The Consultative Committee for Space Data Systems (CCSDS) is a multi-national forum for the development of communications & data systems standards for spaceflight. It maintains space communications & data handling standards to enhance interoperability across governmental & commercial projects. One of the standards published by this group is the CCSDS Space Packet protocol which defines how space missions transfer space application data both sending and receiving. The maximum length of a CCSDS packet is 65536

A CCSDS packet is made of three parts: a required primary header, an optional secondary header, and a User data section. The packet data consists of all parts that are not the required primary header inclusive of the optional secondary header.

Space Packet Definition


bit length


Packet Primary Header


The required CCSDS header

Packet Secondary Header


The optional secondary header

User Data Field


The data component of the packet.


  • application process identifier, APID - A unique identifier for a stream of packets to indicate source, destination, or type.

  • packet primary header - The first 48 bits of every CCSDS packet (or 6 octets).

  • packet data field - The contents of the packet not including the packet primary header. It does include the optional secondary header.

  • secondary header - An optional second header which directly follows the primary header. It usually includes a time code. The primary header contains a field which indicates whether a secondary header is present.

  • octet - An eight-bit word.

CCSDS Header Standard

The mandatory packet primary header consists of four fields contained within 6 octets (each octet is 8 bits) or 48 bits.

Packet Primary Header Definition


bit length


Packet version number


The CCSDS version number. Shall be set to ‘000’.

Packet identification field

Packet type


For telemetry (or reporting), set to ‘0’, for a command (or request), set to ‘1’

Secondary header flag


indicates the presence or absence of a secondary header. Set to ‘1’ if present.

Application process identifier or APID


The APID provides a way to uniquely identify sending or receiving applications on a space vehicle.

Packet sequence control field

Sequence flag


Set to ‘01’ if the data is a continuation segment, set to ‘00’ if it contains the first segment of data.

Packet sequence count or packet name


the sequential binary count of each packet for a specific APID. The purpose is to allow packets to be ordered.

Packet data length


The length in octets of the remainder of the packet minus 1 octet.

For more information see Section 4.1.3 of the CCSDS Blue book.