TROPICS (Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats)
In March 2016, NASA selected t two proposals for new Earth science investigations that will put new instruments in low-Earth orbit to track harmful particulate air pollutants and study the development and lifecycles over much of TCs (Tropical Cyclones).The measurements will provide nearly all-weather observations of 3D temperature and humidity, as well as cloud ice, precipitation horizontal structure and instantaneous surface rain rates. These measurements and the increased temporal resolution provided by the CubeSat constellation, are needed to better understand the TC lifecycles and the environmental factors that affect the intensification of TCs. 1) 2) 3)
Observations of small atmospheric aerosols from the MAIA (Multi-Angle Imager for Aerosols) will be combined with health information to determine the toxicity of different particulate matter types in airborne pollutants over the world’s major cities.
The TROPICS investigation will develop and launch a constellation of CubeSats to study the development of tropical cyclones through rapid-revisit sampling. William Blackwell of MIT/LL (Massachusetts Institute of Technology'/Lincoln Laboratory) in Lexington is the PI (Principal Investigator) of the TROPICS mission.
• Relate the precipitation structure evolution, including the diurnal cycle, to the evolution of the upper-level warm core and associated intensity changes
• Relate the occurrence of intense precipitation cores (convective bursts) to storm intensity evolution
• Relate the retrieved environmental moisture measurements to coincident measures of storm structure (including size) and intensity
• Assimilate microwave radiances and/or retrievals in mesoscale and global numerical weather prediction models to assess impacts on storm track and intensity.
TROPICS mission significance to NASA and NOAA:
• First high-revisit microwave nearly global observations of precipitation, temperature, and humidity
• Fulfills most of the PATH (Precipitation All-weather Temperature and Humidity Soundings) Decadal Survey mission objectives using a low-cost, easy-to-launch CubeSat constellation
• Complements GPM, CYGNSS, and GOES-R missions with high refresh, near-all-weather measurements of precipitation and thermodynamic structure
• Increases understanding of critical processes driving significant and rapid changes in storm structure/intensity.
The TROPICS science program is directly relevant to three of the six NASA Earth Science Focus Areas: Weather, Water and Energy Cycle, and Climate Variability and Change. TROPICS addresses goals and objectives from the 2014 NASA Strategic Plan including advancing the understanding of Earth and developing technologies to improve the quality of life on our home planet (strategic goal 2) and advancing knowledge of Earth as a system to meet the challenges of environmental change and to improve life on our planet (objective 2.2).
The fundamental physical parameters required to address the TROPICS science objectives are 3D atmospheric temperature and humidity, storm intensity, and horizontal precipitation structure. These parameters have a long heritage of being derived from spaceborne PMW imagery and sounding channels (e.g., AMSU, ATMS, SSMIS). Practical considerations of antenna and instrument size and mass for a CubeSat system guide the selection of PMW (Passive MicroWave) channels for TROPICS.
Temperature and moisture profiles are retrievable from seven channels near 118 GHz and three near 183 GHz, respectively. Precipitation structure is obtained from a combination of 90 GHz, 206 GHz, and the temperature and moisture channels, with horizontal resolution matching that of the moisture data due to the high sensitivity to precipitation hydrometeors at 183 GHz. The 206-GHz channel will be sensitive to smaller ice particles than the 90-GHz channel and will generally produce a stronger signal. These observables link back to science requirements and to the primary sensor requirements (horizontal and vertical resolution and sensitivity).
The TROPICS constellation will consist of six 3U CubeSats, each about 30 cm long with a mass of 6 kg, that use scanning microwave radiometers to measure temperature, humidity, precipitation and cloud properties. The CubeSats will be launched into three separate orbital planes to enable the overall constellation to monitor changes in tropical cyclones as frequently as every 21 minutes.
The TROPICS team has previous experience developing CubeSats and analyzing satellite measurements of storms, and includes partnerships with NASA’s Wallops Flight Facility in Wallops Island, Virginia, Goddard, several universities and NOAA (National Oceanic and Atmospheric Administration).
Figure 1: Science objectives and significance to NASA/NOAA (image credit: MIT/LL)
Figure 2: A constellation of identical 3U CubeSats provide sounding (left CubeSat has a temperature profile of a simulated TC (Tropical Cyclone) from a NWP (Numerical Weather Prediction) model and 12-channel radiometric imagery (center CubeSat has simulated radiances from NWP model and radiative transfer model and the near right CubeSat has a single channel radiance image of a TC) with 30-minute median revisit rate to meet most PATH requirements (image credit: MIT/LL, NASA, Ref. 5)
Figure 3: Command, control, communication and data elements for the TROPICS constellation of 12 CubeSats (image credit: NASA)
Table 1: Participating organizations
Figure 4: TROPICS mission timeline (image credit: NASA)
Space Vehicles (SVs)
Each TROPICS CubeSat is a dual-spinning 3U CubeSat (6 kg) 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. Each commercially-procured CubeSat comprises a 2U spacecraft bus with ADCS, avionics, power, and communications, and a 1U spinning radiometer payload with highly integrated, compact microwave receiver electronics.
The spectrometer payload consists of a rotating passive RF antenna measuring spectral radiance as it rotates about the CubeSat velocity vector. The payload is based upon a similar design previously flown by MIT/LL on the MicroMAS-2 (Micro-sized Microwave Atmospheric Satellite-2)mission. However, a significant amount of redesign has been required to meet TROPICS performance and mission reliability requirements. The redesign includes:
1) Antenna modification to optimize ground profile while minimizing side lobes
2) Noise reduction in the analog front end
3) Higher-dynamic-range in the analog-to-digital converter
4) Modifications to spectrometer channel center frequencies and bandwidths
5) Higher-reliability control electronics
6) Higher-reliability and lower-power scanner assembly
A notional SV including the bus and payload is shown in Figure 5. The MicroMAS-2 bus does not have sufficient pointing accuracy or power generation capability to meet the TROPICS mission requirements. The TROPICS bus will match much of the functionality of the MicroMAS-2 bus, but will take advantage of recent advances in CubeSat bus technology and reliability.
BCT will build seven identical XACT-based 3U-class CubeSats for the TROPICS (Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats) mission. The satellites will be divided into three low-Earth orbital planes and will consist of a single high-performance radiometer payload hosted on each spacecraft bus. Each payload includes a BCT-designed motor as well as electronics to control the MIT/LL (Massachusetts Institute of Technology/Lincoln Laboratory) payload spin mechanism. 6)
Project development status
• June 30, 2021: The 2020 Atlantic hurricane season was one of the most brutal on record, producing an unprecedented 30 named storms. What’s more, a record-tying 10 of those storms were characterized as rapidly intensifying — some throttling up by 100 miles per hour in under two days. 7)
- To bring more data to forecasters and have a more consistent watch over Earth's tropical belt where these storms form, NASA has launched a test satellite, or pathfinder, ahead of a constellation of six weather satellites called TROPICS (Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats). Planned for launch in 2022, the TROPICS satellites will work together to provide near-hourly microwave observations of a storm's precipitation, temperature, and humidity – a revisit time for these measurements not currently possible with other satellites.
- “As a lifelong Floridian, I’ve seen firsthand the devastating impact that hurricanes can have on our communities. And as climate change is making hurricanes even stronger, it's more important than ever that NASA and our partners invest in missions like TROPICS to better track and understand extreme weather,” said NASA Administrator Bill Nelson. “NASA’s innovation is strengthening data models that help scientists improve storm forecasting and understand the factors that feed these monster storms. TROPICS will help to do just that and we look forward to next year’s launch of the TROPICS satellite constellation.”
Figure 6: When launched, the TROPICS satellites will work together to provide near-hourly microwave observations of a storm's precipitation, temperature, and humidity. The mission is expected to help scientists understand the factors driving tropical cyclone intensification and to improve forecasting models (video credit: NASA)
- "TROPICS is the beginning of a new era. This mission will be among the first to use a constellation of small satellites for these types of global, rapid-revisit views of tropical storms," said Scott Braun, the TROPICS project scientist and a research meteorologist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
- Since tropical cyclones and hurricanes can change rapidly as they travel across the ocean, the increased observations from the TROPICS satellites will not only advance the science of understanding storm intensity, they also may improve intensity forecasts.
- “The project holds great promise to boost NOAA’s steady improvements in weather and hurricane forecasts by feeding new environmental data into our world-class numerical weather prediction models,” said Frank Marks, director of the Hurricane Research Division of NOAA's Atlantic Oceanographic and Meteorological Laboratory. After all six satellites are launched and positioned in 2022, “this new constellation will provide high frequency temperature and humidity soundings as we seek to learn how hurricanes interact with the surrounding temperature and moisture environment—key data that could improve hurricane intensity forecasts.”
- A critical step to preparing for the constellation is the launch of a pathfinder satellite, a seventh identical copy of the TROPICS smallsats, that will enable full testing of the technology, communication systems, data processing, and data flow to application users in advance of the constellation’s launch. This will allow time for adjustments to the ground system and data products, helping ensure the success of the TROPICS mission.
- "The TROPICS Pathfinder satellite is similar to a screening before the opening night of a big show," said Nicholas Zorn, the Pathfinder program manager from MIT Lincoln Laboratory. "Its mission is a real-world, end-to-end test, from environmental verification through integration, launch, ground communications, commissioning, calibration, operations, and science data processing. Any areas for improvement identified along the way can be reinforced before the constellation launches.”
Figure 7: The TROPICS Pathfinder satellite, pictured above, was launched on 30 June 2021 on the Transporter-2 mission of SpaceX from Cape Canaveral, Florida. The satellite body measures approximately 10 cm x 10 cm x 36 cm and is identical to the six additional satellites that will be launched in the constellation in 2022. The golden cube at the top is the microwave radiometer, which measures the precipitation, temperature, and humidity inside tropical storms (image credits: Blue Canyon Technologies)
- MIT Lincoln Laboratory's William Blackwell is the TROPICS principal investigator. Six years ago, he submitted TROPICS as a proposal to NASA's Earth Venture Instrument competition series and was awarded funding. The Earth Venture Instrument program calls for innovative, science-driven, cost-effective missions to solve pressing issues related to Earth science.
- Aboard each TROPICS small satellite is an instrument called a microwave radiometer, which detects temperature, moisture, and rainfall in the atmosphere. On current weather satellites, microwave radiometers are about the size of a washing machine. On TROPICS’ small satellites the radiometers are about the size of a coffee mug.
- Microwave radiometers work by detecting the thermal radiation naturally emitted by oxygen and water vapor in the air. The TROPICS instrument measures these emissions via an antenna spinning at one end of the satellite. The antenna listens in at 12 microwave channels between 90 to 205 GHz, where the relevant emission signals are strongest. These channels capture signals at different heights throughout the lowest layer of the atmosphere, or troposphere, where most weather we experience occurs.
- By flying the TROPICS radiometers at lower altitude and detecting fewer channels than their larger counterparts, in the channels they do carry, the radiometers deliver comparable performance.
- Miniaturizing the microwave radiometer has been an incremental process over the last 10 years for Blackwell and his team, spurred by the invention of CubeSats, satellites the size of a loaf of bread that are often economical to launch. TROPICS builds on Blackwell and his team’s 2018 success in launching the first microwave radiometer on a CubeSat to collect atmospheric profiling data. The instrument aboard the TROPICS’ six satellites has been upgraded to provide improved sensitivity, resolution and reliability and will make more targeted and rapid weather observations.
- "These storms affect a lot of people, and we expect that with the increased observations over a single storm from TROPICS, we will be able to improve forecasts, which translates to helping people get to safety sooner, protect property, and overall enhance the national economy," Blackwell says, looking ahead to the full constellation launch next year. "It is amazing technology that we have proven out that allows us to maximize the science from the instrument's size factor. To pull this off has taken contributions of so many people."
- The TROPICS science team includes researchers from MIT Lincoln Laboratory and MIT Department of Aeronautics and Astronautics; NASA’s Goddard Space Flight Center; NOAA Atlantic Oceanographic and Meteorological Laboratory; NOAA National Hurricane Center; NOAA National Environmental Satellite, Data, and Information Service; University of Miami; Colorado State University; Vanderbilt University; and University of Wisconsin. The University of Massachusetts Amherst, Texas A&M University and Tufts University contributed to the technology development. Maverick Space Systems provided integration services for the Pathfinder, which was launched from SpaceX’s Transporter 2 mission. Astra Space Inc. is providing launch services for the constellation. NASA’s Launch Services Program based at Kennedy Space Center procured and is managing the Tropics Pathfinder launch service.
• February 26, 2021: NASA has selected Astra Space Inc. to provide a launch service for the agency’s Time-Resolved Observations of Precipitation Structure and Storm Intensity with a Constellation of SmallSats (TROPICS) mission. The TROPICS mission consists of a constellation of six CubeSats and will increase the scientific community’s understanding of storm processes. 8)
- The launch service contract for the TROPICS mission is a firm fixed-price contract valued at $7.95 million. NASA’s Launch Services Program at the agency’s Kennedy Space Center in Florida will manage the launch service.
- The CubeSats, each the size of a shoebox, will provide rapid-refresh microwave measurements that can be used to determine temperature, pressure, and humidity inside hurricanes as they form and evolve. The TROPICS mission’s high-revisit imaging and sounding observations are enabled by microwave technology developed at the Massachusetts Institute of Technology’s Lincoln Laboratory. These observations will profoundly improve scientists' understanding of processes driving high-impact storms.
- Astra Space will launch the CubeSats on the company’s Rocket 3 from Kwajalein Atoll in the Marshall Islands with three separate launches over a 120-day period. The TROPICS mission is targeted for launch between Jan. 8 and July 31, 2022, under a Federal Aviation Administration (FAA) launch license.
• September 7, 2020: Momentus launch provider of Santa Clara, CA, has announced a service agreement with NASA to transport the TROPICS Pathfinder CubeSat to LEO no later than 30 June 2021. The TROPICS Pathfinder CubeSat in the Planetary System Corporation 3U Canisterized Satellite Dispenser will be integrated onto Momentus' Vigoride transfer vehicle currently scheduled to launch on a SpaceX Falcon-9 dedicated rideshare mission. 9)
• The first TROPICS application workshop was held at the University of Miami, Miami, Florida, USA on 8-10 May 2017.
• NASA selected the mission as the winning proposal for the Earth Venture1–Instrument (EVI-3) Announcement of Opportunity in 2016. William Blackwell of MIT/LL (Massachusetts Institute of Technology/Lincoln Laboratory) is the principal investigator for TROPICS. 10)
Launch: Astra Space will launch the CubeSats on the company’s Rocket 3 from Kwajalein Atoll in the Marshall Islands with three separate launches over a 120-day period. The TROPICS mission is targeted for launch between Jan. 8 and July 31, 2022, under a Federal Aviation Administration (FAA) launch license (Ref. 8).
Orbit: Near circular orbit of 600 km altitude (550±50 km tolerance), 30° inclination (±3° tolerance).
Sensor complement (Two Radiometers)
TROPICS will fly two total power radiometers that measure 12 channels spanning approximately 90 to 206 GHz. The “WF-band” radiometer comprises eight channels from 90–119 GHz, and the “G-band” radiometer comprises four channels from 183–206 GHz. The radiometer block diagram is shown in Figure 8. The specific channel properties are shown in Table 2. The full-width at half maximum antenna beamwidths are achieved using an offset parabolic reflector illuminated with two electroformed feed horns that are physically separated, and the beams are combined and collocated using a polarizing wire grid diplexer. 11)
The antenna engineering model is shown in Figure 9. Beam efficiencies for the temperature and water vapor sounding channels are designed to exceed 95%. The simulated G-band antenna patterns are shown in Figure 10 and measured return loss of the G-band feedhorn is shown in Figure 11. Excellent performance is indicated in both the pattern and return loss data. Radiometer calibration is accomplished using weakly coupled noise diodes with known and stable noise output that are turned on and off against the cold space background. Satellite intercalibration is optimized using cross comparisons (12)) and daily calculated numerical model residuals (13)) to derive and implement any needed bias corrections. The W/F-band receiver assembly is shown in Figure 12. A custom SiGe MMIC was developed at UMass-Amherst to provide and RF amplifier, mixer, and IF preamplifier in a highly integrated package.
Figure 9: Fabricated engineering model of the TROPICS antenna assembly. The 90-120 GHz feedhorn is visible in the front of the photo, and the 180-205 GHz feedhorn can be seen through the wire grid (image credit: Thomas Keating, LTD)
The radiometer operates in an “integrate-while-scanning” mode that results in elongated footprints in the cross-track direction. The spatial resolution is thus reported as the geometric mean of the minor and major axes of the ellipse projected on the earth, also accounting for earth curvature. As the constellation of six satellites scans the earth, the footprints near the edge of the scan are revisited more often than the footprints near nadir. This is effect is quantified by calculating an “effective” spatial resolution that weights the spatial resolution of each footprint by the relative frequency by which it is revisited. The nadir, mean-across-scan, and effective spatial resolutions are shown in Table 3. The satellite pointing accuracy and sensor mounting requirements are set to ensure geolocation errors are smaller than approximately 10% of the footprint size.
Table 3: TROPICS spatial resolution (shown in km) for W, F, and G-band channels are shown at nadir and averaged over the 81 footprints in the swath. Also shown is the “effective” spatial resolution that accounts for how often the footprints are revisited across the scan
The temperature weighting functions for all 12 TROPICS channels are shown in Figure 13. Channel passbands are designed to span altitudes from the surface up to 20 km for temperature and 10 km for water vapor. Multiple temperature channels probe the upper troposphere to observe tropical cyclone warm core anomalies.
Figure 12: The TROPICS W/F-band receiver assembly in development by UMass-Amherst. Shown from L–R are the coupled noise diode module, the RF preamplifier module, and the SiGe mixer/tripler/amplifier module (image credit: UMass, MIT/LL)
Figure 13: Weighting functions calculated at nadir incidence over a perfectly emissive surface for a standard tropical atmosphere for both a) temperature/imaging and b) water vapor/imaging channels (image credit: MIT/LL)
TROPICS summary: TROPICS will be the first demonstration that science payloads on low-cost CubeSats can push the frontiers of spaceborne monitoring of the Earth to enable system science and will fill gaps in our knowledge of the short time scale — hourly and less — evolution of tropical cyclones, where current capabilities are an order of magnitude slower. The TROPICS mission will implement a spaceborne earth observation mission designed to collect measurements over the tropical latitudes to observe the thermodynamics and precipitation structures of TCs over much of the storm lifecycle. The measurements will provide nearly all-weather observations of 3D temperature and humidity, as well as cloud ice and precipitation horizontal structure. These measurements and the increased temporal resolution provided by the CubeSat constellation, are needed to better understand the TC lifecycles and the environmental factors that affect the intensification of TCs (Ref. 3).
The TROPICS 3U CubeSats will interface with the KSAT-lite ground station network to allow for satellite command and control and downlink of bus and payload telemetry for each CubeSat in the constellation.
Data Processing: MIT/LL will interact with the mission operations provider to acquire the downlinked raw science data and format it into data products that can be shared with the data processing center at the University of Wisconsin. The data products will be made available to the data processing center via a secured connection. The data will be stored at MIT/LL in a SQL database on a MIT/LL computer system that includes disk redundancy and data backups. The entire mission data set will be stored at MIT/LL for the duration of the TROPICS project. The key elements of the TROPICS mission are shown in Figure 14.
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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).