Here Be Gods

Tag: Physics

Stuff about Physics

John J. Johnson – A Short Story

John J. Johnson was asleep. He floated peacefully in his sleep-harness as his ship hummed around him methodically, hurtling through the near void of space ever so sedately. He had just spent the better part of an earth day attempting to repair a puncture on the exterior bulkhead. While it was not at all critical to his voyage that the repair be effected before he arrived at his destination, he nonetheless had decided the day before that he should endeavor to finish the repair before his arrival at Europa. This determination was a combination of both an attempt to prove to himself his own capabilities in the matter as well as a venture to stave off the otherwise overwhelming boredom that these trips always inevitably entailed. Sure, there were a myriad of mental activities that he could have just as easily enjoyed, but there are only so many movies in a row that one can watch without getting a distinct urge to get up and do something, which on a spacecraft, is a potentially dangerous affliction. Many a tale has been passed around many a tavern across the Sol system of ‘spacers who get bored get dead’.

So it was that when the inch and a half asteroid skipped across the exterior of his craft at a couple of thousands of miles an hour, the wound it inflicted became an omnipresent temptation to get out and do something productive. Giving into his cabin fever had been the easiest part of the enterprise, as suiting up was an ever laborious task that no space-farer gets all the way through without some exhaustion and much frustration. After that, he had to patiently wait for the large empty cargo bay to cycle out the air ever so slowly. His mind had gone over the procedure he had been about to undertake over and over at least a dozen times as the lethargic whine of the aged air pump had grown gradually fainter.

After it had disappeared entirely and the indicator light had finally shown the all clear, John J. Johnson had scrambled out far too eagerly into the vast emptiness of space, showing an almost immature recklessness that was more characteristic of men far less experienced in space than him. It had taken almost fifteen hours of struggling and consternation to get the patch plate bolted into place properly. By the end of the ordeal, John J. Johnson had been cured entirely of his cabin fever, his energy, and his alertness. In such a state he had made his way, only half conscious, back into the cargo bay, waiting interminably for the air to return and pressurize to the proper level. Afterward, the removal of the suit had felt a million times more arduous than normal, and the long crawl to his bunkroom had felt like a marathon. Finally, he had struggled into the sleep-harness and had gratefully passed out.

In doing so, he had entirely missed, in his bleary fatigue, the urgently blinking text on his control console. The hum of his ship was uninterrupted by the standard array of loud warning klaxons that routinely would have gone off, had he not long ago disabled them out of irritation at their agitating volume. Nor was he jolted awake by the auto piloting system making an emergency course adjustment, having never trusted the damn computer to steer the ship, and thus having disengaged it. So it was that John J. Johnson was sound asleep when another asteroid struck his vessel at a couple of thousands of miles an hour. However, as this particular asteroid was over a mile wide and his ship was far less than a mile wide, the asteroid more accurately continued to fly through space virtually unaffected as a smallish collapsible particle impacted its forward facing surface.

How Far Can You Fall and Survive…. On Pluto?!


As we celebrate our newfound imagery (and accompanying scientific data) of Pluto, our quaintly controversial distant solar neighbor, we need to make certain we do not forget to ask the most important of questions. Namely, if you were to fall on Pluto, how high up would you have to be to die on impact?

Sure, Pluto only has 0.063 g (6.3% of the gravity of Earth) to attract you to its surface, but any amount of gravity can accelerate you to an unwanted demise given enough distance on which to act. Without even the aide of an atmosphere of any significance to break your acceleration, it is simply a matter of calculating the velocity of your body when it ‘lands’ on that heavenly body. Well, it is not quite that simple.

You see, the issue at hand is not Pluto, its gravity, or the improbability of your ever being under the influence of the gravity of Pluto. The issue is you. At what height, and thus relative velocity, can you survive a fall here on Earth? There are some astounding records of accidental falls from tremendous heights that some individuals have survived. There are are also plenty of records showing other individuals expiring from incredibly short falls (though mostly these latter are dependent on if they fell on their head or if they are so fragile that any fall of any kind from any height would result in some form of injury).

If we were to go with the more extreme heights possible, you could theoretically fall from very great heights indeed. On Earth. Due to terminal velocity (the atmosphere breaking our fall), our fall from a thousand feet is more or less identical to our fall at ten thousand feet. This does have a limit, however. If you were to fall from Near Earth Orbit, you would accelerate to speeds far in excess of what most people recognize as Terminal Velocity, as the thinner atmosphere at that height would offer far less resistance, and you could then puncture through the thicker gasses at lower elevations like a bullet. This is, of course, irrelevant to the current question, especially since you would likely burn up from the friction of the thicker lower atmosphere long before you hit the earth.

Assuming you are not space jumping, or surfing, into Earth’s gravity well, we can safely state that your maximum velocity upon ‘landing’ would be Terminal Velocity as it is understood in popular culture. Which at 54 m/s (177.165 ft/s or 120.795 mph) is sufficient to render most humans ex-humans, with only the rarest of exceptions. To reach that velocity on low gravity Pluto, you would need to jump from a height of 2500 m (8,202.1 ft or 1.55 miles). That is a long way down. Problem is, it is highly unlikely that you would defy statistics and survive a landing of that velocity, on Earth or Pluto.

Okay then, how do we determine the correct height? We cannot. There are too many factors, such as the softness of the ground, what position your body is in and thus what part of it impacts, if you are relaxed (or unconscious), etc… So I will use this quoted height of 10 m where you will survive with ‘very serious injuries’. At a 10 m drop, your velocity will be 14 m/s (45.95 ft/s or 31 mph). The Plutonian equivalent height you could fall from is 168.1 m (551.5 ft or one tenth of a mile). That is slightly less than the Washington Monument’s height. Or 42 elephants stacked on top of each other, or whatever other silly height equivalent you prefer to measure large numbers in.

So, in conclusion, if you find yourself suddenly ejected into raw space above the surface of Pluto, and assuming you have the basic needs of an enclosed suit with enough air to survive that locality, you had better hope you are only 551.5 feet from the surface, else you are unlikely to live. How you get emergency services to assist you upon your successful, if still likely traumatic, landing is up to you.

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