Thanks, Stranger, I was hoping you might weigh (heh) in at some point. Insightful though not surprising I suppose either.
As far as the argument for microgravity being the raison d’être for every mission for space stations now and yet to come, I’m with levdrakon (and Stranger) on this as well. While there are zero-gravity experiments that are worthwhile, some still underway and more to come, it’s arguably far more worthwhile, at some point, to begin the prototypes and test beds for artificial gravity vessels that can house humans indefinitely if we hope to travel beyond the Earth/Moon system.
NanoRacks handled our CubeSat deployment from the ISS. Worked out fine, though between the Antares kablooey and NanoRacks’ “premature ejection” incident, we may have just lucked out…
Right. It doesn’t need to be habitable, but if you want a rotating, habitable section and a stationary, habitable section, you need a contra-rotating flywheel so that the net angular rotation of the entire station remains zero.
Only in the short term. Three days under microgravity isn’t long enough to cause the problems fractional gravity would be intended to avoid.
Armstrong and Aldrin were only on the lunar surface for less than a day. Even the later J-class missions only had about three days of lunar surface time, which isn’t nearly enough to evaluate long term effects of lunar gravity on astronaut health and performance, and gives no indication of how well future astronauts might fare on Mars or Mercury (although all other large moons are around the same gravity as Luna). By contrast, a transit to Mars would take somewhere between nine months and about the same on the return. Obviously, the lower the tolerable threshold of simulated gravity, the easier the design requirements are on the habitat (i.e. lower forces, reduced rotation radius, et cetera).
A stationary section doesn’t require zero net angular momentum (or rotation), just that the hub counterrotates. There is no reason you couldn’t have multiple wheels rotating at different rates on the same axis although the bearings would have to be capable of resisting the net gyroscopic forces and you probably would want some kind of counterbalance to avoid unbalance torque. A flywheel and ballast system are probably necessary even on a single wheel habitat in order to minimize nutational effects due to shifting mass or other unbalance forces, but it doesn’t need to negate angular momentum.
Won’t a more practical study be how quickly humans adjust to fractional Gravity after microgravity, as they are going to enter the Martian gravity field after mon this in interplanetary space or whatever it’s called? I seem to recall reading that humans retiring from space flight are susceptible to sickness just as those going up get sick at times. Did any Apollo surface astronauts have any episodes in adjusting to Luna gravity? Mars astronauts might need several days to before they can do any serious EVA activity.
There is nothing in the literature about any physiological problems astronauts had adjusting to the Moon’s gravity, and in fact the only significant medical issues were a lack of rest (astronauts were naturally excited and had difficulty adhering to planned rest periods) and inhaling the fine dust that stuck to the A7L pressure suits after EVA. However, they were only in freefall conditions for the ~3 day transit from Earth orbit to the Lunar surface. Acclimating to the Martian gravity (or that of other bodies) after months of freefall conditions is a big unknown, which is another argument for requiring pseudogravity in an interplanetary crewed vehicle. However, that is only one of several technologies that would need to be developed and matured to support interplanetary transit and long term habitation beyond Low Earth Orbit, and until we have the ability to use space-based resources to power and sustain such systems the cost of building and supporting this capability will remain prohibitive.
Just one example of why mouse studies might not apply to humans: We’re tall enough that our blood pressure varies significantly between our head and our feet. Mice may well have a lower average blood pressure than us (that’s my ignorance; I genuinely don’t know), but I doubt that it’s so low that the difference between their top and their bottom is significant. Maybe some of the detrimental effects of free-fall are related to the fact that in free-fall, pressure is equalized throughout the body (which wouldn’t matter to mice, since that’s their default state).
As to the term “microgravity”, it may be widely used, but it’s just plain wrong. Depending on your frame of reference, gravity at the ISS is either nearly as strong as it is on the surface, or exactly zero. There is no interesting frame of reference in which the gravity at the ISS is nonzero but small.
Sure there is. Two things that come to mind are air resistance and tidal effects. Both mean that a human inside the ISS will eventually drift (accelerate) into a wall.
Satellites in LEO which require true freefall conditions (like Gravity Probe B) keep an isolated experimental core and use thrusters to maneuver the rest of the satellite body around it.
ETA: Hadn’t seen Dr. Strangelove’s entry above when I posted. Didn’t / don’t mean to pile on.
As a matter of physics I agree 100%.
As a matter of engineering things aren’t so pristine …
You have the periodic accelerations from firing of maneuvering thrusters, from inertial coupling as the solar panels move to maintain optimum solar alignment, vibration from air conditioning and other pumping systems, jolts from docking events, jostles from astronauts moving around and fending off interior surfaces, etc.
Your experiments and some-day industrial processes are not subject to anything near the vibration or gravity of life on a planetary surface. But they’re also not in a state of pure absolute zero total acceleration when aggregated over material timespans.
This is true of all manned space missions, past, present, and into the foreseeable future. There is no app that economically justifies the cost of maintaining humans in space. Even if we place a very high value on pure scientific research, the money would be better spent on developing more sophisticated, capable robots or sample-return missions.
Exactly. If you were to build a very large space station, the size of a city or the size of Comet 67P, these tiny gravitational forces will be significant enough to hold objects on the outside surface, and also on certain inner surfaces. This might even be a useful feature - at least the dust would settle, eventually.
The problem here is that eventually the robots will be so capable that human exploration will be unnecessary; the robots will clear off and explore the universe, and we humans will be left behind on an increasingly irrelevant Earth.
Given that Telemark mentions ‘lab space’, I’m fairly sure the intent in the term ‘experience’ was ‘do science’, not ‘bounce around joyfully’.
Your citation says a little bit about being a staging base for interplanetary missions, and a whole heaping lot about research in a microgravity environment (and not just research about human survival in that environment.
It’s going to change based on a lot of factors, but by my calculations the tidal acceleration is about 6x10[sup]-5[/sup] m/s[sup]2[/sup]. So definitely in the micro range. I’m assuming a distance of 25 meters from the ISS center of mass to the most distant habitable part of the station and a radial alignment of this axis.
Another ballpark calculation gives 1.8x10[sup]-6[/sup] m/s[sup]2[/sup] of retrograde acceleration from the atmospheric drag. Standing on the prograde wall of the station would be similar to standing on an asteroid with a diameter ~6 km.
