The Lost Art of the Saturn V | Hacker News Reader

The Lost Art of the Saturn V

amyshirateitel.com

132 pointsColinWright66 comments

> "The whole mission, however, depended on the titanic Saturn V rocket, a technology that is lost to the current generation."

NASA engineer here. I think it's actually kind of ludicrous to claim that we have somehow "lost" the technology of the Apollo program. We're not living in some sort of space technology dark ages here, where we've forgotten all of the fundamentals of the 1960s 'classical enlightenment'. In fact, the decades since then have provided invaluable experience in the design and use of reusable launch systems, in-space assembly, astronaut medicine, etc.

If the agency and it's supporting industry contractors were given both an executive mandate and the funding to construct a comparable system to Apollo (for whatever reason that would be), today's engineers would not struggle to do it for lack of technical prowess. We might struggle to do it in the current federal budgetary climate (where we can't predict the whims of legislators 3 months from now, much less 10 years from now - and the Saturn V was expensive as hell to operate), but the "lost rocket science" myth is a bit tiring.

I think people tend to romanticize old technology because it did so much with so little. My dad always makes fun of these people by saying "They don't build 'em like they used to: They build 'em better."

I don't entirely agree with his sentiment but it's still for the most part true. I have no doubt that, given a proper budget and mandate, NASA could once again build a heavy lift vehicle like the Saturn V. However, I think we've lost a certain elegance that was present in that age. Sure, our technology is much more capable now, but it's definitely not as 'charming', for lack of a better word.

I think the point that I'm trying to get at is this: I used to commute on NJTransit, and every day I would get into crappy "modern" brushed aluminum railcars with a freight locomotive pulling them. And one day, while I was waiting, a refurbished Pennsylvania Railroad train rolled through with its beautiful shiny brown paintjob, elegant railcars, and even people in period garb. I have no idea what it was for - it didn't stop at our station - but it was much more pretty than anything we see today. My dad was there too, and for once he actually said without irony, "They don't build 'em like they used to."

But who knows, maybe fifty years from now people will see us the same way we see them.

The New York subway occasionally runs historic trains. They're kind of obnoxiously loud and rattly. I assume they were slightly better when they were younger, but I'll take air conditioning over ceiling fans whenever I can.

That said, there's something to be said for the inhumanity of stark modern designs: http://instagram.com/p/egILDiQAS2/

compared to the older ones: http://instagram.com/p/gbwdmTwAZM/

I'll take the legibility of inhuman, stark designs any day.

I'll take working ceiling fans over non-working air conditioning any day.

But... Helvetica!!

Plz n00b, http://www.myfonts.com/fonts/fdi/wayfinding-sans-pro/

;)

Agreed. I think one of the key things to recognize about this sort of thing is that while, yes, we could do it "better" with today's tech than we could have with the Saturn V, that's unlikely to mean "cheaper". A new heavy-lift system that performs better than Saturn V will, in the absence of a total revolution in technology, cost more even after adjusting for inflation. Because to squeeze that extra 40% performance out of the same amount of weight and fuel, we'll be putting in 80% more work by 50% more people who are paid 30% more using 120% more expensive materials. The reason being that these programs don't operate on mass production. Each of these launch vehicles is very labor intensive to produce. The only real way around those numbers is to go for massive economies of scale, but then you're talking trillions of dollars spent on tens or hundreds of thousands of launch vehicles, but that's the only way to get to true cost savings.

You might want to check out what SpaceX is doing.

We should really pour that money into a space elevator...

The problem, as far as I last knew, is that we do not know of any materials strong enough!

Nanotubes are strong enough, but we haven't gotten them to sufficient lengths (we need ~1-2 meter nanotubes iirc)

Or then have each vehicle doing multiple flights...

"I think we've lost a certain elegance that was present in that age."

Or a certain cold-war inspired desire for robust rocket technology. Yes, the engineers were working for the sake of a moon mission and what not, but the domestic political motivations were never exploration for its own sake.

They build software far worse than they used to, even if it does take longer to build. Maybe that is why this story got upvoted so much?

I came here to post something like this, though I'm not a NASA engineer. I feel like there's been a few articles that have had the same strange claims of "lost" technologies. They lead the reader into thinking that since 1960 we haven't discovered or done anything significant to be able to recreate the space vehicles of that era.

The laws of physics haven't changed significantly since 1960, we understand a lot more about the same challenges of getting things to orbit now than we did even then. Technology, however, has changed a huge amount since then and if our priorities were still to land things on the moon then we would still have great success at it. Priorities and end goals have shifted around the scientific space community since 1960 and the average person seems to think that there's more value in lunar operations than anything else, which is simply not true.

Ignorance of the fact that we don't know enough about what long-term habitation of humans in space means for the body and mind seems to blind people into saying things like "we should have moon bases!", and call for "permanent settlements on the moon!". The research happening on the ISS, very close to home in case things go wrong, is essential to the steps needed to achieve things that people think should just happen because hey, they went there 40 years ago!

I think there's also this naive notion among people who haven't thought it through and/or aren't very familiar with manufacturing processes and the like that if you have the "blueprints" for something, it's straightforward to cart them down to a general-purpose factory and build the thing. After all, if we built it once, how hard can it be to build it again? And even some who may understand that it's not quite that simple still don't necessarily appreciate just how complex and intertwined the relationships are between suppliers, tooling, processes, experts in very specific and narrow domains, and so forth are when building any sort of complex machine.

Yeah, even with the exact blueprints, you couldn't just make a new Saturn V. The tools that made those parts probably don't exist any more, and the properties of metal under stress depend on a bunch of weird circumstances, like exactly how you cooled down the molten metal.

And even if you wrote that down and had all that equipment, the people who actually operated the things are retired or dead. Are you going to operate it the same way they did?

Does your incoming metal to your smelter have all the same properties as it did in the 1960s?

(I'm not a metallurgist, apologies to those who are.)

Yep, we haven't lost the tech, just the in-house skills. Each Saturn V engine had an absolutely insane number of extremely fine welds by master welders. Welding is an art form, and we definitely don't have the same number of welders we used to.

That said, we could potentially replace some of that with new fab techniques. But we probably couldn't do it the same way we did.

Sure we still know how to build rocket engines. But we are also reverse-engineering technologies of the 1960s for incorporation into modern systems [1] presumably because the oral and/or written history has been partially lost.

I also think of JPL -- if we stopped landing robots on Mars and other planets for decades, and the veterans of such missions had retired or expired, how difficult would it be to restart this capability from scratch?

[1] http://www.nasa.gov/exploration/systems/sls/f1_sls.html

I think they're meaning is that it's the engineering that's "lost," not the technology. Most of the "technologies" of the Saturn V are around. But something to replace it has to be re-engineered/re-designed from scratch, which is massive considering how there are plenty of other things from that era that have been subject to incremental and generational improvements continuously. If someone were to make a replica with modern technology every little gotcha that got worked out and worked around in the original would have to be re-discovered and re-worked around.

I'm sure we'd all believe you better if you had the following: a short hairdo, a white button up shirt, dark framed glasses, and an abacus.

Seriously though, Richard Feynman's death in 88 seems like a loss for Physics, and everyone really. Hasn't stuff like that happened at NASA since the Apollo program, and hasn't it affected rocket science negatively?

You're dead right. The major hurdle isn't the technology, it's purely funding. We already have technology far more advanced than the Saturn V, the VentureStar for example could be built using 90's technology, and they were halfway done with a scale model when the project was canned. This was a fully reusable SSTO that would bring down the cost per pound to orbit by a factor of 10.

I think NASA needs to concentrate on its PR front. Tax payers simply don't see the economic benefit that comes from spending money on space exploration, most see it as a waste. Compare this to defence, tax breaks, or national security which are black holes of money.

If you got an order for ten Saturn Vs tomorrow, how easy would it be to make them?

Maybe lost technology isn't exactly the term, but when a project is completed, people move on and retire, and the supply chain moves on, then the capability to make that technology goes away very quickly. And unless a successor follows on continuously, it can be very difficult to get back to where you were if the need arises.

I have no doubt that the NASA of today could be mobilised to make a better rocket, on cost and timescales comparable to or improved upon the original. But if that is the only way to get back to a Saturn V-like capability, it is fair to say that something has been lost.

This needs a [2011] in the title, which is important as the space industry has changed a lot in the last few years, particularly with the arrival of SpaceX and other COTS competitors. Whilst it's true that no-one is planning a beast like the Saturn V (although the Falcon 9 Heavy is getting close), it's also true that these days we don't need that.

Back in the 60s/70s, it was not possible to do an automatic hook-up of modules in space. Today we do these routinely. Those Apollo missions could still be launched today by launching the command module, the service module and the lunar module as separate payloads and joining them in orbit. The crew would launch in the command module.

It's a bit like regretting that Formula 1 cars no longer have big 3.0L V12 engines, and instead have to get by with measly 2.4L V8s, whilst missing the fact that the modern car will eat the V12's lunch, with it's eyes close, in reverse.

Not exactly. The "real" difference is if we cut down to a 4 cylinder at half the horse power, half the torque. While a "newer" engine does achieve higher thrust to weight nobody is building engines with anywhere close to the trust of the J-2.

NASA actually is attempting to rebuild the J-2, with the J-2X program. The problem is nobody knows how the J-2 works and part of the contract included NASA shipping several J-2's back for re-engineering.

I should also remind you that a year ago NASA didn't actually know "how" the j-2 worked. Their numbers said the bell should melt during flight. Eventually they realized that helium is injected on a outer ring of injectors to insulate the bell.

My point was more that you don't need the raw thrust of the F-1 / J-2 so much these days because we've made up for the lack of single-launch capacity by advances in other areas. Look at the ISS - it could not have been launched with Apollo-era tech, because the Saturn V couldn't launch it in one hit, and they didn't know how to put things together on-orbit. +(see edit)

These days it becomes a cost/benefit analysis - is the extra cost of doing things in one big monolithic lift more or less than the extra cost incurred by having to break things into smaller components and assemble on orbit. Clearly heavy lift still has advantages - there's a reason everyone is excited about Falcon 9 Heavy, but rockets are tricky beasts, and multiple smaller launches helps mitigate against catastrophic failure (although it may increase the risk of partial failure).

Edit: Just to be clear, I'm talking about automatic on-orbit assembly, which means that you don't have to launch a pilot + life support each time you want to join two bits together.

Your argument is that orbital assembly didn't exist in the Apollo era, when Orbital Assembly WAS the runner up to the SaturnV single launch option [Source Original Posters Article].

This means logically some times its more cost efficient, or simpler to put 27 tons in orbit in one launch, then assembly 6 5 ton launches.

Actually it is far better to minimize the number of launches to complete any mission. For example, Elon Musk has repeatedly mentioned that he is not currently a fan of in-orbit assembly. So having a really powerful engine is of great utility. The problem is one of cost-benefit. Having a huge engine means a big rocket which needs to be launched multiple times to achieve economy. But there are not too many missions around which require such capacity. Just look at the proposed SLS cadence. So having a Falcon Heavy with 27 engines is a much better solution any way. I cant wait when Merlin 1Ds are replaced with Raptors on first stage on Falcon Heavy. That would be one monster of a rocket.

> Actually it is far better to minimize the number of launches to complete any mission.

Doubtful. To design a big rocket takes a lot of money - and big rocket doesn't get to be used as much as a smaller rocket sometimes, which makes it more expensive per flight.

The opinions of Elon Musk aren't always perfect either. Certain technical decisions are made not because they are best, but because they are available - like, SpaceX just knows how to do that, and considers it expensive to learn the alternatives. Which is quite justifiable on economical grounds.

They (well, contractors) are re-engineering the F-1B as well: http://arstechnica.com/science/2013/04/new-f-1b-rocket-engin...

> I should also remind you that a year ago NASA didn't actually know "how" the j-2 worked. Their numbers said the bell should melt during flight. Eventually they realized that helium is injected on a outer ring of injectors to insulate the bell.

I think this is remarkable, given that film cooling of the nozzle is a known aspect [0] of the first stage engines of Saturn V.

[0] Thrust Chamber Nozzle Extension section on page 3 http://history.msfc.nasa.gov/saturn_apollo/documents/F-1_Eng...

That's wrong. Vulcain 2 on Ariane 5 flew four times in 2013. It's a 1340 kN thrust LOX-hydrogen engine. By contrast the J-2X will have 1307 kN.

Also the F-1 engine has been surpassed in thrust and efficiency by the Russian RD-170 family which flies today in the Zenit rocket.

I'm sure you could learn a lot from studying the J-2 and J-2S. No harm in that. But mystifying Apollo has done a lot of harm to sane space technology engineering and policy.

Sources: http://www.arianespace.com/news-launch-logs/2013-2014.asp http://www.sea-launch.com/missions-q1-past_launches.aspx http://www.spacelaunchreport.com/log2013.html

Agreed. Separate launch was actually one of the scenarios considered by NASA. The had F1 engine ready for Saturn so it was not necessary.

But three ships (live module, landing module and return booster) with randevu at moon orbit is the most fuel efficient scenario.

Actually, NASA is planning a Saturn V-sized launch vehicle, under the name "SLS" ("Space Launch System"). SLS Block II is supposed to match the Saturn V's capacity, but it won't launch until the 2020s.

(There are also rumors of very large rockets in advanced planning at SpaceX, but the only possible component of that program that has yet been announced is a methane-fueled staged combustion rocket engine, "Raptor" --- and they only announced that when they started reserving time for component tests at NASA facilities. So, even if those rumors are true, it's likely to be a while before they're confirmed in any detail.)

F1 Just changed to 1.6 V6 With a Twin Turbo and a massive energy recovery system, and people are doing nothing but complaining.

Then why is Spacex looking at building an engine the size of an F1, or larger?

> Back in the 60s/70s, it was not possible to do an automatic hook-up of modules in space.

Well, maybe not for Americans. The first Soviet space docking (October 30, 1967, a year and a half after the first US space docking, with Gemini 8 on March 16, 1966) was between the unmanned Kosmos 186 and Kosmos 188 and was automated.

Soviet moon missions using multiple launches and automated docking were considered, at least briefly: http://www.astronautix.com/articles/theoblem.htm

Funny time to complain about this, a few days after SpaceX confirms that it will be building a 9-Raptor engine, 6-9M lbf methalox launch vehicle comparable in scope per core to the Saturn V, and suggests strongly that they're going to make a 3-core configuration.

http://forum.nasaspaceflight.com/index.php?topic=34015.msg11...

Ultimately we (our representatives in Congress) decided in ~1970 that actual exploration was simply too expensive. Political goal accomplished, Moon reached, Soviets cowed, mission over. Instead we would pay endless lip service to the idea while cutting budgets as far as possible. The design-by-committee-session Shuttle was a ridiculous project in a dozen different ways and failed to do much of anything (including being cheap), beyond two key elements: firstly, being impossible to cancel. Second, it waved the flag for the notional romance of space in an age of decay, when we became disinterested in funding and structuring programs at a sufficient level to innovate or even seek out the maximum return per dollar by choosing appropriate technology.

http://idlewords.com/2005/08/a_rocket_to_nowhere.htm

SLS and Orion explicitly continue in this legacy. I'm hoping Elon Musk's motivations outlast the US Congress's.

John Aaron saved the Apollo 12 mission with four words, "Try SCE to AUX". And entered the history books as the best controller of the Apollo era. http://www.universetoday.com/98484/this-day-in-space-history...

The original Steely-Eyed Missile Man.

Actually, I believe the words were "Flight, go SCE to AUX." But an awesome story nonetheless.

The author of the blog is particularly known for plagiarism. Whenever I have more time I will double check the originality of this article.

http://www.thespacereview.com/article/2394/1 http://www.friends-partners.org/pipermail/fpspace/2013-Novem...

It's not a loss of art, it's a loss of political will. Given the same budget as in the Apollo years, I have no doubt NASA could produce something better than the Saturn V. But its current funding is a tiny fraction of that. (I mean, Apollo 18 was a complete mission that was scrapped, more-or-less to save the cost of the fuel).

NASA is building something better than the Saturn V: By buying launches from SpaceX, they've enabled a company that is going to fly a rocket that's 1/2 of a Saturn V next year, in a family of rockets that's commercially viable and has a high launch rate.

The Saturn V doesn't really matter anymore - what matters is that we know it can be done (the Falcon 9 Heavy would be impossible without the simple knowledge that the Saturn V existed), and if need be, it will be done.

The second issue is that no one needs that powerful a rocket at the moment - though I believe if it did exist, everyone would suddenly find use for it (like it happened with PC's and smartphones, for example).

> no one needs that powerful a rocket at the moment - though I believe if it did exist, everyone would suddenly find use for it

This is an important and very underappreciated point in life in general. Asking "will I ever need X?" is not a good idea, because it usually leads to the answer "no", whereas if you actually had X, you'd quickly invent many uses for it. It works this way for smartphones ("why would I need Internet in my phone? I have one in my laptop"), other tools, it works in programming languages - it's what pg calls the "Blub paradox" in [0].

I find that the features of our tools limit our thinking and abilities both as individuals and civilizations, therefore when possible I always opt for the most flexible/feature-full solution.

(there's of course a flipside to that, visible e.g. in the ongoing process of police militarization in the United States - don't give better tools to people if you don't want them to start using those tools more and more)

[0] - http://paulgraham.com/avg.html

Several big rockets already were built - and all struggled, more or less, with lack of payloads. First was Saturn-5 - and N-1 arguably was closed because there wasn't enough interest in it, in terms of payloads, for anybody involved. Then it was Energia - again, may be, should USSR survive, it'd still flew, but it was closed, while Proton and Zenit survived. Last was Space Shuttle - which was particularly expensive lately with not enough missions to justify its annual cost.

So, with big rockets, it's doubtful that "build them, and they will be used" approach works. On the other hand, we really don't need big rockets that much anymore - we can do anything with existing rockets. It would be interesting to see how often Falcon 9 Heavy will be employed.

Russians still develop Energia rockets and engines. It is modular rocket system which included soviet space shuttle and some heavy orbital weapons. It has more powerful engines than F-1 used in Saturn.

It is modular system and heaviest configuration were close to Saturn, but are currently abandoned. The lighter configurations are in active use and share the same engines and other components. Plus they develop new types.

I guess it would just take a few months/years to develop Saturn replacement if there is demand.

https://en.wikipedia.org/wiki/RD-170

https://en.wikipedia.org/wiki/Energia

Energia is long gone.

RD-170 family is alive and well though. You'd still need a good sized hydrogen engine - a kind of SSME or RD-0120.

But may be you just don't need too big of a rocket. 25 tons on LEO could be enough for everything, and you'll launch that often enough so a single launch won't be expensive. You can assemble stations, create orbital fuel depots, even make on-orbit manufacturing if you want something really big in one piece.

An interesting comparison of rockets in the context of this article: http://en.wikipedia.org/wiki/Comparison_of_heavy_lift_launch...

Area 51 was the place where v2 where tested. The UFO bs was just a convenient conspiracy theory to hide the fact USA was relying on more than morally unclear methods to get the former IIIrd reich scientists to do their job.

It consisted notably in either stealing precious brains from the germany that was in need, and -more troubling- preventing some persons to face the consequence of their action in front of a tribunal (war crime).

For the record condor and gladio operations also are more than morally questionable and also rely on explicit infringement in what a state is authorized to do on foreign ground: killing people arbitrarily without a trial.

I don't think that creating in relation with stuff like the infamous P12 loge (in which il cavaliere was, and some of well known mafioso) a program of "pseudo communist terrorisms" that were in fact the opposite and resulted in civilian killed by terrorist actions is not kind of consistent with the USA claim of war on terrorism.

USA is looking more and more like the former soviet union. NSA invasive techniques to spy on citizens are now as efficient as the former KGB used to be (that became the FSB and whose latest well known head was V. Poutine)

Perhaps the blogger is not aware that, even if the tons of documentation and data in the National Archives were lost, there are three actual rockets on display across the country, and a good number of stored spare engines and other components. Ars Technica recently ran a story on reverse engineering an F-1 engine to aid in the design of a new heavy lift engine.

The world today is such a wicked place. Fighting going on between the human race. People got to work just to earn their bread. While people just across the sea are counting their dead.
A politician's job they say is very high. 'Cos he has to choose who's got to go and die. They can put a man on the moon quite easy, While people here on earth are dying of old diseases.

A woman goes to work every day after day. She just goes to work just to earn her pay. Child sitting crying by a life that's harder. He doesn't even know who is his father.

- Black Sabbath's "Wicked World" (1970)

I'm a fan of manned spaceflight and exploration (slash finding a high availability arrangement for life from Earth). However, I believe we have more pressing matters to tend at the moment. In the meantime, it seems we need more Encyclopedists. ;-)

There will always be more pressing matters. Prioritizing them is a bad idea.

There are certainly always important things going on at home (Earth). I am not suggesting that these will always be more important than manned space flight; I'm suggesting that they are more important at this time. Are you saying that prioritizing manned space flight, above all else, is always a good idea? If not, what priorities have you before manned spaceflight? What's the rush? Are you concerned with climate change? Is the answer to it to move on from Earth, instead of _first_ trying to nurse it back to health?

Not everyone on this planet shares the same priority.

Even if you wanted to, you cannot force everyone to share same priority.

We have the will and motive to do multiple things simultaneously.

Even if we had the operational knowledge, you'd still be trying to assemble a rocket that is half a century old. I would be amazed if the commodity parts, things like screws and washers and whatnot, were still being made.

I don't know so much about screws and washers but certainly there are any number of components that we don't have the tools to make the tools any longer--and we probably wouldn't want to use those components even if we could. Would be want to use the Apollo guidance computer? Raytheon had better gear back up to make core memory in that case.

The whole "Saturn V plans are lost" meme seems to be an urban legend but it's a red herring in any case. We couldn't easily build a 100% authentic 1965 Corvette either but that doesn't mean that we've somehow lost the technology to do so.

"doesn't mean that we've somehow lost the technology to do so"

I can think of two examples.

The LM had some truly weird chemical milling technology invented mostly because they didn't have the CNC mills and CNC EDM gear we have today. Design and production floor feed back on each other and some design decisions were optimized to production realities such that you could at enormous expense either reinvent the chemical milling processes or simulate them with EDM and/or CNC mills but it would be enormously cheaper to scrap the design for a chemically milled door or whatever and replace it with a door designed specifically to match the modern technologies of EDM and milling machines.

The other example I can think of is I don't think we have the tech anymore to make aerospace grade core memories. Too much info was in the brains of people who died decades ago. To a first approximation the cost would be something like the entire fixed capital expenses of the whole computation industry from 1940-1960 plus many man years of R+D and more importantly reverse engineering and reinventing the QA/QC that man rated aerospace grade core memory would require. It would be a heck of a lot simpler and cheaper to use modern tech.

There is an obvious computing analogy. For a good time check out the "soylent news" project as in soylentnews.org who spent weeks re-implementing modperl 1.0 and apache 1 and all that so as to re-implement /. using the last public release of slash code. Its non-trivial to bring up old software while simultaneously applying a decade or two of security patches and best practices.

I meant that statement in the sense of it's not really as if we've lost the knowledge from some golden age of engineering. I'm guessing it would be enormously difficult and expensive to build an IBM 360 as well. (Or, if that's not a good example for some reason, certainly any number of other obsolete computer systems.) But people don't normally lament the fact that we can no longer manufacture a 1960s-era computer.

But, that said, fair comment. It's the reason that there are always various military projects ongoing to basically replace old technology (such as guidance systems) with modern tech. Not necessarily to upgrade capabilities, but simply because we can't build the old stuff any longer.

ArsTechnica has an interesting article [1] on efforts to recreate the F1 using intact engines and the original design documentation. Reading it, I was surprised how difficult this proved to be in practice, given the extensive information available.

[1] http://arstechnica.com/science/2013/04/how-nasa-brought-the-...

For any engineering effort, there is the documentation and there is the never well documented wisdom of actually building the thing. The plans may say a certain alloy has to be used or part P and the Helium cooling system should not run at more than X psi, but the reasons why it is so could very well be lost in a multitude of memos on failed tests. Sometimes, the reasons of those failures themselves are never known because someone figured out a way that works. Not knowing the complete history of the development of a given machine and why it is the way it is may very well make it almost impossible to continue evolving the design and kill the technology.

Screws, Washers, Nuts & Bolts sizes are prety much standarized, so you can probabbly go to the nearest store and buy one of the same size. Really the main problem is that they may have used an special alloy or quenching or galvanizing.

Nice writeup. One small error I noticed: the first manned flight was Apollo 7, not Apollo 8.

I was confused by that too, until I realised that the article is specifically about the Saturn V.

What the author wrote was: "After only two unmanned launches, the third Saturn V took Apollo 8 to the moon."

Apollo 7 used a Saturn IB booster and so, while it was the first manned Saturn launch, Apollo 8 was the first manned launch of a Saturn V. The two unmanned launches were Apollo 4 and Apollo 6, which both used the Saturn V [1].

Edit: Clarity

[1] http://en.wikipedia.org/wiki/List_of_Apollo_missions#Unmanne...

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