AISSat-1 (Automatic Identification System Satellite-1), Nanosatellite Constellation
In 2000, the IMO (International Maritime Organization) adopted a new requirement for all ships to carry an AIS (Automatic Identification System) device, capable of providing real-time information about the ship to other ships and to coastal authorities automatically. The regulation requires AIS to be fitted aboard all ships of 300 gross tonnage and upwards engaged on international voyages, cargo ships of 500 gross tonnage and upwards not engaged on international voyages, and all passenger ships irrespective of size. The requirement became effective for all ships by 31 December 2004. - Ships fitted with AIS shall maintain AIS in operation at all times except where international agreements, rules or standards provide for the protection of navigational information. 1) 2) 3)
AIS for maritime vessels introduced by the IMO is a navigation aid and basically an anti collision system for vessels at sea. Vessels are broadcasting messages (position reports and short messages with information about the ship and the voyage) on two channels in the maritime VHF band on a regular basis to neighboring vessels for collision avoidance, and to shore stations for VTS (Vessel Traffic Services). AIS messages can also be received by a VHF receiver in space for wide area observation of maritime activity. According to the International Association of Maritime Aids to Navigation and Lighthouse Authorities (IALA), the purpose of AIS is “to improve the maritime safety and efficiency of navigation, safety of life at sea and the protection of the marine environment.”
As of 2008, Norway, a nation of long shorelines, large coastal waters and fishing grounds, is in the process to build its first dedicated satellite (AISSat-1) for such spaceborne monitoring services of AIS signals. The justification for the mission is based on careful modeling of the global AIS detection probability, with particular emphasis on observation of Norwegian ocean areas in the High North.
AISSat-1 is a Norwegian nanosatellite technology demonstration mission in LEO, funded by the NSC (Norwegian Space Center, O) with program management by the FFI (Norwegian Defense Research Establishment). The overall objective is to investigate and assess the feasibility of a much needed national maritime situational awareness service. 4) 5) 6) 7)
Collaboration: The Norwegian Space Center is project owner. The Norwegian Coastal Administration will receive the data and FFI is responsible for the technical implementation.
FFI has examined both technical and organizational aspects of monitoring AIS signals from space, to evaluate the possibility of extending the coverage area of AIS to all ocean areas under Norwegian jurisdiction. A comprehensive observation model for estimating the AIS signal environment in LEO (Low Earth Orbit) has been developed, making it possible to evaluate various concepts for AIS satellite missions to meet Norwegian and also more global requirements.
Figure 1: Ocean areas (blue) under Norwegian jurisdiction (image credit: FFI)
AISSat-1 has been constructed on behalf of the government of Norway by UTIAS/SFL (University of Toronto, Institute for Aerospace Studies/Space Flight Laboratory), Toronto, Canada. The AIS sensor is a software defined radio system developed by Kongsberg Seatex AS (KSX) of Trondheim, Norway.
The satellite design is based on the modular GNB (Generic Nanosatellite Bus) of UTIAS/SFL first introduced in the CanX-6 / NTS mission (launch April 28, 2008). The GNB was originally developed for the BRITE (BRIght-star Target Explorer) constellation of Austria and for the CanX-4/-5 missions (all under development as of 2008), and is now also being leveraged for other missions as well.
The GNB platform is a cube of 20 cm side length, using an Al 6061-T6 structure, featuring two internal trays and six external panels. A dual tray structure was selected to maximize the payload bay and to provide ease of integration. The two trays contain all the necessary components for a basic satellite mission, including communications, attitude determination and control, power and thermal/structural components (Figure 6). A full suite of advanced capabilities is included: 8) 9) 10) 11)
• A dual battery, gallium arsenide triple-junction solar cell based power system that includes peak power tracking capabilities
• A full 3-axis attitude determination and control system that allows arbitrary inertial or orbit-frame alignment (including nadir, along-track and cross-track)
• A powerful complement of on-board computer processing systems, this includes a computer dedicated to payload activities
• A flexible TT&C and payload data communication system, allowing for variable and high speed data downlinks to the ground
• A large accommodation for payloads, including volume, pass, power, and spacecraft surface area.
Figure 2: Photo of the AISSAT-1 spacecra
ft model (image credit: FFI)
Figure 3: Schematic view of the GNB (Generic Nanosatellite Bus), image credit: UTIAS/SFL)
Figure 4: Illustration of the AISSat-1 nanosatellite (image credit: FFI, UTIAS/SFL)
Figure 5: Up-side down view of the AISSat-1 nanosatellite (image credit: FFI, UTIAS/SFL)
AISSat-1 also includes a custom designed VHF monopole payload antenna, as shown in Figure 4. The antenna is pre-deployed and designed to survive launch conditions in any orientation. It is also designed to be easily removed from the spacecraft without removing any of the spacecraft panels, allowing for easier testing, handling, and safety during shipment.
OBCs (On Board Computers): The spacecraft is equipped with three OBCs. Each OBC features an ARM7 microcontroller, 2 MB of EDAC protected SRAM and 256 MB of flash memory. The housekeeping computer is responsible for communications with the ground station and collecting satellite telemetry. The ADCC (Attitude Determination and Control Computer) interfaces with the attitude sensors and actuators and runs the attitude control algorithms.
On AISSat-1, a mission specific payload OBC is responsible for interfacing with and collecting data from the AIS sensor and GPS receiver (the main rational for the GPS receiver is to provide an accurate clock for the AIS receiver). The computer allows different data collection, storage, and processing modes, and permits in-flight updates to the AIS sensor. Each OBC runs a custom made multi-threaded operating system called CANOE (Canadian Advanced Nanospace Operating Environment) allowing it to divide processing time between multiple tasks in parallel.
EPS (Electric Power Subsystem): Spacecraft power is generated with 36 body-mounted triple junction GaInP2/GaAs/Ge solar cells. These cells have a BOL efficiency of 26.8%, delivering up to 967 mW at their peak power point at 28ºC. The energy is stored in a dual-5.3Ah lithium-ion battery system allowing the satellite to operate in extended eclipse periods and to reduce depth of discharge on the individual batteries. The power system architecture contains peak power tracking functionality and provides switched power to the loads and power regulation where required. Finally, over-current protection is provided to prevent damage to the payloads.
Figure 6: Internal structure of AISSat-1 (image credit: FFI, UTIAS/SFL)
AISSat-1 employs mostly passive thermal controls in the form of coatings and structures. As the battery possesses the most stringent thermal requirements, it requires thermal isolation and a trim heater to meet a large variety of orbital scenarios.
ADCS (Attitude Determination and Control Subsystem): The nanosatellite features a full 3-axis ADCS with a fine pointing capability. The satellite is able to point in either an inertial orientation, or in an orbit-frame-fixed orientation, including nadir pointing. The attitude sensors consist of six sun sensors, a magnetometer and three rate gyros.
Figure 7: Illustration of the Sinclair-SFL reaction wheels (image credit: UTIAS/SFL)
Actuation is provided by three orthogonally mounted reaction wheels (Figure 7) which were developed by SFL in partnership with Sinclair Interplanetary of Toronto, and three magnetorquer coils. The coils are used for detumbling and momentum dumping while the reaction wheels provide fine attitude pointing capability. The attitude control system is able to maintain a several degree level pointing accuracy and stability over the course of the entire orbit, including eclipse.
Each reaction wheel fits within a box of 5 cm x 5 cm x 4 cm, has a mass of 185 g, and consumes only 100 mW of power at nominal speed. A max torque of 2 mNm is provided (30 mNms momentum capacity).
The multi-mission-design architecture for the GNB attitude subassembly is shown in Figure 8, where the OASYS (On-Orbit Attitude Subsystem Software), which is comprised of an EKF (Extended Kalman Filter ), and a set of control laws, is constant for every mission. All control laws fly for all missions, however, which ones are actually available and used depends on the particular mission needs and hardware complement. Which sensors and actuators are incorporated depends on the mission. Specific components can be added or subtracted with minimal interfacing effort, giving both the software and hardware significant modularity. 12)
Figure 8: Basic flow diagram of the multi-mission GNB architecture (image credit: UTIAS/SFL)
OASYS is the flight software that performs all the necessary computations for attitude determination and implements attitude-control laws to achieve a desired attitude state (attitude quaternion, and angular velocity in the body frame of reference). It is in part comprised of a satellite-position propagator, a solar ephemeris and an IGRF-11 (International Geomagnetic Reference Field-11th generation), magnetic-field, model of the Earth. These models are used in conjunction with sensors to estimate the satellite’s attitude by means of an EKF. The control laws are then implemented based on the estimated state. The attitude software is run at a fixed-but-configurable frequency of 0.5 Hz on a dedicated ADCC (Attitude Determination and Control Computer ). Each 2 s frame has a series of events, the order of which does not change: read sensors, run OASYS and command the actuators.
A host of control laws have been designed within OASYS to enable a very wide range of missions, however a fundamental suite of three are predominantly used. This includes the B-dot magnetic controller that requires only knowledge of the rate of change of the local magnetic field in the body frame, to null body-rates. Second, in order to prevent the saturation of the reaction wheels, through the action of secular disturbance torques, a magnetic momentum management controller, of the form of a simple proportional controller acting on the error relative to a reference momentum is used. Third, in order to actually point the GNB, a three-axis controller in the form of a linear quaternion and linear bodyrate feedback PID controller is used. This near-minimum-time eigen-axis rotation controller is capable of holding to an inertially-fixed target, or given a set of roll, pitch and yaw angles, tracking a fixed target relative to the moving classical orbit frame (Ref. 12).
AISSat-1 was designed with a full complement of GNB hardware and software in addition to its payload elements, with the exception of a star tracker which was not required. Therefore, the attitude system hardware was comprised of six digital sun sensors, one boom-mounted three-axis magnetometer, and one three-axis rate sensor to round out the determination suite. For control AISSat-1 employs three miniature reaction wheels and three vacuum-core magnetorquer coils.
Figure 9: AISSat-1 ADCS configuration (image credit: UTIAS/SFL)
Figure 10: Electrical architecture of AISSat-1 (image credit: UTIAS/SFL)
The AISSat-1 nanosatellite has a mass of ~6.5 kg.
The primary spacecraft on this flight was CartoSat-2B of India (694 kg), funded by the Ministry of Defense of the Government of India. 15)
Further secondary payloads on this flight are:
• AlSat-2A (Algeria Satellite-2) of CNTS (Algerian National Space Technology Centre) built at EADS Astrium SAS, France (116 kg).
• TISat-1 (Ticino Satellite-1), a CubeSat (1 kg) of SUPSI (Scuola Universitaria Professionale della Svizzera Italiana ' University of Applied Sciences of Southern Switzerland), Lugano-Manno, Switzerland.
The AISSat-1 and TISat-1 spacecraft were launched and deployed with XPOD (Experimental Push Out Deployer) of UTIAS/SFL. UTIAS/SFL refers to this service as NLS-6 (Nanosatellite Launch Service-6). 16) 17) 18)
• StudSat (Student Satellite), a picosatellite (1 kg) built by a consortium of seven Engineering colleges from Hyderabad and Bangalore, India.
Figure 11: Photo of the AISSat-1 nanosatellite in launch configuration (image credit: UTIAS/SFL)
Orbit: Sun-synchronous polar orbit, altitude of 635 km, inclination= 97.71º, equator crossing at 9:30 hours LTDN (Local Time on Descending Node), period = 97.4 minutes.
RF communications: The AISSat-1 platform contains two radio systems: a UHF-band receiver, and an S-band transmitter. The UHF-band receiver, operating at 4 kbit/s, is used for data uplink from the ground station and uses four phased quad-canted monopole antennas which provide near omnidirectional coverage. The S-band transmitter will be used for the data downlink. It is capable of data rates in the range of 32 to 256 kbit/s; it uses two patch antennas mounted on opposite sides of the satellite for near omnidirectional coverage.
According to the contract agreement, UTIAS/SFL is providing the spacecraft platform and the AIS VHF antenna, and providing spacecraft-level management, systems engineering, assembly, integration, and test support. UTIAS/SFL will also be responsible for launch and the commissioning phase, after which the spacecraft will be delivered to FFI for operations.
Following the success of AISSat-1, the Norwegian authorities decided that the AIS-from-space capability had proven to be extremely valuable and the usage of its data in the operational AIS network was of long-term strategic interest. In order to maintain the capability, a second satellite, AISSat-2, was ordered in early 2011. AISSat-2 is a build-to-print copy of AISSat-1.
The second satellite in this constellation series, AISSat-2, has been completed and will be launched in 2014. The third satellite, AISSat-3, is under construction at UTIAS/SFL and will be launched in 2015. 19)
Figure 12: Photo of the flight-ready AISSat-2 nanosatellite (image credit: UTIAS/SFL)
The primary purpose of AISSat-2 and AISSat-3 is to provide a higher level of capability assurance. Specifically, it is to be considered an in-orbit backup to AISSat-1 to avoid a loss of AIS-from-space capability should there be an on-board failure that results in a loss of AIS data capture capability. In this sense, the two satellites will be backups for each other and provide the overall system with a full single fault tolerance capability. Through this redundancy, Norway’s AIS-from-space capability has a higher degree of assurance of continuity.
Launch: The AISSat-2 nanosatellite will be launched in the first half of 2014 on a Soyuz-2.1b/Fregat launch vehicle from the Baikonur Cosmodrome, Kazakhstan. The primary payload on this flight is Meteor-M N2. The launch provider is NPO Lavochkin.
Secondary payloads on this flight are:
• Baumanets-2, a technology microsatellite (~100 kg) of BMSTU (Bauman Moscow State Technical University)
• TechDemoSat-1, a technology minisatellite (~160 kg) of SSTL.
• Monika (Relek)
• UKube-1, a nanosatellite of ~5 kg of UKSA (United Kingdom Space Agency).
• AISSat-2, a nanosatellite with a mass of ~6.5 kg of Norway.
Orbit: Sun-synchronous circular orbit, altitude of ~ 820 km, inclination = 98.8º.
Status of mission:
• 2014: The AISSat-1 spacecraft and its payload are fully operational. The mission continues to provide a very valuable service to the Norwegian Coastal Administration. The mission goal for the satellite was originally 3 years, which it successfully completed in July 2013. With no degradations or problems onboard, the mission might probably provide its service for another three years. 20)
• The AISSat-1 spacecraft and its payload are operating nominally in the summer of 2013 (3 years on orbit). Since the launch of AISSat-1 in July 2010, AIS has gone from being an experimental service to being a fully operational capability that authorities responsible for maritime safety and security worldwide have become more or less reliant on. 21) 22)
To maintain the satellite AIS service to Norwegian authorities, a copy of AISSat-1, namely AISSat-2, has been built to serve as an in-orbit spare for AISSat-1, as well as to provide more vessel traffic data (AISSat-2 will be launched in Q1 2014 as a secondary payload to SPOT-7 on a PSLV rocket of ISRO). Both satellites will operate simultaneously, but since neither satellite has on-board propulsion, the orbits will drift independently from each other (Ref. 21).
• In July 2012, the AISSat-1 nanosatellite marks two years on orbit. In general, the payload operations of AISSat-1 during the first two years of operations can be divided into three periods as shown in Figure 13. The first AIS messages from AISSat-1 were forwarded to the NCA (Norwegian Coastal Administration) already in the afternoon after the launch. From early on, live AIS data were gathered. UTIAS/SFL had in the first month’s responsibility for the commissioning of the satellite, but unless the satellite needed to operate in a special mode due to the commissioning, live AIS data were provided when the satellite was in contact with Svalbard. 23)
Figure 13: Overview of AISSat-1 operations (image credit: FFI)
- AISSat-1 is a very successful operational mission, and has shown that a nanosatellite on a small budget can provide a service that is able to meet many users’ operational requirements globally. AISSat-1 has already provided an exceptional data set for both research and operational use; the project is confident to continue this service for the foreseeable future.
- Except for one weekly interaction for uploading new time tagged commands, new orbit element information and adjust the onboard clocks, the operations of AISSat-1 after 2 years are mainly hands-off. Both the satellite and the on-ground software and hardware are working excellently, enabling FFI to focus more on research than on operations (Ref. 23).
• The attitude subsystem of the SFL’s GNB (Generic Nanosatellite Bus) can support a wide range of missions, as well as a range of platforms, as the GNB ADCS was recently extrapolated for use for SFL’s third generation nanosatellite bus, the NEMO-class bus, which is a 15 kg nanosatellite, and COM DEV’s AIM-class 70 kg microsatellite bus. The GNB ADCS is now flight proven with currently nearly 2 years experience on the AISSat-1 mission, and significant aspects of the attitude system have over four years of flight heritage on SFL’s CanX-2 technology demonstration mission (Ref. 12).
The same reference also outlines the details of the ADCS commissioning phase (prior to Nov. 26, 2010) regarding:
- ADCS hardware checkout
- Attitude solution verification of OASYS
- ADCS control algorithm performance.
• The AISSat-1 spacecraft and its payload are operating nominally in 2012. 24)
• In August 2011, AISSat-1 has operated for more than a year and has provided a new and valuable maritime observation tool to Norwegian authorities for improved maritime situational awareness of Norwegian and international waters. The up-time for AISSat-1 has been better than 95% (Ref. 7).
• In January 2011, FFI ordered AISSAT-2 (a copy of AISSAT-1) from UTIAS/SFL. In 2013, the two satellites will form the first Norwegian observational asset in space with an increased coverage capability. 25)
• In March 2011, AISSAT-1 data was offered to the Japanese Coast Guard by the Norwegian Coastal Administration. After the earthquake and the follow-up catastrophic Tsunami on March 11, 2011, the AISSat-1 steering committee decided to reprogram the satellite so it could be of use in vicinity of the areas where the disaster struck. The steering committee consists of members from the Norwegian Coastal Administration, the Norwegian Defence Research Establishment and the Norwegian Space Centre, which is the owner of the satellite.
Figure 14: Vessel situation around Japan during the catastrophic tsunami (image credit: FFI)
• On January 12, 2011, the AISSAT-1 mission celebrated six months of successful operations in orbit. AISSat-1 was launched on 12 July 2010. 26)
• On Nov. 26, 2010, AISSat-1 GNB commissioning was formally “handed over” by SFL to the Norwegian Defence Research Establishment (FFI) . The Norwegian authorities took over full operational responsibility for the mission using its ground station at Svalbard. However, SFL continues to provide technical support as needed for the mission. - AISSat-1 was recently voted Norway’s top technological achievement for 2010.
With the successful implementation of the AISSat-1 mission, the GNB platform has been verified and the broader utility of capable nanosatellite platforms in solving operationally-relevant real-world problems has been demonstrated. The AISSat-1 mission has demonstrated that a high degree of operational reliability can be obtained in a low-cost, high-performance nanosatellite platform (Ref. 12).
• In the months following launch, all the systems of the satellite were successfully commissioned, including its three-axis attitude control system that enables inertial pointing to within 1-2º. The full pointing control demonstrated by AISSat-1 is likely the first time that such pointing performance has been demonstrated on a nanosatellite.
• Owing to the excellent early operations results, the AISSat-1 payload was activated in its real-time mode for the first time less than 12 hours after initial acquisition and the system was able to receive and disseminate live AIS message traffic from the High North immediately. Thus in a very short time, the mission was able to complete a number of critical mission milestones and demonstrate high confidence in the larger mission.
- Within one day after launch, the satellite was detecting ships over Norwegian waters and a press release was issued with data from space. The satellite was collecting AIS (Automatic Identification System) data very soon after launch and before all its systems had been fully commissioned - and transmitted the AIS messages to a KSAT (Kongsberg Satellite Services) ground station in Svalbard. 27) 28)
Figure 15: First capture of AIS data from AISSAT-1, July 15, 2010 (image credit: Google, KSAT, FFI)
Legend to Figure 15: The yellow and orange symbols shows the new AIS-data that comes in addition to data from coastal AIS infrastructure.
Payload / experiment complement: (AIS)
AIS (Automatic Identification System):
AIS, designed and developed at KSX (Kongsberg Seatex AS, Trondheim, Norway), is a self-organizing TDMA (Time Division Multiple Access) radio-communication system used for the identification and location of maritime vessels - the implementation is referred to as SDR (Software Defined Radio). The AIS signals are sampled and forwarded to the FPGA (Field Programmable Gate Array) for further processing. Using a reprogrammable FPGA enables in-flight finetuning of the AIS sensor based on analysis of received AIS data; it also allows the FPGA to be completely reprogrammed to take advantage of major future design and functionality improvements. 29)
The microcontroller communicates with the satellite platform by sending and receiving data packets on a serial RS-485 line. The controller also holds the radio setup information in addition to FPGA configuration images.
Figure 16: AIS sensor elements for the AISSat-1 nanosatellite (image credit: FFI)
The AIS sensor for this mission is basically a dual-channel VHF receiver, which can be tuned to any of the VHF channels in the maritime VHF band ranging from 156,025 to 162,025 MHz. When listening for AIS messages broadcasted on the two designated AIS channels, the radio will be tuned to VHF channels 87B and 88B (161.975 and 162.025 MHz respectively).
Figure 17: Photo of the AIS receiver (image credit: FFI)
Note: NORAIS (Norwegian Automatic Identification System), practically a duplicate of AIS on AISSat-1, and built by the same team, was brought to the ISS (International Space Station) by the Japanese HTV (H-2 Transfer Vehicle) on its maiden flight (launch Sept. 11, 2009). NORAIS is bound for Columbus, the European space laboratory on the International Space Station. This winter, a specially constructed antenna will be brought to the ISS and fitted on the outside of Columbus. From then on, the testing of NORAIS will start. 30)
Figure 18: Photo of the NORAIS instrument (image credit: FFI)
The ground station is located in Svalbard to acquire data from AISSat-1 during all 15 daily passes over Norwegian ocean areas. KSAT (Kongsberg Satellite Services) already has a major facility for communicating with numerous satellites. The Svalbard Ground Station (also referred to as SvalSat), is located at 78.216º N, 20º E on the Norwegian Svalbard archipelago (also referred to as Spitzbergen) near the town of Longyearbyen.
Stored and real-time data from the satellite is acquired and stored at the ground station for subsequent forwarding to the NCA (Norwegian Coastal Administration) in Haugesund and to the MCC (Mission Control Center) located at FFI, Kjeller, in southern Norway.
The satellites (AISSat-1 and -2) use two physical Earth stations for UHF and S-band frequencies. The S-band station, SG40, is shared with other missions such as PROBA-2. SG40 is scheduled by KSAT scheduling mechanisms outside of the framework’s control, and this information is used to schedule the other Earth station (SG14). The framework’s ability to handle external scheduling mechanisms is utilized here to coordinate operations of the two Earth stations. 31)
Figure 19: AISSat-1 mission architecture (image credit: FFI, Ref. 21)
Figure 20: Schematic view of AISSat-1 & -2 ground segment configuration (UTIAS/SFL, FFI, Ref. 31)
Figure 21: Alternate view of the AISSat-1 mission architecture (image credit: FFI)
AISSAT-1 operations at MCC (Ref. 23):
The MCC runs autonomously most of the time. Status e-mails are generated during each contact with AISSat-1, notifying the operators if anything is wrong. The satellite is run by time-tagged commands generated once a week. Any manned operations take place during normal working hours, and the operators are scientists at FFI. If everything runs nominally, the only manual operations happen once a week when the clock and TLE (Two Line Elements) onboard AISSat-1 are updated, and when new time tagged commands are generated and added to an upload queue.
AISSat-1 is designed to have two basic observation modes. When the satellite is in contact with the Svalbard ground station, AIS messages from vessels within the satellite’s field of view are forwarded to the NCA and MCC in real time (< 1sec latency). This mode basically makes a maritime situational picture available to Norwegian authorities in real time. The program forwarding AIS data from the MCC to the NCA also plots the AIS positions in Tracker to give a visual confirmation that everything is working properly. An example of how “live” data received during a single pass is shown in Figure 22.
Figure 22: AISSat-1 single pass real-time data (image credit: FFI)
2) “Technical characteristics for an automatic identification system using time division multiple access in the VHF maritime mobile band,” ITU-R M.1371-3, January 1, 2007
3) Øystein Helleren, Øystein Olsen, Per Christian Berntsen, Karsten Strauch, Nader Alagha, “Technology reference and proof-of-concept for a space-based automatic identification system for maritime security,” Proceedings of the IAA Symposium on Small Satellite Systems and Services (4S), Rhodes, Greece, May 26-30, 2008, ESA SP-660, August 2008
4) Bjorn T. Narheim, Oystein Olsen, Oystein Helleren, Richard Olsen, Alexander M Beattie, Robert E. Zee, “A Norwegian Satellite for Space-based Observations of AIS in the High North,” Proceedings of the 22nd Annual AIAA/USU Conference on Small Satellites, Logan, UT, USA, Aug. 11-14, 2008, SSC08-III-3
5) Torkild Eriksen, Gudrun Høye, Bjørn Narheim, Bente Jensløkken Meland, “Maritime traffic monitoring using a space-based AIS receiver,” Acta Astronautica, Vol. 58, Issue 10, May 2006, pp. 537-549
7) Bjorn T Narheim, Oystein Helleren, Oystein Olsen, Richard Olsen, Harald Rosshaug, Alexander M Beattie, Daniel D Kekez, Robert E. Zee, “AISSat-1 Early Results,” Proceedings of the 25th Annual AIAA/USU Conference on Small Satellites, Logan, UT, USA, Aug. 8-11, 2011, paper: SSC11-III-6
10) F. M. Pranajaya, Robert E. Zee, “Generic Nanosatellite Bus for Responsive Mission,” 5th Responsive Space Conference, April 23–26, 2007, AIAA-RS5 2007-5005, Los Angeles, CA, USA, URL: http://www.responsivespace.com/Papers/RS5/SESSION%-20PAPERS/SESSION%205-5005_PRANAJAYA/5005P.pdf
11) Grant Bonin, Doug Sinclair, Robert E. Zee, “Peak Power Tracking on a Nanosatellite Scale: The Design and Implementation of Digital Power Electronics on the SFL Generic Nanosatellite Bus,” Proceedings of the 23nd Annual AIAA/USU Conference on Small Satellites, Logan, UT, USA, Aug. 10-13, 2009, SSC09-XI-9
12) Karan Sarda, Alex Beattie, Daniel D. Kekez, Robert E. Zee, “In-flight Experience of the High-Performance Attitude Determination and Control System of the Generic Nanosatellite Bus,” Proceedings of the 4S (Small Satellites Systems and Services) Symposium, Portoroz, Slovenia, June 4-8, 2012
14) Daniel D. Kekez, Robert E. Zee, Freddy M. Pranajaya, “Launches and On-Orbit Performance - An Update on Nanosatellite Missions at the UTIAS Space Flight Laboratory,” CalPoly Summer Workshop, Aug. 7, 2010, URL: http://mstl.atl.calpoly.edu/~bklofas/Presentations/Summer-Workshop2010/Kekez-UTIAS_SFL.pdf
15) “Launch of PSLV-C15 rescheduled,” April 29, 2010, URL: http://www.isro.org/pressrelease/scripts/pressreleasein.aspx?Apr29_2010
17) Daniel D. Kekez, Robert E. Zee, Freddy M. Pranajaya, “SFL Nanosatellite Missions, Nanosatellite Launch Service,”Summer Workshop, Aug. 11, 2007, URL: http://mstl.atl.calpoly.edu/~bklofas/Presentations/Summer-Workshop2007/Kekez_Daniel.pdf
18) Daniel D. Kekez, Robert E. Zee, Freddy M. Pranajaya, “Launches and On-Orbit Performance - An Update of Nanosatellite Missions at the UTIAS Space Flight Laboratory,” 2010 Summer Workshop, Aug. 7, 2010, Logan, UT, USA, URL: http://www.cubesat.org/images/cubesat/presentations/-SummerWorkshop2010/kekez-utias_sfl.pdf
19) Alexander M. Beattie, Øystein Helleren, Robert E. Zee, “In-Flight Operations of a High-Availability Nanosatellite Constellation for Maritime Observation,” Proceedings of the 64th International Astronautical Congress (IAC 2013), Beijing, China, Sept. 23-27, 2013, paper: IAC-13-B4.3.1
20) Information provided by Øystein Helleren of FFI (Norwegian Defense Research Establishment), Kjeller, Norway
21) Andreas Nordmo Skauen, Øystein Helleren, Øystein Olsen, Richard Olsen, “Operator and User Perspective of Fractionated AIS Satellite Systems,” Proceedings of the 27th AIAA/USU Conference, Small Satellite Constellations, Logan, Utah, USA, Aug. 10-15, 2013, paper: SSC13-XI-5, URL: http://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=2988&context=smallsat
22) Alexander M. Beattie, Øystein Helleren, Robert E. Zee, “In-Flight Operations of a High-Availability Nanosatellite Constellation for Maritime Observation,” Proceedings of the 64th International Astronautical Congress (IAC 2013), Beijing, China, Sept. 23-27, 2013, paper: IAC-13-B4.3.1
23) Ø. Helleren, Ø. Olsen, B. T. Narheim, A. N. Skauen, R. B. Olsen, “AISSat-1 - 2Years of Service,” Proceedings of the 4S (Small Satellites Systems and Services) Symposium, Portoroz, Slovenia, June 4-8, 2012
24) Information provided by Freddy Pranajaya of UTIAS/SFL, Toronto, Canada.
25) “Norway signs AISSat-2 deal,” UTIAS/SFL, Jan. 6. 2011, URL: http://www.utias-sfl.net/RecentNews/news-20110106.html
26) “AISSat-1 celebrates six months of success on-orbit, first nanosatellite with high performance pointing,” UTIAS/SFL, Jan. 12, 2011, URL: http://www.utias-sfl.net/RecentNews/news-20110112.html
27) “Norway's satellite - AISSat-1 has started its mission,” KSS, July 15, 2010, URL: http://www.km.kongsberg.com/ks/web/nokbg0238.nsf/AllWeb/E07DD275115AD-521C125776100447D16?OpenDocument
28) “AISSat-1 – Norway’s first observation satellite,” FFI, June 2011, URL: http://www.ffi.no/no/Publikasjoner/Documents/AISSAT-1_Norways%20first%20observation%20satellite.pdf
29) Norwegian AIS satellite? June 25, 2007, URL: http://www.km.kongsberg.com/ks/web/nokbg0238-.nsf/AllWeb/5ABD16FBCA2A-3F12C125730500430A00?OpenDocument
31) Alexander M. Beattie, Daniel D. Kekez, Andrew Walker, Robert E. Zee, “Evolution of Multi-Mission Nanosatellite Ground Segment Operations,” Proceedings of SpaceOps 2012, The 12th International Conference on Space Operations, Stockholm, Sweden, June 11-15, 2012
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.