# Space Colonization Options (Orbiting Stations, planets/moons)

Discussion in 'Science and Technology' started by valkyrie013, Jan 28, 2021.

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Setting aside material problems, the cost to raise a 10 ton spacecraft via space elevator to GEO is about 500GJ [0]

Crucially when the space craft comes down minus 5 ton of cargo (and no need for a heat shield), you get half that cost back.

With a rocket, you'd need 13,300m/s of DeltaV, which is you dump into the rocket equation with a 3km/s engine, you'd need 830 tons of fuel/lox, so with a 2:1 ratio like the Falcon 9 uses, that's 270 tons of fuel at about 40GJ/ton, or 10,800GJ.

So ignoring the weight of the rocket lifting your payload, you'd be far better off burning the rocket fuel to use for electricity to power the lift (which in any case you could power from solar energy in GEO)

To lift 100 tons a day would need 500GJ/day or 5MW, requiring solar panels at 20% efficencty to be 18,000 square metres in size, about 400 tons worth, you'd then have free lift capacity

Obviously this sets aside the cost of building and operating the various systems. We're a long way from having the required technology for a space elevator, but not that far off a 100 ton to LEO lift capacity. Lets just hope people can think of innovative ways to use it.

[0] https://en.wikipedia.org/wiki/Space_elevator_economics#Cost_estimates_for_a_space_elevator

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If a rocket engine wears out, or heat shield ablates, you can replace them (prior to the next flight). If a space elevator cable (or car gets punctured by a micrometeorite, you're boned.

Add to that is the problem of the speed of the journey. The current fastest elevator is in Shanghai and runs around 76km/h. Assuming somehow that could be bettered by means I can't imagine right now, WITHOUT eroding the cable, at TGV average speeds, that's going to be 5 to 6 days, a good deal of it going past the Van Allen belts and therefore spending a significant amount of time in a dangerous radiation environment. If something bad happens health-wise during that time on board, again, there's nothing that can be done. At least ocean liners had rudimentary clinics aboard.

The elevator would need many of the things a spacecraft has or is: ECLSS, rad shielding, passenger accommodation, first aid, rad hardened electronics and quite possibly some kind of RTE life-boat capsule. On top of that, again the constant maintenance of the cable.

The argument against is the cost of the fuel of a rocket. It's always been said that rockets were so expensive, primarily due to the cost of motors that if fuel and oxidizer costs ever became a significant fraction of the cost, the argument was already one.

By the introduction of the Comet 4 and the 707, jetliners were starting to get competitive with ocean liners. you can see on advertisements of the time, that the lowest class tickets on Cunard and others are showing up as "tourist class". They're still cheaper in some cases but in a few more years almost all of the liners would be laid up, a few converted to early cruisers, with the Q.E.2 being the last true operational liner for decades until the QM2 took over her duties. but even before the four engine jetliners, people were starting to transition to long distance air travel, despite the expense. It was quicker.

Getting to orbit on a rocket takes less than 15 minutes. Maybe another day to arrive and dock with your station. That's a significant change from spending a week or more in a can.

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If a spaceship gets punctured by a micrometeorite you're boned. You make a nice tin can with plenty of radiation shielding (water) with a 100 ton elevator car. Certainly nicer than the 6 months+ we send people to ISS for.

Once you reach c. 50km there's barely any atmosphere, so it's just a matter of accelerating, again it comes back to materials. If we are going to assume we have a material strong enough to hold it's own weight to GEO, then why not make it strong enough to allow it to travel at a high speed? I.e. something that can use maglev to provide forward thrust. With no air resistance you can floor it, accelerating at a gentle 0.5m/s relative to the "track" (so 1.5g with the force of earth pulling you back, although as it's a rotating environment that will be less).

If you don't slow down to enter GEO, you'll be at GEO 4 hours after you depart. Slowing down can be faster than acceleration as you can accelerate the cabin at 15m/s.

If you're willing to accelerate faster than half-g you'll struggle to get through the inflight film before arriving in GEO (if that's really your destination)

By comparison assuming you're already in LEO, and accelerate to GTO, the coast phase is 5 hours alone, so the elevator is faster. make the elevator longer than GEO and counterbalance further out and you could be looking at direct flight to places like Mars or the Moon, no Hohmann transfer orbit needed.

But you're looking at this from transporting people. We transport people by planes sure, but when we want to shift thousands of tons it's far more economical to do it by sea, even when it takes weeks.

No human has been above LEO for 60 years, and while Starship will put 100 ton payload into LEO, it can only get 20 tons to GTO (and then you need to equalise your payload in GEO)

I do wonder if you're literally thinking of an elevator in a skyscraper, where people stand awkwardly listening to muzak (or being force blasted adverts as is increasing common)

The cost of the first elevator is astronomical. The cost of the next 500 is trivial. You don't need to worry much about maintaining "the" cable, as you could have dozens of the things per port.

Last edited: Jan 28, 2022

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No, I am not thinking of the SE as a skyscraper elevator, but there are economies of scale. There is only so big this is going to get. And I don't buy the 4 hour transit time. While operating primarily out of atmosphere will help somewhat, it's still going to be pulling against the gravity well, putting some kind of friction on the ribbon/cable (else why need it in the first place) . I do agree it could work as a cargo transport, but I do not think it would ever be used for human passage. Chemical rockets don't have a lot of uses. Long term I don't think they will have much use in interplanetary travel, either, but I do think for some time to come, barring exotic breakthroughs, they will be the best method for leaving Earth.

Regardless, I would love to be wrong, and I am enjoying the discussion.

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I explained the maths, it was rather simplistic and didn't account for the changes in rotational speed, centrifugal effects, and crucially it's entirely off by a factor of 10 as I didn't write it down.

s = 1/2 at². Accelerate at 2.5m/s and in 4 hours (14,400 seconds) you'll have gone 0.5 * 2.5 * 14400*14400 = 259,000 km.

At that acceleration you'd reach GEO at 35,786,000 metres 1 hour 20 minutes after departure. You'd leave GEO at

v² = 2as = 5*35,786,000 = 13.4km/s

Not quite solar system escape velocity from Earth (16.6kps), but not far off. Accelerate a robot probe at a mere 30m/s and you'd reach 46km/s (having spent less than half an hour getting to GEO)

It's an acceleration of 0.25m/2 I was using, which you wouldn't even notice in the cabin. In 4 hours you'll have gone 26,000km, over half way to GEO.

The force due to gravity in Kuala Lumpur is 9.776m/s². In Helsinki it's 9.825m/s². I've been to both, and I can assure you the only extra mass I felt was the lovely slice of cheesecake I had at the airport in Helsinki. That's a 0.049m/s difference. At that acceleration leaving KL, you'd be halfway to GEO in under 4 hours, and at a full stop at GEO in under 8 hours.

It will take longer to fly to the launchpad near Singapore or another Equatorial city than it will to get to GEO, even with almost zero acceleration.

Magnets mean no friction. No worry about bends on a track, or objects you might hit either.

The force needed to hold a 10 ton cabin at sea level would be F=ma, about 100kN. To accelerate that at 2.5m/s² would be 125kN. The force required will go down as it gets further from Earth (in LEO it's still about 9.8m/s², but as you get into mid orbits that force drops dramatically).

If you can hold a 10 ton cabin with a force downwards of 100kN, you can accelerate it at 0.25g (2.5m/s), let alone 0.05m/s for an 8 hour trip.

It's dwarfed by the strength needed for the cable itself.

The magnets would presumably require more power too, but that's just a matter of deploying more solar panels, which is practically free with such an elevator. Power would be there nearly all year round (remember that a station in GEO is in direct sunlight other than for about an hour a day on about 40 days a year, and that's predictable centuries out).

The cost of the raw materials for the solar panels comes down because of mining asteroids which becomes far cheaper with a near zero cost elevator.

The main problem is the material strength needed to support such a cable.

In the case of a cable cut at say 30km shortly after the car leaves the station (say 100m), you'd probably have a problem, as deploying a parachute at that altitude wouldn't work. Once you get to a reasonable height you could have the passenger cabin deploy a (steerable) parachute for a splashlanding. Below that altitude perhaps an escape rocket would do the job (as it does with say an abort when an F9 takes off).

A cut below the cabin wouldn't affect the cabin at all. The cable would be so thin that if it were cut in the atmosphere it would just float down. The GEO station would spool out another 20km of cable, and you've be back in business in a few hours.

A cut in mid-orbit, say at 15,000km, would be problematic. The carriage wouldn't, it would need to be built for reentry speeds - not from orbital velocity of course, but from probably somewhere in the 3-4km/s range. Not insurmountable. The cable would either burn up or float down. Bit of pollution.

6. ### tavorLieutenantRed Shirt

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just a question does the distance between earth and moon vary daily? or in other words does the cable stretch ?

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The cable doesn’t run from the Earth to the moon, but yes the distance varies.

imagine you have a helicopter and you suspend a rope from it to the ground, and you tie it in. The copter can’t go higher, but you can have a passenger climb up the rope. That’s basically how it works. However the helicopter is in a synchronous orbit around the Earth - slightly higher actually so it tries to drift away, keeping the cable taught even with someone climbing up.

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In Gundam 00, here's the various levels of Orbital Rings linked to the Orbital Elevator:

There's a Geo Stationary Satellite at the end of the Orbital Elevator to help stabilize the wire / keep it taught.

Two layers of Orbital Rings:
- High Orbit Ring @ 40k km
- Low Orbit Ring @ 10k km

For reference:
401,280' = 76 mi = 122.310 km ~ 122 km = Space Shuttle uses Aircraft Control Surfaces instead of Steering Thrusters

@ 50k km high, there's 3x ballast satellites at the end of the compressive elevator towers that help keep the elevator structure taught.

There are other issues IMO and it has to with the Earth's wind, the radiation from the Van Allen Belt, requiring MagLev vehicles to ride on the tether up the Orbital Elevator.

The Orbital Elevator Trains would probably need to be battery powered or some equivalent using ElectroMagnetic Levitation to raise it's Cargo PayLoad to orbit and back.

The Orbital Elevator used in Gundam 00 had a modular Armored Panel outter layer, and numerous pairs of lines on the inner layer.

The Armored panel protected the Orbital Elevator Tether lines from the environment: (Rain, Birds, Insects, Wind, Radiation, etc.)

But it was VERY costly to defend and terrorist attacks were always an issue.

When the Orbital Elevator Panels fell, it became a humanitarian crisis where all the local military needed to band together to protect the citizenry by destroying the falling panels, which required "Celestial Being" & all the other factions to temporarily put aside their personal conflicts and temporarily work together to shoot down all the falling panels since each panel is huge and would cause catastrophic damage to anybody below in the city populace.

And since there was no time to evacuate the population of the city below the African Tower, everybody combined forces to blast every single falling panel to save the lives of the local cities populace.

The AMV (Anime Music Video) I linked above is about the collapse of the Orbital Elevator's outter armor panels that protected the numberous Orbital Elevator Train Tethers and the precious cargo used to ferry things into space.

Each Train had Cargo modules on both side and were fully symmetrical, so one train could carry ALOT of heavy cargo into space, including something the size of a Gundam which was HUGE & HEAVY.

The Orbital Elevator's Internal Structure from Gundam 00:

Notice the Hexagonal design with the original Core Tether in the center.
6x Structural Arms for the Outter Armored Panels.
30x Orbital Elevator Train Tether tracks running in parallel.

Here's another close-up shot of the individual Tether Lines in use.

Wide-Angle shot of the Orbital Elevator Tether Tracks along the outter panels.

This is what happens when the outter panels fall due to terrorist attack:

This is what happens when things goes wrong due to Terrorist Attack:
The Trains have fallen off their tether track and are in free fall.

Each Train is designed around 10x Cargo Boxes on one side, 20x in total per train due to each train being double-sided.

The Trains have end cars on both sides so it can easily travel in any direction (Up/Dn) the tracks.

Here's what the AfterMath of the Devastation looks like when the Orbital Elevator gets attacked.
Clouds full of ash and giant armored panels falling to the earth, each one the size of buildings.

Look at how high the ash clouds are from a orbital view over Africa:

Here's what's left with the only thing remaining is the "Core Tether"

Luckily, most of the city centers along the 3x major strips are protected.

Last edited: Jan 28, 2022

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Didn't they have an elevator in the start of the movie Ad Astra?

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No-one is proposing a space elevator between the Earth and the Moon as the Moon is not in geostationary orbit and it doesn't orbit in the Earth's equatorial plane. A space elevator on the Moon could be built with currently available materials as the Moon's gravity is 1/6th that of the Earth.

2.5 m/s is a velocity. I think you mean 2.5 m/s², which is about a quarter of the acceleration due to Earth's gravity at sea level (9.81 m/s²). (Any passenger travelling from Earth to GEO in the car would feel 25% heavier than normal at first but apparent weight would decrease as distance from the Earth and angular velocity increased.) Sorry for my nit-picking.

Last edited: Jan 29, 2022

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So it's completely unrealistic. With a cut in the atmosphere there would be less mass crashing to earth than a rocket going wrong on takeoff.

Quite. Maths is so much easier to write on paper, although I was this many years old when I, partway through that post, discovered I could just press alt-gr+2 to get ²

2.5m/s² feels like a reasonable upper bound for acceleration for a passenger cabin over the course of an hour - 1.25g. 1.5m/s² is a typical elevator acceleration. 0.25m/s² (8 hours to GEO) is way less than an elevator or the acceleration of a plane taking off. 0.025g is unnoticable.

By comparison on an F9 it's 2.8g at MECO.

I'd expect a far smoother ride too - at least once out of the main part of the atmosphere (you'd probably keep speed low, in the 120km/s range, for the first 20km or so and only floor it once the air gets thinner.

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A space elevator works by taking a large base in Geostationary orbit (so at a fixed position above the equator), and unfurling a "rope" towards the earth. This rope eventually gets to the earth and dangles a few centimetres above the floor.

If the centre of gravity (or mass?) is at the exact altitude, it won't move. If it's a little lower than GEO it will slowly move East, if it's a little higher than GEO it will slowly move west.

Now when you start climbing that changes that centre slightly, which is a problem. It's also a pain having to keep your orbit bang on the exact altitude above the earth, what with other objects like the Moon pulling your orbiting space station. So you don't. You keep it slightly above GEO, and you tie the rope to the ground, that solves all the problems, and it's like spinning around with a stone on the end of a string, the string is always tight and the stone always stays the same distance away, even if an ant starts climbing outwards along the rope.

If that string is cut near your hand, what happens? the stone and string fly off, they don't come back to you.

Now because of gravity that "flying off" means they go into a slightly eliptical orbit with the apogee say being the pre-cut distance of GEO altitude plus 100km. 6 hours after the cut would cross GEO, 12 hours after the cut would reach perigee of about 100km below GEO altitude, then voyage back out, reaching the same apogee I think above the same location on Earth 24 hours later.

The only part which would fall to earth would be the rope below the cut. For the rope to be even remotely plausible with modern theoretical materials, it would be tapered, say 1cm in diameter at the Earth, but 1km in diameter out in space depending on the various strengths of the material.

Imagine you were to cut the rope at the level the ISS flys at. It would fall to earth. With a diameter of say 5cm and a mass of 10kg/m you're looking at a terminal velocity of 100-200m/s - if it doesn't burn up on entry. In reality the density would have to be far less than the 10kg/m of a 5cm diameter wire rope, so you're looking at even lower.

You'd cause more damage by dropping a brick out of a helicopter.

The carriage is the tricky part, which is where you'd equip it with parachutes.

If you have the ability to launch an aerial attack on a vehicle in a secure location and no fly zone moving at 200mk/h, you'd cause more damage by shooting down an airliner.

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Speed of climb is limited by the Coriolis force, the available power, and the requirement to ensure the elevator's accelerating force does not break the cable. Current design proposals limit the speed to about 300 km/h so it would take about 5 days to climb to GEO.

Objects release from a terrestrial space elevator extended to 53,100 km would have Earth (but not solar system) escape velocity when released. Transfer orbits to Sun-Earth L1, Sun-Earth L2, and lunar orbit could be achieved by releasing at around 51,000 km.

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hmm.. maybe set them up at the equator, the earth's rotation would cause a centrifugal force, if something snaps it would be launced into space.. although I'm not sure if this planet spins fast enough for that..

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What you're not seeing from a 2D image is that some of the panels in the upper atmosphere are burning up while some of the panels in the lower atmosphere are being vaporized by beam weapons or blown up by missiles.

Literally, Hundreds of thousands to millions of armored panels getting vaporized around the same altitude.

Every time a Armor panel gets Vaporized or Blown up, it's usually not perfectly clean.

So each time a Armor panel gets hit, lots of smoke, ash, particulates gets ejected into the atmosphere.

All in a very short time span, around the same time since there is a very limited window to protect the civilian populace below from the falling armor panels.

The Anime Gundam 00, had it's show's mechanical designers already account for that by having each Orbital Elevator have a giant Hexagonal Armored Shaft Tower with modular armored panels constructed around the Core Tether and the 30 seperate Tether Tracks, each one carrying atleast a single Elevator Cargo Train.

There are 3 Orbital Elevator tethers at the equator that are approximately equi-angularly spaced across the equator.

Last edited: Jan 29, 2022
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Any cable element below GEO would fall back to Earth sooner or later. Anything between GEO and the counterweight would be flung into an elliptical orbit or escape altogether, depending on distance. Of course, the high tension in the cable would additionally impart considerable momentum to each of the sections when the cable was severed.

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with that amount of firepower you’d cause more damage pointing it at a city or the ground station.

My understanding is we’re nowhere near the material science to build one, but if there were a speed limit would only make sense with a physical connection between the cabin and the cable (rather than maglev).

At 300kph you won’t be reaching Earth escape velocity by GEO. I can’t picture how it would work beyond a counterweight, and wouldn’t a counterweight that far beyond GEO put a shocking strain on the cable?

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Not if it’s still connected to the counterweight

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Yeah, only if it's a separated element although any portion remaining below GEO might lower the perigee depending on how momentum is imparted by the release of tension.

At GEO, you would have attained orbital velocity by definition. Escape velocity is √2 times orbital velocity. You'd need to climb out in the direction of the counterweight to gain additional rotational velocity as I mentioned in my earlier post.

ETA: Someone, of course, already did the hard work. The cable needs to be strongest/thickest at GEO. See Space Elevator Taper Profile - Space elevator - Wikipedia and PKASpace Elevators.pdf (wpi.edu).

To ensure the mass of the cable is manageable, the cable's specific strength needs to be at least 48 (MPa)/(kg/m³) so something like single-wall carbon nanotube (100 (MPa)/(kg/m³)) would do the trick.

The taper ratio between the cable cross-sectional area at the Earth's surface, As, and that at GEO, Ag, is given by:

Ag/As = exp(48.5 ρ/T)

where T is the tensile strength of the material in MPa and ρ is its density in kg/m³. For single-wall carbon nanotube, the ratio of areas is 1.627.

Last edited: Jan 29, 2022