CHAPTER 13 SYSTEMS: COMMUNICATIONS AND TRACKING—THE VITAL LINK TO THE INTERNATIONAL SPACE STATION 222 NASA astronaut Jim Voss and Russian cosmonaut Yury Usachov are having some fun with Mission Control as they demonstrate their alternative means for communicating with each other on the International Space Station during the second crewed increment. Some of the most iconic statements in human history such as “Houston, Tranquility base here. The Eagle has landed!” would not have been possible without a good communication system—an essential part of any crewed or uncrewed spacecraft. It is critical that the communication system works. It is the link between the spacecraft and its crew and the flight controllers on the ground. Without a good communication system, the crew will not have adequate insight into the condition of the International Space Station (ISS) and the ground may not be able to help during nominal events or, more importantly, during emergencies. Spacecraft communication systems move information from one place to another. Information on the ISS needs to move between modules of the spacecraft, between the spacecraft and visiting vehicles flying in proximity, and between the spacecraft and the control centers on the ground. The types of ISS information that need to be moved include: n Commands and computer configuration data n Health and status data on the various systems on the ISS n Health, status, and ranging information of visiting vehicles n Science experiment data n Two-way voice and video n Alarm tones The communication equipment is known as the Communication and Tracking (C&T) system because it can be used to follow, or track, the spacecraft. This chapter will discuss the essential aspects of the C&T system. The main communication systems on board the ISS are organized into two prime areas: Radio Frequency (RF) and Baseband. A total of eight types of communication systems are located within these two main areas. Table 1 summarizes the key systems and the number of each type. Table 1. A summary of the different communication systems on the ISS. The RF systems are broken down by the portion of the electromagnetic spectrum that each uses (defined below). The numbers in parenthesis indicate how many of each system exists. Types of Communication Systems on the International Space Station n S-band n Ku-band n Ka-band n L-band (for GPS) n Ultra-high frequency (UHF) n Very-high frequency (VHF) n Audio n Video } Baseband RF } * Includes the original ISS S-band system known as the Early Communication System, a temporary communication system used during the first 3 years of space station operations until the main systems were activated.