UKube-1 is the UK’s first CubeSat mission and the pilot for a national CubeSat programme. Despite measuring a mere 10cm x 10cm x 30cm this sophisticated nanosatellite packs in 6 payloads encompassing science instruments, technology demonstration, outreach and amateur radio. Following on from our successful work developing the onboard software for UKube-1, we were excited to be asked by Rutherford Appleton Laboratory, who are leading UKube-1 operations, to provide key elements of the ground segment, including:
- Mission control software, providing the operator interface to the spacecraft and controlling automated operations.
- A functional simulator of the spacecraft to permit operator training and the validation of onboard scripts before they are uploaded to the spacecraft.
- Infrastructure software to connect the ground stations to the mission operations centre.
We are currently working on taking the core parts of the UKube-1 ground segment, especially the Mission Control Software, and adapting them for wider use in other CubeSat missions as an off-the-shelf product. If you are interested in how this might apply to your project or mission, please contact us.
Ground Segment Architecture
The UKube-1 ground segment consists of two ground stations, one at Chilbolton and the other at Dundee, and the UKube-1 Mission Operations Centre (UMOC) at Harwell. Although the similar locations of the ground stations do not give us much in the way of increased coverage, we will benefit from the redundancy which should help reduce packet errors.
Part of our work was to provide a reliable connection between the ground stations and the UMOC, using the Internet for packet transfer. At the UMOC, a single ground station can be chosen for telecommanding whilst the telemetry packet streams from both ground stations are merged in real time, removing duplicate packets. In case of outages, packets are logged at each location. Logs can be ingested into the Mission Control Software (MCS) for offline processing if required.
The expected orbit for UKube-1 gives us approximately two passes a day, each of about 10 minutes. The nominal downlink (VHF) uses AX.25 framing with a link data rate of 9600bps. This very limited bandwidth, combined with the low contact time, makes operating UKube-1 a challenge. The six payloads each have quite different operational concepts and produce very different quantities of data. At one extreme, the C3D imaging payload can produce images of approximately 1.3MB.
Each ground pass is made up of downlinking status and logged telemetry, downlinking payload data, and uplinking schedules and scripts to be automatically executed by the spacecraft onboard software. These schedules are scripts are determined by the operations team in consulation with each of the payload teams and are expected to be drafted on a weekly cycle.
As a CubeSat mission, the challenge with UKube-1 is to demonstrate new technology and obtain valuable scientific results for a limited budget. For the ground segment this means that operations must be as automated as possible. Our MCS permits operations to be scripted, with passes planned and scheduled in advance. During an automated pass, the MCS is onstantly monitoring the live telemetry stream. Should any telemetry indicate a potential problem, the MCS can be instructed to switch into a safe mode, carrying out only essential opeations and ensuring that no data is lost. It is not necessary for the MCS to attempt spacecraft recovery, as the onboard software will take care of the space segment.
An important part of the automation carried out by the MCS is the management of downlink streams including the automatic prioritisation of data and control of the downlink processes across multiple unattended passes. This is crucial as payload data downlinks could take a large number of passes to complete, and yet it is important this is not done at the cost of essential housekeeping telemetry.
Once payload data has been received, the operations team are resposible for distributing this back to the payload teams to provide results and to inform requests for the next cycle of operations.
The UKube-1 onboard software provides extensive onboard automation features including a powerful scripting language. Whilst this provides crucial operational flexibility, especially for payload operations, there is the potential to create scripts which contain bugs or simply do not achieve the intended aims. The operations team clearly need a way to validate scripts before uplinking them to the spacecraft and enabling their execution. Unfortnuately, a mission the size of UKube-1 does not have the resources for a full set of ‘flight spare’ hardware on which this validation could be done.
To provide the operations team with the assurance they need, we developed a functional simulation of UKube-1 with a focus on paylod operations. Using the unique features of our onboard software, it was straightforward to build the software for a desktop PC environment and to substitute a standard network data connection for the onboard data buses. By adding some relaively simple subsystem simulations we were able to execute the onboard software largely unmodified and observe the results. Combined with a custom user interface, this simulator will allow validation of script and schedule operation.
It is difficult to predict what will arise during operations, but should the extent and fidelity of the simulator need to be improved, the modular architecture will permit us to simulate a wide range of possible scenarios.
Image of Chilbolton courtesy of Chris Westbrook.