Tiandu

Tiandu satellites are a pair of Chinese Lunar Exploration Program's lunar navigation and communications test satellites based on Queqiao-2 relay satellite technology.

Design and development
Tiandu satellites will perform navigation and communications technology verification experiments while flying in formation in lunar orbit. Satellite-to-ground laser ranging as well as intersatellite microwave ranging techniques will also be tested.

The Tiandu satellites' mission is to inform the design of China's proposed Queqiao lunar navigation and communication array. Supporting services for lunar surface operations would be provided by such system. Line-of-sight communications limits affect uncrewed and crewed operations on the Moon, especially at the lunar south pole, an area of great interest, or the lunar far side.

The 61 kg Tiandu-1 carries a Ka dual-band integrated communication payload, a laser retroreflector, a space router and other payloads. The 15 kg Tiandu-2 carries a communication payload and navigation devices.

Mission
The mission was launched together as a single probe with Queqiao 2 in 2024 on a Long March 8 rocket.

After launch, the two satellites (while being attached to each other) underwent lunar orbit insertion on 24 March 2024 at 17:43 UTC and entered a large elliptical orbit around the Moon. In that large elliptical orbit around the Moon, they separated on 3 April 2024 and later satellite-to-ground laser ranging are inter-satellite microwave ranging are to be carried out by these satellites via high-precision lunar orbit determination technology.