Proponents of #SpaceForce think big. They thing space is big. But for security, #space is notably small. I explain.

Earth's land surface is divided into national territories. They're big enough to hide & hoard stuff & they can be controlled & defended by local regimes. +

This applies to national airspace, too. It is actually becoming easier for nations to defend their airspace. As long as nations stay out of each others' airspace (without permission) there is no problem. But above 100 km or so this changes entirely. +

For security purposes, space means mostly orbital space. Low Earth orbit, up to about 2000 km, is militarily important because it's close to the surface. Weapons such as space-based missile defense interceptors or any surface-strike weapons would need to be parked in LEO. +

All low orbits overfly all points on Earth within a band of South to North latitudes. That's why no nation has the right to claim the space even 100 km overhead.

So, as soon as we're outside the atmosphere, different national territories collapse into just one place. +

All orbits also "cross" each other, repeatedly coming as close to each other as their difference in altitude. This means that with small changes in velocity, any object can be made to collide with any other that is orbiting at about the same altitude. +

It is often claimed that this means any satellite can be used as a weapon to attack another satellite. That claim is false; actually very few satellites have the kind of sensors that would be needed or propulsion beefy enough to be militarily useful as antisatellite weapons. +

One kind of satellite that *would* be optimized to hit another are the space-based interceptors as now proposed for missile defense. In fact, these would have enough thrust to reach from LEO out to geostationary orbit where many more important satellites are located. +

So there are a taxonomy of orbits, but to a good first approximation all orbits within a given altitude band are the same place. There can be rules to avoid collisions but one could not militarily defend some national piece, say, of the orbital band between 300-600 km. +

If the US were to deploy space-based weapons in LEO, as sure as night follows day, China & Russia would do likewise. If the numbers rose to thousands, as now contemplated, these weapons systems would pose a short-timeline threat to each other & to other satellites. +

Another aspect of space that makes it all one place is that there's nowhere to hide anything. Satellite observables can be lowered but given multiple sensors, modes and angles, in the end everything is out in the open. This is bad for stability, but good for arms control. +

Space hawks say they're worried that innocent-looking Russian or Chinese sats could conceal antisatellite weapons inside. Or that robotic "servicing" or "debris clearing" satellites could be used as weapons. I worry much more about 1000s of space weapons optimized for war. +

If the threat to our satellites can be limited by binding arms control that forbids antisatellite weapons as well as any weapons stationed in orbit, then we can develop redundancy & resiliency measures to deal with or to limit the risk posed by that limited threat. +

But if we pursue the path of an unconstrained arms race, we are going to create an explosive confrontation between weapons systems co-occupying and seeking to dominate or control the same single crowded, vulnerable place. #