Hongmeng project

Did You Know?

• The project's Chinese name, Hong Meng, is an ancient phrase describing a primeval chaos or the primordial Universe.
• The Hongmeng project is not related to the HarmonyOS system developed by Huawei, despite sharing the same Chinese word.
• The mother satellite is equipped with a high-gain antenna and a powerful on-board computer for processing interferometry data.

Background

The sky at frequencies below 30 MHz is largely unknown because ground observations are hindered by the ionosphere and radio frequency interference. The far side of the Moon offers an ideal environment for such observations, as it avoids the ionosphere and shields Earth's RFI. A lunar orbit observatory like Hongmeng can exploit these conditions more simply than a surface telescope, which would require soft landing, antenna deployment, and power for long lunar nights.

Mission concept

The project uses a single rocket to launch a mother satellite and several daughter satellites into lunar orbit. After insertion, the daughter satellites are released one by one to form a linear array on the same orbit, with the mother satellite at one end. When the array enters the quiet region behind the Moon, the daughter satellites make observations and transmit data via microwave to the mother satellite, which processes the interferometry data, stores it, and communicates with Earth when visible. The current design includes one mother satellite, eight daughter satellites for the 0.1–30 MHz band, and one daughter satellite for high-precision global spectrum measurement at 30–120 MHz. The eight low-frequency satellites are flat with deployable tripole antennas on both sides, forming an interferometric array with baselines up to 100 km. The high-frequency satellite has an ice-cream shape that serves as both antenna and body, minimizing chromaticity, and carries internal calibration mechanisms for precise whole-sky-averaged spectrum measurement. All satellites move in a circular orbit at 300 km altitude and 30° inclination. The mother satellite is placed about 10 km from its nearest daughter; the shortest spacing between daughters exceeds 100 m, and the longest is 100 km. The exact relative positions are not critical but must be accurately determined for interferometry, and the satellites have mechanisms to stay within a certain range.

Scientific objectives

The main science goals are to probe the cosmic Dark Ages and cosmic dawn via high-precision global spectrum measurement; to map the sky and catalog major sources at these wavelengths, revealing new astrophysical phenomena; and to observe the Sun and planets to study interplanetary space dynamics.

Development history

In 2014, a joint team from China, the Netherlands, and Poland proposed the DSL linear satellite array in response to a call by the European Space Agency and Chinese Academy of Sciences. Although not selected, further research continued as a conceptual development project and later as a prototype of the Chinese Academy of Sciences Space Science Strategic Research Project. During the Chang'e-4 mission, the Longjiang-2 micro-satellite was launched into lunar orbit as a pilot experiment for the lunar array concept.