BSG: "Acts of Contrition"

[Steven Snyder]

And if the safety device fails....?

The the primary device fails and the safety device fails, you have a problem. There may be some backup of the safety device, or the device might be so simple tht failure is next to impossible...but in any event that sort of failure would be catastrophic.

Because the craft is no longer accelerating when the pilot ejects.

What, gravity stops working?

It may no longer be accelerating on it's own power, but if it's headed toward the surface of a planet it could very well continue to accelerate towards that planet, at least until terminal velocity is achieved - which will vary depending on atmospheric density.

Which is also a problem for the pilot, because the terminal velocity of the human body is considerably less than that of most aircraft. When ejecting from, say, an F-16 traveling at a high rate of speed it's not the acceleration of the airplane that causes damage, it's the abrupt decceleration the pilot experiences on encountering air resistance. In the lower atmosphere of Earth, the terminal velocity of the human body (under most conditions) is about 120 mph. If you eject from an aircraft traveling at 500 mph (it's a nice, round number), you will very abruptly slow down. Those who have ejected at high speed and lived to tell the tale describe it somewhat as slamming into a brick wall. It does break bones.

If you were to eject at an even higher speed - say, one requiring inertial dampers - the effect would be even worse.

Once the pilot ejects from the craft, his/her velocity isn't changing, and is therefore in a zero-g environment.

If you eject into an atmosphere (which Starbuck did) your velocity will change. You will slow down, and heat will be generated through friction. That is, after all, why things frequently burn up when entering the atmosphere of a planet from space.

Ejecting out of something like an F-16 can lead to multiple bone fractures or even death (also tends to rip the pilot's clothes off, but that's a minor detail...) -- and that aircraft doesn't require "inertial dampers". How much worse would ejecting from a spacecraft that needed such devices be?

If a craft like the viper were still accelerating, he might be impacted by the tail structure.

The aircraft doesn't have to accelerate for you to hit the tail - you only have to slow down relative to the aircraft. That very thing happens to skydivers from time to time - they screw up exiting the aircraft and wind up hitting a wing or a tail. It's not because the aircraft is accelerating - jump pilots are very careful to maintain precise speed during a drop to help prevent accidents, especially since in a person vs. small plane accident of that sort the people in the aircraft are in fact less likely to survive the impact long-term than the skydiver (hitting the tail seriously screws up the tail where you have two major control surfaces, which can make a safe landing impossible). It's because when you exit the aircraft wind resistance slows down the human body.

All of my comments were assuming the fighter was doing those super-high G manuevers in the vacuum of space. When you go atmospheric, things change drastically.

[Broomstick]

Well, I did catch the repeat and was actually able to watch the whole thing again.

Wow - that scene between Starbuck and Adama where Starbuck 'fesses up to passing Zak when she shouldn't have kicked butt!

Got a better look at the Viper-out-of-control scene. MY best guess is that combat damaged her propulsion and probably her manuvering systems as well, resulting in rotation about the center of gravity (CG) of her Viper. That's a spin, yes, but not one aerodynamically generated. It still generates g-forces, though, and the further you get from the CG the greater the forces, which could account for why Starbuck indeed could not reach the controls. But the eject handle was at the side of her seat, closer to her, probably in area under less g-force, so she was able to pull the handle. Which is how these things should be designed.

Upon consideration of the controls... looks like the main instrumentation is a flight management system, computerized to combine information from various instruments. (We have these now - they're even available for low-end airplanes such as I fly, in fact.) The altimeter, artificial horizon gyro, and other "steam gauge" and analog instruments are probably back-up instrumentation in the event of computer and power failures and such. (Civie planes such as I fly have instruments powered by a variety of means, including electricity from the alternator, the engine crankshaft, and ram air. So if you lose the alternator and/or battery you don't lose everything. I don't know what backups modern military planes use, but presumably they, too, take advantage of various alternative power sources, particularly in emergencies)

Under the circumstances of Starbuck's crash a pitot-static system altimeter (that's one that works off barometric pressure) the number displayed would be nonsense on a new planet where you lacked calibration for it, but the fact it's moving at all would indicate you have entered an atmosphere which might be an important piece of knowledge. That's assuming, of course, it is a barometric altimeter.

[SirNitram]

Well, if I might interject, if we assume the primary use of the Vipers is in-system, almost all the planets will have similar barometric pressures.. Mostly because everyone born on those planets can comfortably stand next to each other on the Galactica. So the Viper Altimeter, even if barometric, will work perfectly fine in the Twelve Colonies.

And besides, 'Hi. You've entered an atmosphere and the pressure is rapidly climbing.' is a damn handy peice of info!

[Broomstick]

Well, if I might interject, if we assume the primary use of the Vipers is in-system, almost all the planets will have similar barometric pressures.. Mostly because everyone born on those planets can comfortably stand next to each other on the Galactica. So the Viper Altimeter, even if barometric, will work perfectly fine in the Twelve Colonies.

Quite an assumption.

Human beings live between sea level and around 14,000 feel above sea level. That's a range of barometric pressures between 29.92 (MSL) and 17.57 (14,000 feet) Or 1013.3 mb/hPa to 595.2 mb/hPa, for those of you more comfortable with that measure (millibar=hectopascal). Quite a range. The main habitable zones of the Twelve Colony planets could theoretically exist anywhere within those ranges and "standing next to each other in perfect comfort" would only require a compromise. Probably the lowest pressure comfortable for those used to the highest pressure enviroment. You can also decrease the required pressure by increasing the percentage of oxygen in the air mixture - although that does carry a risk of fire with it.

Then you have the problem of pressure gradients. On Earth, the pressure in the atmosphere drops as you rise - about 1,000 feet for every inch of mercury on the barometer. If you have a larger volume of atmosphere (so it's thicker), or less gravity (so the weight of the air exerts less force), or less air or more gravity or some other combination of factors that pressure gradient - the rate at which pressure falls off or increases along your direction of travel - would also be different. You might need 1500 feet of altitude to change the barometer by one inch of mercury, for example. Or a mere 500 feet for that one inch change. Which would add up to a huge error rather quickly.

Admittedly, I'm not up to figuring out the exact math on this, but to me it's obvious that you can't trust a barometer set for Earth (or Caprica) conditions on a planet with either unknown or very different conditions.

Want some examples from our own solar system? Mars has 1/3 the gravity of Earth (correct me if I'm wrong anywhere, I'm doing this out of strictly out of memory, which can be falliable) but only about 1% of the atmospheric pressure. So... about .3 inches of Mercury, or about 10 milibars. Do you seriously think a barometer manufactured to measure Earth's much higher pressure atmosphere is going to give any sort of sensible reading on Mars?

How about Titan? - its atmosphere is believed to be about 1.60 bars, or 1600 mb, or around 47.30 inches of mercury. (Which, by the way, humans could easily tolerate if it wasn't so cold and full of - to us - useless gasses such as methane and had some actual oxygen.) But it still has less gravity, about 1/6 g, like the moon (another number I'll pulling out of memory, but probably close enough) Let's see.... Do you seriously think an Earth made altimeter would give anything but nonsense on that large lump of rock? Sure, you could calibrate it to 1.6 bars on the surface, but as you go upwards will the pressure fall off at the same rate it does on Earth? I think not. A Martian barometer wouldn't work on Titan either - Mars has twice the gravity but only a fraction of the atmospheric volume. Gravity counts, because pressure is a result of weight and weight is the measure of gravity's effect on an object.

But someone with the math skills to take on the challenge (and who is also willing to get some solid numbers for the calculations) is welcome to try and prove me wrong

[andrewgpaul]

Well, if I might interject, if we assume the primary use of the Vipers is in-system, almost all the planets will have similar barometric pressures.. Mostly because everyone born on those planets can comfortably stand next to each other on the Galactica. So the Viper Altimeter, even if barometric, will work perfectly fine in the Twelve Colonies.

Quite an assumption.

Human beings live between sea level and around 14,000 feel above sea level. That's a range of barometric pressures between 29.92 (MSL) and 17.57 (14,000 feet) Or 1013.3 mb/hPa to 595.2 mb/hPa, for those of you more comfortable with that measure (millibar=hectopascal). Quite a range.

Indeed, that's almost a factor of 2! Now, does that mean, someone from a high altitude could breathe normally with an Oxygen partial pressure of 600mb, with a total air pressure of 1,000mb? or does the fraction of Oxygen to Nitrogen have to remain constant?

[Broomstick]

The oxy/nitro ratio doesn't have to remain a constant. It's the oxygen that supports life, nitro is inert - in fact, deep sea divers can entirely replace nitrogen with helium and happily breath the resulting "heliox". Although it does make them sound funny when they talk. NASA and very high altitude military pilots can breathe an atmosphere at a pressure as low as 3 lbs/sq in - one fifth the pressure at sea level - so long as it's pure oxygen. Which, probably not cooincidently, is about the partial pressure of O2 at sea level. There are limits, of course, but a good rule of thumb seems to be that you need 3 lbs partial pressure of oxygen to support human life - under low pressure that might require a higher percentage of oxygen. Or more red blood cells to extract what oxygen there is more efficiently.

Higher pressure of oxygen can be tolerated as well. In hyperbaric chambers used for medical treatments patients can breathe in an atmosphere of high-percentage oxygen at 3 or 4 times sea level pressure (although prolonged breathing of 100% pure oxygen at high pressure can cause serious problems, so, if I recall, pure oxy is limited to about 15 minutes at a stretch.) The tendency is for the body to simply ignore oxygen present beyond what is actually needed. The red blood cells pick up molecules after all, and can only hold so many. Anything beyond that is ignored (except when you get into very high percentages, where the blood plasma itself is holding quick a bit of oxygen and the quantity is such that the irritating/corrosive tendencies of O2 come to the fore)

Mind you, some of this might require adaptation and quick changes from high pressure to low pressure can trigger the bends if there is nitrogen in the tissues -- but it still remains that we can tolerate a fairly wide range of atmospheric pressures despite high-altitude living and deep sea diving being largley absent from our list of evolutionary pressures. Yes, some humans live in the Himalayas and Andes, but these adaptative talents are common to ALL humans, not just those born and raised at high altitudes.

[andrewgpaul]

The oxy/nitro ratio doesn't have to remain a constant. It's the oxygen that supports life, nitro is inert - in fact, deep sea divers can entirely replace nitrogen with helium and happily breath the resulting "heliox". Although it does make them sound funny when they talk. NASA and very high altitude military pilots can breathe an atmosphere at a pressure as low as 3 lbs/sq in - one fifth the pressure at sea level - so long as it's pure oxygen. Which, probably not cooincidently, is about the partial pressure of O2 at sea level. There are limits, of course, but a good rule of thumb seems to be that you need 3 lbs partial pressure of oxygen to support human life - under low pressure that might require a higher percentage of oxygen. Or more red blood cells to extract what oxygen there is more efficiently.

Thanks. I was wondering if the concentration of O2 was important, or, as your post seems to imply, it's simply the partial pressure of O2.

If you want to continure this, I think we should take it to PM; it's getting a bit OT.

[Broomstick]

Continue? We're about at the limits of my knowledge on the subject as it is.