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Emergency braking in space

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Re: Emergency braking in space

#21

Post by bena »

_bz1e wrote: post #13
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.

Is this 9.8m/s2? So after 1 year at this is 3.156e7*9.8/1000*3600km/h ? Assuming it's just moving in space away from any massive objects in a straight line...1 billion km/h. Isn't it too fast?

Not to mention the power required to continuously accelerate.

Or what happens to anything hitting you when you're traveling at that speed.

Or needing to turn.

Every answer is just a disguise for four more problems.

Re: Emergency braking in space

#22

Post by jimbokun »

In this book, a space flight to Alpha Centauri uses an asteroid which is constantly accelerated at 1g for half the flight, then constantly decelerates at 1g for the second half of the trip:

https://en.wikipedia.org/wiki/The_Sparrow_(novel)

That eliminates need for "artificial gravity" and really drove home to me that 1g is really the limiting factor for long range human space flight.

Re: Emergency braking in space

#23

Post by dhc02 »

jimbokun wrote: post #22

In this book, a space flight to Alpha Centauri uses an asteroid which is constantly accelerated at 1g for half the flight, then constantly decelerates at 1g for the second half of the trip: https://en.wikipedia.org/wiki/The_Sparrow_(novel) That eliminates need for "artificial gravity" and really drove home to me that 1g is really the limiting factor for long range human space flight.

Love that book.

Re: Emergency braking in space

#24

Post by 323 »

franky47 wrote: post #12

One point is left out from this calculation: what's the reference point we're at a "full stop" from? Aren't you always orbiting something when in space (however large or distant)? If you were to kill your orbital (lateral) velocity, you'd only be gaining radial velocity by being pulled towards the orbiting body, some form of thrust would be needed to compensate that. TL;DR: can you really be "at a full stop" in space…

You could consider the start point (roughly) as the reference point. Or the destination point.

Re: Emergency braking in space

#25

Post by throwaway09223 »

jimbokun wrote: post #22

In this book, a space flight to Alpha Centauri uses an asteroid which is constantly accelerated at 1g for half the flight, then constantly decelerates at 1g for the second half of the trip: https://en.wikipedia.org/wiki/The_Sparrow_(novel) That eliminates need for "artificial gravity" and really drove home to me that 1g is really the limiting factor for long range human space flight.

1g isn't all that limiting. Under 1g acceleration you'll reach lightspeed in about a year, at which point you can't go any faster. A year to reach the top speed of the universe isn't so bad.

The truly limiting factor is that we don't have engines that can produce 1g for a sustained period. We can't carry and propel enough reaction mass and reactionless drives only exist in science fiction.

Re: Emergency braking in space

#26

Post by jefftk »

throwaway09223 wrote: post #25
jimbokun wrote: post #22

In this book, a space flight to Alpha Centauri uses an asteroid which is constantly accelerated at 1g for half the flight, then constantly decelerates at 1g for the second half of the trip: https://en.wikipedia.org/wiki/The_Sparrow_(novel) That eliminates need for "artificial gravity" and really drove home to me that 1g is really the limiting factor for long range human space flight.

1g isn't all that limiting. Under 1g acceleration you'll reach lightspeed in about a year, at which point you can't go any faster. A year to reach the top speed of the universe isn't so bad. The truly limiting factor is that we don't have engines that can produce 1g for a sustained period. We can't carry and propel enough reaction mass and reactionless drives only exist in science fiction.

> 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?

Re: Emergency braking in space

#27

Post by rsynnott »

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…

Requires a magic-based energy source; the usual problem with this sort of thing.

Re: Emergency braking in space

#28

Post by TremendousJudge »

ginko wrote: post #19
ericbarrett wrote: post #18

I think it would be impossible for humans to walk around at more than ~1.5 g of acceleration for extended periods of time, and even that is asking a lot. Take the g-force and multiply it by your body weight. That would be how heavy you feel when standing. If you are 70 kg (154 lbs) and under 1.5g of acceleration that is an extra 35 kg (77 lbs) of weight, which is about what we ask a modern soldier to carry. But the s…

>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.

It's not the same though. When at higher gravity, you're not carrying more weight like a backpack or like extra fat -- your regular tissues weigh more. This includes your blood and other fluids, but your heart is still the same strength. I'd expect that to make a difference.

Re: Emergency braking in space

#29

Post by timbit42 »

EddieDante wrote: post #5
xeromal wrote: post #3

Earlier quoted context omitted.

This specific moment where he still makes the noise after having the microphone smacked from him makes me laugh the same as it did when I was a tiny kid. https://youtu.be/rGvblGCD7qM?t=95

Michael Winslow is one of the greats.

He was on AGT a few years ago.

Re: Emergency braking in space

#30

Post by hammock »

TremendousJudge wrote: post #28
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.

It's not the same though. When at higher gravity, you're not carrying more weight like a backpack or like extra fat -- your regular tissues weigh more. This includes your blood and other fluids, but your heart is still the same strength. I'd expect that to make a difference.

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.
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