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[Sheb]

Also, a Falcon Heavy bring 53 tons to orbit, so 2,65 MW. Assuming 10 years lifespan, it'll produce 8,35704×10^14 J.

The Falcon Heavy is basically 3 Falcon 9 strapped together. So it'll use up about 93 400 gallons of kerosene (353,557 l). That's 1,33031992 × 10^13. So launch is only about 1.5% of the total energy produced. You'll make that up by the extra efficiency from being outside the athmosphere, lit up 24/24.

 It's energy efficient. Not practical, or cheap, but energy efficient.

[10ebbor10]

Also, a Falcon Heavy bring 53 tons to orbit, so 2,65 MW. Assuming 10 years lifespan, it'll produce 8,35704×10^14 J.

The Falcon Heavy is basically 3 Falcon 9 strapped together. So it'll use up about 93 400 gallons of kerosene (353,557 l). That's 1,33031992 × 10^13. So launch is only about 1.5% of the total energy produced. You'll make that up by the extra efficiency from being outside the athmosphere, lit up 24/24.

 It's energy efficient. Not practical, or cheap, but energy efficient.

Nah it isn't. You're forgetting the structure, the transmission (I think) and the fact that they shouldn't be deposited in LEO, but near GEO* for maximum efficiency. Also, the energy costs of rocket production and such.

*Sadly there are no numbers for GTO, so I can't use those. However, In general, thepayload to GEO is between half and one fifth of that to GTO. Which would mean about 6000 tonnes for the Falcon Heavy

And just to give an idea how big those costs are:

Power beaming from geostationary orbit by microwaves carries the difficulty that the required 'optical aperture' sizes are very large. For example, the 1978 NASA SPS study required a 1-km diameter transmitting antenna, and a 10 km diameter receiving rectenna, for a microwave beam at 2.45 GHz.

((And just a note. I was talking about the useage of solar power plants to provide power to the prospective Mars base in the original post. ANd more specifically, about retransmitting power using relay sattelites, which is just plain silly))

Edit: The Falcon Heavy weights about 4 times more than the Falcon 9. I doubt their fuel to thrusts ration is lower.

[Sheb]

Falcon Heavy is carrying 12 tons to GTO. If we decide a fifth of the mass is transmission stuff, and that we loose 20% of energy during transfer, Energy production becomes 8,35704×10^14/53*12*0.8*0.8=1,2109824 × 10^14 J.

So launch cost rise to 10% of the total. Still worth it, strictly energy-wise. Of course, as I said, it's not actually practical or anything.

[10ebbor10]

I said GEO. Not GTO. As I noted during my last post (one of many edits) that further halves launch capacity.

And even then you're still not counting solar pannels costs, the construction costs.

Still doesn't matter though, since the ITU is never going to allow such a thing to be build.

[Sheb]

Yeah, I'm just saying we would gain energy from doing such a thing, not that there aren't better ways (like putting those panels in the Sahara) or that it would be worth it.

But why would the ITU care?

[10ebbor10]

Microwaves jam all communication sattelites passing through them.

But yeah, they would probably be energy efficient in Earth orbit. Not near Mars though.

[Sheb]

Well, except on Mars you significantly reduce launch cost.

[Starver]

Ninja ninja ninja ninja ninja ninja ninja, it appears...  Still, I've written it now.

Even a partial space elevator would be a useful thing, as gravity is a system of diminishing returns.

Wut?  you're not building "as far up as practical", you have to start from the stable orbital point and 'build' down.

Here's what you do for a space elevator: Get a 'top' station in geostationary orbit, where you're 'tracking' the ground.  (Or geosynchronous, where you're doing a probably insignificant figure of eight above the ground.)  Lower a cable down towards the Earth.  At the same time either 'lower' a cable outwards (because further out than geostationary, the cable is trying to 'fall up'), or move yourself upwards a little as well.  You're aiming that the centre of mass[1] of you+'groundside cable' stays at the geostationary point.  You also need to ensure you're not spinning (or, rather are spinning at exactly one rotation an orbit, in the same plane)[2].  If you can get something heavy at the top end (captured asteroid?) it doesn't need to be anywhere as long outwards as you need to be inwards to reach the ground.

Eventually, your cable reaches the ground.  Attach to the prepared groundstation, and reel out the counterweight (or length of counterweighting cable) a bit further outwards and you can maintain a bit of controlled tension.  Now send your 'cable enhancer' spiders up and down, as necessary, to change the cable from being a mere thread to being the item that you can reliably send capsules up and[3]/or down.

Now send up more cable-making materials, send them to other points along geostationary orbit and get building, because humanity is going to want more stations for increased traffic, no monopolies, more protection against single-point-of-failure (sabotage or accident), etc.  Although would be a megaproject-and-a-half in the first place, and whoever (probably a consortium) stumps up the cash for the first elevator might well be seeking monopoly (either of a single elevator, or of all of them).  That's for humanity to work out though.


Anyway, assuming no other gravitational influences, Earth geostationary orbit (forgive the tautology!) is 36,000-ish km above the planet's surface.  Areostationary orbit (Mars) is 17,000-ish km, which along with other planetary characteristics (planetside dust-storm damage to the cable aside) makes it a more practical effort to try to accomplish.  Especially while we're still sending stuff to Mars, anyway, perhaps with the cable.  For the Moon, one might imagine that with the Moon tidally locked in rotation to the Earth that the 'selenostationary' point (i.e. w.r.t. the moon) is Earth.  But you couldn't put a cable to Earth, anyway (except, with some clever mechanics, to either meet some mobile ground-station running along an equatorial track, or some 'gimballing' and tether-anchor at either/both poles with enough initial height to clear the ground[5] and enough slack (dealt with somehow or other[6]) to deal with orbital variation)...

But with Earth gravity exerting a pull as well, there's actually the Earth-facing Lagrange point (56,000km or so) and its opposite (slightly more[7]).  No problem with atmosphere at the Moon's surface, either.  But, OTOH, there's a lot less opportunity to choose the spot of your ground stations.  And L3-5 Earth/Moon points (also relatively stationary to the Moon, ignoring distortion by influence by Sol gravity) are awkward.  L4 and L5 are essentially Earth-distance (360,000km or so, give or take), and L3 is in opposition, thus means you have to get around Earth (perhaps attach the cable to your 'Dyson cage' you've been building around Earth ever since you finally linked together every geostationary structure into a ring, and started to build out over towards the poles!).

Or so says my reading of the situation, but it's been a couple of decades since I touched the actual maths.



[1] Sort of.  But I won't go into the maths.

[2] Although see also the potential use of a series of shorter non-geostationary 'spinning tethers' to pick up things at their ends and transfer craft further out.  Sounds complex to me.  Electrodynamic tether operation would be needed to maintain/regain orbit, unless you also balance with downward transfers.

[3] I minded to deploy two cables, one for each direction, with a 'hard link' at the top end.  A longer platform.  But I haven't worked out the maths of how any given separations at top/bottom would be affected in any curvature of the cable.  Anyway, the idea is that you don't need to engineer "one side of cable up, the other side down" methods which means a partial linkage of vehicle to cable, or periodic mechanical 'stepping across' of an upward-going vehicle's linkages across a downward-going one. Also you can double-time the upward (or downward!) traffic at need, plus should there be a failure of one cable you may[4] still have the other in order to get the broken cable's replacement materials up there and constructed again.

[4] Assuming no damage to the second cable by the first, of course.

[5] As it initially leaves 'earth-anchor' horizontally, or even downwards, as a far more complex catenary 'suspension'

[6] You know those "no-snag travel modem cables that has an 'S-'shaped path through the core spool and unreels from opposite ends, with a spring for tension/re-reeling (and ratchet)?  Well, I thought about something like that being the centre of a Pluto?Charon tether link (only with no ratchet, just some 'sprung' tension) to deal with orbital variation.  Or even something at the common barycentre with a geared mechanical linkage between two different spools to pay out/feed in the correct proportion of cable from each end.

[7] Why use the outer Lagrange point?  Well, sending and receiving craft on non-Earthsourced/bound trajectories.  The counterweight station of a Lunar L2 station would be ideally placed to 'drop' interplanetary missions from, for zero initial fuel use, and then you'd just need to adjust for awkward timing and movement out of the moon's elliptic plane.

[10ebbor10]

Well, except on Mars you significantly reduce launch cost.

Not if you launch from Earth, that is. Though technically a Mars orbit might be slightly cheaper than GEO. But then I'm not counting stabilization required to get into the Martian equivalent of GEO.

As for partial spaceelevators. Balloons can support an elevator up to 30 km.

[Starver]

Well, not much can stop it except sheer mass. The Earth's athmosphere is 1 kg/cm^2, so even to get half of the protection (Which would be equivalent to being at 5000m high on earth, so livable), you'd need 5m of waters all around your station. Not going to work.

I don't think that'd be a big problem...  "Water-jackets" around a station would actually be a pretty good viable solution.  Thicker parts around the normal living quarters, lesser around more casually used areas, and a far more water-clad area around a small emergency 'bunker' area to be evacuated into should there be any threat of increased levels, e.g. due to flares.

It might be integrated into the life-support system, i.e. the drinking/hydroponic-irrigation systems, but I suppose I'm wary of micro-organisms (Legionnaire's disease/etc) brewing themselves up in the tanks while out of sight and out of mind.  But perhaps if partitioned into smaller enclosures with regular testing and use/flushing/disinfecting/whatever (also helps deal with micrometeoroid damage, or even larger holes[1]?) so that mightn't be so bad at all.

The big problem is getting the water there.  Taking heavy water (though not actually "Heavy" water[2]) up from Earth would probably contribute a lot of mass, maybe equivalent to the rest of the structure mass itself (or more?).  But if harvesting from Lunar deposits, asteroids, martian poles, Saturnian/Jovian ring-ice (manually or via remote vehicles), or wherever is 'local' to the station there might a handy source.

(Just don't release alien microrganisms of which we have no conception and against which we have no defence!)

[1] I'm wondering if a puncture from the outside would freeze enough water to create a seal.  And then I'm wondering if a puncture to both outside and inside could be handled.  Would the water freeze and plug things up, or would the inner module's escaping air force a path through the forming ice into the vacuum of space?  Probably with rubber membranes slatted perpendicularly throughout the water-pod you could provide for a more survivable situation than otherwise, but I'll admit that's just a thought experiment without any testing behind it.

[2] i.e. D₂O!  Although that'd probably be even better as a pure protection system.

[10ebbor10]

For the autosealing it depends on the size of the leak. If it's small, it might work. To large however, and the thrust produced by the escaping vapourizing water will break whatever seals occur. A multilayer system might be best. Ideally, you could have the layers slowly moving in opposite directions. Also, note that the freezing occurs as a direct result of the evaporation. So most of the ice will be the water that's escaping.

[Aseaheru]

and we still should have everywhere the humans go as far into the station as possable. i.e. the center.

[10ebbor10]

and we still should have everywhere the humans go as far into the station as possable. i.e. the center.

Sadly, if you want artificial gravity, you want humans as far out as possible to reduce stress.

[Sheb]

I think he meant the center as in "far away from any wall", not as in "in the middle of the wheel".

Still, given the massive logistic hurdle of getting those space station up and shielded. Why don't we just colonize the friggin moon?

[PanH]

An moon based station is obviously the first step. And we're still far from autonomous ones.