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2023-11: Warosu is now out of extended maintenance.

/sci/ - Science & Math

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2375764 No.2375764 [Reply] [Original]

What is the fastest speed a spaceship could travel without harming the astronauts?
Let's say we can go, I dunno, half the speed of light. But that wouldn't be possible because it would kill them, right?

>> No.2375772

>>2375764

High acceleration kills people, not final velocity.

>> No.2375777

No, it wouldn't... Velocity is relative. They might be going half the speed of light relative to Earth, but relative to the ship they're riding in, they would be standing still.

Acceleration is what kills you.

>> No.2375780

John Stapp was a guy that survived tests of 46.2 g forces on his body while sitting on a rocket sled.

He suffered permanent vision damage but lived for 45 more years.

>> No.2375778

Scientists in the 18th century found out that traveling at speeds higher than 30 km/h crushes even the strongest humans. There is no way you could go even faster.

>> No.2375779

you also have to consider running into things , like a tiny rock would just go right through the ship , possibly killing people and destroying electrical components.

also i heard the international space station is the same way. its like they are in a tent in the middle of a gun fight.

>> No.2375781

>>2375772
That's really helpful, thanks. So, theoretically speaking, if we had the technology to travel half the speed of light, we could do it, of course without accelerating very rapidly?

>> No.2375785

>>2375781
We already have the technology. A regular old rocket booster can get you to 99.999% of the speed of light if you go out into space and fire it long enough. But "long enough" might be longer than your natural lifespan.

>> No.2375788

>>2375781
yeah, this is the idea behind ion drives, although the slow acceleration is accepted more due to the energy efficiency of the drive

>> No.2375805

>>2375785
>>2375788
Nice, ty.

>> No.2375852

it also depends if you want to say fuck you to Einstein and the limits on travelling the speed of light. The theory is that the closer something is to the speed of light, the less mass it has and more energy. When you reach the speed of light, you would be composed of pure energy, or something like that. It's early and I'm tired so I dont want to go look up how it really works

>> No.2375868

>>2375785
>A regular old rocket booster can get you to 99.999% of the speed of light
No it can't. An engine can only go as fast as the velocity of its exhaust. That's why an ion engine is theoretically able to travel at relativistic speeds, albeit with terrible acceleration. The exaust velocity is super-high.

>> No.2375873

>>2375868
Good point. I oversimplified.

>> No.2375880

>>2375868
Rocket =/= Jet Engine.
There is no intake.

>> No.2375889
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2375889

Wait. There's a question i always wanted to ask so i'm gonna hijack this thread (as it's related).

When you go really fast your mass increases right (due to reltivity)?
So where does this mass come from?
Do the atoms in yor body become "more massive" (wtf?) or do random particles start appearing in your brain organs and bloodstream, wreaking havoc on your body?

>> No.2375911

>>2375889

bump I wanna know this too

>> No.2375930

>>2375889
Well you see... uhh...

Pressure. Yeah.

>> No.2375958

it might be because of a stonger interaction with the higgs-field, comparable to resistance in water... although i'm not a physicsfag and i'm just guessing

>> No.2375973

Physicsfags, can you help explain this?

I think the additional energy behind a fast-moving object accounts for it though.

>> No.2376017

bump ^^

>> No.2376039

You can go as fast as you want, as long as it's less than the speed of light, and you won't feel a damn thing.

Thing you feel is the acceleration, aka the when you're going from speeding up, or slowing down. If you accelerate at 1 earth-gravity you will feel exactly like you do now, and you can get very close to light-speed fairly quickly.

Then when you stop accelerating you will be 'weightless', and be going nearly the speed of light and not feel a damn thing.

>> No.2376070

>>2376039
Sorry for my shitty english, I'm baked.

But seriously, when you're coasting at 98% or 99% the speed of light, you won't even notice it.

>> No.2376129

>>2375880
No, the same rule applies to rocket engines. It's fundamental physics, not some function of our atmosphere. If an engine's exaust speed is 50,000 m/s then the ship (or what have you) cannot travel faster than 50,000 m/s.

>> No.2376136
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2376136

>>2375779
Arthur C. Clarke proposed using an ice shield to protect traveling starships in his book The Songs of Distant Earth. What say you, /sci/?

>> No.2376138
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2376138

>>2375889

I think you've broken physics!

>> No.2376161
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2376161

>>2376136
I like the "dust shield" of the Von Braun ship from the Alien Planet documentary.

>> No.2376182

>>2375889

It has to do with Einstein's equation E=mc^2. As you go faster, your kinetic energy increases. Therefore your mass increases.

It seems like mass is some constant, never-changing property of all matter. This isn't true. Protons lose mass as they form nuclei because they lose potential energy. Every time a system gains more energy it gains mass. If you compress a spring, it gains a very very very tiny amount of mass.

>> No.2376189

>>2376182
So then what, exactly, occurs when we approach closer to the speed of light? What occurs as we gain more mass, and how is this a bad thing?

>> No.2376214

You only get more mass relative to other, non-lightspeed bodies. So, you would be pulled more strongly towards planets for example; but not towards the hull of the ship.

>> No.2376230

>>2376189

>So then what, exactly, occurs when we approach closer to the speed of light? What occurs as we gain more mass, and how is this a bad thing?
According to relativity there is no preferred reference frame of the universe, no way of determining absolute speed. If you went 99.999% the speed of light with respect to planet A, but 0% with respect to planets B, C, and D, what would be your "true" speed? The answer is that you don't actually have one. So if you go really fast, everything seems the same in your own spaceship, you wouldn't notice anything strange, but on planet A they would measure you with a really high mass.

The mass you have depends on whose measuring it. The faster they're moving, the more mass you have to them. You always see yourself with the same amount of mass. Hope that clarifies stuff.

>> No.2376233

>>2375781
The only problem about reaching a speed close to the speed of light is the time during which we can produce an acceleration because there is (almost) no friction in space.

with a constant acceleration you have

d²x/dt² = a

dx/dt = a*t

when t = c/a you have reached the speed of light.
Of course this isn't right because when the speed gets close to c, Newtonian mechanics do not apply anymore, but the reasoning is quite the same.

We just don't have rocket that can produce a constant acceleration during a very long time.

>> No.2376236
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2376236

>>2375868
Wrong asshat. ((Exhaust V)^2) * exhaust mass = force applied to rocket. Normal boosters could get you there.

>> No.2376237

>>2376161
That's stupid. Why would a dust particle, or a rock or whatever not just rip through it and the ship? Also deflecting that much shit constantly = huge losses in thrust, which means a lot when you're using ion engines.

>> No.2376243
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2376243

Dudes.
Imagine like, you're riding at .98% of the speed of light
Your entire ship relies on a quantum ramjet.
For some reason, the fucking ramjet fails.
You cannot restart it.
You are doomed to coast through the universe at .98% the speed of light.

>> No.2376248
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2376248

>>2376237
lrn2 physics
Seriously is it that hard to comprehend that all masses and speeds are relative?
Getting hit by anything, even a dust particle traveling fast enough would be like hitting a truck.

>> No.2376252

>>2376182
E=mc² is not the complete equation.

E² = m²c^4 + p²c² is the the complete one. where p is the linear momentum (p = mv). so when p = 0 (the particle is still) you get

E=mc²

>> No.2376259

>>2376070
You'd probably notice the universe ending around you.

>> No.2376262

>>2376252
>E² = m²c^4 + p²c² is the the complete one. where p is the linear momentum (p = mv).

That's wrong. p = Ev/c^2 = mv/sqrt(1-v^2/c^2)

>> No.2376260
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2376260

>>2376136
>>2376161
Pulled out of my ass intuition is as follows:
I don't think that any physical material would be useful in stopping or deflecting debris while moving at any appreciable fraction of C. The tiny atomic dust in space could be collected or deflected easily using electromagnetism (as detailed by Carl Sagan I believe), but anything larger than a sand grain will be a problem. Penny-sized rocks would become like nuclear bombs.

The only way to deal with this stuff would be to detect it and avoid it. The ship would need to be able to see far enough ahead to make a course correction so it doesn't hit pebbles. The huge speed of the ship and the minute size of the rocks, etc. would make it insanely hard to detect obstacles in time. Even worse would be the acceleration required to move out of something's way while traveling that fast. The G-loading would be mind-boggling in that kind of maneuver. More than a human crew could handle.

For example, let's say the ship could see a penny-sized rock at 300,000 kilometers away. Shit, you say. That's really far, no problem avoiding it! Well, at half the speed of light the ship would have approximately 2 seconds to move entirely out of the way given light travels 299792.458 km/s. No human could survive that motion.

>> No.2376273

>>2376262
yep. sorry for that.
I didn't want to write gamma because i was too lazy.

>> No.2376295

While we're on the subject of space ships...

How densely is hydrogen atoms spread throughout space? I want to figure out how big a collector cone would be needed for a ion propelled probe to sustain long term acceleration. Ionization and thrust would be powered by fission.

>> No.2376296

Assuming that you can safely accelerate a ship to the speed of your choice, as long as the ship itself is intact, so are the astronauts(assuming that the acceleration wasn't above a survivable treshold). The speed of a system has no effects on it's inner observers; only it's acceleration(or else you'd be really screwed in any modern transportation).

>> No.2376429

>>2376248
That was my point, mongoloid. Read before you post.

>warped wougly
Why captcha i do agree.

>> No.2376451

>>2376295
Not very densely, but IIRC, most mass resides between the stars.

>> No.2376458

>>2376295
Just take some fuel along dude, it's not that heavy.

>> No.2376462

>>2375889
>>2375911
>>2375973
Your rest mass doesn't go up. What goes up is your "relativistic" mass. The rest mass, also called invariant mass, is still the same.

http://en.wikipedia.org/wiki/Mass_in_special_relativity

>> No.2376465

>>2376295
http://en.wikipedia.org/wiki/Bussard_ramjet
The estimate varies greatly from km to thousands of km. In this case the scoop is made of an electromagnetic field. Making a physical scoop would be impractical.

>> No.2376467

>>2376458
>implying fuel doesn't make up a huge amount of the total weight of rockets

>> No.2376473

>>2376458
YES IT IS. though i guess lauching a stream of ions along the desired path before lauch would be easier...

>> No.2376501

>>2376465
>Making a physical scoop would be impractical.
Impractical is just another word for awesome. I'd paint "FUCK YOU XENOS" in letters large enough to be made out with a telescope several AU's away (i'd also draw a dick, just in case they don't read english)