Consider it the "mother of all tests."

This summer, the PACE spacecraft (short for Plankton, Aerosol, Cloud, ocean Ecosystem) completed a critical phase of its launch journey: the thermal vacuum test (TVAC), where it was subjected to extreme temperatures and pressures in a specialized chamber at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

The objective? To verify the performance of the satellite once it's launched and operational.

"This is the best way to simulate what PACE will experience in space," said Craig Stevens, spacecraft systems lead.

A comet called Nishimura discovered just a month ago could be visible to the naked eye this weekend, offering stargazers a once-in-a-437-year chance to observe the celestial visitor.

The ball of rock and ice, whose exact size remains unknown, is named after the Japanese amateur astronomer Hideo Nishimura who first spotted it on August 11.

It is rare that comets reach their moment of peak visibility so soon after being discovered, said Nicolas Biver, an astrophysicist at the Paris Observatory.

"Most are discovered months, even years before they pass closest to the sun," he told AFP.

The comet only swings by the sun every 437 years, he said, a long orbital period which sees it spend much of its time in the freezing outer solar system.

In recent decades, drag-free satellites have been used in high-precision missions, such as testing the general relativity, verifying the geodetic and frame-dragging effects, measuring Earth's gravity field, etc. In space gravitational wave detection, drag-free satellites play an important role.

Previous research on the drag-free satellite has focused on the drag-free control algorithm. Nevertheless, science mode and nonscience mode have different control forces, sensor measurement range, measurement noise, and reaction force noise. Therefore, the different controllers for the capture control mode and the high-accuracy control mode of the test mass (TM) need to be designed.

However, it is easy to cause system instability or even uncontrollability when switching between different controllers. Research on the switching control between different modes is very important. In the drag-free satellite, there is little research on the switching control between different modes. Multi-degree of freedom strong coupling and controller saturation remains an urgent problem to be solved.