DEATHRAYTHEORP

System Overview
The space architecture is composed of two separate types of satellites. The first is a constellation of 90 solar power harvesters located at L1. These satellites beam their energy via a high power laser to an intermediary satellite in a GEO orbit above the Earth station. The GEO satellite converts the laser energy into microwave (30GHz) which it beams to the ground station where it is harvested by a rectenna and pushed into the local electrical grid.

Hardening
For the satellite subsystems to function properly over time, the electronics systems must be radiation hardened. All data and communication systems need to be redundant, and all electrical components need to be space qualified or shielded. Components can be made tolerant through physical means such as using radiation absorptive substrates and additional radiation-resistant methods, such as employing ECL instead of CMOS technology. Components can also be designed for greater radiation tolerance through architectural means, such as the fault-tolerant LEON SPARC made by Gaisler Aeroflex. These processors feature redundant caching and extensive error correcting. Software can also provide a capability for hardening by performing error checking during operation.

Pointing
The task of maintaining the RF beam, much less a laser from the Halo orbit, on the rectenna is a substantial challenge. For both cases very precise models of the satellite and its orbit will be necessary, along with a number of instruments. Star tracking and sun or horizon tracking will be necessary along with an IMU. Further feedback will be required by the scientists and engineers monitoring at the ground station. The gimbals needed will require research and development efforts to create devices with the necessary precision and stabilization. The latency in the communication system will make this even more challenging and make the models of the system even more important.

L1 Satellite
Locating the satellites at L1 allows us to maintain a fixed orientation in the Sun-satellite-Earth system. Unlike an Earth-orbiting system which would require independent gimballing of the harvesting panels and power downlink antenna (a feat that's simply structurally impossible given the incredible sizes), the fixed orientation at L1 allows us to construct the satellite as a completely rigid structure.

Solar Array
Each satellite will feature a 160x4500m solar array (150x4200m effective area with almost 95% cell packing efficiency) which produces 175MW of electricity at 20% cell efficiency. The fact that L1 is 1.5 million km closer to the Sun actually gives a small boost to available power density. This gigantic solar array is supported by an inflatable structure which substantially reduces the mass and packing volume of the satellite during launch and transfer. Altogether the solar array weight is estimated in the region of 70,000kg, constraining the cells to a specific efficiency of 2.5 kW/kg. While a solar array over 4km long may sound implausible, research teams have already begun working on arrays nearly four times that long, so the technology should be ready by the time we are ready to launch.

A single launch from an HLV (such as Falcon 9) can loft half of the necessary solar arrays for one satellite to LEO. These would be split into multiple smaller array packages which are linked to each other by a more traditional aluminum support structure. Together these would then be attached to the satellite bus. The arrays themselves would remain packaged until the satellite's transfer trajectory has taken well outside of LEO and the atmospheric drag that would create untold complications. At a designated intermediary point (or even at L1) the inflatable structure is inflated via chemical reactants and rigidized into its final shape, unfolding the solar arrays in the process.

Satellite Bus
Opposite the solar array lies the satellite bus which is dominated by the high power laser array and cryogenic cooling and radiating system. The cooling system will have to be able to dissipate the 87.5MW of power lost due to laser inefficiencies. Such a system would incorporate state-of-the-art power dissipation techniques, such as the next generation of Thermacore's loop heat pipe deployable radiator. The laser itself will require some ability to gimbal and track the GEO satellite though a range of only about +/-1 degree is required which can be done independently of the rest of the satellite with a very high precision. At a 50% conversion efficiency, the laser itself transmits approximately 87.5MW of energy to the GEO satellite.

Estimated at 50,000kg, the satellite bus also contains all of the other core equipment. This includes a small communication antenna for downlink of telemetry and uplink of emergency commands. The ion thrusters as well as the estimated 10,000kg of Xenon propellant necessary for pushing the satellite into its halo orbit and continued stationkeeping throughout its lifetime are also stored in the bus.

In total, the satellite wet mass is estimated at 130,000kg (dry mass of 120,000kg). This number is only realizable with extensive use of inflatable support structures which have shown mass reductions of an order of magnitude (compared to more common metallic structures). Each satellite would require three HLV launches to bring all of its components to LEO for assembly.

GEO Satellite
Unlike the L1 satellites, the GEO satellite can take a much more traditional form. A large inflatable antenna is kept fixed a perpetually pointed at the ground station below it. The laser energy beamed from the L1 satellites is harvested using a relatively small PV array optimized to receive the specific laser wavelength. A chemical rocket kickstage is used to place the satellite into geostationary orbit while several small cold gas thrusters enable stationkeeping and attitude control. The GEO satellite wet mass is estiamated at 9,500kg (dry mass of 6,000kg).

Transmit Antenna
The dominant feature of the GEO satellite is a 150m diameter inflatable transmit antenna. Large inflatable antennas have been flown on a number of recent STS missions and their design and packing is relatively well-studied. Tests on the ground and in space have shown their ability to maintain a surface error relative to the ideal parabola well within our required tolerances for microwave transmission.

Propulsion System
Unlike the L1 satellite, the GEO satellite will transfer from LEO using a more typical chemical rocket kickstage before switching to smaller cold gas thrusters for stationkeeping and attitude control. These systems are much less efficient than an ion thruster (Isp of 450s and 200s respectively) requiring a larger percentage of propellant mass relative to the satellite mass. The much lower GEO satellite mass, however, makes their use cheaper overall.