Saturday, August 02, 2008

What is Merlin 1C? Falcon 1's Awesome Engine

The good thing about having a little bit of free time, is that it just happens that there's a lot to talk about. Here's a diddy on the rockin' Merlin 1C, the main engine of Falcon 1 Vehicle 3.

The pintle style injector at the heart of Merlin was first used in the Apollo Moon program for the Lunar Excursion Module (LEM) landing engine, one of the most critical phases of the mission.


Sea Level Thrust: 78,000 lb - those three F-16s I mentioned earlier
Vacuum Thrust: 138,400 lb - everything is just better in space.
Sea Level Isp: 255 s - Isp is Specific Impulse
Vacuum Isp: 304 s

Now I know you're asking: What exactly is Isp, Kimbal? Well, funny you ask. I just happen to have an explanation...

For the Rocket Scientists out there...

The specific impulse Isp is given by:

Isp = Veq / g0

where g0 is the gravitational acceleration constant (32.2 ft/sec^2 in English units, 9.8 m/sec^2 in metric units). Now, if we substitute for the equivalent velocity in terms of the thrust:

Isp = F / (mdot * g0)

Mathematically, the Isp is a ratio of the thrust produced to the weight flow of the propellants. A quick check of the units for Isp shows that:

Isp = m/sec / m/sec^2 = sec

Now I know that a lot of folks aren't into physics, or if they are, and you still can't figure it out, our friends at NASA have a nice and easy explanation of Isp:

"Why are we interested in specific impulse? First, it gives us a quick way to determine the thrust of a rocket, if we know the weight flow rate through the nozzle. Second, it is an indication of engine efficiency. Two different rocket engines have different values of specific impulse. The engine with the higher value of specific impulse is more efficient because it produces more thrust for the same amount of propellant. Third, it simplifies our mathematical analysis of rocket thermodynamics. The units of specific impulse are the same whether we use English units or metric units. Fourth, it gives us an easy way to "size" an engine during preliminary analysis. The result of our thermodynamic analysis is a certain value of specific impulse. The rocket weight will define the required value of thrust. Dividing the thrust required by the specific impulse will tell us how much weight flow of propellants our engine must produce. This information determines the physical size of the engine. "

And from SpaceX:
"With a vacuum specific impulse of 304s, Merlin is the highest performance gas generator cycle kerosene engine ever built, exceeding the Boeing Delta II main engine, the Lockheed Atlas II main engine and on par with the Saturn V F-1.

Digg It!

1 comment:

Sabrina said...

Are you doing all of this real time?! So impressive AND entertaining... thanks!