LiteBIRD, the next-generation cosmic microwave background (CMB) experiment, aims for a launch in Japan’s fiscal year 2032, marking a major advancement in the exploration of primordial cosmology and fundamental physics. Orbiting the Sun-Earth Lagrangian point L2, this JAXA-led strategic L-class mission will conduct a comprehensive mapping of the CMB polarization across the entire sky. During its 3-year mission, LiteBIRD will employ three telescopes within 15 unique frequency bands (ranging from 34 through 448 GHz), targeting a sensitivity of 2.2 μK-arcmin and a resolution of 0.5° at 100 GHz. Its primary goal is to measure the tensor-toscalar ratio r with an uncertainty δr = 0.001, including systematic errors and margin. If r ≥ 0.01, LiteBIRD expects to achieve a > 5σ detection in the ℓ = 2–10 and ℓ = 11–200 ranges separately, providing crucial insight into the early Universe. We describe LiteBIRD’s scientific objectives, the application of systems engineering to mission requirements, the anticipated scientific impact, and the operations and scanning strategies vital to minimizing systematic effects. We will also highlight LiteBIRD’s synergies with concurrent CMB projects.
LiteBIRD is a JAXA-led space mission for cosmic microwave background (CMB) polarimetry. One of the challenges in terms of the telescope optics is to characterize and suppress the effects of the far sidelobes in the antenna beam patterns, which contaminate the CMB signals with Galactic foreground radiation. For the Low-Frequency Telescope (LFT; 34 - 161 GHz) aboard LiteBIRD, the requirements include the far-sidelobe knowledge of −56 dB. Because the LFT will operate at 5 K, we investigate the technical feasibility of near-field antenna pattern measurements in a cryogenic chamber. We implement a cryogenic-compatible millimeter-wave circuit and motorized stages inside a chamber and scanned the aperture fields of the LFT, which is fully encased and cryogenically cooled in the chamber. As a pilot experiment in the design phase of the development of the LFT, we have demonstrated such a measurement technique using a 1/4-scaled LFT at 150 K.
LiteBIRD is a JAXA-led international project aimed to make high sensitivity measurements of the primordial B modes through cosmic microwave background (CMB) polarization observations. The Low-Frequency Telescope (LFT) is a modified crossed Dragone reflective telescope with a 18° × 9° field-of-view across the 34-161 GHz. To achieve the required observational sensitivity, the telescope’s sidelobe response must be characterized to high precision to minimize signal contamination systematic effects from galactic and foreground emission. We report on the development of LFT optical simulation models that include the reflector optics, optimized serrations, finite absorptivity baffling, and V-grooves, and characterize the LFT sidelobes accounting for multiple reflection and diffraction optical effects. We find that the implementation of triangular and cos2 shaped serrations on the primary and secondary reflectors are effective in reducing asymmetric sidelobe power fluctuations to ≤ 1.42×10−4 and ≤ 1.20 × 10−4, respectively, at 34 GHz at 5.5° ≤ θbeam ≤ 35° from the beam center. Without telescope baffling, the LFT optics show prominent direct sidelobe and diffuse triple reflection sidelobes with peak powers of ≤ −35.49 dB and ≤ −38.65 dB, respectively. It was found that implementing a finite absorptivity focal plane (FP) hood and forebaffle allows for effectively mitigating these sidelobes to ≤ −58.66 dB at 34 and 42 GHz for θ > 45° from boresight. Further including V-grooves in the optical simulation model, it was found that the V-grooves attenuate the far sidelobe power at El < −50° to ≤ −74.8 dB. All these far-sidelobe features are found to be below the LiteBIRD sidelobe knowledge requirement levels.
LiteBIRD is a JAXA-led international project aimed to make high sensitivity measurements of the primordial B-modes through cosmic microwave background (CMB) polarization observations. LiteBIRD is expected to launch in the late 2020s. The Low Frequency Telescope (LFT) has a 400 mm diameter aperture and will observe at 34-161 GHz. The LFT is an optimized crossed Dragone reflective telescope with high order correction terms in the reflector shapes to maximize its diffraction-limited throughput across a 18° x 9° FOV. We will report on the development of the LFT optics design and assess the optical tolerances for potential misalignments and reflector deformations.
LiteBIRD is a JAXA-led international project that aims to test representative inflationary models by performing an allsky cosmic microwave background radiation (CMB) polarization survey for 3 years at the Sun-Earth Lagrangian point L2. We aim to launch LiteBIRD in the late 2020s. The payload module (PLM) is mainly composed of the Low-Frequency Telescope (LFT), the Mid-Frequency Telescope and High-Frequency Telescope (MHFT), and a cryo-structure. To conduct the high-precision and high-sensitivity CMB observations, it is required to cool the telescopes down to less than 5 K and the detectors down to 100 mK. The high temperature stability is also an important design factor. It is essential to design and analyze the cryogenic thermal system for PLM. In this study, the heat balance, temperature distribution, and temperature stability of the PLM for the baseline design are evaluated by developing the transient thermal model. The effect of the Joule-Thomson (JT) coolers cold tip temperature variation, the periodical changes in subK Adiabatic Demagnetization Refrigerator (ADR) heat dissipation, and the satellite spin that generates the variable direction of solar flux incident are implemented in the model. The effect of contact thermal conductance in the LFT and the emissivity of the V-groove on the temperature distribution and heat balance are investigated. Based on the thermal analysis, it was confirmed that the PLM baseline design meets the requirement of the temperature and the cooling capability of the 4K-JT cooler. In addition, the temperatures of the V-groove and the LFT 5-K frame are sufficiently stable for the observation. The temperature stability of the Low Frequency Focal Plane (LF-FP) is also discussed in this paper.
LiteBIRD is a spacecraft to observe the polarization signal of the cosmic microwave background radiation (CMB). In the development of its payload module, it is important to design the mechanical structures with enough rigidity to withstand the launch environment while providing enough thermal insulation to cool the telescopes down to 5 K. We need to reduce the mass of the 5-K structure, which consists of three telescopes, the low-frequency telescope (LFT) led by JAXA and the mid-frequency and high-frequency telescopes (MFT and HFT) led by CNES. In this paper, we report the mechanical design of the LFT and the structural analysis using Nastran. We made a structural mathematical model of the LFT and performed modal and quasi-static analyses. We successfully reduced the LFT mass while keeping the natural resonance frequency higher than requirements. Additionally, we report the mechanical design and the current status of the structural analysis for the payload module.
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