Question How do you estimate the weight of a vessel?

[martins]

You forgot a minus sign in your exponent (or alternatively, you have to invert your mass ratio).

 

[ar81]

I found the solution here.

dV = Ve * ln (m0/m1)

Ve = Isp x 9.81
m0 = vessel mass + propellant mass
m1 = vessel mass (empty)

For an Isp between 4,000 and 40,000 empty mass would represent between 46% to 97% depending on Isp.

How do I estimate fuel consumption to achieve a DeltaV?
How do I estimate burn time?

 

[gertz]

"Формула Циолковского" (sorry, dont know how it will be in english)

M1 - empty mass, M2 - full (with fuel), I - engine Isp, V - max dV.

Русский??

 

[Schimz]

If I want to create a vessel, how do you estimate its empty weight?

If it can takeoff, add weight

 

[EtherDragon]

Here we go...

Where,
V=DeltaV and is known (you choose a DeltaV you require)
I=Isp and is known (You choose an Isp you like)
f=fuel mass (Solve for this)
m=empty mass (When given this)

For a given DeltaV and Isp you can determine the weight to fuel ratio as follows:

V = I*ln(m/(m+f))
V/I = ln(m/(m+f))
e^(V/I) = m/(m+f)
(m+f)/m = 1/(e^(V/I))
1+f/m = 1/(e^(V/I))
f/m = 1/(e^(V/I)) -1
f = m/(e^(V/I)) - m

alternately, to get m when given f:
f/m = 1/(e^(V/I)) -1
m/f = (e^(V/I)) -1
m = f*(e^(V/I)) - f

I think... try that and see how it goes.

---------- Post added at 08:14 AM ---------- Previous post was at 08:06 AM ----------

How do I estimate burn time?

Burn time is simple, it's your flow rate over time. Burn time has no impact on Isp or DeltaV, instead, burn time is inversely praportional to thrust.

Given equivelent Isp:
High thrust over a short time yields the same dV as low thrust over a long time.

 

[mc_]

If it can takeoff, add weight

...if it still can takeoff then, use smaller rocket. That is why i like N-1 - it is always possible to remove first stage. Or even fiirst and second.

Русский??

Написано же - сибиряк :thumbup: