A helicopter satellite communication system that is adapted to perform communication between a helicopter-mounted communication apparatus and a terrestrial station communication apparatus via a communication satellite, wherein the helicopter-mounted communication apparatus is characterised by including: - a blocked-time-rate estimator that is adapted to estimate a blocked-time rate, which is the percentage of the time that a transmission beam that is transmitted from the helicopter-mounted communication apparatus toward the communication satellite is blocked by rotor blades; - a video-encoding-parameter selector that is adapted to select video-encoding parameters based on the blocked-time rate that is estimated by the blocked-time-rate estimator; - a video encoder that is adapted to encode video data according to the video-encoding parameters selected by the video-encoding-parameter selector, and to output video packets; - a data selector that, when the number of video packets that are output from the video encoder is less than a specified number, is adapted to insert null packets to keep the transmission packet rate substantially constant; - a null-packet deleter that is adapted to delete null packets in a packet stream that is output from the data selector and to attach information indicating the number of the deleted null packets to another packet; - a buffer that is adapted to buffer packets after deleting of null packets by the null-packet deleter; and - a modulator/transmitter (206, 207) that is adapted to modulate packets that are stored in the buffer and to transmit those packets toward the communication satellite during a transmittable period; and wherein the terrestrial station communication apparatus includes: - a receiver that is adapted to receive a signal that is transmitted from the helicopter-mounted communication apparatus via the communication satellite; - a demodulator that is adapted to demodulate the signal received by the receiver and to generate a packet stream; - a null-packet inserter that, based on attached information that is included in the packet stream that is reproduced by the demodulator, is adapted to insert null packets into the packet stream and to delete the attached information; - a rate-fluctuation compensator that is adapted to keep the packet rate substantially constant by buffering a packet stream after inserting of null packets by the null-packet inserter; - a data separator that is adapted to separate video packets from the packet stream that is output from the rate-fluctuation compensator; and - a video decoder that is adapted to decode the video packets that are separated out by the data separator. - a blocked-time-rate estimator that is adapted to estimate a blocked-time rate, which is the percentage of the time that a transmission beam that is transmitted from the helicopter-mounted communication apparatus toward the communication satellite is blocked by rotor blades; - a video-encoding-parameter selector that is adapted to select video-encoding parameters based on the blocked-time rate that is estimated by the blocked-time-rate estimator; - a video encoder that is adapted to encode video data according to the video-encoding parameters selected by the video-encoding-parameter selector, and to output video packets; - a data selector that, when the number of video packets that are output from the video encoder is less than a specified number, is adapted to insert null packets to keep the transmission packet rate substantially constant; - a null-packet deleter that is adapted to delete null packets in a packet stream that is output from the data selector and to attach information indicating the number of the deleted null packets to another packet; - a buffer that is adapted to buffer packets after deleting of null packets by the null-packet deleter; and - a modulator/transmitter (206, 207) that is adapted to modulate packets that are stored in the buffer and to transmit those packets toward the communication satellite during a transmittable period; and - a receiver that is adapted to receive a signal that is transmitted from the helicopter-mounted communication apparatus via the communication satellite; - a demodulator that is adapted to demodulate the signal received by the receiver and to generate a packet stream; - a null-packet inserter that, based on attached information that is included in the packet stream that is reproduced by the demodulator, is adapted to insert null packets into the packet stream and to delete the attached information; - a rate-fluctuation compensator that is adapted to keep the packet rate substantially constant by buffering a packet stream after inserting of null packets by the null-packet inserter; - a data separator that is adapted to separate video packets from the packet stream that is output from the rate-fluctuation compensator; and - a video decoder that is adapted to decode the video packets that are separated out by the data separator.