Mark I weather machines are tiny spheres filled with hydrogen and helium, each with an adjustable mirror
Weather machines are very small aerostats, airborne devices originally designed to control the flow of sunlight into, and the flow of radiated energy out of, a planetary atmosphere; they are often used on large open-air megastructures for the same purpose.
Basic (Mark I) weather machines consist of spherical shells of diamondoid, usually from 1mm to 1cm in diameter, filled with a lighter-than-ambient gas such as hydrogen or helium (on a Cytherian-type planet, oxygen or nitrogen can also be used). Each sphere contains a flat mirrored surface which can be adjusted to any angle using micromotors; the angle of this mirror is controlled remotely. When a sufficiently large swarm of weather machines of this type are introduced into an atmosphere, the mirrors can be adjusted to reflect insolation back into space (providing a cooling effect) or to reflect escaping infra-red radiation back towards the ground (providing a warming effect). To a certain extent the mirrors can be used to steer and control the disposition of the swarm itself; in an Earth-like atmosphere the aerostats operate at 30-40 km altitude, above most wind systems. Any aerostats which do get blown out of position become inactive and fall to the surface, where they can be recycled.
More advanced (Mark II) weather machines are similar in appearance but with essentially no moving parts and much greater capability. Mark II aerostats contain solid state phased array systems which can absorb incoming energy and re-transmit it at a wide range of frequencies. These devices can apply localised heating to change local climate and weather patterns, and even focus on very small targets to act as a defensive (or offensive) weapon.
In fact a weather machine system, especially a dense Mk II swarm, can be used as a planetary defence system, capable of focusing a formidable amount of energy on a single spaceship or other object at a distance of more than ten AU.
The energy collected by a sufficiently dense swarm of mark II weather machines can be transmitted to ground receivers and used by the local colony for industry, transport use and computation; several tens of petawatts can be collected in this way on an Earth-like world.
Larger versions can be used in orbit around a planet to focus heat onto a cool planet, or away from an over-warm planet; in many locations orbital weather-machines are in use as an alternative to sunshade or soletta technology. Worlds which make extensive use of weather machine technology to maintain a pleasant climate at ground level include Locus and the Fiarro Twin Worlds.