Buccaneer CubeSat Mission
Buccaneer is a collaborative Australian project to jointly fly and operate two CubeSat missions developed by the DSTG (Defence Science and Technology Group) and UNSW (University of New South Wales) Canberra Space. It is highly significant in the context of Australian space activities as it will be the first, sovereignly developed defence-science CubeSat mission flown by Australia. 1)
The Buccaneer program consists of two missions with the key objectives; (1) calibration of the JORN (Jindalee Operational Radar Network) from space using an HF receiver payload, and (2) acquisition of high quality flight data for correlated Astrodynamics and SSA (Space Situational Awareness) experiments using the Buccaneer spacecraft in combination with ground sensor networks.
The primary objective of the overall two-flight program is to calibrate the radar signals from JORN from the vantage point of a spacecraft in LEO (Low Earth Orbit) where the radar waves are refracted by the ionosphere. 2) The radar transmits in the 3-45 MHz band from sites located in Australia (Figure 1) and is an operational defence facility.
The secondary objective of the program is to provide reliable experimental data to support astrodynamics and SSA research being carried out at UNSW Canberra. This objective will be achieved by measuring the light curves from ground based tracking telescopes in the FTN (Falcon Telescope Network) to develop and correlate models of the reflectivity of the spacecraft in the solar spectrum versus solar illumination angle, viewing aspect angle, spacecraft attitude and atmospheric conditions.
Figure 1: View of the JORN antenna array (image credit: DSTG)
The first mission in the program is the BRMM (Buccaneer Risk Mitigation Mission); currently manifested for launch into a sun synchronous orbit on the ELaNa-XIV launch in November 2017 with the nominal orbital parameters listed in Table 1.
Table 1: BRMM nominal orbital parameters
Buccaneer Risk Mitigation Mission: The BRMM spacecraft bus is a customized Pumpkin MISC3 which complies with the 3U+ CubeSat specification. Table 2 lists the major payload and platform elements and suppliers. The flight model spacecraft has completed its flight qualification and acceptance testing and has been integrated into its CubeSat dispenser. The image of Figure 2 shows the spacecraft immediately prior to integration into the dispenser with all of the deployables stowed in the launch configuration. The 3U CubeSat has a mass of 4 kg.
Table 2: Major subsystems of the BRMM spacecraft
Figure 2: BRMM flight model 3U CubeSat (image credit: Buccaneer collaboration)
BRMM - Technology pathfinder:
One of the critical and enabling technologies for the overall Buccaneer program is the HF receiver antenna on the spacecraft. Given the low TRL (Technology Readiness Level) of the antenna design, the practical obstacles to conducting flight representative tests of the antenna deployment in a terrestrial 1-g environment, and the intractability of developing reliable mathematical models of the antenna dynamics, it was agreed to implement a dedicated technology pathfinder mission; the BRMM (Buccaneer Risk Mitigation Mission) in order to gain flight heritage on this technology ahead of the Buccaneer Main Mission. 3) 4) 5)
There are two obvious challenging aspects to the design of the antenna; firstly, it has a very large operating RF bandwidth of nearly four octaves (3-45 MHz) and secondly, the physical size of the antenna needs to be large to match the wavelength of the signals. The antenna configuration which best suited the Buccaneer requirements is an open bow-tie antenna (Figure 3) with four elements approximately 1.7 m long.
Figure 3: BRMM spacecraft showing the deployed HF antenna in green (image credit: Buccaneer collaboration)
Since the physical size of the antenna is much larger than the dimensions of the 3U+ BRMM spacecraft, the antenna has to be stowed prior to launch and then reliably deployed once the spacecraft is on orbit. The physical volume available to the antenna in the stowed configuration is the "Tuna can"; a ø 64 mm x 36 mm cylindrical envelope defined in the CubeSat Specification. This stay-in envelope places stringent design constraints on the antenna deployment mechanism and on the amount of material that can be used to stiffen the antenna in the deployed state. The selected antenna design consists of four elements of carpenter's tape wrapped on a spool and held down in the launch configuration with staged burn wires. The flight model design of the HF antenna in the stowed configuration and the RF payload elements are illustrated in Figure 4.
The RF payload on BRMM does not contain all of the requisite elements to perform the calibration of the JORN signals, but does include some technically challenging, low TRL electronic circuits which will gain flight heritage and qualification as part of the mission. The BRMM antenna, RF payload and integrated spacecraft have been qualified for flight by passing all their functional, performance and environmental tests.
Figure 4: BRMM payload showing the stowed HF antenna (image credit: Buccaneer collaboration)
Figure 5: BRMM flight model spacecraft during preparation for thermal vacuum testing (image credit: Buccaneer collaboration)
BRMM SSA (Space Situational Awareness) experiments:
The science of astrodynamics applied to understanding the natural perturbations of objects in LEO (Low Earth Orbit) is poorly understood. The interaction of orbiting objects with the space environment can result in apparently chaotic orbital perturbations and give rise to difficulties in tracking, updating ephemeris and predicting conjunction probabilities.
The BRMM spacecraft will be used to conduct experiments to grow the understanding of how spacecraft interact with their environment and the governing physics of the perturbations. Primarily, this will be done by observing the spacecraft with elements of the FTN (Falcon Telescope Network) during passes when the spacecraft is under solar illumination. The telescope will track the spacecraft in its field of view and gather temporally resolved, photometric light curves of the reflected solar light as it passes within the field of regard of the telescope. This light curve data will be correlated with models of the geometric/optical properties of the spacecraft, the solar illumination vector, the spacecraft attitude, the observation vector and the atmospheric conditions. After these models have been validated with the BRMM data, they can then be used to gain an understanding of the physical parameters of unresolved objects with light curve data and improve estimates of their orbit propagation.
BMM (Buccaneer Main Mission):
After the successful launch, commissioning and HF antenna deployment, the BRMM spacecraft will conduct attitude maneuvers to establish the stability margins of the HF antenna. This information will enable BMM to kick off the flight program. The payload on BMM will contain all of the antenna, RF front end and digital back end elements to calibrate the JORN signals.
The Concept of Operations for the BMM is shown in Figure 6. The procedure is initiated (i) during contact with the ground station and the uploading of a set of telecommands to configure the spacecraft and payload. In general, (ii) the payload will be put into a low power mode to conserve electrical power on the platform. As the spacecraft approaches the location for the collection of the RF signals, the payload is switched on (iii), allowed to stabilize and the RF signal collected. Once again, the payload would be put into a low power mode (iv) until the OBC sends a command to the payload (v) to process the acquired RF signal data (vi). Once the data has been processed, it would be put into a low power mode (vii) until the spacecraft makes contact with the ground station and is able to download the payload data (iix) via the S-band link and then put into low-power sleep mode again.
Figure 6: BMM RF payload concept of operations (image credit: Buccaneer collaboration)
The baseline configuration of the BMM spacecraft is to rely on the heritage obtained from the BRMM mission, but other options are to be investigated to assess the benefits of incorporating technologies developed within the wider UNSW Canberra and DST space mission programs and factor in the lessons learned from the BRMM program.
In summary, the DSTG/UNSW Canberra Buccaneer partnership has successfully developed the BRMM spacecraft (Figure 7) and will be the first Australian, defence-science CubeSat mission. The BMM is planned to follow the launch in approximately 18 months afterwards.
Figure 7: Artists impression of the BRMM spacecraft (image credit: Buccaneer collaboration)
Launch: The Buccaneer 3U CubeSat was launched as a secondary payload on Nov. 18, 2017 on a Delta-2-7920 vehicle of ULA (United Launch Alliance) from VAFB, CA, USA. The primary mission was the JPSS-1 spacecraft of NOAA, developed at NASA. 6) 7)
Orbit: The design orbit for the Buccaneer mission is an elliptical sun-synchronous orbit with a perigee of 440 km and an apogee at 810 km, inclination = 97.7º, LTAN (Local Time of Ascending Node) = 13:35 hours.
Orbit of JPSS-1: Sun-synchronous orbit, altitude of 824 km, inclination = 98.7º, period = 101 minutes.
Secondary payloads (ELaNa-14):
• RadFxSat (Radiation Effects Satellite, Fox-1B), a 1U CubeSat of AMSAT and Vanderbilt University, Nashville, TN, USA.
• EagleSat, a 1U CubeSat of ERAU (Embry-Riddle Aeronautical University), Prescott, AZ, USA.
• MakerSat-0, a 1U CubeSat of NNU (Northwest Nazarene University) of Nampa, Idaho, USA.
• MiRaTA (Microwave Radiometer Technology Acceleration), a 3U CubeSat of MIT (Massachusetts Institute of Technology), Cambridge, MA, USA.
• BRMM (Buccaneer Risk Mitigation Mission), a 3U CubeSat technology mission of UNSW (University of New South Wales), Canberra, Australia and DST (Defence Science and Technology) group. The goal is to calibrate JORN (Jindalee Over-the-Horizon Radar Network).
• October 2018: The collaborative Buccaneer Risk Mitigation Mission (BRMM) CubeSat, conducted by the Defence Science and Technology Group and the University of New South Wales Canberra, successfully launched on 18 November 2017 from Vandenberg Air Force Base into a Sun-synchronous low-Earth orbit. BRMM is one of only a few Australian-developed satellites and is a risk mitigation mission for the Buccaneer Main Mission and other future Defence space missions. The key mission objectives of BRMM were: (i) to demonstrate the complex deployment of a high frequency antenna to be used to improve calibration of the JORN ( Jindalee Operational Radar Network) on the Buccaneer Main Mission, (ii) to measure spacecraft light curves to verify Space Situational Awareness models, and (iii) to advance Australian expertise in space mission development and operations. 8)
- The Buccaneer program and its first mission, BRMM, have provided great learning experiences for both the DST Group and the UNSW Canberra, as well as serving valuable Defence and science objectives. BRMM has achieved full mission success, and, as a risk mitigation mission, has informed the requirements and design of the follow-on main mission.
• On November 29, 2017, Australia's first national space mission design facility, named ANCDF (Australian National Concurrent Design Facility), was officially opened at UNSW Canberra. "For the first time, Australia has a facility that will enable spacecraft design engineers and scientists to rapidly design and determine the technical and economic viability of proposed space missions," Professor Boyce said. 9)
- Buccaneer will help calibrate Australia's groundbreaking Jindalee over the horizon radar as well as provide crucial data on predicting orbits of space objects including space "junk".
- Over the next few weeks and months the spacecraft will undergo operations to check and commission its systems before undertaking its risk mitigation activities and experiments in early 2018.
• All CubeSats have been deployed! P-POD 1 released EagleSat-1, RadFXSat and MakerSat-0; Buccaneer deployed from P-POD 2; and MiRaTA deployed from P-POD 3. The CubeSats all are flying solo to begin their missions. 12)
- Orbit: All CubeSats were deployed into an elliptical sun-synchronous orbit with a perigee of 440 km and an apogee at 810 km, inclination = 97.7º.
• Approximately 63 minutes after launch the solar arrays on JPSS-1 deployed and the spacecraft was operating on its own power. JPSS-1 will be renamed NOAA-20 when it reaches its final orbit. Following a three-month checkout and validation of its five advanced instruments, the satellite will become operational. 13)
The Buccaneer ground segment currently features two ground stations, located at DST Group Edinburgh and UNSW Canberra. The latter has recently been supplemented by a receive-only ground station at Yass (New South Wales) which was developed for another mission. Both primary ground stations host a UHF antenna with transmit and receive functionality and an S-band antenna with receive functionality only. The DST Group UHF antenna was designed and manufactured in-house, and features four helical transmit and four Yagi receive elements. GNU Radio was implemented to provide software-defined radio capability on the ground, and a radio control interface allowing for dynamic frequency offset control and notch filtering of local interference was developed (Ref. 8).
The DST Group also developed a user-friendly mission control interface, allowing users to develop mission plans through a graphical user interface, and to incorporate branching into plans to enable go/no go decision points and dynamic commanding based on spacecraft feedback during a pass. Mission control also supports autonomous operations, which has been the primary mode of operations for DST Group during ‘out-of-hours' (night and weekend) passes.
Figure 8: Buccaneer DST Group Edinburgh ground station S-band (left) and UHF (right) antennae (image credit: Buccaneer collaboration)
Mission Objectives: BRMM has five key objectives that demarcate mission success and lead into the mission objectives of BMM,
• Successful uplink and execution of commands, and downlink of telemetry, via UHF from the DST ground station
• Successful uplink and execution of commands, and downlink of telemetry, via UHF from the UNSW Canberra ground station
• Testing and characterization of HF antenna deployment and stability margins
• Operation of the Kea GPS receiver
• Perform initial photometry and atmospheric drag experiments.
It should be noted that the BRMM spacecraft does not have the full HF receiver, and so does not have the functionality to perform the JORN measurements. However, deployment of the HF antenna and analysis of the deployment dynamics, attitude control in a high inertia configuration, and verification of the stability of the antenna are key risk mitigation activities to achieve this objective on BMM.
Although not a formally designated mission objective, a joint aim of BRMM and the Buccaneer program is to advance the space capabilities of both organizations, and to train a cadre of Australian space professionals.
First contact: Various factors including orbit uncertainty, spacecraft misidentification, and ground segment teething issues, make first contact with CubeSats a challenging exercise. Approximately 25% of CubeSats are "dead on arrival", that is, no contact is established with the satellite after launch. The Buccaneer team was aware of this challenge, and put significant consideration into developing a strategy to maximize the likelihood of communication with BRMM during its first passes over the two ground stations. Prior to distribution of the first Two-Line Element (TLE) from the Joint Space Operations Center (JSpOC), the launch service provider sends an Orbital Parameters Message (OPM) to the launch payload teams. The OPM is in a different format and coordinate system to the TLE, and operations teams should be prepared to interpret this string.
The Buccaneer team used the OPM for early orbit prediction and visualization, and to track BRMM's first pass over Australia. The orbit description from the OPM is highly accurate, however, the position of the satellite in the orbit is often uncertain, and thus the precise timing of its pass over a ground station is uncertain. Independent tracking strategies were adopted by the two Buccaneer ground stations for the first contact windows to overcome the pass timing uncertainty: the DST Group ground station pointed at BRMM's predicted point of closest approach during the access window, and tracked this point in inertial space to compensate for the Earth's rotation; the UNSW ground station pointed at BRMM's calculated Acquisition Of Signal (AOS) azimuth angle, where the rate of change of elevation is lowest and therefore the greatest time for potential contact occurs. The ground stations were equipped with the valuable ability to ‘beacon' the spacecraft, bypassing the normal requirement for ‘hand-shaking' between the spacecraft and the ground station. Repeated beacons were sent from the ground to attempt to elicit a response from the spacecraft. This strategy proved successful, and contact was made with BRMM by the DST Group ground station on its first pass over Australia less than six hours after launch.
Subsequent comparison of the times of first contacts with BRMM and the published TLEs revealed that JSpOC had misidentified BRMM as another CubeSat on the launch. Such an occurrence is not uncommon for launches of multiple small payloads and is a risk acknowledged by JSpOC , due to the small size and relative proximity of CubeSats deployed in rapid succession. The possibility of misidentification, and the inclusion of physical or electromagnetic identification tags should be taken into consideration for CubeSat on multi-payload launches.
Commissioning and normal operations: After first contact and confirmation of its TLE, BRMM was commissioned over several weeks to enable and complete initial operational checkouts (IOCs) of the bus subsystems. During commissioning an issue with the ADCS was identified, whereby the reaction wheel speeds consistently reached saturation in pointing modes. The unexpected behavior was replicated in Hardware-in-the-Loop (HIL) ADCS simulations and the cause of this issue traced to an erroneous magnetometer calibration. The calibration constants on the ADCS are reconfigurable and thus the problem was rectified by uplink of the appropriate constants, which were verified through HIL simulations. The issue exemplified the need for thorough test and calibration processes. All other subsystems performed within expected margins during commissioning.
The DST Buccaneer ground segment allows user-in-the-loop dynamic commanding of the spacecraft based on feedback from downlinked telemetry. This has proved to be a valuable capability which has preserved the health of the spacecraft throughout operations, and assisted in the timely achievement of payload and mission objectives. The ability for ground station operators to readily view certain fields of live spacecraft telemetry was found to be crucial to effective dynamic commanding and decision making. It was found that relying on a decoded telemetry downlink log was ineffective at providing this capability, and thus a live telemetry dashboard and attitude visualization was developed at the DST Group ground station, displaying key information such as battery voltage and attitude.
Three further potential improvements to the dynamic commanding capability were identified during operations:
• Firstly, the need for quantitative, agreed criteria to proceed, change branches, or abort a mission plan.
• Secondly, based on these criteria, the potential for automated mission plan modifications based on live spacecraft feedback was recognized. It was also identified that there may be benefit in different command ‘go/no go' and branching criteria for particular mission phases and plans.
• Thirdly, the promptness and appropriateness of user-in-the-loop responses can be greatly improved by ensuing relevant telemetry is readily available to operators, such as through real-time telemetry dashboards and trend charts.
During routine operations, particular sets of commands are routinely sent to the spacecraft to carry out nominal modes of operation, such as pointing its solar panels towards the Sun whilst minimizing drag, and enabling the GPS in daytime periods. The Buccaneer team identified that a great amount of mission planning time and potential for erroneous commanding could be reduced if pre-prepared blocks of commands are constructed and, for time- and condition-dependent commands, scripts for their generation are employed.
Deployments: Deployments are critical mission events, and verification of their success is imperative to understanding the state of the spacecraft and the status of mission objectives. BRMM deployed two UHF dipole antennae, two solar panels, and the 3.4 m long HF antenna.
The UHF dipole antennae were deployed automatically shortly after ejection from the launch vehicle, and success was verified through the ability to communicate with the satellite on its first passes over the ground stations.
The solar panels were deployed via uplink commands, and success was verified through sharp changes in both panel temperature and current telemetry. However, due to current shunting in the solar panels when power generation is high, the latter measure was unreliable. This highlighted the importance of multiple means of deployment verification.
The HF antenna deployment occurred in 12 burn-wire activated stages – each requiring verification of success before proceeding to the next stage. The primary deployment verification method was via one-shot infrared (IR) sensors positioned at 90º intervals about the axis of deployment. The final deployment stages could be verified through images captured by the payload camera. Deployment stages were also associated with a decaying sinusoidal body rate signature in the deployment axis; however, this telemetry typically required multiple passes to downlink and therefore was not a practical verification method. Unexpectedly, on at least one occasion, more than one deployment stage was triggered during the HF antenna deployment campaign due to momentum from the intended deployment stage. The one-shot infrared (IR) sensors were designed for detecting single stage deployments, and therefore the deployment status of the HF antenna was uncertain at stages of the campaign. This again highlighted the importance of multiple reliable deployment verification methods, as well as the limitations of one-shot sensors.
Spacecraft bus health and performance
EPS health and performance: The BRMM EPS has supported mission operations to date, however its on-orbit operation has highlighted some areas for future consideration. On-orbit telemetry indicates that the spacecraft is power positive when the normal direction to the deployed solar panels is aligned with the Sun vector (and all other subsystems and payload enabled), and in some states when in a controlled tumble (ADCS in a rate-nulling mode). Several spacecraft states are power negative, including: in an uncontrolled tumble, when the ADCS control mode is unstable with high reaction wheel speeds, and in ADCS control modes without adequate Sun-pointing of the solar panels. The large number of power negative spacecraft states led to several critical voltage events, and associated entry into a low-power safe mode. These events demonstrated the importance of maximizing CubeSat solar cell coverage and efficiency and battery capacity, and having suitable on-board self-monitoring with associated safety modes so the spacecraft can enter a safe state before battery depletion leads to power-system failure.
Comparisons of on-orbit data with theoretical power models based on initial solar cell efficiencies, documented subsystem power consumptions, constant battery capacity and on-orbit attitude telemetry, revealed significant discrepancies. A large component of this discrepancy is attributable to power shunting and thermal effects. The on-board battery heater was unable to provide the required thermal control to maintain battery performance in the desired range, and this was not accounted for in theoretical models. This finding highlighted both the importance of more detailed power modelling to include thermal behavior, and the value in a battery heater with greater thermal control. The ability to predict power negative states would also be greatly improved by subsystem power consumption monitoring, and battery state of charge and health sensing.
ADCS health and performance: The BRMM ADCS successfully and routinely demonstrated the ability to perform two important control modes: ‘Acquisition' mode, whereby the body rates of the spacecraft are minimized using magnetorquers, and ‘Sun-Ram', whereby the normal to the solar panel face is aligned with the Sun vector in the spacecraft frame, with spacecraft drag minimized as a secondary objective. Both modes will be critical cruise modes for BMM.
The sole on-orbit component failure for BRMM to date has been an ADCS reaction wheel failure approximately 5 months into operations. The cause of the reaction wheel failure has not yet been determined. The failed wheel controlled attitude about the normal axis to the solar panel face (the –X axis). Therefore, it has been possible to continue to achieve an orientation where the –X face dominates the Sun vector in the spacecraft frame with reliability of over 80% of commanded attempts. However, due to the lack of attitude control about the –X axis, the secondary objective of the Sun-Ram mode, to minimize spacecraft drag, could not be achieved. The reaction wheel failure has also significantly reduced the reliability and pointing accuracy of the other pointing modes. The failure gives weight to the consideration of reaction wheel redundancy for future missions.
Attitude control in eclipse was not achieved, which is likely due to the inability to achieve sustained nadir pointing, since the ADCS Earth-horizon sensors require steady view of the Earth's limb. The nadir-pointing challenge was amplified after the reaction wheel failure. Lack of eclipse attitude control hindered the performance of the GPS receiver, since steady space-pointing of its GPS antenna is a requirement for a navigation solution. This attitude control shortcoming is a key consideration for BMM, for which eclipse attitude control, and consistent GPS navigation, is desirable.
TT&C health and performance: Effective and reliable UHF communication with BRMM has been achieved since launch. An issue involving the spacecraft ignoring commands from the ground stations that was first experienced shortly after launch was resolved by adding a capability to dynamically modify the ground station uplink frequency to compensate for frequency drift.
Another notable UHF communications issue is harsh interference environments at both Buccaneer ground stations. The UHF downlink frequency band is in the congested Industry, Scientific and Medical (ISM) band, and therefore spectrum allocation was made on a ‘no protection' basis. The influence of this interference on communication with BRMM has exceeded what was expected by the Buccaneer team, and has prompted examination of the possibility of establishing a remotely located ground station to support BMM.
Hindered by the interference environment, the signal-to-noise ratio at low elevation angles often prevents decoding of signals from the spacecraft. Typically, effective communication with BRMM is only achieved for less than half the total pass duration. It was identified that the proportion of effective communication time could be increased by implementing adaptive data rate communications based on the signal-to-noise ratio at the ground station, and this will also be considered for BMM.
S-band signals have successfully been received and decoded by the DST Group ground station. However, the consistency of communications via S-band has been poor due to failure of the ADCS reaction wheel and the resulting instability of ground pointing modes. Unfortunately, S-band commissioning did not commence until after this failure, and thus S-band communication reliability cannot be assessed on BRMM.
OBC health and performance: The OBC and flight software have served the mission effectively and continue to operate as expected. During spacecraft commissioning, a small number of software bugs and deficiencies were identified, most of which were manageable by implementing workarounds. However, the flight software was designed to allow two images of the operating system to be present at any time, and thus, following the commissioning period, a new version of flight software was uploaded to the second image location. In order to prevent the potential event where the new flight software version is corrupted, the OBC always reverts to the as-launched, safe flight software version when a spacecraft reset occurs. This flight software architecture was very valuable on BRMM, and is highly recommended for CubeSat missions, due to the inevitability of at least minor flight software bugs being discovered during operations. The design also allows for new software configurations, enabling extended mission operations not originally envisioned.
Unexpected spacecraft resets have occurred on BRMM at randomly distributed time intervals with a mean of 8 days and standard deviation of 6 days. Their cause remains unknown, but is suspected to be due to an accumulation of spacecraft charge, producing pseudo-random arc discharge events. The ability to diagnose the cause(s) of these resets could be assisted by information provided by a microprocessor supervisory integrated circuit external to the main CPU.
With each reset, the spacecraft time also resets, which has invalidated scheduled commands and delayed operations activities on several occasions. The key lesson from this inconvenience is to protect the real-time clock against bus resets (for example, via a super-capacitor) in future missions. This would also avoid time discrepancies between the ground station and the spacecraft – since after each reset, when the spacecraft time is set via command from the ground station, there is a non-deterministic delay between the command being sent and it being acknowledged by the spacecraft.
Anomalies: Spacecraft anomalies have been regularly encountered during BRMM operations. To date, 24 documented on-orbit anomalies have occurred. Some anomaly events are suspected to have adversely affected the long-term spacecraft health, and several have delayed the achievement of mission objectives.
Figure 9 displays the qualitative distribution of key anomalies experienced during BRMM operations, in terms of their risk to the mission and the complexity of their resolution. The majority of anomalies posed low to medium risk to the mission and had low to medium complexity associated with their resolution. However, two anomalies presented significant risk to the mission – the first, AR1, a flight software bug in the spacecraft's safe mode which required uplink of a new configuration parameter immediately post-launch; and the second, AR22, the ADCS reaction wheel failure, which could not be rectified.
Figure 9: BRMM operations observed anomaly qualitative distribution by risk to mission and complexity of resolution (image credit: Buccaneer collaboration)
For BRMM, the restricted ground station coverage and low communication data rates regularly prolonged the diagnosis and recovery from spacecraft anomalies and resets. This challenge illuminated the value in autonomous anomaly diagnosis and recovery processes on-board the spacecraft, particularly for common anomalies. For example, the ability to detect abnormally high ADCS reaction wheel speeds prior to critical battery voltage events and autonomously reverting into a passive attitude control mode would have been beneficial to BRMM.
Testing on the engineering model was critical during operations for both anomaly diagnosis and resolution – by replicating transmitted and planned commands and observing the spacecraft response. The engineering model was also key in testing and diagnosing issues with end-to-end over-the-air communications with the ground station prior to launch.
Management: A key lesson learnt during BRMM operations was the value of clearly defined and measurable mission objectives, IOCs(Initial Operational Checkouts), and ‘go/no go' criteria for critical flight operation activities. In order to move efficiently through the early operations and commissioning stages, well-defined IOCs with a breakdown of activities associated with their completion were identified to facilitate the efficiency of validation of subsystem function and performance. The relatively short lifetime of CubeSats, and their susceptibility to radiation damage early in operations, amplifies the importance of completing commissioning activities efficiently. Distinct and determinate mission objectives also address this impetus for operations efficiency and are additionally important in terms of fostering team cohesion and common purpose, ultimately ensuring that the overall purpose of the mission is fully realized.
Important lessons for the Buccaneer team surrounded ground station crewing. A formal, agreed roster for ground station crewing is an important logistical consideration, as are the roles and responsibilities of the crew. The DST Group operations team typically assigned a mission controller, radio controller and operations manager on a rotational basis. For mission critical operations activities, there is significant value in having a relevant subsystem or payload SME present.
Operations teams should also consider the tempo of meetings, reviews, and handovers, both internally and with collaborators. The Buccaneer team recognized that the tempo of these activities should not be fixed throughout operations – for some phases of operations, meetings were required after each pass, and for other phases, weekly meetings sufficed.
Collaboration: At the foundation of many lessons learnt during BRMM operations is the importance of clear, formally defined and mutually agreed mission objectives early in the project. This exercise is particularly important for collaborative missions as it can overcome problems arising from differing risk profiles, ambitions and management styles between organizations. This principle can also be applied to the definition of ‘go/no go' criteria and mission plan priorities. Formalized definition of measurable ‘go/no go' conditions and breakdown of mission objectives into their associated tasks and timelines were identified by the Buccaneer team to improve the efficiency of flight operations.
The cadence and effectiveness of communication at all stages of a collaborative space mission is central to its success. During operations, the Buccaneer team typically used teleconferences for most formal communication, with less formal and irregular communication through messaging services, email and phone calls. The team found it highly beneficial to conduct a weekly teleconference to jointly review the previous week and plan for the upcoming week of operations, and to formally discuss any anomalies or outstanding issues. Valuable teleconferences were also held following the identification of an anomalous events and following passes where critical mission plans were conducted to efficiently share information and jointly determine a forward strategy.
Formal information sharing throughout the project was achieved through multiple platforms. Wikis are an effective means of collaboratively documenting various aspects of operations, including configuration changes, telemetry analysis, anomaly reporting, and meeting minutes. Code repositories are also a requirement for collaborative software development. Another key consideration of inter-organization information sharing is the distribution of spacecraft telemetry and command logs. Web-based services for command logs were used by the Buccaneer team as a simple and effective solution.
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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).