Did China’s Tiandu-1 satellite beat US competitors with critical Earth-moon orbit?

China’s Tiandu-1 satellite has entered a critical fuel-efficient orbit that synchronises with the motion of the Earth and moon, but claims that it is the first spacecraft to achieve the feat have been challenged by US and Canadian experts.

The 3:1 resonant orbit – in which Tiandu-1 completes three loops of the Earth for every circuit made by the moon – is seen as a breakthrough for lunar infrastructure, including a BeiDou-like guidance system that will be needed for interplanetary exploration.

Developer Deep Space Exploration Laboratory said that “the Tiandu-1 navigation test satellite successfully carried out a key manoeuvre at perigee [the point in orbit when it is closest to Earth] on May 22 and precisely transitioned into a 3:1 Earth-moon resonant orbit”.

A Deep Space Exploration Laboratory schematic of the Tiandu-1 satellite taking part in a laser ranging experiment in April, before it was moved into the 3:1 resonance orbit. Photo: DSEL

“This made Tiandu-1 the first spacecraft to enter a round-trip 3:1 Earth-moon resonant trajectory,” according to a statement on the website of the laboratory based in Hefei, Anhui province in central China.

“Its flight data will provide support for advancing technologies such as orbit maintenance, control, and autonomous navigation in complex gravitational environments.”

Experts in the US and Canada immediately challenged the claim, pointing to Nasa’s 15-year-old Interstellar Boundary Explorer (IBEX) probe that entered a near-identical orbit in 2011, where it continues to operate.

Jonathan McDowell, a Harvard astronomer and space historian, and Canada-based amateur stargazer Scott Tilley both said it was debatable whether Tiandu-1 could lay claim to the title, with the IBEX craft’s achievement of near 3:1 resonance.

“Yes, indeed Tiandu-1 has entered a 3:1 resonance orbit. Whether it’s the first is debatable…IBEX launched in 2008 uses a similar orbit,” Tilley said.

South China Morning Post