Assigning ARIN IPV6 Address Space to Server Sky
How many IPV6 addresses will be needed for individual thinsats in a heavily populated server sky constellation?
IPV6 uses a 128 bit address space, and is currently being assigned in very large address blocks, up to 48 bits (the address space for IPV4, comprising most of the machines on the internet, is 32 bits). 48 bits corresponds to 280 trillion unique addresses. This will certainly cover the 100 billion version 2 thinsats permitted in m288, but it may be insufficient for larger constellations of smaller thinsats at greater distances.
It is convenient to assign addresses to particular positions along the orbit. That tells ground antennas where to point. The azimuth angle of the antenna to reach a specific device will then be a simple function of time of day. In fine detail, apogee skew and distance across the constellation will change the angle somewhat, but routers and DNS servers within the ground antenna's narrow "sky spot" can provide further location information to precisely position the beam for subsequent packet exchanges.
m288 will be sparsely populated. Assuming 2 kilometer constellation boxes and a 50 kilometer minor radius, there is room for 40177 angular slices of boxes around the orbit, and 1963 boxes per slice. Slices can be addressed with 16 bits, and boxes with 11 bits. This permits up to 19 bits of addressing within a box, or 512K individually addressable devices. Since large arrays may exceed one million thinsats, and each thinsat may have many IP addresses, this is inadequate, but not greatly so.
If we use 5 kilometer constellation boxes, then there are 16071 slices ( 14 bits ) and 312 boxes per slice ( 9 bits ). We may arbitrarily assume that boxes can rearrange themselves within a slice, and limit slice population to less than 256 ( 8 bits ). That leaves 26 address bits within a box, or 64M individually addressable devices.
In the distant future, deep space arrays at asteroidal distances will consume far more IPV6 bits. Assuming very small thinsats, each consuming perhaps a watt and in total consuming 10% of solar output, with 16 IP addresses per thinsat, the total number of addresses is about 6E26 . That can be handled with 89 bits. A sparse spatial matrix may increase the number of bits to address all the boxes out there, but at those scales the routing will probably be hierarchical and local routing can increase the efficiency of address assignment. So all of solar system space can be handled with 92 bits. That leaves 36 bits to address 70 billion solar systems around the galaxy; perhaps by the time we populate other galaxies we can develop new standards for a larger-than-128 bit address space.