Tuesday, September 24, 2013

Valley Forge on the Moon?

This past July, U.S. Congresswomen Donna Edwards (D-MD) and Eddie Bernice Johnson (D-TX) sponsored an unusual house bill. If passed, H.R. 2617 would designate as National Historical Parks the half dozen Apollo lunar landing sites plus the wreckage of the third stage of Apollo 13's main rocket. Folks seem to think that it's highly unlikely that the bill will ever pass.

Future parks?
Source: Smithsonian Air & Space Museum.

The bill's stated aims are to educate the public about the history of the Apollo program, and protect the Apollo sites from meddling by future commercial and scientific missions. The Department of the Interior would be required to draft a plan for the protection of the sites, funded by the federal government or donations from private or foreign entities. The Secretary of the Interior would also be obliged to apply to the United Nations for UNESCO World Heritage Site status for the parks.

The Apollo sites wouldn't be the first space-related UNESCO sites.
The Chinese Dengfeng Observatory was declared a UNESCO World Heritage Site in 2010.
Source: UNESCO.

Earth's other astronomy related UNESCO World Heritage Site is the Observatory at Jantar Mantar, in India.
Source: UNESCO.

The bill has been criticized from two main angles. First, there's the fact that it wouldn't fund NASA or the U.S. National Park Service to do any of the required activities. The only way you'd end up with park rangers bouncing around on the moon is if someone donated tons of money to the Department of the Interior to make that happen. So the bill couldn't really have a practical effect. Second, if enacted the bill would pretty clearly violate international law and would be unconstitutional. That's because under the national park system's authorizing legislation, national historic parks fall under U.S. federal jurisdiction. So a national park on the moon would be under American control: policed by U.S. park rangers and governed by U.S. federal law, just like Valley Forge National Historical Park.

The March to Valley Forge, painted by William Trego, 1883.
Source: Michner Museum.

Article II of the 1967 Outer Space Treaty is pretty clear on this point: no part of the moon can be subject to the sovereign claim of an Earth nation. The United States has ratified this treaty, and under Article VI of the U.S. Constitution, ratified treaties are the supreme law of the land, trumping all federal laws. So that is the end of that. There won't be any legal national parks on the moon unless the Outer Space Treaty changes.

So why did Reps. Edwards and  Johnson bother to propose H.R. 2617 in the first place? I don't think it was just a quirky attempt to claim U.S. sovereignty over the moon. Both women have scientific backgrounds: Rep. Johnson is a registered nurse; Rep. Edwards, an attorney, worked for a NASA contractor before being elected. Both women have campaigned on behalf of NASA and STEM education. Both women sit on the House's Committee on Science, Space, and Technology (Rep. Johnson is the ranking member).

Rep. Edwards.
Source: Raw Story.

Creating an unconstitutional park wouldn't be Rep. Edwards' first foray into illegality in support of a cause she cares about. Back in 2009 she and several other congresspeople chose to be arrested protesting at the Sudanese Embassy, in order to draw attention to genocide in Darfur.

So, what was the true aim of H.R. 2617? As I mentioned, aside from protecting the Apollo sites, H.R. 2617's stated goal was to educate the public about the Apollo program. The Washington Post, CNN, and many other mainstream news outlets covered the story of H.R. 2617 and the Apollo sites. So maybe Rep. Edwards accomplished at least half of the aim of the bill, without it even passing? And at no cost to taxpayers, beyond the expense of writing an 8 page long bill!

Sources: Discovery; H.R. 2617; 16 U.S.C. 1a-5; U.S. Constitution; Wikipedia; the 1967 Outer Space Treaty.

Friday, September 13, 2013

Salvage Law in the Space Age

Much of the Apollo hardware that brought astronauts to the moon never returned to the Earth. Pieces of Saturn V rockets and one lunar module are orbiting the Earth or Sun, having been jettisoned en route to and from the Moon. One such example is the "mystery object," J002E3. It's a piece of space junk that NASA is pretty certain must be the third stage of Apollo 12's Saturn V rocket. Discovered by an amateur astronomer in 2002, it was originally assumed to be just another asteroid. But then astronomers charted its crazy orbit for a little over a year:

Asked if J002E3 might be an alien spaceship, a NASA official responded, "if it is, the aliens aren't good pilots."
Source: NASA.

And they realized that the object must have been captured by Earth's gravity relatively recently; an orbit like that wouldn't persist over a long period of time. Further, a reading of the spectrum of sunlight reflected off J002E3 indicated it was white... in fact, painted white with the titanium dioxide based paint that was used on the Saturn Vs. Calculating its orbital pattern back in time indicated that it had likely entered an unstable Earth orbit sometime around 1971. But since all Apollo 13 and 14 hardware is accounted for,* it seemed it must be from a slightly earlier flight.

* There's a chance it's one of the panels that covered the Apollo 14 lunar module en route to the moon, but the color is wrong so probably not.

Apollo 12: the bit orbiting the Earth.
Source: NASA.

That's how NASA concluded that J002E3 is most likely the third stage of Apollo 12's Saturn V. But why did that rocket end up as a mystery object in an erratic orbit? The Apollo 12 mission plan was for the astronauts to jettison the nearly used up third stage on the way to the moon. After jettisoning it, Mission Control would remotely triggered the stage to ignite and burn up the last little bit of remaining fuel, powering the rocket into a stable solar orbit. Something must have gone wrong with that final burn, and this is the result.

Apollo 13, on the launch pad.
Source: NASA.

Reading about this Apollo relic got me thinking: what would happen if an interplanetary salvage crew towed the third stage back to Earth to sell it to the highest bidder? Apollo artifacts bring good money, especially those that actually flew in space. Once commercial spaceflight really gets underway, what is stopping folks from salvaging and selling Apollo gear left in outer space? Well, it turns out that would be illegal... Apollo-era rocket parts left in outer space are the property of the U.S. government.

An F-1 rocket nozzle on the bottom of the Atlantic Ocean.
Source: Bezos Expeditions.

A few months ago Amazon founder Jeff Bezos sponsored a space age fishing expedition: Bezos Expeditions located, and then salvaged, parts of Apollo 11's engines from the Atlantic Ocean.  These engines ("F-1" engines), powered the first stage of the Saturn V rocket that propelled Neil Armstrong, Buzz Aldrin, and Michael Collins to the moon. News accounts of the marine salvage operation (which was no small feat- the engines recovered were more than three miles underwater!) noted that the engines were still U.S. government property. That's clearly true under international law: Article VIII of the 1967 Outer Space Treaty, which the United States has ratified, states that objects launched into space remain the property of the treaty signatory state that originally registered the object. This is true regardless of where the property is located.

Cleaning off an F-1 Rocket.
Source: Bezos Expeditions.

The Apollo relics that Bezos recovered are also U.S. government property under maritime law. Since NASA didn't abandon its claim to the F-1 rockets, they are still NASA property, even under several miles of water. This principle was recognized in U.S. federal court, in a case before a U.S. Court of Appeals in 1992 (U.S. v. Richard Steinmetz 973 F.2d 212 (3rd Cir. N.J. 1992)). The court held that the bell recovered off a sunken Confederate States of America warship remained property of the United States, even after it was salvaged from the wreck.

Part of a Saturn V rocket.
Source: Bezos Expeditions.

The decision's author, Judge Dolores Sloviter, seems at times to be making only a modest effort to reign in her excitement at writing on such a Clive Cussler worthy topic. Her opinion (available here, and definitely worth a read) delves enthusiastically into the full tale of the warship, the C.S.S. Alabama. It's quite a story!

From 1862-1864, the C.S.S. Alabama roamed the seven seas, sinking Union merchant ships. Then she was sunk in battle off the coast of France in 1864. Her bell was recovered by a British wreck diver in the 1930s, who sold it to a London pub, in exchange for unlimited drinking privileges. A few years later, the pub was destroyed in the blitz. When the bell was dug up from the rubble of the pub, it was sold and resold a few times before ending up in the possession of the antiques dealer who became the target of the U.S. government's lawsuit.

French impressionist Edouard Manet painted the scene of the Alabama's final battle.
Source: Wikipedia.

As for Judge Sloviter's legal analysis... her conclusion is firmly rooted in maritime law and longtime international practice. The United States government (the successor to the bell's original owner, the Confederate States of America) did not deliberately abandon the wreck and bell. Previous Supreme Court cases had held that some explicit statement of abandonment, maybe even congressional action, is necessary for the U.S. government to relinquish legal ownership. Since no abandonment occurred, the bell remained federal property.

C.S.S. Alabama. It looks like a sailing ship, but it also had a steam-driven propeller.
Source: Wikipedia.

Judge Sloviter goes on to explain that maritime salvage law isn't always quite that simple; older U.S. naval vessels (i.e., pre-Civil War era ships) are sometimes considered abandoned because of the long passage of time. But U.S. government property that was sunk in oceans after 1860 is pretty clearly still U.S. government property.

Apollo 11, post-splashdown.
Source: NASA.

So, under international law and maritime law, all Apollo hardware launched into space is U.S. government property, regardless of where it eventually ends up. Does that mean the U.S. National Park Service can set up a new national park on the moon, preserving for posterity the Apollo landing sites? I will answer that question in my next post! :-)

Sources: Bezos Expeditions; The Space Review; U.S. v. Richard Steinmetz 973 F.2d 212 (3rd Cir. N.J. 1992); 1967 Outer Space Treaty; NASA.

Thursday, August 29, 2013

Wet Feet or Dry Feet?

There seems to be an endless supply of bizarre legal questions involving jurisdiction and outer space. Here's a particularly William Gibson-esque scenario:  The world's first Cuban cosmonaut, Arnaldo Tamayo Méndez, launched into orbit in 1980 aboard Soyuz 38. The U.S. had no functional, manned spaceships in 1980... but imagine it had. What if Cosmonaut Méndez had donned a jet pack and flew from the Soyuz over to an American spaceship? On arrival, could he have claimed asylum in the United States under the "wet feet, dry feet" policy?

The crew of Soyuz 38, pre-launch.
Source: Scoop News.

Here's what I mean by "wet feet, dry feet": apparently Cubans seeking asylum in the United States are treated differently than other nationalities under U.S. immigration law. It seems they are generally eligible to apply for asylum by virtue of the fact that they are Cuban; there is no need to provide detailed documentation of persecution. But, the Cuban must reach the United States before claiming asylum. Under a 1992 Executive Order, Cubans intercepted on boats en route to the United States are repatriated. But under federal law (8 U.S.C. § 1225), a Cuban who "arrives in the United States" can apply for asylum. So a Cuban who makes it to shore in the U.S. (or arrives at the U.S. border) can apply for asylum.

The Vinales Valley, Cuba.
Source: Get in Travel.

What counts as arriving in the United States? Under the 1967 Outer Space Treaty, Article VII, countries have jurisdiction over the objects they launch into space. The United States has ratified this treaty. Would Cosmonaut Méndez, safely aboard Skylab or a Space Shuttle, have "arrived in the United States" within the meaning of federal law?

Negotiating the 1967 Outer Space Treaty.
Source: United Nations.

Of course, I haven't seen any evidence that Cosmonaut Méndez would have been remotely interested in testing this legal theory. Soyuz 38 landed safely in Kazakhstan after a little over seven days in orbit. Cosmonaut Méndez is now a retired Brigadier General, still living in Cuba. In 2011, the newly opened Havana Planetarium held an event in his honor, celebrating the 30th anniversary of the historic flight.

Inside the Havana Planetarium.
Source: Juventud Técnica.

But based on a 2006 federal court decision, we have some idea of how this bizarre hypothetical would play out. In 2006, 15 Cuban refugees (including two children) made the perilous sea voyage from Cuba to the Florida Keys, landing on an abandoned bridge before being discovered by the U.S. Coast Guard. Seven Mile Bridge no longer fully linked to land, though it was still owned by a Florida state agency. The Coast Guard claimed that the Cubans had "wet feet" since the bridge was an "artificial structure without its own territorial sea." The Coast Guard supported its position with a 1907 court decision that defined landing in the U.S. as coming to the shore from a boat.

Seven Mile Bridge.
Source: Lonely Planet.

But when the case was appealed to federal court the judge decided differently: arriving at Seven Mile Bridge counted as arriving in the United States; the Cubans were eligible for visas.* The judge noted that the U.S. Coast Guard's website even states that reaching rocks or bridges or piers suffices; just because a bridge is not connected to land did not mean it is not the United States. Fourteen of the fifteen Cubans chose to apply for asylum. For them, an extremely difficult journey has hopefully had a happy ending.

Seven Mile Bridge, back when it was new.
Source: Friends of Old Seven.

* = The judge added a bizarre footnote to the decision: if you've seen the Arnold Schwarzenegger film True Lies, you've Seven Mile Bridge get blown up! Apparently the movie producers rebuilt the missing part, reconnecting it to land, just so they could blow it up for the movie(!) So for a few weeks in 1993, Cubans could have landed on the bridge and applied for asylum without any legal dispute.

Source: Top Travel Lists.

While it presents an interesting set of facts, the Seven Mile Bridge case is sobering, isn't it? It's terribly frightening to imagine being one of the fifteen people on that bridge. At best, you are starting over in a new country where you don't speak the language, don't have a job, don't know anyone. You many not get see your family and friends back home again for years, or decades, or ever. At worst, you could be sent home, facing danger, and having spent all your savings, risked your life, and endured God knows what to reach the United States.

Sources: This compelling news story describes the plight of a few relatively fortunate Cuban asylum seekers, giving a human dimension to a political issue. Additionally, I drew on 8 USC § 1225; Latinamericanstudies.org; Movimiento Democracia, Inc. v. Chertoff, 417 F. Supp. 2d 1343, 1344 (S.D. Fla. 2006); Executive Order 12807 (1992); the 1967 Outer Space Treaty; and Wikipedia.

Disclaimer: This blog does not constitute legal advice, or form an attorney-client relationship.

Monday, July 8, 2013

Carnival of Space, Week #309!

Welcome to the 309th Carnival of Space! This is my fifth time hosting the Carnival; you can find my first Carnival here, my second carnival here, my third carnival here, and my fourth carnival here


Source: darkroastedblend.com.

Urban Astronomer shares news of Scopex 2013, a telescope and astronomy expo starting July 20th in Johannesburg, South Africa. 

Next Big Future features a recently released study demonstrating that the number of potentially habitable planets orbiting red dwarfs may be double what we previously believedAlso over at Next Big Future there's news from the United Kingdom: funding proposals are moving forward for a super-fast, prototype rocket plane, the Skylon.

Chandra X-Ray Observatory has posted some dazzling photos of supernovas, along with a few interesting facts that scientists have learned about these explosions.

Source: darkroastedblend.com.

We've found some odd new rocks on Mars... the Meridiani Journal shares photos and speculation on these "weird bubble" formations.

Astroblog features some beautiful photos of the Aurora Australis taken last month in Australia and Tasmania. Astroblog also shares the names of Pluto's most recently discovered moons, and features a story on the Asteroid 5099 Iainbanks!

The Venus Transit recalls the history of Israel's first satellite launch, which occurred 52 years ago last week.

Universe Today reports that there's a risk that landing a spacecraft on an asteroid could create an avalanche.

Links Through Space shares news of the European Week of Astronomy and Space Science. It's the annual meeting of the European Astronomical Society, occurring this week in Finland!

Source: Tumblr.

Thanks to all of this week's excellent posters! Stay tuned for next week's Carnival, over at the Chandra X-Ray Observatory Blog...

Monday, May 27, 2013

Do You Need to Wear a Spacesuit on the Moon?

Surprisingly, no! With a few caveats: you'll have to wear warm socks and shoes, a mask hooked up to an oxygen supply, and you better keep on the dark side of the moon (or the shadows of the light side). You won't be comfortable... but the temperature, radiation, and vacuum won't kill you immediately.

Neil Armstrong, partially suited up.
From a stain glass panel at the Naval Museum in Valparaiso, Chile.

Since the moon doesn't really have an atmosphere, there's nothing insulating its surface from wild temperature swings. It gets as cold as nearly -250 Fahrenheit in shadow or on the dark side and up to nearly 225 Fahrenheit in the sun. On Earth, either extreme would quickly be fatal to an unprotected human. And on the light side of the moon, heat radiating from the sun would be dangerous. But the dark side of the moon is a different story. In the near-vacuum of space, your body is far slower loosing heat than here on Earth, because there is no air to conduct heat away from your body. That's why -250 Fahrenheit in the near-vacuum of space would not feel horribly cold. 

However, if you touched anything at the ambient temperature of the dark side of the moon, you'd feel quite a chill, because matter will conduct heat efficiently, unlike the vacuum. So, you'd just need to wear boots with well-insulated soles, otherwise the bottoms of your feet would quickly freeze and would conduct away heat from the rest of your body too. Well-insulated gloves would also be a good idea if you plan to pick up any moon rocks!

Al Bean, Neil Armstrong, and Roger Chafee completing pre-mission geology training.
You could dress like that on the dark side of the moon! (For a while at least...)
Source: senior-crown.tumblr.com.

As long as you can breathe, the vacuum does not pose as big a risk to the rest of your body as you might think. We regularly experience changes in air pressure here on Earth, by swimming underwater or climbing a mountain or flying in a plane. Walking around in an absolute vacuum would draw fluid to your skin, breaking some small blood vessels at the surface and bloating you. But in the short term, you wouldn't inflate like a balloon or explode or anything gross, you'd just look puffy and feel uncomfortable.

Preferably, your breathing apparatus would cover your eyes, nose, and mouth. Otherwise the moisture in your eyes, nose, and mouth would evaporate quickly into the vacuum. And, your exposed skin would dry out uncomfortably. Eventually, radiation would become a concern, too.

During a record-breaking high-altitude jump, Colonel Joe Kittinger 's right suit glove depressurized in near-vacuum.
His hand didn't explode, but it did swell up painfully.
Source: Wikipedia.

So for all those reasons, and because anyone in sunlight would overheat without insulation, astronauts on the moon or on spacewalks wear spacesuits. These bulky, heavy, mobility-limiting pressurized suits (including life support systems, the typically extravehicular activity suit weighs over 300 pounds!) insulate astronauts as they move between shadows and sun. They also provide some radiation protection, and they prevent skin from swelling up uncomfortably.

An alternative to the type of spacesuit astronauts use today is a "hard" spacesuit:
The whole suit is pressurized, but since it is hard, rather than soft, it does not puff up and make joint mobility difficult, and can also be more pressurized than a "soft" suit.
Source:  mlkshk.com.

But there is an alternative to the traditional, fully pressurized spacesuit we're used to. Astronauts could wear a mostly unpressurized spacesuit. The entire suit body could be unpressurized, except for the helmet and maybe the gloves and boots. The main function of an unpressurized spacesuit is to provide insulation, radiation protection, and prevent vacuum-induced swelling. It does these things not by creating an atmosphere inside the suit, but by mechanically compressing the whole body. This is why the unpressurized suit's gloves and boots are still pressurized- all the small joints in the hands and feet make it hard to compress their surfaces evenly and thoroughly.

Back in the 1960s, NASA first worked on creating an unpressurized suit, but that program was discontinued around when the Apollo missions ended. Here's a prototype of the unpressurized suit engineers were designing:

A prototypical unpressurized spacesuit, which compresses the body mechanically.
Source: NASA.

NASA revisited the notion of the unpressurized suit recently, funding the Massachusetts Institute of Technology's development of the "bio-suit." MIT Professor Dava Newman, the lead scientist on the project, models the suit her team designed:

Professor Dava Newman models the bio-suit.
Source: NASA.
Needing to design a suit that would compress the body rather than be airtight, Prof. Newman drew on the experience of an Italian manufacturing company that produces carbon-fiber racing suits for European race car drivers. Unlike the unpressurized suit designed during the Apollo program, the bio-suit's material has elasticity. It stretches with the wearer, and it doesn't overly-compress a person wearing the suit in a pressurized atmosphere.  The old-fashioned Apollo era unpressurized suit had no elasticity. Thus it would squeeze the wearer so tightly that if he or she wasn't in a vacuum, the circulation of blood would be constricted and he or she would pass out in less than a half hour!

While the bio-suit has to be modeled specifically to fit each individual wearer's body, its materials and construction are so much simpler than pressurized spacesuits that it could still be dramatically cheaper to produce. And, as you can see from the above photo, the bio-suit allows normal movement. Unlike the Apollo astronauts, whose suits allowed only partial movement of the knees, elbows, and torso, a bio-suit wearer has a fairly normal range of motion.

A puncture in the bio-suit won't threaten the air supply, either- you can just patch it with a bandage-like wrap. And, the bio-suit could weigh just a small fraction of the weight of a traditional, fully pressurized suit. Even without the air supply, an extravehicular activity suit still weighs over 100 pounds- which isn't a problem in micro-gravity, but would be a serious encumbrance to walking around on a planet like Mars.

The suit looks really futuristic, doesn't it? Not that how it looks matters, of course!
Source: NASA.

I think the bio-suit is so neat! But like so many amazing ideas for space exploration, Prof. Newman's project is not fully funded. Her team has not yet produced a prototype that could safely be tested by actual astronauts in outer space. All research on the suit to date shows that it is a workable, useful concept. So, I hope one day folks can test it out in Earth orbit or beyond!

Sources: NASA; Wikipedia; MIT; Slate; Spectrum.ieee.org; damninteresting.com.

Sunday, April 28, 2013

Carnival of Space, Week #299!

The Sun.
Source: Wall Street Journal.

I am hosting the Carnival of Space again this week!! This is my fourth time hosting the Carnival; you can find my first Carnival here, my second carnival here, and my third carnival hereThe Carnival is a weekly round-up of space stories from around the internet. If you've got a space-related blog, you too can join the Carnival of Space. Email carnivalofspace at gmail dot com to host, share a story you wrote, and to get to know other space bloggers!

This week's Carnival of Space explores our solar system and beyond, and includes a lot of news about spaceships! Read on for some interesting stories...

Source: NASA.

Urban Astronomer shares news of a recent discovery by NASA's Chandra X-ray telescope: a huge halo of super-hot gas that surrounds our galaxy!

Folks in Europe, Africa, Asia, and Australia might have seen last week's partial lunar eclipse, which was the briefest lunar eclipse that will occur this century. Gadi Eidelheit of Venus Transit shares his photos of the partial lunar eclipse.

The Meridiani Journal shares news about Jupiter's atmosphere: it's got lots of water, thanks to the impacts of comets over the years!

Source: One Minute Astronomer.

Earth Science Picture of the Day features a beautiful photo of a chrondrite meteorite and chrondrules, as well as an explanation of their composition and origin.  

Dr. Paul Spudis of The Once and Future Moon explains what we've learned about the composition and formation of the lunar crust from the Apollo and GRAIL missions.

Everyday Spacer shares some space-related activities you can do locally or online. Reading Everyday Spacer is a great way to find out about many different space exploration themed events that you can do- often, right in your hometown!

Cheap Astronomy's fascinating recent podcast tells the story of seven lesser-known astronauts: the "increment astronauts."

Over at Astroblog, Ian Musgrave shares some neat amateur space photos: the Comet C/2012 F6 Lemmon; the occultation of the star Alpha Librae (also called Zubenelgenubi, which means "southern claw" in Arabic); and photos of last week's partial lunar eclipse as well. 

Source: elf_leon.livejournal.com.

The Next Big Future shares recent some exciting recent developments in spaceflight. It features news from the Harvard Business Review, which examined SpaceX's process for cost innovation in spacecraft development, and how SpaceX can serve as a model for other businesses. In more SpaceX news, the Grasshopper recently flew 820 feet straight up in a test flight, and Next Big Future features a video of the flight. Virgin Galactic's SpaceShipTwo is going to embark on a hypersonic test flight sometime in the next few days... and then hopefully it'll be headed into space later this year! The Next Big Future also shares news about the Starship Century Symposium, which is coming up in a couple weeks; attendees of this conference will discuss whether this will be the century we travel beyond our solar system. I wish I could be there, it looks like it's going to be so, so cool!

Lastly, on my blog, I told a story about the Apollo Guidance Computer, and a computer glitch that could have derailed Neil Armstrong and Buzz Aldrin's moon landing.

Source: NASA.

Wednesday, April 24, 2013

Tech Support On the Way To the Moon

In honor of Boston, this week I'm telling a little story about the Apollo Guidance Computer, which was designed and built at the Massachusetts Institute of Technology.

The Apollo 11 lunar module, just after undocking from the command module.
Source: National Geographic.

The Apollo Guidance Computer* gave Apollo astronauts the data they needed to pilot the command module and lunar module during lunar landing, ascent, and docking. There was so little room for error in these tasks that the precision afforded by a computer was necessary. When the Apollo Guidance Computer was built, it was a technological feat... but it is roughly comparable in terms of processing power to today's graphing calculators. Nowadays, if you have some programming expertise and a lot of spare time, you can actually build your own Apollo Guidance Computer, no MIT degree or MIT lab facilities necessary. I wish building a Saturn V rocket was that easy!

 * = Actually, there were two Apollo Guidance Computers aboard every flight to the moon. One aboard the command module, one aboard the lunar module. Plus, there was a launch computer inside the Saturn V rockets and an abort computer in the lunar module.

An engineer with a mock-up of the Apollo Guidance Computer interface.
Source: MIT.

While shockingly simple compared to today's computers, the Apollo Guidance Computer was a very capable piece of equipment. It could multi-task, performing up to eight different calculations at the same time. It could also prioritize its memory as needed. And, it was relatively small and lightweight, an important design feature on a mission that was already consuming nearly a million gallons of fuel just to leave Earth's gravity. At a time when room-size computers were common, the Apollo Guidance Computer weighed 70 pounds and occupied about one cubic foot of space.

An MIT Instrumentation Lab engineer runs tests on the Apollo Guidance Computer.
Source: MIT.
Like any modern computer, the Apollo Guidance Computer didn't always work perfectly. Any number of problems would trip it up, and it would respond by producing an error code. There were many, many possible error codes. Some error codes signaled computer malfunctions, some required immediate corrective action, and some could just be ignored. Astronauts and mission control staff devoted considerable training time to learning what each error code meant, and how they should respond.

The crew of Apollo 11, and the "moon."
Source: ontheunspeakable.tumblr.

NASA Flight Director Gene Kranz's autobiography, Failure Is Not an Option, tells an interesting story about these error codes. Astronauts and ground crew spent weeks and weeks practicing mock missions in advance of the Apollo flights. They'd run through these fake missions just like they were the real thing, with Simulation Supervisors throwing problem after problem at them. Sometimes, mission control would work out a solution in time to salvage the moon landing and save the fake flight. Sometimes they wouldn't figure out a solution in time and the simulation would end with a fake disaster.

A fisheye view inside one of the Apollo lunar module simulators.
Source: howstuffworks.com.

The Simulation Supervisors were always relentless, with one exception. They gave mission control a relatively problem-free flight for the final pre-launch simulation. That way, the practice runs would end on a high note, with mission control engineers feeling that they were completely prepared for the real flight.

So, a few days before the launch of Apollo 11, Kranz and his crew went into the final scheduled lunar landing simulation expecting an easy flight. During the practice descent, the Simulation Supervisor sent the lunar module's Apollo Guidance Computer a "1201" error code. Not a single engineer in mission control knew what this code meant. Without any idea of what had gone wrong, the only safe choice was to abort the landing.

Richard Koos, the Simulation Supervisor, gave mission control the bad news: calling off the landing was the wrong decision. The 1201 code just meant that the Apollo Guidance Computer was temporarily overloaded; it did not indicate an impending computer crash or any other mission-critical problem. Kranz and mission control had just (in pretend) wasted the Apollo 11 flight and ruined their chance at a moon landing because they hadn't known what the 1201 code was.

Crowds in Grant Park, Chicago watch the first moon walk.
Source: Washington Post.

Recounting the story in his autobiography, Kranz tells how furious and ashamed he was. Kranz, along with Jack Garman (the engineer charged with keeping track of Apollo Guidance Computer codes), Chris Bales (a guidance officer) all had that particular series of alarm codes seared into their brains. They would never forget what a 1201 (or a related code, 1202) meant.

Astronauts Charlie Duke, Jim Lovell, and Fred Haise in mission control during Apollo 11.
Source: Wikipedia.

A few days and a few hundred thousand miles later... the real Apollo 11 lunar module was descending to the moon with less than 10,000 feet to go when the Apollo Guidance Computer produced a 1202 alarm code, and then a 1201 alarm code. Neil Armstrong and Buzz Aldrin asked mission control what the alarms meant. Thanks to the final simulation, Kranz, Bales, and Garman knew the answer right away- they were "go" on the alarm! Capcom Charlie Duke told them they could ignore the alarms and keep descending. Just a couple minutes later the Eagle landed safely in the Sea of Tranquility!

Celebrating after the Eagle landed.
Source: wallcoo.net.

What caused the 1201 and 1202 alarms? The Apollo Guidance Computer was receiving too much radar data. Buzz Aldrin (an MIT grad!) had asked MIT engineers to design the computer to be able to track both radar readings from the lunar surface and the command module. This would allow a quick decision to land or return to the module. But the Apollo Guidance Computer couldn't properly track both sets of data. So at the stage in lunar descent when the alarms occurred, the computer was getting simultaneous readings from both radar systems, and it was causing brief system overloads. 

Sources: American Space; Popular Mechanics; NASA; doneyles.com; Gene Kranz, Failure Is Not an Option; Air & Space's The Daily Planet blog; Computer Weekly; Wikipedia.