3 ms·
> Two sources say physicists who’ve looked into the company said a potential challenge could be air resistance on the cargo when the catapult fires. Earth’s atm
by zurp 9y ago
> Two sources say physicists who’ve looked into the company said a potential challenge could be air resistance on the cargo when the catapult fires. Earth’s atmosphere is so dense that it could be like the cargo was hitting a brick wall upon ejection.
Reminds me of the calculation that shows Santa Claus and his reindeer, if they ever existed would have vaporized instantly at the beginning of first Christmas delivery:
...353,000 tons traveling at 650 miles per second creates enormous air resistance — this will heat the reindeer up in the same fashion as spacecraft reentering Earth’s atmosphere. The lead pair of reindeer will absorb 14.3 QUINTILLION joules of energy. Per second. Each. In short, they will burst into flame almost instantaneously, exposing the reindeer behind them, and create deafening sonic booms in their wake. The entire reindeer team will be vaporized within 4.26 thousandths of a second. Santa, meanwhile, will be subjected to centrifugal forces 17,500 times greater than gravity. A 250-pound Santa (which seems ludicrously slim) would be pinned to the back of his sleigh by 4,315,015 pounds of force. In conclusion — If Santa ever DID deliver presents on Christmas Eve, he’s dead now.
- danbruc 9y agoEven ignoring air resistance, if your hypothetical spacecraft centrifuge had a radius of one mile, then the spacecraft would still experience 114 g at 3000 miles per hour. If you more realistically spun up Apple's new headquarter with a diameter of 461 meters [1] to one revolution per second, that makes 3240 miles per hour, the spacecraft and the outer wall of your centrifuge would experience a centripetal acceleration of 928 g. Not going to happen. And 3000 miles per hour is also pretty slow, about half the speed in a geostationary orbit, for a low earth orbit you need about 17,500 miles per hour [2] which is almost 6 times faster and would increase the forces 36 times. [1] https://en.wikipedia.org/wiki/Apple_Park https://en.wikipedia.org/wiki/Apple_Park [2] https://en.wikipedia.org/wiki/Orbital_speed https://en.wikipedia.org/wiki/Orbital_speed
- throwaway99OO 9y agoWhat's wrong with 928 g? A lot of jet turbines can go over 10,000 g at the blade tips. https://en.wikipedia.org/wiki/Turbofan https://en.wikipedia.org/wiki/Turbofan I don't think they are targeting 17,500mph. Guessing they are trying to do something sub Mach 10 for aero reasons to reduce fuel and increase structural margins that are held tight by the rocket equation. Reduced delta v = improved margins. https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation#/media/File:Tsiolkovsky_rocket_equation.svg https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation#/m...
- miketery 9y agoOut of curiosity is it correct to assume launch at the equator going east adds 24,000 miles circumference / 24 hrs = ~1000mph
- andbberger 9y agoYes. That's ~1000mph less delta-v needed to reach orbit. But note that the air is also moving in the same rotating frame, so there is no difference in air resistance upon exit from the launcher whether you are going east or west.
- stcredzero 9y agoEven ignoring air resistance, if your hypothetical spacecraft centrifuge had a radius of one mile, then the spacecraft would still experience 114 g at 3000 miles per hour We can build electronic components that are rated for 100000 g's. I think craft that can withstand 10's of g's are within our capability to build. Why not make the circle the size of the LHC? Why not larger?
- anonytrary 9y agoIt's about the payload. It is also accelerating. It would be flattened to a crisp.
- stcredzero 9y agoAnything like this should be assumed to be launching bulk payloads or hardened payloads. For machines 10's of g's is not that big a deal. It's challenging, but quite doable. For lots of kinds of bulk cargo, it's not a big deal.
- anonytrary 9y agoYeah, I'm sure certain restricted types of cargo may be launched this way. We will still need rockets for the vast majority of cargo types.
- danielbarla 9y agoThose orbital numbers are sobering, but there may still be plenty of reason to investigate a launch mechanism where the "fuel" comes from an external source. I haven't run the numbers, but a quick look at typical delta-V budgets [1] (which calculate atmospheric losses as 1.5 to 2 km/s of delta-v), if one could accelerate something fast enough that it escapes most of Earth's atmosphere (and only then burn for orbital velocity), you'd be saving ~17 to 20% on the delta-v requirements. Due to the nature of the Tsiolkovsky equation, that could be a very substantial saving. That said, I'm also wondering why a centrifuge would be better than say, some kind of low pressure tube / rail, but I'm sure these guys have done their maths and believe in it. [1] https://en.wikipedia.org/wiki/Delta-v_budget https://en.wikipedia.org/wiki/Delta-v_budget
- nine_k 9y agoScaled Composites tried to solve it by launching from a winged aircraft. (Too bad they seem to have stopped.)
- andbberger 9y agoI wonder how much it would help to have multiple projectiles firing in close succession with the payload last. Centrifuges seem like an ideal launcher for such a strategy, since you could finely tune the timing of successive releases. If you can do that, and design a booster to round out the orbit that can withstand the acceleration you're golden. You have a system for cheaply delivering raw materials to LEO. Does a block of aluminum have sufficient tensile strength to be spun up to the required energy at reasonable diameter?
- gameswithgo 9y agowhat if your railgun ran up the side of a 14er in colorado. you get a degree of wind resistance reduction there.
- anonytrary 9y agoI would imagine the cargo being obliterated before taking off. https://www.youtube.com/watch?v=zs7x1Hu29Wc https://www.youtube.com/watch?v=zs7x1Hu29Wc
- amenghra 9y agoBut what if Santa is able to convert all that heat into toys...