code: public function toTDB()
      {
          if ($this->timescale == TimeScale::TDB()) {
              return $this;
          }
  
          $this->toTT();
          $tt1 = $this->jd;
          $tt2 = $this->dayFrac;
  
          $this->toUT1();
          $ut = $this->dayFrac;
  
          $dtr = IAU::Dtdb($tt1, $tt2, $ut, 0, 0, 0);
          IAU::Tttdb($tt1, $tt2, $dtr, $tdb1, $tdb2);
  
          $this->jd        = $tdb1;
          $this->dayFrac   = $tdb2;
          $this->timescale = TimeScale::TDB();
  
          return $this;
      }
docs: Converts this instance to Barycentric Dynamic Time (TDB)
  
  @return static