Diagram of the Boeing Space Tug Engine Module (EM).
Analysis: EM
was a way to make it go. Enter the Engine Module (EM).
This machine would have had everything you needed
to go on a space mission: propellant tanks, a Reaction
Control System (RCS), batteries, and of course, the
reliable RL10 rocket engine. This rocket engine was
useful in that it could have been restarted many times,
) fuel.
2
This meant that the EM could have been reused many
in all of rocketry is appropriately called the Rocket
Equation, also known as the “Tsiolkovsky Equation”
named after its discoverer.
m0
v = vEXH ln( ––– )
m1
It tells rocketeers how much of a change in velocity
propellant weight, and the exhaust velocity (vEXH ) of
the gasses being expelled by the rocket. The exhaust
)
SP
multiplied by the standard gravity of Earth.
Using the information from the Space Tug EM image,
60
60
Credit: Boeing
had an ISP of 460 s. We can thus calculate the rocket
).
EXH
vEXH = I SP g0 = (460)(9.80665) = 4, 511 mps
The EM graphic also tells us that the Inert Weight of
the EM was 5,610 lbs. If we carry a CM with a crew of
10 astronauts on a 22-day mission that weighs 9,540 lbs,
and other payload, the Dry Weight can be calculated.
m1 = WeightINERT + WeightPAYLOAD + WeightCM
= 5610 + 8000 + 9540 = 23,150 lbs
Finally, the EM graphic shows that the propellant
would have weighed 39,800 lbs. We now have
everything we need to solve the rocket equation.
m0 = m1 + WeightPROPELLANT = 23150 + 39800 = 62,950 lbs
Putting everything together, we get
v
62950
ln( ––––––– )
23150
= (4511)(1.000346) = 4,513 mps
www.RocketSTEM .org