Japan’s space exploration legacy is poised to reach a significant milestone with the upcoming launch of the GOSAT-GW satellite, marking the final and 50th mission of the storied H-IIA rocket series.
This mission, officially named the Global Observing Satellite for Greenhouse gases and Water cycle (GOSAT-GW), is a keystone in the nation’s efforts to monitor and understand Earth’s climate, particularly the greenhouse effect and the global water cycle.
As the successor to the GOSAT and GOSAT-2 missions, GOSAT-GW embodies Japan’s commitment to advancing global climate science and supporting international environmental policy.
The Historical Context and Significance
Since its first launch in 2001, the H-IIA rocket has become a symbol of Japanese reliability and technological prowess in space. With a success rate of approximately 98%—having completed 49 out of 50 missions with only one notable failure in 2003—the H-IIA has carried a wide array of payloads, including the Himawari weather satellites and the Hayabusa2 asteroid probe.
The retirement of H-IIA marks the end of an era, as Japan transitions to the next-generation H3 rocket series, designed to reduce costs while enhancing capabilities.
The GOSAT-GW mission is not just a technological milestone but also a critical step in Japan’s long-standing dedication to environmental monitoring. The GOSAT series, which began with the launch of GOSAT (nicknamed “IBUKI”) in 2009 and continued with GOSAT-2 in 2018, has provided unprecedented global data on greenhouse gas concentrations, helping scientists and policymakers understand and mitigate climate change.
Mission Objectives and Scientific Goals
GOSAT-GW is a collaborative effort led by the Japanese Ministry of the Environment (MOE), the National Institute for Environmental Studies (NIES), and the Japan Aerospace Exploration Agency (JAXA).
The satellite’s primary objectives are:
- Continuous Monitoring of Greenhouse Gases: GOSAT-GW will observe the concentrations of carbon dioxide (CO₂) and methane (CH₄) across the entire atmosphere, not just at the surface, providing a more comprehensive picture of these critical greenhouse gases.
- Water Cycle Observation: The satellite will also monitor key parameters of the global water cycle, including atmospheric humidity, cloud properties, precipitation rates, soil moisture, ocean surface winds, and sea surface temperature.
- Support for Climate Policy: By ensuring the transparency and accuracy of national greenhouse gas inventories, GOSAT-GW will support the implementation of the Paris Agreement and contribute to international efforts to combat climate change.
- Refinement of Climate Projections: The mission aims to refine climate change projections by monitoring large-scale emission sources and improving our understanding of how greenhouse gases and water cycle dynamics interact.
Satellite Design and Instruments
GOSAT-GW is a medium-sized spacecraft with an estimated mass of about 2,900 kg and a power generation capability of 5.0 kW. It will be constructed by Mitsubishi Electric Corporation under contract with JAXA. The satellite will be placed in a sun-synchronous orbit at an altitude of 666 km, with an inclination of 98.06° and a repeat cycle of three days.
This orbit ensures consistent lighting conditions for observations and allows the satellite to revisit the same point on Earth every three days, maximizing data collection efficiency.
The satellite is equipped with two advanced instruments:
- TANSO-3 (Total Anthropogenic and Natural emissions mapping SpectrOmeter-3): This high-resolution nadir-scanning infrared spectrometer is designed to monitor the concentrations of CO₂, CH₄, and nitrogen dioxide (NO₂) across the globe. TANSO-3 features two imaging modes: a “Focus Mode” with a spatial resolution of 1–3 km and a swath width of 90 km, and a “Wide Mode” with a resolution of 10 km and a swath width of 911 km.
The instrument measures in three spectral bands (0.45 μm, 0.7 μm, and 1.6 μm), corresponding to the absorption spectra of these gases, and achieves spectral resolutions of less than 0.5 nm for the first two bands and less than 0.2 nm for the third. - AMSR3 (Advanced Microwave Scanning Radiometer 3): This multi-spectral imaging radiometer is tasked with monitoring the global water cycle. AMSR3 operates in 10 frequency channels between 6.925 GHz and 183.3 GHz, with a swath width of 1,535 km and spatial resolutions ranging from 3 km × 5 km to 34 km × 58 km, depending on the frequency.
The instrument will provide data on atmospheric humidity, cloud properties, precipitation rates, soil moisture, ocean surface winds, sea surface temperature, sea ice cover, and snow cover.
Scientific and Societal Impact
The data collected by GOSAT-GW will have far-reaching implications for both science and society. By measuring greenhouse gas concentrations across the entire atmosphere, the satellite will provide a more accurate representation of the global carbon budget than ground-based measurements alone.
This is crucial because greenhouse gas concentrations can vary significantly with altitude, and surface measurements do not capture the full picture of atmospheric composition.
The water cycle observations will enhance our understanding of how water moves through Earth’s system, improving weather forecasting, climate modeling, and disaster prediction.
The ability to monitor soil moisture, precipitation, and ocean surface conditions will help scientists better predict extreme weather events, such as floods, droughts, and typhoons, which have become increasingly severe in recent years.
GOSAT-GW will also play a vital role in supporting international climate policy. Under the Paris Agreement, countries are required to report their greenhouse gas emissions and take steps to reduce them.
The satellite’s observations will provide independent verification of national inventories, ensuring transparency and accountability in global climate action.
Technical Innovations and Challenges
The development of GOSAT-GW has involved significant technical innovation, particularly in the design of its instruments. The TANSO-3 spectrometer, for example, builds on the legacy of its predecessors but offers higher spatial resolution and more flexible imaging modes, allowing scientists to target both large-scale and localized emission sources.
The AMSR3 radiometer, meanwhile, represents a major advance in microwave remote sensing, with improved sensitivity and coverage compared to previous instruments.
One of the key challenges in the mission’s development has been ensuring the reliability and accuracy of the satellite’s measurements. Given the critical importance of the data for climate science and policy, JAXA and its partners have implemented rigorous testing and calibration procedures to minimize errors and maximize data quality.
Another challenge has been managing the satellite’s lifecycle and minimizing its impact on the growing problem of space debris. The Ministry of the Environment has established a study team to develop decommissioning plans for the GOSAT series, ensuring that retired satellites do not contribute to the proliferation of orbital debris.
The Broader Context: Japan’s Role in Global Climate Science
Japan has long been a leader in global climate science, with the GOSAT series serving as a cornerstone of international efforts to monitor greenhouse gases from space.
The data from GOSAT and GOSAT-2 have been widely used by researchers and policymakers around the world and have been cited in major reports such as the IPCC Sixth Assessment Report.
GOSAT-GW is expected to build on this legacy, providing even more detailed and comprehensive data to support climate research and policy.
The mission also reflects Japan’s commitment to international cooperation. By sharing its data with the global scientific community, Japan is helping to build a more comprehensive understanding of Earth’s climate system and supporting efforts to address the urgent challenge of climate change
Launch Details and Future Prospects
This will be the 50th and final launch of the H-IIA Launch Vehicle!
The GOSAT-GW satellite is scheduled to launch aboard the H-IIA rocket from the Tanegashima Space Center in Kagoshima Prefecture. The launch date has been targeted for late June 2025, with recent sources indicating a planned launch on June 30, 2025, at 4:33 PM UTC; however, some reports have listed earlier dates, such as June 23 or 24. The exact date may be subject to change due to technical or weather-related factors.
Once operational, GOSAT-GW is expected to remain in service until at least March 2032. During this period, the satellite will provide a continuous stream of data to researchers, policymakers, and the public, supporting a wide range of applications from climate science to disaster management.
Conclusion
The GOSAT-GW mission represents a fitting conclusion to the H-IIA rocket’s illustrious career, as well as a new chapter in Japan’s leadership in Earth observation and climate science. By combining advanced greenhouse gas monitoring with comprehensive observations of the water cycle, GOSAT-GW will provide invaluable data to help humanity understand and address the challenges of climate change.
As the world faces increasingly severe climate impacts, the insights generated by this mission will be essential for shaping effective policies and safeguarding the planet for future generations.
GOSAT-GW mission is a landmark for Japan, marking the final launch of the H-IIA rocket and advancing the country’s legacy in environmental monitoring. With its state-of-the-art instruments and ambitious scientific goals, the satellite will play a crucial role in global efforts to monitor greenhouse gases, understand the water cycle, and support international climate policy.
As the world looks to space for solutions to its most pressing environmental challenges, GOSAT-GW stands as a testament to the power of international cooperation and technological innovation.
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