Blue Origin Thread (merged)

[CptRichardson]

9 minutes ago, Streetwind said:

I've honestly not seen much in the way of official statements regarding crossfeed either, but it really looks like it's not going to happen anymore. Elon Musk himself confirmed that the payload numbers posted last weekend were explicitly without crossfeed, and that it's not needed anymore. You can pretty much consider it officially cancelled at this point.

As to why, I couldn't say. I'm not knowledgeable enough in fluid dynamics to make statements about that. But considering Musk is a perfectionist, and SpaceX has a reputation of making outlandish concepts work - if they decided to drop this one, there ought to be a very good reason for it.

Well, as you said, it's... not needed anymore. They've bumped up the power enough that it's not really necessary.  They've reached the target mass they originally wanted to launch. No need to complicate things if they can get the same performance without it.Cross-feed would probably be more useful for increasing the mass that can be sent farther, flattening out the mass launch profile. You'd be seeing closer to 30 to 40 tons to mars, for instance, instead of 15-ish.  And, with the MCT... well, look at how much the FH can launch. It'd be easier to jump up to the '100 tons to mars/ohgodwhy to LEO' step instead of incrementally stepping up.

[Elukka]

I suspect two reasons - one, it's not necessary for the desired performance on FH, and two, they probably won't make any more multi-core rockets like FH because it's not a great fit for how they've chosen to approach recovery. If my guess is correct on that then crossfeed would represent a technological dead end for them with no further use after FH.

That doesn't mean crossfeed is a bad idea - just it's not a great fit for SpaceX at this time.

Edited May 3, 2016 by Elukka

[PB666]

3 hours ago, Elukka said:

I suspect two reasons - one, it's not necessary for the desired performance on FH, and two, they probably won't make any more multi-core rockets like FH because it's not a great fit for how they've chosen to approach recovery. If my guess is correct on that then crossfeed would represent a technological dead end for them with no further use after FH.

That doesn't mean crossfeed is a bad idea - just it's not a great fit for SpaceX at this time.

Crossfeed only works well when the post separation velocity can be maintained, his starting accelerations are not that great on the F9 FT, if PL is maxed out the post-booster release TWR could be 1 . . . . wasteful

[AngelLestat]

7 hours ago, Streetwind said:

I've honestly not seen much in the way of official statements regarding crossfeed either, but it really looks like it's not going to happen anymore. Elon Musk himself confirmed that the payload numbers posted last weekend were explicitly without crossfeed, and that it's not needed anymore. You can pretty much consider it officially cancelled at this point.

Not sure how you jump from "crossfeed is not needed to get those numbers"  to "we give up on crossfeed development"

Quote

As to why, I couldn't say. I'm not knowledgeable enough in fluid dynamics to make statements about that. But considering Musk is a perfectionist, and SpaceX has a reputation of making outlandish concepts work - if they decided to drop this one, there ought to be a very good reason for it.

Again.. we dont if they decided to drop crossfeed..  In fact people asked exactly that to Elon Musk and he did not answer, in fact he ignore on purpose that part of the question. 

7 hours ago, CptRichardson said:

Well, as you said, it's... not needed anymore. They've bumped up the power enough that it's not really necessary.  They've reached the target mass they originally wanted to launch. No need to complicate things if they can get the same performance without it.Cross-feed would probably be more useful for increasing the mass that can be sent farther, flattening out the mass launch profile. You'd be seeing closer to 30 to 40 tons to mars, for instance, instead of 15-ish.  And, with the MCT... well, look at how much the FH can launch. It'd be easier to jump up to the '100 tons to mars/ohgodwhy to LEO' step instead of incrementally stepping up.

Improve the efficiency is always important, this can be the difference between recover the 2 boosters or drop it, or land both in ground instead in barges, there is a big difference in cost.
If you have a 55 tons payload, instead use a MCT (which cost will be much higher even in reusable mode) you can use the falcon heavy maybe with enough margin to recover the two boosters.

5 hours ago, Elukka said:

I suspect two reasons - one, it's not necessary for the desired performance on FH, and two, they probably won't make any more multi-core rockets like FH because it's not a great fit for how they've chosen to approach recovery. If my guess is correct on that then crossfeed would represent a technological dead end for them with no further use after FH.

That doesn't mean crossfeed is a bad idea - just it's not a great fit for SpaceX at this time.

You mean they will develope a new rocket to remplace falcon9 and falcon heavy?
Not sure what is the issue with recovery, they had different choices with this platform, is dynamic.. you can recover or not your stages depending the needs.
You are not forced, but if expendable cost works for you, then welcome... And we know that there is no company that can still match their expendable cost.
The extra components that a stage needs to be "crossfeed ready" even for falcon9 is negligible.
It does not add risk neither because you close valves and you seal them with a pipe plug. 
Yeah, maybe Elon is very busy and maybe he does not want to add a complication now after the last launch failure.
But I guess eventually they will develope crossfeed because increase a lot the efficiency.
Also Falcon Heavy will become way more popuplar, maybe with higher launchs than falcon9, because is better for the new constellations sat that are being developed, it decrease a lot the kg price to space.

2 hours ago, PB666 said:

Crossfeed only works well when the post separation velocity can be maintained, his starting accelerations are not that great on the F9 FT, if PL is maxed out the post-booster release TWR could be 1 . . . . wasteful

It can be maintained because most of the atmosphere drag and gravity loses was already countered, @softweir explain this better,  I even try this in ksp with all the realism mods and scale using a falcon heavy style rocket, the benefit is huge. 

Edited May 3, 2016 by AngelLestat

[sojourner]

1 hour ago, AngelLestat said:

The extra components that a stage needs to be "crossfeed ready" even for falcon9 is negligible.
It does not add risk neither because you close valves and you seal them with a pipe plug. 

Good to hear you have the problems all solved with crossfeed. You make it sound so simple. You should call Elon.

[PB666]

54 minutes ago, AngelLestat said:

It can be maintained because most of the atmosphere drag and gravity loses was already countered, @softweir explain this better,  I even try this in ksp with all the realism mods and scale using a falcon heavy style rocket, the benefit is huge. 

1) 1stage core recovery - 2wice faster than if stage 1 core separates with booster, down range pick up point is 5 time futher out.
2) kerbin drops at surface acceleration unit per alt30k. earth drops 1 acceleration unit per alt300k.
3) LKO is v2295, LEO is v7800, LKO has no drag, LEO does.
4) The falcon 9 launch is almost twice the thrust of the closest engine in stock.
5) The crossectional area to mass ratio of Falcon 9 is 1/2 to 1/3rd  anything you can build in the stock game.
6) because of the increase dynamic TWR in kerbin, a F9 FT with a full load of fuel has 10% more thrust to play with, this means at maximum nominal load it can turn to horizontal twice as fast on kerbin than on earth, and gain the needed horizontal velocity twice as fast during the critical turn.
7) kerbin atmosphere scale is 2.6 at 5000, earths is 3 at 10,000, on kerbin Max Q comes quicker and at a lower velocity.
8) Using the F9 even at twr1.1 (dynamic) leaves no room for error or failure. Even burning off 20% of the core stage fuel before separation affords the margin of safety needed to gain altitude or gain horizontal velocity fast. Better not to risk.
9) you did not define the mod you used or the parameters you set.  

A model that is earth-like or real in the space beyond kerbin prolly acceptable, distrust any model that claims it is earth-like on kerbin itself. Even an earth-like planet, the game model is not completely real , it would be too computer intensive to run. 

 

 

[wumpus]

15 hours ago, softweir said:

Regarding the complexity of fuel cross-feed: I can't find it now, but I remember a quote along the lines of "the turbines don't like it". Shutting off one source of fuel and turning on another is not a simple business - SpaceX have to make certain that there is no drop nor spike in pressure during that transition. 

An important thing to remember is that to a KSP-level approximation: rocket engines are turbopumps.  They already have their fuel lines dealing with large changes in acceleration, extreme vibration (less clear about that, airplanes are notorious for vibration issues but over longer periods of time.  Rockets certainly shake a lot, and turbopumps aren't going to be happy).  The catch with rocket science is that it rarely can afford the margins you might otherwise want.  None of the space-x people have found a way to reliably switch from one fuel source to another (or possibly some other issue is holding it up), and I'd tend to believe that a Merlin-(D) engine can only tolerate the fuel inconsistencies of its own fuel tank and can't handle a second one.

Considering the smoke and mirrors used to compare prices with recovery and cargo to LEO without recovery (source: Scott Manley tweet.  But the non-recovered cargo mass is right on the page) I'd hardly claim that "they don't need it.  The claim of $1000/kg has been batted around long enough, but that doesn't include the apples/oranges factor of price_without_recovery/price_with_recovery.  To recover the center stage requires plenty of fuel remaining in that stage, and crossfeeding is a great way to keep it in there.  I'll wait until some explanations of recovery are mentioned (or costs and willingness to sacrifice boosters.  So far Musk has insisted sacrificing boosters is admitting failure).

Personally, I think that the upper stage needs some COTS (or otherwise) SRBs strapped to the sides.  It might violate a cardinal rule of KSP rocket design, but it would allow all the recoverable stages to stop at lower velocities and provide more delta-v where it is needed (getting the upper stage to 4km/s or more before it has to do the rest on its own).  No idea how much Musk and Space-X hate SRBs (it was too late change to this years ago).

[KerbonautInTraining]

@PB666

He was using Real Solar System with realistic Isp/mass values. 

A TWR of 1.1 when you're already going at least 1500 m/s is perfectly fine. The current Falcon 9 upper stage has a starting TWR of ~0.6 and starts at ~2000 m/s. Not to mention it spends much more time at those lower TWR's. 

Edited May 3, 2016 by KerbonautInTraining

[AngelLestat]

2 hours ago, sojourner said:

Good to hear you have the problems all solved with crossfeed. You make it sound so simple. You should call Elon.

I never claim that I solve it, read my first post, I am just saying that the previous arguments that I hear in reddit or other places does not seems to apply with this approach.. I am asking you guys if you help me with a reason why it would not work or what can be the real detail that it will prevents take advantage of this in the near future, but it seems that I am bad guy for even try to solve some of these issues.. so please forgive me.
Of course I will love to ask Elon Musk more details about this and its difficulties, but we can't..  so the only way is searching the best approach to deal with each issue we find, step by step, also we can not assume is not possible due reasons that we did not discover yet.
In addiction..  try to think for our own to find solutions is the best way to learn something.  Maybe that is why teachers push you in the same way.

Edited May 3, 2016 by AngelLestat

[PB666]

35 minutes ago, KerbonautInTraining said:

@PB666

He was using Real Solar System with realistic Isp/mass values. 

A TWR of 1.1 when you're already going at least 1500 m/s is perfectly fine. The current Falcon 9 upper stage has a starting TWR of ~0.6 and starts at ~2000 m/s. Not to mention it spends much more time at those lower TWR's. 

Yes but if you were feeding from booster to core, the burn time would be less for the boosters, the burn time would be less than 66% of falcon9 because of throttle down at 800kmh. You would thus be dropping boosters around 1 minute 20 seconds, and that would be a speed of around 600 meters per second or so, no where near enough speed to alter gravities effect. TWR would be surface TWR for F9 surface, +0.02, x (ISP20k alt/ISP MSL).

 

 

[DMagic]

Is there any reason to assume this kind of perfect fuel crossfeed, where the center stack is receiving 100% of its fuel from the side boosters? Isn't there some alternative scenario where, when the side boosters run out of fuel the center stack is at 50%, or 75% fuel?

There must be some balance between the benefits of not having to continue carrying all of that dry mass, and the relatively low TWR of only a single stack. A curve showing the TWR vs. fuel level might help here.

[KerbonautInTraining]

17 minutes ago, DMagic said:

Is there any reason to assume this kind of perfect fuel crossfeed, where the center stack is receiving 100% of its fuel from the side boosters? Isn't there some alternative scenario where, when the side boosters run out of fuel the center stack is at 50%, or 75% fuel?

There must be some balance between the benefits of not having to continue carrying all of that dry mass, and the relatively low TWR of only a single stack. A curve showing the TWR vs. fuel level might help here.

IIRC the general consensus was they'd feed 6 of the core's engines with crossfeed. 

[Rakaydos]

what if they only crossfed the heavy Kerosene, giving the core a large enough oxygen tank for the whole burn, but burning kerosene from the boosters until separation?

you wouldnt get the full effect of crossfeed as youre still limited by the O2 you can cram in, but it simplifies the plumbing, and your kerosene (the part you didnt take out for more oxidiser) is full at separation.

[Streetwind]

That kind of goes against the idea of leveraging economies of scale by only building identical rocket stages.

I mean sure, the center core will need some reinforcement, but that's stuff you can bolt onto the sides. But the tanks, that's literally what the rocket is built from. it would require a significantly different construction process.

[sevenperforce]

17 minutes ago, Rakaydos said:

what if they only crossfed the heavy Kerosene, giving the core a large enough oxygen tank for the whole burn, but burning kerosene from the boosters until separation?

you wouldnt get the full effect of crossfeed as youre still limited by the O2 you can cram in, but it simplifies the plumbing, and your kerosene (the part you didnt take out for more oxidiser) is full at separation.

LOX is denser than kerosene.

[StrandedonEarth]

Sorry to interrupt this fascinating crossfeed discussion (I'm guessing the gain just isn't worth the complexity) but the usual hold-down test fire preceding every launch was successfully completed Sunday evening. The JCSAT-14 launch is scheduled for Thursday morning at 0521 GMT (or 10:21pm PDT Wednesday night), about 1 day, 5 hours and 30 minutes from now. This is a GTO launch with little margins left for landing, but apparently they will try another barge landing anyways without expecting success. Hopefully the hole will be smaller this time.

SpaceFlightNow article link

[Kerbal01]

Crossfeed is not being developed anymore, can we stop talking about it?

On the actual news front, there have been reports that the regular 1 engine hoverslam will be used, not the new 3 engine one. see SFN

 

Edited May 4, 2016 by DarthVader

[AngelLestat]

3 hours ago, sevenperforce said:

LOX is denser than kerosene.

yeah, and they place that on top because it gives more stability to the rocket.

51 minutes ago, DarthVader said:

Crossfeed is not being developed anymore, can we stop talking about it?

really?  you hear Elon or someone else in spacex saying that they give up on crossfeed?
When they give up in reuse the second stage they say it.
I guess the most likely is that they have other priorities now.  

Edited May 4, 2016 by AngelLestat

[Nibb31]

They don't always announce when they give stuff up...  They usually just lose focus and move on to something else. They aren't actively developing their constellation any more either, after all the hype about it being the cash cow that will fund Mars colonies. There might be a couple of guys still working on crossfeed, constellation, or reusable upper stages, but they seem to just transfer resources onto Musk's next pet project until the old one dies.

[Elukka]

18 hours ago, AngelLestat said:

You mean they will develope a new rocket to remplace falcon9 and falcon heavy?
Not sure what is the issue with recovery, they had different choices with this platform, is dynamic.. you can recover or not your stages depending the needs.

I don't think Falcon Heavy will be replaced any time soon. It'll work, it can be recovered, I just doubt they'll make new multi-core rockets afterwards, at least if reusability works out. For easier reuse you'd rather want a simple two stage rocket like Falcon 9, only bigger, which is what they're doing with the BFR:

"At first, I was thinking we would just scale up Falcon Heavy, but it looks like it probably makes more sense just to have a single monster boost stage."

2 hours ago, Nibb31 said:

They don't always announce when they give stuff up...  They usually just lose focus and move on to something else. They aren't actively developing their constellation any more either, after all the hype about it being the cash cow that will fund Mars colonies. There might be a couple of guys still working on crossfeed, constellation, or reusable upper stages, but they seem to just transfer resources onto Musk's next pet project until the old one dies.

You keep repeating this claim but it's getting no less bizarre. I have no idea what this impression is based on - yes, things get reprioritized, put on the back burner, accelerated. They don't just haphazardly jump from project to project - maybe you're watching whatever they're publicizing most heavily at a time and making the assumption that that's all they're working on now? In particular the idea that they just go for Musk's silly pet projects until he has the next idea seems like something you invented, because I've seen nothing to indicate the company works like this. If it did, they would probably never accomplish anything.

Edited May 4, 2016 by Elukka

[TheEpicSquared]

7 minutes ago, Elukka said:

"At first, I was thinking we would just scale up Falcon Heavy, but it looks like it probably makes more sense just to have a single monster boost stage."

MOAR POWER!!!!!!

[Lukaszenko]

On 5/3/2016 at 5:55 AM, Rakaydos said:

Mainly because that would involve pumping fuel/oxidiser "uphill", under however many Gs the rocket is pulling before separation. The booster tanks would have to be drained from a point higher than the core tanks are pumped into, and the full core tanks have the maximum amount of pressure being applied to resist being pumped into.

Is there any difference between pumping "uphill" and pumping to the bottom, but against the pressure of the "hill"? 

[kerbiloid]

27 single engines on start.
This begins to resemble N-1 with its 30.

10 minutes ago, Lukaszenko said:

Is there any difference between pumping "uphill" and pumping to the bottom, but against the pressure of the "hill"? 

Probably, ~1 bar/10 m * 4 g, i.e. several bars of pressure.

Edited May 4, 2016 by kerbiloid

[Frozen_Heart]

I always assumed that one day the Heavy would be replaced by a 9 Raptor, single stick rocket that looks like an up-scaled Falcon 9.

The Raptor has about 3 times the thrust of the Merlin so its liftoff thrust would be similar, but the much higher ISP and the Bigger second stage would make full recovery easier.

 

Edited May 4, 2016 by Frozen_Heart

[Lukaszenko]

1 hour ago, kerbiloid said:

Probably, ~1 bar/10 m * 4 g, i.e. several bars of pressure.

Which is exactly how much pressure is at the bottom of the rocket, which is how hard you have to shove the fuel to get it in there. Same difference, no?