Monday, November 10, 2014

How the "Interstellar" Spaceship Compares to the Real Thing

Christopher Nolan's new space epic Interstellar opened in theaters late last week. The film follows a team of intrepid astronauts in the not too distant future as they traverse a wormhole to the distant corners of the universe. They navigate black holes and hostile planets in a desperate attempt save the people of Earth from an all consuming, planet-wide dust bowl.

Matthew McConaughey as astronaut Cooper, exploring a frigid planet surface. Image: Paramount.

Legendary physicist Kip Thorne of Caltech was the science advisor and wrote one of the earliest treatments of the movie. General relativity and its weird effects like time dilation, warped space and gravitational singularities are integral to the plot, and we'll have a full rundown of the physics of it all soon.

The film's sleek little Ranger spaceship is as much the star of the show as Matthew McConaughey, Anne Hathaway or Jessica Chastain and I got a chance to get an up-close look at it. The National Air and Space Museum's Udvar-Hazy center is hosting the actual spaceship prop used in the movie. Clearly a field trip was in order.

So I wanted to know, how does it compare to a real spaceship? Fortunately, there was one not too far away I could check out. 
Clearly the film's Ranger is a lot smaller, flatter and more angular than Discovery, but a lot of its motifs are borrowed directly from the orbiter. The most obvious is its black and white color scheme. 

Not only is the monochromatic look stylish, it's meant to be practical as it's modeled after the heat shield tiles that cover much of the space shuttle. When the orbiter lands, they dissipate the intense heat that builds from the compression and friction of air the shuttle is using the slow down. The white tiles can withstand up to about 1,200 degreed Fahrenheit, while the black heavier-duty tiles can last up to about 2,300 degrees. If you look carefully at both craft, you'll see that tiles only cover part of their surfaces. The rest is actually a kind of lightweight, durable heat-resistant fabric NASA started using for some of the later shuttles they call Flexible Insulation Blankets.

There's a ton of other details the film's art department borrowed from the real deal. Like those black thrusters, known as the reaction control system, used by the crews of Discovery to maneuver the shuttle while in orbit…

…bear a striking resemblance to the thrusters behind the crew compartment and in the nose of Ranger. At the same time, that panel of valves and knobs just above the trusters

…looks quite a bit like the shuttle's launch umbilical panel. This is the interface where hoses carrying fuel and electricity are hooked up to the orbiter while it's still on the launchpad.

Which brings us to the space shuttle's engines. Big, round and bell-shaped, they're the classic design of what rocket engines are supposed to look like. Rocket engines work essentially by directing the force of explosions in one direction. When an astronaut fires an engine, it sprays liquid fuel and an oxidizer together inside the combustion chamber and ignite on contact. Instantly the liquid turns into hot, energetic gas which is forced out through the thin neck of the rocket engine and directed by the bell-shaped nozzle that sticks out the back. Because of Newton's first third law of motion, that for every action there is an equal and opposite reaction, the immense force of the hot gas shooting out the back of the rocket pushes the space shuttle forward.

The engines on the back of Ranger look nothing like the shuttle's. They're kind of rectangular with that weird extra fin in the middle. Must be a Hollywood invention, right? Well, not exactly…

Here I really have to give credit to the design team because it really seems like they did their homework. The space shuttle is of course the biggest and by far most successful and famous spaceplane, but it's not the only one. Over the years, NASA and the Air Force have designed a whole mess of different test vehicles including the secretive X-37B, the X-38, the Northrop HL-10 and the canceled X-33 VentureStar whose engines look a lot like those on the Ranger.

Image: NASA

The VentureStar's engine would have been an experimental design called the aerospike. Instead of a big round nozzle, it had a specially shaped fin in its center that directed the flow of burning gas down the length of it and out the back of the rocket engine. Near the Earth's surface, atmospheric pressure keeps the flow smooth against the fin and helped shape it into a narrow column behind the rocket, making it a very efficient design for lifting off of a planet's surface, which the Ranger does a lot.

A NASA test of an aerospike engine. Image: NASA.

The engine detail is onscreen for maybe a few seconds throughout the film altogether. Still, it's pretty cool that the designers seemed to go that extra mile to not only bring in such an obscure engine design, but have it be one that that would actually be optimal for the Ranger if it was real. 


  1. Where are the fuel tanks on Ranger?

    The shuttle fuel tank was larger than the orbiter.

    1. that was used only for getting into orbit. once in orbit, it waas detatched

  2. interesting the engines could be combo of rocket jet and scramjet mixing fuel with air initially ( they have to pick a planet that has at least 21% O2.) take off is like a jet using aerodynamics and lift , then as velocity increases scramjet then when o2 is gone,, rocket. I assume much of the system is automated , and with modern telemetry why you would want to land with multiple humans who weigh 200 lbs perhaps each ( with suit and accessories on) is beyond me, its a waster of fuel.

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  4. @tim

    The concept spaceplane Venturestar (mentioned in the article) used internal fuel tanks. Iirc, they were actually one of the main reasons for its cancellation. They just couldn't make the tanks work. It's possible that the Rangers are incredibly light (the Shuttle was incredibly big, heavy, and needed to do lots of things at once) being that all they do is just bring light payloads (people, robots, snacks, science things) from and back up to Low Orbit.

  5. if you play ksp (kerbal space program) you will know that areospikes use up a lot of fuel very fast. so the ranger would not even be able to get out of earth... just an idea.

  6. What I don't understand is just how aerodynamic is this spaceship? In the movie it takes off from the water planet so it is able to move through an atmosphere. I mean it doesn't have any wings so it wouldn't seem to have that great maneuverability in real life. Could it be possible to build an RC version of this and actually get it off the ground? It seems it wouldn't since it looks like a flying rectangle.