BE55 ATX PLT PERFORMS A GEAR UP LNDG IN SAT.

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ARRIVING SAT FROM AUS; PLANNING A LNDG ON RWY 12R OR RWY 12L. APPROX 10 NM NE OF SAT TWR ADVISED ME TO EXPECT TO USE RWY 3 AND ASSIGNED HEADING 180 DEGS TO ENTER R DOWNWIND. ENTERING R DOWNWIND ABEAM THE LNDG THRESHOLD THE ACFT WAS CONFIGURED FOR LNDG. A GUMP CHK WAS COMPLETED AND I BEGAN A R TURN TO BASE. TWR INFORMED ME TO EXTEND DOWNWIND AND I WAS NOW #6 FOR LNDG. I BELIEVED I WAS IN POS TO BE FIRST FOR THE RWY. I EXTENDED DOWNWIND; RECONFIGURED THE ACFT FOR APCH (FLAPS APCH GEAR UP); AND BEGAN SEARCHING FOR THE TFC I WAS TO FOLLOW. AFTER TURNING BASE; ADVISING TWR I HAD THE TFC THE TWR INITIALLY ADVISED ME TO EXTEND DOWNWIND FOR A FALCON; BUT LEFT ME ON THE BASE AND TOLD ME TO KEEP MY SPD UP. ONCE ON FINAL I WAS CLOSING ON THE CARAVAN SO I RECONFIGURED FOR LNDG (GEAR DOWN; FLAPS LNDG). THIS WAS ABOUT 3 MI OUT. THE WIND WAS DOWN THE RWY AT 20 KTS; GUSTING TO 26 KTS. TURB WAS MODERATE. THE CARAVAN 'DISAPPEARED' IN THE TOUCHDOWN AND APCH LIGHTS OF THE RWY. I WAS LISTENING TO THE TWR TO DETERMINE MY CLRNC FOR LNDG AND THAT THE CARAVAN HAD CLRED THE RWY. MY ACFT CAME TO REST ON ITS BELLY ABOUT 1000 FT DOWN THE RWY SLIGHTLY L OF CTRLINE. IT SHOULD BE NOTED THAT THIS WAS NOT MY REGULAR RTE. I HAD RECEIVED MY 'NEW' RTE UPON THE COMPLETION OF MY FIRST LEG OF MY NORMAL RTE. POSSIBLE CONTRIBUTING FACTORS: RECEIVED A RE-ROUTING TO ARPTS I DO NOT NORMALLY VISIT. (STRANGE FREQS; ATC PROCS; ETC.) ANTICIPATED A LNDG SOONER THAN ACTUAL. (DIDN'T ANTICIPATE DELAYS.) THIS DISRUPTED MY NORMAL CHKLIST FLOW. POSSIBLE FAILURE OF ELECTRIC GEAR MOTOR AND OR ASSOCIATED CIRCUIT BREAKERS AND OR WIRING. (NOT KNOWN AT THE TIME OF THIS WRITING.)