Hypothetical low orbit question...

Hi, I've been wondering about this for a while. If you could build an appropriate craft, how low would it be possible to establish and orbit?

I can't see why it wouldn't be possible to achieve and orbit at say 1 km above the ground depending on the capabilities of the vehicle, lack of obstacles (mountains/buildings/other air crafts) and airspace/sound restrictions of course. Would air resistance really be too much of an obstacle?

So if it were possible to establish an orbit at 1km how fast would you have to be travelling?

Um, most spacecraft orbit power off. Each pass through the atmosphere would slow the velocity (the lower it went the more it would slow) and quite quickly said craft would smack into the ground. If you had infinite power and airframe skins that could take it, you could go low every time but the engine would have to fire to keep the speed up....

For fun, you can plug numbers in the orbit calcs for a specific answer (for circular orbits as that is easiest to do) or for even more fun, search out the freebie game called "Orbiter" on the net. You can do this to your hearts content in that simulation game and it does model the physics quite well....

The mechanics of orbits doesn't work within the atmosphere. Standard calculations assume no resistance from the atmosphere, so being closer than about 200km to the surface means no orbit.

edit: you beat me to it! ;-p

[edit on 18-10-2007 by jim_w]

thats why i said hypothetical, say you could ignore air resistance, or cover your craft in a non-friction surface, what would your circular orbit speed have to be at 1km?

This orbiter programme looks cool, does it let you turn off atmosphere?

According to my calculations (based on en.wikipedia.org...), the period of your orbit at the Earth's surface would be about one and a half hours. That equates to a surface velocity of about four thousand kilometers per hour. Of course this assumes a perfectly spherical Earth, no atmosphere &c..

cheers jim, whoa 4000kph cool. how much difference do you think it would make travelling at that altitude and speed not on a smooth sphere but over seas, hills, cities etc..?
Also would the orbit calculations change if you were following a longitudinal line rather than the equator?

Its called flying really fast if you are only 1Km above the ground. You have to get to at least 200+Km up to be able to sustain an low orbit. To sustain a low orbit youll need to be going 8Km/sec or around 17,280Mph.
Drag is so high at low altitudes , less than 80,000', that the energy requirements are prohibative. Its why there are so few aircraft that go faster than 1,500 mph.
Esentially what you are thinking of is like when a B1B is using its terrain following guidance, except that they fly about 1/6 Km above the ground at mach 1.2