SpaceX Falcon 9/Dragon COTS Demo (C2+) GENERAL DISCUSSION

[krytek]

Can anyone offer a simple explanation of the function of the check valve in a GG turbopump please.
Does it belong to the LOX or RP-1 line? I don't understand what it's job is.

[Retired Downrange]

Can anyone offer a simple explanation of the function of the check valve in a GG turbopump please.
Does it belong to the LOX or RP-1 line? I don't understand what it's job is.

I will begin by saying that I have NO direct knowledge of rocket engine design, and have been wondering about this question also. I believe I have read that this engine uses pressurized fuel as a hydraulic working fluid, and I have wondered if a check valve which is part of that system might be involved... I found the following information which gives me a drawing and explanation to srart trying to understand what this system MIGHT resemble....

  http://www.awesomestories.com/assets/drawing-of-f1-engine-propulsion-of-the-saturn-v

I will add more, but really I would hope someone with more knowledge might help us out.

...from the above document...

NASA provides this drawing of the F-1 engine (five of these lifted the Saturn V rocket from Apollo 11's launch pad) and describes how the F-1 operates:

The F-1 engine has a complex ignition sequence which will be described here. 

...

LOX begins to flow through the LOX pump, starting it to rotate, then into the combustion chamber. The opening of both LOX valves also causes a valve to allow fuel and LOX into the gas generator, where they ignite and accelerate the turbine.

Fuel and LOX pressures rise as the turbine gains speed. The fuel-rich exhaust from the gas generator ignites in the engine bell to prevent backfiring and burping of the engine. The increasing pressure in the fuel lines opens a valve, the igniter fuel valve, letting fuel pressure reach the hypergol cartridge which promptly ruptures.

...

As the flow of fuel and LOX rises to maximum, the chamber pressure, and therefore thrust, is monitored to confirm that the required force has been achieved. With the turbopump at full speed, fuel pressure exceeds hydraulic pressure supplied from ground equipment. Check valves switch the engine's hydraulic supply to be fed from the rocket's fuel instead of from the ground.


-----------

I do realize that the above is a completely DIFFERENT engine... my hope is that someone who knows more about the possible design of the Merlin engine might be motivated by my inept attempt to find an explanation for where "check valves" are used in this system and shed some light on this subject...

Thank You

[GBpatsfan]

Elon posted this to Twitter:
"Simulations show launch ok with bad valve. Still, better to stop & fix. Recalling rockets after launch is not an option."

[manboy]

So now that the launch date has been pushed back when do we expect for Dragon to be unberthed?

[mr. mark]

As far as we know the problem has been fixed. Tuesday is the target day 3:44am Eastern time. No need to dismantle anything as the launch is slight over a day away.

[rdale]

No need to dismantle anything as the launch is slight over a day away.

THat's not what he asked He was curious when Dragon would leave the ISS.

[mr. mark]

oh crud, that's what I get for waking up from a nap and posting! 

[butters]

I speculate wildly that SpaceX has seen this failure mode before on the test stand. Otherwise how could they have been able to find root cause, R&R the valve, and move confidently toward a 72-hour scrub turnaround?

I was thinking about how SpaceX is having a lot of great low-cost learning experiences on the launch pad, but this doesn't look like a learning experience to me. This looks like SpaceX knows their vehicle pretty well at this point. It looks like they've seen this before -- probably enough times to know that the fix is reliable.


I will go further out on a limb and speculate that they know this failure mode so well that it was a consideration in the design of the new turbopump for M1D.

[beancounter]

I speculate wildly that SpaceX has seen this failure mode before on the test stand. Otherwise how could they have been able to find root cause, R&R the valve, and move confidently toward a 72-hour scrub turnaround?

I was thinking about how SpaceX is having a lot of great low-cost learning experiences on the launch pad, but this doesn't look like a learning experience to me. This looks like SpaceX knows their vehicle pretty well at this point. It looks like they've seen this before -- probably enough times to know that the fix is reliable.


I will go further out on a limb and speculate that they know this failure mode so well that it was a consideration in the design of the new turbopump for M1D.

Would a valve failure mode be a consideration in the design of a turbopump.  I would have expected it to be in a redesign of the valve, not the turbopump.  You need to fix the root cause, not make allowances for it. 

I recall one of the MER launchers (Delta II) having a check valve problem.  They didn't have such a tight launch window and simply! recycled the valve (opening/closing) 8 times I think, then launched.
Just a bit of history.  Probably a different valve though!

[Jim]

[
I recall one of the MER launchers (Delta II) having a check valve problem.  They didn't have such a tight launch window and simply! recycled the valve (opening/closing) 8 times I think, then launched.
Just a bit of history.  Probably a different valve though!

It was the LOX fill and drain valve.  And they did have a tight launch window.  They had two 1 second launch windows, about 40 minutes apart. 

[apace]

It was the LOX fill and drain valve.  And they did have a tight launch window.  They had two 1 second launch windows, about 40 minutes apart. 

I want to have Jim's secret book about all this details. It's amazing what you know!

[Jason1701]

It was the LOX fill and drain valve.  And they did have a tight launch window.  They had two 1 second launch windows, about 40 minutes apart. 

I want to have Jim's secret book about all this details.

That would be the mother of all L2 sections.

[Jim]

It was the LOX fill and drain valve.  And they did have a tight launch window.  They had two 1 second launch windows, about 40 minutes apart. 

I want to have Jim's secret book about all this details. It's amazing what you know!

It was one of the missions I worked.

[Antares]

I speculate wildly that SpaceX has seen this failure mode before on the test stand. Otherwise how could they have been able to find root cause, R&R the valve, and move confidently toward a 72-hour scrub turnaround?

I was thinking about how SpaceX is having a lot of great low-cost learning experiences on the launch pad, but this doesn't look like a learning experience to me. This looks like SpaceX knows their vehicle pretty well at this point. It looks like they've seen this before -- probably enough times to know that the fix is reliable.

I think it's confidence in knowledge and abilities and, moreover, different risk management philosophies.  Most people are accustomed to NASA standing down and pencil whipping everything and FMEAing it all.  If one can spend a third the time and be 98% as confident (i.e. not checking all of the other possible things), maybe that's the better tack.

But, unless the system gets simpler and more repeatable, Elon should buy a hotel in Cocoa Beach.  The launch-on-time reliability is not there yet.  Scrubs are not a low-cost form of testing.

[dcporter]

Scrubs are not a low-cost form of testing.

True true.  (They are, though, a much cheaper form of testing than LOM.)

[TOG]

Team-

The scrub and the valve replacement got me thinking...
   Would it be to SpaceX's advantage to do a static fire closer to launch time?  I was thinking in the six to nine hour time period.  That way they could make sure that they are running within tolerance, and if necessary run a couple of simulations and tweak the conditions if necessary without putting the launch window in danger.  Could even perform one or two minor repairs if they have to.

Thoughts?

[Antares]

No time to recover from a real hardware problem nor enough time to review the data.  Also human factors: that would be a bloody long day for the launch team.  And, the USAF guys with the big red buttons won't go over 12 hours without relief - so SpaceX would have to pay for two crews.

[jongoff]

Scrubs are not a low-cost form of testing.

True true.  (They are, though, a much cheaper form of testing than LOM.)

Yeah, post mortems and data-trace "tea leaves and entrails" exercises are no fun.

~Jon

[Kabloona]

Team-

The scrub and the valve replacement got me thinking...
   Would it be to SpaceX's advantage to do a static fire closer to launch time?  I was thinking in the six to nine hour time period.  That way they could make sure that they are running within tolerance, and if necessary run a couple of simulations and tweak the conditions if necessary without putting the launch window in danger.  Could even perform one or two minor repairs if they have to.

Thoughts?

The launch team is probably already running ragged. Short turnaround from an abort, with a not-insignificant anomaly resolved on tight schedule, and these guys are under major scrutiny/pressure. They were probably all seriously sleep-deprived by T-0 Saturday morning...so there's a limit to how much you can accomplish in a day. On a launch campaign like this, you're running right up against the limits of what can be accomplished humanly without burning out your team.

[MP99]

Team-

The scrub and the valve replacement got me thinking...
   Would it be to SpaceX's advantage to do a static fire closer to launch time?  I was thinking in the six to nine hour time period.  That way they could make sure that they are running within tolerance, and if necessary run a couple of simulations and tweak the conditions if necessary without putting the launch window in danger.  Could even perform one or two minor repairs if they have to.

Thoughts?

One thing that had occured to me - if Saturday's launch attempt had failed early in the count, would there have been value in cycling and treating it as a WDR, or possibly even a static fire?

I hesitate to suggest taking things as far as the static fire - another ignition cycle on the engines seems to be stress worth avoiding.
And yet if Saturday's count had terminated before ignition, we would be facing the 0.5s abort tomorrow morning.

In terms of avoiding extra stress, would it even be worthwhile avoiding the chill-down cycle on the engines if the launch attempt was aborted before that point?

Of course, this would require reserving the range beyond the launch window, which sends out it's own signals, but nothing Ms Shotwell wasn't prepared to state at the pre-launch event ("we've never hit a T-0 yet").

cheers, Martin

Edit: plus Kablona's point above re stress on the launch team.