11:00 AM - 1:00 PM
[PCG18-P13] Analysis of the feasibility of communication using Iridium in the Kanazawa University's satellite "KOYOH"
Keywords:Iridium, KOYOH, Synchronous sub-recurrent orbit, Microsatellite
Kanazawa University has been developing a micro satellite, "KOYOH". KOYOH's mission is to estimate the arrival direction of gamma-ray burst observed simultaneously with gravitational waves, and quickly send that information toward the ground. We're planning to use the Iridium satellite communication system to transmit this rapid report. The Iridium satellite communication system is a cell phone system that uses Iridium satellites as base stations, and KOYOH uses the SBD (Short Burst Data) module for communication. Communication between KOYOH and the ground station is possible even when KOYOH is not visible from the ground station because KOYOH communicates directly with the Iridium satellites. However, since the Iridium communication system was originally designed for use on the ground, the accessible area, the area where communication between KOYOH and the Iridium satellites is possible, may become much smaller in the satellite orbit. Therefore, we investigated the communication with the Iridium satellites in KOYOH's orbit and analyzed the factors that affect the access time with the Iridium satellites.
KOYOH will be put into a synchronous sub-recurrent low earth orbit at approximately 560 km in altitude and 97.6 degrees inclination, and descending node at 09:30:00.000. On the other hand, the Iridium constellation consists of 66 satellites, spread over six orbits at approximately 780 km in altitude and 86.4 degrees inclination. The co-rotating orbits are spaced apart by 31.6 degrees, and 11 satellites are spaced out in approximately equal intervals in each orbit.
The factor that affect the access time is the precession movement of the orbit. The presession movement causes the change in the traveling direction of KOYOH and the Iridium satellites. The orbits of the Iridium satellites are geosynchronous, whereas KOYOH's orbit is sunsynchronous, which means that the traveling direction of them changes reversely about every eight months. This change affects the access time, the time for KOYOH to pass through the accessible area. We call the state in which the traveling direction of KOYOH is in the same of the Iridium satellites as "co-rotating state", and the state in which the traveling direction of KOYOH is in the opposite of them as "counter-rotating state". To confirm the effect of the traveling direction on the access time, we simulate the access time at STK (Systems Tool Kit).
From the simulation results, we found that the access time is shorter in the counter-rotating state than in the co-rotating state. Furthermore, we also found that the degree of change in the access time varies with the latitude at the access, and the change is large for the access outside the poles, with the access time decreasing from 200 to 600 seconds in co-rotating state to 10 to 20 seconds in counter-rotating state. For the access near the poles, on the other hand, the change in the access time is relatively small, ranging from 10 to 200 seconds in the co-rotating state and from 10 to 160 seconds in the counter-rotating state.
From the above, it was found that the effect of the traveling direction on the access time depended on the latitude, and that there is almost no effect on the access time near the poles, ensuring a stable access time. On the other hand, for the access outside the poles, a long access time is ensured in the co-rotating state, but only a short access time is ensured in the counter-rotating state.
KOYOH will be put into a synchronous sub-recurrent low earth orbit at approximately 560 km in altitude and 97.6 degrees inclination, and descending node at 09:30:00.000. On the other hand, the Iridium constellation consists of 66 satellites, spread over six orbits at approximately 780 km in altitude and 86.4 degrees inclination. The co-rotating orbits are spaced apart by 31.6 degrees, and 11 satellites are spaced out in approximately equal intervals in each orbit.
The factor that affect the access time is the precession movement of the orbit. The presession movement causes the change in the traveling direction of KOYOH and the Iridium satellites. The orbits of the Iridium satellites are geosynchronous, whereas KOYOH's orbit is sunsynchronous, which means that the traveling direction of them changes reversely about every eight months. This change affects the access time, the time for KOYOH to pass through the accessible area. We call the state in which the traveling direction of KOYOH is in the same of the Iridium satellites as "co-rotating state", and the state in which the traveling direction of KOYOH is in the opposite of them as "counter-rotating state". To confirm the effect of the traveling direction on the access time, we simulate the access time at STK (Systems Tool Kit).
From the simulation results, we found that the access time is shorter in the counter-rotating state than in the co-rotating state. Furthermore, we also found that the degree of change in the access time varies with the latitude at the access, and the change is large for the access outside the poles, with the access time decreasing from 200 to 600 seconds in co-rotating state to 10 to 20 seconds in counter-rotating state. For the access near the poles, on the other hand, the change in the access time is relatively small, ranging from 10 to 200 seconds in the co-rotating state and from 10 to 160 seconds in the counter-rotating state.
From the above, it was found that the effect of the traveling direction on the access time depended on the latitude, and that there is almost no effect on the access time near the poles, ensuring a stable access time. On the other hand, for the access outside the poles, a long access time is ensured in the co-rotating state, but only a short access time is ensured in the counter-rotating state.