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Comment by jccooper | Hacker News Reader

There are no commands the other way. F9 flies entirely autonomous, including termination. Based on the FCC filings, I'm pretty sure it doesn't even have receivers.

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There was a reddit thread from a guest lecture a few years ago that said that around T-1 they turn off all receivers on Falcon 9.

https://www.reddit.com/r/spacex/comments/lw6yk1/notes_from_a...

Those same notes mention that the flight termination system was unencrypted. Now it's autonomous.

More info on AFSS.

https://www.spaceflightinsider.com/space-centers/ccafs/autom...

I know the Air Force claims this makes it safer by avoiding the need for a range officer to make a time sensitive safety call but it’s not like there isn’t a precedent of software goofs in this area of software controlled termination

https://apnews.com/article/1d85f290e31cad8532636fcb576f4788

The launch termination system at least needs a receiver

Isn’t this only the case if the intent is for a range officer to abort? I.e., if this system is fully autonomous and on-board, a receiver wouldn’t be necessary?

Yes

What the OP seems to be saying is that the emergency abort system actually operates on a “lysine deficiency” basis: if the signal is no longer received, the self-destruct system goes BOOM.

I suppose this classifies as “fail-safe”, though if there’s folks riding on the tip of this large sharp shard with the explosive force of a small nuclear weapon I’d be rather concerned about radio transient interference and things like that.

In that case, is it not really autonomous? Who’s stopping the signal? I’m assuming the range officer?

When passengers are on-board, there’s generally a launch abort engine that is supposed to help them leave safely in a abort scenario

The way the automated FTS works is essentially that the USAF blasts a "DO NOT BLOW UP" signal with a very high power transmitter to the FTS. If the FTS doesn't receive that signal, it triggers and then you have a RUD.

That sounds terrifying

I don’t disagree, but that is in fact how it works!

True, but it’s the safest configuration because you want the default condition to abort. The inverse set up is less safe because there are more failure modes for a receiver to break, meaning if a abort command was sent there’s more chance it won’t respond. It’s like choosing a normally-open or normally-closed valve; you want the default (power off) configuration to be the safer one. Inadvertently aborting is safer than not aborting when you should have

RUD: Rapid Unscheduled Dissassembly

I prefer the term distributed landing.

I’m hereby notifying you that I have now appropriated that term for my own future use. :)

It does not. F9 FTS is onboard and entirely automated. There is no ground trigger.

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