Weir's The Martian.

[smartcooky]

I was left wondering about rotating artificial gravity compartment. Wouldn't it act like gyroscope and resist all attempts at changing attitude? I didn't see any contra-rotating weights. Would such gyroscopic forces damage the ship if attitude was forcefully changed?

Lurky

Firstly, the gyroscopic effect doesn't so much "resist" change in attitude as cause the attitude to change in a different direction to the applied force. The rule is that when a force is applied to a gyroscope to change its spin axis, the resulting motion is in the same direction as the force, but 90° in the direction of rotation.



I can't remember which way the Hermes centrifuge spun, but if it was in the direction of the yellow arrow, and thrust was applied in the direction of the red arrows, then the spacecraft would yaw in the direction of the green arrows. Of course you are right that the shape of the spacecraft (long and narrow) would have a very large "moment of inertia", and too much thrust could wreck it.

Secondly. IIRC, in the movie, they de-spun the centrifuge during retro-firing and course corrections, so I imagine that it would also be de-spun for attitude changes.

Anyone know if NASA took gyroscopic effect into account in Apollo when they used the 'barbecue roll". I imagine they would need either take it into account or de-spin the spacecraft when making course corrections.

[Northern Lurker]

So having another artificial gravity compartment or counterweight contra-rotating the gravity compartment would simplify maneuvers and remove fuel expenditure in spinning up and down gravity compartment(s). But gyroscopic effects can be taken care of in astrogation software and all that extra weight would require extra fuel for every acceleration or deceleration. So having just one rotating compartment is plausible?

[smartcooky]

So having another artificial gravity compartment or counterweight contra-rotating the gravity compartment would simplify maneuvers and remove fuel expenditure in spinning up and down gravity compartment(s). But gyroscopic effects can be taken care of in astrogation software and all that extra weight would require extra fuel for every acceleration or deceleration. So having just one rotating compartment is plausible?

I can't see any reason why not. A second rotating compartment would be additional expense, mass (that would need to be lifted to orbit for construction) and complication. Would the fuel savings offset the additional hassle?

Also, a contra-rotating centrifuge will not make the gyroscopic effect go away. Each centrifuge will have the gyroscopic effect pulling in opposing directions. There would be a lot of additional stress on any part of the spacecraft structure between them, effectively the stresses would be doubled as the gyroscopic effect of any attitude change would pull the intermediate parts of the spacecraft in opposite directions. The two centrifuges would have to be positioned right alongside each other. 

[Northern Lurker]

Also, a contra-rotating centrifuge will not make the gyroscopic effect go away. Each centrifuge will have the gyroscopic effect pulling in opposing directions. There would be a lot of additional stress on any part of the spacecraft structure between them, effectively the stresses would be doubled as the gyroscopic effect of any attitude change would pull the intermediate parts of the spacecraft in opposite directions. The two centrifuges would have to be positioned right alongside each other.

I imagined the centrifuges being side by side.

Lurky

[ka9q]

So having another artificial gravity compartment or counterweight contra-rotating the gravity compartment would simplify maneuvers and remove fuel expenditure in spinning up and down gravity compartment(s).

In space flight fuel (i.e., propellant) expenditure is everything. It's even more important than energy since solar panels can generate arbitrary amounts of energy (if you wait long enough).

[smartcooky]

So having another artificial gravity compartment or counterweight contra-rotating the gravity compartment would simplify maneuvers and remove fuel expenditure in spinning up and down gravity compartment(s).

In space flight fuel (i.e., propellant) expenditure is everything. It's even more important than energy since solar panels can generate arbitrary amounts of energy (if you wait long enough).

AIU Weir's concept, Hermes in normal operation is on a sort of Mars Recycler. Its main engines are Ion Thrust fuelled by electrostatically-charged argon. It would be these Ion engines that are used for TMI/TEI and MOI/EOI at each end of the journey

Its manoeuvring (Attitude Thrust) engines use oxygen/hydrazine rocket fuel. If the Hermes orbital mechanics works as Weir is suggesting then propellant isn't really a great issue because the propellent used for course corrections would be the same propellant used for de-spinning and spinning up the centrifuge, and not the same propellant used for entering and leaving orbit.

So, the debate here is, would the propellant expenditure saved by not having to de-spin the artificial gravity centrifuge in order to make course corrections without compensating for gyroscopic effect, be offset by the additional mass (and therefore more propellant needed) of an extra centrifuge. Also keep in mind that the additional complication of having two counter-rotating centrifuges will make construction problematic with the additional stress of having two opposing gyroscopic effects, and that may require additional structural strength, and therefore additional mass.

Its easy to see why rocket science isn't easy!

[Echnaton]

My thoughts about this type of spacecraft is the viability of rotating air seals for a long duration flight.  Particularly the wear on bearings or other mechanism over that long of a time that will ultimately cause some wobble and degradation of the airtightness.  I can imagine some of the wobble problem could be taken care of by a tuned mass in the extremity of the rotating section, but degradation of seals would occur, it is just a matter of how fast.  One supposes this could be a maintenance item corrected by depressurizing part of the ship to adjust bearings and replace seals.

This would, it seems to me, argue against a more complex counter rotating scheme which would require additional seal and bearing structures to be maintained.   

[ka9q]

Good point about the seals. The other problems of rotating joints such as getting electrical connections across, are not that difficult. Rotary transformers work well.

[ka9q]

Speaking of rotary habitats, one thing I would really like to see them do in one of these movies is to depict someone jogging around one opposite its direction of rotation, and then lifting his legs and just continuing around.

[Northern Lurker]

In the movie all Hermes's crew spaces were one continuous room which requires airtight seals.

Could the seals be bypassed using pressurised "elevator"? One would move from 0g compartment through airlock to "elevator", the "elevator" would detach and match the spinning of centrifuge and move to 1g compartment which is entered through another airlock. Air seals would exist only to block hard vacuum entering the "elevator" area.

[Dalhousie]

Speaking of rotary habitats, one thing I would really like to see them do in one of these movies is to depict someone jogging around one opposite its direction of rotation, and then lifting his legs and just continuing around.

How would this happen?

[VQ]

How would this happen?

They would be stationary relative to the non-rotating spacecraft core, but appear to be moving relative to the spinning artificial gravity hab.

[smartcooky]

Speaking of rotary habitats, one thing I would really like to see them do in one of these movies is to depict someone jogging around one opposite its direction of rotation, and then lifting his legs and just continuing around.

Mission to Mars?

[Dalhousie]

How would this happen?

They would be stationary relative to the non-rotating spacecraft core, but appear to be moving relative to the spinning artificial gravity hab.

Because they are under tangential acceleration until the moment they lift their legs they'll rapidly hit the deck.

[Echnaton]

The jogging scenario would require a very loose definition of jogging. 

Wouldn't a jogger "continuing around" already have to be in relative weightlessness, to the deck, before lifting his feet.  Which would have made even the slightest prior foot contact send him away from the surface.  Or perhaps he could use his last step to null out the motion, but that seems practically improbable.