My favorite stories have just enough reality to be relatable and grounded before launching into the improbable, fanciful, or impossible. The transition from fact to embroidered truth to wholesale fantasy is an art. When done well, you can’t help but think, “What if…?” even when firmly in the fantastical. Terry Pratchett is a master of it. His Discworld series is a broad satire of humanity and human history. With characters ranging from humans to trolls to anthropomorphic personifications of Death, etc. the stories skew silly, peppered with hilarious tangential footnotes, yet Pratchett delves into very human predicaments, past and present.
Similarly, I love songs that that do the same thing. Pratchett used entire books to weave his tales, but a song? You’ve got 3-4 minutes, give or take, to carry a listener into your world. This past weekend I had a chance to sit down and listen to Frank Turner’s most recent album, Positive Songs for Negative People. I was excited for the album but I was reluctant to listen to the track he wrote about the astronaut Christa McAuliffe, who died in the Challenger explosion, entitled Silent Key.
I was 3 when the Challenger blew up. Can 3-year-olds have memories? I have an image of sitting on my parents’ bed with my mom, surrounded by their gigantic down comforter in its thinning cotton pinkish cover, watching the launch on tv. As the shuttle took off, exploded, and split the blue sky with arcing white trails of debris, I remember fear, panic, and a very clear understanding of the finality of death. Death, like how plants die in the winter, but with people there’s no little bulb tucked away in the earth under the snow - there’s no spring for them. I remember the futile hope that someone would’ve defied the laws of physics, and there’d be a survivor in the water after the Challenger’s passenger compartment fell into the ocean. I don’t know if this is a real memory or something that grew up with me based on my parents’ stories.
Silent Key, however, is absolutely fucking beautiful. Who even writes songs about o-rings failing? No one. No one sings about technical disasters or engineering hubris unravelling, never mind imagining what a teacher-astronaut hurtling to her death might have thought on her way back to earth, which could be presumptive in the hands of another. But the equally simple and horribly complex conclusion Turner-as-McAuliffe reaches with the able help of both Esme Patterson’s vocals and the Sleeping Souls’ musical accompaniment, is an artistically and technically perfect match with the rest of the song.
So I’ve been going around all gratified and uplifted in a heartbroken kind of way, since that’s where paying close attention to the lyrics of a Frank Turner album will get you. And then I couldn’t help but ask, “What if…?” While irrefutably fictional, how far can we push the truth of Silent Key’s narrative? Given that people can and do communicate with the International Space Station via ham radio from the comfort of their own homes, where is that point in Silent Key when fact is forced into embroidered truth? When does it become fiction? Is there a nonzero physical possibility that this narrative could have occurred?
(Science ALWAYS helps. Also, greatest tshirt ever. Available here.)
I don’t know that much about ham radio, but let’s start with the geographical information we know from history and what FT (Frank Turner) divulged lyrically:
- The Challenger took off from Cape Canaveral, Florida.
- The apex of the crew cabin’s trajectory was 65,000 ft, or 19.812 km (somewhat morbid NASA source).
- The ham radio in the song was in Hampshire, England.
- Distance between launch and the radio was “four thousand nautical miles, as the crow flies.”
Nautical miles aren’t easily convertible to SI units. Google says 4000 nautical miles = 7408 km. Google maps says the distance between Cape Canaveral and Hampshire is 6873.51 km.
(Convert to km at your leisure.)
You won’t convince me that “six thousand eight hundred seventy three point five one kilometers” is more lyrically compelling than “nautical miles as the crow flies,” because art. That said, I’m going to use the google result, because science.
First, let’s consider the direct distance between the apex of the crew’s cabin and Hampshire. Intuition tells us that almost 20 vertical km is not a significant change from the distance between Cape Canaveral and Hampshire, but for completeness’ sake, let’s holla at our boy Pythagorus:
Intuition verified. Vertical distance of the Challenger cabin increases the distance between itself and Hampshire by a negligible few hundredths of a km.
The next question is can you get a radio signal to cover that much distance over the horizon? Yes. Yes, you can. It is physically possible at relatively low frequencies to have ground wave transmission - radio waves that follow the curvature of the Earth’s surface and can travel long distances beyond the horizon. However, those frequencies are only available for military and commercial purposes. Amateur (ham) radio is authorized to operate at higher frequencies, in which long distance ground waves aren’t physically possible, and let’s assume that hypothetical 4-year-old FT wasn’t engaging in illegal radio operation.
(This is a portion of the US Navy Cutler VLF (very low frequency) Array in Maine. This is what you need to operate a radio at those frequencies. No idea what FT’s family did/does, but I’m going to guess they didn’t have casual access to something like this. Sidenote - Doesn’t this picture remind you of Whistler’s Nocturne: Blue and Gold - Old Battersea Bridge?)
But at certain higher frequencies, radio signals can bounce off the ionosphere and the Earth’s surface, a process called hopping, which can increase signal transmission distance by thousands of kilometers. The ionosphere is a portion of Earth’s atmosphere containing ionized particles. They can act like small antennae to help pass a signal along. But in order to hop, an astronaut reaching Hampshire from Cape Canaveral would have to broadcast a frequency no greater than the maximum usable frequency. The maximum usable frequency is the frequency at which a transmission will bounce off the ionosphere, and this is how you calculate it:
(This very cool old paper from the 1930s from the NIST library is the source. Should you ever find yourself in Gaithursburg, MD, you can go to the NIST library and see a descendent of Newton’s apple tree.)
(This is what the angle of incidence is. Big black dot is the source of the transmission, the little spots are representative of the ionosphere, solid arrow is the radio transmission, and the dotted line is perpendicular to Earth.)
The maximum usable frequency is calculated via the above relationship between the critical frequency and the angle at which it hits the ionosphere. If you use a higher frequency, it won’t reflect off the ionosphere, your signal goes into space, and no hops for you. The critical frequency, fc, is the maximum frequency at which a vertically transmitted signal (angle of incidence = 0) gets reflected by the ionosphere. This is influenced by electron density per cubic meter. Electron density is dependent on ultraviolet and other more energetic radiation coming from sources such as the sun (among other things). When exposed to high-energy radiation, electrons are separated from their molecules and atoms, thus ionizing them (now you know where the term “ionizing radiation” comes from). Those freed electrons? They’re what we’re concerned with when we’re establishing the reflective properties of the ionosphere. Essentially, anything that affects the electron density, measured by the ionization levels of the gases in our atmosphere, will affect fc, maximum usable frequency, and the ability to hop a radio signal. Electron density in the ionosphere changes with the sun’s activity, seasonally, and even night to day.
So, yes! There is a nonzero probability, a physical possibility, that FT could have heard a transmission from the Challenger, if McAuliffe happened to be carrying a ham radio that worked in that ideal range. But this is where the truth acquires its [very lovely] embroidery and FT’s flight of fancy is cleared for takeoff.
While possible, it’s hard to say FT’s lyrical situation would be likely. The radios carried by astronauts on the International Space Station, for example, receive and transmit at frequencies intended to go entirely through the atmosphere. Even if McAuliffe or FT were using one of the OSCARs (small satellites intended to increase amateurs’ signal ranges), calculating Doppler shifts is a hell of an advanced undertaking for either a panicking adult or a 4 year old. Also - fair warning - this is where the physics ends, and biological limitations begin. According to NASA’s Challenger report (it’s here and is as tragic as you think), sudden decompression at nearly 20 km up was enough to knock the crew unconscious. Perhaps that was a more merciful end than being conscious for an impact more forceful than a plane crash.
All that said, it’s not a choice of what to believe; it’s not science versus fantasy. Facts exist and are true whether we believe in them or not. (In a nutshell, if you don’t “believe” in science? Great. Gravity gives exactly zero fucks.) But if someone finds the space to see through the facts to a deeper personal truth, and they share it via a departure from what is real as FT does so deftly, I’m there for that. It’s liberating, because we lie to ourselves all the time. As Terry Pratchett illustrates via a conversation between Death (all capitals) and Death’s (mostly) human granddaughter Susan, humanity is built on telling ourselves stories:
(From The Hogfather. Binky is Death’s horse. Just read the story. It’s very entertaining. It’s a quick read, kind of like brain candy, but made entirely of whole grains and with a lot of vitamins and minerals.)
That’s more or less why there needs to be stories and imagination; it’s why we all need to stretch and relax, and let our hearts be broken. Nature and the universe has had eons to play weighted games of probability with itself, but we get nothing more than a cosmic blip. We can’t afford to just slam bare facts together until something better happens. We have to push the facts as far as they’ll go and ask, “what if…?”
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