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The epic chicken

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#26
Well waiting for others to do it won't get you anywhere somebody's got to go first
I'm just trying to figure out how to squeeze 12000 m/s of Dv out of that high efficiency stage from my failed Jupiter mission

Only got 6500 rn, is that enough for a sun flyby

Edit: I've got no idea how to get a close fly off the sun, so I should probably not do that
 
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Marmilo

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#27
Hey Mooncrasher what's considered a sun flyby? Below 1Mm?
 

Mooncrasher

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#28
500 000 km. :) You can and should improve efficiency via gravity assists, but it's reachable from LEO
 

The epic chicken

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#29
Yea, I think I'll just land a couple pods on mercury, I've got no idea on how to get that much efficiency (I suck at gravity assists)
 

Mooncrasher

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#31
Can I do this with a shuttle? I love to do everything with shuttles.
Sure, no restrictions on what your rocket looks like.
Not YET you don't!!!! I already have most of the ship I need is ready, I just need to get Hermes-2 and Arizona ready on Venus(I sent them two days ago). AND Anaheim Station will help it..
You'd better provide screenshots of launching all those things, and they count for your total mass. Might not end up going well. :p
 
T

TtTOtW

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#32
I'm just trying to figure out how to squeeze 12000 m/s of Dv out of that high efficiency stage from my failed Jupiter mission

Only got 6500 rn, is that enough for a sun flyby

Edit: I've got no idea how to get a close fly off the sun, so I should probably not do that
Max delta v for Titan and Hawk is about 5416 m/s. Kolibri offers 5866m/s. Valiant can squeeze out 6313m/s and Frontier sees the end of its potential before 6550m/s. So first of all I can already tell you are using Frontiers. And b, it's not gonna get better, no matter how much fuel you add. So um... More efficient flying is your only option.

Also, you'll need to add, best case scenario, 311000t of fuel tanks to your stage to get the last available about 40m/s. So um...
 

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#33
Max delta v for Titan and Hawk is about 5416 m/s. Kolibri offers 5866m/s. Valiant can squeeze out 6313m/s and Frontier sees the end of its potential before 6550m/s. So first of all I can already tell you are using Frontiers. And b, it's not gonna get better, no matter how much fuel you add. So um... More efficient flying is your only option.

Also, you'll need to add, best case scenario, 311000t of fuel tanks to your stage to get the last available about 40m/s. So um...
Yeah, so I probably shouldn't do the sun mission
 

Mooncrasher

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#34
More efficient flying is always good, but don't forget about more stages;) Get off the diminishing returns curve
 

Mooncrasher

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#36
Nice visualization! So yeah, in many cases if you're on the really steep part of the curve, you'll gain more dV by splitting the fuel off into an extra stage.
 
T

TtTOtW

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#37
Yeah. Y axis is the amount of full fuel tanks in tons required. X axis is delta v achieved.

You can also clearly see how the different engines have different limits to how much delta-v can be achieved by them.
 

Altaïr

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#41
Yeah, so I probably shouldn't do the sun mission
Staging is not forbidden chicken :)

I've already made some calculations to optimize the ΔV per mass unit, and while it's difficult to give a precise threshold, what's clear is that if you start hitting 3500 m/s with a single stage, you should really consider splitting it into 2 stages. This is assuming the stage is running on Valiant or Frontier engines of course. Ion engines are on another level.

You should never even hit the steep part of the curve given by TtTOtW
 

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#42
Staging is not forbidden chicken :)

I've already made some calculations to optimize the ΔV per mass unit, and while it's difficult to give a precise threshold, what's clear is that if you start hitting 3500 m/s with a single stage, you should really consider splitting it into 2 stages. This is assuming the stage is running on Valiant or Frontier engines of course. Ioen engines are on another level.

You should never even hit the steep part of the curve given by TtTOtW
Yea, I know staging is allowed, but I'm not so confident in my gravity assists
 

Marmilo

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#48
I thought DeltaV is a logarithmic function, not an exponential function lol
Altair will you enlighten me?
 

Altaïr

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#49
I thought DeltaV is a logarithmic function, not an exponential function lol
Altair will you enlighten me?
ΔV is a logarithmic function, with the rocket mass in the logarithm, but we consider the inverse function here, where the rocket mass is expressed in function of ΔV. And the inverse of the logarithm is exponential. :)

You usually have:
ΔV = Ve × Ln(mass / dry_mass)
(Ve = exhaust speed = g×Isp)

So by inverting it:
mass = dry_mass × Exp(ΔV/Ve)

I usually write mass = fuel_mass + dry_mass, so you can also write it that way:
fuel_mass = dry_mass × (Exp(ΔV/Ve) - 1)

Also, the curve given by TtTOtW has an hyperbolic behaviour: it becomes infinite when you hit a limit. It's because when you add some fuel, you also have to consider the added dry mass from the tank. A fuel tank has a "total mass to dry mass" ratio of 10, so the "mass/dry_mass" ratio of your rocket will always be lower than that.

That's why the maximum delta-V for a stage is:
ΔVmax = Ve × Ln(10)

You would have to take this into account to get the curve showed by TtTOtW, but I already reached the quota of authorized maths per post :p
 

Marmilo

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#50
ΔV is a logarithmic function, with the rocket mass in the logarithm, but we consider the inverse function here, where the rocket mass is expressed in function of ΔV. And the inverse of the logarithm is exponential. :)

You usually have:
ΔV = Ve × Ln(mass / dry_mass)
(Ve = exhaust speed = g×Isp)

So by inverting it:
mass = dry_mass × Exp(ΔV/Ve)

I usually write mass = fuel_mass + dry_mass, so you can also write it that way:
fuel_mass = dry_mass × (Exp(ΔV/Ve) - 1)

Also, the curve given by TtTOtW has an hyperbolic behaviour: it becomes infinite when you hit a limit. It's because when you add some fuel, you also have to consider the added dry mass from the tank. A fuel tank has a "total mass to dry mass" ratio of 10, so the "mass/dry_mass" ratio of your rocket will always be lower than that.

That's why the maximum delta-V for a stage is:
ΔVmax = Ve × Ln(10)

You would have to take this into account to get the curve showed by TtTOtW, but I already reached the quota of authorized maths per post :p
Thanks!