The Expanse Physics is Kind of Right With Circling Ships

Check out Dementikko's video!
• The circular trajector...
If you want to mess around with the code:
github.com/Che...

[@RyanRidden]

Thanks to Demetikko I don't have more Kerbal's stranded in deep space! Check out their video: kzbin.info/www/bejne/f2aodqaXiZyZmK8

[@jls1337]

What if the thruster not only acted along the mid axis but also made she ship rotate on its long axis? Like a spinning top or a coin. Then, you know how when the spinning top or coin don't rotate fast enough they start to wobble? Could the ship experience similar wobbling, changing the direction of the main thruster and thus fly in the circular trajectory?

[@felasowande879]

Its actually kinda rare and the exception that the expanse gets the science wrong but regardless, I love how this show sparks physics discussions like this.

[@springbloom5940]

Accurate and 'right' are not the same thing.

[@scottdorfler2551]

There's actually another physical inaccuracy in the same seen. The Razorback is shown from a distance in the wrong orientation while preforming a breaking burn. I also don't get the motion of the stars behind Naomi during her close up after jumping from the Chetzemoka.

[@jamiesettle4348]

I learnt more about physics in this single video than I have in the entirety of high school so far

[@RyanRidden]

And we made a computer do all the hard stuff!

[@michaelmayhem350]

My high school didn't even offer physics 😔

[@Great_America]

Apparently you weren’t paying attention in school. I knew these basic Newtonian physics in the 9th grade 😜

[@MikeAben]

It's awesome all the great discussions that can fall out of something like this. I was a little perplexed why the show went here. First, if the ship were moving in a circle around Naomi you can still get to her by approaching from outside the plane of the circle. Second, dramtically, didn't we already have enough? She was hurtled out of the ship in a suit with no air. Would Bobby and Alex see her? Would they get to her in time? The circling ship just doesn't seem necessary. I think it's a situation where it feels physicsy and they just got it wrong. Like Alex's slingshot ride through the Jovian system from season two.

[@ronmani9476]

I like to think of myself as a reasonably smart guy...... then I come here. Its like being in a class where you kinda get it but your totally hoping the teacher doesnt ask you a question lol.Thanks for the informative videos.

[@thomasmain5986]

That's the difference between Star Wars and the Expanse, in the Expanse you have mathematics and physics that are used to calculate the accuracy of the science in the show, in Star Wars you have Han Solo who will shoot you in the face with a blaster, if you question the science in Star Wars.

[@amosk3938]

It's science fiction plus star wars is good.

[@bagindov]

lmao

[@eds1942]

“take the professor to the back and plug him into the hyperdrive.”

[@ermwhatdaheck]

@@amosk3938 No one here is saying Star Wars is bad bud lmao

[@douglaslinemanful]

I believe Hans Solo would only say “That’s not how the Force works!” 😜

[@big_little_drift]

So the razorback is matching velocity with the chet to prepare to dock, so if that nav system is in relative velocities, then it works ignoring the single truster rotating the ship 90 degs across 2 planes.

[@RyanRidden]

The concept is right only the presentation was off

[@scalien225]

Thank you. This was what my clumsy comment was trying to indicate. I appreciate all your explanations and was left scratching my head after the last video how explain why the circle was there. Reference frames are a pain when they do not line up.

[@i.3315]

Hi Ryan. I love the Expanse show. Thank you for sharing your knowledge. 💙

[@RyanRidden]

It's a great show, I'm glad you like learning about the physics behind it!

[@CircusOfFive]

Its great that The Expanse series allows us the opportunity to even talk real physics as most sci-fi these days only allows us to talk about magic.

[@geraldwatts5492]

Yea, no hyperspace, no FTL, no spore drive. Just physics!

[@thomasb1889]

@@geraldwatts5492 Well, there is the gate and please don't mention that Star Trek abortion called Discovery. At least Picard was dealing with the very Trek question of what is life.

[@devinthierault]

@@thomasb1889 Well not even the gate really violates laws.

[@thomasb1889]

@@devinthierault Very true

[@travcollier]

@@devinthierault Yes, the protomolecule stuff breaks the laws of physics. Some characters say pretty much exactly that when Eros starts accelerating. That was actually pretty beautiful IMO. Instead of doing some hand-waving technobabble, the characters in universe just had to accept that their understanding of physics was woefully incomplete and there was a lot to learn. PS: The hyper-efficiency of the Epstein Drive is pretty much the only big "magic" technology humans understood in the Expanse. And that is fine because they actually explore the implications of that technology being applied to lots of things instead of just using it to overcome one specific limitation. There are some other minor things like the autodoc, general anti-cancer meds, ect., but nothing too glaring or universe shattering. The protomolecule was universe shattering Clarketech... sort of key to the plot.

[@Scooper910816]

Hello Ryan! Just stumbled upon your channel a week ago, and I'm really happy I did! Great content, super presentation, pleasant voice, interesting science. Keep it up!

[@tonycrabtree3416]

Any, I’m pretty sure that when we reach space travel at the level of the Expanse that advanced navigation and telemetry guided thrusting means space ships are no more difficult than usdriving the modern car to the humans of the time in the Expanse. IOW, none of us care about the math of anti-lock brakes or electrical signal to the fuel injectors. Just that it is there.

[@jdmills123456789]

I was thinking about this during your previous video- just didn’t have the mathematical eloquence to describe it, so thank you!

[@pi.actual]

I think that without the math it's much simpler. The side thruster puts the ship into a constant rate tumble. When Naomi jumps off she is no longer under acceleration, her velocity is now fixed. The ship, as it tumbles is under acceleration in the initial direction for 180 degrees and deceleration in that vector for 180 degrees. They cancel each other so it's sum velocity is also fixed. It will circle Naomi but not in a spiral as people are imagining. It will lead and lag in a flat plane. In other words, it would work.

[@georgelionon9050]

Except there is no way for Naomi to get in the center and stay there. She would fly of tangentially, well she could counteract that tangetinal velocity by the intial jump (a human (as I for example) can jump stronger than 1g otherwise I could never jump up, only on earth, gravity catches me again). But if she does that, she gets hit by the ship on it's next rotation. She could even jump off in a way she would slowly move off into the center of circle.. However, why would she do that? She is supposed to me smart ;)

[@pi.actual]

Yes, it would be nearly impossible to end up in the exact center but if she were to step off the ship at the exact moment the side thruster fired she would be close. Bear in mind that the ship is accelerating so stepping off of it would be relatively the same as jumping off a bridge. The ship would accelerate away from her and veer off in the direction of the tumble until it had turned 180 degrees at which point it would decelerate relative to her and she would pass it. As it reached the 270 degree point it would begin to move back towards her and accelerate back to her speed then at 360 degrees it would begin to pass her on the opposite side.

[@leovin00]

To make the situation sound even more plausible, you can’t be certain that the brief thrust to the side was made perfectly in one direction. If there was some irregularities in that thrust (if the ship was spinning during the short bit of thrust for example) you’d have some kind of weird circular motion in more than one plane

[@RazorSe7en]

My head is spinning with all these physics, but fascinating nonetheless! I very much enjoy your videos regarding The Expanse, keep them coming Dr. Ryan.

[@zupmine]

So here is the thing, you actually can't create circular motion by firing an engine and then making it turn, in most cases it will simply make that jumpy shape you showed in the video. For circular motion to take place, the force HAS to be applied towards the center of the circle (elipse). This can be done if the spacecraft starts with an initial velocity and then fires its engine towards a specific location (Cannot be in the same direction as the initial velocity), then as it begins to turn it adjusts its direction such that it continues to point towards that same location. For this to happen there would need to be a very specific ratio between the initial velocity, the force applied by the main engine and the torque applied by the side engine. If at any moment the force deviates away from the chosen center location, it will NOT travel in circular motion. Note: If you look closely you can actually see that the spaceship on the KSP video you showed is always pointing straight towards the kerbal, which I will say from personal experience, ain't easy to do!!

[@dsdy1205]

Not really true. If your ship is spinning at a certain angular velocity, it IS definitely tracing a circle, but only in the reference frame where the angular velocity matches the radius of the potential circle as you've pointed out. Keeping in mind that in the Razorback you have maneuvering capability and can really inherit any reference frame you like, it would make sense that Alex would select the frame of reference that generates circular motion.

[@DrakeCaesar]

Naomi's trajectory after she jumps would be a tangent to the circle, unless she jumps with a specific force at a specific angle, so at least hypothetically, if her legs had super strength, she could end up on a trajectory that would trace a chord or a diameter of the circle. How much force would she have to put in such a jump tho?

[@kyelangrehr183]

If you consider the ship would still put an uneven gravitational pull on the subject it my be possible for them to come to rest in the center at rest in the reference frame he described. It would all depend heavily on the mass and conditions so you cant actually wave that info away for simplicity. It might be doable with human strength as you can simply decrees thrust and rotation period in tell it is manageable you could do the calculation for something as week as a flea. all you would have to do is using the center reference frame jump with a force that will cancel the angular momentum completely and give your self a nudge of x force that will come to rest in the center after being slowed down by the uneven gravitational field applied by the ship. but to be fair that kind of set up would probably take a literal eternity for realistic subject and craft masses as gravity is pretty week.

[@ZeroGravitas]

@Dominik Cisár - Yeah. If she jumped counter to the ship's pseudo-orbital direction, with exactly the same (but opposite) speed, she'd effectively stay in place. So the ship would hit her the next time around. But if she also had a little 'upwards' velocity component, towards the centre of the 'orbit', she might very slowly transit the centre of that circle. So she could be said to be 'stuck' in the middle, for a time. Certainly longer than her breathable air. Plot plausibly viable. On-screen diagram definitely BS.

[@hampusastrom8190]

Exactly my thought, I tried plotting her trajectory assuming her jump strength is negligible in my fork of the repo: github.com/HampusAstrom/Chetzemoka_path feel free to explore what the parameters vxn and vyn would need to be for that to happen (It's not too hard to find).

[@schneider90000]

Well, a human jumping can provide at least 1g of acceleration momentarily.. So IDK if one would need need 'super strength'

[@berlindude75]

Didn't she run before jumping to avoid the giant exhaust plume? As depicted in the show it looked as if she was jumping away from and thus out of the corkscrew trajectory of the ship. And with that initial force from running she would keep moving away from the ship continuously?

[@jadli814]

Great stuff there! For the next videos, I think it would be very interesting if you looked into the other few instances of "controversial" physics being used in the Expanse... Such as when in S02 Alex did the maneuver around Jovian moons to get into Ganymede without using the engine (the scene was obviously fast forwarded, but still many things to look into), or you could for example look into when in S03 E3 or E4 the UN destroyed the secret nuclear MCRN bases ... PS: thanks for sharing the python script, might have some fun with it in my own astrophysics studies :D

[@andrewxu3602]

The Season 2 Jovian moons maneuver was something the showrunner apologized for.

[@zariumsheridan3488]

No shame in admitting you got something wrong initially (BTW so did I, in this case). Good job with this analysis and the math :)

[@SteveBurnap]

There was a great old space flight simulator called "Independence War" that used realistic physics. It was fun because the tactics you had to use were nothing like what you normally see in games that just translate air combat into space. One of those tactics was to approach at a slight angle, then at the right moment, turn towards the target with thrusters on. This kept your guns pointed at the target while you basically orbited the enemy ship.

[@tedarcher9120]

Yes, Niomi would fly away from the circle at the initial velocity of her jump, but the acceleration of the ship at 1g will make the circle so big she wouldn't have time ro fly away from it

[@ArnandKularajah]

Not if she was jumping at right-angles to the direction of thrust at the moment of separation. She would have some combination of the thrust of the rocket and her jump acceleration at right-angles to the thrust of the rocket at that moment.

[@sam2753]

I never thought I would be coming to KZbin to learn orbital dynamics and astro-navigational computations...

[@Xanman64-p6q]

The odds of a single thrust making this happen would be tiny, to say the least. In essence, you are using your main engine to duplicate the acceleration of gravity you would experience in a circular orbit around a planet. It has to point inward to your original velocity vector and be perpendicular to it, but your maneuver would be done while constantly accelerating. If not, you get a spiral. Like to see someone do that in KSP.

[@edmcguirk8603]

Not really, any sideways thrust will create a constant rotation of the ship. From that point forward the ship will have no choice but to travel in a circle that is moving forward at a constant velocity. (a spiral is a circle moving forward at a constant velocity except the axis of rotation is at an angle not perpendicular to the original motion - in this case the axis would be perpendicular unless there were two or more sideways thrusts ) The rotation period of the ship is the same as the circle period of the ship. Every acceleration form one side of the circle will be exactly canceled by the acceleration from the other side of the circle. The only difference will be that the size of the circle which will depend of the size of the sideways thrust. The size of the circle will be the same as a rotating space station with 1/3G and the time for the ship to make one rotation. The path of the center of the circle will be pointed in the same direction as the ship was pointed when the sideways thrust was executed, just displaced off to the side by the radius of the circle.

[@Xanman64-p6q]

@@edmcguirk8603 Talking about the original velocity vector and the graphic as shown. No way a single side thrust makes the motion depicted happen. The original velocity vector would turn into a 2D spiral on some random plane depending on what side the thruster was on. It in no way could it become a helix around the original central line. The velocity vector would become a curve of constantly decreasing radius (spiral) and eventually settle into a moving circle. Add a temporary thrust line (1D) to a straight acceleration line (1D) and you get a 2D motion, not a 3D spiral (helix) as shown in the show. The center of the circle would still have a forward motion, but that line wold be in the same plane as the circle, not perpendicular, and definitely not line up with the pre-thrust motion, giving the track a sort of curlicue appearance like you get from a point on the edge of a wheel rolling down a hill. Also, the settling out of the circle would take some time and likely have a number of "overshoots" as the acceleration and momentum found the balance point. Now, if by some oddity they mount a thruster to produce rotation on 2 axes at the same time, the motion would be more complicated but the result would still not come close to the graphic - more of a 3D curlique. Not that they would design a thruster to do that. Maybe if it was damaged and out of alignment I guess.

[@edmcguirk8603]

@@Xanman64-p6q Good point that you cannot add two vectors and get a result outside the original plane. I said the axis of actual (not depicted) rotation would be perpendicular to the original path. Any depicted spiral would not have an axis of rotation perpendicular to the original path. I agree that the show's depiction is not possible with 1 sideways thrust. 3 thrusts could do it but not one (1-y direction 90 degrees, 1-cancel y direction, 1-z direction). The direction of the resulting center of the constant velocity circle (spiral) would be in some direction I cannot calculate but it would not be in the original direction unless the 90 degree rotation and cancellation was near instant. The transition from linear acceleration to constant velocity rotating circle would occur in the first 90 degrees of rotation. Those first 90 degrees would include a sideways thrust that is not cancelled by the opposite side of the circle. So, the path would NOT be in the same direction as the original ship's path as I said, it would be some angle dependent on the speed of the rotation. However whatever path the center of the circle was following at the 90 degree point would be the new constant velocity path.

[@bobthemathcow]

The single thruster firing would have a hard time making the change in attitude to start the spiral trajectory, but the display on the Razorback is correct IF it is displaying both ships in a heliocentric reference frame. The Chet started on a powered trajectory but lost its forward acceleration when it entered the spiral, so is making a circular path around the now ballistic trajectory that it was making at the moment the thruster fired. This would create the spiral trajectory that we see in the Razorback's display.

[@evilbeardedman]

Random youtube suggestions on the Expanse videos bring me to all the best channels.

[@briani4959]

So its like you stretched out a spring and looked through the end of it, it would still look circular from that view point but if you looked at it from the side you'd see a spiral. Right?

[@Yora21]

I think so. The path of the ship is simply a corkscrew or spring shape. The holo diagram of the course looks weird because the several loops of the spring are that close together. But since the ship still keeps going in its original direction at its original speed, I think the spring should actually look very stretched out. I don't see how you can get such big rings that are this close together. It looks wrong.

[@benbunch4159]

@@Yora21 sure but we don't know how their UI works. It might compensate for the relative reference frame based on the differences in the speeds of the ships etc.

[@ghislainbugnicourt3709]

@@Yora21 There are only 2 thrusters involved and both are in the same plane including the center of gravity, so the motion would actually be in 2D. The display is definitively wrong.

[@mmathman]

To get the corkscrew motion and put Naomi drifting through the centre of rotation, she has to cut the main drive, rotate the ship 90 degrees away from the direction of motion with a burst and counter-burst, put the ship into a tumble on its short axis parallel with the direction of travel, fire up the main thrusters, then leap from the nose in the direction of thrust. She will tumble at the same angular velocity as the ship if she does not counter the motion, but she will pass through the centre of rotation. That does require cutting off the drive and three maneuvering bursts before restarting the drive, which of course, the show did not do. You could do it with two maneuvering thrusts, but the second thrust would not be coplanar with the first.

[@beny874]

Its fascinating seeing the two trains of thought and understanding of the same concept come together. That being those with a practical or abstract understanding, and those with a theoretical understanding. I was immediately confused when it was said it doesn't work, because visualisation all the vectors, angular velocity and rechecking my assumptions, it still made sense. My final visualisation was exactly what old mate did and picture it in Kerbal Space Program. But as old Ben Kenobi was said, "what I told you was true, from a certain point of view". Frame of reference is everything. The Expanse's visual display wasnt from a fixed frame from the razer back, but rather two frames mushed in one. The first one was the motion of the barycenter of the vessels circular motion, the second being the non rotating frame of the vessels motion around the barycenter. Like, imagine the differences of plotting the motion of a satellite in a heliosyncronis earth polar orbit with respect to a non rotating earth, vs plotting its motion with respect to the Sun. With respect to the sun it would look like a spiral around earths flat orbital trajectory.

[@beny874]

I'll add. For my Kerbal nerds out there. KSP doesn't model reference frames correctly since it uses patched conics. Try out the Principia mod, a mod that changes KSPs physics to an N-Body simulation, there you will HAVE to plot manuevers with respect to different reference frames. Its fascinating and very insightful.

[@scottdorfler2551]

There's another physical inaccuracy in the same seen. When the ,"Screaming Firehawk," AKA, "Flying Alamo," AKA,"Razorback," is preforming its, "juiced to the gills,"breaking burn the Firehawk is shown from a distance. The ships drive plume is pointed in the wrong direction for a breaking burn. Then they jump to a close up of the Firehawk and it's in the correct orientation wickedly performing a breaking burn. I can't believe this inaccuracy made it to air. Still my favorite Sci-fi show EVER!!!!

[@Great_America]

You can also induce vector change through the use of reaction wheels that would generate torque upon the main axis (attitude change) of the ship. Not as effective as thrusters with regards to force over time, but far more efficient.

[@prdoyle]

Thanks for posting this. Much respect!

[@tobiasbandt161]

Glad to see you making so much effort into the feedback from your community and even more glad to see you being able of admitting that you "should have picked this up the first time around" :D Follow up question: You've stated that naomi wouldnt be able to get stuck in the perfect reference frame to end up in the motion where the ship would be circling her, but in every example you make naomi leaves the ship at a perfect tangent as she would just let go of the ship. Since in the show she actually ran before she jumped out of the ship she wouldnt leave it at a tangent, but altering her vector compared to the vector the ship has at the point of her jump, wouldnt she? If thats true, can you find a possible jump for her that makes her be stuck right inside the circling motion following that pefect path in that reference frame with minimal deviation from that perfect path that gets her stuck inside the ships circle for at least... let's say half an hour? What kind of speed would her jump have to be at what angle with what radius of the ships circle and with what rotational speed of the ship? is a jump like this physically and humanly possible with if she was unlucky enough to get her stuck because she hit all the needed parameters? (i would try to find a solution myself but atm thats a bit above my paygrade and knowledge in the necessary mathmatics xD )

[@edmcguirk8603]

There is way to jump off the ship and be left floating in the center of the circle but you would need a really long ladder off the top of the ship. Given that the circle circumference is equivalent to a rotating space station at 1/3G, the ladder might not even need to be that long. There is an easier way to think of the ship's trajectory. You can think of the initial condition of the ship as an accelerating non-rotating reference frame before the maneuvering thruster is fired. But once the thruster is fired, the ship is experiencing a constant angular rotation. Therefore it is no longer in an accelerating frame, it is in a frame moving at a constant velocity with the ship moving in a circle. Before the thruster fired, acceleration is constant in the x direction. After the thruster is fired, there will be an equal amount of main drive thrust in the -x as in the +x direction. Also an equal amount of main drive thrust in the y and -y direction. All because the ship is rotating at a constant angular velocity. The period of the circle is equal to the period of the ship's rotation. All accelerations from one side of the circle are canceled by an equal amount of acceleration from the other side of the circle. Yes, the ship's trajectory from the point of view of a third party would not look like the show's depiction because the plane of the circle is parallel to the original flight path not perpendicular as the show depicted. It would be necessary to execute at least 3 precisely coordinated thruster burns to circle in the z plane. (I didn't read all the other comments so I don't know if this point of view has already been expressed)

[@DavidAWA]

Amazon Prime should put links to videos like these after each episode.

[@Ryan-rq6dx]

It has been interesting to watch these 3 videos

[@peaksingularity3032]

Great video, it's a shame that an opportunity was missed here : then in the end show from an "outside" observer point of view the path of the ship *together* with the path of the "inside" observer that sees the ship trajectory as a circle.

[@wbalthrop]

An orbit could also be achieved by facing the target, and then thrusting exactly equal to the centrifugal force. Just need a slight trim on the nose to keep it facing the enemy.

[@jamesbrooks9321]

i was definitely confused as to how she ended up stuck inside glad i'm not crazy

[@ArnandKularajah]

You are forgetting that Naomi has some initial acceleration away at a right-angle vector from the thrust of the ship at the point that she jumps out the airlock. She and the ship retain the majority of their initial velocity from days of acceleration so should be traveling in roughly the same reference frame.

[@androkguz]

Naomi ran and jumped out of the ship. She didn't just let herself go. Which means that she could jump towards the center of the circle. At that point she would be in inertial movement and could never get to *stay* at the center, but that's not the point. The point is that she was inside the circle and waiting for her to get out of that circle would have meant her asphyxiation.

[@sgpsimonb]

You are correct that she ran. Even if we credit her with running at 20 km/h, she exited a ship that had been burning @ 1G for hours if not days. Her velocity would be dictated by the speed and vector she inherited from the ship, not the tiny fraction thereof that she imparted to her motion when she jumped. You might be right that she imparted a change of vector and speed, but in the context of the motion of the ship, it counts for little. Sorry.

[@androkguz]

@@sgpsimonb I admitted Naomi couldn't have gotten into the circle, but you have the wrong reasons why. People keep pointing speed out as if she had to compete against some fraction of the speed of light. It was a ship rotating around a point in space. She had to compete against the speed of the ship as seen from the point of view of the center of the circle. If the ship was accelerating at 0.3g like most belter ships and rotating at something like once every five minutes (1/300 hertz), then the linear velocity of the ship with respect to the center of the spin is 90m/s (centripetal acceleration equals omega times linear speed for a rotating motion with no angular acceleration). Less if you assume it spins faster. That is more than what she can run, but not enough to make it insignificant. The only problem is that she didn't jump toward the center of the spin as I was pointed out above. The center would have been towards her head in the direction of the ship's roof. But had she somehow climbed the ship at 20m/s it would be credible for her to stay inside the ship's circular rotation long enough to asphyxiate.

[@sgpsimonb]

@@androkguz Even if we agree that the passenger-free belter ship was accelerating at 0.3G, it had been for some time. Again, putting aside that the flight path shown in the show was not actually possible, the linear velocity would have been higher. You can do the maths, but what you can't do is ignore the head of steam that ship built up in the many hours/days prior to her exiting the ship.

[@androkguz]

@@sgpsimonb yes you can ignore that because the circle's center is not accelerating and it's moving at that exact amount of speed that the ship accumulated before starting to spin.

[@sgpsimonb]

@@androkguz hmmm. that makes sense. sold for cash...

[@matthewkaiser7803]

In the Expance, Since the main engine is always on, thrusters have to have the same capability, otherwise dangerous situation occur - i.e. hotgas thrusters - as opposed to coldgas thrusters of current rockets. Naomi broke the thruster and caused it to be on. We're not shown or told (in the books) that she stopped it. Therefore, since hotgas thrusters take gas from the main engine, so it's conceivable that -- the thruster was constantly on ---, even if at a small fraction of the main engine thrust. the navigation displays don't really tell us the diameter of the circle or give us any kind of scale, also the nav displays show one other course adjustment, turning into the circle. if Naomi only damaged one thruster there had to be a brief vehicle rotation along it's axis.

[@matthewkaiser7803]

it's also conceivable Naomi reduced the thrust of the main engine to match the thruster and have the appropriate thrust vector.

[@kyelangrehr183]

Still think saying a person on a ship in such a situation can't end up in the middle ignores that the entire system could be the same as a centrifugal gravity ring and their is one place you can let go in one of those and stay in the center. The center.

[@reezlaw]

So basically the ship was drifting like a car

[@markdavis160]

The fact that even when The Expanse gets physics wrong its still accurate-adjacent, is impressive.

[@ArnandKularajah]

We're still not sure that The Expanse is entirely wrong. We only see Naomi transit an inner chord of the circle for a short while before she's rescued.

[@zairac2564]

@@ArnandKularajah excellent point. They have a time limit imposed on them, so they couldn't just wait for her to transit the chord. I'd also be nervous about a chord that involves a rocket.

[@philakayoungyork]

You did us PROUD boy!! Good job!!

[@takokick]

Well, Bobby said it's circling her, not that she is in the dead center while the ship runs circles around her. From all the other evidence it seems that she meant that the ship will circle back and approach her position. I see it's plausible that Naomi mostly cancelled the tangential velocity by running out the door (she explicitly runs out instead just jumping off) and this would place her in the future path of the ship. Checking the scene again, it seems the doorway she uses to egress is on the correct side of the ship for this to be possible. If she would have been able to throttle herself in any other direction, this would not have happened.

[@alinnastac9475]

You said that the nose thrust does not cause a translation motion... I beg to differ, the nose thrust generate 2 motions: a translation and a rotation. Translation motion would be cancelled by a second tail thrust oriented in the opposite direction and placed at the same distance from the mass center as the nose thrust. In this case torque applied to the ship will be double and translation motion will be 0. Also, we all agree that Naomi's ship is seen as following a circular path from Naomi point of view. Therefore, if Rocinante happens to have the same speed vector as Naomi at the moment of her jump, the Naomi's ship trajectory will look like a spiral from Rocinante point of view.

[@HaraldSangvik]

This :D

[@stephenkolostyak4087]

"what is this red squiggle?" A corkscrew.

[@juliankrapfl9343]

Oh, i have to correct myself there as well. Didn't give the Chet's path on the Razorback a close enough look. If i get it right now, Naomi's ship would need a series of thruster impulses. At first to turn the ship for 90° (but not more, so there also has to be a counter impuls to stop at 90 degrees) and then the "initial" impuls like in the show, to start the cycling motion in her original direction of movement. And sry if there are any mistakes in the comment, my native language is German 😆

[@Amadrath]

Well explained. Let me add, that the trajectory, shown in the show, also shows the Razorback approaching Naomis ship from the side, instead of parallel. Thus it could not have had the same frame of reference.

[@MichaelMiller-by4vi]

The reference frame doesn't really matter. I can choose polar or rectangular coordinate system if makes the math easier but all three bodies still move the same way. Alex seems to match the original trajectory, in parallel, but it doesn't change the relative motion of it Naomi or the ship.

[@Amadrath]

@@MichaelMiller-by4vi Maybe I should clarify. I initially assumed, that the Razorback was performing a deacceleration burn on a parallel course to the Chetzemoka (Naomis ship), when the course projection was shown in the TV series. But the footage, shown at 6:15, shows the trajectories of both ships, with the Razorback approaching from the side. This shows, that the trajectory projection was not from the frame of reference of the Razorback, because in this case the Razorback would not have a trajectory, but be stationary at the center of its own frame of reference. Also the two ships did not have similar velocity vectors, before the Chetzemoka started spinning, which is necessary for the relative circular motion to work. On top, the trajectory shown (the corkscrew), can not be achieved, without firing maneuvering thrusters multiple times.

[@caseyjp1]

Love what you're doing. My question would be: What if the side thruster doesn't just do a "puff" and quit? What if the initial jet of gas is visible, but it continues to trickle slowly? It isn't as if Naomi pushed a button to give a single squirt...she hammers the valve open. Accurate or not, it was an awesome sequence...even with the PC garbage death of the character Alex Kamal. :-(

[@whiteknight0275]

I didn't understand any of this, maths were never my strong point. I just love the show. However, I still maintain pie are round and cobbler are square. The sooner you guys can accept this fundamental fact of existence, the sooner we can all work together to make the Expanse version of the future real.

[@elkikex]

Someone pointed out that, in the books, the rotation is generated by shutting down one of the multiple main engines. I feel they asked a consulting physicist how to achieve the same movement with only one main engine.

[@dapeach06]

No, that isn't what happened in the book. In the book, it essentially happened the same as it did in the show, it was a thruster that fired, and the Chezmoka only had one main drive

[@elkikex]

@@dapeach06 Huh, my bad then. I haven't read the books myself, just saw that on one of the previous videos.

[@TheTokuin]

she could end up within the circle if she jumped out as the cone thruster fired, because her acceleration would stop as she exits the ship. The ships acceleration relative to her would also stop because the thrust from the ship is now being wasted on that circular motion. Of course in the show she jumped out slightly after the burn started so yeah she technically should have flew off.

[@TheAllMightyGodofCod]

The KZbin algorithm brought me here. Bad, algoritm....bad, bad algorithm. I'm bored, I am off to watch "The Expanse".

[@paulwilson269]

As the ship is also spinning, wouldn't there be a point where the rotation of the ship cancels out the circular motion? Imagine a ship without the constant thrust, but it was set rotating. If you jumped off the centre of mass, you would not be flung away from the ship. However, the further you go from the centre of mass the more force you would have flinging you away. Now, with a ship making a circular trajectory, if you jumped off the ship you would be flung away from the ship because of the ship is under acceleration to make that circular trajectory. There are two different forces that fling you away from the ship. There would be a point (and maybe even within the ship depending on the forces involved), where the force fro the rotation of the ship cancels out the forces from the circular trajectory. If this is the case, the it could be possible to jump from the ship and end up with non (or more likely minimal) velocity away from the ship and your velocity from your jump make you drift (within the few minutes she had to survive) in the centre of the circular trajectory.

[@geraldwatts5492]

Love the calculus-based physics applications!

[@NuncEstBibendumX]

Great stuff and I think you would make an awesome teacher!

[@nulnoh219]

What kind of Education the future has that any layperson would know something like this... They be doing calculus in elementary school in the belt... Orbital mechanics by highschool, Shop class with spaceships.

[@federicoxcc4966]

Momentum conservation

[@panagiotispotamitis9872]

Wouldn't the thruster at the top of the ship actually create a translational motion in addition to the torque though? The sum of all forces on the horizontal axis at the moment when the thruster is ignited equals only the force of the thruster itself, so i presume that the spaceship would gain velocity with a direction to the left. The same force being applied at the second half of the rotation might cancel out the effects on the first half, though, so i am not so sure.

[@afromaximus]

my gut told me the motion was possible, but the naomi being stuck in the center was based on the 5 minutes of motion she was floating out there. Suggestion for next video - two words - rail gun

[@kiwiruna9077]

or three words big ass railgun

[@nielsandersen6164]

Yeah, me too, and I criticized the simulation in the first video to the extent that the amount of spin was ridiculous. I believe that Naomi’s relative speed would have made her traverse the circle slowly, possibly making it look like if she was in the center for a few minutes. She would already have been dead by then, off course.

[@MichaelMiller-by4vi]

I believe we see her trigger thruster while inside the ship. she would have had to use her suit thrusters to correct to the original trajectory of the ship AFTER she left. We see her just step out into the black.

[@georgelionon9050]

Very, very nice! It's all cleared up now ;). Very nice blackboard presentation too, what kind of Software&Hardware do you use?

[@RyanRidden]

I use a Frankenstein approach of sharing my ipad screen through Zoom and recording that with OBS. There will be a better way, but this works pretty well!

[@georgelionon9050]

@@RyanRidden I see, thank you. It looks very nice! In the pandemic need for online teaching looking for ideas what works ;)

[@grapheggspecies8907]

Ok after doing some thinking, I came with an idea of how to set all this up. Since the centripetal force acts toward the axis of rotation, the torque on the CM has to cause the ship to turn about its CM while also moving with a velocity from the force that applied the torque. This way the main engine causes centripetal force and we have rotation. Was I right? I'll now watch the video haha. All this has to be done keeping the radius in mind.

[@grapheggspecies8907]

Great i saw the first bit and it seems i was somewhat right! YAY im relieved i can continue with my day.

[@paxon57]

Naomi started running and jumped out of that airlock towards the inside, Kerbal just kind of let go so it flew away. Ship in the expanse was doing very slow and big circle so centrifugal force was small. I guess she coulkd actually go towards the inside of the circle instead of being ejected outwards

[@georgelionon9050]

Yeah, but she wouldn't stop in the inside.. she would fly through.. and if she is "lucky" hit her ship on the other side...

[@paxon57]

@@georgelionon9050 yeah she wouldn't stop but she would be inside the circle for some time. In the show they needed to save her ASAP because of no air. So at the time, ship was circling her

[@georgelionon9050]

@@paxon57 But this would imply Naomi made it on purpose difficult to save her ;)

[@paxon57]

@@georgelionon9050 Well she kind of did so they would approach the ship because it would explode :p And if you mean jumping out of the airlock, she had only access to one and she had to run so she wouldn't hit the ship after jumping

[@kodguerrero]

Nothing in space moves in a circle, it has to have some momentum in a parallel direction so it moves in a spiral

[@klausgartenstiel4586]

now, after "debunking the myth", how about "recreating the myth"? in good old myth busters fashion 😎 so what would it take to create that circular path we see in the series? you'd at least have to change the vector along the third axis i wager.

[@MichaelMiller-by4vi]

Am I missing something? The last two videos failed to take into account the helical motion of the person-ship system since the thruster and constant acceleration won't have a net effect on the original motion, from the outside observer. The ship could be circling if, as shown in the show (magic plot arrival), only a small amount of time has passed. The Moon circles the Earth which circles the Sun which moves around the galactic orbit. If I'm stationary, I see the Sun moving away from me and everything else in the solar system on a spiral chasing the Sun. If Naomi, whom is the smartest person that Drummer has ever met and is an expert in orbital mechanics, can launch herself on the original trajectory; she should stay at constant velocity since the rotating ship acceleration is no longer contributing to its previous vector.

[@prdoyle]

The moon is moving quickly relative to Earth (about 3600 km/h), so it would require a big delta-V for someone on the moon to match the velocity of Earth. Likewise, it would take an unrealistically large delta-V for Naomi to match the average velocity of the ship.

[@ghislainbugnicourt3709]

@@prdoyle It took me 10min to realize you're right, and then 10 more to doubt it. I was first convinced that Naomi could jump without effort when the tangent to the ship trajectory aligns with the direction of its average speed but you made me realize that at that moment it's going faster than the average speed (or slower, on the other side of the orbit). Instead, she can jump at any time but she has to match the delta-V between the ship speed and its average speed (earth speed in the example). Seems impossible. However, if the ship's rotation around itself is quick enough, the delta-V isn't that high because the circle is small. So it might be possible to jump just right, although it requires a big initial thruster push, and not being too dizzy with all the spin, and not minding having the ship ram you in the next rotation shortly after you jump. Oh shit, now I realized that it might have been Naomi's plan all along : she wanted to have her speed match the average speed of the ship as much as possible in oder to remain visible for a longer time. That's why she had to run ! Luckily there was a door in the right direction too (towards the rear of the ship's rotation).

[@auklon3372]

while i had no doubt the ship could be maneuvered in such a way, i was trying to wrap my head around how Naomi would or could have been caught in the middle. Considering she would have had to use an airlock that was facing toward the outside of the turn/cork screw, that inertia would send her clear of the ship. Also the first squigley you came up with on the star map would or should also make a circle depending on your frame of reference, albiet a smaller one over a great distance.

[@RyanRidden]

You are quite right, for the first squiggle you need to match the initial y velocity and the introduced x velocity to get circular motion.

[@auklon3372]

@@RyanRidden BTW nice video! I really enjoyed content

[@pi.actual]

Frame of reference is the key. For something that is traveling the exact same speed as the ship at the moment it begins to tumble it would appear to orbit you (Naomi) but it will no longer be accelerating because the tumble will cause it's velocity to remain constant. From a fixed point of reference the ship would stop accelerating and continue at a fixed velocity on a wobbling path as shown in the simulation. It will accelerate then decelerate but the sum velocity will be constant.

[@auklon3372]

@@pi.actual looking again at the diagram they gave us from the Razorback with the one thruster engaging not sure how it would make the 90 degree turn then start the corkscrew even with the inertia from the main engine burning prior to maneuver. Going into a corkscrew No problem but the turn then corkscrew seems off. But if she had made the jump within a few moments of the bow thruster engaging, yes seems plausible for her to get stuck with the ship circling. With out more than one thruster vectoring it, its hard to see how this is possible.

[@felasowande879]

It wasn't clear that the airlock was on the outside of the loop.

[@krap101]

So a force acting at a distance from the center of mass does not result in a translational acceleration? The original problem was not laid out as a couple as you'd see in spacecraft attitude control. If the force is also not acting through the major axis of the spacecraft, does it not also induce a rolling moment/acceleration? Would a combination of thrust from the main engine and thrusters not be possible to roll and yaw the spacecraft at a rate such that the thrust would be tangent to the flight path resulting in a corkscrew?

[@jacqueaulanterne6328]

There is another thing that either is scientifically wrong, or where I do not understand the physics behind it: When you see a ship explode, e.g. after being hit by a missile, the debris is shooting away from the center of the detonation with high velocity, only to slow down rapidly, like in a liquid or gel, and then floats clustered together in a cloud of debris in space. I would expect all those pieces to fly away as a high velocity halestorm of bullets and canonballs in all direction, likely shredding every structure that is in a radius close enough so that the scrapnell density is still high enough to pieces, creating even more debris. But somehow a ship in eyesight of the explosion is not hit by any debris, and can then approach the floating cloud of junk safely just moments later. Was that "narrative liberty" by the authors, or am I missing something?

[@jls1337]

What if the thruster not only acted along the mid axis but also made she ship rotate on its long axis? Like a top or a coin. Then, you know how when the spinning top or coin don't rotate fast enough they start to wobble? Could the ship experience similar wobbling, changing the direction of the main thruster and thus fly in the circular trajectory?

[@diegoj190]

So the thruster gives it a spin and the circular trajectory is due to gyroscopic precession?

[@Hofslagare]

But! What if her jumping off with some speed canceled out her tangential speed? It would be a really low chance of that happening but... Remember, she was running out of air, so even if she drifted off the ship going 3m/s they would have had to rescue her while she was close to the ship for her not to die, and again, depending on the tangential speed of the ship, could she run off and cancel that vector of speed with her speed running out of the airlock?

[@benbunch4159]

Is it not implied that the thruster is constantly firing?

[@timesthree5757]

Im a mechanic. But let me see if I got this right. My car is going straight on the salt flats. At high speed I take a turn. But because the turn cannot overcome the direction of travel I either spin out of control or corkscrew in the direction of travel. Is that close?

[@williamgorham7339]

I’m sorry I’m late I hate perform station critical maintenance on my south Texas house (50 miles south of Houston) . I now though have power (one extension cord, and internet throughout the house! 😊

[@DrJon07]

Me: This guy is such a Nerd! ........ Also Me: Just binge watched his whole channel in 1 day

[@ralfschuster7952]

Hi Ryan, thanks for your great videos dealing with the physics in the Expanse. I also like how the books and the show are trying to display the physics in an accurate way. Have you or anyone else wondered if the trajectories of the missiles fired at the Rocinante in episode 7 are reasnably displayed in the last episode at minute 46:30? I think they are. In the moment where the missiles are launched from the Zmeya they should have the same velocity like the ship, right? Then they are immediatley falling back although the engines are firing in the same direction as the Zmeya, but with less acceleration, indicated with a yellowish exhaust colour. Though, one missile is indicated with a blue exhaust (the one with the proto-molecule) being faster accelerated and outperform the velocity of the Zmeya. Do you agree on this?

[@eds1942]

I had couple issues with this season too. The situation in this video, those missiles like you point out and three others. My guess with the missiles is that the ship changed velocity or that the missiles aren’t ejected out straight away. The other issues being; the seemingly gentle venting of atmosphere, and the relatively little effect of high G and directional changes on the crew except for one character in ep 10, and entire ship explosions whichI suppose could be rationalized. Whether or not these works right, continuity matters.

[@dapeach06]

@@eds1942 there are plenty of videos, including on this channel, that address what you're concerned with, and the explanations mostly vindicate The Expanse, because they did things accurately

[@eds1942]

@@dapeach06 Yeah, I just rewatched one of the scenes in slow motion, which resolved two of the issues I had.

[@letsgocamping88]

What about the “coriolis” pouring on Ceres in season 1. Doesn’t seem right to me.

[@gavinkemp7920]

You couldn't have naomi stay permanently in the middle but for a short while it is possible. you are forgetting that naomi is also applying a force when she run out of the ship, that force can be adjusted to counter act the acceleration or the ship and have her slowly drift towards the centre of the circle. that force is definitely with in her capabilities to produce since she was standing quite happily under that acceleration. Now in fairness this is not what is shown in the show, at least not clearly, because to do this she'd have to kick herself of the roof or pull herself down with her mag boots. a tricky and very unintuitive maneuver to us but maybe one that an experienced belter used to space walks on rotating stations like naomi might know how to do she is described in the book as being very graceful when moving around in 0 G. Now I could see a reason she would do this, her primary reason for jumping was to communicate to the razorback that the ship she was on was a bomb, for that to work she needs to be as easy to find as possible and that requires staying close to the ship. This is grasping a straws a bit but in theory possible.

[@TheDetailsMatter]

Main thruster firing constantly. Secondary thruster fires briefly, once and never again. I can see where this might result in a new, tangential course. I can see where alternatively, it might result in the ship continuing on the original course but now spinning on its own axis. But unless Naomi is exerting a gravitational force the like of a planet, I can't see it resulting in the ship orbiting Naomi. Not without that secondary thruster firing short bursts at regular intervals to achieve regular course corrections, which is precluded by the established situation. A ship spinning rapidly enough would be next to impossible for another ship to dock with. It would need to spiral rapidly around the first ship while extending its docking tunnel, a maneuver both risky and fuel-intensive. Most pilots would think it impossible; only a brave idiot would even make the attempt. Cue Alex Kamal.

[@Hofslagare]

Thank you

[@tweetyericsson]

I don't speak math. My understanding is that the thrust changed the momentum of the front part of the ship, is that right? If the main thruster wasn't on, the ship would be spinning.

[@Yora21]

Isn't the motion simply a corkscrew spiral? Looking at it end on, it looks like a circle. Looking at it from the side is a cycloid.

[@JTheoryScience]

im sorry... I feel im the dumbest or smartest and im not sure which.. it made sense to me that the ship would create a circular motion when i was watching the episode. i must have been creating my reference point for its observation in the same way the show intended it to be observed/imagined. unless im just weird, it all felt perfectly fine from a physics pov and when you said it wasnt realistic i still was not confident in your assessment. It felt, from my good knowledge of physics.. pretty normal, it is just a lorenz transformation anyway.

[@MsArchitectschannel]

This maths is 1/2 way between being not complicated enough and too complicated it's too complicated because any ship with a constant rotation and a constant thrust will create some kind of circular motion and from a stationary point of view that WILL look like a circular motion yet for some reason you go into all of this maths then plot a line out on a 2d plane and claim "SEE. NO CIRCULAR MOTION" completely ignoring the 3rd dimension entirely making it far more complicated than it needs to be without going into enough detail as to actually see why it would be circular motion Go into ANY game with physics on rockets (eg kerbal space program) and do this EXACT thing and you WILL get circular motion from basically every angle almost all of the time

[@aoabali]

When I watched the show,I didn't think the thruster was on for a short time. Can you model what happens if truster remains on for the whole duration?

[@Hofslagare]

Well, it would ju spin faster and faster and faster

[@pcuimac]

The trajectory of the ship was completely bogus in that mission. The script writers just wished for Naomi to be in this stupid configuration with the ship circling around her. The ship were under constant acceleration. The moment she left the ship, the ship would have accelerated away from her, while she would have flown away with her initial velocity and direction. Would have been no problem to pick her up. They just wanted to kill Alex in a dramatic way. Was a bit immersion breakjng for me. What the heck did Alex (his actor) do to the girls, that they needed to get rid of him that way? It was an ugly execution with soooo many crocodile tears.

[@jrm371]

What do you use to draw and present? Asking for a teacher 😅

[@koboldprime2257]

They rushed the script to get rid of the actor. But daum nice vids.

[@redelephantsdotnl]

It rarely happens on KZbin that I can honestly say... I don't get it.

[@oatlord]

We will never be spacefaring. Could you imagine the terror of arguing with politicians on an ark ship millions of miles away from earth?

[@shraka]

Yeah this stuff is hard to get your head around. Show does a great job but there are lots of little errors like this. On thing that bothers me is that when something explodes the debris decelerates rapidly. I dunno what they think is decelerating it, but it does look less strange than the debris just flying off into deep space at a consistent speed.

[@shraka]

The main thing that wigged me out about Naomi jumping from the ship was she passes into it's engine wash. I'm fairly sure that a torch drive as efficient as the Epstein drive would have burned her alive right through the suit.

[@ericssmith2014]

@@shraka I found her proximity to the engine a bit questionable, too. Scenes on accelerating belter ships and on the moon don't really sell as low g, aside from a few effects shots, so maybe we can imagine a surprisingly low acceleration for her ship if it fixes the other problems... What if the ship's only accelerating at like 0.1 g - that gets us much less fearsome engine exhaust than we're used to, a tighter "circle" for the ship to be moving in because it travels fewer metres per rotation, and makes her jump a more believably significant part of the equation (I haven't followed the math closely enough to know if it really helps).

[@shraka]

​@@ericssmith2014 It helps a little if it's at very low thrust, although when she jumps off it does look like it was running at least 0.3g, (if not more like 0.8 or more). The issue is that the drive is extremely efficient - we know this because it doesn't carry much remass at all, and an epstein drive can maintain 1g for extended periods. An efficient drive is a drive that has faster exhaust. Those high energy particles are going to hit her and cause massive cancer in her every part. Just... Just all over. In all her everything. While it's a bit dicey to try to calculate, the epstein drive is at least up the top of the theoretical maximum efficiency of a fusion drive. It's more likely to be above fusion, in the total conversion range - ie. anti-matter drive. That's a heavy particles traveling at near light speed kinda drive, AKA instant cancer exhaust.

[@edding8400]

Yeah but in the show the thruster is fired for just a second so does your code incorporate a dF/dt from the thruster? Or do you model it with a constant force?

[@ericssmith2014]

He sketches it as firing briefly, not continuously.

[@Species1571]

And she did it just by manually forcing a thruster. No complex mathematical calculations.

[@nielsandersen6164]

Told you so! And I didn’t need to calculate anything to see that your argument was wrong. I told you that the rocket in your simulation was spinning too fast to reproduce the conditions in the show. You could simply have made a new simulation with very slow spin and you wouldn’t have needed all your code and two videos showing off elementary school math. And yeah, we (hopefully) all could see that Naomi wouldn’t have ended up floating in the center of the circle. She could, however, have slowly crossed the center of the circle if she was running and jumping from an airlock that was facing inwards at the right time.

[@cornflakeboy36]

You seem angry.

[@nielsandersen6164]

@@cornflakeboy36 I am. But not at the creator, though I am quite disappointed. Why not listen to the feedback and change a simple variable in your simulation?

[@guiart1553]

Isn’t it a helix?

[@nommy8599]

Watch the video linked in the description - you can see it's more like a car that has hit a low wall and started front-flipping end over end I think. But, if one of the passengers is flung from the vehicle and the vehicle had a rocket strapped to it it would appear to that unlucky motorist to be circling them. For a time. Then everything would suck.

[@dapeach06]

@@nommy8599 except that was wrong, because the thrust of the Epstein drive is WAY more than that of the thruster

[@ZeroGravitas]

👍 🙂

[@tonycrabtree3416]

Well, it is science FICTION after all. 🤣