I have not blogged in quite a while. Some of the air went
out of my Manned Orbiting Laboratory (MOL) balloon with my blockbuster exposé
of the little-known and under-appreciated fact that the Gemini-B capsule was to
be depressurized and off-limits to its pilots during for the duration of their
30-day MOL reconnaissance missions. (I am being facetious: no blocks were
busted and my exposé has not stimulated any follow-up whatsoever.) Never fear:
I plan to return to the biomedical aspects of MOL, especially since no one is
doing it, or has done it in several decades.
However, this blog entry is on another favorite topic, or
topics, actually. One topic is the earliest history of extravehicular activity
(EVA), or space walking (or as the Russian more accurately put it, space
swimming). My research interest is especially in the parallel development of
underwater neutral buoyancy for EVA training by several different groups
simultaneously with little interaction, and how one group seems to have
prevailed in an almost Darwinian way. (For a spoiler on who won, go here .)
The other favorite topic is orbital mechanics, in which I have had no
professional training whatsoever, and lack competence in any but the simplest mathematical
skills required, but for which I have a fascination bordering on reverence, and
so have memorized a few convenient facts.
During on-line research into EVA history, I discovered an
interesting newspaper column from April 1963 (ref. 1) containing some of the earliest public discussions about EVA during NASA’s
upcoming Gemini missions. The columnists, Robert S. Allen and Paul Scott,
reported that NASA had calculated that the astronaut floating outside of his
Gemini capsule would be traveling at the same speed as his capsule, but that
this “untested theory” was challenged by unnamed astronauts who had actually
flown in space. The astronauts reportedly believed that the spacewalker would
travel at a slower speed than the capsule, just like the “firefly” particles
knocked off their spaceships during flight, and thus would be pulled along by
the 20-foot tether connecting him to his Gemini. They did not say why he would
lag so.
This is funny because it is true, but probably not in the
way the authors meant. In fact, I cannot say how the authors meant it: they offered
no explanation beyond the observation that it was an untested theory—as if the
deductions of Newton, Kepler, LaGrange, Einstein and others had not been
confirmed by four centuries of measurements on natural and man-made satellites.
I assume that Allen and Scott were afraid that wind
resistance would hold the extra-vehicular astronaut back, just as a skydiver
falls behind his airplane when he jumps. After all, even in the 21st
century many people still do not understand that wind resistance is minimal at
orbital altitude because the atmosphere is vanishingly thin. This
misapprehension seems to underlie the oft-repeated wonderment that
rendezvousing spacecraft can approach each other even at the blistering speed
of 17,500 miles per hour—as if there is some force or perturbation inherent in
that speed that would cause a hazard—like, say, wind turbulence, maybe.
In the grossest sense, we now know from almost five decades
of observations that EVA astronauts do not lag behind their host space
vehicles. Interestingly enough, in a pure vacuum a passive and completely
immobile astronaut really would lag behind for reasons having nothing to do
with wind resistance. Orbital mechanics is the reason. But the effect would be
negligible. The speed of an object in orbit around a planet depends on, among
other things, the sum of the mass of the primary object (in this case, the
Earth) and the mass of the secondary object (the astronaut or the capsule). An
amateur orbital mechanicist, on whose calculations lives and treasure do not
depend, may comfortably ignore the contribution of the mass of any man-made
satellite to that sum since the mass of the Earth is literally billions of
billions of times larger.
But a small, lightweight satellite such as an astronaut really
will be travelling infinitesimally slower than another more massive satellite
such as a Gemini capsule at the same orbital altitude. This is because the sum
of the masses of the Earth plus the astronaut in the Earth+astronaut system is very slightly less than
that of the Earth plus the capsule in the Earth+capsule system. The difference is so small that it would probably
take years for the astronaut to lag behind the capsule by the length of his 20-foot
tether. During that time, many other factors would overwhelm the drift-away:
the very tiny “wind resistance” from the microscopically thin atmosphere at that
altitude actually would do more to cause the lighter astronaut to lag behind
the heavier, denser capsule, but even that effect would be overwhelmed by other
factors such as the astronaut’s maneuvering in performing his assigned
tasks—after all, nobody goes EVA without some purpose requiring movement, and
certainly not to float passively for a few years—and the usual small air leaks
from his spacesuit, among other things.
Even in the absence of these confounding effects, orbital
mechanics itself (themselves?) would cause another effect much more quickly. If
the slower astronaut were to find himself lagging behind the capsule, being
dragged along by his tether, he would actually be boosted by the tether to the
same speed as the capsule. But this would be faster than the speed required—and
allowed—at that distance between the two bodies in the “Earth+astronaut”
system. Thus he would find himself propelled into a slightly higher orbit, in
effect flying above his capsule as if he were a kite in a stiff breeze, but
without the breeze.
The column from 1963 also said something else that appealed
to another of my interests, namely early spacesuits for astronauts. It said
that on the upcoming daylong Mercury flight of astronaut Gordon Cooper, he
would remove parts of his spacesuit for comfort. In fact, no Mercury astronaut
removed so much as his gloves or helmet in flight, and Cooper was not planning
to do so. At that time, the B.F. Goodrich was working on a prototype spacesuit
for the Gemini program, due to start in just over a year, that would have
permitted the astronauts to unzip their spacesuit sleeves and “pants legs” for
comfort. It appears that Allen and Scott simply inferred that Cooper would be
wearing such a suit on his Mercury flight. However, the Goodrich suit was not
adopted for Gemini and was not developed further.
All of the foregoing makes me wonder if the columnists were extrapolating
from incomplete information or from their incomplete understanding of some real
information. They got maximum value out of the “quotation mark” key on their
typewriter, using it to apply emphasis to too many words in their column:
“spectacular”, “flight plan”, “heat, cold and meteoroid puncture”, “firefly”,
“environmental control system”, “life line” (twice) and “walk in space”,
“walking” and “walk”. This suggests that they were unfamiliar with the
vocabulary of spaceflight, no sin during those early days of the space age.
Or maybe they were being strung along by real space
professionals, perhaps the astronauts themselves. For example, they reported
the orbital velocity in question as being 15,000 mph—nearly 15% lower than the
actual speed of about 17,500 mph—and called the Gemini hatch a “trap door”
(without the quotation marks, surprisingly) as if they were being spoon-fed a
series of simplified factoids.
I hope space professionals then and now would rather correct
misunderstandings than perpetuate them. However, these columnists did not
usually write about spaceflight topics, so they were already out on a limb. One
of them, Robert Allen, a Washington D.C. correspondent and Washington bureau
chief for The Christian Science Monitor, had actually published Soviet propaganda
early in his career, albeit during World War II to make the Soviet Union attractive
as an ally of the United States (ref. 2).
References.
- Allen, Robert S. and Paul Scott, “Astronauts Will Try Daring Experiments,” Washington Report, Oakland Tribune, April 9, 1963, p. 17, http://newspaperarchive.com/oakland-tribune/1963-04-09/page-17?tag=allen+scott+gemini&rtserp=tags/allen-scott-gemini?psb=dateasc&page=2&ndt=ex&py=1963&pm=4 (accessed Mar. 10, 2013).
- “Robert S. Allen,” http://en.wikipedia.org/wiki/Robert_S._Allen (accessed Mar. 7, 2013).
