   Physics possibility: g-spinner inside spaceship to get more max thrust?
  I had a new invention idea, a way to expose a human to more than 12gs of acceleration without killing them, allowing people to travel to distant places much faster, as fast as a robot or rover at 120+gs of acceleration/force. The trick would be to include a g-spinner inside the rocket, one that can produce as much force as the motor, and make the g-spinner always produce a force that is opposite the main thrust of the engine via a spinning movement. I'm assuming this is possible, although I'm not an expert in mechanics...however I think it is possible to create a g-spinner that can exert the force in any arbitrary direction by accelerating/rotating the end of the swingarm rapidly in a certain 3-D movement pattern...with humans able to accelerate faster than 12gs, it would be very possible to put people on Mars as fast as we did the rover, which would also cut down on the water/food/air storage requirements.   
  The problem with accelerating spacecraft is not that the people inside can't stand it. It's that we don't have a fuel with sufficient energy/kilo density to get anywhere near those sorts of accelerations.Using a constant 1g thrust would be a) useful from the perspective of the occupants and b) sufficient to reach nearby STARS in reasonable (experiential) time, never mind Mars.[1]We just don't have a fuel source which can provide 1g thrust for those extended periods of time.There was a nice rule of thumb for understanding the effect that fuel energy density has on missions that the reason the amount of lunar rock that could be returned from the moon was so restricted is that the mass of the launch vehicle goes up by the cube of the mass delivered to escape velocity.Since the lunar trip involved two escapes (from the earth and then from the moon), then one has to deliver the cube of the return mass on the first launch. Which means that every increase in return mass means a SIXTH ORDER increase in the original launch mass.You have to launch the fuel to launch the fuel to launch the fuel to launch the fuel to launch the fuel to launch the fuel to launch the rocks that you want to bring back...{What's worse is that the cost of space vehicles basically rises roughly on the cube of their launch mass...}[1] Assuming you're going to accelerate halfway, flip over and then decelerate halfway, your journey time is the root of your acceleration over the distance.For Proxima Centuri it's about 4 × 10^16 metres. G is 10m/s^2, so you're looking at root(4x10^15) seconds which (in my head) I make to be about 8x10^7ish. That sounds a lot... but it's actually 2.5 years. Now clearly P.C. is 4.something ly away, so you're not going actually to be doing that. Not in this universe anyway. But the crunchy bit here is that sustained 1g acceleration -- which isn't beyond our reasonable grasp -- will make relativistic speeds in months.We don't NEED 12g acceleration. We need to be able to do 1g or 1/10g for much, much longer.s = 1/2 a t^2. It's that t^2 that's the diamond. Making "t" bigger is much more rewarding than making the "a" bigger.;  How did the mars rover get there so fast? The rover probably weighs more than a few people, and it may also be easier to do a powerful short burst than a long extended burst. As for fuel density, the space shuttle uses the densest fuels possible, which I assume are nuclear, but actually are not. So I suppose one way to get a lot more thrust would be to use nuclear or post-nuclear fuel, which should be able to provide more thrust with the same volume and mass, albeit with a potentially higher production cost and probably engine complexity. On the off chance the shuttle is already firing a nuclear missile every time it launches, probably well above the atmosphere where any radioactive particles would blend in with the radioactive particles coming off the sun (note: the sun in space looks similar to the sun from earth, it's too bright to look at, and there's no shade unless you're directly behind a planet or something. So it's always high noon, although the sun does get a little larger + brighter or smaller+dimmer as you get close and further away, nobody's ever actually gone very close or far from the sun except around 1-earth distance from it, with the exception of that time in the 70's when a bunch of dudes taped a wireless digital camera to a big rocket and flung a few of them in carefully aimed and corrected trajectories, including a few that were carefully fired into the orbit of a nearby galactic sized asteroid.Also your scale is way off. There is a huge difference between the moon and mars and traveling to another sun. It is probable that humans will colonize the solar system well in advance of colonizing another one. I should note that with more acceleration trips to the moon would be much more practical, taking perhaps 5 hours instead of the 3 days the apollo rockets required. Ultra high acceleration vehicles could also be used for point to point transfers around the earth, possibly skimming above the atmosphere to reduce friction and achieve incredible speeds, potentially traveling anywhere on earth in 50 to 90 minutes at 120gs (estimate). Note this would be very expensive if nuclear fuel were required to operate it, although the president might get a much cooler jet out of the deal.You're also assuming space has zero friction, which is probably not accurate. At the very least there's observed low density "sand" floating around, although very sparse there's a large number of tiny asteroids which would collectively cause friction to a large vehicle moving at speeds well in advance of the 15,000km/sec that NASA attained, although at those low speeds there is essentially zero friction. The NASA space shuttles all put the maximum force on the astronauts that humans can take, and astronauts are required to be able to withstand 7-8gs of force and still pilot the space shuttle or do other duties, which is very challenging since a 200 lb person weighs 1600 lbs at 8gs.I'm also still not convinced that the speed of light cannot be accelerated smoothly through simply via application of sufficient thrust, with no mass increase or time travel happening. Sort of like how prior to the 40's, nobody thought it was possible to travel faster than sound, and they predicted all sorts of incorrect things that would happen when someone did it. Then NASA found out that if you use enough thrust, you can accelerate past the sound barrier, as they did with the jets when reaching around 770 mph. They noted that passing 770 mph was not eventful in any way other than intellectually as traveling faster than sound and the sonic boom effect, that for most engineering purposes 770 was the same as 570 and 1270 mph.   ;  Space exploration in 3 easy steps :- Make sure you have a good grasp of the laws of physics.- You're not making any sense. - This is the wrong forum.   ;Quote:Original post by aersixb9I'm also still not convinced that the speed of light cannot be accelerated smoothly through simply via application of sufficient thrust, with no mass increase or time travel happening.That's only because you don't understand Special Relativity. But, hey!, at the beginning of the thread you already established that you don't know the first thing about mechanics, and that your intuitions for it are wrong.Note to moderators: As much fun as it is to consider a collision with an asteroid at 15,000Km/s and call if "friction", I think someone should close this thread before I lose it and start calling this guy names.;  "The NASA space shuttles all put the maximum force on the astronauts that humans can take"I assure you it doesn't. Crashing your car puts you through easily 10x the acceleration of a shuttle launch[1]. It turns out the human body can withstand 50-80g provided it's not for very long. The story of the man who proved this (and massively improved road safety along the way) is actually quite funny because in order to reduce the amount of time it all took, he simply tested things on himself.I don't recommend actually participating in car crashes as an entertainment though.Also force is not the same as acceleration."The rover probably weighs more than a few people"Rover : 185Kg.Delivery system : ~800Kg."How did the mars rover get there so fast?"Flight time was about six months. You can get to Mars that fast with people but you might not want to. Why? They were sent on a relatively high speed trajectory. If their Martian orbit injection had failed, they would have been lost. They're only robots, so it would merely have been expensive.Humans, at least sane ones, are likely to want to fly on a route which provides a fail-safe low energy return path, looping around Mars. Just in case something nasty happens along the way. This would result in the same sort of abort option that Apollo 13 used."with no mass increase or time travel happening"I'll have to introduce you to people round here sometime. Cambridge Uni's physics people are SUCH stick-in-the-muds on the subject of whether relativity works or not. You could probably shake them right out of it. I don't have a hope 'cos I only studied physics & cosmology to S-level.;Quote:Original post by aersixb9I had a new invention idea, a way to expose a human to more than 12gs of acceleration without killing them, allowing people to travel to distant places much faster, as fast as a robot or rover at 120+gs of acceleration/force. The trick would be to include a g-spinner inside the rocket, one that can produce as much force as the motor, and make the g-spinner always produce a force that is opposite the main thrust of the engine via a spinning movement. I'm assuming this is possible, although I'm not an expert in mechanics...however I think it is possible to create a g-spinner that can exert the force in any arbitrary direction by accelerating/rotating the end of the swingarm rapidly in a certain 3-D movement pattern...with humans able to accelerate faster than 12gs, it would be very possible to put people on Mars as fast as we did the rover, which would also cut down on the water/food/air storage requirements.What you propose is simply not possible. It violates Newton's third law of motion.Cheers,Mike;  Say you have a cart in the spaceship that can translate back and forth (e.g., it's on rails), which contains the astronauts.  And say it starts at the front of the craft.  Now you wish to accelerate the spaceship at a rate 'a.'  "Fine," you say, "I'll just accelerate the cart backwards relative to the ship, also at a rate 'a,' so that relative to an inertial frame the cart hasn't accelerated at all, and the humans have experienced no inertial forces."  That's all well and good.  But here's the problem: Eventually, the cart reaches the end of the track at the rear of the ship.  What do you do now?Any version of the problem, whether it be with spinning capsules or what have you, reduces to this.   ;Quote:Original post by EmergentBut here's the problem: Eventually, the cart reaches the end of the track at the rear of the ship.  What do you do now?See, now that isn't even a little bit hard: all you need is the portal gun! Place portals at either end of the trak, and ta-da!   ;  To provide a more concrete demonstration of why what you propose is FAIL, consider how a G-spinner works. You sit in a bubble, and are spun round in a circular path at some distance from a central axle. You are under constant acceleration since this is required to prevent you from flying off at a tangent to your current circular path. This acceleration is always directed towards the central axle. Now, when you put your G-spinner inside your spaceship, and carefully set it up so that as you ignite your ACME UBER-BOOST rockets providing 12g acceleration, the 4g acceleration generated by your G-spinner when you are at the front point of your circle reduces your net acceleration to 8g. Then, as you reach the back end of your arc, you realise your mistake as the G-spinner is in fact generating acceleration for you in the same direction as the rocket thrust, and your HEAD ASPLODES under the net 16g acceleration skywards.Of course, if you can design a G-spinner which always accelerates you downwards with no net movement, then you should probably patent it.   