What Is Wrong With Lots of Rocket Engines?
Human Exploration Drives Space Launch System, Aviation Week
“It doesn’t seem likely that NASA and it’s congressional backers will trust human lives anytime soon to a 27-engine vehicle that bears an unfortunate resemblance to the ill-fated Soviet N-1 Moon rocket, which had 30”.
Keith’s note: Odd comment from Aviation Week given that NASA has been putting American astronauts on Soyuz launchers for a long time and they use 20 engines just to leave the pad. Oh yes, his rocket actually is a Soviet design.
Keith the Soyus rocket technically only has 5 rocket engines on it’s first stage each motor has four combustion chambers and nozzles.minus the smaller one’s for thrust vector but they also run off the main rocket motor.
Yea yea and the Titan 1/Titan II only had one engine. If anything SpaceX has more redundancy and reliability than the Soyuz does. If one Soyuz “engine” fails ….
Redundancy which has already proven to work. Another nice thing about Merlin is that since so many are needed, there are many firings, resulting in a lot of data which can be used to improve the design.
A very large engine is costly to test fire, and few are needed for a launch vehicle, so problems arise at a slower pace if you use number of launches as your yardstick.
While true, each combustion chamber does add another potential point of failure. So you can’t just equate a rocket engine as a turbo-pump, even if that is how rocket engines/.chambers are usually counted. It is more than just the turbo-pump. (even if the turbo-pump is the most common point of failure)
By having 20 combustion chambers does not mean using 20 engines. Soyuz uses 5 engines to get off the pad, but each engine has 4 combustion chambers. I just wanted to correct this mis-statement and I don’t have anything against using high amount of engines. 🙂
Not 20, “just” five engines. These engines are RD-107/RD-108. Each engine has four combustion chambers/nozzles which share a single set of turbo pumps. Still, a very impressive and extremely reliable system.
By having 20 combustion chambers does not mean using 20 engines. Soyuz uses 5 engines to get off the pad, but each engine has 4 combustion chambers. I just wanted to correct this mis-statement and I don’t have anything against using high amount of engines. 🙂
To say that the Soyuz launcher uses “20 engines just to leave the pad” is not 100% anatomically correct. While there are indeed 20 thrust chambers, it is, in fact, only 5 engines as each “engine” as constituted has 1 set of pumps and 4 thrust chambers. Therefore, the number of failure modes is lower than it would be for 20 engines, but the consequence of a specific failure may be higher (I don’t believe you can shut down a single thrust chamber if something is wrong, for instance).
That being said, your point still holds to a large degree.
Well, actually, the Soyuz rocket uses five quad-chambered main engines and sixteen dual-chambered verniers at blast-off but I see your point. A closer analogy would be Saturn-IB that used eight main engines at launch. You know, that thing that NASA used in the ’60s and ’70s with no problems whatsoever?
Why is he talking about Falcon Heavy lifting humans? I doubt if Falcon Heavy will ever be human-rated. It is a cargo vehicle. The pair – 9 & Heavy make a formidable means to deliver humans and then supporting cargo to orbit and beyond. For the Mars plans that Musk has, it is the SpaceX Falcon X (Heavy) & XX that are likely to be human-rated in order to lift dozens of passengers sharing the destination Mars. And those future heavy and super heavy lift vehicles will employ a 3 and 6 F1 class engines per core.
I recall reading some where that the falcon heavy will be a human rated vehicle. isn’t it made up of three human rated falcon first stages??
Also I was under the impression that the methane merlin 2 or raptor will be in a cluster of nine just like falcon 1.1??? Which I guess was MCT. Am I wrong? You know a secret?
Question after reading how methane does not coke the engine parts (burns much cleaner, I recall spacex saying kerosene Merlin’s have been tested to about 25 relights. I would guess that spacex will want falcon 2.0 R to burn methane. Has anyone heard if Spacex is planning to build a merlin d replacement pretty soon? I’m sure they would want to reuse their boosters a hundred times not 25??
http://nextbigfuture.com/20…
Raptor is the last family of engines that SpaceX plan to build. It’s a Methalox fuel/fuel staged combustion engine expected to exceed 650klbft (vac thrust of 1 million lbft) and it’s planned to power Elon’s MCT.
A Raptor-powered F9 equivalent vehicle has been discussed and seems more than likely. This vehicle would lift at least SLS Block 1 & 2 payloads. Also a Raptor-powered F9 lift somewhere around Saturn V payload. Raptor-powered FH could be the MCT or Elon’s SHLV but who knows.
Raptor is in development and an agreement has been signed to test at least components of the engine at Stennis.
NasaSpaceFlight has the most up to date info’ and particularly the pay area (very reasonable) L2.
Cheers.
Yeah, as the Bean from down under states, Raptor, not Merlin 2, is now SpaceX next gen engine – Liq Methane & LOX. Here is the article I had read recently http://www.nasaspaceflight…. ; chronological – go half way down the article to read latest news.
That article states that Falcon X 1st stage cores would use 9 Raptors, totaling 40,000 kN vs. Saturn V’s 34,000 kN. It seems like a Falcon 9 could have all nine Merlin 1-Ds replaced by a single Raptor engine, despite having less thrust than nine 1-Ds, its thrust/weight ratio is much better. Furthermore, designer Tom Mueller of SpaceX, speaking in public, might deliberately under-state the numbers so as to not tip off competitors too much.
This seems to be their pattern. They underestimate capacity, but come in late. (The original figures for FH was 32 tonnes to LEO, flying in 2013. Now they’re projecting 53 tonnes, flying in 2015… maybe.)
Who’s rumoring 1st flight in 2015?
Musk as of a couple of weeks ago. Apparently they need cores to meet the demands of their manifest, so FH will have to get in line.
I wonder what the bottleneck is? Materials, machinery or the hands to build them?
How about launch pads??? They only have Florida since California is only good for polar flights. Right??
Also I would think that it is smart to put Falcon Heavy off till they get the booster return thing working. Seems likely that when Heavy makes first test flight by middle of next year that landing and reusing at least two of the boosters is likely.
Which brings to mind a few questions.
Will falcon 9R boosters be interchangeable with either of the Falcon Heavy cores??
Are falcon heavy cores standard falcon cores PLUS connecting/staging hardware??
Where are the cross fuel pumps? On the outer core or central core?
I would think the pumps would be on the two outer stages so that added weight is dropped earlier??
Are pumps easy to add and remove or intergrated into the falcon heavy’s engines?
Wouldn’t it be smart if Spacex’s first Falcon Heavy test/demo flight was flown with three refurbished boasters which had flown before. That could save him a few development bucks???
That would definitely be impressive if they had such confidence for the first launch. But I’d think they play it safe.
the bottleneck is actually none of the above. it’s scheduling. Canaveral has a packed launch schedule, with many different people competing for time to launch. that means SpaceX has to squeeze in customer launches there whenever it can. also, it means that all the Falcon 9 cores currently made (last time i saw a picture of their production line floor at their Los Angeles facility, there were 4 cores in various stages of production http://www.spacex.com/sites… ) need to be used to launch the backlog in their manifest. the test flight of the Falcon Heavy is a lower priority than making customers happy, so it’s getting bumped down.
SpaceX now has exclusive use of one of the old shuttle launch pads, though it will take a while before that gets refurbished, but even then it will have to compete for time in the Canaveral launch schedule. this is why SpaceX wants its own dedicated launch facility, so it can control when they launch. it will still be a few years before that gets built, but that will dramatically increase their launch rate and decrease their backlog.
So they need more cores and customers come first. However, Vandenberg launch of F-H is not so much a constraint. They built their own pad. So as for F-H, it is the lack of cores not schedule bottlenecks. So that leaves cores and the question remains whether it is a shortage of labor, materials or machinery or some combination? The other possibility is that the launch crews have 100% of their time consumed on commercial and cannot support a trip to Vandenberg and still complete the needed commercial launches.
they have their own pad at Vandy, but they have their own pad at Canaveral, too. they need to fit in launches with the schedule at Vandenberg, as well, and most of their customers don’t require polar orbits.
the lack of cores is due to the priority to launch customer payloads, and those slip due to scheduling at their launch sites, and one slip causes all else to slip, etc.
the schedule slips are much alleviated with their own launch site.
it’s not that they need more cores. they have plenty, if they wanted to divert 3 to the Falcon Heavy, they could do so, but they’d be pissing off a lot of customers that way.
the plain fact of the matter is that launching their customer’s stuff is a higher priority.
Thanks. This makes also makes it more clear that they really need the Brownsville, TX site to meet demand for launches. Florida near the Cape and Wallops probably do have a sound argument for more launch services. As SpaceX launch prices force competitors to lower theirs, demand across the board could require those additional sites. There’s no doubt demand will rise with lowering costs to orbit but hundreds of nanosats (PlanetLab, etc.) won’t amount to the demand to float all boats at the lower cost. Its more tied to what SES rep’s commented during their GEO launch by SpaceX. There is the developing countries that can now afford launch costs. Also interests in North America and Europe that can afford to fly.
Aside from this, I can’t imagine LM and Boeing sitting on their hands while SpaceX is approaching reuse of their cores. Michael Gass’s arguments of performance (processing, timeliness) and reliability will not hold up very long. The DOD contract and what they have with NASA probably buys them the time to respond to the SpaceX challenge. But I suspect that they are facing a high cost to design and then build a competitive manufacturing system that builds reusable launch vehicles (which it boils down to now).
i’ve had a talk with one of my friends who works at SpaceX. i’m told that the production goal for this year (2014) is 18 Falcon 9 cores. the factory in Hawthorne, CA is configured to be able to produce up to 40 cores per year. i’m given to understand they will eventually ramp up to that number when they can actually do that many launches per year, my guess is that we may see them approaching that number in 3-5 years. I also learned that one of the problems they are having is acquiring the grade of aluminum they need to manufacture the fuel tanks for the rocket cores. basically their supply chain for materials is (and has been) an issue. recall that stuck valve that gave them trouble with a Dragon thruster? the manufacturer changed the specs of a part without telling them… that sort of issue has been problematic for SpaceX and the way Musk would like to do it is own the entire supply chain and build everything in-house … though for some reason i think that breaks a monopoly or antitrust law or two.
http://www.aviationweek.com…
“With plans to compete with ULA for launches of heavier payloads in the coming years, SpaceX is also preparing to test and qualify the new Falcon Heavy launch vehicle in 2015.
Although it was initially slated to debut this year, SpaceX founder, CEO and Chief Designer Elon Musk says the company’s production schedule is too tight to support a test flight of the heavy-lift rocket from Vandenberg AFB, Calif., in 2014.”
Musk says Q1, 2015 launch. Which, based on past performance, probably means delivering the vehicle to the launch site for final integration by Q3, 2015.
Have a look at the size of their launch manifest. There are only so many months in a year.
Sure, the manifest is brimming and they claim staffing must be increased dramatically to meet demand. Even if they could hire everyone needed right now, do they have the materials supply chain and manufacturing equipment to meet the demand?
wasn’t the 32 tons for the original Falcon 9 heavy, which they scraped and replaced with the Falcon Heavy?
In answer to the title of the article, nothing at all.
What is wrong with lots of engines? COST! One large engine is cheaper to make than bunch of small ones. RELIABILITY! doubling the amount of failure prone parts does not just double break down probability, it more than doubles probability of failure. And of course CONTROL, every additional engine adds the control system interdependency with all the other engines.
MTBF, mean time between failures. I am not a reliability engineer but let me respond. With the 9 engine configuration the loss of 1 or 2 Merlin engines still permits achieving orbit. If a stage has one to three engines, I’m pretty sure that with any design, the loss of one engine means failure to achieve orbit. With a nine engine configuration you could lose one or two engines during every launch and still maintain 100% success rate to orbit. Not with, say, one to three engines. Eventually one will have a loss of an engine and lose a launch vehicle and payload.
Shuttle never had a catastrophic loss of a turbopump which early on was considered one of the most likely reasons for losing a Space Shuttle. Catastrophic failure during launch of American made rockets has been due to solid rocket motor casings – Delta 2 and Shuttle SRB. The reliability and confidence level for many engine components build upon past performance of many designs. Also the failure rate of these engines does not go up or down appreciably as you make them larger or smaller. I think the conclusion one reaches is that you design with sufficient redundancy to achieve orbit with loss of one or two engines. Past performance history shows that the probability of an engine failure that causes loss of multiple engines is very low. The engines work in parallel rather than in series; not leading to chain reaction failures.
It seems that having a small number of first stage engines can also create safety risks at certain phases of a launch. Saturn V for example, losing just one engine during the first 3 seconds after liftoff would have been catastrophic as the rocket would have fallen back to the pad. Then for about ten seconds as they went through max-Q, the loss of just one outboard engine could have resulted in structural breakup which would have happened within about a half-second of the failure, possibly sooner than the LES could save the astronauts.
Maybe current designs are more robust in this regards, I don’t know.
Losing a Merlin engine during max-Q would certainly impose less stress than losing the much larger F-1. I don’t know if losing a Merlin at lift off would cause the same problem as with Saturn. However, the Falcon 9 now with extended cores does lift off the pad noticeably slower – less margin. Also note that one capability that gives Falcon’s an edge is test fires on the launch pad. I do not think Saturns, Deltas or Atlases have that capability.
While Delta’s and Atlas’s don’t do hot-fire at the pad, they do verify engine performance before lifting off.
As far as losing a Merlin at Max-Q, that actually DID happen (CRS-1), but the Falcon 9 continued on as nothing had happened, just adjusting the trajectory and burning the remaining 8 for a little bit longer.
the Delta IV did at least one hot fire on the launch pad: http://spaceflightnow.com/d…
I don’t know whether or not they continue to do them, my guess would be they do not. I don’t think SpaceX is required to do these hot fires either, AFAIK, NASA is not asking for them. I think they just do them to build experience and confidence with their launch teams.
“the probability of an engine failure that causes loss of multiple engines is very low”
The nightmare exception being a commonality among the engines such as buggy software or a defective batch of parts. As happened with STS-51-F which nearly had a fatal outcome when three faulty temperature sensors which had already caused one engine to shut down were threatening to shut down a second engine, during a period when the loss of a second engine could have meant impacting the ocean. This was pre-Challenger when they didn’t have bail-out capabilities. Only the quick thinking of steely-eyed missile woman Jenny Howard, who concluded that the sensors were defective and inhibited the spurious readings saved the day and possibly the lives of the seven astronauts. Although post-flight analysis showed that the second engine probably would not have shut down, it was still a close call.
Yes but risks inherent to any system be it with 1, 5 or 9 engines. I’m not a Shuttle historian but those are interesting stories. One story unrelated that was incredible but downplayed was the last use of the satellite deployment mechanism from the Shuttle cargo bay. The satellite spun up and sent shrapnel flying every direction in the cargo bay. Something like that.
” RELIABILITY! doubling the amount of failure prone parts does not just
double break down probability, it more than doubles probability of
failure.”
Only if you assume failure of even single engine is LOM. SpaceX’s ability of engine-out is proven.
“What is wrong with lots of engines? COST! One large engine is cheaper to make than bunch of small ones.”
This is far from clear. Larger engines are more expensive to develop and test. If you use smaller engines you have the advantage of mass production. (Just look at how expensive the RS-68 is)
I think the cost advantage of a larger engine vs multiple smaller engine actually is towards the smaller ones. SpaceX and F9 is one example.
Phrase the question this way—-would you trust human lives more, or
less, to a vehicle with 9 engines (Falcon 9), that might easily have
flown 50 times by 2021, or to a vehicle with 27 engines (Falcon Heavy)
that might easily have 10 flights under it’s belt by 2021, or to a
vehicle with 5 engines (SLS), that would have flown once before 2021
(assuming all succeed)?
Ditto on the spacecraft side, Orion or
Dragon, or whoever wins commercial crew. Draw out the reliability growth
curves. Yes, lets’s do the math. Orion will never have a confidence/reliability, at it’s low flight rates,
combined with SLS, as to ever have any sound number crunching show it
can even approach the Shuttle demonstrated reliability on loss of
crew (98.5%) over any conceivable lifetime (math carrying SLS/Orion
flights past the year 2100 not included!).
You can throw us in the brig. We’ll still be screaming – “You’re going the wrong way”.
can you imagine a car race… 40 – 50 cars … and none of the engines started? gosh … what are the odds that even ONE engine doesn’t start? I just do not understand this obsession over the number of engines… MILLIONS of engines start up every morning for work… they are engines…. only 8 of 9 have to work. only 24 out of 27 have to work … are not smaller engines cheaper? Are not smaller engines easier to build? Do not smaller engines usually have less parts? Are smaller engines easier to move around during production? Can not smaller engines be mass produced easier?
I agree, way too much fuss in this debate for what is rather straight forward if this, that sort of math. The first time I got embroiled in this debate was in the 90s. My take was that the number of engines as a measure of goodness of design was just one factor, and unless one simplified to all other things being equal, the real understanding of the topic had to be more realistic.
A comparison of two plans would have to consider manufacturing cost for example. If company A wanted to emphasize that, they could end up with less cost than company B, even for more engines. Ditto on development and reliability. If company A had a very efficient development practice, they could test-fail-fix more cycles, ending up with a more reliable single engine, more of which could be ganged together, into a more reliable engine set than company B with wasteful development processes, even if company B’s design had fewer engines.
The all other things being equal is a nice generalization, but it only starts the more useful, interesting understanding which occurs when things are not equal.
Reliability and confidence are statistical concepts that when applied to large systems (such as the Space Shuttle or Proton or whatever) over time can be misleading. History in space systems shows that what appears to be a uniform appearance of reliability from the larger perspective is actually misleading and can lead to a false sense of confidence.
The reason for this is that almost all large systems are experienced small internal changes in hardware, software, and processes to larger systems. If these changes are not thoroughly tested before being put into use, the chances for a failure are increased. Some of these changes are driven by external forces (environmental regulations or changes in suppliers), some by “make-it-better” (safety and performance), and many by changes in processes (manufacturing, testing and launch processing) and personnel — usually to drive down costs. The Chinese just had a launch failure caused by contamination in a fuel supply line that wasn’t blown down sufficiently to remove FOD. The 98.5% for Shuttle is just as misleading, given the number of non-catastrophic failures the program experienced over its history.
The most recent NASA Aerospace Safety Advisory Panel report has an excellent discussion: “Accretion of risk: how safe is safe enough?” Well worth reading, if for no other reason than to appreciate how humility is necessary when we discuss matters or argue comparative merits.
Haha, well done with the Soyuz image
This would be a base heating nightmare. Not only with the plume-induced heating of the base heat shield but the external nozzle sections as well. This configuration is not ideal.
The dinospace apologists are getting desperate. Somebody please throw the Senator from Alabama under a bus. Metaphorically speaking, of course.
AWST is not claiming the number of engines is the issue. The first paragraph of the article makes it clear that the real reason for the SLS is politics (i.e. corruption) particularly involving Senator Shelby.
“NASA still wants to build the heavy-lift Space Launch System, and as long as Sen. Richard Shelby is alive, it will. The U.S. space agency needs the Alabama Republican, who is the ranking member of his party on the Senate Appropriations Committee, and he needs the SLS to keep his constituents at the Marshall Space Flight Center happy.”
This comment by Frank Morning Jr. in his “In Orbit” column really surprised me. It’s out of character for him. I actually wrote a letter to AW&ST before passing along the tip to Keith. The comment has no basis in reality and pretty much came out of left field. It’ll be interesting to see if AW&ST addresses it in any way.
Sorry, which comment? And what was the tip? Just trying to understand.
The topic of this post is a quote from an commentary in Aviation Week and Space Technology by Frank Morning Jr…
“It doesn’t seem likely that NASA and it’s congressional backers will trust human lives anytime soon to a 27-engine vehicle that bears an unfortunate resemblance to the ill-fated Soviet N-1 Moon rocket, which had 30”.
I thought this was out of character, unfounded, biased and a pretty outrageous thing to say so I wrote a letter to AW&ST about it and also sent a heads up to Keith.