Relay Satellite Introduction
The relay satellite acts as a buffer between the probes descending into the Neptunian atmosphere and the Earth. It would be quite difficult if not impossible for the probes to maintain a direct link with the Earth to transmit the data. Therefore, a satellite will be placed in Geostationary Neptune Orbit to receive all of the probe data.
When appropriate, the relay satellite will transmit the data gathered by the probes and transmit them to Earth. The relay satellite is the solution to the once power-limited and line-of-sight-limited system. As the satellite rotates around Neptune, it is essential that the transmitting antenna is pointed in the direction of the Earth. Spacecraft are usually equipped with state-of-the-art navigational systems and can identify the location of other objects in space such as the Earth. The transmitting antenna will therefore be required to be controlled through a motor drive system so that the antenna will always be pointing towards the Earth.
While it will be shown that the relay satellite can reliably transmit the data collected from the probes back to the Earth, there will only be certain times of the day that data will be received. When the satellite goes behind Neptune, all communications will be lost. With a Geostationary Neptune Orbit of 83,503.9 km travelling at a rate of 9.04706, the satellite will be out of view of the earth for
For 1.8 hours of each Neptune day, the satellite will not be able to communicate with the Earth. Therefore, the data will be stored on the solid state hard drives until ready for transmission. During the time that transmission takes place, the data will be transmitted in real time (24 kbps) to the Earth.
The amount of data to be collected from the probes is
It will take about
to transmit the data in its entirety. The solid state hard drives have enough capacity to store this data throughout the mission. Should an error occur, the relay satellite will repeat its transmission back to the Earth until a control signal is received from the DSN to confirm that all the data has been acquired. When this control signal is received, the satellite will disable itself, and initiate a controlled burn to alter its orbit, allowing it to be grasped by Neptune's gravity and plunging into the atmosphere.
The following pages will introduce two different communications systems. The first system discussed is the receiver for the data from the Neptune probes. The second system is the transmission of this data back to the Earth.
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