Research
Space Transportation System Laboratory (STL) has studied issues that appear in spacecraft during atmospheric entry. Various phenomena occur in entry, descent, and landing (EDL) processes. One of the most critical stages in space missions is characterized by the fact that the spacecraft enters into the atmosphere with a high velocity and is decelerated by aerodynamic forces.

Targets
The flow field around spacecraft widely varies in the EDL phase. For example, the following phenomena and problems occur in the spacecraft:

• Effects related to free molecular flow and rarefied gas dynamics are notable at low Earth orbit at an altitude above 100 km.
• Hypersonic and low Reynolds number flow appears at the entry phase between altitudes in 100 km and 50 km. In the region, aerodynamic heating and radio-frequency blackout are important problems for spacecraft.
• Aerodynamic instability has been confirmed at the decent phase between altitudes in 50 km and 10 km. In this region, transonic or supersonic flow with turbulence significantly impacts spacecraft’s aerodynamic characteristics. Critical events such as parachute opening are also at this altitude.
• Aerodynamic deceleration is almost complete and the spacecraft reaches terminal velocity at the landing phase at altitudes below 10 km. The uncertainty of gust and atmospheric density becomes important for the aerodynamics of the spacecraft. Accurate prediction of the aerodynamic characteristics is strongly demanded, to improve the accuracy of landing point prediction.

We are trying to solve these phenomena and problems by using computational approaches and wind tunnel tests.

Methods
STL is involved in computational approaches using high-performance computers such as the Fugaku, and in experiments using large wind tunnels at JAXA and other institutions. STL is collaborating with JAXA and several universities to contribute to spacecraft design and development and to space missions using spacecraft.