Re:Orion has splashed down off the coast of Baja, California
by skykooler on Monday December 12, 2022 @03:18AM
(#33952226)
A space elevator needs to be far thicker than one inch at high altitude. Even assuming the absolute minimum diameter to safely lift a 2-ton capsule of about half an inch at the bottom (which means the cable will break when the first piece of space debris encounters it), any current material - the best currently available is Kevlar - needs to be about 800 feet wide at geostationary orbit before tapering down again. This would weigh about 130 million tons per mile. Of course, the cable tapers to the ends, so I averaged over the whole length to reach that figure.
Also, energy that goes into ablation doesn't just disappear - it dissipates into the atmosphere as heat, which means it contributes to the overall energy from the impact. And in falling it does not slow down, but rather speeds up - descending from geostationary orbit will accelerate something to about 10e3 m/s, further increasing the energy.
Re:Orion has splashed down off the coast of Baja, California
by dmitrygr on Monday December 12, 2022 @02:45PM
(#33959204)
I mentioned that... But it needs to be light. The quoted weights are unrealistic for ANY material
> descending from geostationary orbit will accelerate something to about 10e3 m/s, further increasing the energy.
In vacuum, yes, but we have air...resistance
Re:Orion has splashed down off the coast of Baja, California
by skykooler on Monday December 12, 2022 @07:06PM
(#33962441)
Air resistance is only a factor up to forty miles or so; most of that acceleration happens in the preceding twenty thousand miles. And again, air resistance just means more energy dissipation in the form of a blast wave.
> equivalent of two Hiroshima bomb every mile along the equator as its kinetic energy is rapidly converted into heat.
Little boy was 15 kilotons of TNT (63 TJ). Kinetic energy is 1/2 mv^2.
So you are claiming that the mass of a mile of the cable is such that mv^2 = 126e12 J
At equator the planet rotates at 463.8 m/s so you are assuming that the bottom mile of the cable weighs 585.5e6 kg? Ok, you're completely off base here.
Maybe let's look at a higher segment (at geosync orbit). Velocity there is 3.1e3 m/s. You are assuming a mile of that cable weighs 13e6kg. But on the way down it will both ablate (lowering mass) and slow down (lowering velocity), so you are assuming an even more insane higher number.
For comparison, a mile of one inch thick steel cable is ONLY 4e3 kg. Sure, space elevator needs something stronger, but even more so, lighter.
Yeah, you are just off by MANY orders of magnitude, and that claim was likely pulled out of nowhere