The Black Hole Explorer (BHEX) is a proposed space-based mission aimed at detecting and measuring the shape of the photon ring around supermassive black holes M87* and Sgr A*. The photon ring, predicted by general relativity, is a bright, thin ring formed by photons orbiting the black hole before escaping. It is insensitive to the details of the surrounding emission and provides a direct probe of the Kerr geometry of the black hole. BHEX will use radio-interferometric observations at frequencies of 100 GHz to 300 GHz from an orbital distance of ~30,000 km to measure the photon ring's shape, confirming the Kerr nature of the black hole and estimating its mass and spin. The photon ring's structure is determined by the black hole's mass and spin, and its shape can be analyzed through interferometric signatures in the visibility domain. The mission will target the photon rings of M87* and Sgr A*, with the choice of orbit crucial for detecting these rings. BHEX will use space-based VLBI observations to access the visibility window containing one full period of the photon ring's ringing. The mission's design enables the measurement of the photon ring's shape, providing insights into the black hole's parameters. The photon ring's interferometric signature is a characteristic periodic oscillation in the radio visibility, which can be extracted from the visibility plane. The shape of the photon ring is determined by the black hole's mass and spin, and its measurement can provide information about the black hole's parameters. The BHEX mission aims to measure the photon ring's shape, confirming the Kerr nature of the black hole and estimating its mass and spin. The mission's design enables the measurement of the photon ring's shape, providing insights into the black hole's parameters. The photon ring's interferometric signature is a characteristic periodic oscillation in the radio visibility, which can be extracted from the visibility plane. The shape of the photon ring is determined by the black hole's mass and spin, and its measurement can provide information about the black hole's parameters. The BHEX mission aims to measure the photon ring's shape, confirming the Kerr nature of the black hole and estimating its mass and spin.The Black Hole Explorer (BHEX) is a proposed space-based mission aimed at detecting and measuring the shape of the photon ring around supermassive black holes M87* and Sgr A*. The photon ring, predicted by general relativity, is a bright, thin ring formed by photons orbiting the black hole before escaping. It is insensitive to the details of the surrounding emission and provides a direct probe of the Kerr geometry of the black hole. BHEX will use radio-interferometric observations at frequencies of 100 GHz to 300 GHz from an orbital distance of ~30,000 km to measure the photon ring's shape, confirming the Kerr nature of the black hole and estimating its mass and spin. The photon ring's structure is determined by the black hole's mass and spin, and its shape can be analyzed through interferometric signatures in the visibility domain. The mission will target the photon rings of M87* and Sgr A*, with the choice of orbit crucial for detecting these rings. BHEX will use space-based VLBI observations to access the visibility window containing one full period of the photon ring's ringing. The mission's design enables the measurement of the photon ring's shape, providing insights into the black hole's parameters. The photon ring's interferometric signature is a characteristic periodic oscillation in the radio visibility, which can be extracted from the visibility plane. The shape of the photon ring is determined by the black hole's mass and spin, and its measurement can provide information about the black hole's parameters. The BHEX mission aims to measure the photon ring's shape, confirming the Kerr nature of the black hole and estimating its mass and spin. The mission's design enables the measurement of the photon ring's shape, providing insights into the black hole's parameters. The photon ring's interferometric signature is a characteristic periodic oscillation in the radio visibility, which can be extracted from the visibility plane. The shape of the photon ring is determined by the black hole's mass and spin, and its measurement can provide information about the black hole's parameters. The BHEX mission aims to measure the photon ring's shape, confirming the Kerr nature of the black hole and estimating its mass and spin.