SpaceX Falcon 9 v1.1 - Dragon - CRS-5/SpX-5 -Jan. 10, 2015 - DISCUSSION

[guckyfan]

Actually, I believe once they know exactly how much control authority they have in each part of the flight they may be able to steer with a lot less hydraulic fluid.

[Dudely]

People underestimate the difference in complexity between an open hydraulic system and a closed one. An open system is much, MUCH simpler for several reasons mentioned in the thread linked a few posts back .

[jabe]

Not sure if it was discussed before but just decided to rewatch the launch and noticed that during the solar panel deploy when they split the screen, the right screen showed the solar panels cover fly off.. Is there a non split screen version of this any where?
the deploy happens at 28:01 of the video or T+12:02 of mission.  The right screen is about 2 seconds behind so is a delay between sequences.
jb

attached is screen cap showing panel fly off...

[billh]

Not sure if it was discussed before but just decided to rewatch the launch and noticed that during the solar panel deploy when they split the screen, the right screen showed the solar panels cover fly off..

Good eye! That's pretty cool.

[MP99]

Wow, in that case it sounds like return circuit would at least provide more reliability than some arbitrary increase in hydraulic fluid. What if the random aerodynamic forces cause the next return flight to consume more than the extra 50% fluid allocated? How much mass are we talking about here - pounds, or tens of pounds, or hundreds?

Or instead of hydraulics, couldn't they try to use electromechanical, or pneumatics, or something else?

It sounds like those hydraulics are going to pose a reliability issue in the longer run.

For electromechanical, how much would the batteries weigh?

Cheers, Martin

[Roy_H]

Wow, in that case it sounds like return circuit would at least provide more reliability than some arbitrary increase in hydraulic fluid. What if the random aerodynamic forces cause the next return flight to consume more than the extra 50% fluid allocated? How much mass are we talking about here - pounds, or tens of pounds, or hundreds?

Or instead of hydraulics, couldn't they try to use electromechanical, or pneumatics, or something else?

It sounds like those hydraulics are going to pose a reliability issue in the longer run.

For electromechanical, how much would the batteries weigh?

Cheers, Martin

I really don't understand that some people think SpaceX is so stupid as to not have considered alternatives. pneumatics are cheap simple and light. However they have no ability to precisely position the vanes and hold them there. Electro i.e. servo motors would weigh more and as pointed out above require significant battery weight. Open loop hydraulic is by far the best choice for this application.

What I am wondering is, is the hydraulic fluid RP1? and if it is, can the used RP1 drain into the main fuel tank to be burned by the rocket engine?

[MarekCyzio]

What I am wondering is, is the hydraulic fluid RP1? and if it is, can the used RP1 drain into the main fuel tank to be burned by the rocket engine?

Where else would it go? Outside?

[kevin-rf]

I really don't understand that some people think SpaceX is so stupid as to not have considered alternatives. pneumatics are cheap simple and light. However they have no ability to precisely position the vanes and hold them there. Electro i.e. servo motors would weigh more and as pointed out above require significant battery weight. Open loop hydraulic is by far the best choice for this application.

What I am wondering is, is the hydraulic fluid RP1? and if it is, can the used RP1 drain into the main fuel tank to be burned by the rocket engine?

That's a fair amount of plumbing to get from the grid fins down to the RP-1 lines, or even tank... And honestly, I don't see why they would be considered a reliability issue. This is not the first rocket to have run out of hydraulic fluid during powered flight due to incorrect modeling (Delta III, Conestoga 1620). Once properly modeled, it should fail to be an issue.

[Kabloona]

What I am wondering is, is the hydraulic fluid RP1? and if it is, can the used RP1 drain into the main fuel tank to be burned by the rocket engine?

Where else would it go? Outside?

Dumping hydraulic fluid overboard (eg stage 1 TVC hydraulic fluid) is a common practice in some other rocket designs, so it's entirely possible that the F9 fluid is simply dumped into the slipstream. Another possibility is a simple unpressurized catchment tank inside the interstage that does not recycle the fluid.

There's 5 pages of discussion on that particular topic over here so we don't need to reinvent the wheel: 

http://forum.nasaspaceflight.com/index.php?topic=36536.0

[Lar]

Yes, please ... no more about hydraulic fluid on this thread. Thank you for the link, Kabloona.

[FutureSpaceTourist]

Interesting background on SpaceX’s preparedness for booster landing on this mission (landing failed due to lack of hydraulic fluid but clearly they needed enough software written to even attempt ASDS landing for this first time):

The event has started, many questions already answered!

I think this nicely demonstrates Elon’s and SpaceX’s philosophy:

What is the single craziest/most impossible thing management (aka Elon) has asked you to do?

spacexfsw Official SpaceX
27 minutes ago
I recall for F9-14 I was in Elon's cube telling him the news that there was no way we could get all of the new S1 landing code done in time for the upcoming launch in 2 weeks. After some thought, he looked over to Lars Blackmore who was there with us and asked if we implement the code, what was our probability of landing. Lars said around 90%. Paraphrasing, Elon looked at us and basically said "can you give me 50%". I said in 2 weeks we can definitely write enough of the logic to get to a 50% probability of landing! We didn't land F9-14 (you can see it on our blooper reel) but we learned a LOT from it, and it was instrumental in eventually landing F9-21. A critical part of our success is our willingness to fail in ways that won't compromise the mission, as long as we are constantly learning from our failures. - Jeff

[Sesquipedalian]

Brilliant story.  Thanks for cross-posting this!  It definitely caught my eye, whereas the other thread wouldn't have.  I wondered "why would someone be bumping a thread for this over-five-years-old mission?"