So time to share the work that I did mainly last night in preparation for this Russian DA-ASAT test.

We knew that this was likely coming because the NOTAMS matched previous Nudol tests. It's still unclear whether there was an actual target, or it was a flight test.

By the way, you can see where Seesat was talking about this a couple days ago here:
http://www.satobs.org/seesat/Apr-2020/0092.html

The NOTAM for the first stage was active between 15:00 and 21:00 UTC, and the NOTAM for the splashdown over the Arctic Ocean was between 15:15 and 15:21. Not sure why there's a discrepancy there, but that would put the launch sometime around 15:00 UTC today.

The launch was to the northeast out of Plesetsk and was set to splash down over the Arctic above Eastern Russia.

So I set up a scenario to search for everything that was passing through a corridor between the launch site and the splashdown zone.

Now there's a lot of stuff up there, so let's just focus on the Cosmos satellites first, which is a generic identifier for a large number of Russian satellites. There are a handful that run across the area.

Out of these, there's one that looks potentially promising as a target ASSUMING THAT THEY WERE AIMING FOR SOMETHING. Again, we have no reason to believe that yet. But if they were, Cosmos 1356, an old ELINT satellite, could be in the right place at the right time.

But guess what? @LeoLabs_Space has calculated state vectors for Cosmos 1356 since, so it's still up there.
https://platform.leolabs.space/catalog/L132 

So now let's talk about everything else up there, because reminder: there's a ton of stuff in space. And that NOTAM gets very busy once you start looking at everything.

Note: I'm re-running some of my analysis at the moment. Nothing wrong, I'd just like a more thorough look. Still believe that this was just a flight test.

Alright, I'm back and ready to write some more. Removing small pieces of debris and isolating only things that passed through the flight path, there's still a lot of stuff. So I also narrowed it down to objects that could feasibly yield a near-head on collision.

At this point, let's set some ground rules to narrow it further.
Assumptions: Russia would not try and target anything but a Russian satellite. This is common sense. And it allows us to narrow it a lot.

Once we get rid of those, we're only left with a few potential targets.

A few more can be eliminated based on the direction that they're moving through the field.
And now let's tackle these objects individually.

10114: A Soviet rocket body from 1977. Up at 500km, so I would hope that that would be far too high for a test.

42800: A Russain rocket body from 2017. Only at ~200km, which would be very, very attractive for a test.
BUT: It's barely in the area at 15:00 and is out nearly immediately.

And the rest of the objects are what space-track calls "analyst objects". These are objects that are from an unknown launch, so it's hard to determine who "owns" them. They're usually small, and most likely wouldn't be used for a test.

Additionally, all of the analyst objects left are over 500km up, and again, I think that is much too high for a test.

So in summary, I don't think there were any great candidates for an orbital object to hit even if they wanted to based on the timing of this test.

As @planet4589 said here, we'd most likely see a launch of a small dummy satellite into a very low orbit if they were going to go for an actual hit-to-kill test. That's what India did with their 2019 test, and the last US test hit a re-entering satellite. https://twitter.com/planet4589/status/1250538503768768518

The end. Enjoy some pretty orbit plots.

I lied, I'll keep going with just a little bit more. If you remove the assumption of a head-on collision, you have a couple more interesting objects in the firing line.