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Emergency braking in space

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Re: Emergency braking in space

#71

Post by hinkley »

dhosek wrote: post #14
throwaway09223 wrote: post #7

If a ship is capable of continuous 1g acceleration then it shouldn't be designed with rotating centrifugal rings for gravity. Instead, design the ship with the floor towards the engine and travel at a constant 1g to wherever it is that you're going. Decelerate at the same speed.

That was how the interstellar ship¹ in The Sparrow by Mary Doria Russell worked. For the first half of the trip they accelerated at 1g, then the ship rotated and they decelerated at 1g for the second half of the trip. ⸻ 1. Which was actually a hollowed-out asteroid and used the asteroid itself as propellant to achieve continuous acceleration and deceleration for the trip. One of the better attempts at providing a pla…

Achieving a given acceleration takes a certain amount of force per unit of mass. If one made the (dangerous) assumption that the propulsion system doesn't wear out over time, then it's more plausible to assume that at the beginning of the voyage you would achieve less than 1g, hopefully ramping up fast enough to keep atrophy to a moderate risk. Toward the end, as the asteroid gets lighter, you would run the engines at less than 100% for comfort. In this scenario the acceleration phase continues well past the halfway point.

And even without magic engines, any acceleration to match velocity with the destination doesn't need to be cancelled out, so the first 'half' of the trip is going to be slightly longer than the back half, even if you could do 1g the whole way (which the rocket equation has some problems with).

Re: Emergency braking in space

#72

Post by luis8 »

What about using a long ship and then using a high tech spring to apply the deceleration over the length of it. Relocate the passenger at the front and repeat until you reached the desired speed.

Just thinking out loud maybe that will be counterproductive in the amount of time needed

Re: Emergency braking in space

#73

Post by hinkley »

mateo1 wrote: post #53
dhosek wrote: post #14

Earlier quoted context omitted.

That was how the interstellar ship¹ in The Sparrow by Mary Doria Russell worked. For the first half of the trip they accelerated at 1g, then the ship rotated and they decelerated at 1g for the second half of the trip. ⸻ 1. Which was actually a hollowed-out asteroid and used the asteroid itself as propellant to achieve continuous acceleration and deceleration for the trip. One of the better attempts at providing a pla…

It's just barely feasible with fusion energy densities. To accelerate a million tons to 0.1c you need as much kinetic energy as is theoretically contained in a million tons of hydrogen you'll fuse. Maybe with antimatter, but traveling so fast causes a ton of other issues, like every single particle you encounter is also traveling at ~0.1c.

I believe the math works out such that any slag you create while refining construction or fuel materials needs to be launched out the back of the ship as fast as you can (frequency and velocity) so that you're not accelerating it along with the rest of the rock.

Though probably not exactly straight out the back, since that would create a navigation hazard for the next ship...

Re: Emergency braking in space

#74

Post by hinkley »

throwaway09223 wrote: post #47
tomrod wrote: post #43

Earlier quoted context omitted.

Why would an ion thruster engine not be feasible?

The X3 ion engine has a weight of 230kg and a thrust of 5.4N. This is about 500 times less force than is needed to propel the engine forward at 1g (even if we pretend the entire rest of the spaceship doesn't exist - in reality it would need to be thousands of times more powerful) Ion engines cannot currently produce anywhere close to this level of force. Adding more engines won't help because each engine can't even p…

ELI5: Ion engines are the slowest tortoise you can imagine and to feel like gravity you need the hare.

Re: Emergency braking in space

#75

Post by satori99 »

Mister_Snuggles wrote: post #8
throwaway09223 wrote: post #7

If a ship is capable of continuous 1g acceleration then it shouldn't be designed with rotating centrifugal rings for gravity. Instead, design the ship with the floor towards the engine and travel at a constant 1g to wherever it is that you're going. Decelerate at the same speed.

I'm really surprised by this oversight as other things (magnetic boots) from The Expanse were explicitly mentioned. In The Expanse, this is exactly how ships are set up. The "floor" is towards the engine and the continuous 1g acceleration provides "gravity". When a ship starts decelerating there is a "flip and burn" where everyone straps in while the ship literally turns around and starts accelerating at 1g in the op…

As well as strapping in to gel couches before high G maneuvers, the crew also connected themselves to IVs for auto injection of anti-clotting drugs so they could minimize the chance of a stroke or aneurysm.

Re: Emergency braking in space

#76

Post by dTal »

tantalor wrote: post #15
jermaustin1 wrote: post #11

Earlier quoted context omitted.

Seems like that would cause terrible motion sickness. Rotating would cause centripetal force, so another vector of acceleration on your body PLUS a constantly changing vector of acceleration due to deceleration.

I imagine amelius intended a regular "flip" like a hospitalized patient to avoid bedsores, not constant rotation.

Immersed in liquid would be the way. Internal organs would still have to bear the load, but your skeleton and musculature could be spared.

Re: Emergency braking in space

#77

Post by ksaj »

tablespoon wrote: post #36
hammock wrote: post #30

Earlier quoted context omitted.

That’s a really interesting point. I wonder if there are “artificial exohearts” or something that we could install on the extremities to keep vital body fluids like blood and lymph flowing when the heart is not strong enough.

> That’s a really interesting point. I wonder if there are “artificial exohearts” or something that we could install on the extremities to keep vital body fluids like blood and lymph flowing when the heart is not strong enough. Isn't that basically a g-suit, like fighter pilots already wear? https://en.wikipedia.org/wiki/G-suit Also, from that page: > The resting g-tolerance of a typical person is anywhere from 3–5 g…

This is akin to the landing impact when you jump from something low enough that you won't die from it. You wouldn't survive it in a sustained manner, but the brief jolt, while maybe causing your innards to ache, is tolerated.

Re: Emergency braking in space

#78

Post by ksaj »

sneak wrote: post #41
ginko wrote: post #19

Earlier quoted context omitted.

>Go higher and it gets even less plausible. 2.0g is like carrying your twin. FWIW there are people who weigh well beyond 150kg so I'd argue it would be plausible. Will people be able to perform at peak physical level? No. Will they probably manage for a couple of days? I'd say so.

> FWIW there are people who weigh well beyond 150kg so I'd argue it would be plausible. Those people have been training for months/years to carry that weight.

Indeed. It's also not pulling down with that same weight on each of their internal organs.

Re: Emergency braking in space

#79

Post by tgb »

scrumbledober wrote: post #44
jefftk wrote: post #26

Earlier quoted context omitted.

> you'll reach lightspeed in about a year, at which point you can't go any faster I don't think that's how relativity works?

assuming constant acceleration it kinda does, but constant acceleration requires asymptotic infinite amounts of energy.

As measured relative to the destination, yes, but if so then that means the passengers get crushed under infinite gs.

Re: Emergency braking in space

#80

Post by tgb »

lrem wrote: post #69
jefftk wrote: post #26

Earlier quoted context omitted.

> you'll reach lightspeed in about a year, at which point you can't go any faster I don't think that's how relativity works?

Yup, it would take 6 years instead. Ship time ;) Source: https://gregsspacecalculations.blogspot.com/p/blog-page.html... and ignoring all the other fun aspects.

That’s just what it shows after rounding up. The site correctly doesn’t let you enter 1c for velocity since it’s not possible.
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