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Comment by mabbo | Hacker News Reader

Musk tweeted last night that there was a potential leak issue that might cause a scrub during the launch. They added an automatic check for the problem, and it appears that's what caused the scrub.

Since this is a launch to the ISS, the launch window was tiny- miss it by a second, you've missed it completely.

They'll fix the issue and probably try again tomorrow.

Edit: my mistake, Musk has tweeted that there was another probably-unrelated-maybe-issue, and they called it off just to be safe. Still, provided the minor issue doesn't turn out to be something more major, tune in tomorrow at 9:30 am EST.

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The issues were unrelated. The leak from yesterday was in the system that spins up the turbopump prior to engine ignition (using compressed helium).

The scrub today was related to some wonky readings on a sensor that measures the position of a hydraulic actuator that controls the direction of the second stage engine (the 'TVC' or 'thrust vector control' actuator).

How tight is the launch window for rendezvousing with something in orbit? A second? A few milliseconds?

It depends on the capabilities of the launcher. For Falcon 9 it's several minutes, but since that's shorter than the amount of time it takes to 'recycle' from an abort (even if the issue can be fixed in zero time), it's effectively an instantaneous window.

Depends on the orbit and the fuel available anything from seconds to hours. A fully loaded Dragon will have an "instantaneous" window, but with spare fuel for corrections during launch it can be an hour or more.

This seems informative:

https://www.reddit.com/r/spacex/comments/3vcoxh/why_spacex_h...

Not super tight, but they don't have a lot of leeway either.

And this is why we write unit tests!

Ars now says that Musk is claiming to have personally scrubbed the otherwise "green" launch due to irregularities he spotted in a control system for the upper stage. Not sure we are getting any full story yet. Not sure he has full a story yet to give.

https://arstechnica.com/science/2017/02/behind-the-scenes-of...

Does he literally have a finger on an abort button? I find that very hard to believe.

NASA provided a live video of the launch prep. Maybe an hour before the launch, the commentator discussed two issues, and said that for both of those issues, they would make a call on it at T-1 minute.

Later on, the video showed SpaceX launch control center, with a group of people huddled together talking - I'm assuming they were discussing the issues.

One of those issues was resolved quite a while before the launch, but not a lot was said about the second issue - the second-stage engine actuator.

The launch was scrubbed at T-00:00:15. In the SpaceX video [1], you hear someone saying "Hold hold hold", followed by "Launch abort is started".

If I were to speculate, I'd suggest that the second-stage anomaly went away, but no-one could explain why. I think the launch was scrubbed, not because someone said "This will go wrong", but because no-one could say "This will go right". Even if Musk did personally scrub the launch, it was for an issue that had been an ongoing discussion for maybe an hour, and that they had already determined would be a (literal) last-minute decision.

[1] https://www.youtube.com/watch?time_continue=1834&v=V5bG37hzw...

Thanks for the link.

I find the people that work on this stuff fascinating!!

To have that much precision (with 15 seconds left, left just stop).

I can right-click and deploy some changes to a production server or run a database script that has a massive impact on the data.

But to imagine that many movings parts (ie those workers specifically involved in the launch) and to have those parts all working together. A database change has a massive impact to "our data". When a launch goes wrong - really puts into perspective what "massive" really means...

Amazing!

think...

#> shutdown -h now

> Does he literally have a finger on an abort button? I find that very hard to believe.

Why? Anyone can call a hold until the T-10 second mark (after that the computer is the only thing that can call an abort). All they have to do is call "Hold, Hold, Hold" on the countdown net, and the person who actually has their finger on the button will press it.

So "anyone" actually means those on that line ... not the engineers at home watching on TV and certainly not the general public

Yes... Is that terribly surprising...?

There was a large grouping of people talking in the control centre visible on stream about T-1m. I imagine it wasn't "I suddenly decided to call it off on a whim at T-10s" more like "I noticed an anomaly, talked to the team, and decided to call it off, the final decision was made by me at T-10s"

Looks like yes.

https://twitter.com/elonmusk/status/832995083519614976

From the replies to that: "During a launch, anybody can call Elon and abort the launch." [0]. It seems like they want to go in the complete opposite direction of when NASA launched the Challenger despite an engineer telling them it would explode [1].

[0] https://twitter.com/zlsadesign/status/832995766436179969

[1] http://www.npr.org/sections/thetwo-way/2016/01/28/464744781/...

Sounds like the Andon cord[1] approach. It does seem to be superior in many contexts to a strict command and control hierarchy.

[1] https://en.wikipedia.org/wiki/Andon_(manufacturing)

Just want to clarify that by "anybody can call Elon" he means "anybody at SpaceX." [0].

[0] https://twitter.com/zlsadesign/status/832995820328804352

"Anyone can call" ... i hope the howard stern crowed dont get wind. With public events you have to filter incomming information. I assume that "anyone" actually means spacex people on the team. He isnt watching twitter.

Think of someone shorting stocks. Even a one-day delay can impact all sorts of companies. A good prank call could make a real difference.

Huh? I've worked on lot's of construction jobs where "anyone" can stop work if they see an unsafe situation. Obviously "anyone" doesn't refer to every human on the planet, it refers to relevant personnel. How is it even possible to be confused by this?

I was also wondering the same as there is another comment above about the exact same thing. Some people on HN really take things too literally.

There's no way he can't just command an abort from wherever he is.

No. With something as important as a space launch, the idea of a 10-second abort based on a phonecall is crazy. They need to be sure it isnt disinformation. That late in the game i would expect all communications to be only from verified sources, sources on a list with dedicated pathways and roles. Millions, billions are on the line.

I have taken issue with musk tweets that have been less than accurate before. Time will tell.

It doesn't cost nearly millions or billions to scrub a launch... It definitely costs that much to have a failed launch.

He was on site with engineers. This is such a bizarre thing to be doubtful of.

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