LiteBIRD Successfully Passed Mission Definition Review #2, Advancing to Phase A
The LiteBIRD international space mission, led by the Japan Aerospace Exploration Agency (JAXA), has successfully completed its Mission Definition Review #2 (MDR#2).
LiteBIRD is an international space mission designed to observe the polarization of the Cosmic Microwave Background (CMB) over the entire sky. Its primary scientific objective is to test cosmic inflation by searching for the primordial B-mode polarization signature generated by primordial gravitational waves in the early Universe. In addition, the mission is expected to deliver a broad range of scientific results in cosmology, particle physics, and astrophysics through its high-sensitivity, multi-frequency polarization observations.

MDR#2 provided a comprehensive assessment of the mission’s scientific goal and objectives, system configuration, development plan, and international collaboration framework. The completion of MDR#2 represents an important milestone in further developing and consolidating the LiteBIRD mission concept and implementation plan. The project will now continue the processes toward the Project Preparation Stage (Phase A) while advancing the design of the spacecraft and scientific instrument, the science data-analysis framework, and the international development organization.

During Phase A, the mission team will further accelerate the design of the instrument and spacecraft in parallel with the requirement flowdown studies. It is also essential to advance the development of the science ground segment, data analysis infrastructure, and international collaboration framework required for the mission.
LiteBIRD is a global collaboration involving research institutions across Japan, Europe, and North America. Successfully passing MDR#2 was made possible by the dedicated efforts of scientists, engineers, and partner agencies and organizations worldwide. The collaboration will continue working together toward realizing the mission and addressing some of the most fundamental questions about the origin and evolution of our Universe.

The mission of LiteBIRD is to uncover the origins of the universe and how it began. The Big Bang theory of the universe is now widely accepted after the accumulation of empirical evidence from many prior space and ground-based experiments. But the Big Bang alone cannot fully explain the evolution of the current universe or what happened in the earliest moments of time. The addition of the theory of cosmic inflation, a short period of rapid exponential expansion of space in the early universe, is the prevailing theory that can explain these shortfalls. The LiteBIRD mission aims to find evidence of cosmic inflation through observations of the cosmic microwave background (CMB).

The CMB radiation is remnant light from when the early universe was still a hot plasma. The CMB is very uniform up to approximately one part in 100,000, but these faint variations or anisotropies allow us to accurately probe the earliest state of the universe. Inflation is theorized to create unique primordial gravitational waves that imprint a distinct pattern in the CMB’s polarization signal called the primordial B-modes. These B-modes are “smoking-gun” evidence of cosmic inflation.

The LiteBIRD mission will aim to detect the primordial B-mode signal through developing a CMB spacecraft with a millimeter-wave polarization-sensitive telescope installed. The LiteBIRD spacecraft will observe the entire sky for 3 years at the Sun-Earth Lagrangian point L2 in space. LiteBIRD will achieve unprecedented sensitivities through implementing in total approximately 4,000 transition edge sensor detectors across 12 observational frequency bands and will be capable of distinguishing between the CMB and foreground (dust, synchrotron radiation, etc.) signals. The telescope will be cryogenically cooled to 5 K low temperatures to reduce thermal noise. LiteBIRD will uniformly observe the entire sky with its wide field-of-view and optimized scan strategy utilizing the spacecraft’s spin.

LiteBIRD is a JAXA-led international mission in collaboration with various space agencies and research institutions in Europe (France, Germany, Italy, the Netherlands, Norway, Spain, Switzerland, and the United Kingdom) as well as Canada. The domestic collaborators include the University of Tokyo and Okayama University. The LiteBIRD mission is aiming for a launch in JFY2036 (JFY: Japanese fiscal year).

2024-10-09  The following was reported to the government’s space science and exploration sub-committee:
In response to KEK’s management decision to relinquish their responsibility for the development of their original technological contribution, the LiteBIRD team will continue investigating reformation plans for approximately one year. After which ISAS/JAXA will judge the continuation of the project.

2025-09-25  The reformation plan was evaluated, and it was concluded that the team should continue and further accelerate the development toward the mission definition review planned in the summer of 2026. The international team will continue collaborative and unified efforts for the reformation studies.

2026-06-26  The Mission Definition Review #2 was conducted to evaluate the significance and value of the reformed mission, as well as the validity of the project plan. As a result, the ISAS/JAXA concluded that the project is ready to proceed to the Project Preparation phase (Phase A).