Well, in my opinion anyway. I found the story of James Cameron’s Avatar to be highly derivative. It is the details that make his movies shine. Part of this is Cameron doesn’t half-ass things (story aside, but the series isn’t done I suppose so I’ll wait and see what the sequels bring), and his brother is an aerospace engineer too so that helps. As South Park put it, James Cameron does what James Cameron does because James Cameron is James Cameron, now if only he could raise the bar in reality as in that episode…
I digress though.
So, as you have probably figured out by now, this is the post about the ISV Venture Star I promised a while back. The header image of this blog is a concept render of the ship that appeared in Avatar, but not the only picture of it. There are quite a few, but besides some concept renderings it is all stills from the literally 30 seconds of screen time the ship has in the movie. Such a crime to deny the ship the true time it deserved to be shown off. Why is that such a crime? Because James Cameron doesn’t half-ass the details, and therefore this ship is designed with all the intent of actually using it for an interstellar mission in reality (assuming Pandora and Unobtanium actually existed, more on that later). It is likely the novelization of Avatar devoted more than a page to the ship but when the rest of it is still about Na’vi, misrepresented human interests, and Jake Sully’s poor life choices I haven’t bothered to read it to find out.
Beauty shot, I use this as my Google+ and Twitter header images because shiny.
Mmm… where do I start? Well let’s get some background first. In the movie humans travel to and from Pandora, a fictional Earth-like moon orbiting a gas giant (Polyphemus, also technically fictional, though not impossible) in the Alpha Centauri star system which is the closest star system to ours ranging about 4.37 light years away (1.34 parsecs for astronomy buffs or anyway that prefers that unit). As you might recall from my other posts, space travel is really frakking hard and space is really frakking huge. It takes months to years for our probes to make it to other planets, and Voyager 1 you’ll recall has been flying for over 30 years now and is only just about to go into interstellar space. Voyager 1 isn’t headed toward Alpha Centauri but if it was, at its current velocity (17 km/s) it would take another 77,000 years to get there. The moral is if you want to do interstellar travel, even to the closest star in the sky, you need more than your average space ship.
But wait! Sci-fi has the answer right? Warp Drive! Wormholes! We are saved! Wait.. wait… actually no. You see despite human-like aliens (which I’ll probably cover in my speculative alien biology post if I ever write it) Avatar is actually a hard science fiction story, just one disguised with pretty 3D and special effects so the standard populace won’t get bored. Now not all hard sci-fi is without FTL (Faster than light) travel, as it is the sine qua non of sci-fi nowadays. As Atomic Rockets says it “They want it, you want it, everyone is doing it.” Avatar eschews the easy way out though and decides humanity hasn’t figured that out yet, whether it is possible or not. I found this very tasteful since it takes place in the 22nd century and I don’t see viable FTL by then as likely (only in my dreams).
Ok, so standard modern-day propulsion is out, no FTL either. That means we can go no faster than the speed of light (actually slower because you can’t travel at the speed of light without being light itself). I won’t go into the details of special relativity now because I think I did in a post about warp drive a while back. Ok then, not perfect because even light takes a while to go places; it means we can’t get to Alpha Centauri any faster than ~5 years but that is a lot better than 70,000 years. This means we need some serious power and thrust to bring a ship close to the speed of light, or what is known in the trade as relativistic velocities. Currently there are only three technologies that could allow that in a feasible way: Solar Sails, Nuclear Fusion, and Antimatter.
The Venture Star actually uses a combination of all three. Though you only see evidence of the latter two. Cameron’s design notes actually state antimatter is the main method of propulsion when the photon-sail is not in use because ‘conventional’ fusion rockets just don’t have the efficiency needed for interstellar velocities, but are said to be used commonly in the solar system (in fact the TAV’s, Trans-Atmospheric Vehicles, in the movie that go from the ship to the planet are fusion driven). I say both antimatter and fusion though because his notes also state the engines use a hybrid of the two.
My favorite image, because I am an engineer I like technical diagrams, too bad it is hard to read.
Ok, first I’ll tackle the solar sail. This is a concept that is in its infancy now in the real world but has been thrown around in fiction for decades. The idea is a super lightweight material that is really thin but has a very large area is folded out in front of a spacecraft. The Sun emits light as photons which have no mass but have momentum so when the sunlight hits the sail material which is designed to be reflective it imparts a small force. This is small but it adds up over time in a vacuum and eventually gets a spacecraft moving. This makes solar sails a passive propulsion system since you aren’t directly imparting force to move. There is a faster way to get up to speed though that is used by the Venture Star: Lasers. In Avatar Cameron has it that a bunch of laser arrays in orbit of the Sun shoot beams at the Sail pushing it with far more power than the Sun alone can do. This is said to push the ship at 1.5 g’s for 0.46 years which gets it moving out of the solar system at 70% the speed of light. The logistics of this are actually a bit scary because for laser arrays to push the ship that much in that time would require MASSIVE power, and these lasers would be so powerful that anyone controlling them (RDA probably knowing the corporate power they seem to wield in this movie) could also hold everyone on Earth hostage because those lasers are already way beyond weapons grade. This is called Jon’s law for SF Authors on Atomic Rockets, and it reads “Any interesting space drive is also a weapon of mass destruction.”
That is how the ship leaves, at that point it folds the sail up and hides it in the cargo section, before that it attached to the boom in between the radiators. This is why you never see the solar sail in the movie because you never see it leave Earth. If you think you see the sail, you are actually seeing a mirror shield used to protect the ship from the lasers which is also part of the whipple shield, more later. The sail is actually 16 kilometers in diameter, dwarfing the ship which is 1.5 kilometers long. The ship then coasts for most of the trip before it flips over and then uses its two antimatter/fusion engines to slow down at Pandora.
This is how you see the ship in the movie, call outs show what each part is, as well as the direction of travel (green) and the direction of the engine exhaust (pink).
So quick lesson, antimatter is the opposite of normal matter, the same in every way except with opposite charge. One of the biggest mysteries of the universe is why everything is normal matter and not antimatter since there should have been equal amounts at the start. When matter and antimatter touch, they self-annihilate each other in a burst of energy. This makes the conversion of mass to energy 100% by the equation E=mc^2. Now you know a real use of that equation if you didn’t before! Basically no fuel can do better than that, so antimatter is the prize jewel. We can make it.. but not very well, it is really hard to contain. The record is some atoms of anti-hydrogen being held for about 15 minutes. A magnetic field in a vacuum could do it indefinitely if we figure out how to make it in large/useful quantities (we can’t yet).
So the engines use hydrogen and anti-hydrogen in those spherical tanks you see and annihilate them slowly which releases massive energy which is controlled with by superconducting magnets and channeled out the engine nozzles. extra hydrogen is thrown into this plasma to add more thrust. It is likely due to the magnetic field and the extreme energy of the plasma that the injected hydrogen will undergo some fusion adding more energy, hence why it is called a hybrid antimatter/fusion engine. These two engines decelerate the ship for another 0.46 years at 1.5 g’s again. The entire trip by the way takes a total 6.75 years one way, with most of it being coasting with no propulsion except for small correction maneuvers. However at 70% speed of light, the trip will only be slightly less than 5 years for those on the ship due to relativistic effects of time dilation. Long trip, but better than the alternative.
From the front you can see the massive radiators, the sail attachment, the remass tanks and the engines.
You might have noticed something though, the engines are at the front of the ship. It can be hard to tell at first what the front of the ship is, but in fact the big part with the radiators and the engines is the front when the ship is under propulsion (when not thrusting there is technically no front because in space ships do not need to point in any specific direction except for defensive reasons). It might seem weird that the engines are in front and the rest is behind them but this is not a new design. Robert Goddard’s rockets did that too, and the fictional Valkyrie by Charles Pellegrino and Jim Powell did the same. Dr. Pellegrino is actually a friend of James Cameron from when he made Titanic since also happens to be an expert on that ship too, so not hard to see where Cameron got the idea. This configuration of rocket engines pulling the ship like a tractor or a horse pulling a carriage instead of ones pushing a ship is more efficient believe it or not. Since for such a long trip mass saving is necessary every gram counts and if you pull a ship using a tensile truss like Venture Star does, it requires less mass. This is because a large distance is needed between the engines/reactors and the crew section due to the radiation they emit. There are many designs where this is done with conventional push rockets but not on this scale, and loading for compressive stress requires more mass and the tensile truss combined with using a lightweight material that works best in tension (carbon nano-tubes, the current miracle material next to graphene which is actually the same thing in a different form) does the same job with a 10th of the mass. This means less fuel is needed too.
The thermal shields keep the truss from melting when the engines are firing exhaust hotter than the sun out of the nozzles.
The engines are canted slightly away from the center of the ship so the thrust plumes which are brighter and hotter than the sun don’t hit the ship, and the truss has some thermal shielding to protect it as well. The engines also have giant heat sink radiators on top of them. This I loved because you almost never see this done right in science fiction movies. You see all spacecraft will generate a lot of waste heat because of how thermodynamics is (because the universe hates you and everyone in it) and if left alone this waste heat will eventually melt the ship and boil the crew alive. The solution is to radiate that heat out into space using giant radiator fins. Actually there are other ways you can do it but that is the easiest way that will always work. If you are thinking you can just use the same technology as a refrigerator instead, well first the refrigerator actually creates/moves a lot of heat which it just dumps into the air outside the fridge. Two that is technically what you are doing anyway, a coolant removes the heat from the ship and takes it to the radiators since there is no air in a vacuum to dump the heat in, so you need to radiate it into space. In the movie you see the radiators glowing a dull red because the engines just shut off having arrived at Pandora. They will glow dull red removing the heat the engines made for two weeks after thrusting according to Cameron.
Another close up without the call outs. Here you see the engine nozzles, which use magnetic fields to control the exhaust plume. Good view of the truss too.
So that covers the front half of the ship, or the drive section. Now for the back section being towed by the truss, which is the payload section. This is the whole point of the entire ship. If you are thinking this is a lot of effort for one small section, then you sorely underestimate the difficulty of space travel. The payload section is separated into four parts: The cargo section, the TAVs, the Habitation module, and the crew module. The cargo section is a set of four ranks each divided into four modules which have six cargo pods each. These hold all the non-living materials being transported, going to Pandora it takes supplies and updated technology to the settlement there. Going back to Earth it mostly transports mined unobtanium (the mineral from the movie in this case).
A robotic arm can move the cargo pods around and load them off or onto the Valkyrie shuttles. Also, an antenna dish!
The TAV’s are the surface-to-orbit shuttles. TAV stands for Trans-atmospheric Vehicle. They look more classical to what people think of as a spaceship due to the public image of the space shuttle, this is because they have to be designed for fly in an atmosphere. These are a lot larger than the Space Shuttle though and run on fusion engines. They have spacious cargo holds that can transport 6 cargo pods to and from the surface of Pandora, or 2 cargo pods and 100 passengers. When the Venture Star leaves Pandora the TAV’s stay behind and become part of the local space fleet there since Earth can build more on site to use when ships return but the infrastructure is not quite in place for that on Pandora. They spend most of their time on trips to Pandora’s host gas giant Polyphemus skimming the atmosphere for hydrogen fuel. Somewhere in orbit or on the moon the humans can make fresh antimatter to refuel the ISV as well.
The shuttles just sit there for the trip and get the most use at arrival. Since the ship leaves them at Pandora it has a lot less mass on return.
The Habitation section is where biological cargo is stored, which is sometimes known a people. The passengers are kept in a state of suspended animation for the entire trip, so the ride seems pretty short for them. In reality we have not perfected a system for suspended animation which would help long-term manned spaceflight quite a bit, but in the 22nd century in the movie they had it worked out (the trick is figuring out how to freeze someone without forming ice crystals in the blood that get deadly, and some other things). Unlike other parts of the ship, the habitation module is made almost entirely of non-metallic materials (composites mostly and maybe some ceramics) because when metal is hit by galactic cosmic radiation it can transmute and give off secondary radiation which could hurt the passengers. It also cannot support everyone being awake at once except when they are departing or arriving on the ship. So if the hibernation system fails before the ship arrives then it causes a problem. In this case the passengers will be euthanized by the computer instead of woken up. Sounds harsh but it is better than suffocating. The cost of transporting people means on return fewer people are sent back then came, and they are usually those who have finished their RDA contracts or tours of duty with the PMC marines.
Best shot of the Habitation module. It is actually in three parts, ones of these I think is focused on carrying the Avatar bodies in their tanks.
The crew section is the final part of payload, it consists of two crew modules connected to booms coming from the center of the ship. The crew modules are for two on-duty crews that are not asleep for the trip that stay awake to make sure everyone goes well. They don’t stay up the whole 6 odd years though, cause they’d go mad with cabin fever. There is a relief crew in sleep and they takes turns every 2 years at the most. 15 crew members are awake at a time with 10 other medical crew they can wake when needed or for assisting in passenger wake up at destination. In the movie you can see the crew modules are rotating around the center, this is for centrifugal artificial gravity because being a hard sci-fi story there is no magic gravity generators. You don’t want to be spinning those while thrusting though because it would create some weird forces on the crew, so when the sail is being pushed or the engines are firing the two modules are stopped and folded down so that their bottoms (the floors) are facing the opposite of the direction of travel. When this is done the crew experiences simulated gravity due to the force of acceleration from the engines. The spinning is resumed during coast phase and when in orbit of Pandora. Thanks to this the awake crew doesn’t have to worry about the effects of weightlessness on their bodies.
The spin hub for the two crew modules, note the hinge, in the technical diagram earlier you can see the modules folded down for thrust configuration.
Better shot of the module itself. I imagine there is a flywheel in the spin hub to converse angular momentum and keep the rest of the ship from spinning.
The final section of the ship is one of the most important. It is the mirror/whipple shield. It’s job is two-fold, but its purpose is always to protect the ship. First it is used to protect the ship from the lasers used to boost it out from Earth, it blocks the lasers from vaporizing the ship, but allows them to still hit the sail (hence why it is so small and reflective). What is seen in the movie vs. the production models suggests the shield can open up and expand after thrust phase, that or they just changed it at the last-minute for some reason. That aside after thrust the ship flips around and the whipple shield is set to its full position. What is a whipple shield? It protects the ship from dust particles that might hit the ship in flight. If you are thinking that doesn’t sound dangerous, imagine a baseball thrown at 30 mph vs one thrown at 90 mph. The latter, a normal speed for a major league pitcher will hurt more when it hits you. Now imagine a dust particle hitting you at 70% the speed of light. It will destroy you and your ship in less than a second. The whipple shield prevents that by placing three barriers separated by empty space in between the ship and direction of travel. The idea is a particle hits the first barrier, fragments into plasma bits due to the speed and those hit the second barrier with less force and fragment more. By the time they reach the third the barrier can stop them entirely with little or no puncturing. A fourth barrier exists as a backup though in case that does happen. Cameron’s notes say the barriers are 100 meters apart and super powerful magnetic fields are used to deflect most stray particles, the shields are insurance for those they can’t deflect. Whipple shields are real by the way and in use on the International Space Station. They are a lot smaller though since the station is not moving at 0.7 C.
Shield in its simplest state
Close up of whipple shield in fully extended form. Clearly some changes were made in the final model from this production model.
The purpose of the Venture Star is not to explore space though, rather it is basically the equivalent of a cargo train or a really expensive interstate tractor-trailer. The primary mission past supplementing the human camp on Pandora is to tow the valuable unobtainium material from Pandora to Earth. The movie does a poor job of explaining it, but unobtainium is actually a room temperature superconductor. Superconductors are special materials that in the right conditions have zero electric resistance and magnetic field expulsion. This makes them incredibly valuable and useful as superconducting materials can hold an electric current indefinitely with no losses, something that is usually impossible. It also allows for magnetic levitation, which you may have seen before in videos of small magnets floating on a super-cooled table. That last part is important because every good thing comes with a price, and superconductors only work when cooled below a certain critical temperature depending on the material. This requires massive refrigeration systems that make mass-produced use of them rather difficult.
Room-temperature superconductors are therefore a holy grail in material science since they would allow superconductivity at temperatures no lower than 0C (32F) which is easy to maintain. However as of today no such materials have been discovered, but it is a field of study since the uses of such a material are vast. Unobtainium in the Avatar universe is the first humanity has discovered but it only exists on Pandora and they haven’t found a way to synthesize it, so they need to transport it. By the time of the movie life on Earth has become pretty crappy and they need the stuff to support the infrastructure that makes it possible for humans to live on Earth safely. As such while it looks like an evil corporate endeavor (and RDA is clearly milking their ability to mine and deliver the stuff for every penny they can get), they need it to keep humanity from dying out due to the past mistakes that left Earth so messed up (mostly global warming/climate change and a polluted atmosphere). So think twice next time you watch the movie who the bad guys are, and what the ending means for the near 9 billion people back on Earth who just got cut off from something they need to survive (whether Cameron intended this is somewhat unclear since he failed to mention it in the movie proper). The Venture Star itself has unobtainium in it, because the engines need superconducting parts to safely control the antimatter reaction. Without unobtainium the ship would need a massive refrigeration system and would be four times the size it is.
Real engineering applied to fictional space ship. That is one of the best things for someone like me.
That is my article on the ISV Venture Star, which by the way is only one of 12 ships of its class in the fiction that take turns on trips to Pandora. It is easily one of my favorite sci-fi ships and why I put it on the site banner since it is where science and fiction truly come together. I may not like much of the rest of Avatar as a movie, but because of this ship, I am willing to forgive the rest. Hope you enjoyed the details, and as always, stay shiny spacers.
State of Flux 