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| || velocity || $ v_0 = \omega a = \sqrt{ \mu / a } $ || | || velocity || $ v_0 \sqrt{ \mu / a (1 - e^2) } $ || |
Near Circular Orbits
MORE LATER add pointers to orbit discussions
General Elliptical Orbits
In the orbital plane, neglecting the J_2 spherical oblateness parameter :
gravitational parameter |
\mu = a^3 \omega^2 = G M |
||
semimajor axis |
a = \sqrt[3]{ \mu / \omega^2 } |
||
angular velocity |
\omega = \sqrt{ \mu / a^3 } |
||
period |
2 \pi / \omega = 2 \pi \sqrt{ a^3/ \mu } |
||
velocity |
v_0 \sqrt{ \mu / a (1 - e^2) } |
||
eccentricity |
e = ( r_a - r_p ) / ( r_a + r_p ) |
||
true anomaly, orbit angle from focus |
\theta |
||
eccentric anomaly, ellipse center angle |
E =( e+\cos(\theta) )/( 1+e\cos(\theta)) |
||
mean anomaly, |
M = E - e \sin( E ) |
||
time from perigee |
t = M / \omega |
||
radius |
r = (1-e^2) a / ( 1 + e \cos( \theta ) ) |
r_p = ( 1 - e ) a |
r_a = ( 1 + e ) a |
perpendicular velocity |
v_{\perp} = v_0 ( 1 + e \cos( \theta ) ) |
v_p = ( 1 + e ) v_0 |
v_a = ( 1 - e ) v_0 |
radial velocity |
v_r = e v_0 \sin( \theta ) |
periapsis ( general ) |
apoapsis ( general ) |
total velocity ( tangent to orbit ) |
v = \sqrt{ \mu \left( 2/r - 1/a \right)} |
perigee (earth) |
apogee (earth ) |
orbit energy parameter |
C_3 = \mu / a |
perihelion ( sun ) |
apohelion ( sun ) |
Periods of M orbits
M orbits describe the number of minutes an orbit takes travel once around the earth and return to the same position overhead. For server sky, these are integer fractions of a 1440 minute synodic day; this makes it easier to calculate the sky position given the orbital parameters and the time of day. the M288 orbit returns to the same apparent position 5 times per day, or 365.256...*5 times per year. That position moves around the earth 365.256...+1 times per year. So the total number of orbits per year, relative to the stars, is 365.256...*6+1 orbits per year. That is divided into the year length in seconds to yield the
Sidereal orbit time = ( 365.256... * 86400 ) / ( 365.256... * 6 + 1 ) = 86400 / ( 6 + 1/365.256... ) = 14393.43227 seconds
1 year = 365.256363004 days of 86,400 seconds, or 31558149.7635456 seconds
Note: The following table uses the classic formula \omega^2 a^3 = \mu from the books, and does not take into account the oblate spheroid shape of the Earth, which adds centripedal force for low orbits and thus should increase \omega and | C_3 | . So please check these numbers.
The eccentricities for the M orbits assume orbits mapped onto a 50km minor radius toroid.
symbol |
|
LEO 300Km |
M288 |
M360 |
GEO |
Moon |
Earth |
units |
\mu |
gravitation param. |
3.98600448E+14 |
3.98600448E+14 |
3.98600448E+14 |
3.98600448E+14 |
3.98600448E+14 |
1.32712440E+20 |
m3/s2 |
|
relative to |
earth |
earth |
earth |
earth |
earth |
Sun |
|
a_g |
gravity |
8.938095E+00 |
2.437062E+00 |
1.911369E+00 |
2.242078E-01 |
2.697573E-03 |
5.930053E-03 |
seconds |
T |
sidereal period |
5431.009959 |
14393.432269 |
17270.543331 |
86164.099662 |
2360591.577436 |
31558149.763546 |
seconds |
T_s |
synodic period |
5431.944772 |
14400.000000 |
17820.000000 |
86400.000000 |
2551442.900000 |
31558149.763546 |
seconds |
T/2\pi |
Sidereal / 2pi |
864.372081 |
2290.785853 |
2748.692283 |
13713.440926 |
375698.721205 |
5022635.529703 |
seconds |
\omega |
Angular velocity |
1.15690919E-03 |
4.36531419E-04 |
3.63809367E-04 |
7.29211585E-05 |
2.66170722E-06 |
1.99098659E-07 |
rad/sec |
|
orbits/year |
5810.73318 |
2192.53822 |
1827.28185 |
366.25640 |
13.36879 |
1.00000 |
|
a |
semimajor axis |
6678000.00 |
12788970.60 |
14440980.32 |
42164169.86 |
384399000.00 |
149598261000.00 |
meters |
R_a |
apogee radius |
6678000.00 |
12838970.60 |
14490980.32 |
42164169.86 |
405696000.00 |
152098232000.00 |
meters |
R_p |
perigee radius |
6678000.00 |
12738970.60 |
14440980.32 |
42164169.86 |
363104000.00 |
147098290000.00 |
meters |
e |
eccentricity |
0.000000 |
0.001951 |
0.001728 |
0.000000 |
0.055401 |
0.016711 |
|
V_0 |
mean velocity |
7725.84 |
5582.79 |
5253.76 |
3074.66 |
1023.16 |
29784.81 |
m/s |
V_a |
apogee velocity |
7725.84 |
5571.90 |
5244.68 |
3074.66 |
966.47 |
29287.07 |
m/s |
V_p |
perigee velocity |
7725.84 |
5593.68 |
5262.84 |
3074.66 |
1079.84 |
30282.55 |
m/s |
C_3 |
orb. specific energy |
-59688596.59 |
-31167516.16 |
-27602035.26 |
-9453534.82 |
-1036944.55 |
-887125553.00 |
J/kg |