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CanX-2 is a nanosatellite mission of UTIAS/SFL (University of Toronto, Institute for Aerospace Studies/Space Flight Laboratory) within the framework of the Canadian CubeSat program. A unique spacecraft program was created in Canada where students develop valuable skills through hands-on training. 1)HYPERLINK "#foot2%29"2)HYPERLINK "#foot3%29"3)HYPERLINK "#foot4%29"4)HYPERLINK "#foot5%29"5)
The mission objective of the CanX-2 spacecraft, a triple-cube configuration, is twofold:
- The main goal is to demonstrate several technologies critical for the upcoming CanX-4/5 formation flying mission planned for 2009 (CanX-2 serves as a risk mitigation mission). These technologies include a custom cold-gas propulsion system, a 30 mNms nanosatellite reaction wheel as part of a three-axis stabilized momentum-bias attitude control system, and a commercially available GPS receiver.
- The secondary objective of CanX-2 is to provide rapid and cost-effective access to space for the Canadian research and development community (this includes several university experiments and an atmospheric spectrometer).
Figure 1: Illustration of the triple-cube configuration of CanX-2 (image credit: UTIAS/SFL)
CanX-2 includes experiments in GPS technologies (atmospheric occultation experiments), a miniature atmospheric spectrometer to detect greenhouse gases, advanced materials, and space communication protocols. In addition to the science payloads, CanX-2 will also fly engineering payloads such as a momentum-bias attitude control subsystem, an experimental S-band communications system, a custom onboard computer, and a miniature propulsion system. The CanX-2 program at UTIAS/SFL is supported/sponsored by a number of Canadian government institutions, industry, and universities as partners.
The spacecraft structure of CanX-2 is triple in size of CanX-1, measuring 10 cm x 10 cm x 34 cm with a mass of about 3.5 kg (triple-cube standard). This CubeSat design option permits the triple volume available for payloads and a larger surface area for more power generation. The S/C bus employs an Al 6061-T6 tray-based design to simplify assembly and integration. Most subsystems are directly mounted to a tray, as are most of the body panels that enclose them. Externally, four aluminum rails act as contact surfaces with the CubeSat deployer, the XPOD (X-Picosatellite Orbital Deployer) a custom, independent separation system that was designed and built at UTIAS/SFL.
Power is provided by 22 surface-mounted triple-junction GaAs solar cells with 4 W of average power (2-7 W depending on S/C orientation and orbit). Electrical energy is stored in Li-ion batteries with a capacity of 3.6 Ah. Use of an unregulated satellite power bus operating nominally at 4.0 V.
Figure 2: Overview of the CanX-2 bus and device locations (image credit: UTIAS/SFL)
The ADCS (Attitude Determination and Control Subsystem) utilizes three magnetorquer coils (max. magnetic dipole of 0.13 A m2). In addition, a reaction wheel is used, developed by UTIAS/SFL in cooperation with Sinclair Interplanetary. It is a 30 mNms wheel based on a custom (scalable) motor design. The wheel uses a vacuum grease and does not require a pressurized enclosure. Attitude is sensed with a suite of sun sensors and a 3-axis magnetometer (the magnetometer is deployed on a boom). The goal is to achieve both attitude determination and pointing with an accuracy of Â±10° and to maintain a pointing stability of Â±1°.
Figure 3: Illustration of one reaction wheel (image credit: UTIAS/SFL, Sinclair Interplanetary)
Figure 4: ADCS components: magnetometer and sun sensor (from left), image credit: UTIAS/SFL
CanX-2 features an OBC, developed at UTIAS/SFL, that utilizes ARM-7 based processors (redundant units on two boards) with 3 MB of SRAM memory and EDAC (Error Detection and Correction) software. Each processor has 16 MB of flash memory for data storage.
An SFL-developed operating system, CANOE(Canadian Advanced Nanospace Operating Environment), runs all the application software and handles all internal communications. CANOE is a multithreaded operating system and is the highest-level software state on CanX-2. This operating system allows multi-tasking of operations and full spacecraft-functionality. One of the primary tasks of CANOE is running the OASYS(On-orbit Attitude System Software). OASYS is responsible for calculating the attitude state vector based on attitude sensor inputs and commanding actuators to attain a desired attitude state. 6)
RF communications: CanX-2 takes a three-pronged approach.
1) A custom full duplex amateur radio system is used in UHF. The downlink includes an improved power amplifier providing a transmitter power of 30 dBm (1 W). The downlink data rate is 4 kbit/s using a GFSK (Gaussian Frequency Shift Keying) modulation scheme. A quad-canted turnstile antenna provides a near omnidirectional coverage required during the commissioning phase.
Figure 5: The UHF radio receiver (image credit: UTIAS/SFL)
2) In addition, a VHF beacon is used able of transmitting identification and several telemetry parameters (the beacon broadcasts basic telemetry to Earth via Morse code at a rate of 15 words/minute).
3) S-band transmitter, developed by SFL. The objective is to evaluate the performance of the miniaturized technology scheme for nanosatellites. The transmitter has a maximum power output of 27 dBm (0.5 W), designed for high-speed data transmissions. The data rate and modulation scheme can be adjusted dynamically as the link conditions vary in orbit (32 to 256 kbit/s in downlink and 4 kbit/s in uplink). By selecting interchangeable components during assembly, the S-band transmitter can operate either in the Amateur Satellite UHF-band or in the Space Research S-band frequency allocations. - If the S-band transmitter functions nominally, the baseline communications for CanX-2 will be configured such as to use UHF in uplink and the S-band in downlink. This permits full duplex communications and increases the data rate by an order of magnitude.
Launch:A launch of CanX-2 as a secondary payload took place on April 28, 2008 on a PSLV launch vehicle of ISRO from SDSC (Satish Dhawan Space Centre), Sriharikota, India. The primary payload on this flight was CartoSat-2A, a high-resolution panchromatic imaging satellite of the military of India, developed by ISRO (based on CartoSat-2). In addition, ISRO launched its own microsatellite, IMS-1 (Indian Microsatellite-1), of 83 kg.
Furthermore, the shared launch included eight secondary payloads with the following CubeSats or nanosatellites:
CanX-2 of UTIAS/SFL; AAUSat-2 of Aalborg University, Denmark; COMPASS-1, University of Applied Science, Aachen, Germany; Delfi-C3 of the Technical University of Delft, The Netherlands; SEEDS-2 of Nihon University, Japan; CUTE-1.7+APD-2 of of the Tokyo Institute of Technology (TITech), Japan; NTS (Nanosatellite Tracking of Ships) of COM DEV / UTIAS/SFL, Toronto, Canada; and Rubin-8-AIS (7 kg) an experimental space technology mission of OHB-System, Bremen, Germany.
The launch of the 8 nanosatellite payloads was executed under a commercial contract between the University of Toronto, COSMOS International (a company of the OHB Fuchs Gruppe, Bremen, Germany), and the Antrix Corporation of Bangalore, India (the latter is the commercial arm of ISRO).
Six custom-built XPOD(eXperimental Push Out Deployer) units were provided by UTIAS/SFL to deploy all smallsats - except the CUTE-1.7+APD-2 (3.5 kg) double cube of TITech which used its own TSD deployer system.
Figure 6: CanX-2 &NTS integrated along with the rest of the smallsat XPODs to the upper stage (image credit: UTIAS/SFL)
The XPOD deployment system is a jack-in-the-box type concept where, once a deployment door is opened, the satellite is pushed out of an aluminum or magnesium box-frame by a spring-loaded plate. The XPOD deployment door is secured in place during launch by a cord. This securing cord is burned and cut using a heater when a deployment signal is issued by the launch vehicle. Each XPOD is equipped with sensors which confirm spacecraft deployment.
Orbit:Sun-synchronous orbit, altitude = 635 km, inclination= 97.4°, the local equatorial crossing on the descending node (LTDN) is at 9:30 hours.
Mission status:CanX-2 is operational since April 2008. Over 80% of the objectives were accomplished in the first 4 months of the mission.
â€¢ The CANOE operating system was loaded upon completion of the commissioning activities in BL2. These commissioning tasks include verifying the stability of the BL2 (Bootloader-2) software and sequentially powering up each sun sensor and the magnetometer in order to verify that these sensors do not cause any shorts.
â€¢ Within the first three weeks after launch, significant headway has been made with respect to the orbital commissioning of the CanX-2 spacecraft. The commissioning procedure involved incrementally building on the spacecraft functionality by enabling progressively more capable software modes and testing systems, actuators and sensors as they are required.
â€¢ Upon ejection from the XPOD, CanX-2 powered up and booted up into the Bootloader-1 (BL1) software state. The BL1 software is stored on a pre-programmed EPROM and is the lowest-level software state.
â€¢ CanX-2 (as well as all spacecraft of the mission) were launched and deployed successfully. First contact with the UTIAS/SFL ground station was established on the second pass after deployment. The telemetry indicated that CanX-2 as well as CanX-6/NTS spacecraft were perfectly healthy following launch and ejection from the XPOD.
Sensor/experiment complement: (NanoPS, CMOS/APS imagers, Argus 1000 Spectrometer, GOE, ASME, Communication Experiment)
NanoPS (Nanosatellite Propulsion System):
The NanoPS experiment wasdeveloped at UTIAS/SEL. The objective is to demonstrate and evaluate its performance. The propulsion system consists of a liquid-fueled cold-gas thruster system \[using sulfur hexafluoride (SF6, high storage density) as a propellant\] with a total mass of <0.5 kg. It features a thrust level of 50-100 mN with a specific impulse of 500-1000 m/s providing a total delta v of >35 m/s. The nozzle is oriented such that thrusting induces a major-axis spin on CanX-2 (NanoPS involves mainly attitude control maneuvers that spin the satellite about one axis). NanoPS on CanX-2 is regarded a precursor instrument (scaled prototype) for the future formation flight missions of CanX-4 and CanX-5. 7)
Figure 7: Photo of the partially assembled NanoPS device (scale in cm, image credit: UTIAS/SFL)
A color imager and a monochrome imager are being used. The imagers are COTS CMOS imaging chips manufactured by National Semiconductor. Each imager has its own lens system. The imagers utilize a wide field-of-view (FOV) lens of 30° with a detector size of 1280 x 1024 pixels. The monochrome imager provides the option of doing star tracking experiments (assessment of the capability of CMOS imagers as nanoscale star trackers). The color imager is mainly used to take snapshots of targets of interest (Earth, moon, etc.).
Argus 1000 Spectrometer:
Argus is a miniature technology demonstration instrument designed at York University, Toronto, Canada (manufacturer: Thoth Technology Inc., Kettlby, Ontario). The objective is to detect greenhouse gas constituents in the near infrared region using Earthshine spectra. Argus features only an along-track footprint of 1 km x 1 km (there is no scan capability in cross-track). Initial tests will be carried out to detect pollution plumes of industrial origin. Once Argus has demonstrated and validated the detection of greenhouse gases, then 3-axis control of the spectrometer will be implemented on future missions (an application could be the support of the goals of the Kyoto protocol). 8)HYPERLINK "#foot9%29"9)
Carbon Dioxide (CO2)
1.24 Âµm (10-21mol cm-2)
1.42 Âµm (10-22mol cm-2)
0.90 Âµm (10-21mol cm-2)
1.2 Âµm (10-21mol cm-2)
1.4 Âµm (10-19mol cm-2)
Carbon Monoxide (CO)
1.63 Âµm (10-22mol cm-2)
1.67 Âµm (10-20mol cm-2)
Hydrogen Fluoride (HF)
1.265 Âµm (10-19mol cm-2)
Table 1: Argus measurements of atmospheric species
Argus uses an adjacent spectral range 900-1700 nm to record nadir spectra of the radiation emitted from a 1 km footprint under the spacecraft's path, as shown in Figure 8. The gaseous composition of the air mass along the instrument's line of sight may be inferred through measurement of absorption features associated with a particular gas. Argus will observe carbon dioxide, methane, carbon monoxide, hydrogen fluoride and water-absorption bands in order to determine near-surface column amounts for pollution monitoring.
Figure 8: Argus observation geometry for pollution detection (image credit: York University)
Argus is a micro-spectrometer observing in the spectral range of 900-1700 nm with a spectral resolution of about 6 nm. An InGaAs detector with diffractive optics is used. An IFOV of 1 mrad is used to provide a high resolution pollution-mapping capability for this prototype instrument. The device includes a programmable Peltier-effect cooler that enhances noise performance and that can be programmed to operate over a wide range of integration times from microseconds to seconds.
Figure 9: View of the Argus 1000 spectrometer (image credit: York University)
The instrument's functional design is shown in Figure 10. The instrument includes a micro controller that controls the device and acquires spectra. The command interface accepts commands via prime and redundant serial interfaces and delivers spectra and engineering data via the same interface. The instrument consumes <1 W of power and includes internal power isolation and regulation. Fore optics discriminate infrared radiation; a grating element diffracts it spectrally, and the signal is then focused onto a linear InGaAs photodiode array with 256 high-quantum efficiency pixels.
With a low mass of 0.250 kg and dimensions of 50 mm x 60 mm x 80 mm, the micro-spectrometer has minimal accommodation requirements. Argus employs an infrared optical triplet lens in the fore optics to provide an image tile tightly focused on a beam stop that provides the spatial filtering for the device. An order filter prevents visible radiation (below 900 nm) from entering the spectrometer chamber. The device employs 35 mm optics to collimate radiation from a 1 km tile onto a diffraction grating and then focus it onto the detector array.
Instrument calibration: Argus is calibrated in a three-step process. First, a wavelength calibration is conducted using infrared lasers at 1064 nm and 1532 nm. An infrared laser source is passed through a collimator optics that fills the instrument field-of-view. This simulates radiation emitted by a ground tile and received by the spectrometer. The spectrometer is mounted on an adjustable vernier kinematic mount with five degrees of freedom.
Figure 10: Argus functional diagram showing optics (blue), hardware layer (tan), driver layer (red), software layer (green), ground system electronics (yellow), Image credit: York University
0.9-1.7 Âµm infrared range at approximately 6nm spectral resolution (enhanced detectors extend range to 2.5 Âµm)
Single aperture spectrometer
FOV (Field of View)
0.1° viewing angle around centered camera boresight with 15 mm foreoptics
40 mm x 45 mm x 80 mm (base x height x length)
256 element InGaAs diode arrays with programmable peltier cooler for enhanced noise performance
12 mm x 12 mm plane gratings, 200 to 600 g/mm
8 bit microprocessor with 12 bit ADC, 3.6-4.2 V, input rail 250-1000 mA
- Continuous cycle, constant integration time
- Continuous cycle, adaptive exposure
- Single shot
Fixed length parity striped packets of single or co-added spectra with
sequence number, temperature, array temperature and operating parameters
100 Âµs to 8 s
Two-wavelength laser calibration and radiance calibration prior to flight
Less than 0.1% volatile internals by mass
Table 2: Specification of the Argus 1000 spectrometer
GOE (GPS Occultation Experiment):
GOE was designed by the Department of Geomatics Engineering at the University of Calgary. The objective of this science experiment is to perform refractive radio occultation measurements of Earth's atmosphere (vertical profiles of refractivity in the troposphere). GOE consists of a dual-frequency receiver and a directional antenna mounted on the outer surface of the satellite. - Data from ground-based GPS stations are being used in conjunction with the spaceborne data, and differential GPS processing methods are employed, to recover the atmospheric properties such as TEC (Total Electron Content) of the ionosphere and tropospheric water vapor as a function of altitude. GOE will also permit the monitoring of auroral activity.
ASME (Advanced Surface Material degradation Experiment):
ASME is amaterial science demonstration developed at the University of Toronto. This experiment uses a photon detector to measure the surface degradation of a material sample exposed to the space environment. The sample is divided into two identical units: one having been given a special surface treatment and another one without surface treatment. The objective is to monitor the changes in sample thickness as a result of atomic oxygen erosion to evaluate the effectiveness of the special surface treatment (the electrical resistance is measured over time for a deduction in sample volume changes).
Figure 11: CanX-2 science instruments: Argus spectrometer (left), GEO antenna (center top), GEO receiver (center bottom), and ASME (right), image credit: UTIAS/SFL
Satellite communication protocol experiment:
The communication experiment was developed at Carleton University, Canada. The aim is to allow satellites to dynamically transfer data. That is, the network protocol on a given satellite activates in response to incoming data: it in turn relays information to other satellites or ground stations as they come into view.
This CanX-2 experiment will use the networking protocol under the open-source operating system eCOS and evaluate it in a LEO environment. During the experiment, XSTP(eXtended Satellite Transport Protocol) will be used instead of NSP (Node Switch Protocol) that is generally used for all monitoring functions.- The protocols include a network layer and a transport layer. The network layer protocol comprises an algorithm using dynamic source routing. The system remains silent by default and reacts dynamically when it perceives traffic. In a self-organizing network approach, a satellite can automatically make use of ground stations or other satellites - when available to reach a given target. The transport layer protocol is called XSTP; it addresses data transport errors that occur in particular in LEO satellite links. The CanX-2 experiment will interact with available ground stations for demonstration purposes. 10)