Author Topic: MCT Speculation and Discussion Thread 4  (Read 505557 times)

Offline arnezami

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Re: MCT Speculation and Discussion Thread 4
« Reply #1280 on: 01/02/2016 09:35 AM »
Not sure if this video has been posted yet..but a schematic of a 100MT lander is illustrated at 46 min mark.
Interesting vid but warning lots of physics!! :)
Cheers
Jb


Here is the relevant paper:

http://www.ssdl.gatech.edu/papers/phdTheses/CordellC-Thesis.pdf

Maxwell is referring to the configuration where the nozzles are located in the afterbody. In the paper, chapter 4.3.2 introduces this concept and in chapter 6 goes much deeper into it.

Attached are two figures from the papers, one with the afterbody nozzles turned off, the other with the nozzles turned on.


Offline Johnnyhinbos

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Re: MCT Speculation and Discussion Thread 4
« Reply #1281 on: 01/02/2016 02:27 PM »
Though somewhat click bait-y, there's a few tidbits worth reading. (I'd inline quote, but iPhone Tapatalk makes it a pain...)

http://www.universetoday.com/126457/will-2016-be-the-year-elon-musk-reveals-his-mars-colonial-transporter/
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Offline Miker66

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Re: MCT Speculation and Discussion Thread 4
« Reply #1282 on: 01/02/2016 04:05 PM »
MCT Daily Gravity Dose

This is probably a crazy idea, but how about this for simulating gravity on a Mars trip?

Around the inside of the hull is a circular rollercoaster track. On it is a bicycle, the sort you lie on your back to pedal, maybe with hand cranks too. Each astronaut does, say, 30 minutes a day on the bike. You start out stationary, pedal up to speed, keep going for your 30 minutes, then slow down and get off when stationary. Assuming an MCT internal diameter of 40 feet how fast would you need to go to experience 1g? Or maybe ˝g would be enough.

You’d be lying flat on your back, so your head and feet are travelling at the same speed, experiencing the same ‘gravity’. Though you could of course sit upright if you wanted to drain fluid down from your head or get some spine compression. EDIT: even 10 minutes on your back, 5 minutes on your left side, 5 minutes on your right side, 5 minutes on your front and 5 minutes bolt upright to get some g in all the directions you would on earth?

The "bicycle" is reversible – the next guy goes round in the opposite direction to avoid imparting cumulative spin to the rocket. Though would 'anti-pedalling' to slow down undo all the spin you imparted?
« Last Edit: 01/03/2016 01:54 PM by Miker66 »

Offline Paul451

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Re: MCT Speculation and Discussion Thread 4
« Reply #1283 on: 01/02/2016 04:53 PM »
You'd be lying flat on your back

Remember that laying flat is used as a crude proxy for weightlessness in research on Earth, precisely because it causes many of the issues experienced in space even though you are under 1g. Hence, your bike method will achieving no more than peddling on a stationary bike in weightlessness.

Better to simply have a ring-track around the widest inside diameter of the hab section. And use centripetal force to hold you down as you jog/run. A la Skylab & 2001.

Though would 'anti-pedalling' to slow down undo all the spin you imparted?

The total energy of the ship and rider (or runner in my case) are conserved, unless mass is thrown overboard. So there'll only be induced spin during the exercise itself; but zero net spin, regardless of which direction(s) you ride.

If you don't want the ship to spin at all, you would probably use a flywheel large enough to store the momentum during the exercise sessions, (reversed when they stop.)

Offline Stan-1967

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Re: MCT Speculation and Discussion Thread 4
« Reply #1284 on: 01/02/2016 05:32 PM »
You'd be lying flat on your back

Remember that laying flat is used as a crude proxy for weightlessness in research on Earth, precisely because it causes many of the issues experienced in space even though you are under 1g. Hence, your bike method will achieving no more than peddling on a stationary bike in weightlessness.

Better to simply have a ring-track around the widest inside diameter of the hab section. And use centripetal force to hold you down as you jog/run. A la Skylab & 2001.

Though would 'anti-pedalling' to slow down undo all the spin you imparted?

The total energy of the ship and rider (or runner in my case) are conserved, unless mass is thrown overboard. So there'll only be induced spin during the exercise itself; but zero net spin, regardless of which direction(s) you ride.

If you don't want the ship to spin at all, you would probably use a flywheel large enough to store the momentum during the exercise sessions, (reversed when they stop.)

I like the idea of a bike track that the rider lays relatively "flat" to the outer circumference.   Quick calculations for a 40 ft inner diameter track says a rider needs to be going 25 feet per second ( 12 rpm ) inside the track for 1g, and 17 feet per second ( 8.4 rpm ) for .5g.      Those velocities ( 11.5 to 17 mph)  are easily achieved by a bicycle, but not to easy for a person to sustainable run and get any benefit of daily "g" doses.   

I'd minimize flywheel demands by having to tracks that different riders can go opposite directions to cancel out the angular momentum issues.   A computer could direct each occupant to step up the pace, or back off on the effort to keep things in balance.  Make it a game and take the boredom of out of going in circles.  Concurrent riders can match each other in weight.  Heck, there's even no reason you couldn't couple the forces produced by the rider to a counterweight rotating in the opposite direction that would cancel his own momentum.  It would just add resistance, which is the whole point of exercise.

Offline Miker66

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Re: MCT Speculation and Discussion Thread 4
« Reply #1285 on: 01/02/2016 06:02 PM »
Quote
I like the idea of a bike track that the rider lays relatively "flat" to the outer circumference. Quick calculations for a 40 ft inner diameter track says a rider needs to be going 25 feet per second (12 rpm) inside the track for 1g, and 17 feet per second (8.4 rpm) for .5g. Those velocities (11.5 to 17 mph) are easily achieved by a bicycle, but not too easy for a person to sustainably run and get any benefit of daily "g" doses.   

I'd minimize flywheel demands by having two tracks that different riders can go opposite directions to cancel out the angular momentum issues. A computer could direct each occupant to step up the pace, or back off on the effort to keep things in balance. Make it a game and take the boredom of out of going in circles.  Concurrent riders can match each other in weight.  Heck, there's even no reason you couldn't couple the forces produced by the rider to a counterweight rotating in the opposite direction that would cancel his own momentum.  It would just add resistance, which is the whole point of exercise.

Thank you for your thoughts and for doing the sums.

One revolution every 5 seconds to get 1g is not too fast, and (say) 30 minutes at 1g a day (lying flat and/or sitting up) would hopefully help combat muscle and bone loss.

I like the idea of two competing tracks and so forth. However, simplicity/weight/space may mean a single, simple track. On reflection, one person accelerating to 17mph would not have much spin effect on a huge spaceship, and negligible once they have decelerated.

Maybe it's not such a crazy idea after all.
« Last Edit: 01/02/2016 06:34 PM by Miker66 »

Offline Mongo62

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Re: MCT Speculation and Discussion Thread 4
« Reply #1286 on: 01/02/2016 06:17 PM »
For artificial gravity, I would simply go with two MCTs linked by a long cable, spinning about each other. The longer the cable, the better.

This does imply that an MCT fleet would preferably consist of an even number of passenger vessels (although a passenger vessel linked to a cargo vessel should work too).

Offline The Amazing Catstronaut

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Re: MCT Speculation and Discussion Thread 4
« Reply #1287 on: 01/02/2016 06:21 PM »
For artificial gravity, I would simply go with two MCTs linked by a long cable, spinning about each other. The longer the cable, the better.


Not attempting to be rude, but wasn't this idea suggested a long time ago and debunked? It adds numerous mission complications (and contingency risks) and the absence of zero-G increases volume limitations to a spacecraft that is already volume limited.

As to the bike idea - if you were going to use flywheels for rotational control/pitch control anyway on the trip to Mars (no idea how it scales), then just connect the bike to that. Saves you an extra flywheel.

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Offline Miker66

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Re: MCT Speculation and Discussion Thread 4
« Reply #1288 on: 01/02/2016 06:41 PM »

As to the bike idea - if you were going to use flywheels for rotational control/pitch control anyway on the trip to Mars (no idea how it scales), then just connect the bike to that. Saves you an extra flywheel.

No flywheels involved! Please see original post:

https://forum.nasaspaceflight.com/index.php?topic=37808.msg1468713#msg1468713

Offline Stan-1967

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Re: MCT Speculation and Discussion Thread 4
« Reply #1289 on: 01/02/2016 07:45 PM »
I'm in agreement with making operation of a bike track impart as close to zero angular momentum to the spaceship whether it be by cancelling the effect of an rider on a track by coupling to a flywheel, or by having a counter rotating mass ( other rider) cancelling the same. 

Over even minutes of operation, I am pretty certain that significant angular motion would be imparted to even a large craft like an MCT.   Communication arrays, solar arrays etc. would go out of alignment if not compensated for.  Think of those "strongman" shows where some big huge dude pulls a semitruck with a rope.  I've seen one guy get a truck up to 5mph in very little time.   The key part is that if you just want to give a person exposure to g's, you can do it with very little change in momentum once they are moving.  That becomes a problem of minimizing drag/friction on the track.  If you want this to also be resistance training for muscle preservation, you need resistance, which require you to push against something (i.e the spaceship) and that will impart a large angular momentum change.   That is much different problem, hence the complexity I am imagining with multiple tracks.

My thoughts on multiple tracks was that this is being discussed in context of a MCT with upwards of 100 colonists on board.  If the goal is to give a daily dose of 1g, plus resistance training for preserving muscle mass, how are 100 colonist going to cycle through a single track in any frequency that gives regular benefit?   If each colonist were to be assigned 1 hr per day of exersise, that would require 6 tracks operating 18 hours per day.  The number of tracks could be reduced by putting multiple riders in the same loop.   ( computers are going to have to be involved for adjusting resistance for collision avoidance!) 

Furthermore, if the track resistance adjust to make the average energy output of each rider around 150-200 Watts, I'm going to think it is worth the effort to make this space hamster wheel an electromagnetically coupled generator.   It would deliver about the equivalent of a kilowatt of continuous power when operating.   That is worth some reduced weight in solar arrays to offset the weight of the track.

I also don't think a bike track contraption necessarily has to take up too much space.   Given you can constrain the tracks, each lane should not need to be more than 2 ft wide and maybe 3 ft high.  Think of each track as a tube around the inner circumference.   If you have 3 track ( 6 ft ) total, that are 3 ft high, that would be volume around 1100 ft^3 or 31 m^3.  Not a show stopper for the size of MCT and the importance of human health during the journey.


Offline Miker66

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Re: MCT Speculation and Discussion Thread 4
« Reply #1290 on: 01/02/2016 08:09 PM »
Good point: if there are 100 on board, two tracks in opposite directions could be good. Tandems - nice idea. The tracks - two rails attached to the hull - would weigh very little and the bike(s) could be very light and indeed wouldn't take up much space.

Even if there was only one track, one person accelerating to 17mph against a ship with mass of 100 tonnes wouldn't have too much spinning effect on the ship. (Though if one track would induce spinning, I think by that logic two opposite-direction tracks would induce tumble? So you're back to reversing each bike's direction each time.)

There would be some friction loses, and of course air resistance, so some work for the cyclist to do even to maintain a steady speed. I suppose you could couple to a dynamo, but my instinct says just keep it simple. This is mostly about getting a dose of g - let's make that as easy as we can for the guys.

Original idea https://forum.nasaspaceflight.com/index.php?topic=37808.msg1468713#msg1468713
« Last Edit: 01/02/2016 08:19 PM by Miker66 »

Offline The Amazing Catstronaut

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Re: MCT Speculation and Discussion Thread 4
« Reply #1291 on: 01/02/2016 08:26 PM »
Position relative to CoG would influence tumble.
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Offline Stan-1967

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Re: MCT Speculation and Discussion Thread 4
« Reply #1292 on: 01/02/2016 09:06 PM »
Position relative to CoG would influence tumble.

Correct!   Isn't space fun!  All moments need to be accounted for and cancelled to maximize any such scheme.

Offline KelvinZero

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Re: MCT Speculation and Discussion Thread 4
« Reply #1293 on: 01/02/2016 09:09 PM »
Would some sort of flywheel/gyroscope be implemented anyway?

I can imagine people building up habits of circulating in a specific way, statistically. This would slowly rotate the vehicle which might interfere with pointing antenna or keeping a certain orientation to the sun for thermal reasons. It might not be predictable. On different flights the passengers might develop different conventions.

So have some gyroscope that can deal with a bit of this. If passengers develop really peculiar habits that saturate the flywheel, such as they decide to have hundred person sprinting races, diplomatically instruct them to stop or how to do it without interefering with the ships orientation. If there is something like a bike track or running track they should join the emptier side that moves in the counter direction, which they would probably do anyway. Or there could be a little gyroscope status indicator on the wall and one civic minded jogger could unwind the angular rotation of 99 not quite randomly circulating co-passengers.

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #1294 on: 01/02/2016 09:46 PM »
Because of Coriolis disorientation, only very small amounts of gravity (0.1g?) are practical within a single vehicle.  This is certainly useful for some things - showering, natural convection airflow, mechanical work - but probably not health-related things.

For higher gravity you're going to need multiple parts connected by long (100m - 1000m) tethers.

Why this design over something with a smaller overall diameter and spinning faster with a larger tube diameter, why so few spokes? Why not just go with the more common proposal of docking at the hub? It just looks like a pretty design with no engineering offered as to why that design is an improvement over countless others.
Coriolis Nausea afflicts very small diameter designs.  Reasonable rotation rates are up to 2-4rpm;  Above 7rpm there seem to be intractable issues in the short term.

At 480m radius, you can get 1G at 1.365rpm - a guaranteed comfortable experience apparently
At 120m radius, you can get 1G at 2.73rpm - Some side effects, but everyone can acclimate to the condition eventually
At 60m radius, you can get 1G at 5.46rpm - Extremely uncomfortable, some people can eventually acclimate, some can't

Any sort of artificial gravity scheme requires major compromises and mitigations for things that need to be statically pointed, like comms, thermal shielding on prop depots, and SEP;  A tether system is the lightest-weight way to make long spans, but it also requires a greater degree of autonomous control in the slung loads (independent propulsion is preferable).

With that said:
For artificial gravity, I would simply go with two MCTs linked by a long cable, spinning about each other. The longer the cable, the better.


Not attempting to be rude, but wasn't this idea suggested a long time ago and debunked? It adds numerous mission complications (and contingency risks) and the absence of zero-G increases volume limitations to a spacecraft that is already volume limited.

As to the bike idea - if you were going to use flywheels for rotational control/pitch control anyway on the trip to Mars (no idea how it scales), then just connect the bike to that. Saves you an extra flywheel.



It adds lots of mission complications, but unlike the bike idea, it is mathematically adequate for achieving the gravity specified.  Are there any real *showstoppers* for it, in a situation where SEP is not used?

A "flywheel" in this instance, a 'control moment gyroscope', is a solid metal or perhaps carbon fiber cylinder spinning at tens of thousands of RPM so it takes up as little space as possible and can be turned on three or four axes.  From what I recall, the flywheels on the ISS are presently insufficient to handle active turning;  Instead, propulsive thrusters are used for both attitude change maneuvers, and for desaturating the CMG's when they reach their angular momentum limit;  mostly they only handle short-duration loads like someone moving around the station.

Offline Vultur

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Re: MCT Speculation and Discussion Thread 4
« Reply #1295 on: 01/03/2016 01:56 AM »
and the absence of zero-G increases volume limitations to a spacecraft that is already volume limited.

Yeah -- I think this would be more important than the health effects of zero-G on a trip of 3 - 8 months. (We know this duration of zero G is do-able from Mir and ISS.)

Online darkenfast

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Re: MCT Speculation and Discussion Thread 4
« Reply #1296 on: 01/03/2016 07:14 AM »
I'm pretty sure we've gone through this discussion before.  Attempts to simulate gravity on a Mars-bound spacecraft would take up mass and space that could be put to better uses.  Adjusting to Mars' lower gravity will not take long.  The crew does not need to rush out and do handsprings.  If they need to move around right after landing for an emergency, then they will do just as Soyuz passengers returning from the ISS have done after an off-target landing: they will cope. 

Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #1297 on: 01/03/2016 10:23 AM »
I'm pretty sure we've gone through this discussion before.  Attempts to simulate gravity on a Mars-bound spacecraft would take up mass and space that could be put to better uses.  Adjusting to Mars' lower gravity will not take long.  The crew does not need to rush out and do handsprings.  If they need to move around right after landing for an emergency, then they will do just as Soyuz passengers returning from the ISS have done after an off-target landing: they will cope.

I fully agree. If we ever send a manned vehicle, refuelled at Mars orbit, to explore the outer planets on a multi year mission, we may need to think of artificial gravity, but not to Mars.

Offline Johnnyhinbos

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Re: MCT Speculation and Discussion Thread 4
« Reply #1298 on: 01/03/2016 12:47 PM »
I think perhaps there's merits to it (artificial gravity on a Mars insertion/return), especially for paying colonists.

As a side note, this paper on one potential Mars exploration architecture - in part authored by Boeing - feels that AG was important enough to include...

https://www.researchgate.net/profile/Ruth_Bamford/publication/233988445_Modular_Space_Vehicle_Architecture_for_Human_Exploration_of_Mars_using_Artificial_Gravity_and_Mini-Magnetosphere_Crew_Radiation_Shield/links/09e4150dcdd2965e62000000.pdf?inViewer=0&pdfJsDownload=0&origin=publication_detail
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Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #1299 on: 01/03/2016 01:08 PM »
NASA administrator Charles Bolden has declared this year in a Congress hearing that they know how to mitigate zero gravity effects for the duration of a Mars mission. Even an orbital missionon that does not land but goes to orbit, leaving them in micro gravity for almost two years.

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