The mode of propogation of radio  waves which travel in stagiht linesfrom transmitting antenna to receiving antenna is called space wave communication

Communications between a vehicle in outer space and Earth, using high-frequency electromagnetic radiation (radio waves).Provision for such communication is an essential requirement of any space mission. The total communication systemordinarily includes (1) command, the transmission of instructions to the spacecraft; (2) telemetry, the transmission of scientificand APPLICATIONS data from the spacecraft to Earth; and (3) tracking, the determination of the distance (range) from Earth tothe spacecraft and its RADIAL VELOCITY (range-rate) toward or away from Earth by the measurement of the round-trip radiotransmission time and Doppler frequency SHIFT (magnitude and direction).

 

(i) Ground wave or surface wave propagtion. 

(ii) Sky wave propagation or ionospheric 
propagation.  
(iii) Space wave propagation / LINE of sight 
propagation

When radio waves (frequency range 3 MHz to 30 MHz), emitted from the transmitting antenna, reach the receiving antenna after reflection from the ionosphere which acts as a reflector for radio waves the corresponding mode of propagation is known as sky wave propagation.