Human Tolerance for Gs

[zero]

Hi there, its been a while!

I've been debating on creating a rather hard scifi ATU Traveller game based around the colonisation of Mars, based on the success of a moon base being set up. The game is going to be set around the 2050s.

Now, I wanted to build up new ships with reaction drives, something that could reach Mars in a month, probably looking at a 3G+ vessel with fuel not determined yet.

Now, I remember in Chthonian Stars there was the Transit Drive, which was a pulse drive which was theorised to boost to 9G at such lengths over it's week of activity (on average 20 seconds per hour, not sure how the pulses were distributed length and gap wise aside from that amount) to chunky salsa stow-away rats and needed the use of a Grav-couch by ship crews to also not get pasted to the wall behind them.

I am looking at a ship that will either be accel/decceling for long amounts of time (counted in minutes) and have a thrust probably 3G+.

I wondered how much I can push the thrust of a ship before I start to press my crews into salsa on the walls behind them and for how long?

Thanks guys

 

[locarno24]

Best reference document I can throw you at off-hand is here:

http://spacemedicineassociation.org/timeline/1956/27004.pdf

Page 4 has a useful graph.

3G sustained seems to look fine - that's not going to be good for people's health but I doubt it's going to matter too much for a few minutes.

 

[zero]

I looked through the pdf and it seems Grey Out is the biggest risk when it comes to something like that. Still, I need a better read-through of the document and hopefully gain a better understanding. Loss of vision for a period of time is a pretty big thing unless a computer has been plotted with a course by the astrogator and it still has a risk of bumping into something, unless the computer is built with Evade software for accidental bumps with other ships.

I'm still doing ship math to be fair and dependant on fuel space I might manage with 2G, depending. Still, any more opinions on these matters, especially with grey out now, would be helpful.

 

[rust]

The most important factors are the duration and the direction
of the acceleration, humans can tolerate high g-forces well for
a short time and in a horizontal position (e.g. on an accelera-
tion couch), and even better if the acceleration increases slow-
ly and does not come as a sudden push. Under such conditions
an average human should well be able to tolerate up to 3 G for
about 15 minutes or so. However, keep in mind that the vic-
tims of this have to remain at rest for the entire time, working
(even lifting an arm) under 3 G is rather difficult and no plea-
sure for muscles and heart.

Edit.:
The linked document seems to be from 1956, I would hesitate
to consider it a reliable source since it was written before the
first experiences with human spaceflight.

 

[locarno24]

It is. The experimental data is from centrifuge chair tests.

 

[Hopeless]

The first episode of UFO mentioned experiments in trying to improve on that through them being also in a liquid environment with breathing apparatus obviously.

Is that a possibility or just a theory from the seventies when the series was made?

 

[rust]

Is that a possibility or just a theory from the seventies when the series was made?

As far as I know, the jury is still out on this one, mainly
because there has been little incentive to test the theory.
A G-Suit solves the usual problems pretty well, and it en-
ables the person to remain active, while a person immer-
sed in liquid would become a passive passenger.

http://en.wikipedia.org/wiki/G-suit

 

[CosmicGamer]

As rusts indicates, the g forces for acceleration and deceleration of a space ship are from a predictable single direction unlike the maneuvers of a fighter pilot. 3G is for "the average person" and some roller coasters can surpass this. While 3G is about the max for shuttle launch and reentry, drag racing, formula car racing and aerobatic flying can exceed this. The Apollo 16 exceeded 7Gs on reentry. A properly trained person in a Anti-G suit should be capable of 6 to 9 Gs. I don't know how long this can be sustained. John Paul Stapp was able to exceed 40G briefly. Perhaps some combination of lower G thrust and high G bursts would work?

Loss of vision for a period of time is a pretty big thing unless a computer has been plotted with a course by the astrogator and it still has a risk of bumping into something, unless the computer is built with Evade software for accidental bumps with other ships.

First, from your setting description, where are all these uncharted ships flying randomly coming from? Second, thrust could be diminished toward the end of the trip so that the crew will be less effected by G forces.

 

[F33D]

Now, I wanted to build up new ships with reaction drives, something that could reach Mars in a month, probably looking at a 3G+ vessel with fuel not determined yet.

At 1G you can reach Mars from Earth in <4 days.

3Gs for a month, most will die.

 

[zero]

No, I'm using reaction drives, so acceleration/deccel would be for a short time, then the ship would drift at a set velocity. There is no way a shuttle in a low tech setting could accelerate for days on end with the reaction drive (from High Guard incase some here haven't got that supplement).

The ships in Chthonian Stars use Grav-couches (the crew are suspended in gel once they reach essentially the low tech version of a Jump Point) as they can accelerate past 1.25 AU in a week with the Transit Drive, assuming roughly 9G pushes for twenty seconds per hour (its a pulse drive, not something that continually accelerates/deccels for a week). It is said in the fluff anything not in a grav-couch gets chunky salsa'd in the week. Apparently G-Suits aren't enough to sustain this level of sudden acceleration/deccel.

So we assume the pilot directs the ship in a general line for the astrogator's set course in the accel period, so they'd need to actively fly the ship... perhaps 2G at a length is fine to do so, then they activate a Drive that is similar to the Transit Drive but at a lesser thrust, or the pilot is in an Anti-G suit? I guess for the pilot, they'll be placed in an acceptable horizontal position.

I don't particularly want to get into the math of figuring out a pulse drive and how it accels/deccels unless someone can give an online calculator or some formulas for it. My main thing was being able to have a ship that can have a reaction drive and reach Mars from Earth in a manageable time.

At some point I shall post up the statblock for an advanced space shuttle similar to the one given in High Guard that hopefully fulfils what I am after. My main thought though is that it may have to have Gs dropped or alot more reaction fuel added. I'm also thinking about Orbital to see what I can achieve in a 2050s era campaign, but I am thinking more about this ship for the meantime.

 

[F33D]

The ships in Chthonian Stars use Grav-couches (the crew are suspended in gel once they reach essentially the low tech version of a Jump Point) as they can accelerate past 1.25 AU in a week with the Transit Drive, assuming roughly 9G pushes for twenty seconds per hour (its a pulse drive, not something that continually accelerates/deccels for a week). It is said in the fluff anything not in a grav-couch gets chunky salsa'd in the week. Apparently G-Suits aren't enough to sustain this level of sudden acceleration/deccel.

USAF tests fighter pilots (in a sitting position with G suit) up to 9 G's for a few seconds. SO, a healthy person lying flat on back could probably do this for 20 seconds.

"Suspended in gel" doesn't negate G's felt. Anymore than floating in a pool feels like free fall...

 

[rust]

"Suspended in gel" doesn't negate G's felt.

It would help to reduce the potential damage somewhat,
pressing the body onto a soft surface that adapts to the
shape of the body is less painful and damaging than pres-
sing it on a harder surface - but an acceleration couch is
fully sufficient as a soft surface, suspending the person in
gel would be over the top.

SO, a healthy person lying flat on back could probably do this for 20 seconds.

A breathing apparatus used to ensure that the lungs are
not compressed so much that the oxygen supply to the
brain is interrupted would help a lot.

 

[F33D]

A breathing apparatus used to ensure that the lungs are
not compressed so much that the oxygen supply to the
brain is interrupted would help a lot.

Yes, if you are accelerating for more than a couple minutes. Otherwise no big deal.

 

[zero]

Of course when I mention the gel in Grav-couches, thats a trope of the Chthonian Stars setting. One would assume that the Grav-couch user has a breathing apparatus and due to being placed in there in a week (in a setting with zero types of stasis) they're going to be feeding tubes and the such. The thing is basically like the Grav-couch from Event Horizon, if anyone has seen that film.

But that's not want I want to know, though the knowledge of G and length of pulse accels might be good to know for a C-stars game, as stated before it accelerates 1.25 AU in a week and reaches a velocity (or deccels from) 296,991.137793025 metres per second (All this took an age to work out btw), which is close to 1 AU per 5.83 days.

--

However I didn't particularly want to discuss the Transit Drive from Chthonian Stars, more what kind of G acceleration I can get away with over a length of time. As I'm dealing with a Lower Tech Level setting (like 8), I assume I won't be going over 4G in thrust.

I'll throw up statblocks and give out some comparitive space math that you guys can go over and see if the accel/deccel is tolerable. Obviously with 4G accel/deccel, it will be less time than the 2G one, though that will also affect ship statblocks as I have reaction fuel dtons to consider.

 

[F33D]

Of course when I mention the gel in Grav-couches, <snip>

So, what is your actual question?

 

[zero]

Actual question would be;

How long could one accelerate/deccel at continual G (from continual 2 to continual 4) before horrible side-effects come in? (So my low-tech space-craft aren't killer rockets)

--

To be honest from what has been said here, it seems like if the astronauts are horizontally positioned in the accel/deccel and wearing G-Suits, they should be fine whatever happens, with possible breathing apparatus for higher G accel/deccel.

Again, hoping tomorrow to spring up some prospective ship statblocks to be checked over along with what kind of accel/deccel they do on a regular basis.

 

[CosmicGamer]

To be honest from what has been said here, it seems like if the astronauts are horizontally positioned in the accel/deccel and wearing G-Suits, they should be fine whatever happens, with possible breathing apparatus for higher G accel/deccel.

A 20 megawatt VASIMR ion engine with nuclear power can produce 4G thrust and by firing continuously during the first half of the flight to accelerate then turning to decelerate the second half would reach mars, depending on orbits, in 40 days.

If you are looking at "real" space science for thrust and G's, how about the long term effects of space radiation and a microgravity environment on mars?

 

[F33D]

To be honest from what has been said here, it seems like if the astronauts are horizontally positioned in the accel/deccel and wearing G-Suits, they should be fine whatever happens, with possible breathing apparatus for higher G accel/deccel.

"G suits" are used for a vertical sitting position. They aren't useful in a horizontal position. 2G's should be okay for quite a while. 4G's, probably not too long as brain injury might occur as it is pressed against the inside of the skull at 4 times its normal weight.

 

[Ash247]

If you are only doing the thrust for a short amount of time then drifting before decelerating, why not just do more manageable thrust for longer.

example: instead of doing 3G for 10mins, do 1G for 30mins - same energy expended same result just much easier to manage.

 

[zero]

Fair point about managing thrust, doing lower Gs for longer. I came up with some basic space math using rough approximations and I came up with it taking just under 10 minutes of accel at 5G to reach a velocity to drift to Mars in a month.

I do not think 5G accel for that length of time is a good thing at all. So I may just look into lowering G (I want a minimum of 2, tbh) and having a lengthy accel based on that. Of course, I am just running off some approximations before I do the real number crunching down to the second and then double the reaction fuel (for the return journey! :roll: )

The ship I'll use (when finished) I shall post up. I'm also using a Fission Plant to represent this old pulp hard scifi ship.

Comments still welcome. If Fuel becomes a big thing, the ship will probably have a TL 8 prototype Drop Tank which may limit Thrust too.