Figure 11.1.: Ground Segment Architecture and Communication Links
The first two EXPRESS Pallets will be launched during the assembly phase of the Space Station and will provide accommodation for the European Early Utilisation external payloads. The European Early Utilisation will use three EPA locations on zenith and/or earth oriented Pallet(s), for a period of three years.
The payloads accommodated on the EXPRESS Pallet Adapters can be returned to the ground at the end of the three year period and replaced with different payloads by in-orbit exchange of adapters which have been pre-integrated with payloads on the ground. The EXPRESS Pallets themselves, following initial launch, are intended to remain attached to the ITA throughout the lifetime of the Space Station.
The Columbus Orbital Facility (COF) ground segment is described in general terms in ESA SP-1202 (RD3) and will not be repeated here. The ground segment architecture and communication links are summarised in Figure 11.1. This communications infrastructure provides the capability to exchange data, video and voice between:
The overall authority for payload operations is within the US Payload Operations Integration Centre (POIC). It is assumed that preparation and execution responsibilities for operational, technical, and planning aspects are delegated to Europe.
The main impact of the ground operations on the users of EXPRESS Pallet during the Early Utilisation is that the ground operations will still be developed during this period and it can not be assumed that the mature system described in RD3 will be in place when these EPAs are launched.
Figure 11.1.: Ground Segment Architecture and Communication Links
The European Early Utilisation EXPRESS Pallet Adapters will be delivered to the ISS as part of fully integrated EXPRESS Pallets carried in the NSTS Shuttle Orbiter cargo bay. Figure 11.2. shows an integrated EP in this location. Once at the ISS, installation of the EXPRESS Pallet on the ITA will take place using the SSRMS. This process may take several days, during which time payloads can, if required, make use of stay-alive power. The first flight installation process using the SSRMS is shown in Figure 11.3.
Figure 11.2.: Integrated EP in NSTS Shuttle Orbiter Cargo Bay.
Figure 11.3.: Express Pallet - Initial Launch and Installation using SSRMS.
For subsequent flights, EXPRESS Pallet Adapters may be delivered singly, in which case they are transported on the Station Logistics Carrier (SLC) - a modified Spacelab Pallet (Figure 11.4). For the change-out of the European Early Utilisation payloads after three years, the SLC will be used to return the EPAs to the ground. Deinstallation of the individual EPAs is effected by the SPDM. This exchange operation is shown in Figure 11.5.
Figure 11.4.: The Station Logistic Carrier (SLC) with EPA.
Figure 11.5.: EPA Exchange and Return using SPDM and SLC.
Following the Assembly Phase, the steady-state utilisation phase of Space Station will offer continuous flight opportunities for a period of the order of 10 years.
This period is subdivided into increments of 3 months duration where beginning and end of an increment is marked by successive Shuttle visits to the Station. At the occasion of these visits, the crew is rotated and - more relevant for utilisation experiment hardware can be rotated, servicing and resupply material will be brought up, and processed materials, samples, specimens, etc. can be returned to Earth. It should be noted that some shuttle flights are reserved only for pressurized equipment transport and so cannot be used for external payloads. There is approximately 1 unpressurised logistics flight per year. However for the Early Opportunity mission no resupply to the European EPAs is planned during their in-orbit life of 3 years.
At the end of each Shuttle visit the Space Station's orbital altitude is increased in order to compensate for the altitude loss resulting from the drag of the residual atmosphere. Upon completion of the required "reboost" maneuver no further orbital altitude control is exercised until after the next resupply period. There will be a natural orbital decay as qualitatively shown in Section 3. At each reboost maneuver the operational altitude is increased by a value dependent upon when the reboost occurs during the Solar Cycie and on the duration of the period between two consecutive reboosts.
Payload flight operation activities cover on-orbit installation, test and verification of new payload, payload science operation, servicing and maintenance, and reinstallation for return to ground.
Following successful verification, the routine operation of a payload element can start, under the control of the crew, internal payload automation, extemal robotics, the user on the ground, or a combination of all four. The crew may control the payload using a laptop computer connected to the ISS data management system. Automated procedures can run under the control of payload internal processors, with additional support from the SPLC, if required.
Direct real time control -telescience - of the payload by the user at a User Home Base (UHB) is possible within an operational window, a resource envelope specified in the Short Term Plan, and using a set of validated commands derived in the preparation for flight. The user is able to monitor all payload science and housekeeping data. The COF-CC and POIC will oversee these operations but will not interfere with them unless there is a potential impact on the crew, other payloads or the system, and will ensure that the payload operation remains within the pre-defined operational window. Payload commands are routed via the POIC/SSCC for uplink via TDRSS depending on coverage and availability.
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