code: public function toTT()
      {
          if ($this->timescale == TimeScale::TT()) {
              return $this;
          }
  
          $this->toTAI();
  
          $tai1 = $this->jd;
          $tai2 = $this->dayFrac;
          IAU::Taitt($tai1, $tai2, $tt1, $tt2);
  
          $this->jd        = $tt1;
          $this->dayFrac   = $tt2;
          $this->timescale = TimeScale::TT();
  
          return $this;
      }
docs: Converts this instance to Terrestrial Dynamic Time (TT)
  
  @return static