Why do space ships and comets get so hot returning to Earth?
Most people know that comets turn into a big ball of flames that burn up as they hurdle through the sky, and that space vehicles get extremely hot during re-entry into Earth’s atmosphere, but why?
There is a misconception that this is because of the friction of the air passing around the object, but that’s not the case.
If you’ve ever put your hand out the window of your moving car with your palm pacing forwards, you know what wind resistance feels like—that pressure pushing your hand backwards. Chances are, unless you or the driver had a death wish, you haven’t been doing much greater that 60-70 mph doing it.
All pressure generates heat because it compresses the atoms closer together than they would be if they weren’t under pressure. At 60-70 mph, not much heat is generated. At 18,000 mph, the speed that spacefraft are doing when they are in orbit however, a massive amount of heat will be generated as the spacecraft falls towards Earth through our atmosphere. Comets and other celestial bodies may even be going much faster than that depending on what forces sent them careening through space in the first place.
So the heat is from the pressure of the object pushing on the air in front of it which can’t get out of the way fast enough.
Another great example of this same phenomena are the rail guns the U.S. military is testing. These guns use magnets to fire an entirely inert projectile at thousands of miles per hour. They don’t use any explosives, gun powders, etc., whatsoever. Instead, they use magnets to repel the projectile away like when you put a magnet near another magnet with the same pole.
Yet, when the projectile is fired, it is launched at thousands of miles per hour; much faster than a traditional projectile. In the video below, you can see the flames all around it. Again, with no explosives used whatsoever, this is entirely due to the heating up of the air in front of it—just like a comet entering Earth’s atmosphere.
Do planets really orbit stars?
Technically, planets like Earth don’t orbit around their stars like our sun, they orbit around the center of the mass between the two objects.
Imagine a planet and a star had the exact same mass, they would both orbit round the point in space exactly between the two. If the sun for instance, was twice as big as Earth, the sun’s orbit would be half the size of Earth’s, and so on.
Think of a bola (See image below); a weapon that’s two balls tied to either end of a string. When you throw it, the two balls spin around a point at the very center of the string.
Scale it up to make those two balls a planet and a star, the string is gravity.
Since our sun has so much more mass than Earth (or any other orbiting body in our solar system), the sun’s orbit is mass-proportionate to the orbital motion of Earth (and the other planets, dwarf planets, and asteroids). For instance, an object that is 1/100th the mass of the sun would have an orbit 100 times larger than the sun.
All the planets, dwarf planets, etc. are many in numbers, so their orbits aren’t perfect circles, as they all affect each other dependent upon how close they are in relation to each other, and the proportionate mass of each of them. But the sun as well as the planets are all orbiting around a central imaginary point to all of them.
Warp-Drive – Not so awesome after all
In many Sci-Fi movies, you see space travelers go from a standard space cruising speed, to some “warp-drive” feature that sends them to light speed within about one second.
There’s a problem with this though. That acceleration puts G-Forces on the body.
Gravity is measured in m/s/s (meters per second per second), and gravity’s standard value for this on Earth is 9.8m/s/s.
I know that’s a tad confusing, so let me explain.
Since this is theoretical, to be literal, you would have to remove all the air from Earth so there would be no wind resistance first. But once that is done, if you dropped any object above Earth, the first second, it would fall at 9.8 meters per second. The 2nd second would be 19.6 meters per second. The 3rd, 29.4 meters per second, and so on…each second increasing in speed 9.8 meters per second.
This is the acceleration of gravity, or often referred to as 1 g.
Knowing this, just to give you some examples of G-Forces people experience, many top fuel dragsters accelerate so fast, the drivers are exposed to 5 g’s of gravity, fighter pilots can get over 15 g’s of gravity, but risk black-outs doing so.
How many g’s can a person withstand?
Over a period of time, 15 g’s is about the most we can endure, and even then, only if you’re in peak physical condition. Because at 15 g’s, your effective weight is 15 times greater than normal, making your average 200 lbs. male a whopping 3,000 lbs.
But for a brief moment, like slamming into a wall (which are negative G’s, or deceleration vs. acceleration), humans have been known to survive as much as 46 g’s.
See link below, and poor John Stapps face, while achieving those negative g’s. He voluntarily strapped himself into a contraption that exposed himself to those high g’s for scientific research. If there was ever a hero who took one for the team of science, it’s that guy.
Now, here’s where the problem comes in for warp-drive.
In space, the fastest mankind has ever went is about 25,000 mph, when we went to the moon. So let’s assume that’s the approximate “cruising” speed that our Sci-Fi characters are bumbling about at.
25,000 mph is approximately 11,176 meters per second (m/s).
The speed of light is “slightly” faster, at a whopping 299,792,458 m/s.
So that means, that the acceleration is 299,781,282 meters per second per second (m/s/s) if they went from 25,000 mph to the speed of light in one second. If my calculations are right, and of course 1 g is 9.8 m/s/s, then that means that our Sci-Fi characters would be exposed to 30,589,927 g’s of force, roughly. Or 30,589,881 g’s more than any human has ever survived.
In order for them to accelerate to light speed from 25,000mph, and achieve no more than 10 g’s, a force that is still virtually unbearable, it would take approximately 3,058,992 seconds, 50,983 hrs, 2,124 days, or 5.8 years, then doubling of course to allow for the the equally powerful negative G-forces you’d achieve slowing back down.
So the moral of the story, is that they’d be human pancakes in a fraction of a second—which is not so cool after all. Not to mention, their space ship would be torn to shreds as well. While the writers at Star Trek deserve a little credit for identifying this problem and coming up with the idea of “inertial dampers” to overcome the effect, such inertial dampers fall under a category I like to call literary bullshit.