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related: skyhook https://sites.google.com/view/sources-skyhooks/

great video: https://youtu.be/dqwpQarrDwk

⬐ mleonhard

If one's spacecraft missed the skyhook on arrival, it could not decelerate and would fly off into space. The thought is terrifying. The film Aniara deals with this scenario. Spacecraft relying on skyhooks for deceleration would need lifeboats that can decelerate and return to the destination after a missed skyhook rendezvous.

⬐ cee_el123

safeguards are of course necessary in any system.

here it can be lifeboats, backup hooks, spacecraft with backup thrusters, separate mechanisms for moving people vs stuff, and potentially many more

Combine balloons with skyhooks. https://www.youtube.com/watch?v=dqwpQarrDwk

Edit:

According to proprietary imtringued numbers the hydrogen for a balloon capable of lifting 1kg to 50km would be $800 if you do not reuse the hydrogen. The skyhook would accept vehicles at an altitude of 100km so no, keep balloons out of the space launch industry.

Surprising that no one here has used the term "skyhook" in the comments here. Adding it to increase discoverability of this thread. Could SpaceX's starship reach the tether without the superheavy 1st stage?

The video in the article is here: [1] and the sources to the video [2].

[1] https://www.youtube.com/watch?v=dqwpQarrDwk

[2] https://sites.google.com/view/sources-skyhooks/

Regarding the time it could take to travel between Earth and Mars, I recently saw a very interesting video on a concept called a "skyhook" that suggests it might be able to economically reduce the transit time to "just" two months or so, though I assume you'd still want to wait for an appropriate launch window, and in addition it probably wouldn't be operational in time to benefit the first few generations of travelers. :P https://m.youtube.com/watch?v=dqwpQarrDwk

⬐ Richard_East

More info: https://en.wikipedia.org/wiki/Skyhook_(structure)

Isaac Arthur: https://www.youtube.com/watch?v=TlpFzn_Y-F0

⬐ ClumsyPilot

Isaac Arthur's series is great!

⬐ ur-whale

Is it just me or the narrator has the same weird accent as the character Barry Kripke in the Big Bang Theory tv show ?

⬐ luc4sdreyer

From the show notes[1]:

> It’s also interesting that certain designs, such as the one proposed by Moravec (1977), consider a tether whose rotation is chosen such that its instantaneous velocity when touching the atmosphere is minimized, and effectively zero at the tip during the moment of maximum extension into the atmosphere.

[1] https://sites.google.com/view/sources-skyhooks/

⬐ sandworm101

There is no free lunch. To be useful, skyhooks need to be much much heavier than the stuff they throw around. Getting them up there, and servicing them, is something beyond anything. Think of every launch ever in the history of space. That, to biuld skyhook A.

⬐ jspdown

That sounds incredibly expensive to send such mass, same for the cable looking at the current payload weight a ship can send (22,700 kg) [1]

1. https://en.wikipedia.org/wiki/Space_Shuttle

> The typical payload capacity was about 50,045 pounds (22,700 kg) but could be increased depending on the choice of launch configuration

⬐ wolfram74

Additionally, this one of the first times I've seen a description of the skyhook that brings up what I've always been wondering about: Conservation of momentum. Admittedly, since a skyhook would already be in orbit, it can use much more efficient ion/plasma engines, but it will still need to re-boost periodically. Especially since for a long time earth is going to be a net-mass exporter.

⬐ OnlineGladiator

The video covers this. For every vehicle it launches into orbit, it will also be used to decelerate returning ships back into the atmosphere - conserving its momentum.

So it works in theory. I have a hard time imagining it work in practice.

⬐ anotheryou

Just send some stones from where you send your cargo in exchange than. Just the payload of what rockets carry today is really not that much.

⬐ shkkmo

If SpaceX hits their goals with Starship, this might become feasible. I would imagine that the economic viability of a spacehook will lag well behind having sufficient launch capacity to build one.

> SpaceX clearly intends to build dozens of Starships. With an eventual flight rate of once per day per Starship, we’re looking at roughly a million tonnes to orbit per year. That exceeds the current launch market of about 500 T/year by a substantial margin. [0]

[0] https://caseyhandmer.wordpress.com/2019/10/29/the-spacex-sta...

⬐ jcranmer

I'm skeptical that those goals can be hit. By my rough calculations, hitting that target of lift would require the consumption of about 10% of world natural gas production, just for the rocket fuel to get to orbit.

⬐ Geee

SpaceX plans to build a capacity of 10 million tons of payload to orbit per year with their Starship fleet. Also this won't cost too much, just $130-$200B.

https://twitter.com/elonmusk/status/1192547668817375232

⬐ cma

With a one-time tolerance for some nuclear fallout to get it in place it could be done.

⬐ me_me_me

You can bring an asteroid over for quite cheap.

I think we are more-less capable of doing it currently.

⬐ ClumsyPilot

I dont agree. Skyholk is infrastructure, so you want it to lift smaller payloads daily, rather than a heavy payload once a month.

If you typical rocket lifts 20T, you would built a small sky hook to lift like 1T, and use it to lift fuel and other consumables cheaply. That would bootstrap you to build larger one in the future

⬐ theothermkn

I think what bothers me most about this kind of paid fluff is that it fools the viewer into thinking they've learned something worthwhile, when they've only seen something pleasant. Another poster linked to a brief Wikipedia article, and even it mentioned that the technology is nowhere near ready, citing erosion by atomic oxygen as one concern.

What we have here is a glossed-up version of the simple observations that spinning things spin, and "rolling" things move faster at the top than at the bottom. The rest has been left as an exercise for the reader's active and uninformed imagination. Don't fall for it.

FWIW, my guess is that exactly 0 tethers as described in the video will ever play an important role in getting humans into space, for various reasons of various veracity. But it's all guesswork, which is all any of us have. Oh, and sign up for Brilliant.com.

⬐ ohiovr

Actually, chunky salsa problem for people aside, why couldn't this technology be used for sweeping out space trash? Maybe waste management or Rumpky could make a deal.

The teather could also be electrodynamic. By putting a current on it it can push against the earths magnetic field like an electric motor. This can help with momentum loss slinging trash into the atmosphere.

⬐ jspdown

Is there any company working on prototypes? This is the first time I hear about this type of infrastructure, is there any downsides not covered in this video? What if the hook is not used for a long time?

⬐ tambourine_man

How about acceleration?

I find the concept fascinating, but would humans withstand it?

⬐ ohiovr

Its not a stupid question. How do you go from 900 meters per second to 6.5 km/s in a few moments without being turned into chunky salsa?

⬐ tambourine_man

Thank you

⬐ wiradikusuma

What happen if the payload got slingshot off-course? Since it has no rocket on its own (the reason to use skyhook), it could end up in the middle of nowhere.

⬐ anotheryou

not much different with a rocket, if you miss your target to e.g. sling around a planet for your return you're lost.

⬐ ClumsyPilot

Sky hook gives it a boost to reduce delta-v requirements, you would still have small engines for on -orbit maneuvering, like all usual satellites do.

⬐ sandworm101

Not mentioned in video: there can be only one. We couldnt have multiple 1000km long objects on different orbital planes. Collissions would be inevitable. These things change speed with every 'hook' event. Predicting collisions would be extreemly difficult, and impossible to do in time to setup an avoidance. And just give up on those 30,000+ unit sat constellations. Flies to the flyswatter.

We would have to keep them all in one plane, probably to line up with the moon. This would seriously limit thier use beyond orbits in that one plane.

⬐ m4rtink

I think thats too pesimistic - indeed, with current sats limited by current high launch costs to no or low available delta-V, it would be difficult. With more advanced hight delta-V sats & tugs to move dead sats it should be perfectly possible to avoid collisions via active guidance.

⬐ jessriedel

> And just give up on those 30,000+ unit sat constellations. Flies to the flyswatter.

The satellites in these constellations are constantly maneuvering. There's no reason they couldn't easily avoid a sky hook with active correction.

> We would have to keep them all in one plane, probably to line up with the moon.

What keeps them from being synchronized? By moving counter-weights up and down the tether, you can adjust the rotation speed with no net expenditure of energy. So as long as there is a schedule such that skyhooks in different orbital planes are "horizontal" when crossing each other, you can actively maintain that schedule even as ships are extracting and depositing energy from the skyhook.

⬐ Richard_East

Sounds like a massive first-mover advantage to whoever builds one first and controls access - USA or China.

⬐ kempbellt

I am picturing it being similar to a ferris-wheel. You could add more carts (more hooks), allowing for more capacity.

But I'm also imagining a more sophisticated ferris-wheel, where you stick two together (side-by-side), allowing for even more capacity.

Picturing it like spokes on a bicycle wheel might also help.

I wonder if there would be much need for more than one.

⬐ sandworm101

Except you cant. The rotation of one tether changes witg each hook event. No two would ever be turning at the same rate. So you cannot bolt multiple into a wheel system. You could certainly improve one, make it heavier/longer/bigger, but it cannot have multiple strands.

⬐ kempbellt

https://youtu.be/dqwpQarrDwk?t=360

Fair point, that would indeed be a problem.

This part of the video alludes to what I'm getting at. Granted, they are using a moon as the weighted object, so rotation wouldn't be affected by hook events.

I wonder how massive the weighted object would have to be to make rotation changes negligible, or at least manageable.

⬐ sandworm101

Even with a moon, there would be considerable wobble. A strand lifing a ship would slow down relative to the moon. The moons rotation would eventually accellerate the strand back up to the moon's rotation rate, but there would be considerable back-and-forth motion. Pick up too heavy a load and the strand may start to wrap around the moon.

⬐ 77544cec

There is much that is strange, but nothing

that surpasses man in strangeness.

He sets sail on the frothing waters

amid the south winds of winter

tacking through the mountains

and furious chasms of the waves.

He wearies even the noblest

of the gods, the Earth,

indestructible and untiring,

overturning her from year to year,

driving the plows this way and that

with horses.

And man, pondering and plotting,

snares the light-gliding birds

and hunts the beasts of the wilderness

and the native creatures of the sea.

With guile he overpowers the beast

that roams the mountains by night as by day,

he yokes the hirsute neck of the stallion

and the undaunted bull.

And he has found his way

to the resonance of the word,

and to wind-swift all-understanding,

and to the courage of rule over cities.

He has considered also how to flee

from exposure to the arrows

of unpropitious weather and frost.

Everywhere journeying, inexperienced and without issue,

he comes to nothingness.

Through no flight can he resist

the one assault of death,

even if he has succeeded in cleverly evading

painful sickness.

Clever indeed, mastering

the ways of skill beyond all hope,

he sometimes achieves brave deeds.

He wends his way between the laws of the earth

and the adjured justice of the gods.

Rising high above his place,

he who for the sake of adventures takes

the nonessent for essent loses

his place in the end.

May such a man never frequent my hearth;

May my mind never share the presumption

of him who does this.

Antigone, Sophocles

⬐ rini17

I fear that by the time this becomes feasible, the orbit will be too crowded already with satellite megaconstellations. Surely the satellites will be equipped with collision avoidance, but tether is bigger target than another sat.

⬐ baby

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