With real world technology, satellites maintain their gross orbital position through orbital mechanics, maintain precise position (such as geostationary longitude) with station-keeping rockets (ion engines today, monopropellant engines in the past), maintain alignment with reaction wheels, and power themselves with solar panels.
technology, orbital mechanics will still be the cheapest, most reliable way to maintain gross orbital position. Photovoltaic panels may well remain the cheapest and most reliable way to power them (because even with cheap access to space, maintaining a non-photovoltaic power plant requires paid technicians). Reaction wheels might remain the best way to maintain alignment. The only thing that definitely changes is station-keeping; reactionless maneuver drives never need fuel, and if the job can be done with the miniscule thrust of an ion engine, a really small maneuver drive powered by the photovoltaic panels should be able to handle the job, unless they have some inconvenient minimum size.
Nobby-W wrote: ↑
Mon May 29, 2017 6:24 pm
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If you're interested in the physics, the Chelyabrinsk meteor is estimated to have weighed something like 12,000 tons, and was completely vapourised when it entered the atmosphere at approximately 20km/sec. The Tunguska meteor of 1908 made a much bigger bang (estimated about 30MT), but is estimated to have been more like a million tons or so.
From this, we can infer that te-entry at 20km/sec will almost certainly vapourise a starship hull in the upper atmosphere before it does any harm, . . .
The fate of a meteorite depends on a variety of factors, including type (icy-cometary, stony, nickel-iron, fragile space junk, tough space junk, reentry vehicles), velocity (high atmospheric, low orbital, interplanetary, constant-G, relativistic), and angle. Finned tungsten baseball bats are likely to make it through any habitable atmosphere; even if they melt, a blob of high velocity tungsten will ruin your day. By contrast, even a huge cometary object is likely to vaporize if it arrives at an angle just deeper than an atmospheric skip angle. The Arizona Meteor Crater was believed to have been a nickel-iron meteorite that struck at a low angle, and tore into lots of small bits -- but the central bulk of the cluster of small bits made a pretty impressive hole.
To the point, you're not going to find any planetary governments (or balkanized worlds' starport organizations) willing to bet that a failing or suicidal starship will vaporize between space and population or economic targets on the surface. Orbital facilities are even more vulnerable to collisions, so any defense system that can protect a highport will also protect surface targets.
Incidentally, a vacuum or trace atmosphere world is pretty much equivalent to a highport with a structural backbone (and possibly gravity) provided by nature.
Nobby-W wrote: ↑
Mon May 29, 2017 9:10 pm
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Trajectories that hit the ground (sometimes known as Lithobraking) are not generally sensible orbits.
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I love this expression. As a space nerd, I'm surprised I hadn't heard it before.