Seriously, "catching " a legless, orbit-class rocket on a gantry? That is so crazy.
So crazy.
So Elon.
Genius-level crazy.
So crazy.
So Elon.
Genius-level crazy.
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e-FTW
New electron smell
Saw that SpaceX wants to get a Boring Co. tunnel done in Boca Chica to provide an alternative route to the beach for the numerous times when they will need to close the road to move a rocket.
IANAE but tunnels in what looks like very wet, very low, very flood-able areas seems problematic. I mean NYC just got their train tunnels flooded by Ida.
IANAE but tunnels in what looks like very wet, very low, very flood-able areas seems problematic. I mean NYC just got their train tunnels flooded by Ida.
Only when the above ground parts get flooded. At least Boring doesn't have a live third rail to deal with.
Nikxice
Active Member
Imagine with only 2 entry/exit points engineers could probably mitigate Boca Chica tunnel flood issues. Before last night's flood, NYC probably wishes they had already implemented this giant airbag plug solution.
New York City's giant inflatable ‘plugs’ could keep subway tunnels from flooding
New York City is the first city to test "tunnel plugs" as a way to stop future flooding. Could it work for other cities around the world?
www.google.com
Ben W
Chess Grandmaster (Supervised)
It occurred to me that if Starship uses a similar catching mechanism as Super Heavy, the load-bearing catching arms would make perfect attachment points for artificial-gravity tethers. Envision two Starships en route to Mars, noses facing each other, 500m apart, catching arms connected via Kevlar/Zylon tethers, spinning at ~2RPM for ~1G centripetal acceleration near Earth, tapering down to ~0.4G on approach to Mars. The tethers would mass a few tons, but I imagine Kevlar would also be a fairly useful thing to have on Mars, so it's not wasted payload. Designing a deployment mechanism for something like this ought to be pretty fun, too.
e-FTW
New electron smell
Scott with the answers, as is often the case:
Can The Human Body Handle Rotating Artificial Gravity?
Ben W
Chess Grandmaster (Supervised)
Thanks for the link! It seems that ~3rpm is the upper limit for comfort without requiring specific adaptation, so a ~200m tether should be sufficient for 1G acceleration. (For more comfortable 1G @2rpm, a ~450m tether would be required.) Unanswered questions for the feasibility of this idea:
1. Will Mars-bound crewed Starships have the catching arms at all? Landing legs will be required to land on Mars for the foreseeable future (at least until Mars has its own Mechazilla, which presumably is a long ways off), but the landing legs for Mars gravity could be more lightweight than for Earth gravity, so catching arms might still make sense for the return trip and Earth landing. What fraction of crewed Starships would be expected to eventually return to Earth?
2. Will Starship require a particular orientation with respect to the sun for solar power, thermal considerations, and/or radiation shielding? For balanced insolation, the spin axis would want to point north/south out of the plane of the ecliptic, but for fixed solar panels it would want to point toward/away from the sun. Presumably during a solar storm Starship would want to stop spinning and point directly away from the sun; how long would it take to spin down the rotation, how much propellant required to spin up/down, and would there be a risk of tangling the tether?
3. If the tether had rungs like a ladder, could spacewalking astronauts use it to "climb" between Starships? Would this enable a method of evacuation in the event of non-catastrophic failure of one Starship? Or would it make more sense (and be feasible) for two Starships to directly dock to each other in zero-G to enable personnel/goods transfer?
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@scaesare
what an intriguing physics problem, factoring in gyroscopic precession et al.
remember the Shuttle mission, April 11, 1984, where they repaired the Solar Max satellite, and we got to see, in real-time, “live on tv” an tiny example of such? and it was only ?500? pounds.
not withstanding, the crew quarters are in the nose, so you would have to fool around near the engines, which you really depend on for safe landings, and hook up those together, not the noses.
Chesley Bonestell has a few paintings of Mars ships
Ben W
Chess Grandmaster (Supervised)
I would think that onboard gyroscopes/flywheels ought to be able to compensate pretty well for transient stability issues, without requiring propellant. (Some propellant would be required to spin both Starships up/down, but it might be enough to use ullage gas that would be bled off anyway.) It may depend whether Starship has any significant asymmetry in radial mass distribution. If so, there will be a most-stable and least-stable axis for spinning. (Envision a domino spinning; there are always two stable axes and one unstable axis. See e.g. Tennis racket theorem - Wikipedia) As long as a stable axis is chosen, or if it's possible to redistribute mass to make the desired axis stable, it should be ok. Presumably the "flat spin" axis (up-down when Starship is bellyflopping) would be stable.
I don't think there would be a need to "fool around near the engines". The tether attachment points (the load-bearing catching arms, already designed for this exact load configuration) are near the nose, with the noses pointing inward. That's a more stable configuration than noses outward, since most of the mass is near the engines. With a reasonably long tether, the whole Starship would be under similar centripetal acceleration. (Slightly lower in the nose, slightly higher at the engines.) E.g. with a 450m tether, if the engines were experiencing 1G, the crew compartment would be at around 0.85G. But the whole point of the idea is that the catching landing arms provide ready-made tether attachment points for a nose-to-nose spinning configuration; attaching anywhere else would require a significant structural redesign.
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The vehicle itself is designed to withstand massive launch loads, and so intuitively there wouldn't be much redesign required to support the contemplated tension loads in other places either. At least assuming cognizant attach point location and quantity, the individual loads at each location should pretty well be enveloped by the local structure's design. Maybe just some basic additional features to incorporate (or bolt on once underway) some kind of bracket.
Each vehicle would definitely require active stability control via wheels once in a steady state, as perturbations will introduce constant instability...solar pressure, dynamic mass movement within the vehicles, etc. And because over time wheels saturate with momentum, propulsion is imperative to desaturate. (Unlike something flying in the van Allen belts that can use torque rods to desaturate, the only practical way to desaturate wheels out there--even GEO--is some kind of propellant. )
Propulsion would of course also be required for initial positioning (some kind of 'fly them side by side' to hook it all up), initial spin up, and long term stability from various perturbations. Good news is the vehicle already has a propulsion system, and the contemplated use case would be a fraction of its fundamental design.
As a general rule of thumb, reaction based concepts like wheels (torque rods, gravity gradient, etc.) can only control the 3 attitude axes. An external input is required for full 6DOF control, and propulsion is really the only practical answer.
Ben W
Chess Grandmaster (Supervised)
The launch loads are compressive, and distributed through the thrust puck. Artificial gravity loads would be tensive, and would need some sort of distribution from the tether attachment points. In hindsight, Starship is already clearly liftable by a crane, so presumably whichever attachment points are already used for that, could be used for the tether, instead of the catching arms. Also presumably if they're strong enough to hold Starship suspended in midair over the launch mount for an hour, they're strong enough to hold indefinitely for artificial gravity spinning.
I think only the 3 attitude DOFs really matter for purposes of stability. The other three DOFs are displacement of the overall center of mass, which might be important for e.g. navigational course corrections, but not for realtime stability control. It's possible that the small propulsive maneuvers to initiate/terminate spin could be timed/oriented in such a way that they would assist course correction as a by-product, so the propulsion wouldn't be wasted.
Flywheel momentum saturation should build up slowly and predictably enough that it may be possible to balance/reverse it to some extent using the same mechanisms that brought it on. (E.g. tilting solar panels.) But either way, offsetting this should take only a tiny amount of propellant in the scheme of things.
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In this shot from Tim Dodd's Starbase tour you can see the relatively beefy attachment points used for lifting Starship:
Given the discussion is around providing artificial gravity, we are only talking 1G loads for starship without a full fuel load, so those would indee seem to be capable.
My earlier musing about lateral acceleration had more to do with the challenge of getting the rotating evenly around a central axis evenly in a stable "orbit". It seems to me you'd have to:
1) Park the Starships nose-to-nose
2) Attach tethers
3) Use thrusters to back away from each other, fully extending the tether
4) Use side thrusters on each ship to begin moving radially around a central point
#3 would be tricky... you'd have to accelerate then stop relatively precisely to avoind any snap-back one you get to the end of the tether, or yanking the other ship around
#4 seems even trickier: your acceleration is around an imaginary central axis with a flexible attachment point. Each ship would have to accelerate in a very synchronized manner, and with almost exactly identical acceleration in order to keep the tether straight and keep the orbital axis in the center of the 2 ships. It seems like even small variations in mass/thrust or timing between the two ships would set off oscillations that would be difficult to control.
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Likely there is also need for unmanned cargo Starships. Those doesn't need gravity or mind spinning. Most of tethering structures could be located not in imaginary central axis but in spinning and spinn controlling central cargo starship. That would keep manned starships structurally more simple.
number 4
it could be more than a bit tricky loading up the empty starships after you get the 2 spinning,
initial thought seems to me that loading fuel/passengers/cargo would slow angular momentum or if fuel sloshes around, induces unwanted oscillations, a bunch a passengers moving en mass to look out windows.
doing a gravity assist slingshot steals angular momentum from the larger mass
do a simple exercise
you know a sub c = v*v/r (centripetal acceleration equals velocity squared divided by radius)
you want 9.8m/s
example
”…A rotating space station is said to create “artificial gravity”—a loosely-defined term used for an acceleration that would be crudely similar to gravity. The outer wall of the rotating space station would become a floor for the astronauts, and centripetal acceleration supplied by the floor would allow astronauts to exercise and maintain muscle and bone strength more naturally than in non-rotating space environments. If the space station is 200 m in diameter, what angular velocity would produce an “artificial gravity” of 9.80 m/s2 at the rim?.”
9.8=v*v/100
980=v*v
v=31.3m/s
circumference is 628 meters so it spins @ about 3rpm
what i’m a bit unsure of, is the 2 Starships are about 120m long, you have a hypothetical teather 450m long, the starships each have a capacity of 100 metric tons (220,000 pounds)
so you are spinning 2, 100 metric ton more or less weights in a circle ~690 meters in diameter, nicely balanced, no wobbles, that are accelerated and decelerated up to speed.
you are going to need attitude adjuster jets and such, for spin up/spin down, and other stuff.
will there be any kind of gyroscopic precession that needs compensation and types
(ultracentrifuge explosions are kinda spectacular slamdances)
(there were folks who pointed out problems for Larry Niven’s “Ringworld” and wobbling but i don’t have those references but needing somewhat constant attitude adjustments from rim mounted jets)
you may also remember Ernst Stuhlinger’s ion drive ships to Mars, there was a Disney short about it in the late 1950’s,
december 4th, 1957.
mars journey starts at 40 minutes in
a newer one here on vimeo
they had an acceleration of 7x10 -5th G, about .75mm/sec/sec (you spiral out past lunar orbit in a little under 4 months, 115 days)(but acceleration is constant, so about 400 days to mars)deceleration from midpoint)(definitely not tau close to zero)
(there are also “beam riders” with a constant 1g acceleration where a pair of ground based lasers push ”solar sail” from start and finish points)(seem to recall folks working on a small version of that out west)
anyway, just musing on the weekend
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