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

[Grandpa to Two]

Elon tweeted in reference to the hypersonic fins,"worked extremely well from hypersonic velocity to subsonic but ran out of hydraulic fluid right before landing." I'm curious to read this. Any hydraulic system I've seen is a closed system so something may have gone wrong with it. If it's one system feeding also the landing legs I can understand a hard landing. Any engineers that can answer this?

[Avron]

Elon tweeted in reference to the hypersonic fins,"worked extremely well from hypersonic velocity to subsonic but ran out of hydraulic fluid right before landing." I'm curious to read this. Any hydraulic system I've seen is a closed system so something may have gone wrong with it. If it's one system feeding also the landing legs I can understand a hard landing. Any engineers that can answer this?

  open system is simple and weights less.

[llanitedave]

Hydraulic fluid doesn't get used up unless there's a leak.

Or unless they decided to used an open system in which the hydraulic fluid is simply dumped downstream of the actuator, which makes for a simpler system and eliminates the mass of a collection tank and associated plumbing.

And will get you the opportunity to explain yourself to the EPA.

??  open system hydraulics have been used on numerous aerospace vehicles (see Conestoga LV, for example).

You're using common sense.  Not applicable here.

I was involved with a seismic project using a thumper truck that had a hydraulic system of canola oil.  There was a spill.  Next thing we saw were guys in haz-mat suits racing around doing a full-up toxic cleanup protocol.

Yes, there were face-palms happening.

[Jim]

Elon tweeted in reference to the hypersonic fins,"worked extremely well from hypersonic velocity to subsonic but ran out of hydraulic fluid right before landing." I'm curious to read this. Any hydraulic system I've seen is a closed system so something may have gone wrong with it. If it's one system feeding also the landing legs I can understand a hard landing. Any engineers that can answer this?

The legs are gas deployed and the fins are on an open system

[Robotbeat]

Rocket hydraulics tend to be open, from what I can tell.

[ericspittle]

Hydraulic fluid doesn't get used up unless there's a leak.

Or unless they decided to used an open system in which the hydraulic fluid is simply dumped downstream of the actuator, which makes for a simpler system and eliminates the mass of a collection tank and associated plumbing.

And will get you the opportunity to explain yourself to the EPA.

??  open system hydraulics have been used on numerous aerospace vehicles (see Conestoga LV, for example).

You're using common sense.  Not applicable here.

I was involved with a seismic project using a thumper truck that had a hydraulic system of canola oil.  There was a spill.  Next thing we saw were guys in haz-mat suits racing around doing a full-up toxic cleanup protocol.

Yes, there were face-palms happening.

Was the work for a gas company by any chance? The company I work for has a subdivision that runs fresh water for fracking crews in PA, and if any of this fresh water (mind you this is sourced either out of a local river or a holding pond) gets spilled it must be cleaned up exactly as if it were a hazardous spill, including the same formal reporting and everything.

[rcoppola]

Concerning telemetry, recorders, etc.:

Mission Control stated, "Landing platform has received acquisition of signal." This was stated before MECO or 2nd Stage Sep. I heard that as meaning the first stage has locked onto the position of the ASDS as it's return target.

It sounds to me just like MC said: the barge (or GO Quest?) locked onto a signal from the rocket, probably a telemetry stream.

This has been discussed to death elsewhere, but I doubt the stage is receiving anything from the barge. It's guiding itself to pre-programmed GPS coordinates and expecting the barge to be there, then landing with whatever radar system they tested on GH in order to judge vertical distance from the deck. IMHO.

To near-death perhaps but we now have an actual attempt with actual MC call-outs. If it is as you suggest then why would the "landing platform"  need to acquire any signal from the core. I really don't think it's for telemetry as that would be more logical for Go Quest. So the call-out would have been, "Go Quest has received acquisition of signal."?

I guess I agree with Avron then.

[pericynthion]

Do they use RP-1 as the fluid? Is it sourced from the main fuel tank?

[OSE]

Question from @alankerlin:

The question plenty of people are asking about those tweets from @elonmusk is aren't hydraulic systems closed? So how do they run out?

Answer by @elonmusk:

@alankerlin Hydraulics are usually closed, but that adds mass vs short acting open systems. F9 fins only work for 4 mins. We were ~10% off.

[Robotbeat]

Multiple rocket failures within the last few decades have been caused by depletion of hydraulic fluid (although that wasn't the root cause, having more hydraulic fluid might have saved them). For instance Delta III (remember that? even the "big boys" can make an unreliable launch vehicle... only 1 somewhat tainted success out of 3 total launches... Space is hard.) and Conestoga each had guidance issues that led to depletion of the hydraulic fluid and subsequent loss of control.


...this is why SpaceX (wisely!) uses kerosene as hydraulic fluid for Merlin.

[mmeijeri]

Any idea why pressure-fed hydraulics are preferable over pneumatics? What are the pros and cons of each?

[Garrett]

Hydraulic fluid doesn't get used up unless there's a leak.

Or unless they decided to used an open system in which the hydraulic fluid is simply dumped downstream of the actuator, which makes for a simpler system and eliminates the mass of a collection tank and associated plumbing.

And will get you the opportunity to explain yourself to the EPA.

From what I've just read on open hydraulic systems, they are called "open" because they return the fluid to a tank instead of the fluid remaining in a closed pressurized loop. So from a pollution viewpoint, open and closed systems appear identical to me.

[pagheca]

Probably this has been already pointed out in this thread. However, if the information we got are correct, I think that this landing has been more than a 50% success.

In fact, there were two main targets here:
(1) landing on the barge
(2) recover the stage

My point is that _if_ (1) is required in order to allow to release a "license" from FAA for real RTLS, even if they haven't recovered the stage, they accumulated evidences they can pinpoint a landing spot, that is a requirement for next step: real RTLS.

If by chance they had a floating, recovered stage, but at 1 mile from the barge this time, it would be quite bad because even if they got on target on the next flights they would get 50, 66, 75% etc success and this would impact on their plan progress more than one more stage lost.

So, at the end of the day, I'm very happy with today stunt. No (cuban) cigar maybe, but a glass of a good red wine would be ok.

[Robotbeat]

Well, they probably still recovered a bunch of pieces of the first stage! Maybe enough to analyze for flight performance.

[NovaSilisko]

Fingers crossed they got an only slightly dented Merlin out of the deal...

[cambrianera]

Any idea why pressure-fed hydraulics are preferable over pneumatics? What are the pros and cons of each?

Pneumatic actuators lack the stiffness of hydraulic.
In control loops sloppiness is noxious.

Pneumatic: lighter, cheaper
Hydraulic: stiffer, higher thrust and dynamic
But sooo many different applications means this is only generic.

[edkyle99]

From Elon

@elonmusk: Didn't get good landing/impact video. Pitch dark and foggy. Will piece it together from telemetry and ... actual pieces.

Another explosion, another missing video.  What are the odds? 

But I see these landing experiments as an interesting side-show.  The real news continues to be the repetitive success of this launch vehicle.

 - Ed Kyle

[Robotbeat]

In the near-term for SpaceX's financial viability (and for all those great payloads on Dragon!) and for bringing commercial space launch back to Merica, yeah, the reliability is more important.

But for the long-term ability of the human race to expand into the cosmos, convincing everyone that reusable launch is not only possible but economical is much more important (next attempt has a good chance of proving it's feasible, but it'll take a good dozen or so reused flights before it is beyond a doubt that reuse is able to be significantly more economical than the status quo). SpaceX has already done a great deal in furthering that goal, as you can see from whispers from Europe and ULA about reuse (where before there was mockery, at least from Europe).

[Elmar Moelzer]

Quite a few - the accuracy today may have been pure luck.

I want to have your kind of luck. You must be a frequent winner in the lottery.

[savuporo]

Well, they probably still recovered a bunch of pieces of the first stage! Maybe enough to analyze for flight performance.

hopefully no hydrazine fumes and girls in pink coats this time..