**Ask a monkey a physics question thread**

[OngBonga]

How much rocket fuel would it take to carry a 2 ton rod of tungsten into space?

Don't forget to factor in how much rocket fuel is needed to carry the rocket fuel needed to carry the tungsten!

Also, how fast would the rod need to be travelling through the atmosphere for it to turn the air it displaces into plasma? What other signatures would such a falling object be likely to have? Could it be detected by radar, or infrared or ultraviolet cameras on satellites?

In case you wonder why I ask, there is a theory that the Tianjin explosions last year were an act of war, an attack by USA in retaliation for the devaluation of the Yuan and threats to dump their dollar reserves.

It seems to me that it would be counterproductive to protect the economy by sending very heavy rods of tungsten into space and then dropping them on a target. Also, there is no evidence of a falling object at high velocity on any of the footage I've seen. I'm skeptical of this one.

[MadMojoMonkey]

As a broad rule of thumb, the fuel is about 90% the total mass of a space-bound rocket. The fuel tanks, engines, and the structures which hold it all together and control it are all in that remaining 10% of the total mass, and whatever is left is payload.

The Falcon 9 has a listed max payload of 13,150 kg or about 14.5 tons at surface gravity.

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Another concidental rule of thumb is that the entry speed into the atmosphere in m/s is equal to the peak shock layer temperature in K. E.g. a spacecraft entering the atmosphere at 7.8 km/s would experience a peak shock layer temperature of 7,800 K. Air can become a plasma at temperatures in a range of 7,000 to 10,000 K - hotter than the "surface" of the sun. So a vehicle entering the atmosphere at ~7 to 10 km/s would ionize the atoms in the air, creating a plasma.

As for other emissions, the only I can think of would be to look at the meteor streak with a spectroscope and see if the spectral lines associated with Tungsten are there.

I'm sure the atmospheric entry and compression heating is producing a blackbody radiation signature which has a bandwidth of all wavelengths greater than 0. I.e. there is a non-0 chance of the thing emitting a photon of any conceivable energy, but the probability is like a bell curve with one short tail and one long tail. I suspect any light sensor pointed at an atmospheric entry will see it, because it will emit radio waves, microwaves, infra red, optical, ultra violet, hopefully not too much gamma.