Rocket packs have drawbacks.
Jet packs carry chemical fuel but uses atmospheric oxidizer. About 10 minutes before the fuel is used up.
Rocket packs carry both fuel and oxidizer. About 30 SECONDS before the fuel is gone.
Hard to increase duration, short of nuclear energy.
Users typically fly with rocket packs at an altitude too low to use a parachute (below 30 meters) but too high to survive the fall (above 9 meters)
@nyrath
seems like, for in-atmosphere use, some kind of ducted fan gear would be a *lot* more practical for personal flight
(wouldn’t really help with the issue of operating in that no-survival envelope, though...)
A physicist I knew gave me equations to calculate the power usage of a scifi antigravity device that obeyed the laws of physics
https://www.projectrho.com/public_html/rocket/antigravity.php#parahover
@tkinias @nyrath Something might have been lost in the translation of quoting this. Luke and I have done lots of calculations on all sorts of things through the years, and I don't think he wouldn't be careless about power vs energy.
Anyway, in case you didn't follow the calculations, the energy requirements for hovering in place - with these equations - is zero. Gravitational potential energy is neither lost nor gained during hover.
But for the original question, the point is moot. In order to hover in place, the energy requirement according to these equations is zero, and zero divided by any time interval is also zero - thus the power requirement is zero. (Luke Campbell explains this principle with the example of "a chair".)
[part 2 of 3, because Mastodon sucks]
@isaackuo
Presumably we have some amount of power, though, to keep the device ‘on’—if the antigrav turns off you fall like a rock, so that suggests *something* is consuming power to keep the lights on (as it were).
Perhaps this is the antigrav equivalent of keeping your superconducting magnets cool?
@nyrath
Larry Niven mentions the gravity drag in his short story "Flatlander".
"...The beautiful thing about a gravity drag is that it uses very little power. It converts a ship’s momentum relative to the nearest powerful mass into heat, and all you have to do is get rid of the heat..."
I'm not sure what that means, exactly. Sort of like aerobraking without the air. Needs a heat radiator. How does it know which mass is nearest?
@nyrath @cerebrate @tkinias @isaackuo@mastodon.social Yeah i’m not sure that makes sense. sorta the whole point of gravity is that you don’t know how its affecting you until you collide with something else, because its not actually a force
@nyrath @cerebrate @tkinias maybe you can handwave something about the gravity gradient across the object you want to decelerate. like the gravity version of a thermocouple
You mean like tidal forces?
I wonder what the implications would be. Imagine great needles eerily flying around while holding themselves erect, to maximize the tidal gradient across the structure.
Forget any notion of sleek fighter-jet-like craft.
Just some dude perched on top of an impossibly-slender pole like a bamboo stalk, except it tapers to nothing well before reaching the ground.
Or, more likely, hanging from a pole that sticks up like the pole on a bumper car. 😁
Turn it on when it's resting on the ground and nothing happens because there's no vertical displacement between the two ends of the device, but tilt it carelessly and it threatens to give you a savage uppercut like those foam kickboards at the pool. 🤣
"He'll be fine. Kids are durable. Remember when you were learning to ride one?"
@cinebox @nyrath @cerebrate @tkinias It transfers energy and momentum between masses, isn't that literally the textbook definition of a force?
@nyrath @cerebrate @tkinias @isaackuo
As usual, Niven offers an explanation which is not quite right.
Gravity drags require three orthogonal high-density cylinders rotating at ridiculous angular velocities. The cylinders are etched via x-ray lithography in a repeating circuitry pattern.
Spinning them up generates gravity wave vibrations that are very attractive to certain nearly ubiquitous masses in a parallel universe. As they gather towards the signal, they flatten out the curvature of space-time from the other side.
[It's a set of prayer wheels that call eldritch god-mice.]
@dashdsrdash @nyrath @tkinias @isaackuo
Isn't this how you get the gnurrs to come from the voodvork out?
@cerebrate @nyrath @tkinias @isaackuo
No, you just squinch your eyes and play a little tune on -- no, wait:
Always hum to the right kind of fife.
@nyrath @cerebrate @tkinias @isaackuo If gravity drag were a thing, one would expect to be able to use it against the pseudo-absolute framework of the cosmic microwave background.
@cerebrate @tkinias @isaackuo
In a few Larry Niven stories with something like that. He called it a "gravity drag"