China uses nuclear power to launch a mission to Neptune

Over the next decade (2023-2032) NASA will carry out a number of space missions in our Solar System, including orbiting and probing Uranus, in which they will study the structure the planet's interior, atmosphere, magnetosphere, and rings. Along with that is sending probes to the orbit of Enceladus - Saturn's sixth largest moon - and surface landers to study the active plumes emanating from the south polar region on Enceladus.

Enceladus is the sixth largest moon of Saturn. It was discovered by astronomer William Herschel in 1789. Before 1980, little was known about Enceladus other than the presence of water on the moon's surface. Enceladus is about 500km in diameter, one-tenth the size of Titan, Saturn's largest moon.

Not to be outdone, China is also contemplating building a nuclear-powered Neptune Explorer with the aim of exploring the ice giant planet in our Solar System (Neptune) and the largest moon. its (Triton), and its satellites and rings.

In fact, this mission was the subject of a study conducted by researchers from the China National Space Agency (CNSA), the Chinese Academy of Sciences (CAS), the National Atomic Energy Administration, and the Chinese Academy of Sciences. China University, China Academy of Space Technology, and many other universities and research institutes. The paper describing their findings (published in the journal Scientia Sinica Technologica) was written by Guobin Yu, a researcher with the School of Astronautics at Beihang University and the CNSA's Department of Science, Technology and Quality, top.

In fact, ice giants like Neptune are a treasure trove of potential scientific discovery, as the authors describe in their paper. In addition to its fascinating internal structure (including its rain of diamonds), Neptune is thought to have played an important role in the formation of the Solar System. In short, its composition includes a large amount of gas that is part of the protostar nebula from which our Solar System formed. At the same time, its position can also provide information about where the planets formed (and how they moved to get to their current orbits).

There are also ongoing mysteries about Neptune's largest moon - Triton - astronomers suspect that this is one that was splashed from an outer Solar System and then captured by Neptune's gravity.

The appearance of this moon is also thought to have caused certain effects with the natural satellites of Neptune, causing them to break apart and re-associate to form a new moon. It is also hypothesized that Triton will eventually break apart and form a ring around Neptune or collide with it. Essentially, the study of Neptune, its satellites, and the dynamics of its orbit can provide answers about how our Solar System formed, evolved, and how life began. .

Unfortunately, however, due to difficulties in sending deep space missions (including launch windows, power supply and communications), only one mission has visited so far. Neptune - Voyager 2 probe, it passed Neptune in 1989 and this is also the ship that gives us most of the knowledge about this ice giant and its system at the moment. in.

Furthermore, the nature of Voyager 2's scientific tools placed certain limitations on the amount of data it could capture. In recent years, NASA has proposed sending a mission to explore Neptune and Triton. However, this mission is not a priority for the next decade and has been transferred to the Uranus Orbiter and Probe (UOP).

But with the potential and enormous improvements that have been made in spacecraft instruments since Neptune was last visited, scientists in China realized that it was time for a new mission. another service to Neptune.

And when combined with NASA's Uranus exploration project, the data obtained from these missions will keep astronomers and planetary scientists busy for decades and could reveal a Some truly groundbreaking things about the outer Solar System - at least its history.

The Hubble Space Telescope's 2021 looks at Neptune, finding that a new "dark spot" storm detected in 2018 has reversed course and is moving north.

Design

Of course, the challenges mentioned above remain. Looking at the power supply problem, Guobin Yu and his colleagues needed a source that could safely and reliably supply electricity for 15 years. They determined that a radioisotope thermoelectric generator (RTG) with an energy capacity of 10 kilowatts (kWe) was sufficient. This type of nuclear battery is similar to the one used by the Curiosity and Perseverance rovers - converting heat energy from radioactive decay into electricity. As they say in the report:

"Considering the technical maturity of space reactor power supplies at different power levels, detector and electric motor power requirements, launch vehicle capabilities, and funding, the output capacity of the power supply for the space reactor for the mission Neptune is determined to be 10 kWe".

They further recommend that the power supply system is based on a scheme using a heat pipe, a thermoelectric converter and a radiator as a generating unit. And on board they will design many such generating units, which will then connect in parallel to power the spacecraft.

They write that the system will be able to provide the mission "8 years of maximum power operation of 10 kWe and 7 years of low power operation of 2 kWe, which can effectively guarantee the reliability and safety of the system." throughout the entire mission".

Schematic diagram of the 10 kW heat-tube fast reactor and power supply of the thermoelectric space reactor.

The team also identified several key processes required for the safe and reliable operation of this system. Among them, generators must ensure continuous and controllable heat generation from nuclear fission, heat transfer in reactors, efficient thermoelectric conversion and waste heat removal. To achieve this, their reactor design required Uranium-235 rods, a solid uranium-molybdenum alloy, and rod-shaped ceramic elements that allow for highly efficient transmission with a compact, lightweight core.

The spacecraft will also carry a number of instruments to study the planet, its systems, and objects along the way. This includes a Neptune Atmospheric Probe (NAP) to study the planet's interior and a Triton Penetration Probe (TPP) which will examine the moon's crust. Several smaller satellites (CubeSats or nano) will also be deployed along the way to explore the Main Belt and Centaur asteroids.

Mission Profile

To begin with, the team explored several possible methods for exploring Neptune (remote sensing, flybys, orbital observations, soft landings, etc.). Remote sensing and flybys were immediately ruled out because these would not allow the mission to effectively measure Neptune's deep composition and internal structure. They said: "The requirements are very high, and the task size, technical difficulty and funding are extremely large. Based on the scientific objectives, technical level and funding scale, the detection method identified as polar orbital detection".

Another consideration is that given the distance involved (average 30 AUs from the Sun) and the capability of a deep space mission, the probe's cruising speed should be increased as much as possible in the future. early stage. They further concluded that the best way to do this (and slow down to orbit Neptune) would be to do a launch around 2030, since it would be gravity-assisted by this time. Jupiter and the destination date would be 2036. Other launch opportunities include 2028, 2031, and 2034.

After completing orbit, the spacecraft will launch a series of small satellites and two probes to explore Neptune's atmosphere and Triton's surface.

China's space agency has made some pretty impressive moves in recent years, demonstrating how the country has become a space power. These include the development of heavy launch rockets such as the Long 9/3, the deployment of space stations (the Tiangong programme), and their success with the Chang'e and Tianwen programs that have brought explorers robot to the Moon and Mars.