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The Evolution of ESA Ground Station Communications to Internet Protocol The Evolution of ESA Ground Station Communications to
Internet Protocol


Manfred Bertelsmeier, Gioacchino Buscemi, Íñigo Mascaraque et al

ESA-ESOC, TOS-ONC, Robert-Bosch-Str. 5, D-64293 Darmstadt, Germany
Emails: manfred.bertelsmeier@esa.int, gioacchino.buscemi@esa.int,
inigo.mascaraque@esa.int


Abstract


ESA operates a worldwide system of ground stations for telemetry, tracking and
commanding known as ESTRACK. The stations are connected to the mission operations
control centre via a real-time communications network known as OPSNET. OPSNET
also handles the communications of the mission control centre with launch sites, with
science control or science data centres, with other space organisations and with spacecraft
validation and test sites.

Data transmission with the ground stations uses the X.25 protocol, a connection-oriented
packet switching protocol. In other OPSNET elements, however, such as local area
networks (LANs) and inter-centre and inter-Agency links, including those targeted to
support Space Link Extension (SLE) services, IP is in use, this being the standard
protocol of the Internet era which is supported by default on virtually all communications
and computing equipment. - After evaluation of the future needs and options for a
communications infrastructure for space mission operations, it was decided to standardise
on the TCP/IP protocol suite, and to embark on a migration of ESTRACK from X.25 to
TCP/IP. The paper will deal with this migration, the ESTRACK X.25 Communications to
IP Technology Evolution - EXCITE.

The scope of the migration is explained on the basis of a representative end-to-end chain
from the mission control centre to the ground station back end. Functional and
performance requirements are identified. Both the target system and the current
implementation are described, and the needs for adaptation and modernisation
summarised. This covers all major building blocks, addressing system architecture and
design aspects, and distinguishing between the systems that are the users of
communications services, and the systems that provide the communications. Network
access security and the interfacing to other IP-based networks is addressed. Special
emphasis is put on optimisation of throughput over links with a high bandwidth-delay
product (e.g. high speed satellite circuits), including transmission errors.

The migration aims to avoid impact on missions in orbit or in advanced preparations and
is thus targeted to last a few years. The strategy is to modify all subsystems and facilities
to be capable of handling both X.25 and IP. The actual mode of operations will be
selectable and configurable by the operations control centre depending on the space
mission served. The communications bearer system will initially be an IP overlay network using frame-relay services of the existing packet switching network. - In the
completion phase of EXCITE, the packet switches will be phased out and the IP network
will make direct use of wide area circuits. - The EXCITE schedule is aligned with the
ESA mission model and with two major other activities, namely the building of the deep
space ground station in New Norcia, Australia, and the upgrade of several ESA ground
stations to next generation base-band equipment.

The paper will conclude with the status of the implementations to date in the ground
station and in the control centre and with the results of validations in reference
installations and in the ESA Stations Redu and New Norcia.