Comments on: Falcon 9 aborts automatically at T minus 0

By: Steve Golson

Steve Golson — Mon, 16 Mar 2020 20:42:51 +0000

Diane Wilson-

In later years, as computers got faster, a nanosecond was too slow. So Hopper started handing out packets of pepper. A flake of pepper represents the distance light travels in a picosecond: one trillionth of a second.

To a designer of modern integrated circuits, a nanosecond is a really, really long time. On the other hand, ten picoseconds, now that’s pretty speedy.

By: sippin_bourbon

sippin_bourbon — Mon, 16 Mar 2020 16:53:00 +0000

They should have known not to try to launch on March 15th.

Beware the Ides of March.

By: wayne

wayne — Mon, 16 Mar 2020 15:25:46 +0000

Andi-
IIRC– for the Cray, no critical connections are more than 1 foot apart. (didn’t this come up ‘like a year ago for something else?)
Tangentially related– “Krytron,” an extremely fast switch used for early RADAR, and to trigger a symmetrical implosion detonation for nuclear weapons.

Diane–
I really enjoy your ‘inside-baseball’ tidbits!

By: Andi

Andi — Mon, 16 Mar 2020 15:00:31 +0000

“light travels 1 foot in 1 nanosecond.”

Spot on!
(300,000,000 m/sec) / (1,000,000,000 ns/sec) = 1/3 m = about a foot

By: Diane Wilson

Diane Wilson — Mon, 16 Mar 2020 14:48:47 +0000

Grace Hopper, the Navy officer who invented the COBOL programming language, used to hand out “nanoseconds” to her students. They were one foot lengths of wire.

By: Andi

Andi — Mon, 16 Mar 2020 14:17:49 +0000

IIRC, when they built the first Cray supercomputer, propagation delay along the wires was a major consideration. One of the reasons why that computer was circular in shape was to reduce the length of the interconnecting wires.

By: wayne

wayne — Mon, 16 Mar 2020 13:56:14 +0000

David–
Great factoids!
(Does that Lecture, exist anywhere?)

If I’m recalling correctly— light travels 1 foot in 1 nanosecond.
Electrical signals theoretically propagate at the speed of light but that depends heavily on the type of cable through which it’s running. (as you noted)

By: David

David — Mon, 16 Mar 2020 02:57:47 +0000

There’s pretty much no possibility of human in the loop for most of the T-0 conditions, things happen too quick, and holding the rocket on the mounts long enough for a human to evaluate things and make a decision is highly undesirable. One of my college compsci classes actually had a fascinating lecture series on the design of the controller logic of, if I recall correctly, one of the later Delta launchers. They had to go so far as to have decisions being made in the engine controller itself, because sending the raw data behind that decision the extra few meters to the main rocket controller imposed too much lag, and also required more bandwidth (and thus more heavy cable and interconnects) than they really wanted to route through that part of the rocket. I can only imagine how that scales to 9 not to mention 27, Merlin engines.

By: Scott M.

Scott M. — Sun, 15 Mar 2020 19:12:01 +0000

Most of the time I don’t like the notion of humans being ‘out of the loop’ for things like this. But given how fast the onboard computers shut things down, I do see the appeal of having such a quick response.