SpaceX Falcon 9 : CRS-16 (Dragon SpX-16) : December 5, 2018 - DISCUSSION

[dnavas]

https://twitter.com/elonmusk/status/1070388894875545600

Pump is single string. Some landing systems are not redundant, as landing is considered ground safety critical, but not mission critical. Given this event, we will likely add a backup pump & lines.

Uhm, pre-DM-1?  How likely are they to get an exception for this...?

[kevinof]

It has nothing to do with the launch. It's for landing only.

https://twitter.com/elonmusk/status/1070388894875545600

Pump is single string. Some landing systems are not redundant, as landing is considered ground safety critical, but not mission critical. Given this event, we will likely add a backup pump & lines.

Uhm, pre-DM-1?  How likely are they to get an exception for this...?

[Lars-J]

https://twitter.com/elonmusk/status/1070388894875545600

Pump is single string. Some landing systems are not redundant, as landing is considered ground safety critical, but not mission critical. Given this event, we will likely add a backup pump & lines.

Uhm, pre-DM-1?  How likely are they to get an exception for this...?

Why do they need one? The landings are not part of the main mission.

[envy887]

https://twitter.com/elonmusk/status/1070388894875545600

Pump is single string. Some landing systems are not redundant, as landing is considered ground safety critical, but not mission critical. Given this event, we will likely add a backup pump & lines.

Uhm, pre-DM-1?  How likely are they to get an exception for this...?

They don't need to change anything for DM-1.

[kevinof]

https://twitter.com/elonmusk/status/1070399755526656000

[oldAtlas_Eguy]

https://twitter.com/elonmusk/status/1070388894875545600

Pump is single string. Some landing systems are not redundant, as landing is considered ground safety critical, but not mission critical. Given this event, we will likely add a backup pump & lines.

Uhm, pre-DM-1?  How likely are they to get an exception for this...?

This is a recovery issue only. DM-1 can proceed even if no changes are made.

The only impact from NASA HSF Safety is that multiple flights with the new hardware fly demonstrating no interaction of the changes with any launch systems before DM-2.

[StuffOfInterest]

I wonder if the control software could be modified so that when a fin freezes the fin on the opposite side can be placed in a position to dampen the action of the first one and then let the two other grids fins do all the work?  There wouldn't be as much control but if it can avoid a roll then there may be enough to get the booster down.

[VoodooForce]

wow amazing footage

[Lars-J]

Based on the full landing video that Elon posted, looks like the leg deployment momentum shift had the most impact in reducing the roll. (like a spinning figure skater)

And it looks like the grid fins were locked in a position to increase the roll... So the RCS fought that roll all the way down.

[yokem55]

https://twitter.com/elonmusk/status/1070388894875545600

Pump is single string. Some landing systems are not redundant, as landing is considered ground safety critical, but not mission critical. Given this event, we will likely add a backup pump & lines.

Uhm, pre-DM-1?  How likely are they to get an exception for this...?

Because it's a recovery only system that has no impact on the safe flight of the primary mission. And as demonstrated today, thus particular system was able to fail in a way that preserved the safety of life and property.

[quagmire]

https://twitter.com/elonmusk/status/1070388894875545600

Pump is single string. Some landing systems are not redundant, as landing is considered ground safety critical, but not mission critical. Given this event, we will likely add a backup pump & lines.

Uhm, pre-DM-1?  How likely are they to get an exception for this...?

In all reality, this shouldn't affect DM-1 as it involves the landing systems and as Musk stated, it wasn't Mission critical.

In conspiracy theory world, yeah the anti-new space faction may want to go, " What else is not considered mission critical and need another complete review of the Falcon 9's systems!" in order to get Starliner to be the first.

[toruonu]

I wonder if the control software could be modified so that when a fin freezes the fin on the opposite side can be placed in a position to dampen the action of the first one and then let the two other grids fins do all the work?  There wouldn't be as much control but if it can avoid a roll then there may be enough to get the booster down.

If you look at the video Elon shared it looked like none of the fins worked. So likely that a fin was working for a moment as this span out, but they locked in place pretty soon after...

[ugordan]

I wonder if the control software could be modified so that when a fin freezes the fin on the opposite side can be placed in a position to dampen the action of the first one and then let the two other grids fins do all the work?  There wouldn't be as much control but if it can avoid a roll then there may be enough to get the booster down.

How do you propose to do that if all the fins are powered by the single pump?

[CorvusCorax]

At what point when you don't have complete control of your rocket flying back toward land does range safety kick in? While i'm sure they are happy they got their rocket back (albeit a little wet) I expect we will need to be asking some questions about whether the automated flight termination system worked as it was designed - and if it did - who didn't trigger a manual termination and why not? Dangerous as hell.

From what we heard in press conferences, the AFTS is completely autonomous, there is no "red button" at the range anymore, instead the rocket itself destructs itself if it leaves a predefined safety corridor (or is about to leave and has insufficient control authority to go back to it)
while F9 was obviously having troubles with control authority, the stage was apparently fully aware of its state and had at least "some" control (otherwise the water landing would have failed) as such its likely it never left or even trended outside of the save-flight corridor and as such the AFTS had no reason to ever command a destruction. It did behave exactly as designed for an off-nominal landing, which is land at the safety-backup point just off shore.

I'm sure no-one at SpaceX expected to see that code branch executing outside of a simulator test anytime soon, but it did, and apparently, flawlessly

In the history of space flight, automatic termination has been commanded based on much simpler triggers, such as exceeding certain angle of attacks, attitudes or rotation rates, but that was at an age when state estimation wasn't as good and you had to assume that such a flight situation was unrecoverable anyway due to inertial systems failing and being unable to compute the state.
Falcon 9 goes through some pretty extreme maneuvers during ordinary missions - for example during flip- and boostback but also during reentry and supersonic High-AoA flight. Its unlikely it would have exceeded the design limits of its control system per se, the only issue was the stuck fin(s)

[ellindsey]

How does a single engine counter roll?  This was a single-engine landing, not a three-engine landing, unless I'm mistaken.

[DanielW]

I wonder if the control software could be modified so that when a fin freezes the fin on the opposite side can be placed in a position to dampen the action of the first one and then let the two other grids fins do all the work?  There wouldn't be as much control but if it can avoid a roll then there may be enough to get the booster down.

If you countered the roll it would change the angle of attack to something undesirable.

[edzieba]

  It'll be interesting, how do you approach such a thing unless there's a way to de-pressurize it?  Then once you have it under tugboat control what do you do with it?? 

Same way the Europeans recovery potentially explosive boosters after splashdown: with Frenchmen.

[mlindner]

WOW!

https://twitter.com/elonmusk/status/1070399755526656000

It's amazing watching the entire structure flex and bend from the torques being put on the grid finds and then the whole structure twist when it impacts the water but holds together! That's some incredible engineering!

[Lars-J]

How does a single engine counter roll?  This was a single-engine landing, not a three-engine landing, unless I'm mistaken.

I think he by "engines" meant the RCS thrusters working together with the main engine to try to wrestle back control.

[Johnnyhinbos]

I wonder if the control software could be modified so that when a fin freezes the fin on the opposite side can be placed in a position to dampen the action of the first one and then let the two other grids fins do all the work?  There wouldn't be as much control but if it can avoid a roll then there may be enough to get the booster down.

One pump - no fin actuation period. So software can't help...