On January 19, according to foreign media reports, American space exploration technology company SpaceX installed a full set of flight protective cover on its super heavy rocket booster prototype BN4 for the first time, which will become the killer mace for the recovery of its rockets and star ships < p > < / P > < p > this flight protective cover is called aerocover. In fact, it is a thin steel shell installed on six metal box frames outside the booster. They can protect the booster from the earth's atmosphere during ground test, takeoff, ascent and re-entry. In addition to protection, the grooves on the top of aerocove also provide redundancy for hydraulic systems, pressure vessels, avionics and heat exchangers for ultra heavy boosters < p > at the same time, the interior of the flight protective cover is also covered with electronic equipment, composite materials, thousands of meters of wires and thin pipes. However, for safety purposes, they are far from the Raptor engine. In order to survive re-entry and still land and recover under good enough conditions, each component installed outside the super heavy booster needs to be carefully protected. This is the original intention of SpaceX to install the flight protective cover < p > except for the steel used in the booster body, other parts directly exposed to supersonic vibration and heating during re-entry may fail or be completely destroyed. SpaceX's Falcon 9 rocket booster almost always uses re-entry combustion to slow down and creates a heat shield through its own exhaust design. In contrast, SpaceX's ultra heavy booster can withstand all the pressure during reentry without additional combustion to cushion the impact < p > before installing the full flight protective cover on BN4, SpaceX installed the protective cover on a pair of hydraulic and heat exchanger racks, but did not cover all four composite outer packaging pressure vessel (COPV) racks and umbilical ports. On December 30, BN4 left the launch pad for the third time, and both newly installed shields were unloaded. However, on January 14, 2022, SpaceX quickly installed all six shields for the first time and began sealing them. On January 17, SpaceX even installed aerocover around the protruding umbilical port of BN4, eliminating any envisaged airflow around the equipment < p > before installing the main aerocover, SpaceX also installed at least six small boxes, which should be to protect some important metal detectors. They can pass through the storage tank and shell of the super heavy booster and connect to the inside of the avionics box. Since then, the project team has also completed the BN4 Raptor engine heat shielding system, using a large number of similar steel plate covers and panels < p > at present, BN4 may be completed with only a few parts, and full preparations have been made for static ignition test. More likely, these flight shields and Raptor heat shields are essential for the BN4, allowing it to conduct multiple tests at once without requiring immediate major maintenance. Starships mostly test three engines, only a few static ignition tests of six engines, and BN4 may eventually ignite all 29 Raptor engines at the same time < p > when so many engines are involved, even the simplest precombustion test may fail, resulting in the destruction of the tail of the booster. For static ignition tests, raptor engines usually produce smaller, shorter (but still large) fireballs, which is another potential source of damage to any sensitive hardware located anywhere in the thrust part of BN4. Therefore, the importance of flight protective cover in static ignition may be as important as that of booster in launch and recovery landing < p > it is not clear whether or when BN4 will be returned to the orbital launcher for pre launch status training (WDR) and static ignition test of key facilities and equipment. The test window of SpaceX is still unclear, but it is planned to be carried out from 10 a.m. to 10 p.m. on January 19 and 20 et. (small) < / P > < p >