• ESA
• GENSO
• Spacelink
• European Space Agency
• Network
• Java
• Ground Station
• Spacecraft
• Satellite

Enhancing the Global Educational Network for Satellite Operations by an Active Spacelink

Summary

The thesis describes the work carried out during a six-months stage, from 9th of March until the 31st of August 2009 for the Education Office (LEX-E) in the European Space Agency Research and Technology Centre (ESTEC) at Noordwijk in The Netherlands, as a developer in the GENSO project.

The GENSO project is intended to develop and operate a satellite ground station network. The purpose of a ground station network is to increase significantly the data output from satellite missions by sharing ground station hardware amongst multiple space missions.

Various ground station networks exist for commercial and high-level scientific missions which are non-geostationary. Besides established, commercial ground station networks which are a requirement to reliably operate space missions of any kind, non-commercial ground station networks focusing on radio amateur, academic and educational spaceflight have been established in the last couple of years.
A huge amount of remotely operated ground stations have raised in the past couple of years. Nearly every ground station is remotely controllable and can deliver received data over the Internet to mission controls. Data is hereby usually transferred using virtual serial ports and, in case of baseband audio data, audio stream servers.
GENSO' s purpose is to develop a real ground station network.
The purpose is not to replace other ground station network but to interoperate and interconnect to them to share resources and increase productivity.
GENSO' s purpose is furthermore to provide a free, non-profit, non-commercial ground station network service to stimulate the community of non-commercial and primarily educational space engineering and greatly enhance the mission return of current and future space missions.

The conceptual design of GENSO is based on three types of entities:
1.Ground Station Server (GSS)
2.Mission Control Client (MCC)
3.Authentication Server (AUS)

which are described shortly in the following.

1.GSS runs on a computer connected to the local hardware, making it possible to control the GS. Every GS must have this software running, to be able to control the GS. Additionally the GSS is able to schedule and to book spacecraft passes. Finally the GSS is able to communicate, both with MCCs and with the AUS, to receive requests for passes, and overall coordination.

2.The MCC is associated with a Spacecraft (SC). The MCC is operated through a Graphical User Interface (GUI), and used when a SC owner wants to communicate with his SC. Additionally the MCC is able to retrieve data in the form of pass reports from the GSS. Besides communicating with the GSS, the MCC is also able to communicate with the AUS, who has a list of all received pass reports, and manages which pass reports are for which MCCs.

3.The AUS authenticates MCCs and GSSs when they identify themselves, and maintains an overview of the participating entities. Due to the overview, the AUS is used to authenticate newcomers in GENSO, and to distribute these informations to participating entities in GENSO.


Main task has been to enable an active spacelink between MCC to the SC. In fact, the pass reports mechanism permits to retrieve data from the SC using the GENSO network only after the GS tracked entirely the SC and saved the pass report of the session.
The purpose of the Active Spacelink capability is to provide a real-time communications link between the MCC and the SC (via GSS) for transmission of telecommands and reception of telemetry. In GENSO Release 1, the system does not provide any mechanism for MCC to book an Active Spacelink in advance, but this can be achieved with the cooperation between MC and SO outside the system.
The Active Spacelink is actually scheduled as a normal pass. The session effectively becomes an Active Spacelink when the MCC requests (and GSS accepts) a real-time connection. The request can be made during the tracking of the satellite ( Pass session ).

The Active Spacelink may be configured in the following ways: the data communications may be either digital (e.g. KISS frames to/from TNC) or analogue (baseband direct to/from Radio). In release 1 the MCC can upload only telecommands and not audio.
MCCO selects through the GUI the GSS that is tracking its own satellite and can download data or baseband audio from the radio in real-time or upload data, through encrypted connections that are established using the GENSO Network API, according to the overall settings and without affecting the pass report mechanism that keeps to work in the background.
Those settings permit both in GSS and MCC to stream the data received to a serial port (configurable through a GUI configuration panel ) in order to run an external application linked to that serial port and look at the data streaming. Further settings concern configuration of audio input and output devices, accessing the audio hardware resources of the machine. GSSO can enable or disable to record and stream audio and configure its sample rate and bits per sample.
GSSO can accept or refuse an active spacelink request coming from an MCC actively through a pop-up window or enabling a default behavior.
All the data transmitted and received are saved in a log folder, together with a XML metadata file that contains useful information about the active spacelink session (e.g. serial port used, type of data transmitted, GSS name, MCC name, SC name and so on).


List of Abbreviations

API Application Programming
AUS Authentication Server
GENSO Global Educational Network for Satellite Operations
GS Ground Station
GSS Ground Station Server
GSSO GSS Operator
GUI Graphical User Interface
MCC Mission Control Client
MCCO MCC Operator
SC Spacecraft
XML eXtensive Markup Language