Flying Inverted At Escape Velocity To Change Course and other Questions - Deep Space Questions 19

[@alexandresen247]

regarding the JWST thrusters: JWST has 2 sets of "big thrusters" (called SCAT), one for the mid-course correction burns with a thrust vector through the stowed center of mass, and one set for the final insertion and station keeping burns with a thrust vector through the deployed COM. the SCATs are bi-propellant and the "small thrusters" (called MRE) are mono-prop. the MREs are used for attitude control during SK burns and for momentum unloads. the specific impulses for these are what you'd expect for these types of engines and the propellant lifespan that NASA is giving is highly reliable and on the conservative side, assuming everything goes to plan. source: I worked on JWST

[@dirtypure2023]

What kind of work did you do on JWST?

[@alexandresen247]

@@dirtypure2023 I was on the flight ops team

[@therealjamespickering]

Why did they not make it possible to refuel the JWST? Surely, if you're going to spend $10 billion on a telescope you could add a fuel cap?

[@nickdumas2495]

@@therealjamespickering Should be fairly obvious? If you're going to spend that much money on a telescope you're not going to make the fuel tank leaky. Much more sensible IMO would be an attachment point for a new tank & thruster module that is self contained; slightly less likely to destroy the telescope that way, but still very risky. Although if you're going to send something else out there in 20 years, it might as well be a new higher tech telescope.

[@therealjamespickering]

@@nickdumas2495 I was being somewhat facetious, regarding a fuel cap. What you said is exactly what I was thinking. The telescope itself is probably good for many decades of use, so why not allow for the possibility of extending its use by designing in the ability to give it a boost somewhere down the line.

[@edwardbarton1680]

My personal preference for orbital access is the orbital ring, where you have a ring in LEO with elevators going up to it from multiple points on the equator. It's held up with mass travelling around it faster than LEO orbital speed. Make that fast mass be an inner section, and it can even be lower than any stable orbit, as the outside skin would be stationary. The fast mass could also be used as a catapult to send ships/cargo into higher orbits.

[@unitrader403]

quite similar in idea to the Orbital Elevator of Gundam 00. This system has 3 Towers/Elevators, and a lower Orbital Ring at 10.000km, and a higher Orbital ring at 40.000km/GEO The purpose of the lower Ring is to keep the whole Structure stable by moving and redirecting a mass through it (i think it was some kind of molten Metal, but i cannt find sources anymore)

[@shoot2splatter]

Anyone interested in this should check out Isaac Arthur's Upward bound playlist.

[@Br3ttM]

An orbital ring doesn't have to be equatorial, either, as long as you have some way of turning it with the earth.

[@GreywulfFoo]

If the LEO ring is spinning that fast, how would you access the elevators? Also, drag.

[@unitrader403]

@@GreywulfFoo the lower ring is also geostationary, the lift it needs comes from the mass moving through it which moves faster than the orbital speed for its height, so it provides a counter-force.

[@spacechannelfiver]

Probably worth noting that reaction wheels basically work by storing angular momentum, and eventually they get saturated; at this point a conventional thruster is used to cancel this stored angular momentum and return the reaction wheel to normal operation. There's an article on wikipedia about it.

[@DrewLSsix]

They have also used solar pressure to desaturate wheels, angle the satellite so that it recieves a torque through solar pressure on a panel of some sort that the wheel then counters through deceleration. The neat part is we are actually gaining practical experience with solar sail navigation while extending service lives of older sats.

[@dougpowers]

@@DrewLSsix if you're in a magnetic field, you can also use an electromagnet to create a torque and cancel your wheel momentum.

[@CarFreeSegnitz]

@@dougpowers Outside a magnet field a spacecraft will have exposure to the solar wind. A charged conductor loop can harvest some momentum from the wind. Angled correctly it would allow a reaction wheel to desaturate. In the extreme a pair of charged plates can harvest momentum from interstellar gases.

[@221b-l3t]

Scott has videos on wheel saturation too.

[@hayleyxyz]

@@221b-l3t Yeah - " Reaction Wheels - Things Kerbal Space Program Doesn't Teach "

[@metachuko]

13:04 Thanks for talking about skyhooks! Much more practical than space elevators

[@tissuepaper9962]

Reminds me of that SpongeBob episode.

[@e1123581321345589144]

I didn't get how these work from Scott's description. Something else that could be done is an orbital ring. Basically a huge particle accelerator that wraps around the Earth at the equator, just outside the atmosphere. The whole thing would be kept in orbit by a stream of particles going around the Earth close to the speed of light. But that requires active support and correction. The moment it shuts down, it would crash into the Earth. But if we're talking a space elevator, something like that is within the realm of possibility and would actually make a lot of sense, on the Moon. And since the Moon always shows the same towards the Earth, you could even anchor the structure by placing the counterweight beyond the Moon-Earth L1 point, basically using the pull of the Earth to keep the thing in position. This would shave off a significant amount of fuel for Earth to Moon trips.

[@FruitingPlanet]

Yep skyhooks are pretty cool, those and launch loops are the most realistic megastructures we could build within a few decades, if many countries would come together maybe even an orbital ring.

[@fenyx-uo9kw]

Scott Manley always help me learn. Tomorrow I will fly to Laythe in a safe.

[@zakiranderson722]

Have a safe trip buddy.👍

[@ChaineYTXF]

Fly safe

[@ChaineYTXF]

...in your safe

[@pluto8404]

fly safety is the number one rule to ensuring mutual cohabitation between humans and mosquitos.

[@fork9001]

If it is airtight, you could slap a massive safe with an adapter onto a rocket and use it as habitation and pressurised cargo. Basically Mars 94 from For All Mankind S3.

[@ThePocketMedic]

The "momentum exchange tether" described @13:03 is in the novel Seveneves by Neal Stephenson

[@sylvanelite]

A Skyhook also features prominently in the anime Bubbgum Crisis 2040. Though, that’s much more fiction setting than anything too realistic.

[@FastSloth87]

It's also featured on the Netflix movie Stowaway (for which Scott was actually consulted).

[@giaxxone]

Heard any news on the movie?

[@MikeKobb]

Came here to say this. 👍🏻

[@ThePocketMedic]

@@FastSloth87 the tether in Stowaway is different from the "momentum exchange tether" referenced here. The former is a method of generating artificial gravity, and the latter is for getting things into orbit.

[@kurtmayer2041]

for more detailed looks into space elevators and sky hooks i highly recommend Isaac Arthur's "Upward Bound" series

[@pluto8404]

space elevators dont work

[@johndododoe1411]

Don't forget Clarke's classic "Fountains of Eden"

[@jursamaj]

I can't watch Isaac Arthur's stuff. His speech impediment make it unbearable.

[@DrewLSsix]

@@jursamaj you are going to have a terribly reduced life if you are so weak THAT of all things shuts you down.

[@rickstorm4198]

His speech impediment has gotten much better than it was years ago. Personally, that stuff never bothered me personally.

[@KnightRanger38]

17:20 - Blaise cary's Q1: Some historical examples of rocket stages with tanks side by side are first stages of the Proton, Saturn 1, and Saturn 1B all were designed with a central propellant tank and six (Proton) or eight (Saturn) smaller tanks equally spaced around that central tank.

[@ericpopcorn6607]

The reason for why each did this is not because of design effects. The proton tanks needed to be shipped by rail so tanks could only be so big. For Saturn 1 it is because they had the tanks from smaller rockets being made so it was cheaper and faster to just strap them together than make new tanks.

[@personzorz]

@@ericpopcorn6607 how Kerbal of them

[@AnthemAnimation]

Has everyone forgotten the otrag series of rockets? they're the embodiment of the side by side thin tanks philosophy

[@mikeshort4291]

Smarter Every Day has a video on the JWST sun shield and how it is made and operates. His father was involved with measurements and it is very intricate.

[@malikd6708]

@@ericpopcorn6607 It should be noted that that the tanks in the Saturn I and IB weren't just old Redstone tanks strapped together. They were actually a bit longer than the Redstone tanks, but used the same tooling and thus were really cheap.

[@murasaki848]

8:40 First "realistic" attempt at space war I read was in Harry Harrison's To The Stars Trilogy (1981). The story as I recall it: Nobody had ever fought an actual battle in space, but the Earth government had ships carrying nuclear missiles. Beam weapons existed, but beam divergence meant they were useless at the engagement distances in space. The rebels came in with a bunch of kinetic-kill weaponry (rapid fire cannonballs and clouds of flechette) and overwhelmed them. I also remember the Traveller roleplaying game (late 1970s) introduced "sand casters" which interfere with other types of weapons (ablative to beams and damaging to missiles), similar to real world "shotgun" anti-satellite weaponry.

[@Golinth]

It’s a newer series, but I think the Boboverse books has the first “realistic” space battles I read.

[@fluffly3606]

The background material for Children of a Dead Earth mentions that in their first space war no one had a real contingency for being stranded in interplanetary space which is more horrifying the more you think about it

[@Tomyironmane]

When I see those pictures of James Webb's sunshield unfolding, I'm always reminded of some 19th century sailing ship. And when you come down to it, the JWST is a tall ship, with stars to steer it.

[@AndrewJonkers]

Yes I looked at that cart wheeling space elevator idea several years back - If I recall correctly it was originally some Russian who came up with the concept. Surprisingly the biggest problem was taking people up in it - the G forces accelerating from stationary interception point to orbital velocity and the spinning centrifugal acceleration are extreme except for very very long cables - even interception at speed at altitude rather than coming to rest relative to earths surface was problematic. My personal favorite alternative is a rail gun accelerator project on the moon.

[@barongerhardt]

For the side by side pencil design, you also get a pressure differential in the area between the cylinders that causes a lot of turbulence and added drag. Any connecting structure adds more drag again. So you will want to wrap the faring around them to have an oval cross section. At that point, you might as well stack them and make it a cylinder again, reducing structural material and mass. The reason some boosters are strapped onto the outside is parallelization of thrust and staged weight shedding.

[@5Andysalive]

13:30 i think, something like that was used in Seveneves (Neal Stephenson). In the ... later part of the story. He plays with some interesting orbital mechanic ideas there.

[@Cranberrie123]

The stacking tanks side by side thing is mainly done in Kerbal because you don't always have access to a bigger batter tank+engine, (in career mode) so adding side by side tanks might help to squeeze out a bit more thrust to weight ratio. Like you said though in real life they generally opt for just a bigger single rocket with a first stage booster maybe. Its also a lot less moving parts which is safer and simpler which matters more in real life than in kerbal , where you can magically weld everything together.

[@vikkimcdonough6153]

Also, some KSP designs rely on drop tanks, which pretty much have to be mounted laterally.

[@ccib00]

Ah, you mentioned the space yeeter, my favorite space elevator alternative. Work even better with the Loftstrom loop!

[@CosmicDoggoo]

11:04 It's really neat how some video game devs do their best to stay true to reality. Elite Dangerous has this exact concept. When your ship is getting to hot, you can jettison a heatsink from your ship.

[@DrWhom]

13:30 In Heinlein's _Friday_ this system is in operation, and people call it The Beanstalk. (If memory serves, it's mentioned on page 1 of the story.)

[@1a1u0g9t4s2u]

Hello Scott, I really enjoy your content on this channel. My son steered me to this. I have learned so many interesting things, example: why a person cannot throw a baseball to land on earth from orbit. Hope you continue this for a very long time.

[@snaaail]

The rotating tether concept is called a Skyhook, some interesting concepts on skyhooks from the 60s

[@thewiirocks]

Indeed. Jack McDevitt used Skyhooks in several of his books to provide sub-orbital to orbital transfer for his characters. IIRC, in one book the shuttle couldn't get to orbit, but were able to time a skyhook left behind by a long-dead alien civilization who had put one in a repeating orbit. McDevitt's writing can be an acquired taste, but he does have interesting ideas.

[@henryefry]

I've thought about drones in an expanse type setting. You could have drones with all kinds of active sensors and jamming tech, that relay back to a ship via tightbeam. The ship could determine how far the drone was based on ping response times or something like that, it could also determine angle of the drone pretty easily. So having a handful of those drones you could track enemy ships and try prevent them from trying to slip away. I've also thought about drones with either inline or pivot mounted PDCs. Deploy those a between you and the enemy ship to give you some more breathing room to shoot down incoming torpedoes. Or send them on the offensive to strafe the enemy ship.

I think is sort of mentioned in the absolution gap series where you have 2 ships in chase at relativistic speeds, they start manufacturing different weapons to send ahead or behind to disrupt the other one, and then you have a mini arms race

[@hartmutholzgraefe]

14:25 the 1st stage of the Saturn 1B actually did just that, having LOX and RP1 tanks side by side for the full height of that stage. Ok, it was not just two tanks, but actually four LOX and four equal size RP1 tanks arranged around a fifth, larger extra LOX tank at the center. And they only did it that way, even though it meant quite a bit of extra mass, as the outer tanks were actually refurbished Redstone rocket tanks around a central refurbished Jupiter rocket tank. So they traded extra weight for construction time, as those earlier rockets tanks were already readily available, and then threw out that design for properly designed new first and second stages with tanks stacked on top of each other for the Saturn V ...

[@jacobspadt2567]

A very minor correction, but those tanks are not directly from the Redstone and Jupiter rockets, instead they were tanks of the same diameter that were stretched lengthwise. This allowed the use of the same pre-existing tooling and machinery to manufacture the tanks, decreasing the overall cost as new tooling didn't need to be built.

[@ryanhamstra49]

The spiraling elevator reminds me of the Bolo’s from the book seveneves

[@GrigoriZhukov]

Also Existence (no spoiler) but it's dramatic and ironically hilarious outlook on first contact is refreshing.

[@ryanhamstra49]

Haven’t read that. I’ll add it to my list

[@VolcanicSpacePizza]

Regarding the aero-gravity assist, I remember years ago i saw and Orbiter video about using this sort of maneuver for plane changes. It did work since the energy lost due to drag was way less then what would have been needed for the plane change.

[@zenithparsec]

5:03 I just noticed on the Arecibo message on the screen, with the coloring they used to highlight the parts, the double helix nucleotide estimate number looks like a rocket, while the red human looks like flames, especially as the image slid upwards into place, and a little like a returning booster as it slid back down, and then the flame disappeared.

[@mskellyrlv]

Regarding aero-assist maneuvers, they are indeed feasible, and have been used for every manned spacecraft starting with Gemini and Soyuz. No wings are required for "ballistic" capsules. The capsules are axially symmetric - lift is achieved by tilting them with respect to the flow, thus generating an aerodynamic side force (lift). The tilt is accomplished by making sure the capsule center of mass is displaced laterally from the capsule centerline, causing the capsule drag to exert a pitching moment on the capsule. It stabilizes at a constant angle of attack. The capsule can be controlled directionally by rolling the capsule so that the lift vector is in the desired direction, giving a surprising cross-range capability. Mostly, though, the lift vector is pointed up, which reduces the "g" forces on the crew dramatically. One thing you don't get from lift is more energy. Lift, by definition, is perpendicular to the velocity vector. In physics, work (change of energy) is the dot product of force moved through a distance. Being perpendicular to the velocity vector makes the dot product of lift and distance zero. The only energy change possible from aerodynamics is to decrease the energy of a body, which is what drag does. Drag is defined as being parallel to the velocity vector, so its dot product is just Drag times Distance travelled.

[@onedeadsaint]

7:31 I like how your hand movement synced with the screensaver!

[@jamesowens7176]

I had a coworker who developed a "wrist joint" for the momentum exchange system you described (MXER). The wrist joint was required for pointing solar panels and antennae while the giant cable flipped end over end.

[@clarktaylor1873]

The rotating teather is also called a Skyhook and yes, it is really cool. You can build them in orbit bit by bit and can do it with "normal" materials. You can have "breaking" points that ensures that all parts are breaking at the right time if something goes wrong. In that case most parts will fall to earth (no Kessler). You even can CATCH incoming spacecraft that needs to break at earth. And you can build them at different planets or moons even in different orbits so that you have a network of skyhooks. In this case you always have "outgoing" spacecraft which will decrease the energy of the skyhook and you have "incoming" spacecraft which will increase the energy. In other words, you can get some energy back that you needed to climp up. Furthermore you can rotate them at such a speed, that you will fell 1g at the tips. And because of the length of hunderts of kilometers, you will have almost no problems due to coreollis effects. But Skyhooks have their own problems. If you want build them for human (1g and below the van allen belt) the dv-gain you can reach is significant, but not as good as you may think. With a 700 km long one, you still need to travel around 4,4 km/s. Much less that orbital velocity, but not nothing. A single booster with a crew capsule will do the job. Most people think, that dooking is a problem but to be honest, you need to accalerate to 1g at the right time and the right 3D-coordinates ... I think some small company already do this (space y or samething like that). You see I'm fascinated by skyhooks. I've done some maths and in my eyes they should be an important part in The Expanse :-D (BTW I created a pen and paper universe situated in such a setting) IF somebody wants to read more: www.niac.usra.edu/files/studies/final_report/355Bogar.pdf www.niac.usra.edu/files/studies/final_report/391Grant.pdf

[@CAMacKenzie]

A railgun projectile weapon would create a recoil, just like a powder powered gun, though there would be the advantage of the lack of recoil from powder gas.

[@Rasip]

There would be recoil, but only for the mass you are firing. If you are firing mass 1/10000th of a percent the mass of your ship recoil is going to be negligible.

[@DrewLSsix]

The description was a gun that's released from the ship before being fired, so the recoil is only effecting the rest of the weapon and not the host ship. While very wasteful it has the dual benefits of not effecting the host ships trajectory and presumably simplifying all the required calculations for maneuvering and targeting, as well as reducing the mass of the host ship. Imagine something like a space born attack ship (helicopter) with missile pods, except the missiles arnt missiles but self contained rail guns. The shim approaches f9r an attack, drops the pods/missiles/rail guns, the ship then is able to maneuver away even faster than before due to greatly reduced Ed mass while the rail gun pods fire on the target without effecting the gunship. There's all sorts of questions concerning what tech would be required to make this even possible, and what doctrine might be adopted to make it practical. But it's not too different from what has been done for decades now, lots of war machines have been basically one shot delivery devices, nobody argues that torpedo dive bombers are wasteful because they drop both the warhead AND its propulsion system all at once before running home for a refit.

[@bob2859]

@@Rasip Recoil depends on how much momentum you transfer to the projectile. A railgun pushes both directions equally, and while the projectile is small, it is going very, very fast. Consider that a 8-gram bullet is only 1/10000 a human's body mass, but you can still feel it when you launch it at under mach 2. A railgun would kick much harder.

[@LowVoltage_FPV]

@@bob2859 All you need is to position yourself in between two enemies. One would get hit by the bullet, the other would get hit by the gun.

[@Rasip]

@@bob2859 except no. With a chemically propelled round you are experiencing the recoil of both the bullet, and the super heated gas which is providing thrust out the end of the barrel like rocket exhaust. Recoilless rifles redirect some of that thrust to cancel it out.

[@S1nwar]

10:14 LOL the armor of that ship: "1mm titanium + 2cm fused quartz fiber + 1cm diamond + 20cm boron (against neutron radiation i assume) + 1m aerogel + 0.5mm aluminum + 1m aerogel + 0.5mm aluminum + 1cm graphite + 1cm aluminum"

[@neohermitist]

McDonnell Douglas was working on an aero-assist (or brake) demonstration project in the early 90s. I was an intern on the project. It got canceled before development beyond a mock up. The plan was to loft it up in the Space Shuttle and ignite the rocket on a path that would send it through the atmosphere. The mock up resides at the NASA museum in Hunstville.

[@___Alastor___]

Regarding the second question, it goes even further than that, Scott, The mirrors are arranged so that there's total reflection and that heat gets channeled away as an optical fiber would

[@brianhiles8164]

(14:00) The _Space Pinwheel_ is, ah, formally constructable, but much would have to be accounted for. For instance, the side dipping into the considerably thicker atmosphere, especially if it were presumed that one could “hook on“ to it, would result in drag that would make it curve back. Yes, this could be compensated for (but not by increasing the stress capability of the structure!), but just as much concern is the matter that the shortening of this arm would unbalance the entire system, therefore making it precess (wobble). This wobbling would effect just as many concerns as any other. To be accounted for are a complex and changing geometry, fatigue from ongoing stresses from vibration, fatigue from varying tension (more than you think!), and capture and guidance dynamics that would make doing the thing that you need it to do considerably more challenging than any naive presumption. I now propose my solution: “Building“ a 100 km (hollow?) spire on the north or south pole. A simple elevator lifts the payload into the centi-gravity environment of near space. Such a colossal structure would need to be on an Earth pole to mitigate orbital pertubations, as it would be a small but non-trivial fraction of the weight of the Earth itself. I put the word _building_ in quotes because it is only theoretical practicable if the structure is crafted in orbit from a captured iron-nickel meteor of suitable dimensions and mass. I name it the _Earth Penis._ The only facet that I cannot resolve for this lunatic but theoretically possible contrivance, is how to “install“ it without ending all life on Earth, like the _dinosaur incident_ debacle about 65 million years ago. That would be bad. Incidentally, someone proposed many decades ago that mega-structures could be fabricated in space by ionized deposition of material (viz, another captured iron-nickel meteor!) onto a lightweight trellis, powered by concentrated light energy from the Sun. _Easy peezy._

[@uriba107]

Regarding space combat. Some sci-fi got it right. Missiles are slow, but can out manuver everything human. But they can be intercepted. Railgun and energy based weapons are still "slow" as they are limited to the speed of light. So the target will probably won't be where you expect it to be with everything above a few light seconds. And when FTL comes up, it will get even more complicated.

[@Kualinar]

I remember reading «Paradise Fountain». In that novel, they talk about the 10+ years exclusively dedicated at clearing the space around the Earth from space debris. That included removing pretty much ALL satellites NOT in geosynchronous orbit and emptying the grave yard orbit above geosynchronous orbit. The scrubbing operation was still ongoing even when the space elevator was closing completion.

[@jessepollard7132]

I always thought they missed having a shield around the elevator - just bring shipments of water to lower levels. then just spray it out horizontally. Since it is below orbital velocity, the water would just freeze into droplets around the elevator and fall back to Earth. Anything entering the shield would be slowed by the droplets and be redirected down and away from the elevator (the source of the droplets sprayed away from the elevator). One or two interactions with the shield could decellerate the debris to the point of re-entering the atmosphere and burn up.

[@Kualinar]

@@jessepollard7132 Well... About 10 years of debris removal, using «brush» satellites would have removed pretty much all small debris. A brush satellite would be something like a launch of clusters of Eco like balloon satellited, but with 3 or 4 layers separated with sizable gaps. All of witch are made of the most elastic plastic available. Those have a very large cross section, causing them to «brush» out a lot of debris. And, given their low mass and large cross section, their orbit will decay quickly.

[@zubble7144]

RE: subcaliber railguns. Instead of launching subcaliber railguns, launch shape-charged warheads capable of orienting the jet at the target. you launch multiple of these (swarm) to surround the target and then detonate the shaped charges. IOW overwhelm defensive measures.

[@ProfessorJayTee]

Your "momentum exchange tether" used to be called a "Bolo." With the proper length and rotation speeds, the tether will "dip" into the atmosphere at only a couple hundred km/h, allowing easy attachment of a "lift module." Alternate ends of the Bolo touch the same three points around the planet. The lift modules can be dropped off one or two rotations (two or four "dips") later for on-Earth transits, or be released (or other loads picked up) anywhere from the outer end for solar system transportation. One neat thing is that incoming ("downward") loads power the system. As long as more mass comes down to Earth than is going up, there is no cost to keep it rotating. Consider it a "spacewheel" instead of a waterwheel.

[@benjaminshropshire2900]

Another possible application of inverted arobraking (et al) would be to allow capture from higher above escape velocity without increase the thermal load. The idea would be to increase the duration of the drag phase much like the shuttle does but by pulling it down rather than lifting up.

[@williamfrohlich]

My favourite theoretical launch system is the bolo launching system described by Neal Stephenson in SevenEves. Two "hangars" attached by a 400km long cable orbiting at 200km doing cartwheels as it goes; timed perfectly that the hangers take turns dipping into the atmosphere and stopping instantaneously a few km of the surface. Aircraft can rendezvous with the hanger and be flung up into orbit.

[@ruud9767]

That was an interesting twenty minutes. Thanks!

[@peterstickney7608]

The oldest reference I've seen to using "downward" lift for trajectory modification was in a 1950s Wernher von Braun book outlining a Mars flight and return. (Post Collier's - seems about the time of the Disney Man into Space series. The Mars-Earth Return/Reentry vehicle was described as a Delta-wing glider, which, upon originally entering Earth's Atmosphere would roll inverted and pull Gs toward the Earth to help keep it in the atmosphere longer for more effective aerobreaking - sort of an inverted "Saenger Skip" (Although I'd like to stick pins into whoever originally translated that - it's not a "skip" - bouncing off a sharply defined change of density (Atmospheres don't work that way) but an aerodynamic climb as the dynamic pressure rises high enough to generate sufficient lift to pull up.)

[@grahamrankin4725]

As a faculty colleague used to answer when a student would ask if the questions would be like on an upcoming exam. "Questions are the same; I just change the answers"

[@AndrewBlucher]

With a little nod to a certain Einstein :-) My answer was "the question text changes but the meaning is still the same: did you do the prac work?"

[@saumyacow4435]

On that issue of using CO+O2 as a fuel to return from Mars, I did a design for a Mars ascent vehicle (Mars to orbit) some years ago. It works out that your ascent vehicle has to be so much more massive that it makes more sense to simply use Mars produced O2 and then import (land) the necessary liquid methane. The lower Isp of CO means larger tanks. Larger tanks means more mass, means larger engines, means more mass and so on. Once you crank the numbers, you end up with a ship 2.5x the mass. And of course you have to produce more oxygen. That means a bigger oxygen production facility, a larger power source, more mass imported to Mars in the first place. Again, the simplest solution is simply to import the methane to Mars. I eventually designed a fully reusable and fully propulsive Mars lander and ascent vehicle using methalox. A notional dry mass of 12 tonnes and a propellant load of 36 tonnes. Hence you only need to import 8 tonnes of methane per ascent. We're talking a crew of 4, maximum 6. The nice thing about this kind of vehicle is that with the same propellant load (sourced in orbit) you can land fully propulsively. That has a number of advantages. One is you get a maximum 1.5 gs on descent (not the bone crushing 5 to 6 gs you'd expect from Starship). Another is when land or go to ascend, you're only a few steps from the surface (not 50 metres for Starship). Another is a fully propulsive lander is capable of landing literally anywhere on Mars, even on Olympus Mons - its not confined to low altitude areas. Plus its capable of surface to surface hops, orbital flights (excursions to Phobos) etc.

[@ambushell5778]

Scott I would love to hear your thoughts on magnetic ferrofluid reaction "wheels" for spacecraft

[@trevorlybbert3640]

Woah wait what??

[@weatheranddarkness]

would that help when it comes to time to desaturate?

[@thomasrogers8239]

I really like the idea of the skyhook too

[@XavierBetoN]

I do aero-gravity assist all the time with my BSTO HTOL craft (Bombardier Stage to Orbit that ejects only tanks instead of engines and drops them over the Pasific Ocean after a smooth take off from Cape Canaveral) (KSP QSRSS)

[@bjornstabell2970]

Wow, would be a really cool scifi story element to see a two-stage launch system consisting of an "Indian rope trick tower" combined with a momentum exchange tether that picks up things shot out from that tower. :)

[@johnmorrell3187]

Seveneves by Neal Stephenson has the second idea, the pinwheel, as well as launch systems made of self assembling train car sized robots arranging into giant bull whips.

[@getahanddown]

I'm just waiting till Steve Mould hears about Scotts plan for a levitating chain space elevator and tries to do it first.

[@MarkBarrett]

Supposedly craters on the Moon build up large electric charge from solar wind. Seems like you could use it as a power source, and lower risk of going in the crater at the same time.

[@TheEvilmooseofdoom]

The polar craters but so far no measurements, but it IS an interesting thing to be explored.

[@llejk]

Nice. Charges would be more or less steady ,well, during moon-day, and could be harvested with relatively lightweight wires. Depends on the gain, compared to photovoltaic, of course.

[@keith0alan]

Another problem with side by side fuel tanks is the shift of center of gravity. With stacked tanks you can keep the center of gravity fixed. With side by side tanks the center of gravity shifts toward the tail of the rocket. Having the center of gravity too far back causes stability problems.

[@alexandruianu8432]

Inverted hypersonic flight can also be used for the fastest theoretically possible flights on Earth as well, since you could move faster than the escape velocity of the Solar System, while staying in the atmosphere. I think the record in the Orbiter Space Flight sim is under 20 minutes from Florida to St. Helena island (start -> stop) using a scramjet space plane.

[@richardm.newlands2417]

Hi Mr Manley, you doubtless heard about Aero-Gravity-Assist back in Scotland in the 1980's/90's. Stu (see below) and I, and others in ASTRA, held a weekend workshop at Glasgow Uni for the benefit of James Randolph of JPL, and Terry Nonweiler - the creator of the Waverider concept. The workshop discussed ideas for an AGA around Venus to get the Parker Solar Probe to the Sun. I was 14 when I first met Jim Randolph at a Waverider meeting in Largs; I'd been a member of the Paisley Rocketeer's society for less than a week. That was a life-changing week! I'm astonished that it took another four decades for the Solar Probe to get to the Sun: when I was a naive 14-year-old, I thought three years would do it!

[@FraCarroll]

RE JWST Fuel: the press conference last week said ... 20 years.

[@reubenbuckley3647]

I’ve been toying with the idea for a polar ring for things like a space elevator, but also power generation and a habitable complex (space city). It would essentially be placed at just above 100km for least impact to current space activities, It could be mounted at the poles and rotate so that it is always on the day/night line (offset by the earths tilt of course) and thus have the least impact on the visibility in the sky for skywatchers and observatories, while also being ideally oriented to place solar panels on the sunlight side to power it and if there’s left over power generation (something of this size I’d think there’s be a significant amount of excess generation), to be sent back down to the ground. Because it’s technically not in orbit but rather as it wraps around earth would be essentially a big tension bridge, it would be quite rigid and wouldn’t have to worry about atmospheric heating as it would only be rotating at the same speed the earth rotates, in the opposite direction to stay on the day night line. Since it would be connected to earth and has plenty of solar panels, it could also have ion thrusters to adjust it and keep it in place.

[@ambassadorkees]

13:36 "traditional space elevator". Yep, we have a long tradition of building these contraptions!

[@John_Longbow]

Flying Inverted At Escape Velocity pretty much sums up my cats day. Her relentless efforts to gnaw of my computer cable finally payed off this afternoon. Let me tell u, there are a surprising amount of Delta V in an electrocuted cat.

[@AndrewBlucher]

John, as a cat lover I was cackling and in tears! I can just see it. How is the cat?

[@John_Longbow]

@@AndrewBlucher The Eagle has landed👍

[@michaelluttmer2486]

The primary weapon systems in the Honor Harrington series by David Weber was missiles that launch 6-12 single use laser 'warheads'. The explosion of the missile would somehow power the laserheads and take out a ship systems in detail or destroy it outright. Its a pretty neat concept.

[@jasonlast7091]

Spitting these out. Man I love it

[@susume6]

Battle Angel series has some great skyhook settings in various parts of the story.

[@randycampbell6307]

@6:00: Aero-Gravity Assist, if I may say it's likely "Old Home Week" for you Scott! An organization you might be familiar with called "ASTRA" (Association in Scotland To Research into Astronautics) did a bunch of wave-rider and AGA work in the late 70s and early 80s up to and including some basic research into a 'flexible' interplanetary wave-ride concept. You should look it up. @11:40: Rather than a Momentum Exchange Tether that dips into the atmosphere, (cool idea but almost as many issues as a Space Elevator and it takes constant energy input to keep it going) keep it all outside the atmosphere and shoot a payload up to meet it. Sure you essentially still need a reusable first stage vehicle but Mach 6 to 10 is a lot easier than full orbital velocity and there are tricks to drop it even further. (Keywords are HASTOL study and Hypersonic Skyhook)

[@ndprice89]

Wasn't this type atmospheric gravity slingshot the premise of Farscape? It's pretty cool to learn that it was slightly grounded.

[@zyeborm]

I was waiting for Scott to say the downside of performing this manoeuvre is when the Scarrens attack you ;-)

[@spacemanmat]

Smarter Every Day did an excellent video on JWST heat shielding.

[@ptonpc]

Regards Elliot Foss's question, that is basically what the Farscape 1 was supposed to do in the show Farscape.

[@gregzsidisin]

Aero-gravity assist plane changes are mentioned in the book Space Vehicle Design by Griffin and French, and are a plot device in Geoffrey A. Landis' novel Mars Crossing

[@Dovorans]

The other trick Orbex's coaxial configuration exploits is that because the density of subcooled cryogenic propane and cryogenic oxygen are quite close, the pressure differential across the inner tank wall at the bottom is much smaller than the pressure differential across the bulkhead between the bottom of one tank and the top of the other. This means that even though the coaxial tank wall has a larger area it can be built much thinner and therefore slightly lighter than the bulkhead of traditional stacked tanks.

[@frankgulla2335]

Scot, thanks again for the public update to questions.

[@ThomasBensler]

13:42 ... "a traditional space elevator" as we used to say

[@Lucius_Chiaraviglio]

A skyhook as described here will have some drag, because the atmosphere has significant thickness, so when one end is coming down or going up, it will be passing through air but also have some motion relative to the ground. However, this would not be a problem for Lunar skyhooks. The Wikipedia article has a concept for an Earth skyhook of putting it entirely above significant atmosphere and using a suborbital launch vehicle to transfer payload to it, thereby getting around the drag problem (apart from the extreme outermost layers of the atmosphere reaching up there as they do for Low Earth Orbit satellites). Of course, the skyhook still has the problems that you have to keep boosting it to compensate for the momentum it transfers to its payloads (also shared with a space elevator), and that since it will be spinning many times per orbit, it will have extreme acceleration at the ends, which would be too much for people.

[@novicegreenenergy2059]

Oh hell yeah! I've done freeish inclination changes with spaceplanes in KSP.

[@ruspj]

i like your description of active support for a space elevator. but am suprised the concept of an orbital ring isnt more popular. while it could carry much more and be more feasable than an elevator it is on a larger scale and would require much more mass in orbit to build.

[@WthyrBendragon]

We learn in introductory calculus courses that for a given volume a sphere has the smallest surface. Next in line would be a cylinder with semispherical ends.

[@SimonLanghof]

"Space Trampoline" - another one for the list of band names

[@mrpicky1868]

BTW when Webb will be out of fuel its no like it crashes into something right away. it can just drift . main thing is maintaining orientation

[@JustFamilyPlaytime]

Required reading list for this episode - AC Clarke, The Fountains of Paradise (1979). I M Banks, Feersum Endjinn (1994). Larry Niven & David Pournelle, Footfall (1985),

[@WthyrBendragon]

Improvements in non-chemical propulsion may give us some substantial improvements to equipment life for a future device to replace/extend the JWST. Perhaps a larger diameter microwave bandwidth capable system that can see even farther back in red-shifted time?

[@eekee6034]

That momentum exchange tether is so wild! Dipping only part of itself into the atmosphere, rotating for coolness and ease of hooking on... :D 18:38 Huh! Tides for space elevators.

[@pewterhacker]

Vehicles launched from a Tethered Ring mounted mass driver would probably make use of aero-gravity assist or aero-maneuvering to help circularize their orbits.

[@1959Edsel]

15:58 The tanks were the same size. The fuel tank was positioned farther out due to its contents being less dense.

[@bar04z]

If you're taking CO/O2 synthesizing equipment to Mars for return rocket purposes, it may also be worth bringing a fuel cell and using it for ground based power. It's a tradeoff though, since a Li battery would have a _much_ better roundtrip efficiency. It'll depend on how power-limited your synthesizer is vs how often you need to launch rockets. I think.

[@jasonlast7091]

The thing about a space elevator that I feel like people keep forgetting is the conservation of angular momentum. You can’t just space elevator things straight up in the sky on a tether because that would cause the tether to lag behind the rotation of the Earth. I could imagine some kind of forward load bearing tether that transfers the load into the earth itself maybe (slowing the earths rotation by negligible amounts). But by conventional sense you would need some kind of propulsion at the top that boosts forward as things come up the tether, which mean plumbing fuel up there, which also needs forward propulsion…

[@GuillaumeMoesching]

The cable would have to be kept under tension and fixed on the earth. If the mass above stationary orbit is "lagging behind", the tension will bring it back to place by pulling on the earth, no need to fire up something up there.

[@karl0ssus1]

Tbf, it's only the mass of cargo that needs to be accounted for, as the elevator car pays all its momentum exchange back on the way down. Also the mass of the tether would be extraordinary, so the effect wouldn't be particularly pronounced on an individual trip basis. As such, maybe it's not super unreasonable to just arm wave it away as a problem that can be fixed by shipping a few tonnes of propellent up each month

[@IanZainea1990]

13:42 I really like your pinwheel idea

[@flintcoat2596]

I know this was posted a year ago and few will read it, BUT Robert Heinlein in the 40's or 50's (I'old,what can I say ) wrote a novel about racing around the solar system where aero maneuvers were used to increase the bend in their course

[@dragonridley]

As to what percentages of energy are shed in what forms, I was reading about this for meteors. The percentage of kinetic energy radiated as visible light is called the luminous efficiency. It's poorly constrained and variable, but most figures I've seen have been on the order of magnitude of about one percent.

[@nomar5spaulding]

Oh man, Scott, as an Eve player, when you said, "Radiators... they're not that good because they can get shot off," please tell me your mind instantly went to Charlie Fodder and Saul arguing about Clear Skies getting it's "top wingy bits" shot off repeated.

[@SirFloofy001]

The problem with an exclusion zone for something like a space elevator is every single earth orbit has to pass through the equator. The only way i think that could work is if all satellites were required to maintain an orbit that never crosses x amount of miles/Km's close to the tether and i dont think that leaves many orbits open.

[@btickson]

Your portion about the laser radiator heat sinks being vulnerable reminded me of something interesting I saw. The F22 fighter plane has some sort of ejectable heat sink device on it. Some system creates a lot of heat and they want to dissipate it as fast as possible to lessen the IR signature of the aircraft. So they just yeet it off into someone's house, I guess. (Eric Johnson F22 walkaround)

[@petersmythe6462]

IMO space-based point defense is best done using missiles that lock onto an incoming projectile some distance ahead and impact or detonate on it.

[@richb313]

Thanks Scott for trying to explain something I still don't understand.

[@pseudotasuki]

There are some examples of rockets where propellant tanks are stacked in parallel. In particular, the S-I stage used by the Saturn I, or the first stage of Proton.

[@AlvarazCMSB]

aero-gravity assist was the crux of my bachelor senior design program!

[@lonjohnson5161]

The alternates to a space elevator have been detailed by Isaac Arthur on SFIA.

[@Etheoma]

I prefer launch loops, it works on the same concept as a space tower but it only needs to be like ~2000km long vs geostationary which is 35,900 km long basically you raise a bridge to about 50km via accelerating mass though the launch loop, and if you lose power it's no biggy because the reason it's called a launch loop is that it's a massive loop and you loop accelerated mass around the launch loop so it would take weeks to come down because of how much latent energy is in the launch loop, also it's low enough down that small bit's of space junk would have burnt up before that point and larger trackable space junk will quickly deorbit in a rather predictable manner. Also as to the Skyhook that really is best used in tandem with other launch systems, like you can reduce the launch loop down to 500km and get over half the velocity you need to get into orbit from the Launch Loop and you can get the rest from the Skyhook. Also you can just use regular rockets in tandem with a Skyhook because if you half the velocity you need to reach with rockets you don't simply double your payload mass for the same sized rocket, it's more like 15x. Because to get to half the velocity you don't half the fuel required, because accelerate to double the speed you need to carry yes double the fuel to accelerate that last half of the burn, but you need to originally carry fuel to accelerate the extra fuel you need later.

[@callmeadmin]

CO energy content is relatively small. Only 4368 kj per kg. It is slightly heavier gas than air, 1,25g per litre @ 0C. It's boiling temp. Is -191,5C. While methane energy content is 23811 kj per kg. And it's boiling point is -161C. For comparision hydrogen energy content is 61068kj per kg. But it needs huge space and is very hard to liquefy. At boiling point -253C. Only 20K over absolute zero.

[@MCsCreations]

About space elevators, there was a fantastic episode from Star Trek Voyager. Of course it's fiction, not actual science, but it's more than fun enough.

[@germansnowman]

Not to forget the Foundation series.

[@tonychesser8710]

Aero-maneuvering is what the X-37B uses. It's in orbit. It dips close to the atmosphere, which allows its small flight controls to significantly-alter its heading. Consequently, it can recon very different paths from one orbit to the next. The Secretary of the Air Force, some years ago, mentioned this and the fact that its less-predictable orbits drive opponents to the USA nuts. Since the X-37B can significantly-alter its path using this, this is demonstrated fact.

[@connoroshaughnessy4327]

To me I feel like the James Webb space telescope is one of those things where we build it to last 5 years and then it ends up lasting 25 years or longer

[@michaelhart7569]

5:20 forwards. You just made the best argument against electric aeroplanes (and some other "green" technologies). It's energy density. Short of nuclear power, we probably already have it. It is the combustion of hydrocarbons using a freely available environmental source of oxygen (in Earth atmosphere).

[@darkfur18]

Instead of circling the metaphorical drain you're balancing around the top of the metaphorical hill, adding small amounts of energy as you ride to maintain elevation

[@chasethevioletsun9996]

There is a fantastic scene in Larry Niven/Edward Lerners' "Destroyer of Worlds", where a crew returning to the Homeworld arrive just in time to see the last of the Space Elevators crash, obliterating what little is left from the fall of their, um... 'civilization'.

[@tedferkin]

If you want to learn about the shield mirrors, there is a semi-decent video from Engineering Everyday, whose father worked on the testing of the shield and he got first hand access to the test centre

[@RCAvhstape]

The concept of using aerodynamic forces to change an orbit plane goes back a very long way, and was considered to be used for the canceled X-20 Dynasoar program and is described in the literature from the early 60s.