What "mass and added complexity"? At Mars gravity and 4-6 RPM, AG is almost free. The only reason not to do it would be out of spite.
There must be added mass and complexity to do this.
Quote from: douglas100 on 09/04/2017 04:14 pmThere must be added mass and complexity to do this.Sounds like a religious tenet.
Obvious disadvantages: ....., communication with Earth and Mars, ....
I made a mock up picture of two ITS ships connected by a 200m long cable. Enough for 1g gravity at comfortable 2 RPM.
If you look at the ITS design from the original presentation you'll see that there is no provision for docking. Two ITS spacecraft can't dock, let alone spin together for AG. Providing that capability would add extra mass.
A cable is a bad idea. Picture a 200m (or 400m, for 1g/2RPM) cable hanging in still air, with an ITS-like platform hanging off the bottom, with dozens to a hundred people moving around. It will twist and oscillate like crazy.
In free-space it's actually worse, the oscillations dampen very slowly (bouncing back and forth along the cable).
The suggested alternative is a tensegrity structure, a combination of tensile and compressive structures; eg, a truss held under compression by cables.
IMO, 2RPM is ridiculously low.
And 1g is too high, if you expect people to permanently colonise Mars. (If 0.38g isn't sufficient, we aren't colonising Mars, so the point is moot.)
4RPM and 0.38g gives you 40m total length. Including the length of the ITS cabins, it's barely worth the cable.It would be nice to know for sure; since radius/diameter scales with the square of RPM, so doubling the RPM quarters the length. And linearly with g-load, so double the RPM at 38% gravity gives you a ten-fold reduction in length.
I'm not sure what you envision all those people are doing, but I can't imagine anything they could be doing that would make an ITS twist and oscillate.
and the rotation keeping the cable under tremendous compression forces
Just stringing a cable between two ITS and getting them rotating without free body issues will be tricky by itself, but having to inflate things in between is going to be even harder.
Are you familiar with the website SpinCalc?
Quote from: Coastal Ron on 09/04/2017 07:53 pmand the rotation keeping the cable under tremendous compression forcesQue?
Quite the contrary, it makes everything easier, that's why it's suggested.
Of course. (Although I use my own spreadsheet for quick'n'dirty RPM/radius/g-load calcs.) Ted is extremely conservative in his red/yellow/green warnings, which he has acknowledged in other presentations. He does link to the more recent Lackner and DiZio paper, which is part of modern AG research (including ultra-high RPM research like the "Space Cycle" exercise platform), but doesn't actually use it in the calc.
For myself I'm OK with "worst case", [...] because if I can come up with solutions that work out OK with "worst case", then I should be OK with "reality".
It just occurred to me, maybe a single cable can work. [etc]
If you insist on 1g and 1 or 2RPM, then you've virtually ruled out AG in advance, because of course others are going to say "It adds too much mass/complexity", and any consideration of the idea dies.
In fact
We end up with a radius of only about 3500 meters.Assume MCT weighs 200 tonnes during cruise, and you want to simulate Mars gravity. Using three redundant Dyneema fibers, 50% engineering margin (NASA standard), 50% live load allowance, and 100% overhead for space environment protective coatings, I get a mass of 7.5 tonnes (or 3.8 tonnes per MCT). So it's totally doable.The other thing is spin/despin fuel. That's another 8 tonnes per MCT.