Bob Bruninga wrote:
at take off we go from zero to 17580 Mph in what 10 minutes or so and are in orbit. Yet the other way around going from 1780 to zero in 45 minutes causes the fireball effect with the friction.
Why not on the way up?
It does, its just that all the energy is being burned at the rear end of the rocket to produce the acceleration... see the flames... On the way down, you have to decelerate that same amount of acceleration in the opposite direction and remove all that LAUNCH energy, to come back down.... hence the flames.
No the flames are from friction with the atmosphere. if they had enough fuel they could do a 8 minute burn, and come straight down. The "Fuel" in this case is Gravity. The fuel on the way up is used to over come gravity.
The difference is that going up, you are going slowly in the higher density atmosphere which is continually lessening as you go up letting you go faster and faster with less and less friction. THus, no multiplying build up of friction.
But see where are the numbers to verify this? People make this statement all the time. but have yet to show any data that verifies this. Why is this soo hard to verify?
Coming down, everything is against you. As you come down, into denser and denser atmosphere, the friction is increasing and increasing, the temperature building and building you are going slower and slower and falling faster and faster. Into one ultimate fireball.
Yes and no, you are in free fall the whole time you are in orbit.
we can go from zero to 17580 in ten min on the way up with no fireball, but take a slower, 450% slower return rate and it almost fries to a crisp.
Thats why I'm thinking there might be a way to change your drag coefficient as you come down to reduce the crescendo build up of heat and spread out the descent. But still, for something as small as a cubesat you still have to disipate about 300KWH of energy and even if you do this over an hour, thats still 300 killowatts of heat... (a number they used here in the presentation.. I'd like to see confirmation)...
I'd like to see any data of speed vs altitude..
Joe
Still seems like a fireball..
Bob, WB4APR