assumptions (F9R vs future RLV).

And MeekGee, you really cant imagine a future SSTO RLV with intact abort? (That's pretty much what it would take) It seems pretty narrow minded to exclude such a possibility.
Title: Re: Reusability as abort functionality
Post by: meekGee on 11/11/2013 04:30 am
It's interesting how arguments continue even when its been accepted that the thing being argued about is impossible.
...impossible isn't accurate. Someday, reusable launch vehicles /will/ have intact abort capability.

I'll very certain that they won't.
Payloads - maybe.  Maybe some.
Vehicles? I can't see how or why.

Sigh... People in this thread keep talking across each other with different assumptions (F9R vs future RLV).

And MeekGee, you really cant imagine a future SSTO RLV with intact abort? (That's pretty much what it would take) It seems pretty narrow minded to exclude such a possibility.


No, sorry...   

I'm not excluding it because "it's so different from how it's done today".

I'm excluding it because I can't think of any vehicle configuration that is able with any reasonable likelihood to perform an intact abort when it is in a sick state.

The only example of something that can do an intact abort is an airplane, or a train - and that's because a) you have a captive audience inside, and b) the structure/fuel/payload ratios are sane.   And even in jetliners, turning around right after takeoff is already dicey.

Once the payload is distinct from the payload, the motivation for intact abort drop to almost zero.

Meanwhile, the rocket equation hints strongly that the price of intact abort is very high, if not infinite.

So no, can't see it, sorry....  :(

I can see at some point a standardized payload pod, that has self-abort capabilities just like a capsule does.  It is optional, it obviously costs a LOT of mass, but maybe.  That's about it.
Title: Re: Reusability as abort functionality
Post by: mlindner on 11/12/2013 08:43 am
It's interesting how arguments continue even when its been accepted that the thing being argued about is impossible.
...impossible isn't accurate. Someday, reusable launch vehicles /will/ have intact abort capability.

Which means this should be in Advanced Concepts, not SpaceX General.