MicroMAS-2 (Micro-sized Microwave Atmospheric Satellite-2)
MIT/LL (Massachusetts Institute of Technology/Lincoln Laboratory) followed up on its MicroMAS-1 experience by building a second MicroMAS-2, which is planned for flight on a commercial launch vehicle by late 2017. While similar in design to MicroMAS-1 (e.g., 3U CubeSat), it contains more channels, by way of an additional miniaturized receiver, to provide more accurate temperature and moisture information. MicroMAS-2 also contains a slightly larger solar array in order to generate approximately 3 W of power for the payload, or about 60 percent more power than MicroMAS-1. 1)
Microwave instrumentation is particularly well suited for implementation on a very small satellite, as the sensor requirements for power, pointing, and spatial resolution (aperture size) can be accommodated by a nanosatellite platform. The MicroMAS-2 mission is in development with an advanced four-band radiometer observing near 90, 118, 183, and 206 GHz to provide precipitation, temperature, and humidity measurements from a 3U CubeSat.
Figure 1: Satellites provide the most forecast skill: Impact of GOS components on 24 hr ECMWF global forecast skill (image credit: Erik Anderson, ECMWF) 2)
Figure 2: Microwave atmospheric sensing: The frequency dependence of atmospheric absorption allows different altitudes to be sensed by spacing channels along absorption lines (image credit: MIT/LL)
The traditional approach of microwave sounding was to use large satellites, like Suomi NPP launched in 2011. These implementations are rather costly and have long development cycles. The newer small satellites, nanosatellites and microsatellites, offer profound benefits and architectural resilience. They can be launched as secondary payloads. Constellations of smallsats provide improved revisits to observe severe storms and improved coverage.
Figure 3: The way to EON-MW (Earth Observing Nanosatellite-Microwave) sounding (image credit: MIT/LL)
Each MicroMAS-2 CubeSat is a dual-spinning 3U CubeSat equipped with a 12-channel passive microwave spectrometer providing imagery near 90 and 206 GHz, temperature sounding near 118 GHz, and moisture sounding near 183 GHz. 3) 4)
In order to effectively collect data with the radiometer sensor, the spacecraft must simultaneously sweep the radiometer field of view perpendicular to the groundtrack while maintaining a 3-axis stabilized orientation fixed in the local vertical local horizontal frame. Analysis determined that it would not be possible to spin the entire satellite and simultaneously maintain the LVLH (local Vertical Local Horizontal) orientation. This attitude control problem led to a novel design solution to implement a dual-spinner design on the CubeSat architecture, in which a custom designed spinner assembly, would join the rotating payload module to the rest of the satellite.
Table 1: MicroSat-2 design changes
The overall objectives of the MicroMAS-2 mission are:
• Develop a 3U CubeSat all-weather sounder at 4 bands: 89 GHz (window), 118 (temp), 183 GHz (humidity), 207 GHz (cloud ice).
• Demonstrate dual-spinner local-vertical local-horizontal attitude control.
• Risk reduction for NASA TROPICS , NOAA EON-MW CubeSat missions.
The MicroMAS-2 mission consists of two spacecraft:
1) MicroMAS-2a with a launch on the ISRO PSLV-C40 mission in January 2018.
2) MicroMAS-2b, also being built by MIT/ LL for a flight on NASA ELaNA-20 in 2018.
The MicroMAS-2 CubeSat consists of a 2U platform section and a 1U payload section connected to the platform via a spinner assembly that rotates the payload at 30 rpm. The 3.8 kg nanosatellite measures 10 x 10 xy 34 cm and employs three-axis stabilization, deployable solar panels and data management to fulfill its task of autonomously collecting radiometry data that is transmitted to Earth for processing and analysis for use in weather models.
The satellite bus consists of an 0.5U external ADCS (Attitude Determination and Control Subsystem) coupled with a 1.5U skeleton chassis provided by Pumpkin Inc., widely used in CubeSat applications. The 2U bus is attached to the payload via the spinner assembly that includes a 6 mm gap for spinner clearance (Figure 4).
The ADCS consists of reaction wheels that are used to stabilize the 2U satellite bus and keep it in an Earth-pointing attitude with one panel facing Earth. The ADCS is tasked with eliminating any transients and disturbances from the spinning system and keep the satellite bus pointed correctly while the payload spins. Attitude determination is accomplished using an IMU (Inertial Measurement Unit), a three-axis magnetometer, Earth horizon sensors and sun sensors.
In the de-tumble mode, the satellite uses three torque rods and its IMU and magnetometer to reduce rates on all three axes to<1º/s. This leaves the spacecraft in an arbitrary attitude from which it will recover by switching to slew mode using the reaction wheels and the TRIAD navigation method that compares the magnetometer and sun vectors using a model of Earth's magnetic field and an astronomical almanac for sun position comparisons. In slew mode, the torque rods are used for momentum dumps of the reaction wheels. The Earth horizon sensors provide a final verification of the correct attitude for scientific measurements.
Electrical power is provided by four 3U double sided solar panels that are deployed in a dart-type arrangement at an angle of 120° to the satellite structure. An additional 2U solar panel is installed on the zenith-facing side of the satellite platform. The satellite uses UTJ (Ultra Triple Junction) solar cells to generate an average power of 9.1 W. Power is stored in 30 W hr lithium polymer batteries and an EPS card conditions the power buses at 3.3, 5 and 12 V and provides bus protection.
The satellite motherboard is a standard CubeSat board provided by Pumpkin using a PIC24 microcontroller that serves as flight computer that runs on Pumpkin's Salvo Real Time Operating System. The satellite uses CubeSat-Kit interfaces for the reaction wheels, communication system and mass memory while the PCB ((Printed Circuit Board) is used for the attitude sensors, motor controller and payload. Payload data is stored in an SD card.
Figure 4: Illustration of the MicroSat-2 3U CubeSat (image credit: MIT/LL)
Communications are provided with a half-duplex L-3 Communications Cadet UHF nanosatellite radio. Operating at a frequency of 450MHz for uplink, the system achieves a data rate of 9.6 kbit/s with GFSK modulation and 16 kbit/s with FEC (Forward Error Correction). The downlink uses the 468 MHz UHF frequency for low data volumes and an S-band transmitter to reach 3 Mbit/s for payload data downlink services.
Figure 5: Block diagram of the MicroMAS-2 bus (image credit: MIT/LL)
Figure 6: MicroSat-2 elements (image credit: MIT/LL, Ref. 2)
Launch: The MicroMAS-2a nanosatellite was launched a secondary payload on 12 January 2018 (03:59 UTC) on the PSLV-40 flight vehicle (XL configuration) of ISRO. The launch site was the SDSC (Satish Dhawan Space Center) SHAR (Sriharikota) on the east coast of India. The primary payload on this flight was CartoSat-2F (formerly CartoSat-2ER) of ISRO with a mass of 710 kg. 5) 6)
Orbit: Sun-synchronous orbit with an altitude of 550 km and an inclination of 97.55º.
The co-passenger satellites comprise one microsatellite and one nanosatellite from India as well as one minisatellite plus 2 microsatellites and 25 nanosatellites from six countries, namely, Canada, Finland, France, Republic of Korea, UK and USA. The total mass of all the 31 satellites carried onboard PSLV-C40 is about 1323 kg.
The 28 international customer satellites are being launched as part of the commercial arrangements between Antrix Corporation Limited (Antrix), a Government of India company under Department of Space (DOS), the commercial arm of ISRO and the International customers.
• TeleSat LEO Phase 1, a communications minisatellite mission (168 kg) of Telesat Canada, built by SSTL, Surrey, UK.
• Carbonite-2, a microsatellite (~100 kg) of SSTL (X50 platform) to demonstrate video performance for the future Earth-i Vivid-i constellation. Earth-i is located at Surrey Research Park, Guildford, UK.
• IITMSAT [IIT (Indian Institute of Technology) Madras Satellite], also referred to as INS-1C, a student built microsatellite (11 kg) to study the energy spectrum of charged particles in the upper ionosphere.
• Microsat of ISRO in the 100 kg class, that derives its heritage from IMS-1 bus. This is a technology demonstrator and the forerunner for future satellites of this series. The satellite bus is modular in design and can be fabricated and tested independently of payload. 7)
• PicSat, a 3U CubeSat (3.5 kg) of the Paris Observatory, France. PicSat is an astronomy mission to measure exoplanetary transits.
• CANYVAL-X, 1, 2, a technology demonstration CubeSat mission (1U and 2U CubeSats) of Korea's Yonsei University and KARI (Korea Aerospace Research Institute) in collaboration with NASA; the goal is to demonstrate a Vision Alignment System.
• CNUSail-1 (Chungnam National University Sail-1), a 3U CubeSat solar sail test of Chungnam National University, Korea (4 kg).
• KAUSAT-5 (Korea Aviation University Satellite), a 3U CubeSat (4 kg) to observe the Earth with an IR camera and measure the amount of radiation around LEO.
• SIGMA (Scientific cubesat with Instruments for Global magnetic field and rAdiation) or KHUSAT-3 (Kyung Hee University Satellite-3), a 3U CubeSat to measure the global magnetic field and radiation.
• STEP CubeLab (Space Technology Experimental Project CubeSat Laboratory), a 1U CubeSat of Chosun University, Gwangju, Korea. The objective is to exploit core space technologies researched by domestic universities and verify the effectiveness of these technologies through on-orbit tests using the CubeSat.
• ICEYE-X1, Finland's SAR (Synthetic Aperture Radar) microsatellite with a mas of <100 kg.
• CICERO-7, a 6U CubeSat (~10 kg) of GeoOptics, USA, built by Tyvak, to demonstrate radio occultation observations.
• Arkyd-6A, a 6U CubeSat of Planetary Resources Inc., USA (formerly Arkyd Astronautics) to test attitude control, power, and communication systems as well as a photo-display-and-retransmission system.
• Fox-1D, a radio amateur and technology research 1U CubeSat, developed by AMSAT, USA and hosting several university developed payloads (University of Iowa, Virginia Tech, and Pennsylvania State-Erie).
• Lemur-2 x 4, 3U CubeSats of Spire Global Inc., San Francisco, CA.
• Landmapper-BC3 (Corvus-BC3), a 6U CubeSat (10 kg) of Astro Digital (former Aquila Space), USA to provide multispectral imagery of 22 m resolution on a swath of 220 km.
• MicroMAS-2a, a 3U CubeSat mission (3.8 kg) of MIT/LL (Massachusetts Institute of Technology/Lincoln Laboratory) of Lexington, MA, USA. Test of a compact microwave spectrometer and radiometer payload in orbit.
• SpaceBEE x 4 picosatellites, built to 0.25 CubeSat form factor, a technology demonstration, USA
• Flock-3p x 4, 3U CubeSats of Planet, San Francisco, USA.
• Tyvak 61C, a 3U CubeSat and a technology demonstration and astronomy mission of Tyvak Inc., Irvine CA, USA.
• May 3, 2018: According to William Blackwell of MIT/LL, MicroMAS-2a has been deployed and is working splendidly.
Figure 7: MicroMAS-2a on-orbit: First CubeSat microwave atmospheric sounder data (image credit: MIT/LL)
Figure 8: Lower tropospheric water vapor channel (image credit: MIT/LL)
Figure 9: MicroMAS-2 / TROPICS program of MIT/LL (image credit: MIT/LL)
• Cartosat-2F and 29 of the PSLV's secondary payloads separated from the PSLV in a 505 km sun-synchronous type orbit in the first 25 minutes of the mission. All satellites separated in 7 minutes (Ref. 5).
- The fourth stage of PSLV-C40 fired twice for short durations to achieve a polar orbit of 365 km height in which India's Microsat successfully separated.
Sensor complement: (Scanning Radiometer)
MicroMAS-2 uses a total-power passive microwave radiometer/scatterometer that is similar to deployed instruments, but uses miniaturized systems to fit within the 1U form factor in terms of mass, size and power/data availability.
Figure 10: The 1U form factor scanning radiometer of MicroMAS-2 (image credit: MIT/LL)
The microwave radiometer observes the radiance of the atmosphere at microwave wavelengths that are detected by an antenna which uses support electronics to detect and amplify the signals of given frequency bands. The detected power level for each frequency band is used to generate temperature and moisture profiles through the various regions of the atmosphere. Elements present in the atmosphere have different absorption spectra, allowing radiometers to observe different atmospheric constituents.
MicroSat-2 features a 12 channel radiometer in four microwave bands observing near 90 GHz for water vapor measurement and correction, 118 GHz for temperature, pressure and precipitation, 183 GHz for humidity and precipitation , and 206 GHz as another water vapor band.
Figure 11: Channels of MicroMAS-2 (image credit: NOAA)
Figure 12: Illustration of the MicroMAS-2 3U CubeSat with a spinning payload (image credit: MIT/LL)
1) William J. Blackwell, "New Small Satellite Capabilities for Microwave Atmospheric Remote Sensing ," Seventh Conference on Transition of Research to Operations, Seattle, Washington, AMS (American Meteorological Society), January 25, 2017, URL: https://ams.confex.com/ams/97Annual/webprogram/Paper314487.html
2) W. Blackwell, D. Cousins, L. Fuhrman, "New Small Satellite Capabilities for Microwave Atmospheric Remote Sensing: The Earth Observing Nanosatellite-Microwave (EON-MW)," August 6, 2017, URL: https://digitalcommons.usu.edu/cgi/viewcontent.cgi?filename=0&article=3571&context=smallsat&type=additional
3) "The MicroMAS-2 CubeSat," MIT, URL: https://tropics.ll.mit.edu/CMS/tropics/The-MicroMAS-2-Cubesat
4) W. Blackwell, J. Pereira, "New small satellite capabilities for Microwave Atmospheric Remote Sensing: The Earth Observing Nanosatellite-Microwave (EON-MW)," WJB May 20, 2015, URL: http://mstl.atl.calpoly.edu/~bklofas/Presentations/SummerWorkshop2015/4_Blackwell.pdf
5) "PSLV Successfully Launches 31 Satellites in a Single Flight," ISRO, 12 Jan. 2018, URL: https://www.isro.gov.in/update/12-jan-2018/pslv-successfully-launches-31-satellites-single-flight
6) Stephen Clark, "India's PSLV lifts off on first flight since fairing failure," Spaceflight Now, 12 January 2018, URL: https://spaceflightnow.com/2018/01/12/pslv-c-40-coverage/
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).