23

I assume this hasn't got a precise answer, but I was wondering if anyone had an indication of the maximum survivable long term g-forces, if the persons positioning was optimal?

For example, could you accelerate a craft 3g for say, 16 hours a day with the traveller in a prone position, and 1g for 8 hours a day so they can get up and exercise?

Or could you do even 6g in prone position for most of the day?

Like I said, I accept the answers would be estimates, but any discussion based on current research would be good.

TildalWave
  • 75,950
  • 13
  • 274
  • 455
Clinton
  • 331
  • 1
  • 2
  • 4

3 Answers3

16

It is hypothesized that the only acceleration that can be tolerated for looong time without side effects is the normal acceleration. Human subjects have been exposed to continuous high-G environment at most for seven days at 1.5 G. Although no immediate ill effects were found, extrapolation of the data to longer periods may be dangerously risky.

Relevant PubMed abstracts:

https://www.ncbi.nlm.nih.gov/pubmed/23926661 https://www.ncbi.nlm.nih.gov/pubmed/11542364 https://www.ncbi.nlm.nih.gov/pubmed/591467

I have not found any studies of chronic high-G exposure (beyond 1 hour limit). However, our esteemed fellow user cites Claude Piantadosi from Duke U.'s Center for Hyperbaric Medicine and Environmental Physiology.

Human G tolerance, like other physiological strains, is limited by different physiological factors at different levels of G stress.

There may be astronauts who can tolerate higher accelerations (and indeed, there have been tests subjecting humans to a week-long 1.5G regimen), but you don't want to stress cardiovascular system without need. If you can provide standard 1-g environment, you should do that.

Source: NASA-STD-3001 VOL 2.

Rationale: The limits in these figures represent safe levels of sustained translational acceleration under nominal and off-nominal conditions. Exposure to acceleration above these limits could significantly affect human performance for maneuvering and interacting with a spacecraft. The limits for return to Earth are lower than launch limits because crewmembers could have degraded capabilities because of deconditioning from exposure to reduced gravity. For the extreme conditions of a launch abort or emergency entry, limits are higher because it may be necessary to expose the crew to accelerations more severe than those experienced nominally. Humans are never to be exposed to translational acceleration rates greater than these elevated limits, as this significantly increases the risk of incapacitation, thereby threatening crew survival. In using figures 2 through 6, the acceleration vectors are relative to the “axis” of the upper body, particularly with a focus on a line running from the eye to the heart. However, the acceleration limit charts do not account for all body types or temporary off-axis accelerations or body positions. This is why the limits are set conservatively. Therefore, brief excursions past the limits in one axis should be reviewed and may be found to be acceptable.

enter image description here

                                                                   Data for Curves

enter image description here

                     Figure 2 — +Gx Sustained Translational Acceleration Limits

enter image description here

                                                                   Data for Curves

enter image description here

                     Figure 3 — -Gx Sustained Translational Acceleration Limits

enter image description here

                                                                   Data for Curves

enter image description here

                     Figure 4 — +Gz Sustained Translational Acceleration Limits

enter image description here

                                                                   Data for Curves

enter image description here

                     Figure 5 — -Gz Sustained Translational Acceleration Limits

enter image description here

                                                                   Data for Curves

         enter image description here

                     Figure 6 — ±Gy Sustained Translational Acceleration Limits

6.5.2 Rotation Limits

6.5.2.1 Rotational Velocity [V2 6065]

The system shall limit crew exposure to rotational velocities in yaw, pitch, and roll by staying below the limits specified in figure 7, Rotational Velocity Limits.

Rationale: The limits in this figure represent safe levels of sustained rotational acceleration for crewmembers under nominal and off-nominal conditions. Exposure to rotational acceleration above these limits could significantly affect human performance for maneuvering and interacting with a spacecraft. The limits for return to Earth are lower than launch limits because crewmembers could have degraded capabilities because of deconditioning from exposure to reduced gravity. For the extreme conditions of a launch abort or emergency entry, limits are higher because it may be necessary to expose the crew to accelerations more severe than those experienced nominally. Humans are never to be exposed to rotational acceleration rates greater than these elevated limits as this significantly increases the risk of incapacitation, thereby threatening crew survival.

APPROVED FOR PUBLIC RELEASE — DISTRIBUTION IS UNLIMITED

Deer Hunter
  • 11,401
  • 2
  • 52
  • 108
  • 2
    I seriously wonder, if over long time - many months - one could train adaptation to higher accelerations. Say, the spaceship acceleration increasing by 0.1g per month and the crew undergoing a constant training regimen. – SF. Dec 02 '14 at 17:49
  • @SF. - yes it could be possible, but we lack the empirical basis and the need to undertake such experiments. – Deer Hunter Dec 02 '14 at 17:51
  • You can imagine gaining weight steadily. Not nice, by any measure. – Deer Hunter Dec 02 '14 at 17:57
  • 2
    It would be compensated by increasing muscle mass; I believe at the end of such travel the astronauts could enter Strong Man competition easily. Also, obese people live somehow despite the same body structure supporting two-three times as much as in case of slim people. – SF. Dec 02 '14 at 18:03
  • @SF. - the most suitable case for such conditioning is exploration of heavier planets. – Deer Hunter Dec 02 '14 at 18:05
  • 1
    I don't get the answer. You claim 1 g and then quote NASA material showing 4 g sustained. (when lying on your back, "eyeballs-in acceleration but the question specifically allowed for optimal posture) – MSalters Dec 02 '14 at 19:19
  • 1
    @MSalters - I do not know about 16-hour centrifuge experiments. – Deer Hunter Dec 02 '14 at 19:22
  • 1
    @MSalters - fixed the text with some refs to PubMed. – Deer Hunter Dec 02 '14 at 19:30
  • @SF as for fat/obese people - they also strain they cardiovascular system (and not only that) much more. Also, the bones would need strengthening, ant that would might take a bit longer than a couple of months. – peterph Dec 02 '14 at 21:43
  • 1
    The best PubMed reference seems to be "Physiological adaptation to high-G tolerance." but even that isn't saying how much adaptation is possible. I guess there's just no practical justification for such research - we're not even close to sustained 1g flight. – MSalters Dec 02 '14 at 22:53
  • From running, I can state that muscles and cardiovascular adapt to increased loads far faster than the bones & joints. How fast they respond probably depends on the person and their age but I'd say weeks to a few months for the first two and many months to a few years for the second two. – Jim2B Mar 02 '16 at 16:12
2

For -Gz @ 1g (hanging upside-down), this article suggests anecdotally at least a few hours ( > 104 sec ) : How Long Can a Person Safely Hang Upside Down?

GrapefruitIsAwesome
  • 648
  • 6
  • 20
ThompPL1
  • 39
  • 4
  • 1
    While the question specifies "...if the persons positioning was optimal?" this is an interesting factoid and part of the envelope, so a conditional +1 Welcome to Space! and thank you for this excellent answer – uhoh Jul 17 '20 at 01:59
-3

CONSTANT 1 G EXPOSURE: If I have to say, the amount of variation in human body is drastic and requires a control set to fully understand the effect imparted by humans and 1 G EXPOSURE is dangerous for an untrained body any thing could happen; If someone specifically trained for withstanding G's then 1.45 G's is the max they might be able to withstand . Cardiovascular system is sensitive and can be rendered useless if put through a treacherous situation; stress tolerance is the biggest variable, I've seen cases that people experience tremendous G-force and survived to tell the tale, Coordination and communication is greatly affected if put through such situations.training can only do so much, yet we all are human's and sadly not super human's.

SANATANI
  • 1
  • 1
  • 1
    With reference to 1G exposure being dangerous, that is true since humans on earth die, but suspect this is intended to be 2G? And there are various answers for max survivable Gs for trained humans for varying time periods but it certainly is not 1.45, see answer by Deer Hunter. – GremlinWranger Aug 21 '22 at 11:12
  • Welcome - please read our [answer] page to see what we expect from an answer post. You may wish to delete your post before it gains more downvotes... – Rory Alsop Aug 21 '22 at 15:08