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The Expanse Bad Science Roundup (Page 5)
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reader50
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Aug 28, 2022, 11:33 AM
 
Originally Posted by subego View Post
I still want an answer to what they’re using as reaction mass.
I think water is the main reaction mass, mixed with helium from the reactor. Either that, or straight helium after fusion.

In S1, Miller is snooping around the Ceres docks, and there's a near-riot. Martians are trying to stock up their water, and Belters don't want to top them up. Until Dawes says to give the Martians their water.

Water is an oxygen source for life-support, and a hydrogen source for the reactor. But they shouldn't need much of either in a closed ship - the only significant losses are reaction mass. And/or the hydrogen fuel to accelerate the reaction mass.
     
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Aug 28, 2022, 11:50 AM
 
Originally Posted by OreoCookie View Post
In what way are they weak?
Because “if you don’t do what we say we will stay and die in the tsunami” is an exceedingly bad negotiation strategy.
     
subego  (op)
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Aug 28, 2022, 12:14 PM
 
Originally Posted by reader50 View Post
I think water is the main reaction mass, mixed with helium from the reactor. Either that, or straight helium after fusion.

In S1, Miller is snooping around the Ceres docks, and there's a near-riot. Martians are trying to stock up their water, and Belters don't want to top them up. Until Dawes says to give the Martians their water.

Water is an oxygen source for life-support, and a hydrogen source for the reactor. But they shouldn't need much of either in a closed ship - the only significant losses are reaction mass. And/or the hydrogen fuel to accelerate the reaction mass.
My knee-jerk response is that squares poorly with the Cant’s shuttle. They only had enough O2 for one last pressurization, but enough reaction mass to get somewhere?
     
reader50
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Aug 28, 2022, 12:53 PM
 
Recall that moisture was accumulating on surfaces and people towards the end of the Knight. This indicates loss of dehumidification, and possibly loss of internal temp control. They're unable to salvage water from the air - a serious life support failure.

If the water tank was punctured, then they only have the oxygen and hydrogen that's already separated and in tanks. Enough spare oxygen to repressurize the ship once, and enough hydrogen to get somewhere before they're breathing their socks.

Side note - no spare oxygen is another reason why they couldn't just charge Alex's suit back up. Even if a recharge station still works, that oxygen is for refilling the ship.
     
subego  (op)
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Aug 28, 2022, 01:06 PM
 
If the water tank was punctured, then all their reaction mass would be gone though, right?
     
reader50
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Aug 28, 2022, 02:37 PM
 
If water is the reaction mass, that would follow. If helium is the reaction mass, then you only need the hydrogen tank.

The Epstein Drive is super efficient, but not impossibly so. I've read that bleeding plasma from a reactor at 100 million degrees or so would not be efficient enough. You need to harvest the energy, then accelerate reaction mass to near-lightspeed. That would give you the required efficiency. In which case helium might be the reaction mass, with water supplying the hydrogen fuel.

Water might be an optional add-on, to lower exhaust velocity. Such as in atmosphere, or maneuvering near a station. Hitting atmosphere with a near-lightspeed particle stream would generate X-rays at a minimum. Plus lots of secondary particles.
( Last edited by reader50; Aug 28, 2022 at 02:55 PM. )
     
subego  (op)
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Aug 28, 2022, 09:12 PM
 
Originally Posted by reader50 View Post
If the water tank was punctured…
I posit they’d either have multiple tanks, or if it’s a single tank, it would be one of the most armored components on the ship.

This is fuel, oxygen, and possibly reaction mass. If it shits the bed, everybody dies.
     
subego  (op)
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Aug 28, 2022, 10:12 PM
 
Originally Posted by reader50 View Post
Hitting atmosphere with a near-lightspeed particle stream would generate X-rays at a minimum. Plus lots of secondary particles.
Not to mention a rather large kaboom.
     
subego  (op)
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Aug 29, 2022, 10:00 AM
 
Originally Posted by reader50 View Post
If water is the reaction mass, that would follow. If helium is the reaction mass, then you only need the hydrogen tank.
I have enough respect for the show at this point to assume they ran some numbers, but I’m still (goddamn fucking) curious how much reaction mass they need. Especially for a ridiculous 20G acceleration.

Impossible to tell how big those fuel pellets are solely from that shot. They came across as ping-pong balls there, but judging from other shots with people looking into a reactor, it’s more like a bowling ball.

I’m wondering if there’s a clue in the color temperature of the exhaust.
     
subego  (op)
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Sep 1, 2022, 01:54 PM
 
Tow cable was drooping.

Also, when towing, get your face as close to the cable as possible.
     
subego  (op)
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Sep 1, 2022, 07:51 PM
 
I forgot ”Just Amos Things”.

Holden: I guess this means I can say I took you in a fight.
Amos: You can say whatever you want.


Also, Avasarala‘s closet of saris was kinda funny.
     
subego  (op)
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Sep 2, 2022, 06:34 AM
 
Question of the type that’s a pain in the ass to find an answer to without spoilers.

Which actor plays the Martian cop/crime lord? The one employing Draper.
     
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Sep 2, 2022, 01:10 PM
 
Paul Schulze as Esai Martin.
     
subego  (op)
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Sep 2, 2022, 04:06 PM
 
TY!

Remember him now from 24.
     
subego  (op)
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Sep 3, 2022, 02:08 PM
 
Oh, I forgot. More towing shenanigans.

Drone ferries over the tow cable to Naomi. It zooms towards her and then suddenly stops.

It would have needed to fire rockets into her face for that to happen, or at least a massively inefficient burn with all the nozzles flared out.
     
subego  (op)
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Sep 4, 2022, 12:44 AM
 
Well, that’s it for S4.

Our final bad science of the season is Ashford singing after he gets spaced.


Not bad science, but I’m disappointed I didn’t get to see the Roci have a showdown with the Edward Israel.
     
subego  (op)
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Sep 8, 2022, 01:29 AM
 
Started S5

reader50 spoiler space begins










Only got through three-quarters of E1. Very slow beginning. I waited a year for this?
     
subego  (op)
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Sep 12, 2022, 12:41 PM
 
Watched the end of that episode, and to be fair to it, they backloaded the best parts.
     
subego  (op)
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Sep 12, 2022, 04:55 PM
 
Originally Posted by OreoCookie View Post
Amos is much more interesting character than Animal Mother…
Pulling this out of the archives to complain.

I’m not sure it’s fair to compare the characterization of a supporting character in a movie to an ensemble main in a six season series.

I mean, Animal Mother’s entire character is in his name. He’s a vicious animal, who viciously protects what he cares about. If I had to encapsulate Amos’ character in two words, I could do a lot worse.

I should also add, though the characters are very different, Baldwin played Jayne on Firefly, which made me unconsciously connect them.


As an aside about naming characters…

Charlotte means “little and feminine”.
Sam is fundamentally a masculine name.
Miranda is (among other things) a legal concept.
Carrie carries the show.
     
subego  (op)
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Sep 22, 2022, 11:45 AM
 
It’s kinda lost my dad. For the first time since we started, last night he was like “let’s watch something else”.
     
Thorzdad
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Sep 22, 2022, 01:06 PM
 
Originally Posted by subego View Post
I should also add, though the characters are very different, Baldwin played Jayne on Firefly, which made me unconsciously connect them...
Miranda is (among other things) a legal concept.
Miranda is also the planet where the Reavers were accidentally created by the Alliance in Serenity, which would also be a Firefly hook.

That said, you don’t create a character named Miranda in a drama and not be aware of work by this guy named Shakespeare.
     
subego  (op)
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Sep 22, 2022, 01:52 PM
 
Sex and the City was a comedy tho.

I’m not that familiar with The Tempest. Are there obvious character parallels? With SitC I always drew a straight line between “Miranda” and her being an attorney.
     
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Sep 22, 2022, 02:32 PM
 
Miranda is a moon of Uranus.
I have plenty of more important things to do, if only I could bring myself to do them....
     
reader50
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Sep 24, 2022, 02:10 AM
 
Originally Posted by subego View Post
Sam is fundamentally a masculine name.
So a girl named Samantha would go by the nickname ... Saman? Sounds like a fish dinner.

ps - I don't blame people for their birth names. Blame their parents.
     
Thorzdad
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Sep 24, 2022, 05:07 AM
 
It’s actually kind of cool how you can give a woman pretty much any traditionally “masculine” name and it actually works.
     
subego  (op)
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Sep 24, 2022, 12:49 PM
 
Originally Posted by reader50 View Post
So a girl named Samantha would go by the nickname ... Saman? Sounds like a fish dinner.
Fundamentally, not exclusively.

If there’s no other context, I posit most will assume a Sam is male.
     
subego  (op)
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Sep 24, 2022, 12:51 PM
 
Originally Posted by Thorzdad View Post
It’s actually kind of cool how you can give a woman pretty much any traditionally “masculine” name and it actually works.
Like Ralph.

     
subego  (op)
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Sep 24, 2022, 04:48 PM
 
Originally Posted by reader50 View Post
Blame their parents.
My uncle’s first name is Thomas.

His last name is also Thomas.
     
ghporter
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Sep 24, 2022, 07:15 PM
 
I have encountered several women named "Michael". And my first name, Glenn, is also a relatively common name for women (Glenn Close, for example). An OT classmate's grandmother was named Glenn, and my classmate got her middle name from her.

And dang it! Now I have the SNL "Pat" character stuck in my head. Argh!

Glenn -----OTR/L, MOT, Tx
     
subego  (op)
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Sep 24, 2022, 08:16 PM
 
The current grand dame of Chicago gossip columnists is Mike Sneed.
     
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Sep 24, 2022, 09:21 PM
 
Originally Posted by subego View Post
My uncle’s first name is Thomas.

His last name is also Thomas.
Are the parents in jail for child abuse?
(That’s really dumb. People whose last name is also a first name are at a natural disadvantage, but doing this to a child is a crime. How often did that poor person have to explain that he doesn’t have a stutter or a tic, that Thomas is really first and last name?)
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Waragainstsleep
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Sep 24, 2022, 09:21 PM
 
Originally Posted by subego View Post
My uncle’s first name is Thomas.

His last name is also Thomas.
What sound does he make if you hit him?
I have plenty of more important things to do, if only I could bring myself to do them....
     
subego  (op)
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Sep 24, 2022, 09:45 PM
 
Originally Posted by OreoCookie View Post
Are the parents in jail for child abuse?
(That’s really dumb. People whose last name is also a first name are at a natural disadvantage, but doing this to a child is a crime. How often did that poor person have to explain that he doesn’t have a stutter or a tic, that Thomas is really first and last name?)
The family name is originally something like Tomasunas, so it’s possible his last name at birth wasn’t Thomas. I’m not sure of the timeline, but somewhere along the way my grandparents anglicized across-the-board. For years I thought my mom’s maiden name was Thomas. She was definitely born before it happened.
     
reader50
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Sep 25, 2022, 01:43 AM
 
Originally Posted by subego View Post
Tow cable was drooping.

Also, when towing, get your face as close to the cable as possible.
Agree, small errors in the closeups. They should have countered the cable droop with some wire supports erased in post. The faces thing is practical filming - gotta see the cable, and their faces. The simplest way is if the actors constantly study the tow cable for insects.

Originally Posted by subego View Post
Oh, I forgot. More towing shenanigans.

Drone ferries over the tow cable to Naomi. It zooms towards her and then suddenly stops.

It would have needed to fire rockets into her face for that to happen, or at least a massively inefficient burn with all the nozzles flared out.
Disagree. A cable or chain has no compression strength. If you stop the end, the rest keeps coming. It stops when you tension the reel at the other end. So it's correct if the ferry drone does not brake.

Bonus points: the Roci is applying tension to the tether off-center to route past the main engine. So it needs to thrust sideways at the bow, to prevent being torqued towards the cable mount. And the attitude jets are indeed firing during the tow sequence, in the correct direction to counter the off-center torque.

Minor nit: why not have the Roci fly sideways, pull on the cable from the cargo bay, and use the side thrusters exclusively? No roller tower, and the tether pulls from the center of mass, so no inefficient side thrusting needed. Presumably to reduce atmospheric drag on the Roci, and because it would look funny on screen. Perhaps the rear thrusters are slightly more efficient. But the minor savings from reduced drag are probably lost many times over to the bow thrusters keeping the Roci straight against the off-center torque.
     
subego  (op)
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Sep 25, 2022, 12:19 PM
 
I’m not sure I understand. Are you arguing the tension on the cable stopped the drone?
     
reader50
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Sep 25, 2022, 02:08 PM
 
A rope / chain / tether is a loose object, not solid. It will deform freely. Imagine you are lowering a rope from a balcony. When the lower end touches the ground, it will "brake" to a halt. Does this stop the rest of the rope from rolling down? No, the rope will not stand up. Rather, the rest of the rope keeps coming, so long as you keep feeding it from above. You end up with the rope piling up on the ground, until you stop lowering more rope.

In the balcony example, there is a continuous force pulling down (gravity). In a space tether, there is only inertia. But you get the same result. Stopping the leading end doesn't stop the rest of the rope. All the parts after the end will remain in motion, piling up or rolling past the end that has stopped. The rope never stands and stops itself.

So you have to apply braking force on the opposite end to control it. In the balcony example, the person lowering the rope stops the motion when the ground is reached. The person on the ground cannot stop the rope from coming.

The drone on the end is perfect for pulling, but irrelevant to braking. Think of it as an inertial weight on the leading end of the tether. When the source guys brake the tether to stop its motion, the drone is decelerated to a stop too.
     
subego  (op)
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Sep 25, 2022, 03:13 PM
 
The drone would absolutely need to fire rockets to brake, but I had it wrong they’d fire into Naomi’s face. Counterintuitively, the drone has to accelerate towards the Roci to brake.

If we ignore things like the tether stretching, no momentum is lost when the tether goes taut. The tether redirects it all in the opposite direction.

Without rockets, the drone would get to the end of its rope and then the rope would pull it backwards at the same velocity.



I think.
     
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Sep 25, 2022, 09:22 PM
 
Originally Posted by subego View Post
The drone would absolutely need to fire rockets to brake, but I had it wrong they’d fire into Naomi’s face. Counterintuitively, the drone has to accelerate towards the Roci to brake.
No, it would not need to fire rockets. In fact, if it did fire rockets, the cable would continue traveling in a straight line and hit the drone — and get right into Naomi's face. That's because you can't push on a shoe string or a cable, you can only transfer force in tension.

So what I assume happened is that they slowly engaged the brake on the winch. That did two things: it not only increased cable tension, but it coupled the mass of the entire ship to the cable. Total momentum is conserved, but momentum (for slow, non-relativistic speeds) is mass times velocity, if you increase the mass by 1,000x, you decrease velocity by 1,000x (I of course don't know the “real” weights of the drone and the ship, but the ship is massively bigger than the drone). For all practical purposes the drone comes to a standstill.
Originally Posted by subego View Post
If we ignore things like the tether stretching, no momentum is lost when the tether goes taut. The tether redirects it all in the opposite direction.
Momentum is not lost, but it is distributed across the drone and the entire ship.
Originally Posted by reader50 View Post
In a space tether, there is only inertia. But you get the same result. Stopping the leading end doesn't stop the rest of the rope. All the parts after the end will remain in motion, piling up or rolling past the end that has stopped. The rope never stands and stops itself.

So you have to apply braking force on the opposite end to control it.
Yup, that's it.
And since the other aspects of towing are included in the episode (e. g. carefully applying braking to make sure the cable does not snap), I reckon the writers of the episode have thought of this quite carefully.
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subego  (op)
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Sep 26, 2022, 12:10 AM
 
If I throw a ball in zero-G, both myself and the ball go in opposite directions.

Now attach a rope between myself and the ball. Neither of us stop when the rope becomes taut, we reverse directions and meet back at the point where I initially threw the ball.
     
reader50
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Sep 26, 2022, 12:25 AM
 
Your example rope is springy - it will stretch a bit, then contract (pull) back to the real max length. The outcome from the example would depend on how hard you apply the brake to the rope. Apply it gently, and the rope (with attached ball) keeps sliding through your hand, at slower and slower speeds. Presently coming to a slow halt without stretching. So rope and ball remain where they are. Apply braking force suddenly, the rope stretches under the tension, then contracts enough for the ball to come back towards you.

With a metal space tether, there is little elastic effect, and they brake gently to prevent that. Anytime you work with long or massive objects in motion, you brake gently. So the large inertia won't ruin your day. They probably also play out small amounts of spare tether from the winch to cushion-out sudden tension events.
     
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Sep 26, 2022, 03:46 AM
 
Originally Posted by subego View Post
Now attach a rope between myself and the ball. Neither of us stop when the rope becomes taut, we reverse directions and meet back at the point where I initially threw the ball.
You won't reverse direction, but if the rope is attached to a large mass, the ball and the rope will essentially come to a stop — if you brake gently. I write essentially, because you technically impart the momentum of the ball and the rope to the conglomerate of the big mass (= the ship), the ball and the rope. Like I wrote previously, if the mass of drone and cable are a factor 1,000 times larger than the ship, then the speed of drone, cable and ship taken together will be 1/1,000th of drone and cable.

Reader's explanation is spot-on. The brake on the wrench resists the free motion of drone and cable, i. e. you are applying a force to drone and cable that points back towards the ship the two are tethered to. Because it is a cable, and you can only apply force in the direction that increases tension.

If you brake the wench very suddenly, then the drone will bounce back. Think of a tennis ball caught in a hand vs. throwing a tennis ball against a rolling train — in the second case, the ball will be reflected at twice the speed of the train (to good approximation). Total momentum of drone, cable and ship is still conserved even though momentum of the individual constituents changes.

This explanation changes once you consider the two ships that are tethered together: it is no longer true that one ship is much, much heavier than the other. Also, braking suddenly here would be fatal for the cable, and indeed, this is what, sorry for the pun, creates a lot of the tension throughout this episode.
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subego  (op)
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Sep 26, 2022, 06:32 PM
 
Originally Posted by reader50 View Post
Apply it gently…
Originally Posted by OreoCookie View Post
If you brake gently…
Absolutely!

I posit applying gentle braking force solely by means of varying the rate the tether plays out is a non-trivial task. The rate the tether needs to play out must almost exactly match the changing velocity of what it’s attached to. Any deviation and the tether is either providing too much braking force or none at all.

In contrast, if the drone is using rockets to pull against the tether, the velocity of the drone inherently matches the rate the tether is played out. Once the velocity is zero, then the gentle braking occurs by slowly turning down the rockets.

With the ball, which has no rockets and is now attached to a thin, steel cable so there’s no stretching. My hand will almost inevitably provide more force than it should, the cable will play out too slowly, and the ball will start flying back towards me because the braking maneuver was too sudden.

With the drone, and an AI calculating it, we might get in the zone, but it’ll still oscillate between too much braking and no braking. Why bother when the drone has built-in rockets?
( Last edited by subego; Sep 26, 2022 at 07:57 PM. )
     
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Sep 26, 2022, 08:40 PM
 
Because the rockets in the drone wouldn’t brake the cable. Instead, the cable would continue traveling in a straight line, slamming into the drone and eventually Naomi’s face.
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subego  (op)
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Sep 26, 2022, 08:44 PM
 
Another way to put this is use the drone to create artificial gravity holding the tether taut. Like it was the string in a plumb line.

Reel out the tether to the required length, then slowly shut off the artificial gravity.
     
subego  (op)
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Sep 26, 2022, 08:46 PM
 
Originally Posted by OreoCookie View Post
Because the rockets in the drone wouldn’t brake the cable. Instead, the cable would continue traveling in a straight line, slamming into the drone and eventually Naomi’s face.
What brakes the cable is stopping the winch.

The drone doesn’t slam into Naomi’s face because it’s leash isn’t long enough.
     
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Sep 26, 2022, 10:27 PM
 
Originally Posted by subego View Post
What brakes the cable is stopping the winch.
Now you are conflating two scenarios: if you engage the brake in the winch, not only the cable will stop, but also the drone (assuming that the tethering point does not break) as the drone is tethered to the cable and the force due to the drone wanting to continue increases tension in the cable. So in that scenario, the drone does not need any thrusters to slow down — which was reader's and my argument.

You can in fact do this experiment on earth to very good approximation: create a level track for a sled. Attach a string to the sled and attach the other end of the string to a wall or something that is much, much heavier than the sled. Make sure that your tether points and the string are sturdy. Use your finger to accelerate the sled on the track. When the string is pulled taut, it is “reflected”, i. e. violently pulled backwards. If you neglect friction and assume that the mass the other end of the tether point is attached to is infinitely heavier than the sled, the speed of the “reflected” sled will be the same as before, it will just travel in the opposite direction. This is the scenario that reader explained. Note that gravity does not enter the equation here if the track is perfectly level.

Now do the experiment where you replaced the other fixed tether point by a winch that you can slowly brake. Feel free to modify this experiment. But you can really do these experiments on earth to good approximation. E. g. you can perform them in vacuum and use superconducting magnets to minimize friction.
Originally Posted by subego View Post
Another way to put this is use the drone to create artificial gravity holding the tether taut. Like it was the string in a plumb line.
You don't need gravity to keep the cable taut, all you need to do is wind out the cable at the speed of the drone. In fact, we know from General Relativity that acceleration due to gravity is the same as acceleration due to other forces in terms of its effects.

However, I don't think it is particularly desirable to have a lot of tension in the cable when it is not needed. Not only might the drone's thrusters have to work against the brakes if the speed isn't matched perfectly, but cables under tension are very dangerous. You store a lot of potential energy that could be released violently.
Originally Posted by subego View Post
Reel out the tether to the required length, then slowly shut off the artificial gravity.
What problem are you solving with that exactly? Artificial gravity would just act like a thruster. The direction of the thrust would depend on where you create the artifical gravity, i. e. in front of or behind the drone.
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subego  (op)
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Sep 27, 2022, 02:58 PM
 
What we want to do is have the drone at a specific position relative to the Roci, and with zero velocity relative to the Roci.

As you both correctly pointed out, this must be done gently. If it’s not gentle, the tether will translate the velocity of the drone in the opposite direction, just as in your first experiment. In fact, in zero-G with no friction, this will happen no matter how gently the braking occurs. The best we can hope for is the brake occurs gently enough the velocity reversal is negligible.

Now take your second experiment. What I’m arguing is applying exactly the force needed to the string to stop the sled at a precise location on the track with no velocity rebound like in the first experiment is difficult.

If I use too little force, the sled overshoots the target. If I use too much force, I get rebound. Also note the amount of force needed changes throughout the braking maneuver. As I said, this will be difficult to pull off.

Now, add thrusters to the sled. This makes controlling both the velocity of the sled and the point it stops on the track trivial. The velocity of the sled will automatically match the speed the tether is played out, and the distance the sled travels down the track will precisely match the length of played out tether.
     
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Sep 27, 2022, 05:02 PM
 
A situation with negligible rebound is good enough - the tether gets to Naomi, so she can snap it to the Roci's tether. My guess is the winch side didn't brake it to the final stop - allow a tiny continued feed so Naomi has enough play to connect up the ends. They apply tension after it's connected to eliminate that play.

So the science holds up for the tether delivery scene. A pity they didn't do the extra supports for the cable in closeups, to hide the sag.

btw - it's skipped over in the episode. I think both ships ran spare metal through a 3D printer, to create the tethers, as well as most of the hardware on each end. I don't think either had lengths sitting around. The Belter ship had more metal they could spare (bigger ship), so they made most of the tether.

New science continuity issue: when they ditched the tether, it burned up almost immediately. It wasn't deeper atmosphere entry - the two ships didn't develop a plasma envelope. I think it was exposed to the Belter ship's drive plume. The burn direction and timing are right, but drive plumes are highly directional. I don't think there's enough side spillage to burn metal. And it seems like we've seen vessels that close before, without taking sideways burn damage. Best answer I can think of is the Belter ship has a shitty engine.
     
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Sep 27, 2022, 05:07 PM
 
They mention the tether is made from the Belters’ cargo nets.
     
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Sep 27, 2022, 05:09 PM
 
Originally Posted by reader50 View Post
My guess is the winch side didn't brake it to the final stop
That would require rockets in Naomi’s face, no?
     
 
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