code: public function toTAI()
      {
          if ($this->timescale == TimeScale::TAI()) {
              return $this;
          }
  
          $this->toUTC();
  
          $utc1 = $this->jd;
          $utc2 = $this->dayFrac;
          IAU::Utctai($utc1, $utc2, $tai1, $tai2);
  
          $this->jd        = $tai1;
          $this->dayFrac   = $tai2;
          $this->timescale = TimeScale::TAI();
  
          return $this;
      }
docs: Converts this instance to International Atomic Time (TAI)
  
  @return static