Discussion Should SpaceX create a larger engine to reduce the number of engines of the Falcon 9?

[RGClark]

A suggestion to upgrade the Merlin to another thrust level to reduce the number of engines on the Falcon 9 for reliability:

Re: On the lasting importance of the SpaceX accomplishment.
http://exoscientist.blogspot.com/2012/10/re-on-lasting-importance-of-spacex.html

Elon Musk recently mentioned the possibility of creating a large new rocket engine several times the thrust of the Merlin 1:

SpaceX aims big with massive new rocket.
By: ZACH ROSENBERG WASHINGTON DC
http://www.flightglobal.com/news/articles/spacex-aims-big-with-massive-new-rocket-377687/

He says this in regards to producing a super heavy lift 100+ mT vehicle, not for the Falcon 9. It's also not clear from this article if he said this after the failure of one of the engines in the last launch.

My suggestion is if they are going to produce this large engine that they go first to an intermediate sized engine that could be used also on the Falcon 9.

This article on NasaSpaceFlight.com suggests the failure was in the "fuel dome":

Dragon enjoying ISS stay, despite minor issues – Falcon 9 investigation begins.
October 19th, 2012 by Chris Bergin
http://www.nasaspaceflight.com/2012/10/dragon-iss-stay-minor-issues-falcon-9-investigation/

The image on this site shows the area that would have been breached:

http://www.neowin.net/forum/topic/1...ply/page__st__30__p__595235009#entry595235009

This is an area in the combustion chamber. A breach of the combustion chamber is very serious because the combustion chamber is where both the pressures and heat are highest. Note that this would be at the top where most of the complex and delicate engine components are located. Quite likely hot combustion products shooting out at high pressure in this area would have produced shrapnel from this part of the engine.

This is very serious because these lead directly into the propellant tanks. This means likely if the engine had not been shut down it would have led to an explosion. This is a different scenario from an engine just being shutdown because it is giving anomalous readings while the engine remains intact.

This puts it in a different and more dangerous class than other engine shutdowns.


Bob Clark

 

[Cripion101]

---

 

[Kyle]

The Merlin used on the F9 is designed for redundancy. That is, if one fails, even explodes, all 8 can take the rest of the load into orbit, as we saw with the Falcon 9 launch. If you have a 3 engine first stage, if one fails, you're going to have a bad day.

 

[RGClark]

The Merlin used on the F9 is designed for redundancy. That is, if one fails, even explodes, all 8 can take the rest of the load into orbit, as we saw with the Falcon 9 launch. If you have a 3 engine first stage, if one fails, you're going to have a bad day.

The argument against having so many engines on the Falcon 9 was in comparision to the Soviet N-1 moon rocket with so many engines that one always failed. Proponents of the SpaceX approach is their increase in reliability made that comparison invalid. However, the experience with the Falcon 9 is that one engine has failed in each launch, so it can't really be said they have higher reliability.
IF it really is the case that in this latest launch the combustion chamber was breached there is no way that NASA would certify the Falcon 9 for manned launches.


Bob Clark

 

[ADSWNJ]

I'd rather have more engines, in N+1 or N+2 redundant configuration than all-eggs-in-one-basket. Although there's more mechanically to go wrong, the impact is smaller. I presume you need to do the same work to make one engine reliable, regardless if it's by itself or in an array, except (a) you have less volumes to work out the kinks, (b) the trust pressures will be higher, and (c) the stakes are higher. All goes to cost.

 

[zerofay32]

The argument against having so many engines on the Falcon 9 was in comparision to the Soviet N-1 moon rocket...
Bob Clark

I don't think the 9 engine falcon, has anything in comparison to the 30 engine(first stage) N1.:dry: The N1 had more issues than just a lot of engines.

I find the number perfectly acceptable. Where it does get harder to manage is in a Falcon Heavy configuration. But by the time that fly's, much more data on the current engine config will be available and I don't think will longer be an issue. The more these things fly, the more knowledgeable spaceX become of them.

 

[Hlynkacg]

The argument against having so many engines on the Falcon 9 was in comparision to the Soviet N-1 moon rocket with so many engines that one always failed. Proponents of the SpaceX approach is their increase in reliability made that comparison invalid.

The n1's problems didn't arise from the engines but from the fuel system.

However, the experience with the Falcon 9 is that one engine has failed in each launch, so it can't really be said they have higher reliability.
IF it really is the case that in this latest launch the combustion chamber was breached there is no way that NASA would certify the Falcon 9 for manned launches.

The experiance with the Falcon 9 is that it reaches orbit.

 

[T.Neo]

Any argument against engine redundancy that brings up the N-1 is a fairly poor one. The N-1 didn't fail because it had 30 engines, it failed because there were other problems with it, like the fact that it was horribly rushed.

I am really unsure of where the reason for stating that F9 has lost an engine on every flight comes from. This is huge news to me, as the only other engine issue on an F9 that I know of was the flight on which a couple engines went oxygen-rich on shutdown.

In regard to the rationale for engine-out capability, not all engine failures are catastrophic (the safety advantage of engine redundancy depends on what percentage of failures are). The redundancy of engine-out enables you to survive a non-catastrophic engine failure. You can also engineer things to survive violent failures- as SpaceX claims to have done (kevlar liners to stop turbine RUD fragments), and has demonstrated with this fuel dome incident.

Having more engines means that you also have more cumulative burn time experience and higher production runs- which not only serves to increase experience and therefore safety, but decrease cost.

Of course SpaceX isn't going to waste hundreds of millions of dollars developing a larger engine simply because of the mere notion that engine redundancy (which has quite sound logic behind it) is a fallacy.

 

[RGClark]

...
Of course SpaceX isn't going to waste hundreds of millions of dollars developing a larger engine simply because of the mere notion that engine redundancy (which has quite sound logic behind it) is a fallacy.

It would not be a waste if NASA would not certify it for human flight with an engine shutdown occurring on every flight. Note also that oxygen rich condition on the prior flight would have led to combustion chamber burn though, if not explosion, if it had not been shutdown.

Bob Clark

 

[garyw]

It would not be a waste if NASA would not certify it for human flight with an engine shutdown occurring on every flight.

But an engine shutdown has NOT occurred on every flight. Also, human rating has more to do with black zones than with engine outs. In this case the astronauts would have survived and made it to the ISS - what is not to pass?

Don't forget that Apollo had engine out issues and STS-51F performed an abort to orbit.

 

[N_Molson]

Don't forget that Apollo had engine out issues and STS-51F performed an abort to orbit.

Sure, but Apollo wasn't in the same context, time was a constraint back then, and STS-51F followed an already long serie of very successful flights. What's sure is that the Falcon IX has to demonstrate a good serie of unmanned flawless flights to be considered crew-safe.

 

[garyw]

Sure, but Apollo wasn't in the same context, time was a constraint back then

Time is ALWAYS a constraint. That's something that can be managed but will never go away.

and STS-51F followed an already long serie of very successful flights.

Not at all. many early shuttle flights were plagued with issues. The IPR list for Shuttle was thousands of items long.

What's sure is that the Falcon IX has to demonstrate a good serie of unmanned flawless flights to be considered crew-safe.

Successful doesn't mean without problem. Every single shuttle flight had a problem or one sort or other. There has never been a flawless flight. However, I do agree that Falcon does need more end to end testing and more modelling before becoming human rated.

 

[Hlynkacg]

It seems to me RGClark that you want SpaceX to make thier rockets more like NASA's.

Over designed, over priced, and unlikely to fly.

The ONLY question that matters in terms of safety is "Will a failure result in injury or death of a crew member?"

All other's are nonsense.

NASA's "Man Rating" is a left over from the days when we were still using ICBMs as launch vehicles. ICBMs were never designed to be highly reliable, because to do so would have dramatically increased their costs (many hundreds of them were built), and it wasn’t necessary for their mission. Some estimates at the time of the reliability of the Titan II was only 80% based on the fact that eight of its initial thirty-three test launches were failures. 1 out of 5 was good enough for a weapon launched as part of a fusillade of hundreds but not for a single flight carrying a human, particularly with the whole nation watching.

 

[N_Molson]

Successful doesn't mean without problem. Every single shuttle flight had a problem or one sort or other.

Yes, I agree (and how could it have been differently, given that the Shuttle was the most complex machine ever built !), but still engines failures seems pretty high to me in the hierarchy of problems, even if the structural design is good enough to be a safeguard.

"Will a failure result in injury or death of a crew member?"

And the answer to that question can't be a "maybe". Failure is not an option.

 

[Hlynkacg]

And the answer to that question can't be a "maybe". Failure is not an option.

Bull

There will always be risk.

The only way to make spaceflight 100% safe is not to engage in it.

 

[garyw]

And the answer to that question can't be a "maybe". Failure is not an option.

Failure is not an option? You can't engineer out failures, what you can do is engineer in safety features.

What's fascinating is that the document that NASA wrote which talks about requirements for human rating wouldn't allow either the Shuttle or Soyuz to pass.

 

[T.Neo]

It would not be a waste if NASA would not certify it for human flight with an engine shutdown occurring on every flight.

Except, as garyw has said, there has not been an engine shutdown on every flight. You are the only person I know of anywhere on the internet or otherwise who is claiming that every F9 flight has had an engine shutdown.

Furthermore, even if every F9 flight up to now lost an engine (which is not the case), all four of those launches have reached orbit. That would not demonstrate unreliability of the nine engine layout (if it demonstrated anything, it would likely be the opposite), just that SpaceX would need to work really hard on improving their engine reliability.

But as has been said previously, this string of engine failures you describe is fictitious.

Note also that oxygen rich condition on the prior flight would have led to combustion chamber burn though, if not explosion, if it had not been shutdown.

The 'oxygen rich condition' occured during shutdown. In other words, the engines went oxygen rich while they were shutting down. And they were shutting down because they were commanded to do so, because the burn had ended. The issue is mainly relevant due to SpaceX's ambitions for reusability.

The ONLY question that matters in terms of safety is "Will a failure result in injury or death of a crew member?"

On a crewed flight, that is the utmost concern. You can tolerate a total LOM as long as the crew comes back safe. Without lives at stake, a loss of mission itself is the safety issue.

 

[kamaz]

The whole idea behind this launcher is to mass-produce engines, so they are cheaper. So decreasing the number of engines per rocket would be the very opposite to what SpaceX is trying to do.

Also, regarding the comparisons with N-1 -- remember that sensor and computer technology went a great deal forward since 40 years ago. Much more fine-grained engine control is possible today than in 1970.

 

[N_Molson]

Bull

There will always be risk.

The only way to make spaceflight 100% safe is not to engage in it.

That's pretty obvious. But a launch vehicle must be considered safe before you use it, if not you are running straight into catastrophic failures. If you consider "nominal" that one engine or two have problems during ascent, there will be a huge failure sooner or later. Kevlar coating is a good thing, but unless you make it very thick (and heavy), I doubt it can handle the worst failures.

So those engines have to be tested more, that's all. Which is going to happen anyway.

 

[Hlynkacg]

That's pretty obvious. But a launch vehicle must be considered safe before you use it, if not you are running straight into catastrophic failures. If you consider "nominal" that one engine or two have problems during ascent, there will be a huge failure sooner or later. Kevlar coating is a good thing, but unless you make it very thick (and heavy), I doubt it can handle the worst failures.

So those engines have to be tested more, that's all. Which is going to happen anyway.

Considered safe by whom?

As Garyw has already been pointed out niether the Space Shuttle nor Soyuz (nor any other manned mission for that matter) met the current NASA safety standards, and if we were to apply those same standards to civil aviation niether would most aircraft.

To paraphrase an old joke...

Rocket is not safe, rocket is rocket.