But AFAIK Lisp isn't in space anymore, at least actively, right? Wasn't even the remote control agent rewritten in C++?

It is, at least, in James Webb https://www.stsci.edu/contents/newsletters/2018-volume-35-is... for the scheduling system.

Scheduling runs ground side as normal Unix app

Surely that doesn't matter? Seems like they can be real-time, even if they are no longer?

What am I missing?

You're missing that I asked for current projects in Lisp.

That's completely irrelevant, though.

- Claim: "it is possible to write hard-real-time lisp, as evidenced by people having done it in the past."

- You: "nobody is doing it right now"

That's not a counterpoint.

I have no idea what you are even talking about. I'm asking about current projects in Lisp for real time, so it's very relevant. You might need to work on your reading comprehension.

>within a tight deadline

Isn't hard real-time only about upper-bound of tasks? Like if every task could be proven to run under t seconds (not necessary small), it is eligible for being called hard real-time.

Formally, yes. Practically, once t is large enough, violations of the constraint are much more likely to involve "acts of god" (power outages, rogue backhoe operators, natural disasters, wars, etc.) even if conventional best-effort techniques are applied.