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Jairo
2005-Jul-07, 03:16 PM
I was trying to calculate the delta V of the ascent stage of lunar module by myself, to check for some people that it could actualy leave the Moon.

I know the full (4,691kg) and dry (2,333kg) mass, and I know the specific impulse of the engine (3,050Ns/kg). Using the rocket equation, this gives me a delta V of 2,120m/s, wich is indeed higher than the speed required for orbit (1,845m/s).

But I suppose this equation aplies only to absence of gravity. Is it wrong? How do I calculate that the right way?

Thanks.

papageno
2005-Jul-07, 03:22 PM
I was trying to calculate the delta V of the ascent stage of lunar module by myself, to check for some people that it could actualy leave the Moon.

I know the full (4,691kg) and dry (2,333kg) mass, and I know the specific impulse of the engine (3,050Ns/kg). Using the rocket equation, this gives me a delta V of 2,120m/s, wich is indeed higher than the speed required for orbit (1,845m/s).

But I suppose this equation aplies only to absence of gravity. Is it wrong? How do I calculate that the right way?

Thanks.

Is the rocket used at full throttle?

Argos
2005-Jul-07, 03:27 PM
Delta V calculator (http://www.strout.net/info/science/delta-v/intro.html).

Saluki
2005-Jul-07, 03:55 PM
If you calculated your minimum orbital speed correctly, it should include the effects of gravity. Therefore, if your ΔV exceeds the orbital speed, you should have proven that the ascent module could reach the specified orbit.

Jairo
2005-Jul-07, 05:10 PM
If I were using an ion engine, I think I would have an even greater specifc impulse and delta V, but I surely wouldn´t be able to leave the ground. Right?

That´s why I think that still isn´t a definitive proof.

Ravaun
2012-Feb-19, 04:14 AM
The 'basic rocket equation' does not account for the Thrust required to lift the mass which you're moving. For simplicity's sake, use 33.85 MN thrust/3097.891 kg/3,057.044086031 m/sec. That's 1 kN thrust/1,000 kg GROSS MASS/279.775165753 m/sec of Δ-V.

(Basis used is Saturn V rocket stack, using 199,000 kg payload, 1996 kg I.U. Final Δ-V to LEO = 8,081.130749123 m/sec.)

That should correct your thrust calculations, so you can select the proper thruster unit to utilize.

Ravaun
"The reason we haven't figured out what makes gravity is because the Earth sucks!"

Garrison
2012-Feb-19, 08:56 PM
The 'basic rocket equation' does not account for the Thrust required to lift the mass which you're moving. For simplicity's sake, use 33.85 MN thrust/3097.891 kg/3,057.044086031 m/sec. That's 1 kN thrust/1,000 kg GROSS MASS/279.775165753 m/sec of Δ-V.

(Basis used is Saturn V rocket stack, using 199,000 kg payload, 1996 kg I.U. Final Δ-V to LEO = 8,081.130749123 m/sec.)

That should correct your thrust calculations, so you can select the proper thruster unit to utilize.

Ravaun
"The reason we haven't figured out what makes gravity is because the Earth sucks!"

Ravaun the last post in this thread was almost 7 years ago, so I don't think you are going to get a response from Jairo

DoggerDan
2012-Feb-23, 09:42 AM
Ravaun the last post in this thread was almost 7 years ago, so I don't think you are going to get a response from Jairo

Oh, let him exercise his brain a little! He's not hurting anything or anyone by crunching the numbers. If anything, he's improving his number-crunching.