BA46 FLC DIVERTS TO ANOTHER ARPT DUE TO LOW FUEL WHEN ARPT OF INTENDED LNDG HAS EXTENDED CLOSE DUE AN EMER AND AN ALTERNATE REQUIRED LENGTHY DELAYS BECAUSE OF BEING A MIL AIRFIELD.

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DEPARTED DEN WITH 10000 LBS OF FUEL. NO ALTERNATE REQUIRED. FUEL BURN TO RAP PLANNED AT ALMOST 5000 LBS. AVERAGE BURN INFLT = 5000 LBS PER HR. UPON ARR IN RAPID CITY AREA; USING ELLSWORTH AFB APCH RADAR; WE WERE ADVISED RAP RWY 32 WOULD BE CLOSED FOR ABOUT 15 MINS DUE TO AN EMER IN PROGRESS. AFTER THE 15 MIN HOLD; OUR FUEL WAS DOWN TO 4000 LBS. THE CTLR TOLD US RAP WOULD BE CLOSED FOR ANOTHER 5-10 MINS. OUR CONTINGENCY FUEL (45 MINS) IS 3000 LBS. I ASKED APCH IF IT WOULD BE POSSIBLE TO LAND AT ELLSWORTH AFB IF WE GOT SHORT ON FUEL. HE SAID WE COULD IF WE DECLARED AN EMER. ANOTHER 15-20 MINS PASSED AND THE RWY AT RAP WAS STILL CLOSED. WHEN WE GOT DOWN TO 3000 LBS; I TOLD THE CTLR I WAS DECLARING AN EMER AND WANTED TO LAND AT ELLSWORTH AFB. HE TOLD ME IT WOULD BE OVER 1 HR BEFORE WE COULD LAND. I REQUEST AN IMMEDIATE CLRNC TO GILLETTE; WY; CALCULATING WE WRE 20 MINS FROM GCC AND WOULD BURN ABOUT 1400 LBS. WE LANDED IN VFR CONDITIONS AT GCC WITH 1700 LBS REMAINING. THE PROB AROSE FROM RECEIVING SEVERAL DIFFERENT ESTIMATES OF HOW LONG IT WOULD TAKE TO OPEN THE RWY. I SHOULD HAVE DIVERTED AFTER THE FIRST ESTIMATE DIDN'T HOLD UP.