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Altaïr
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Altaïr
Space Stig, Master of gravity
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I can answer the first 2 questions.
1- You need the vis-viva equation for this:
v^2 = μ×(2/r - 1/a)
μ is the gravitational parameter (μ = G×M in astrodynamics formulas), a is the semi great axis : a = (periapsis + apoapsis)/2
If you use this in the context of the game, don't forget that periapsis and apoapsis have to be measured from the body's center, not from ground level like ingame. So you have to add the body radius to the values you get from the game.
For the gravitational parameter, you can calculate it from the planet data file:
μ = g×radius^2
Note that the formula works for any type of trajectory, but as there is no semi great axis for hyperbolas, you should use the following form:
v^2/2 - μ/r = constant.
If you know the speed at one point (periapsis for example), then you know it at any point.
2- Now you need the Kepler equation:
M = E - e×sin(E)
e is eccentricity
E is eccentric anomaly
M is mean anomaly
You can calculate eccentric anomaly that way:
tan(E/2) = sqrt((1-e)/(1+e)) × tan((θ-φ)/2)
θ is the argument (the angle at which the ship currently is), φ is the argument of periapsis.
Then the mean anomaly is proportional to the delay the ship needs to go from periapsis to its current position:
M = sqrt(μ)/a^(3/2) × T
(T is the delay in the equation).
Another way to write it is to use the orbital period: T_orb = 2×Pi×a^(3/2)/sqrt(μ)
Then you have M = 2Pi × T/T_Orb = E - e×sin(E)
The Kepler equation allows you to calculate the delay (T) that separates 2 positions, but the equation can't be reversed to calculate a starting position from a delay and an ending position. However, some numerical analysis methods (like the Newton-Raphson method) are very efficient to calculate this in practice.
But as you see, overall this is much more complicated than applying a formula. If you want to calculate the closest encounter this requires an iterative approach, there's no direct way to achieve this.
3- I'll use a joker for this one
1- You need the vis-viva equation for this:
v^2 = μ×(2/r - 1/a)
μ is the gravitational parameter (μ = G×M in astrodynamics formulas), a is the semi great axis : a = (periapsis + apoapsis)/2
If you use this in the context of the game, don't forget that periapsis and apoapsis have to be measured from the body's center, not from ground level like ingame. So you have to add the body radius to the values you get from the game.
For the gravitational parameter, you can calculate it from the planet data file:
μ = g×radius^2
Note that the formula works for any type of trajectory, but as there is no semi great axis for hyperbolas, you should use the following form:
v^2/2 - μ/r = constant.
If you know the speed at one point (periapsis for example), then you know it at any point.
2- Now you need the Kepler equation:
M = E - e×sin(E)
e is eccentricity
E is eccentric anomaly
M is mean anomaly
You can calculate eccentric anomaly that way:
tan(E/2) = sqrt((1-e)/(1+e)) × tan((θ-φ)/2)
θ is the argument (the angle at which the ship currently is), φ is the argument of periapsis.
Then the mean anomaly is proportional to the delay the ship needs to go from periapsis to its current position:
M = sqrt(μ)/a^(3/2) × T
(T is the delay in the equation).
Another way to write it is to use the orbital period: T_orb = 2×Pi×a^(3/2)/sqrt(μ)
Then you have M = 2Pi × T/T_Orb = E - e×sin(E)
The Kepler equation allows you to calculate the delay (T) that separates 2 positions, but the equation can't be reversed to calculate a starting position from a delay and an ending position. However, some numerical analysis methods (like the Newton-Raphson method) are very efficient to calculate this in practice.
But as you see, overall this is much more complicated than applying a formula. If you want to calculate the closest encounter this requires an iterative approach, there's no direct way to achieve this.
3- I'll use a joker for this one
Oh yeah, food for thought. Since you know fluid dynamics.
You know how pressure head loss, be it minor or major, both equations are gravity dependent right? If say I am to optimize a moon lander's propellant plumbing according to the moon's gravity. Does that mean it will outright cock up when operating under earth gravity?
You know how pressure head loss, be it minor or major, both equations are gravity dependent right? If say I am to optimize a moon lander's propellant plumbing according to the moon's gravity. Does that mean it will outright cock up when operating under earth gravity?
T
It is generally well known that rockets use rcs to shunt any liquid fuelled orbital spacecraft ever so gently forward, so as to shift the free floating fuel in the tanks to the outlets to feed the engines. Once on the move, whether at low or high throttle, it just works.this leads me to believe that gravity/thrust itself is important to keep the engine fed, not the scale of it.
Altaïr
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Pink
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Passive = not active.
What I actually meant by passive was the 'passive' pressure due to pull of gravity, that isn't made by your pumps and stuff. So when you're on the moon, you're feeling a different passive pressure in the piping than in mother Russia (for example).
So, is there anything in a rocket engine that relies on the 'passive' pull of gravity to work?
What I actually meant by passive was the 'passive' pressure due to pull of gravity, that isn't made by your pumps and stuff. So when you're on the moon, you're feeling a different passive pressure in the piping than in mother Russia (for example).
So, is there anything in a rocket engine that relies on the 'passive' pull of gravity to work?
Pink
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Nah, doesn't have to be, equations aren't location fixed.
Ah that's just the gravity factor. We have many things that affect the overall plumbing of the engine, currently what I am worried about is pressure head loss. That has a gravity factor in it.
Temporarily ignore whatever cycle the system depends on, pressure fed or pump fed.
Ah that's just the gravity factor. We have many things that affect the overall plumbing of the engine, currently what I am worried about is pressure head loss. That has a gravity factor in it.
Temporarily ignore whatever cycle the system depends on, pressure fed or pump fed.
Alright, forced myself to do the math, really easy.
Just divide 9.81 by 6 to get a crude moon gravity, and your head loss drops almost 6 times usual. So yeah, your system doesn't need to work as hard on the moon. Elementary math.
Answered my own bloody question in 20 seconds, why did I go through all that trouble for.
Just divide 9.81 by 6 to get a crude moon gravity, and your head loss drops almost 6 times usual. So yeah, your system doesn't need to work as hard on the moon. Elementary math.
Answered my own bloody question in 20 seconds, why did I go through all that trouble for.