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Size: 3753
Comment:
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Size: 3731
Comment: changed flat-sat to thinsat
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| Deletions are marked like this. | Additions are marked like this. |
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| We can minimize night light pollution, and advance perigee against light pressure orbit distortion, by turning the flat-sat as we approach eclipse. The overall goal is to perform 1 complete rotation of the flat-sat per orbit, with it perpendicular to the sun on the day-side of the earth, but turning it by varying amounts on the night side. | We can minimize night light pollution, and advance perigee against light pressure orbit distortion, by turning the thinsat as we approach eclipse. The overall goal is to perform 1 complete rotation of the thinsat per orbit, with it perpendicular to the sun on the day-side of the earth, but turning it by varying amounts on the night side. |
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| Another advantage of the turn is that if flat-sat maneuverability is destroyed by radiation or a collision on the night side, it will come out of night side with a slow tumble that won't be corrected. The passive radar signature of the tumble will help identify the destroyed flat-sat to other flat-sats in the array, allowing another sacrificial flat-sat to perform a "rendezvous and de-orbit". If the destroyed flat-sat is in shards, the shards will tumble. The tumbling shards ( or a continuously tumbling flat-sat ) will eventually fall out of the normal orbit, no longer get $ J_2 $ correction, and the flat-sat orbit will "eccentrify", decay, and reenter. This is the fail-safe way the arrays will reenter, if all active control ceases. | Another advantage of the turn is that if thinsat maneuverability is destroyed by radiation or a collision on the night side, it will come out of night side with a slow tumble that won't be corrected. The passive radar signature of the tumble will help identify the destroyed thinsat to other thinsats in the array, allowing another sacrificial thinsat to perform a "rendezvous and de-orbit". If the destroyed thinsat is in shards, the shards will tumble. The tumbling shards ( or a continuously tumbling thinsat ) will eventually fall out of the normal orbit, no longer get $ J_2 $ correction, and the thinsat orbit will "eccentrify", decay, and reenter. This is the fail-safe way the arrays will reenter, if all active control ceases. |
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| Neglecting tides, the synodic angular velocity of the m288 orbit is $\Large\omega$ = 4.3633e-4 rad/sec = 0.025°/s. The angular acceleration of a flat-sat is 13.056e-6 rad/sec^2^ = 7.481e-4°/s^2^ with a sun angle of 0°, and 3.740e-4°/s^2^ at a sun angle of 60°. Because of tidal forces, a flat-sat entering eclipse will start to turn towards sideways alignment with the center of the earth; it will come out of eclipse at a different velocity and angle than it went in with. | Neglecting tides, the synodic angular velocity of the m288 orbit is $\Large\omega$ = 4.3633e-4 rad/sec = 0.025°/s. The angular acceleration of a thinsat is 13.056e-6 rad/sec^2^ = 7.481e-4°/s^2^ with a sun angle of 0°, and 3.740e-4°/s^2^ at a sun angle of 60°. Because of tidal forces, a thinsat entering eclipse will start to turn towards sideways alignment with the center of the earth; it will come out of eclipse at a different velocity and angle than it went in with. |
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| If the flat-sat is rotating at $ \omega $ and either tangential or perpendicular to the gravity vector, it will not turn while it passes into eclipse. Otherwise, the tidal acceleration is $ \ddot\theta = (3/2) \omega^2 \sin 2 \delta $ where $ \delta $ is the angle to the tangent of the orbit. If we enter eclipse with the flat-sat not turning, and oriented directly to the sun, then $ \delta $ = 30° . | If the thinsat is rotating at $ \omega $ and either tangential or perpendicular to the gravity vector, it will not turn while it passes into eclipse. Otherwise, the tidal acceleration is $ \ddot\theta = (3/2) \omega^2 \sin 2 \delta $ where $ \delta $ is the angle to the tangent of the orbit. If we enter eclipse with the thinsat not turning, and oriented directly to the sun, then $ \delta $ = 30° . |
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| The orientation of the flat-sat over a 240 minute synodic m288 orbit at the equinox is as follows, relative to the sun: | The orientation of the thinsat over a 240 minute synodic m288 orbit at the equinox is as follows, relative to the sun: |
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| The angular velocity change at 0° takes 250/7.481 = 33.4 seconds, and during that time the server satellite turns 0.42° with negligible effect on thrust or power. The angular velocity change at 60° takes 750/3.74 = 200.5 seconds, and during that time the server satellite turns 12.5°, perhaps from 53.7° to 66.3°, reducing power and thrust from 59% to 40%, a significant change. The actual thrust change versus time will be more complicated (especially with tidal forces), but however it is done, the acceleration must be accomplished before the flat-sat enters eclipse. | The angular velocity change at 0° takes 250/7.481 = 33.4 seconds, and during that time the server satellite turns 0.42° with negligible effect on thrust or power. The angular velocity change at 60° takes 750/3.74 = 200.5 seconds, and during that time the server satellite turns 12.5°, perhaps from 53.7° to 66.3°, reducing power and thrust from 59% to 40%, a significant change. The actual thrust change versus time will be more complicated (especially with tidal forces), but however it is done, the acceleration must be accomplished before the thinsat enters eclipse. |
Night Side Maneuvers
We can minimize night light pollution, and advance perigee against light pressure orbit distortion, by turning the thinsat as we approach eclipse. The overall goal is to perform 1 complete rotation of the thinsat per orbit, with it perpendicular to the sun on the day-side of the earth, but turning it by varying amounts on the night side.
Another advantage of the turn is that if thinsat maneuverability is destroyed by radiation or a collision on the night side, it will come out of night side with a slow tumble that won't be corrected. The passive radar signature of the tumble will help identify the destroyed thinsat to other thinsats in the array, allowing another sacrificial thinsat to perform a "rendezvous and de-orbit". If the destroyed thinsat is in shards, the shards will tumble. The tumbling shards ( or a continuously tumbling thinsat ) will eventually fall out of the normal orbit, no longer get J_2 correction, and the thinsat orbit will "eccentrify", decay, and reenter. This is the fail-safe way the arrays will reenter, if all active control ceases.
Maneuvering thrust and satellite power
Neglecting tides, the synodic angular velocity of the m288 orbit is \Large\omega = 4.3633e-4 rad/sec = 0.025°/s. The angular acceleration of a thinsat is 13.056e-6 rad/sec2 = 7.481e-4°/s2 with a sun angle of 0°, and 3.740e-4°/s2 at a sun angle of 60°. Because of tidal forces, a thinsat entering eclipse will start to turn towards sideways alignment with the center of the earth; it will come out of eclipse at a different velocity and angle than it went in with.
If the thinsat is rotating at \omega and either tangential or perpendicular to the gravity vector, it will not turn while it passes into eclipse. Otherwise, the tidal acceleration is \ddot\theta = (3/2) \omega^2 \sin 2 \delta where \delta is the angle to the tangent of the orbit. If we enter eclipse with the thinsat not turning, and oriented directly to the sun, then \delta = 30° .
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Full power night sky coverage, maximum night light pollution
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Partial night sky coverage, no night light pollution
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Complete night sky coverage, some night light pollution
This maneuver will put some scattered light into the night sky, but not much compared to perpendicular solar illumination all the way into shadow.
The orientation of the thinsat over a 240 minute synodic m288 orbit at the equinox is as follows, relative to the sun:
time min |
orbit degrees |
rotation rate |
sun angle |
0 to 60 |
0° to 90° |
0 ~ \Large\omega |
0° |
60 to 100 |
90° to 150° |
1 ~ \Large\omega |
0° to 60° |
100 to 140 |
150° to 210° |
4 ~ \Large\omega |
60° to 300° |
140 to 180 |
210° to 270° |
1 ~ \Large\omega |
300° to 0° |
180 to 240 |
270° to 0° |
0 ~ \Large\omega |
0° |
The angular velocity change at 0° takes 250/7.481 = 33.4 seconds, and during that time the server satellite turns 0.42° with negligible effect on thrust or power. The angular velocity change at 60° takes 750/3.74 = 200.5 seconds, and during that time the server satellite turns 12.5°, perhaps from 53.7° to 66.3°, reducing power and thrust from 59% to 40%, a significant change. The actual thrust change versus time will be more complicated (especially with tidal forces), but however it is done, the acceleration must be accomplished before the thinsat enters eclipse.
MORE LATER