What do you think of the SLS?

[R0cketC0der]

Only if the fuel was staying there, but it isn't. It's going out the engine. So not all of its energy is transferred back to the rocket, producing a net torque.

This can easily be cancelled out with gimbal king the engine a tiny bit.

[cantab]

I understood your use of net torque correctly, I think. If I'm not mistaken, you're ignoring the force imparted by the fuel coming to a stop in the rotational direction when it arrives in the destination tank.

Using your analogy, if we start walking on the turntable and stop, will it still be turning?

No, but it will have turned. And if we both jump off when it's turning, ensuring our jumps are radially outwards so they don't apply any new torque, then the turntable will continue turning. That jumping off is the analogue to the rocket expelling burnt fuel from its engines.

Or to simplify further, if we remove the two connected tanks from the core stage and pump fuel from one to the other, will the whole thing move (other than adjusting for the center of mass moving)?

Two tanks round the core, like Falcon Heavy, creates no problems in the first place. It's when there's more tanks with feed around the rings, like we often do in KSP, that has the rotation issues.

[Red Iron Crown]

Dkmdlb,

The red isn't a force, as near as I can tell, it's just for clarity of flow direction. Seriously, do you think if I put this contraption on a cart and turned the pump on, the cart would continue accelerating to the right?

SargeRho,

Pushing the fuel down after it arrives in the destination tank doesn't change the fact that it must stop moving in the left/right direction first.

[Dkmdlb]

Dkmdlb,

The red isn't a force, as near as I can tell, it's just for clarity of flow direction. Seriously, do you think if I put this contraption on a cart and turned the pump on, the cart would continue accelerating to the right?

No, it would move slightly to the right as the center of mass moved slightly to the left. The center of mass wouldn't move, but the cart would move in the opposite direction of the fuel flow.

Edited April 29, 2014 by Dkmdlb

[Red Iron Crown]

No, but it will have turned. And if we both jump off when it's turning, ensuring our jumps are radially outwards so they don't apply any new torque, then the turntable will continue turning. That jumping off is the analogue to the rocket expelling burnt fuel from its engines.

The fuel is not moving around the ring anymore when the engine gets it. It had to stop moving around the ring, which implies a force to counteract the initial acceleration given by the pump. You ignored this question:

"If we time it so that I'm starting just as you're stopping (and we mass the same), would it move at all?"

Which is the most analogous to the pump situation, fuel is constantly being accelerated in one direction by the pump and constantly stopping in the destination tank, producing the counteractive force.

Two tanks round the core, like Falcon Heavy, creates no problems in the first place. It's when there's more tanks with feed around the rings, like we often do in KSP, that has the rotation issues.

Sorry, I wasn't clear, I meant two tanks from one side of the asparagus. See the above diagram for what I mean.

[Wahgineer]

since the fuel is moving in an asparagus ring, doesn't the fact that each tank is paired with another one affect it? While one tank is pumping fuel from right to left, the other tank will be pumping fuel from left to right (since one side of the stack is an exact mirror image of the other side.) This fact means that any torque/force created by one side will be canceled out by the other side. So both sides are right: the pumps will exert torque on the rocket, but since fuel is flowing in opposite directions on either side, the forces will cancel each other out automatically.

[Red Iron Crown]

No, it would move slightly to the right as the center of mass moved slightly to the left. The center of mass wouldn't move, but the cart would move in the opposite direction of the fuel flow.

So we're talking about a small effect, then. If all the mass was fuel, the rocket would rotate 60 degrees through the burn of a stage in a core-plus-six asparagus configuration, and stop once on its own once the stage is burnt out. Assuming the stage burns for a non-trivial amount of time, I don't see why this would break asparagus staging at all, such forces could easily be counteracted by vectored thrust or aerodynamic control surfaces. Or simply ignored for that matter, it's not like the rocket is going to spin faster and faster until it's uncontrollable.

[Dkmdlb]

Oh my god.

awsumindyman:

If there are opposing sideways forces on a rocket, it will spin. Exactly what we've been saying. Not cancel out.

Edited April 29, 2014 by Dkmdlb

[cantab]

Sorry, I wasn't clear, I meant two tanks from one side of the asparagus. See the above diagram for what I mean.

The problem then is that your diagram is not complete, it's only part of the rocket. I'll try and do one of the full rocket later, hopefully it'll be clearer than the analogies.

since the fuel is moving in an asparagus ring, doesn't the fact that each tank is paired with another one affect it? While one tank is pumping fuel from right to left, the other tank will be pumping fuel from left to right (since one side of the stack is an exact mirror image of the other side.)

They aren't mirror images, but 180 degree rotated counterparts. Mirror images would be worse since the centre of mass would shift radially away from the centreline of the rocket. (Incidentally, such a shift is something KSP *does* model.) Edited April 29, 2014 by cantab

[Dkmdlb]

I don't see why this would break asparagus staging at all, such forces could easily be counteracted by vectored thrust or aerodynamic control surfaces.

I don't have anything to say about that. My only point in this discussion is that asparagus staging will exert torque on a rocket that, if not countered, will cause it to rotate.

[Wahgineer]

Oh my god.

If there are opposing sideways forces on a rocket, it will spin. Exactly what we've been saying. Not cancel out.

Oh. Now that i realize it, you're right: i imagined them running head on. Please excuse me for such a stupid mistake (not sarcasm).

[Red Iron Crown]

The problem then is that your diagram is not complete, it's only part of the rocket. I'll try and do one of the full rocket later, hopefully it'll be clearer than the analogies.

I was trying to simplify by showing that if there is no net force on one half of the asparagus, there cannot be a net force on the rocket as a whole. I'll have to leave the better diagram to you, my MS Paint skills are very modest.

I think Dkmdlb is correct in saying it will rotate as the center of mass of each side of the asparagus moves, but I think that rotation will be at most 180 degrees for a single ring asparagus, spread through the entire asparagus-staged burn, and it will stop rotating of its own accord when the last asparagus stage is expended. It's not going to spin like a bullet from a rifle, or increasingly faster. Definitely within the limits of realistic control authority.

[KASASpace]

@KASASpace

Asparagus in real life isn't as easy as it is in ksp. As sgt_flyer already mentioned, there are a lot of possible complications with the pumps, but aerodynamics are also a huge limiting factor. Try installing FAR and kerbal engineer/mechjeb in ksp and compare the delta-v you need to get into orbit in a streamlined vehicle to the dV needed for an asparagus pancake. Also if you don't go reusable, the rocket itself will always be more expensive by an order of magnitude than the fuel, so the fuel is the worst place to save money. And reusability is way harder than simply sticking parachutes on your booster because liquid fuel rocket engines don't tend to like salt water and most first stage engines aren't designed to be reused.

I know it's difficult. But who in their right mind would ever make an Asparagus PANCAKE? I mean like the Falcon Heavy but with four extra stages, using similar pumps for all of them. The first two tanks dropped pump into the second pair which pump into the third pair which pumps into the final core. I know it's not easy, but it's a good way to make a low energy rockets provide a large amount of payload.

And plus, if you could use Balloon tanks, the cost of the stage is actually not as big as you would expect.

[KASASpace]

@KASASpace In any case it's still a non sequitur. What evidence do you have for your other claims. If you have non then your argument is because it isn't using asparagus staging it is a worthless and horrible rocket. I don't know why you bought it up. Have you just abandoned those arguments? It sounded trollish because you avoided the question and didn't justify your arguments.

My point is that SLS is expensive and can be done with low energy technologies. Using Asparagus.

Fine, I'll say it's my OPINION that it isn't safe and shouldn't be used for manned flights.

NASA should be developing new technologies, not sticking to the old ones. Like if they went with SLS they should use LRBs instead of SRBs, as LRBs aren't very common.

Plus, they should be developing Asparagus staged rockets, as no one has as of yet.

NASA knows that low energy rockets are cheaper, because the price of LH2 is large, and not even counting all the handling requirements! LH2 can leak through the tiniest hole in the tank. It also requires more insulation than LOX and a thick common bulkhead. But it provides high energy and thus is okay for upper stage use.

[R0cketC0der]

I know it's difficult. But who in their right mind would ever make an Asparagus PANCAKE? I mean like the Falcon Heavy but with four extra stages, using similar pumps for all of them. The first two tanks dropped pump into the second pair which pump into the third pair which pumps into the final core. I know it's not easy, but it's a good way to make a low energy rockets provide a large amount of payload.

And plus, if you could use Balloon tanks, the cost of the stage is actually not as big as you would expect.

That would still be about than seven times the drag that a streamlined rocket would experience.

Making an asparagus staged rocket would be possible, but whether the gain is enough to make up to the more complicated engineering is questionable.

[R0cketC0der]

NASA knows that low energy rockets are cheaper, because the price of LH2 is large

As I have already said, the fuel price doesn't really matter that much in real life. I would bet that less than 5 million dollars of the 500 million dollars per launch is the price for the fuel.

[KASASpace]

As I have already said, the fuel price doesn't really matter that much in real life. I would bet that less than 5 million dollars of the 500 million dollars per launch is the price for the fuel.

Most of the launch price is the logistics! The actual rocket is probably only 1/5 of that 500 million.

Seriously. :|

It costs money to prepare the pad, to transport the vehicle, and to pump all the fuel inside.

[sgt_flyer]

Balloon tanks are not structurally viable as side boosters. (too fragile - especially against the thrust they'll have to support against drag)

there's a reason for balloon tanks to be contained inside of fairings.

besides, your mass fraction would be even more against an asparagus design with a balloon tank weight. (it's built to be lightweight - not cheap. if you add a structural frame, you should go for a true tank instead...)

one thing that works wonderfully well in today's rocketry, is stages and a half... which a lot of current rockets use AKA central core with sustainers. (delta IV, Atlas V, Ariane V)

Energia was a 1.5 stage rocket, with the payload having to circularize on it's own.

several 'updates' of saturn V asked for boosters.

SLS is a 2.5 stage rocket.

the main difference with asparagus, is you have to take more fuel inside the central tank (or throttle down the central engine in delta-IV heavy case) - and fuel is the cheapest thing in rockets (you only have to stretch the fuel tanks).

with asparagus, you'll have to add heavy additionnal plumbing, and devellop extremely reliable fuel pumps. (if a single one breaks, things are going to go haywire fast)

besides, most rocket engineers want to limit separation events (that's the most dangerous parts during flights), and a 6 tank asparagus add a lot of separation events (should one fail to ignite it's separation SRB motors, you have a huge risk of colliding with the tank next to it in a 6xtank around a core configuration) - when you drop all boosters at the same time, there's less chances to hit another valuable booster.

and if you are afraid of the logistics of a standard stage and a half rocket, imagine the price of the logistics needed to support asparagus staging...

heck, even in KSP, stages and a half are extremely efficient.

also, LRB's are quite common...

Soyuz use LRB's, Energia too used Zenit Kerolox first stage LRB's, Delta-IV Heavy, Angara will make use in some configurations, some Long March rockets, some Ariane IV configurations used LRB's, etc. so no, not that uncommon.

and the Pyrios LRB booster is in competition for becoming SLS block II boosters (and with what ? a rebuilt/rethinked F-1 engine.)

Edited April 29, 2014 by sgt_flyer

[KASASpace]

That would still be about than seven times the drag that a streamlined rocket would experience.

Making an asparagus staged rocket would be possible, but whether the gain is enough to make up to the more complicated engineering is questionable.

I'll give you that, but the drag wouldn't actually be that big of a problem. The biggest problem is more than likely Max-Q......... but onto drag! The most drag experience would be when the rocket isn't pointing towards its velocity vector. So, to minimize drag, you only point a few degrees off at all times.

And plus, the 9,144 m/s of Dv needed to get to orbit takes into account drag if I'm not mistaking..........

[KASASpace]

Balloon tanks are not structurally viable as side boosters. (too fragile - especially against the thrust they'll have to support against drag)

there's a reason for balloon tanks to be contained inside of fairings.

besides, your mass fraction would be even more against an asparagus design with a balloon tank weight. (it's built to be lightweight - not cheap. if you add a structural frame, you should go for a true tank instead...)

one thing that works wonderfully well in today's rocketry, is stages and a half... which a lot of current rockets use AKA central core with sustainers. (delta IV, Atlas V, Ariane V)

Ballon tanks are actually fairly viable, as they are light. But you could add a few structural emplacements to make it lighter than a typical tank, like a semi-balloon tank.

It doesn't look like you know what 1.5 stage means. The Atlas LV-3b was a 1.5 stage. The Space Shuttle was a 1.5 stage.

1.5 stage means all the engines fire at launch, but then the heavier engines are dropped, aka the booster engines and then the sustainer is left.

[sgt_flyer]

Ballon tanks are actually fairly viable, as they are light. But you could add a few structural emplacements to make it lighter than a typical tank, like a semi-balloon tank.

It doesn't look like you know what 1.5 stage means. The Atlas LV-3b was a 1.5 stage. The Space Shuttle was a 1.5 stage.

1.5 stage means all the engines fire at launch, but then the heavier engines are dropped, aka the booster engines and then the sustainer is left.

i know exactly what a stage and a half means. and all examples i gave you are stages and a half design where all lower engines fire at the same time.

and for note : i said stage and a half, not 1.5 staging.

Soyuz / longmarch are 2.5 stage, so is SLS and Ariane V.

Energia was 1.5 stage.

dropping the engines with or without the fuel tanks (like the Atlas-3B) doesn't change anything to the staging.

and balloon tanks are not meant to support the full weight of the rocket (or the full thrust of the lower stages) - only the payload at low TWR.

for now, i'll stop feeding the troll you seem to be...

real life rocket engineers want rockets to be as simple as possible to limit risks of failures, and you keep wanting to add complex things to rockets...

Edited April 29, 2014 by sgt_flyer

[KASASpace]

i know exactly what a stage and a half means. and all examples i gave you are stages and a half design where all lower engines fire at the same time.

and for note : i said stage and a half, not 1.5 staging.

Soyuz / longmarch are 2.5 stage, so is SLS and Ariane V.

Energia was 1.5 stage.

dropping the engines with or without the fuel tanks (like the Atlas-3B) doesn't change anything to the staging.

and balloon tanks are not meant to support the full weight of the rocket (or the full thrust of the lower stages) - only the payload at low TWR.

for now, i'll stop feeding the troll you seem to be...

real life rocket engineers want rockets to be as simple as possible to limit risks of failures, and you keep wanting to add complex things to rockets...

Then kindly explain why the Atlas LV-3b used Balloon tanks. It was a booster launch vehicle, and they placed an upper stage on it. The Centaur.

Atlas V is not a 1 and a half stage, Ariane V is not. And I'm quite sure that the Delta IV isn't as well.

Atlas V: ONE RD-180 first stage engine. Sure, you can add booster stages, but those aren't individual engines, those are entire stages.

Ariane V: Has a second stage, albeit small. UPDATE: Plus, the SRBs contain their own fuel.

Delta IV: Also has a second stage, using the RL-10. The upper stage was planned to be adapted for the SLS' first two missions : EM-1 and EM-2.

[sgt_flyer]

if you can't read 'Stages' and a half, i can't do anything for you.

there's a reason 2.5 stage to orbit keeps coming back with very lightweight upper stages (compared to the rest of the rocket)

i even specifically made the distingo between 1.5 and 2.5 stages in my post.

Soyuz / longmarch are 2.5 stage, so is SLS and Ariane V.

Energia was 1.5 stage.

besides, i'd like to see your sources for the Atlas-LV3b where they talk about balloon tanks...

except for the Centaur upper stage, which is a balloon tank i don't seem to find where in the rocket's first stage they used balloon tanks...

besides, space shuttle could be considered 2.5 stages to orbit by dropping the External Tank.

ignition : SSME's from external tank + SRB's

SRB drop

SSME's extinction + external tank jettison

circularization with OMS engines.

Edited April 29, 2014 by sgt_flyer

[KASASpace]

if you can't read 'Stages' and a half, i can't do anything for you.

there's a reason 2.5 stage to orbit keeps coming back with very lightweight upper stages (compared to the rest of the rocket)

i even specifically made the distingo between 1.5 and 2.5 stages in my post.

besides, i'd like to see your sources for the Atlas-LV3b where they talk about balloon tanks...

except for the Centaur upper stage, which is a balloon tank i don't seem to find where in the rocket's first stage they used balloon tanks...

besides, space shuttle could be considered 2.5 stages to orbit by dropping the External Tank.

ignition : SSME's from external tank + SRB's

SRB drop

SSME's extinction + external tank jettison

circularization with OMS engines.

"Stages and a half" looks like you mean multiple launch vehicles with stage and a half design. You wouldn't say "stage and a halves" would you?

http://www.astronautix.com/lvs/atlas.htm

That's the Encyclopedia Astronautica. One of the best resources for space flight. If you look in the very first paragraph it says:

Its innovative stage-and-a-half and 'balloon tank' design provided the best dry-mass fraction of any launch vehicle ever built

It *could* be considered that (the STS).

(Although, I have to commend you on your Saturn family.......)

Edited April 29, 2014 by KASASpace

[sgt_flyer]

well, you have 2 stages and a half for example

saying 2 stage and halves would make little sense

else, Wikipedia's article on the atlas is more expansive on the balloon tank

it just 'needs' to be kept under at least a pressure of 5 PSI - for such a light payload it carried

you would need way higher pressures for keeping the high thrust engines in check for a superheavy rocket boosters. (or you'll need a support structure - but that's what those tanks already are - notably the Space Shuttle External tank - they needed to build a support structure to support everything above) - so the gain between a balloon tank + support structure around it would be mitigated.

one of the best structures to support heavyweights posed on top of it remains a tube after all

Edited April 29, 2014 by sgt_flyer