Spoiler warning: Firefly ended over 10 years ago and it's been 7 years since its subsequent film, Serenity*, came out, so the spoiler statute of limitations is officially up. Proceed at your own risk.*
Like many fans of the Joss Whedon space western Firefly*, Kyle Hill was shocked by the end of the* Serenity movie, when fan-favorite character Wash (Alan Tudyk) was unceremoniously impaled by a Reaver harpoon. Unlike most fans, Hill – a research assistant with a degree in Environmental Engineering and a contributor at Scientific American – decided to try and rewrite (fictional) history by proving that Wash's death was scientifically impossible, using the power of math, physics and fandom. His article originally appeared online at Scientific American, and Wired publishes this updated version with permission.
I was late to Firefly. Nearly 10 years after the show first aired and then was subsequently cancelled, I holed up in my room, coffee and external hard drive in hand, aiming to blaze through one of the most beloved sci-fi series.
A mix of science fiction and “spaghetti-western” genres, Firefly was wonderful. It certainly awakened the fanboy in me, and I quickly understood why my girlfriend envied me for being able to watch the series for the first time.
It all ended abruptly, due to early cancellation, with the last episodes of Firefly barely answering any central questions or exploring the rich universe that had been so lovingly crafted by creator Joss Whedon. It was to my delight to learn that in 2005 there was a full-length movie in response to public (and private) outcries for more of Serenity and her crew.
Watching Serenity let me spend a bit more time in the ‘verse, and the film thankfully resolved a number of outstanding loops justwaiting to be closed. But the forced end of Firefly also forced Joss Whedon’s hand. He put in scenes that would only have appeared in a last hurrah like Serenity. One scene in particular shook me, like the unexpected sight of a Reaver ship. It’s a scene that drove me to NASA forums and technical reports, glass manufacturers, my calculator, and eventually to this post.
Late in Serenity, after crash-landing at the mysterious base of “Mr. Universe,” pilot Hoban "Wash" Washburne meets his end at the tip of a Reaver spear. The immediacy of the violence, and his wife Zoe’s touching reaction, kept my mouth agape well into the next few minutes of the film. One of my favorite characters just died, as Firefly died. I couldn’t stand it. I had to be sure.
What if the Reaver spear couldn’t plausibly make it through the forward windows of Serenity? The movie may have been set in the future, but we too have built spacecraft with windows, and they are made to withstand impacts. If I could prove that a modern shuttle window (assuming that a future window would be even better) could withstand the impact that killed Wash, I could have the ultimate in fanboy closure: the movie is “wrong,” and my version of the story lives on.
Objects in Space
In terrestrial situations, a speck of paint is less than harmless. In space, it’s deadly. Travelling at a blistering 10,000 meters per second in orbit, the equations deem it lethal. It becomes a “hypervelocity” bullet.
Our spacecraft obviously must account for this deadly debris. Tens of thousands of pieces of extraterrestrial trash litter the orbit of Earth [PDF], meaning that a shuttle’s final impact could come from an errant hex nut. Shuttles today are outfitted with shielding to prevent such disasters, and feature two-and-a-half inch thick windows—the thickest pieces of glass ever produced in the optical quality for see-through viewing.
The largest impact to a shuttle window occurred when a fleck of paint struck STS-92—a flight to the International Space Station. A shuttle window has never been penetrated by a hypervelocity impact, but it doesn’t have to be. A deformation large enough could eventually cause window failure upon repeated take-offs and re-entries.
After engineers examined the crater in the window of STS-92, the shape that best explained the damage was a sort of miniaturized plate. But to begin making comparisons, I’ll consider the fleck of paint to be a similarly sized metal sphere. This will bring the numbers in line with the hypervelocity testing that NASA has already conductBased on the size and the speed of the fleck that hit STS-92, I calculated that the window weathered an impact with around 20 Joules of kinetic energy—equivalent to four milligrams of TNT or a decently thrown baseball. It created more than enough damage to warrant a window replacement. And such replacements from serious impacts are commonplace. Robert Lee Hotz notes in the Wall Street Journalthat “NASA shuttle engineers have replaced the spacecraft’s debris-pitted windows after almost every flight since since 1981, at a cost of about $40,000 per window.”
Such little flecks can be catastrophes. An orbiter unlucky enough to be hit by anything much larger than the paint chip that hit STS-92 is in for some trouble. Debris measuring five centimeters in diameter packs the punch of a bus collision. Any larger than that and we begin making comparisons to sticks of dynamite.
The shuttle windows are tough, to be sure, surviving nearly 1,400 impacts intact over 43 sampled missions, but are they strong enough to save Wash? Tiny particles are elevated to terrifying status because of their ridiculous speeds, not their mass. Conversely, the Reaver spear that killed Wash was larger, but moving much more slowly. A few assumptions and some physics equations would determine if I could save him.
I Am A Leaf on the Wind…
To get the general dimensions of the spear that killed Wash, I had to (unfortunately) go back to the scene in question, excruciatingly slowing down an emotional moment to be replayed over and over.
Diving back into Serenity, I used an earlier Reaver chase scene to guesstimate the spear size and speed. If Reavers shoot spears slow enough to be dodged (which they do), the spear that kills Wash can’t be moving much faster than a Major League fast-ball, putting the upper limit on speed around 100 miles per hour (45 m/s). This is orders of magnitude slower than the hypervelocity impacts that a shuttle deals with, but the spear is thousands of times more massive than a fleck of paint. Assuming it’s fashioned out of an “average” metal, and given its size, I’d guess it’s around 100-200 pounds (45-90 kg).
Kinetic energy is easy enough to calculate. The kinetic energy of a moving object is one-half of its mass multiplied by the square of its velocity.
This equation gives the Reaver spear a frightening 45,500 Joules at the low end. This is over 3,700 times the energy of the largest recorded impact to a space shuttle window – equivalent to a detonation of a pencil made of TNT or a medium sized anvil dropped on it.
What are the risks? via Aerospace.org
Based on hypervelocity testing undertaken by NASA, the Reaver spear would be like an aluminum sphere with a one-centimeter diameter hitting the window at 10 kilometers per second (assuming that the tip of the spear is comparable to a 1cm diameter point). Seeing that the damage threshold for a shuttle window based on this testing is 0.004 centimeters, my hopes quickly vanished. With this kind of energy, the Reaver spear could pierce a shuttle’s wing, its thermal protection tiles, or even its crew cabin.
The math doesn’t lie—Wash didn’t stand a chance.
Watch How I Soar...
I thought I had found the perfect fanboy out. The windows in Serenity looked flimsy and thin, surely not something a space-faring craft would be outfitted with. If the windows were anything like what we use to traverse the ‘verse today, perhaps all that would have happened is a jolt of fright from a deflected Reaver spear, or so I hoped.
But even delving through a hundred page NASA technical report [PDF] on impact shielding couldn’t ease my psyche.
Now, this is at its core a fanboy rant. No matter what I found, Wash dies in the movie. It’s part of the larger story and serves as a plot point, not a meaningless killing-off. But I selfishly wanted closure; I needed to resolve the dissonance between a character’s death and the fact that we know he wouldn’t have died if the networks saw better numbers from Firefly.
Maybe this is a testament to the enduring qualities of the show. To create characters important enough, and in only fifteen short stories, to warrant hours of research and calculation that ultimately proves useless in the larger story is an outcome of a great narrative. It’s typical of a fan base that will still pack a Comic-Con panel ten years after the airing of the show.
In the end, I like the story better this way. It takes a great narrative to make someone care so much about a character that he takes real world steps to resolve his own dissonance. If I could have 'proved' that Wash wouldn't have been killed, a whole can of worms would open. What about the fact that Serenity was an old ship with sub-optimal gear? What about space-age technologies like super-strong window polymers? The scene obviously resonated with people (especially me), and the fact that I failed is a better story than a discussion of faulty film physics.
