I don't know about that NYT article, but virtually NOBODY thought that anything but a powerful enough, and lightweight enough motor stood in the way of heavier-than-air flight.
Not to put too fine a point on it, but you're saying that the _only_ concern of engineers regarding powered flight was about finding a powerful enough engine to get off the ground, and _nothing at all_ about stability or control or vibration or wobbling issues while in the air not rigidly connected to any stationary object? Interesting.
Is it really that appealing though? I think we can all agree SX will build starship variants for different missions; I don't think anyone would pushback on the notion that it will be inconsequential for SX to build an "AG" variant that has structurally appropriate attach points elsewhere on the vehicle.
No doubt there will be specialized variants, but given that Starship already has the load-bearing attachment points where they are (and presumably so will all Mars-bound Starships, because that's how they're hoisted onto the Earth launch mount and how they would be caught when returning to Earth), it would just add unnecessary mass and complexity to add additional ones elsewhere.
The tether-on-arms concept also requires the vehicles to fly raptor-out. This both a) results in a much harder to control inertial environment (since the mass of the SS's is farther out) and so the control system needs to be enhanced accordingly, and b) creates a situation where you're wasting existing on orbit "structural length" for the connection (a SS has ~30m of structure between the base of the vehicle and the "base" of the payload bay/habitat). In other words, even in a situation where you actually tether two SS's vs rigidly attach them you'd want the vehicles to fly raptor-in...and thus you'd attach the tether to the base of the vehicles and not the catch arms.
Having the mass farther out makes the system more stable, not less stable. It may be counterintuitive, but it's much easier to vertically balance a baseball bat on your hand with the barrel up (center of mass farther from the pivot) than barrel down. The center of mass of each Starship is closer to the engines than to the nose, making the nose-in spinning configuration more dynamically stable than nose-out. The extra 30m distance is not too significant anyway when you're talking about a 300m tether.
As an aside, if you connect two starships ~raptor-to-raptor and spin the system at a tenable ~3rpm, that puts the habitats at ~Mars gravity. ~2rpm ends up being ~Moon gravity. (There's actually a pretty significant gravity gradient across the "height" of the habitats, but I digress...). For these kinds of early missions that go before dedicated habitats are available, that sure does seem to land squarely in the Job Done column...
I suspect that the optimal gravitational environment for Mars transit (for the health of the crew members) will turn out to be somewhat closer to Earth gravity, and somewhat slower than 3rpm, but agreed that tail-to-tail spinning could be a potential halfway solution. One downside is that the crew compartment (and entire ship) would have to be designed to operate in three gravitational regimes: nose-up (for launch), nose-down (for spinning), and heatshield-down (for reentry). Whereas nose-inward tethered spinning would simplify the design of the crew compartment because the "floor" is always in the same place, and I'd speculate there may be additional reasons not to want fuel to be gravitationally [centripetally] pulled away from the engines.
Indeed. As one contemplates top-of-the-V type mission elements one quickly get to the point where a rigid structure makes total sense over a floppy tether with all kinds of complicated designs and caveats and constraints. Damping becomes a non issue in all conditions with a rigid structure; modes analysis is Structures 101. Mass (again) likely ends up a little higher than the high-scool-physics theoretical tether, and really is all but a non-issue lifting anyway.
It's a stretch (no pun intended) to call a tether under several hundred tons of tension "floppy", but ok. I'm still pretty sure that a 300m solid connection rigid enough not to have similar damping issues as a tether would incur a very significant mass penalty. For a point of reference, a 300m tall radio tower on Earth (which appears extremely lightweight and slender) typically masses about 220 metric tons, versus about 3 metric tons for an equivalent 300m Zylon tether capable of comfortably supporting two Starships at 1g tension. Obviously it's not apples-to-apples (e.g. the radio tower is under compression, not tension), and you may be able to make it an order of magnitude lighter than that, but probably not two orders of magnitude. Not to mention the difficulties in deploying and constructing such a thing en route to Mars. In any case, it's a starting point for napkin math.
I appreciate your passion for your solution here, but you're really ramming it into the bottom of the V. Seriously, using two starships is a great idea. Take that win.
Using a tether clearly is a bad idea. Don't sweat that loss.
If I were taking your and daniel's technical concerns at face value, I'd be right there with you. But I don't think many of them are accurate, hence the pushback. (It's been a while since my college engineering and theoretical mechanics days, but I do have a technical career and try to keep in practice.) It's also occurred to me that Starship has an _excellent_ built-in damping mechanism for tether-induced wobbles and vibrations, which is simply the tons of onboard liquid fuel + baffles. Any oscillations in the overall system will quickly be converted to sloshing and turbulence in the fuel, which will just as quickly become non-oscillating heat energy. (Not enough heat energy to problematically warm the fuel, but enough to damp out quite a lot of oscillation.) To be fair, this helps in the rigid-connection scenario as well, but it also makes the tether scenario that much more plausible.
They'd always have to synchronously act through their own Starship's cg, coaxial with the cg's velocity vector. That's a pretty serious over-constraint on ops...
In practice it would probably be a linear combination of firings from several thrusters, so no single one of them would have to be precisely positioned or aimed. Granted, in a sci-fi world where you're envisioning Super-Draco-class thrusters spinning up the system in 30 seconds, it would have to be precisely synchronized, but with small ullage-gas or ion thrusters spinning up the system over hours or days, it wouldn't have to be. A partially-fueled Starship has a LOT of inertia; it won't turn (or even wobble much) on a dime.
