BEIJING, May 21 -- China is seeking payload proposals for its Mars sample return mission and inviting overseas researchers to participate.

The China National Space Administration (CNSA) has called on overseas research institutions, including those in Hong Kong and Macao, to submit proposals for developing payloads for the Tianwen-3 mission.

The mission, a significant part of China's planetary exploration program, is scheduled for launch around 2028.

The Tianwen-3 spacecraft comprises a lander, an ascent vehicle, a service module, an orbiter and a return module, and it is equipped with six scientific payloads.

The six payloads, namely, the Raman fluorescence spectrometer, ultra-wideband exploration radar, mid-infrared superfine imaging spectrometer, Mars global multicolor camera, descent ENA aurora detector and high-precision vector magnetometer, are all open to overseas researchers, according to a notice released by the CNSA.

The CNSA requires that all payload projects be led by a domestic institution, with no more than five entities involved in the joint development of a single payload.

Last month, the administration announced that it would offer payload resources for international cooperation, with up to 15 kilograms available on the orbiter and 5 kilograms on the service module.

The primary scientific objective of the mission is to search for signs of life on Mars. Other areas of exploration include the Martian climate and its evolution, the planet's geology and its internal processes.