History of Research in Space Biology and Biodynamics
- PART V -
Later Deceleration Studies on the High-Speed Track
[68] A separate monograph described how research at Holloman on escape from aircraft (as distinct from aircraft crash forces) led to high-speed track studies of windblast and deceleration that reached an early climax in Colonel Stapp's sled ride of 10 December 1954. That experiment was followed by further research studies with chimpanzee subjects on the high-speed track, but later experiments followed two increasingly divergent paths, one concerned with windblast per se (as described in the previous study) and one with high-g, horizontal deceleration. The tests designed expressly for deceleration finally attained such high g-forces that windblast effects, if any, were wholly overshadowed. There also came a point, impossible to specify exactly, where g-forces produced were so much greater than even the momentary peaks likely to occur in an escape situation that such tests were no longer directly relevant to the aircraft escape problem. The fact that the tests went right ahead reflects a continuing interest in basic research data on deceleration, whether or not an immediate practical application was apparent.9
Colonel Stapp, on 10 December 1954, experienced a g-plateau of twenty-five g's and peak force of forty g's. By November (1955, chimpanzees were being exposed to as much as eighty g's programmed deceleration at 4860 g's per second rate of on-set. A final series of fifteen high-g experiments was held from October 1956 through March 1957, just after the track itself had been extended from 3550 to 5000 feet. Greater velocities and substantially higher g-forces now became possible even with the relatively heavy deceleration sled Sonic Wind Number 1. Programmed deceleration in this test series ranged up to 120 g's, but peak forces went considerably higher. A force of 247 g's was produced on one subject for a millisecond on 2 February 1957. Rate of onset for that same test was 16,800 g's per second, which was also a record; and total duration of the decelerative phase was 0.34 second.
The effect on chimpanzee subjects naturally varied with the number of g's, duration, and also body position. The run of 2 February 1957 that attained a peak of 247 g's caused only "moderate" injures to the test subject, but this happened to be the one run in the series in which the chimpanzee was seated facing backward. A run of 12 January 1957, with the subject facing forward, proved fatal even though the peak force was only 233 g's for one millisecond (total duration .35 second) and rate of onset slightly over 11,000 g's per second. One other fatality occurred at considerably lower deceleration, but in this case the subject's death was apparently due in large part to an ailment unrelated to g-forces. Speaking of the entire series of high-g runs on the 5000-foot track, Colonel Stapp later observed that "significant" injuries began in the neighborhood of 135 g's-with extremely short exposure, and with the subject enjoying the benefit of maximum restraint." He also hypothesized that in the two standard seated positions, backward- and forward-facing chimpanzee tolerance to transverse g was roughly comparable to that of human beings; but this is a subject of some controversy, and admittedly, when it came to probing the range of severe to lethal jury, no human test subject would attempt to verify the assumption.10
The later deceleration experiments were undertaken essentially as a form of basic physiological research, but the test results have been cited--by Colonel Stapp among others11--in connection with such problems of space flight as takeoff and re-entry of manned space vehicles. To be sure, rocket acceleration at takeoff will involve moderately high g-loads, which are generally regarded as tolerable on the basis of centrifuge tests and actual rocket experiments with animal subjects. Total durations would be longer than in the high-speed track deceleration tests, but it predicted that peak g-forces will be on the order of eight to twelve g's.12
In the case of re-entry, a vehicle coming back from extreme altitude or outer space must encounter high deceleration forces as it comes in contact with denser layers of air. Such deceleration poses a complex problem for potential travelers whether human space crews or animal test...

Captain Jophn A.Recht Seated on "Bopper"

[70] ...subjects, and two basic solutions have been suggested: to come straight down, experiencing high g-forces but holding them to short duration, or to follow a gradually descending path, with moderate g-forces but long duration. Other possible solutions lie in between. In any case, scientists concerned with the re-entry problem wanted a mass of data on tolerance to deceleration including data on the forces that would be required to produce serious biological injury; and the tests on the Holloman high-speed track helped supply the information needed.

No one expects that re-entry configuration will call for exposure to forces even approaching the extreme decelerations applied in some of the Holloman tests. On the other hand, re-entry patterns are more problematical than the acceleration anticipated in manned space travel. A year and a half ago, before the various Soviet and United States satellites contributed new knowledge on the density of the upper atmosphere, re-entry patterns were even more problematical than they are now. In reaching conclusions about human tolerance from chimpanzee test results, moreover, it is desirable to have a wide margin for possible error. At the very least whether for re-entry or for other operational problems, it is comforting to know that fellow primates have experienced forces above one hundred g's with only minor injury, and in one case actually lived through a deceleration of almost 250 g's.