Questions on space travel for a sci-fi story

  • Thread starter StarkRavingMad
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  • #51
Danger
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It certainly could be turned off, but it wouldn't be a good idea as long as it isn't a serious power hog. There are serious medical problems associated with long-term freefall, such as bone decalcification and circulatory issues, not to mention the commonality of space-sickness. Also, why go through the inconvenience that it causes for gravity-acclimated people? Just simple stuff like having a shower or using a toilet are complicated, and that's nothing compared with trying to make a decent Baked Alaska.
 
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  • #52
StarkRavingMad
Danger said:
It certainly could be turned off, but it wouldn't be a good idea as long as it isn't a serious power hog.
Thanks. That is what I figured. I wouldn't think it would normally be turned off either, but I was wondering if it could without endagering the crew in emergencies.

I wouldn't imagine it would hog that much power in a space age setting. The generators would probably draw more power compensating against acceleration than just maintaining 1 G in freefall. I'm considering having some kind of gravity harness or chamber rather than making a generator try to apply equal gravity across an entire ship during high speed maneuvers, or during the acceleration burst to get from escape velocity to c.

What would happen to a body under the stress of prolonged double-digit g-forces? Would they just pass out, or would there be physical damage?
 
  • #53
Danger
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StarkRavingMad said:
What would happen to a body under the stress of prolonged double-digit g-forces? Would they just pass out, or would there be physical damage?
'Double-digit' covers a lot of territory. To start with, only people in very good physical condition can handle 10 g. Secondarily, the effect of acceleration depends upon in which direction it's applied. Bird-driver terminology refers to it as 'eye-balls in', 'eyeballs-up', etc., dependent upon the vector. 'Eye-balls in', for example, means positive acceleration in the direction that the pilot is facing. It comes from the fact that your eyes move backward into your head in that situation. You can extrapolate the rest.
A positive acceleration will impose black-out, wherein there isn't enough pumping force from your heart to get the blood to your brain against gravity. Negative acceleration produces red-out, which happens when too much blood is forced into your head.
I believe, although there are others here who know a lot more about it, that NASA or US Air Force shock suits can keep the pilot conscious up to about 18 g (I'm tired of italicizing that). Even at that, more than a few seconds, or minutes at most, is very hazardous.
If I'm not mistaken, this is an area in which Russ Watters is very knowledgeable. Fred Garvin can probably weigh in significantly as well. I know that Integral is also a pilot, but I'm not sure if he has had military or aerobatics experience.
 
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  • #54
russ_watters
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Answer to pm/thread....
StarkRavingMad said:
The question atm is about the extent of heavy g-forces on a human body in space. The acceleration that we're talking about is pretty huge... the amount of thrust needed to push a ship from escape velocity to relativistic speed, like .3c. So it's kind of hard to use numbers.

How much g-force are we talking about here, and in the absense of some kind of gravity compensating against that force, what would it do to a body?
Early astronauts took something like 12-15 g for a few minutes during re-entry. Regardless of the intensity, though, the effects are the same (just multiplied by higher intensity): Primarily, your muscles, particularly your heart, abds, and your diaphram have to work harder to do their jobs. 2 or 3 g might be analogous to a brisk walk, 5-7 to good run, and 12-14 an all-out sprint. And the only way to handle more than about 8 for more than a few seconds is in the prone position in an ergonomic couch, with a g-suit. Your heart simply isn't capable of working against that much pressure and you'll pass out from lack of oxygen to your brain, otherwise.

So .3C.....

At 10g, that's a little more than a month to reach that velocity. I doubt even in an induced coma, with a breathing apparatus and IV for food a person could survive that. You'd probably die of a heart attack in a day (as if you had tried to run 6 marathons in a row, at 4 hours each).

I would guess a person in good shape could probably handle 2g for a few months and 1.5 indefinitely. That kind of acceleration doesn't help you if you are looking to travel within the solar system in days, but it would do you just fine if you are trying to travel to the nearest stars in a human lifetime.
 
  • #55
StarkRavingMad
I was thinking more of science fiction timeframes, where a ship accelerates from supersonic to sublight in a matter of minutes and then freefalls the rest of the way until it needs to adjust course.

Actually now that I think about it... wouldn't adjusting course by more than a few degrees while travelling at something like .3c (in the absense of some kind of internal gravity generator) create ungodly g-forces, too?
 
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  • #56
StarkRavingMad
From rereading all of this, including the links, I've come to the conclusion that interstellar travel at the kind of speed in science-fiction is just not possible without a localized gravity well.

It seems that accelerating from mach 6 to .3c in under a minute would create more thrust than a human(oid) body can handle. You'd need a compensator pulling in the opposite direction to equalize so that the passengers are constantly experiencing somewhere around 1G.

Is that safe to say?
 
  • #57
DaveC426913
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StarkRavingMad said:
From rereading all of this, including the links, I've come to the conclusion that interstellar travel at the kind of speed in science-fiction is just not possible without a localized gravity well.

It seems that accelerating from mach 6 to .3c in under a minute would create more thrust than a human(oid) body can handle. You'd need a compensator pulling in the opposite direction to equalize so that the passengers are constantly experiencing somewhere around 1G.

Is that safe to say?
Yep. That's safe bet.

StarkRavingMad said:
But what I am curious about is a space station in DEEP space, far from any planets to anchor it. Would there be a way orbit a system the same as a planet?
Something to keep in mind.

1] When you get out into the outer solar system, g-pull from the Sun is so weak, you don't really have to worry about orbits for short term use, like a spaceship. You can basically just park. Sure, you'll fall inward, but really slowly. It would be irrelevant, especially since there's be nothing nearby to even notice your drifting.
2] Pluto takes 260+ years to orbit. Park a space staion out there, and you don't have to give it much motion in order for it to be in a stable orbit. Go out a few multiples of Pluto's distance and it would be centuries before you'd noptoce let alone care whether you're in a stable orbit. Again, your tangential motion is so small, you're practically parked.
 
  • #58
Astronuc
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I agree with DaveC. However, one would have to avoid comet type orbits with shorter periods.

The Voyager craft are 'leaving' the Solar System.

Voyager 2:
Voyager 2 has visited more planets than any other spacecraft, swinging by Jupiter, Saturn, Uranus and Neptune. Voyager 2 was deflected downward by Neptune and is heading southward below the plane of the planets. With a somewhat lower speed than Voyager 1, it is about eighty percent as far from the Sun.

Voyager 1:
Voyager 1 is the most distant human-made object in the universe, At the beginning of 2005, the spacecraft was about 94 times as far from the Sun as is Earth. It was deflected northward above the plane of the planets' orbits when it swung by Saturn in 1980 and is now speeding outward from the Sun at nearly one million miles per day, a rate that would take it from Los Angeles to New York in less than four minutes. Long-lived nuclear batteries are expected to provide electrical power until at least 2020 when Voyager 1 will be more than 13 billion miles from Earth and may have reached interstellar space.
http://www.nasa.gov/vision/universe/solarsystem/voyager-interstellar-terms.html
http://www.nasa.gov/vision/universe/solarsystem/voyager_agu.html

I was thinking more of science fiction timeframes, where a ship accelerates from supersonic to sublight in a matter of minutes and then freefalls the rest of the way until it needs to adjust course.
Once a spacecraft shuts down its propulsion system, it coasts. If it has achieved escape velocity, it will keep on traveling.

As for large accelerations, it would be difficult for humans to function with an acceleration much greater than 1g. Think about 2g, a human body of mass 75 kg (165 lbs) would have a 'weight' of 330 lbs - not too many humans could deal with that on a prolonged basis - muscle fatigue/strain would like result in short time.

Science fiction (e.g. Star Trek) can invoke some anti-gravity or zero-gravity or constant gravity field, which as far as we know in not possible in our reality. At present, we understand that 'gravity' requires 'mass', and lots of it to generate a field of 1 g. Mass requires a force to cause it to accelerate, and any force applied over a distance requires energy, and to make it happen, requires lots of momentum.

http://en.wikipedia.org/wiki/Standard_gravity#Strongest_g-forces_survived_by_humans - I am not sure how valid these are, but I they are rather exceptional examples.

This looks interesting
http://www.saferparks.org/are_rides_safe/dynamic_force/gforce_2002.php [Broken]

One could volunteer to test the effects of acceleration
http://news-service.stanford.edu/news/2002/march20/centrifuge-320.html
 
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