CanX-4 & CanX-5
CanX-4 and CanX-5 are identical satellites based on SFL’s Generic Nanosatellite Bus that provides all the required subsystems for the operation of a variety of payloads leaving about 30% of its total volume open for use by payloads. Using the same platform for several previous missions led to a quick build-up of flight heritage and performance data which is of great value when conducting experimental missions.
Data handling and satellite control is provided by an ARM7 housekeeping computer that handles standard telemetry and communications while a second computer supports all attitude determination and control functions. A third computer board is in charge of the operation of the science payload and handles its data. Each processor board uses the ARM7/TDMI processor with a code memory of 256kB and 2MB of hardware SRAM memory used to store program variables and data. A 256MB flash memory is used for long-term data storage.
The communications system of the satellites includes a UHF receiver, an S-Band Transceiver and a VHF beacon. The UHF receiver will be used for the command uplink from the ground at a data rate of 4kbit/s in the amateur radio band using quad-canted monopole antennas for omni-directional coverage. The VHF beacon transmits the satellite’s identification and some basic telemetry values for satellite tracking and the initial commissioning of the spacecraft.
The S-Band system is used for data downlink to the ground and the Intersatellite Communication System to allow the exchange of position, velocity and attitude data between the two satellites. The system consists of two patch antennas installed on opposite side panels of the satellites connected to the main S-Band Transceiver. The downlink data rate can be selected between 32 and 256kbit/s while the inter-satellite data rate is about 10kbit/s up to a separation distance of 5 Kilometers.
The CanX-4 and 5 satellites were to launch firmly attached to one another using an Intersatellite Separation System for the separation once in orbit and fully commissioned to kick off the formation demonstration. However, the satellites will launch separated from each other and the separation system will not be put to use. The Intersatellite Separation System, ISS for short, consists of two nearly identical interfaces that are installed on the connecting side panels of the two satellites. ISS is comprised of a spring-loaded cone interface that builds the bonding surface between the two spacecraft coated in an electrically debonding agent that acts as a glue holding the satellites together.
For the separation, ISS applies a small voltage to the mechanism which causes the glue to weaken so that the loaded springs can overcome the adhesive force and push the two satellites apart. The two springs are loaded at a force of about 70 Newtons to impart a delta-v of about 8cm/s to each satellite at separation which is reduced to 2.6cm/s in the along-track direction by conducing the separation partially in the orbit-normal direction. This is done to set up the proper conditions for the first formation test.
In the Projected Circular Orbit formation mode, the deputy enters an orbit with a slightly different inclination and eccentricity which, when observed from Earth, will seem like the deputy is orbiting the passive satellite. The PCO mode will be demonstrated at distances of 50 and 100 meters.
Each of the formations will be maintained for ten orbits with one orbit of reconfiguration maneuvers in between each formation mode or distance. The criteria for mission success are twofold – first, the level of accuracy to which the satellites can control their relative position in each formation will be assessed, and second, the ability of the deputy satellite to calculate the most efficient maneuvers will be studied to minimize fuel consumption.
Because the two satellites are identical, they can swap roles in the mission. Although the primary mission can be completed with one satellite acting as deputy and expending its fuel, a possible extended mission would be to use the previously passive satellite as deputy to repeat the formation exercise with different parameters. This mission design also adds redundancy in the event of a propulsion system failure on one satellite.