The Ground Models is a family of SIMSAT compatible models enabling realistic simulations of all ground systems between the spacecraft (or spacecraft model) and the control centre at ESOC. The family consists of the following components:
- GMM: this Ground Model Manager is in charge of creating, monitoring and deleting instances of ground equipment models.
- TTC Streams: a set of services providing a simulation of the satellite to ground radio frequency transmitter-receiver protocol.
- MCS-DIF: MSC Direct Interface is a ground model that simulates the whole connection from a satellite simulator to an MCS (Mission Control System).a set of generic space models that ease the developments of the spacecraft models used in operational
- TMTCS Interface (TIF): this component will be a ground model enabling the direct exchange of TM/TC data between the TMTCS (TM/TC System) (or TMTCS model)
The logical model of the ground system is given in Figure 2 as a diagram of collaborating objects, showing the ground objects interacting also with external objects to provide an overview in the system context.
The GMM (Ground Model Manager) is the central object in the Ground system. It is in charge of creating, monitoring and deleting instances of ground equipment models. In addition it manages ground-wide data, by providing a corresponding command set.
The TTC Streams (Telemetry and Telecommand Streams) component provides support for modeling the flow of data from any number of transmitters to any number of receivers. This data is expected to be telemetry and telecommand data, but is by no means constrained to these types.
The TTC Streams do not execute a model of a transmitter or receiver; however, they can be used to model theproperties of the transmitter and receiver aerials and the links between them.
Normally this link is a radio frequency link and the TTC Streams specifically provide mechanisms by which the properties of such links can be modeled, however, the TTC Streams could equally well be used to model othertypes of data link.
The TTC Streams can be seen as a passive component in the simulation. Activities take place only as a result of requests (calls) received from the TTC Streams clients. To determine whether or not a data exchange isviable, TTC Streams exchange information between the transmitter and the receiver(s).
This information is referred to as the stream characteristics. The transported data is treated as a simple stream of octets with no interpretation being placed on their contents. In particular the data being passed bya stream is not assumed to conform to ESA TM or TC standards.
TTC Streams is launched by SIMSAT as a simulation-wide service. The simulation-wide service is a SIMSAT facility, which was introduced specifically to support the TTC Streams, and similar components, which require accessibility at a level, which is not supported by the current SMI (Simulation Model Interface) implementation.
This MCS-DIF (Mission Control System Direct Interface) model is used for fast testing of the TM and TC data exchange between MCS and simulator. The connection from the simulator to the MCS is direct, over TCP/IP, and there is no need for an X.25 network, or for an NCTRS system. The MCS DIF is a router process between a satellite simulator and a mission control centre, capable of forwarding telemetry as well as telecommand messages. This router process is embedded in the Ground for Windows system and thus many of its operations, in particular its user interface, are similar to those of the other Ground equipment models (GEMs). Like the other GEMs (and, in fact, like any real ground station equipment) the MCS DIF supports the following main interfaces:
- A space link, which connects to the satellite.
- A network link, which connects to the OCC over a network.
- A user interface for monitoring and controlling the application.
Although the MCS DIF can be viewed as 'just another GEM', it is different from the other Ground models in that it does not attempt to model any particular equipment type existing in a real ground station. Another difference is that the MCS DIF is capable of concurrently handling TC and TM data streams, where the other models forward either telecommands or telemetry, but not both. The diagram below shows MCS-DIF in use with a satellite simulator testing an MCC.
This component will be a ground model enabling the direct exchange of TM/TC data between the TMTCS (or TMTCS model) and the TTC STREAMS component. It supports the following operations:
- Simulation of ground station visibility
- Simulation of TM/TC link failures
- Reception of CLTU(s) and forwarding of TC transfer frames using the same TCP/IP interface as between the real TMTCS and the IFMS
- Reception and forwarding of TM transfer frames using the same TCP/IP interface as between the real TMTCS and the TCDS (part of the IFMS).