Is it possible for an object to orbit the Earth at a height of 5 feet above the ground? Is this physically impossible, very impractical with the technology we have now, or simply not done because there’s no use for it? Or maybe there’s no where in the world where an object could orbit at that height without bumping into something?
Five feet above the ground, you’ll run into something. Namely, the atmosphere. When you’re going fast enough to circle the globe in an hour and a half, air resistance is nothing to sneeze at (because if you try to, you’ll get snot all over your face). As a matter of fact, even orbiting at the altitude of the Shuttle or the Space Station (which is a very low orbit indeed, compared with the radius of the Earth), you still have to worry about air resistance. That’s the only reason that the ISS’s orbit isn’t completely stable, and if left to its own devices, it would eventually spiral in and hit the Earth. To prevent this, every so often, we hook up a rocket to it and boost its orbit slightly.
I remember this being the premise of a “Deputy Dog” cartoon, but I can’t vouch for the writer’s research skills.
This website calculates the necessary speed of “orbital velocity at the Earth’s surface” (using a train moving on a equatorial track as an example) at 7.905 km/s, which is pretty speedy. At the very least, this would certainly invite unwanted attention from the highway patrol.
So does that mean you could do it on the moon?
This was also the premise for a 1953 short story by Jerome Bixby, called “The Holes Around Mars”.
Yes, if we could find a debris-free path.
And, in theory, it would be possible to send a golf ball into orbit around a very small asteroid with a nine-iron.
All of the math and physical laws we need were discovered in the 1600s by Sir Isaac Newton, incidentally: At these speeds and gravitational accelerations, relativistic effects can be ignored.
It likely would not be a very stable orbit though, as lunar mass concentrations (mascons) would jerk a low flying satellite around.
Well, yeah, but I was idealizing everything into two point sources. In the real world, you’d need a much, much higher orbit to achieve stability.
My point was that, in theory, any two physical objects can orbit each other unless there’s forces more powerful than gravity involved. (Gravity is a very weak, very pervasive force. At short distances, most forces overcome it, but it’s difficult to maintain any other force at a very long distance.)
Some planets are so small you can go into obrbit if you run too fast…
See?
IANAAstronomer, but I believe there is an additional item that must be considered, called the Roche Limit. One of Mars’ moons is in danger of being torn apart due to these forces. From Nineplanets.org:
Another consideration to the 5-ft high orbit proposal – since an orbit is an elipse, or in special cases, a circle, the planet would have to have a surface uniformly less than 5 feet from the satellite’s orbit to avoid a collision. That is, unpowered satellites don’t skim at a fixed distance from the surface as an airplane pilot might, using the ground as a reference point.
This might be a good question to pose at Phil Plait’s BadAstronomy Forum.
The Roche limit is only relevant to objects held together by their own gravity. For objects the size of moons, this is the case, but for smaller objects like people and man-made satellites, structural strength from the electromagnetic interactions between atoms are much more relevant.
I’m not questioning your statement or knowledge, Chronos, but nothing in the OP mentioned size of the orbiting object.
Ben Bova wrote a very tongue-in-cheek story about supercomputers being necessary on the Moon because there were so many extremely low-flying-orbit bullets left over from a skirmish between Americans and Russkies that they had to constantly keep track of where they were all going. (No atmosphere on the moon to slow them down).
And Jerome Bixby not only wrote a short story about this, he also wrote a screenplay that was made into an unjustly forgotten movie circa 1959 – The Lost Missile, the premise of which was that an alien missile travelling at high speed ends up in orbit around the earth, and its incredibly high temperature makes it lethal to anything or anyone under its path.
I thought of that story upon reading the thread title. The story deals, among other things, with an inverterate punster, and ends with one of his puns.
Unfortunately, I have never been able to figure out the pun, and, hence, much of the point of the story is lost to me.
Q.E.D., can you enlighten me?
An invertebrate punster? Of course, that should read “inveterate” punster.
The size was implied, though: the OP asked about an object orbiting five feet above ground level, which surely excludes objects over ten feet in diameter.
I’ve always taken it as…
Bottomos sounds like “Bottommost”, as well as fitting in with the names of the other two moons.
Ok, so not hilariously funny, but it got a snicker out of me.
OK, OK, I guess that works…
One of Nancy Leibowitz’ buttons reads:
Invertebrate Punster – Spinelessly Unable to Resist a Pun. So Slug Me!