Space Propulsion - IAP/TU Wien
Space Propulsion - IAP/TU Wien
Space Propulsion - IAP/TU Wien
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<strong>Space</strong> <strong>Propulsion</strong><br />
Example 1: Simple Coplanar Orbit Change<br />
Consider an initially circular low Earth orbit at 300-km altitude. What velocity increase<br />
would be required to produce an elliptical orbit 300 x 3000 km in altitude? What would be the<br />
fuel consumption for a 750 kg (empty) S/C if I sp<br />
= 3100 m/s ?<br />
The gravity parameter of Earth is μ=398,600.4 km 3 /s 2<br />
Radius of Earth is ≈ R = 6387 km<br />
velocity on initial circular orbit:<br />
semimajor axis of final elliptical orbit:<br />
V 398,600.4<br />
= μ =<br />
= 7.726 km s<br />
r (300 + 6378.14)<br />
/<br />
ra<br />
+ rp<br />
a =<br />
2<br />
(300+<br />
6378) + (3000+<br />
6378)<br />
=<br />
= 8028<br />
2<br />
[ km]<br />
velocity at periapsis of final orbit:<br />
velocity change =<br />
V 2μ<br />
μ 2(398,600) 398,600<br />
= − =<br />
− = 8.350 km s<br />
p<br />
r a 6678 8028<br />
/<br />
ΔV = Vp −V<br />
= 8 .350 − 7.726 = 0.624 km / s<br />
fuel consumption<br />
⎡ ⎛ V ⎞ ⎤ ⎧ ⎡ (624) ⎤ ⎫<br />
mp m<br />
f ⎢exp ⎜<br />
Δ<br />
=<br />
⎟ −1⎥<br />
= 750⎨exp<br />
−1⎬<br />
= 167. 2<br />
I<br />
⎢<br />
sp ⎩ (3100)<br />
⎥<br />
⎢<br />
⎣ ⎝ ⎠ ⎥⎦<br />
⎣ ⎦ ⎭<br />
kg<br />
Velocity changes, made at periapsis, change apoapsis radius but not periapsis radius, and vice<br />
versa; the radius at which the velocity is changed remains unchanged. As you would expect, the<br />
plane of the orbit in inertial space does not change as velocity along the orbit is changed. Orbital<br />
changes are a reversible process.