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http://www.centauri-dreams.org/?p=31375
24GW will accelerate a 3 tonne payload at 100m/s^2 for 27 minutes, reaching a velocity of 163km/s and arriving at Mars 8.7 days later.
Of course, we want heavier payloads (300 tonnes should do nicely), and perhaps lower acceleration (the humans should be able to handle it if properly encased, it's only for half an hour, but it drives up the power requirements). Perhaps we could get away with a system that requires 250GW and an acceleration of 1g (yes, the magsail will have to be larger), putting Mars within 9 days travel? Then later, get to the point where Jupiter is accessible in a month, and then on to Saturn...
Could we build a fuel cell system big enough to store that power, or are we better off with batteries? The heavier the better, we need quite a lot of mass to deal with the recoil. Maybe we can tow an asteroid into position to use as an anchor...
Use what is abundant and build to last
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One G of acceleration is 9.78 m/s^2, so the 100m/s^2 you're talking about is 10.225 Gs. Fighter pilots have to be certified to withstand 9 Gs for a certain number of seconds without blacking out. Not everyone can do it. And that's with a G suit. The G suit uses air bladders to squeeze the pilots legs and lower abdoment, squeezing blood to the upper body. You want to sustain 10 1/4 Gs for half an hour?
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Fighter pilots also aren't in the optimum position (lying down) to be enduring high accelerations, nor are they suspended in fluid.
GW has more information on this, I think?
Use what is abundant and build to last
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Eyeballs-back vs eyeballs-down makes a really big difference to high-gee tolerance. Fighter pilots are mostly eyeballs-down, although the seat in the F-16 is semi-reclining. F-16 pilots could therefore cope with 9 gees longer than the pilots of most other fighters. Still only times measured in 10's of seconds, though.
Centrifuge studies seem to indicate that 10-15 gees is feasible for times measured in minutes to hours for reclining humans. Maybe even more. The Apollo return from the moon was a 3-minute long pulse of deceleration that peaked for several seconds at 11 gees. What they contemplated for free returns from Mars missions was worse, perhaps 15 gees or so. Similar pulsed profile of gees vs time.
The brief pulses of gee in the rocket sled tests in the 1950's revealed a max level of tolerable gee for humans: about 40-to-45 gees. Exceed that, and your body is literally torn apart. The films from the animal experiments are quite gruesome. Paul Stapp endured about 40 gees on the sled, which nearly killed him. He was hospitalized for a long time, but recovered. We're talking exposures under 1 or 2 seconds at levels like that.
That level fed into ejection seat design: limiting ejection gees to under 40 gee, for the newer "zero-zero" seats introduced in the 1960's. You'll survive, but you will be injured, perhaps seriously. Usually spinal injuries. Which is why most test pilots refer to ejection seats as a means of committing suicide in order not to be killed (in the crash).
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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