This document briefly describes some considerations and variants for the communication architecture for the HSI mission.
Introduction and rationale
The numbers and figures in this document relates to numbers in other design documents and are summed up in HSI for CubeSat.
In order to save time, which is likely the most valuable resource for this project, it is advised that the payload downlink (and other communication systems) will be bought together with the satellite bus. The requirements will be presented to suppliers in form of a tender in Q4 '17 or Q1 '18. From this, it is expected that bidding suppliers will suggest hardware and systems that will meet our requirements. Various suppliers will have different equipment and possibly also different requirements/options/offerings for GSs. This goes both for the comm systems (TM/TC, payload downlink, ground stations) as well as software for operation.
Space segment
At the time of writing, a payload S-band (2 GHz) downlink capable of 1-4 Mbps seems reasonable, as it is a product available for CubeSats. These systems will also have an output power that can be supported by the CubeSat. In practice, this output power will be quite low (typical 1-10 W). In order to close the link budget, such systems will require an antenna dish of some size (TBC), perhaps with a diameter of 3 to 4 meters on a steerable mast. This must be verified with a link budget calculation when the space segment sub-system is known.
Suppliers such as GOMSpace, ISIS, ClydeSpace and UTIAS SFL all have S-band radios available. If higher datarates are needed, X-band (8 GHz) can be an option, but availability of such systems will be more limited.
The amount of data generated by the payload must controlled in order to meet the capabilities of the downlink radio system. The communication system might be a bottleneck, so scheduling and operation planning must be done in an efficient manner in order to maximize the amount of data that can be downloaded.
Ground segment
Several architecture options are possible; (1) either only own ground station (possibly enhanced with ground stations at partner universities and organizations), (2) use of commercial stations or (3) a combination of (1)&(2).
(1): Local university ground stations
At the time of writing, our own ground station is currently not near meeting our requirements wrt. S-band capabilities. The VHF/UHF TM/TC-part is also not fully operational. However, funding for a heavy upgrade looks very promising. We should know this month, I think. The ground station hardware/software could, depending on cost/schedule/options be based upon GS hardware/software from the satellite supplier or set up our own general equipment (or both). An example of a typical ground station can be found here: https://www.isispace.nl/product/full-ground-station-kit-s-band/. Generally, the ground station will consist of antennas (dish for S-band, Yagi for VHF/UHF), amplifiers and switches as well as a radio supported by operation software.
A general, versatile ground station based on the use of SDR and GNURadio are being set up at by the university radio club. An upgraded version of the HAM-station (VHF/UHF) for the student satellite project is on-going and planned to be finished by end of '17.
Partners such as Porto, Vigo and also other universities can be potential supporters and help with data acquisition. However, cost and time to build ground stations must be considered. They should set up their own ground stations of similar capabilities compared to ours. The partners must endure the time and cost to implement it.
Access to NASAs large antennas could be very interesting, especially if things does not work out as it should. This can also be of interest wrt. setting up more advanced experiments based on the SDR-payload in next steps.
Setting up own ground stations also has a value by increasing the competence of the organization. In addition, these stations can be used by other missions and might also be included in global ground station networks such as SATNogs when they are not used by the project.
(2): Commercial stations
The use of for example the KSAT Lite should be considered. This will be a solution requiring a cost during operations. However, it can be vise to have a backup communication architecture available if the local ground stations cannot be used for some reason.
Another option to explore is to partner with Statsat and gain access to Kystverkets station in Vardø. This will also have a cost for the operation.
Both KSAT and Statsat are Norwegian companies with stations far north. This is highly advantageous for the operations and might be preferred for this reason. There are also other companies such as Leaf Space https://leaf.space/leaf-line/ providing ground station services for small satellite missions.
Cost and possibilities for all options must be clarified in the next project phase.
(3): Combination
Especially if the we do not get several other partners onboard, the need for a commercial partner can be strong in order to get as much contact time to the satellite as possible. Trondheim is far north and will most likely see up to 5 to 6 passes every day (for TM/TC), but S-band downlink might require high elevation angles in order to close the link budget (TBC) so only 1-3 passes might be usable pr. day. This must be further simulated and calculated. Generic coverage simulations can be performed now, but accurate link budget calculations are only possible when the hardware is known.
KSAT Svalbard and Vardø stations are far north and will therefore see the satellite more times during the day, this alone can be a reason for having to use these stations during mission aquicition operations. Local ground stations can be used for TM/TC and simple operations in order to not incure more costs than necessary.
Ground station and operations software
The satellite bus suppliers will, depending on our needs, deliver software for operating the satelliets. When their specification is known, we can derive the need for our own mission planning/scheduling software. Software for interperting data/distribute data will be needed and should be agnostic wrt. the operations software.
Some partner universities have software to consider.
The Norwegian company Statsat are doing operations of the AIS-satellites and NORSat satellites. They now have four satellites operational, and a staff of only four-five people doing everything. They are in the process of re-writing their software based on the 5-6 years of experience they now have, in order to further simplify and stream-line operations. They are delivering an operational service for Kystverket, in addition to more ad-hoc support to research teams with other payloads on the NORSats. It could be very beneficial to try partner with them on mission software and control room ops.