Why does an asteriod burn up in the atmosphere but a space shuttle wont?

lundyjb

Is it because the speed at which the asteroid is coming in greatly increases the friction between it and the air molecules in the atmosphere?

kevinferreira

The shuttle was made to survive it (aerodynamics, materials, mechanics), the asteroid wasn't.

berkeman

More specifically, the heat shield tiles on the Space Shuttle (or the heat shield on earlier re-entry vehicles/capsules) are designed to have a very low thermal conductivity from the outside ionized air to the inside metal vehicle parts:

http://en.wikipedia.org/wiki/Space_S...tection_system

The asteroid has no such protection.

SteamKing

Who says that a space shuttle won't burn up on re-entry?

Look up the space shuttle Columbia, 2003.

Astronuc

Certainly it will if the Thermal Protection System is compromised, as was the case with Columbia. If the TPS is intact, Shuttles return to earth safely as they have done 128 times.

lundyjb

So does it have anything to do with speed and friction? If i were moving at 50 miles an hour from the tip top of the atmosphere to the ground, i wouldn't burn up, right?

chill_factor

you will accelerate until you hit terminal velocity which is still quite high. however just because you're at terminal velocity doesn't mean your potential energy stops dropping; it is still dropping and being converted to other forms, such as heat.

Drakkith

No, you would survive easily. An asteroid is moving at several miles per second on average I believe. The space shuttle re-entered at about around Mach 25, 8,200 m/s (30,000 km/h; 18,000 mph).

chill_factor

but you can't stay at 50 mph. you need external power to resist acceleration downwards. even when you stop accelerating your potential doesn't stop dropping, that potential just gets turned to heat.

Drakkith

Yes I realize that. But the question was if your speed remained at 50 mph. If you could remain at 50 mph, which really isn't that far fetched, you would not burn up. I'm sure a very lightweight probe or something could be rigged with the right gear to keep it at 50 mph during its fall.

StrayCatalyst

Lightweight or not, if it had mass it would accelerate towards the Earth to greater than 50 MPH. If it were able to enter the atmosphere at a low enough speed, the thin air striking it would not have enough friction to burn it up, but unless you're using antigravity, a space elevator, or some similar, your mass will be gaining speed until it hits terminal velocity. As the atmosphere gets thicker, terminal velocity gets to be MUCH slower - but your craft would already be going fast enough that the friction of the air would become a problem.

The shuttle is shaped to present a single surface to the rushing air, and has heat tiles, which are both insulative and ablative - they carry away most of the heat as opposed to conducting it to the shuttle itself. When the tiles are damaged or compromised, the shuttle and its contents die upon re-entry - just like an asteroid, or anything else that hits the atmosphere at a high enough speed.

Take a theoretical mass - call it a pingpong ball - and drop it from outside of the atmosphere. It has mass, so it's attracted to the Earth, and gains speed as it goes (about 9.81 m/s, disregarding the difference in gravity from that distance), accelerating without drag until it hits the atmosphere. If it's going slowly enough - ie, if it was dropped from just above the atmosphere, and didn't have time to gain a lot of speed - it will hit the air and slow down to terminal velocity (which gets slower as the air gets thicker, but the ball would probably survive). If it's dropped from a greater height, it's going fast enough that when it hits the air, the friction generated will turn it from solid to gas almost instantly - it's a shooting star, white-hot for a fraction of a second, then gone without a trace as dispersing gases in the upper atmosphere.

russ_watters

What's wrong with a regular-old rocket engine?

Drakkith

That's what I was thinking of. Or anything to create thrust or lift.

Astronuc

Yes - speed and momentum/energy transfer, as well as friction, which is a shear force.

http://www.faa.gov/other_visit/aviat...om%20Space.pdf

Meteors do not have thermal protection systems, but rather as they heat up, the heat generated at the surface can melt or vaporize the meteorite. It can slow down quickly, and in some cases survive to the surface.

To avoid melting/failure, the thermal protection system must radiate heat away, while preventing conduction of heat to the structure supporting it.

http://www.grc.nasa.gov/WWW/BGH/hihyper.html

http://www.nasa.gov/mission_pages/sh...anding101.html

lpetrich

Actually, an asteroid would survive entering the Earth's atmosphere. The Earth has numerous meteorites and impact craters, which are plenty of evidence of that.

dgh856

I'm not sure keeping something falling through the atmosphere at 50 MPH is as simple as you think. Even with a very lightweight probe, the amount of fuel you would need to keep it at 50 MPH with a rocket engine after de-orbiting it would be incredible, and add incredible weight. Other systems, like parachutes, wouldn't become effective until the atmosphere is significantly thick, before which the body would undergo catastrophic friction anyway.

The actual ΔV to slow a falling body, especially a lightweight one, to 50 MPH wouldn't be that extraordinary, but keeping it at 50 MPH for the hours it would take to pass through the atmosphere at that velocity would be impossible. You'd need literally tons of fuel or a parachute the size of a medium-sized state.

Drakkith

Why are we even talking about how feasible it would be? I never claimed it would be easy, only that an object moving at 50 mph would not burn up. I'm sure we can all agree that the OP is simply trying to understand the way friction works during re-entry, not develop a way to fall at 50 mph through the atmosphere.