
When people say "USDA", this isn't what I imagine.
Northrop Grumman and L3Harris Technologies have won contracts worth up to $1.3 billion to build a 28-satellite constellation to support missile warning and tracking by the US Space Development Agency (SDA). The first of the satellites are scheduled to launch in April 2025 and all 28 will eventually be tasked with collecting …
...that the US doesn't already have a constellation up there for this very purpose. Of course, maybe they have, but they can no longer put the upgrade through the "black ops" budget and, of course, everyone knows this is possible now so no need to keep it secret this time around so potentially cheaper if they can go open ten der for the cheapest bidder :-)
I suspect the types of missiles and the means of tracking them is far more complex than the old cold war era systems of ICBMS. Cruise missiles, medium range missiles, hypersonic missiles, stealth technologies, are all (relatively) new threats to deal with. I would guess the older sensors aren't up to the task, plus the need to integrate the information into the "battle net" in real time is a factor as well.
The modern battlefield is basically a giant mesh network of sensors and and weapons. The pace at which technology evolves will result in more and more frequent updates to satellites and ground based monitoring platforms.