Quote from: Spendulus on January 30, 2019, 01:09:59 PM

Quote from: BADecker on January 30, 2019, 06:27:53 AM

Quote from: Spendulus on January 29, 2019, 02:25:09 AM

Quote from: Spendulus on January 16, 2019, 03:56:53 AM

Quote from: Artemis3 on January 16, 2019, 02:26:32 AM

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You are wrong. There is a spacecraft planned, its what goes on top of the ~~bfr~~ "Super Heavy"... Called "Starship":

In this CGI picture the launch vehicle "Super Heavy" is returning back to earth while the spacecraft "Starship" goes to an earth orbit to refuel with a similar shaped (but fuel only) vessel; to then carry on with its mission carrying people and cargo.

Here is the official site of their plans: https://www.spacex.com/mars
And here are more details of the spacecraft: http://spaceflight101.com/spx/its-spaceship/

Some quick back-of-the-envelope calculations tell me this will burn up on re entry 100% reliably.

I tried to post this but seem to have messed up a prior post.

Anyway the idea was to use stainless steel with water cooling the skin for the heat of re entry. But using numbers for the Space Shuttle, that would take the better part of 2000 kilotons of water.

Double that for a return from Mars or the Moon.

Maybe I'm not thinking about this clearly, but, when they use liquid hydrogen and liquid oxygen as fuel, the result coming out of the rocket engine is water... in vapor form, of course. My question is, why wouldn't a returning rocket be able to ride on a thin layer of water vapor?

If the rocket descended nose first until it almost reached the ground, why not spray a thin stream of water out of the tip of the nose? This water would be turned into "steam" immediately because of the friction. Then it would envelope the whole rocket as it slid by, taking up the extra heat, and sliding it past the falling rocket......

Because for the vehicle to slow down, it has to dissipate that heat. Musk wants to do exactly what you are guessing at. But take the total kinetic energy, and see how much water would be changed to steam to take up that amount of energy, and it's about 2000 tons of water.

This is a good question... a difficult one to visualize without computer models. The heat is dissipated by not even reaching the rocket skin. It is dissipated in the steam. However...

In a simple V8 car engine that has a 9.5:1 compression ratio, in optimum conditions, a wide-open burn of the air/fuel mixture in the cylinders produces a temperature in excess of 5,000 degrees F. But that is under some reasonably high pressures. The heat drops off substantially as the piston moves; some of the heat is absorption into the piston head, the engine head, and the cylinder walls. Most of it goes out the exhaust system.

What are the burning gasses that are so hot in the V8 engine? In optimum running conditions, they are essentially only water (steam) and CO2 (gasoline burns into these).

What amount of gasoline does it take, say, for a 350 cu. inch V8 engine to reach that heat? The droplet of gasoline per cylinder per double stroke would be less than a 0.2 inch diameter sphere of fuel per cylinder. The resulting steam and CO2 are slightly more than the size of the gasoline, because of the air added to burn the gasoline.

The point is that there is a lot to take into consideration. Look at the amount of fuel it takes to get the rocket up there in the first place. There is some heating of the skin of the rocket on the way up. But most of the fuel is used to lift.

Since there is no lift action required on the way down, I would think that the amount of water to make the steam to cool the skin would be a lot less than the amount in the tanks on the way up.

Intriguing question. Did Musk run the simulations? Or is he only talking at this stage of the game?

Cool