Author Topic: SpaceX Falcon 9 FT - ORBCOMM-2 - RTF (Return To Flight) DISCUSSION THREAD  (Read 910893 times)

Offline CameronD

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Thanks for the clarification.  I would not have thought it was worth it for such a small gain, but I guess every little bit counts when aiming for max performance.

Reading  Kabloona's links, it looks like there's a 10% gain from chilling the liquid oxygen and a 5% gain from the RP-1. Theyre also stretching the RP-1 tank.

Just to be clear, we don't really know the actual % gain that SpaceX will shoot for in the RP-1 density. All we know is that Gwynne said they would "slightly" chill the RP-1, which implies something less than the 5% gain mentioned by Green Shrike, which I believe is a theoretical maximum. So the word "slightly" suggests something less than that.

..and "slightly" is all that makes sense to me - keeping the RP-1 above or not much below 0degC.  Especially given (a) the structural changes involved in modifying tank volumes to suit, (b) changes to fuel characteristics if they chill the RP-1 too far and (c) the cost of modifying pad equipment to suit the new "cryogenic" liquid.

Sometimes the benefits aren't worth the risks.. but, like everything else we've seen from SpX, no doubt they know what they're doing and have good reasons for doing it.

« Last Edit: 08/04/2015 11:02 PM by CameronD »
With sufficient thrust, pigs fly just fine - however, this is not necessarily a good idea. It is hard to be sure where they are
going to land, and it could be dangerous sitting under them as they fly overhead.

Offline Helodriver

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Thanks for the clarification.  I would not have thought it was worth it for such a small gain, but I guess every little bit counts when aiming for max performance.

Reading  Kabloona's links, it looks like there's a 10% gain from chilling the liquid oxygen and a 5% gain from the RP-1. Theyre also stretching the RP-1 tank.

Just to be clear, we don't really know the actual % gain that SpaceX will shoot for in the RP-1 density. All we know is that Gwynne said they would "slightly" chill the RP-1, which implies something less than the 5% gain mentioned by Green Shrike, which I believe is a theoretical maximum. So the word "slightly" suggests something less than that.

..and "slightly" is all that makes sense to me - keeping the RP-1 above or not much below 0degC.  Especially given (a) the structural changes involved in modifying tank volumes to suit, (b) changes to fuel characteristics if they chill the RP-1 too far and (c) the cost of modifying pad equipment to suit the new "cryogenic" liquid.

Sometimes the benefits aren't worth the risks.. but, like everything else we've seen from SpX, no doubt they know what they're doing and have good reasons for doing it.

Whatever the RP-1 temperature, it is cold enough to freeze out water vapor condensation from the atmosphere on the fuel tank skin of the rocket. Seen on the Inflight Abort Test Booster doing tanking and propellant densification tests at Vandenberg this spring.

From experience flying aircraft at altitude and chilling the wing fuel to the point it frosts the aircraft skin, that fuel temperature is probably somewhere below -30 degrees C

Offline CameronD

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Whatever the RP-1 temperature, it is cold enough to freeze out water vapor condensation from the atmosphere on the fuel tank skin of the rocket. Seen on the Inflight Abort Test Booster doing tanking and propellant densification tests at Vandenberg this spring.

Cool..(pun intended). Thanks for the pic. :)

From experience flying aircraft at altitude and chilling the wing fuel to the point it frosts the aircraft skin, that fuel temperature is probably somewhere below -30 degrees C

Sure.. that's why FSII was invented.  Can they use FSII in RP-1 in a rocket engine??  I'd have thought that might not work so well!!
« Last Edit: 08/05/2015 12:04 AM by CameronD »
With sufficient thrust, pigs fly just fine - however, this is not necessarily a good idea. It is hard to be sure where they are
going to land, and it could be dangerous sitting under them as they fly overhead.

Offline Kabloona

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Whatever the RP-1 temperature, it is cold enough to freeze out water vapor condensation from the atmosphere on the fuel tank skin of the rocket. Seen on the Inflight Abort Test Booster doing tanking and propellant densification tests at Vandenberg this spring.

From experience flying aircraft at altitude and chilling the wing fuel to the point it frosts the aircraft skin, that fuel temperature is probably somewhere below -30 degrees C

I don't doubt your experience flying at altitude, but it seems to me frost would form on the F9 tanks at sea level at well above -30 C. In theory that should be able to happen at fuel temps almost as high as 0 C. And since Gwynne said they are only "slightly" chilling the RP-1, my guess would be it's in the range of 0 C to -5 C, just cold enough to frost the tanks.

And since RP-1 "freezes" at -37 C (according to deruch's earlier post; I  assume he's correct) I don't imagine they want to get anywhere near that low due to viscosity issues.
« Last Edit: 08/05/2015 12:06 AM by Kabloona »

Offline Helodriver

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We won't really know the temperature of the RP-1 until someone at SpaceX tells us, but in an aircraft wing, if the fuel is above -20 degrees C, the wing will be merely wet with nonfreezing condensation with no frost forming unless it is very cold outside, or very high humidity, or there is no sun shining,  neither which was the case for RP-1 tank on the test booster that day at Vandenberg. That tank frosted completely on all sides, even the sun facing, on a 24 degree C day.

Offline Kabloona

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We won't really know the temperature of the RP-1 until someone at SpaceX tells us, but in an aircraft wing, if the fuel is above -20 degrees C, the wing will be merely wet with nonfreezing condensation with no frost forming unless it is very cold outside, or very high humidity, or there is no sun shining,  neither which was the case for RP-1 tank on the test booster that day at Vandenberg. That tank frosted completely on all sides, even the sun facing, on a 24 degree C day.

Interesting. So they may be closer to "freezing" RP-1 than I would have guessed.

Offline CameronD

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We won't really know the temperature of the RP-1 until someone at SpaceX tells us, but in an aircraft wing, if the fuel is above -20 degrees C, the wing will be merely wet with nonfreezing condensation with no frost forming unless it is very cold outside, or very high humidity, or there is no sun shining,  neither which was the case for RP-1 tank on the test booster that day at Vandenberg. That tank frosted completely on all sides, even the sun facing, on a 24 degree C day.

Interesting. So they may be closer to "freezing" RP-1 than I would have guessed.

As Helo notes, we won't really know until someone at SpaceX tells us.

As has been touched on before, RP-1 is comprised of a rather interesting mix of hydrocarbons (better defined than for jet fuel, but not by much) plus entrained water (it's hygroscopic) and as the temperature drops below zero, some of it will start to freeze, some will go waxy and some of it won't.

One way around this is to use fuel line heaters to bring the temperature back up to the point where fuel flow is predictable again - but this adds weight and if you're only gaining a few percent extra volume, any performance gain might be offset by the extra weight.

In summary: AIUI, densifying LOX/LH2 makes some sense to me, but densifying RP-1 is a fine line and it would be interesting to know where SpaceX plan theirs.
 
« Last Edit: 08/05/2015 04:22 AM by CameronD »
With sufficient thrust, pigs fly just fine - however, this is not necessarily a good idea. It is hard to be sure where they are
going to land, and it could be dangerous sitting under them as they fly overhead.

Offline MP99



We won't really know the temperature of the RP-1 until someone at SpaceX tells us, but in an aircraft wing, if the fuel is above -20 degrees C, the wing will be merely wet with nonfreezing condensation with no frost forming unless it is very cold outside, or very high humidity, or there is no sun shining,  neither which was the case for RP-1 tank on the test booster that day at Vandenberg. That tank frosted completely on all sides, even the sun facing, on a 24 degree C day.

Interesting. So they may be closer to "freezing" RP-1 than I would have guessed.

As Helo notes, we won't really know until someone at SpaceX tells us.

As has been touched on before, RP-1 is comprised of a rather interesting mix of hydrocarbons (better defined than for jet fuel, but not by much) plus entrained water (it's hygroscopic) and as the temperature drops below zero, some of it will start to freeze, some will go waxy and some of it won't.

One way around this is to use fuel line heaters to bring the temperature back up to the point where fuel flow is predictable again - but this adds weight and if you're only gaining a few percent extra volume, any performance gain might be offset by the extra weight.

In summary: AIUI, densifying LOX/LH2 makes some sense to me, but densifying RP-1 is a fine line and it would be interesting to know where SpaceX plan theirs.

Note that fuel is used for regenerative cooling of the combustion chamber, etc. This definitely counts as heating the fuel. :-) But, I'm not sure if the full fuel flow volume follows that path.

Also, it doesn't cover the fuel lines from the bottom of the fuel tank to the inlet of the cooling jacket. But, these are relatively short, wide pipes, so maybe this isn't so much of a concern.

Also, this may be one of the elements of engineering (testing) they're going through to get this engine package ready to fly - just dealing with the issues around cold RP-1.

Cheers, Martin

Offline the_other_Doug

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Musk mentioned in the preliminary findings presser that one change we can expect to see is the move from Dragon v1 to Dragon v2 for CRS flights.  The statement, ISTR, was in Musk-speak which made it sound like the changeover would be immediate, that all future cargo vehicles to ISS would be Dragon v2's.

I just wanted to sort of reality-check that, here -- are we agreed that CRS-8 will almost definitely still be a Dragon v1?  And, if that is so (and it seems almost inevitable), are we talking about a changeover to v2 only after the current scheduling of development for the crewed v2?

(Oh, and as a complete aside -- it would be nice if the text formatting and smiley controls could be fixed sometime soon.  It's a huge pain in the butt to have to type in the frikkin' text commands by hand, just to italicize something.)
-Doug  (With my shield, not yet upon it)

Online Hywel1995

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Musk mentioned in the preliminary findings presser that one change we can expect to see is the move from Dragon v1 to Dragon v2 for CRS flights.  The statement, ISTR, was in Musk-speak which made it sound like the changeover would be immediate, that all future cargo vehicles to ISS would be Dragon v2's.

I just wanted to sort of reality-check that, here -- are we agreed that CRS-8 will almost definitely still be a Dragon v1?  And, if that is so (and it seems almost inevitable), are we talking about a changeover to v2 only after the current scheduling of development for the crewed v2?

(Oh, and as a complete aside -- it would be nice if the text formatting and smiley controls could be fixed sometime soon.  It's a huge pain in the butt to have to type in the frikkin' text commands by hand, just to italicize something.)

I believe it will be Dragon 1 for a few more missions. I would think they would have at least one prepared if they were on schedule pre-mishap. If I got from the conference call a week or so ago, the demo flights of D2 will have cargo. However this might not be a CRS mission, or go towards the contract.

Online douglas100

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The cargo Dragon must be able to berth with the station while the crew version docks. That makes the two vehicles substantially different at the front end even if the future cargo version has  commonality with the manned version.
Douglas Clark

Online guckyfan

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I thought I have seen every significant public statement by Elon Musk in the last few years. I have not seen him saying they will switch cargo to Dragon 2. I recall statements that they may use Dragon 2 some time in the future. I have heard him say they may do a Dragon 2 or two with cargo to prove out the system. I think NASA would agree with that. They don't need the wide berthing port on every cargo flight so why not allow SpaceX to use Dragon 2 to prove it out before crew is flying? But that is not the same as an instant switch to Dragon 2 for cargo.

Offline drzerg

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v2 cant dock without adapter. and size of the v2 hatch is smaller. see https://en.wikipedia.org/wiki/International_Standard_Payload_Rack

p.s. sorry for wrong link at first
« Last Edit: 08/05/2015 04:33 PM by drzerg »

Offline rpapo

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This isn't exactly on topic for this thread, but I don't see any reason why they couldn't have the same basic structure for Dragon V2 Cargo as for Dragon V2 Manned.  If the cargo version gets the same new parachute arrangement and SuperDracos as the passenger version, then the only part that needs to be different is the very top.  The passenger version gets a docking adapter and nosecone.  The cargo version gets a berthing ring, and would probably not retain the nosecone.

And if the top portion is bolted on, rather than welded, then the two versions could be interchanged rather quickly.  Unless doing it that way compromises the pressure vessel.

Another question: Will they move entirely to the new trunk design?
An Apollo fanboy . . . fifty years ago.

Offline Zed_Noir

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This isn't exactly on topic for this thread, but I don't see any reason why they couldn't have the same basic structure for Dragon V2 Cargo as for Dragon V2 Manned.  If the cargo version gets the same new parachute arrangement and SuperDracos as the passenger version, then the only part that needs to be different is the very top.  The passenger version gets a docking adapter and nosecone.  The cargo version gets a berthing ring, and would probably not retain the nosecone.

And if the top portion is bolted on, rather than welded, then the two versions could be interchanged rather quickly.  Unless doing it that way compromises the pressure vessel.
...

You could not fitted the current CBM hatch onto the the Dragon 2. IMO they will continue to build cargo Dragons for all CRS flights in more or less the current configuration.

Online PreferToLurk

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Musk mentioned in the preliminary findings presser that one change we can expect to see is the move from Dragon v1 to Dragon v2 for CRS flights.  The statement, ISTR, was in Musk-speak which made it sound like the changeover would be immediate, that all future cargo vehicles to ISS would be Dragon v2's.

The change over will not be immediate.  The software upgrade to allow Dragon 1 to fire its chutes in an emergency situation will happen immediately.  SpaceX has a Dragon assembly line for the current CRS contract and Dragon 2 isnt just some simple mod.  "And then with respect to the abort thrusters, the abort thrusters are really quite a radical change in design, and it wouldn't be easy to retrofit those to Dragon 1. Dragon 2 is very different from Dragon 1. It sort of looks, maybe, sort of similar from an external standpoint, but there's no reasonable way to just sort of tack on the abort thrusters." -- Elon Musk at the failure presser

Now, he did go on to say, "The best thing to do is try to get Dragon 2 to fly at the earliest opportunity, because it is a step function improvement in capability and flight resilience. Although, as I said, we are going to make the software change to Dragon 1." But the "earliest opportunity" is likely a reference to the upcoming CRS2 contract. The current CRS contract calls for at least 8 more Dragon 1 flights (9 if they tack on a re-flight of CRS7).

Immediately after someone asked if an "early version" of Dragon 2 could carry cargo, and Musk didn't seem to completely understand the question (probably since he basically already answered it) but replied that it is already planned for the first flight or two to only carry cargo, but made no reference to any attempt to speed up Dragon 2 development, only to the fact that Dragon 2 will need a shakeout flight or two before carrying crew.  And its not like they are dragging their heels on Dragon 2 anyway, it will be ready when it's ready.

After Dragon 2 is ready, it is possible (maybe even likely) that SpaceX will submit a proposal to modify Dragon 2 with a nice wide berthing adapter for future cargo flights and then retire the Dragon 1 entirely.

Offline Lars-J

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I thought I have seen every significant public statement by Elon Musk in the last few years. I have not seen him saying they will switch cargo to Dragon 2. I recall statements that they may use Dragon 2 some time in the future. I have heard him say they may do a Dragon 2 or two with cargo to prove out the system. I think NASA would agree with that. They don't need the wide berthing port on every cargo flight so why not allow SpaceX to use Dragon 2 to prove it out before crew is flying? But that is not the same as an instant switch to Dragon 2 for cargo.

I think this "CRS switching over to Dragon 2" is just a misunderstanding, coming from the comment that Dragon 1 will get some Dragon 2 software for abort parachute deployment.

Offline wannamoonbase

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Musk mentioned in the preliminary findings presser that one change we can expect to see is the move from Dragon v1 to Dragon v2 for CRS flights.  The statement, ISTR, was in Musk-speak which made it sound like the changeover would be immediate, that all future cargo vehicles to ISS would be Dragon v2's.

I just wanted to sort of reality-check that, here -- are we agreed that CRS-8 will almost definitely still be a Dragon v1?  And, if that is so (and it seems almost inevitable), are we talking about a changeover to v2 only after the current scheduling of development for the crewed v2?

(Oh, and as a complete aside -- it would be nice if the text formatting and smiley controls could be fixed sometime soon.  It's a huge pain in the butt to have to type in the frikkin' text commands by hand, just to italicize something.)

I'd bet a nickel that all of the currently contracted CRS flights will be on Dragon v1.
Excited to be finally into the first Falcon Heavy flow, we are getting so close!

Online guckyfan

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I'd bet a nickel that all of the currently contracted CRS flights will be on Dragon v1.

You might lose. It is entirely possible, after what Elon Musk said. Not a switch to Dragon 2, but one or two to test out the system. In that case the docking adapter would not matter much because not every flight has bulky goods.

Offline Comga

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Dragging this discussion back to the topic in the title.....

There is a page of the July FPIP in a ISS document linked in an ISS Status thread.  It has the SpX-8 details greyed out, but the SpX-9 and SpX-10 flights are unchanged.

The next Visiting Vehicle listed after HTV5 departs on 9/26 is the arrival of Orb-4 on 12/6.  The launch of SpX-8 could be delayed by up to 68 days to 11/5, stay at the ISS the full 30 days, and still not overlap with Orb-4 or the scheduled SpX-9 berthing.

There is a beta angle >60 deg cut-out 10/28-11/03.  My guess for the SpX-8 launch remains around the latter date.
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

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