Eventually, orbital stations and deep-space manned craft will have to incorporate some kind of rotating habitat within a fixed shell, akin to designs appearing in recent sci-fi flics. The superstructure of a spaceship would not rotate, but would contain a rotating element accessible from the zero-G axis.
An orbital station would likely be similar, with a rotating section and a stationary section, for ease of docking and to reduce the dangers of space walks (we don't want astronauts flying out the airlock at 1 g acceleration). I believe this was the flaw in the orbital station in 2001: A Space Odyssey.
The criticism of centripetal force as a substitute for planetary gravity is that it has directional vectors of force that would make you dizzy every time you turn your head. Presumably, the larger the structure, the more subtle these forces become. Perhaps humans can get used to these lateral forces over time, if indeed it is an issue at all. Having the simulated gravity would be very useful, especially in medical situations but also simply for the purposes of maintaining bone density and muscular health, both of which suffer enormously in zero-G conditions over long stretches.
I'm reading Neal Stephenson's Seveneves at the moment - it explores (in a sci-fi way, of course) what it would take to simulate 1g in orbit (with the rough equivalent of current space hardware).
> The criticism of centripetal force as a substitute for planetary gravity is that it has directional vectors of force that would make you dizzy every time you turn your head. Presumably, the larger the structure, the more subtle these forces become. Perhaps humans can get used to these lateral forces over time, if indeed it is an issue at all.
I wonder if astronauts would develop "land sickness" that affects some people coming from cruises - constant dizziness when out of spin gravity.
Also, rotating cylinders might provide spin gravity without the lateral forces. Entry/exit access at the ends. The downside is the chaos that will ensue if the mechanism rotating the cylinder loses power and people/objects begin raining down. The raining down might only be an issue while under thrust though since objects might otherwise just float off the cylinder wall.
No, just enough to overcome friction. What might be harder is keeping it all in balance. Also a large mass rotating is going to make directional changes for the entire spacecraft harder, due to the gyro effect.
All this could be avoided by fully implementing artificial gravity on deep-space journeys. This should not be particularly difficult and would involve just taking the last rocket stage along for the ride, tied to a tether. Rotate to produce gravity.
Even if the zero-g journey to Mars is uneventful, astronauts will be severely weakened by the time they arrive there, even with heavy exercise and preventative measures. And in the first few weeks they actually do the most and heaviest work.
So there's a little mystery why NASA insists on trying to find a pharmacological or mechanical workaround when artificial gravity is right there.
How do you propose this would work actually? The last article I read on the subject suggested that AG isn't viable near term as the space craft would have to be prohibitively large. I recall the primary issue being that living quarters have to be a certain distance from the axis of rotation.
A radius of 224 meters is 1 g acceleration at 2 revolutions per minute. It is directly proportional, so half the acceleration is half the radius. 0.5g or less might be good enough.
Now this is a pretty huge space craft, but compare that with the ISS which is already 108 meters wide by 73 meters long. It's a huge undertaking but in the realm of possible. Of course, there's still the issue with mass and thrust required to propel a huge craft to an interplanetary trajectory.
The question is whether artificial gravity is a requirement for interplanetary human expeditions.
That assumes the ship's radius is a limiting factor. It isn't if you spin the ship against a counterweight with a tether (the spent third stage which is going with you on the same trajectory more or less).
Well, there's no "consume" in terms of matter, stuff isn't thrown overboard. Besides, the food and water (or what they become) is still valuable radiation shielding.
The tethering happens after the upper lift stage is exhausted. It's then spun from a tether for the duration of the trip, then disconnected before the deceleration burn to orbit Mars. There's no mass exchange while the tether is connected.
Why? As long as the system is dynamically stable. The only issues are that the g is slightly different at different heights, and the Coriolis force, which should be relatively constant.
If you want 0.3g at 6RPM, it means a radius of 30m.
...meaning a diameter of almost half a kilometer, or over a quarter mile-- more than four times the longest part of the current ISS, which took over 12 years and 150 billion dollars (and is essentially flat when compared to the cylinder shape needed for AG).
I can see why this might be a bit of a challenge, the time and costs involved would be enormous.
Why would you need a full cylinder? Living quarters on one side, (rocket stage) counterweight on the other, tether in between.
You'd probably want all that stuff reeled in together for acceleration and deceleration, but you can unspool the whole thing while you're coasting in between.
so how do we stop the rotation while reeling in for acceleration? Shortening the tether would accelerate the objects at the end and we'd end up with a rotating drum filled with seasick astronauts.
Thrusters require energy and reaction mass (or chemical propellants). For every course change of the spinning construct you'd need to stop the rotation, reel in the drum - now you suddenly need thrust to keep the bodies apart while reeling in, change course, reel out (requires thrust), spin up.
All of that requires reaction mass and energy (or chemical rockets).
On top of that you can't do work on the outside of the space ship since everything (including the space walker) would fly away. You need a double tether at least for safety, etc. Storing the propellants for the thrusters will be an issue: solid boosters won't do because they can't be stopped. Storing oxygen/hydrogen over long periods is an issue in itself.
It _is_ a low level physics problem, but the practical implications are massive.
Yes, obviously. (Unless that microwave drive from earlier this year turns out to be really for reals).
> For every course change of the spinning construct you'd need to stop the rotation, reel in the drum...
I'm not convinced that this is entirely true. Doing so would simplify the math required to perform the course alteration, but I expect that altering the course of the craft while it is spinning is not impossible.
Regardless, as pavel_lishin mentioned in the first comment you replied to in this subthread, you can reel the tether in when making craft course changes.
> On top of that you can't do work on the outside of the space ship since everything (including the space walker) would fly away.
Unless -as you go on to say- you're attached to the outside of the craft.
> Storing oxygen/hydrogen over long periods is an issue in itself.
...if you're going to take a long journey in space, this is one of the problems you're gonna have to have solved, no?
So, I'm a little confused.
We go from:
> so how do we stop the rotation while reeling in for acceleration? Shortening the tether would accelerate the objects at the end...
to:
> Thrusters require energy and reaction mass (or chemical propellants). ... It _is_ a low level physics problem, but the practical implications are massive.
You're moving the goalposts. Your first question asked "How do we maintain the speed (and -thus- the g-forces in the craft) while altering the length of the tether?". Your follow-on comments to the answer to your question say -in a nutshell- "Gosh, solving that problem would make maneuvering too hard, and is thus kinda impractical.". :/
If you want to use the energy stored in the rotation you'd need stiff tethers, not a slack line - more mass, shear forces acting on the tethers, can't be reeled in. Moving to a non-rotating part of the ship requires a hub and a way to move to the hub - that would either require a space-walk up-hill against the artificial gravity (yay, climbing about a quarter of a km in space with an eternal fall if you loose grip) or a tether that's massive enough to move through - but then we're talking a very massive space ship, not about a rocket stage as counterweight.
Aside from the manueverability problem mentioned in other comments, the tether has a materials problem: it needs to hold the combined ship and couter weights at approx 1g.
Reliable reeling mechanisms that actually work in vacuum seem a yet unsolved problem, and there's occasional research into it. Sure, there could be more, but it's not like the lack of gravity is the only (medical) problem to solve for a Mars flight.
Oh shoot, I accidentally downvoted you when I meant to upvote. Terribly sorry!
Parent commenter presents this idea occasionally without justification. At present stage of research, as you correctly point out, tethering in space is further out than biomedical research.
Mind you, I'm not against research in either drugs or mechanical solutions (better exercise machines), but they could serve as backup in case the main system - centripetal acceleration - is malfunctioning.
One question NASA has yet to answer is the minimal level of gravity necessary to prevent muscle and bone degradation. Is the Moon or Mars human-habitable in terms of gravity? If that's not the case, then mission plans would have to include rotating habitats for planetary surfaces, which makes matters a little more complex.
Hundreds of resources from nasa.gov regarding research into bone and muscle degradation don't automatically translate to what the parent asked for, for NASA "to answer (...) the minimal level of gravity necessary to prevent muscle and bone degradation".
Is there one? I imagine it is a proportional effect. You'd experience degredation at .9g, it just wouldn't be nearly as bad. The more interesting, and difficult I'd wager, is what is the minimum healthy level.
Lots of things in large organizations are done for political, budgetary, turf-war, ideological and finally idiot-in-charge reasons, not necessarily for "good reasons".
See the awesome "The Expanse" series for some fleshed out thoughts and ideas along these lines!
I don't want to give away any spoilers here but the authors describe a huge ship designed for long-term deep space travel/living with the capability to "spin up the drum". The drum is a ~2km long tube that generates spin gravity when engaged, inside which the ship crew can live and farm.
There are also frequent but subtle mentions of the effects of spin gravity. For example, the apartments closer to the center of stations are cheaper due to the higher spin forces.
I am just starting the fourth book but the first three have been great. Quick, light reading but still a full-fledged space opera that is thought provoking and engaging.
The objective reality of our world and this (Eurasian part of) its species is that we have already reached the sorry apex of our "space travel": in other words it's not getting any better or more involved or complicated, or indeed gory and dangerous than it is now. EVAR. This is it: humans (9 times out of 10, air force personnel - not scientists, not engineers) spinning safely albeit wildly, around this planet at an altitude of 350-400 kilometers in a bunch of excruciatingly expensive modules ("ISS") with artificially created 0 gravity (actual low Earth orbit gravity at that altitude is about 96-97 percent of what it is right where I, and you, sit now).
.... and if anything goes wrong, the Ruskies ship them down to Earth ASAP to get operated on, or whatever. That's all.
So - what was that thing about "surgery in space"? Where? When? What species might have to do it? Not _us_ - I assure you, BBC, you poor Buzzfeed competitor, you.
And those people up there "in space" are, as of Nov. 30 and the latest news, being sent "caviar, fruit, and chocolate" - but no vodka?
I wouldn't wanna be on that "space station" when the Russian segment finds out about this conspicuous and inexplicable lack of the core "good times" component.
Haha, you guys, us Russians can't live without vodka, right? What witty observational humor! And I sure do hope they shipped a 40 of malt liquor up there when astronauts of African descent were up there, too, yeah?
His gratuitous insult of Russians was absurd and uncalled for.
However, his other point has a lot of validity. Sending people into space and keeping them there is extremely expensive. Absent any major cost breakthroughs, I agree with his assessment of 'the sorry apex of our "space travel"'. Where will the money come from?
You sure extracted a lot of meaning out of some rambling. Technology tends to go up and up and up - at any given point, you're almost certainly at the apex of something, without necessarily a clear path to the next hilltop.
An orbital station would likely be similar, with a rotating section and a stationary section, for ease of docking and to reduce the dangers of space walks (we don't want astronauts flying out the airlock at 1 g acceleration). I believe this was the flaw in the orbital station in 2001: A Space Odyssey.
The criticism of centripetal force as a substitute for planetary gravity is that it has directional vectors of force that would make you dizzy every time you turn your head. Presumably, the larger the structure, the more subtle these forces become. Perhaps humans can get used to these lateral forces over time, if indeed it is an issue at all. Having the simulated gravity would be very useful, especially in medical situations but also simply for the purposes of maintaining bone density and muscular health, both of which suffer enormously in zero-G conditions over long stretches.