Abstract: Water boiling in daily life is a common phenomenon of boiling, which contains profound and complex scientific mysteries. The understanding of boiling heat transfer has supported the first industrial revolution marked by steam engine and many subsequent industrial and engineering applications. Boiling process has great heat transfer capacity due to the release of latent heat of phase change, which is especially conducive to the lightweight design of thermal control system, and thus has important application potential for the development of related aerospace technology. The great difference between the density of gas and liquid phases in boiling phenomenon leads to the fact that the boiling characteristics are often dominated by gravity in the normal gravity environment on the ground. Due to the different gravity environments encountered in space missions, there is an increased demand for studying the gravity influence on boiling phenomenon. The project of vgBOILING, which is one of the first batch of scientific experimental tasks aboard the Experimental Module I of the Chinese Space Station (CSS), will study the scaling law of gravity on pool boiling heat transfer and bubble thermal dynamical behaviors. Using the long-term, stable variable gravity conditions provided by the Varying Gravity Rack (VGR) aboard the CSS Experimental Module I, the bubble thermal dynamical behaviors and related heat transfer performance of pool boiling in different gravity conditions will be studied experimentally, to reveal the influence and the underlying mechanism of gravity on boiling phenomenon, and then to construct the gravity scaling law of boiling process. The project will deepen the understanding of boiling heat transfer and support mankind's endless exploration of the mysteries of the universe.