[Spaceships] Homebrew: Alternate Chemical Rocket Fuel

[Anthony]

Originally Posted by Brett

Isp (specific impulse) is not measured in seconds in the SI, only in US customary units.

If it's labeled Isp, it's commonly measured in Seconds even under SI. If instead it's labeled as Ve, it's not measured in Seconds, despite the fact that these two names are measuring exactly the same thing.

[Agemegos]

Originally Posted by Anthony

If it's labeled Isp, it's commonly measured in Seconds even under SI. If instead it's labeled as Ve, it's not measured in Seconds, despite the fact that these two names are measuring exactly the same thing.

That is bizarre, freakish, and bound to lead to confusion. Also, not what I was taught in my physics courses.

[malloyd]

Originally Posted by DaltonS

I've noticed that changes in ΔV vary inversely with those of thrust; therefore, the acceleration provided by a chemical rocket using a different propellant would be 3×484/Isp = 1,452/Isp Gs. The endurance of the tank would be Isp squared times 0.00031×3600/(1452×21.8) = 0.000035 seconds.

Generally, tanks, pumps and engines of the same size would be more likely to have the same volume flow rate rather than mass flow rate, which would mean thrust is proportional to density x Isp, - this matters quite a bit because pretty much everything is denser than hydrox, and therefore gets better thrust despite lower Isps - and endurance is unchanged. I crunched through a lot of numbers for GURPS Vehicles at one point - http://www.gurpsnet.org/Archive/Vehi...struction/V2ad for chapters 2 and 7.

[DaltonS]

Originally Posted by malloyd

Generally, tanks, pumps and engines of the same size would be more likely to have the same volume flow rate rather than mass flow rate, which would mean thrust is proportional to density x Isp, - this matters quite a bit because pretty much everything is denser than hydrox, and therefore gets better thrust despite lower Isps - and endurance is unchanged. I crunched through a lot of numbers for GURPS Vehicles at one point - http://www.gurpsnet.org/Archive/Vehi...struction/V2ad for chapters 2 and 7.

Which explains why in Spaceships all the alternate reaction masses mentioned divide the delta-V by the thrust multiplier. The fuel tanks are constrained by mass, not volume, so fuel density is not the issue. (Not too realistic, I know.)

Dalton “who is looking forward to your "Spaceships Additions" files ;)” Spence