​The objective of the SLS area is to address all of the point-to-point communications links and protocols that interconnect a spacecraft with its ground-support system, or with another spacecraft, by developing standards for efficient and reliable space link communications systems addressing nominal as well as emergency scenarios. Specific attention is given by SLS to needs for higher data rates and better link performances, a standard security mechanism, and lower cost, mass, and pow​​er.

SLS area objectives focus on Layers 1 & 2 (of the Open Systems Interconnection [OSI] protocol stack)—i.e., the Physical Layer and the Data Link Layer. This means that SLS concentrates in particular on radio-frequency and optical systems, modulation, synchronization and channel coding, and data link protocols, for both long-haul (e.g., spacecraft-to-ground) and proximity links (e.g., orbiter-to-lander). Moreover SLS concentrates also on two additional functions essential on the space link: data compression for end-to-end data transfer optimization, and ranging for accurate orbit determination.

The SLS area needs to coordinate:

  • with CSS for the identification of relevant parameters for service management;
  • with CSS for the inner behavior (i.e., the implementation aspects and not the terrestrial interface characteristics) of the CSTS to be made available to other agencies;
  • with MOIMS and CSS if the need of standardized exchange of meteorological and orbital data will be required for optical communications;
  • with SEA for Delta-DOR issues;
  • with SEA for development, adoption and integration of security-related recommended standards and practices;
  • the SANA-recommended practices for registries and repositories.

The strategic goals of the SLS area are presented below.


​Enable efficient bi-directional transmission for near-Earth spacecraft (including missions to—and/or orbiting around—the Moon and at Lagrange points) and deep-space spacecraft (especially Mars missions) by developing appropriate modulation schemes for telecommand, telemetry, and ranging signals in the applicable frequency bands while providing narrower bandwidth and higher data returns.​


​Produce efficient standards for coding schemes and synchronization, providing new generations of space missions with telecommand and telemetry capabilities beyond current technologies, such that spacecraft interconnection with its ground support system, or with another spacecraft, can accommodate higher data rates and better link performances, together with lower cost, mass, and power.​


To provide efficient and inter-operable space data link protocols and related interfaces to space link transfer services (for e.g. Space Packet Protocol, Encapsulation Service, IP over CCSDS) capable of satisfying the needs of current and future missions; i.e., to produce or maintain standards to support emerging capabilities (e.g. enabling higher data rates, greater throughput, higher reliability) with seamless interface to both user applications and communication technologies over radio frequency (RF) and/or optical links.​


​Develop data compression standards enabling efficient data rates and data volume reduction to optimize the usage of available space links bandwidth and onboard storage capacity. These internationally agreed data compression standards will foster interoperability and multi-mission development of compression functions.​


​Provide security functions operating at Layers 1 & 2 (of the OSI protocol stack) of CCSDS space links. The targeted security services include authentication, integrity check, anti-replay, and confidentiality both for uplink and downlink. The corresponding security protocols/functions shall be compatible with CCSDS TM, TC, AOS and USLP data link protocols and be independent from any specific cryptographic algorithm. Develop associated management functions for monitoring and control, key and security association management. Security at Physical Layer level should also be considered.​


​Establish a common framework of standardized services for space optical communications for interoperability and cross support by creating new standards for optical links (ISO Layers 1 & 2), taking into account the uniqueness of these types of links, such as very high data rates, geographic station diversity, and atmosphere (“weather”) influences. Consider also the services to be offered/required to/by space data link protocols and relevant procedures. Finally, identify the needed coordination with other CCSDS areas.​