The Astros’ $21 million experiment was never going to work. No matter how many times the rebuilding organization’s main voices ignored baseball reality while pointing toward the 2012 American League West champion Oakland Athletics and saying, “Hey, that can be us in 2013.” No matter how nice a six-game winning streak that bridged May with June — when the Astros were the hottest team in baseball and finally appeared on “SportsCenter” for something other than ridicule — briefly was. Right now, the Astros are again the worst team in Major League Baseball. Thirty-one games below .500 after being blown out 12-5 by Seattle on Sunday at Minute Maid Park; outscored by a combined 155 runs this season; 231/2 games behind the first-place A’s; on pace for 107 defeats after losing 213 contests the last two years; dead and discarded again before Aug. 1. With Sunday’s sudden promotion of shortstop prospect Jonathan Villar and underperforming veterans Carlos Pena and Ronny Cedeno being designated for assignment, the Astros’ $21 million payroll experiment is finally over. It began with analysts and critics questioning how a mix-and-match roster filled with unproven second-tier young players and late-career veterans affected the integrity of the sport. It ended as a late-July failure. A directionless team that exited the field Sunday ranked last in MLB in everything from ERA (4.92) and offensive strikeouts (900) to defensive efficiency ratio (.674) at last moved into its next era by erasing Pena and Cedeno and promoting its second legit prospect in just nine days. Even more critical numbers: Righthanded starting pitcher Jarred Cosart is 23, and Villar is 22, while Pena was the Astros’ biggest offseason free-agent signing and second-highest-paid player ($2.9 million). Now, the Astros are cheaper and technically weaker. They also instantly have become much more interesting and exciting. Cosart threw eight-plus brilliant innings of two-hit shutout ball in his big league debut at Tampa Bay on July 12, outdueling reigning American League Cy Young winner David Price and again putting the Astros in the lead spot on “SportsCenter.” Villar hit .278 with eight home runs, 41 RBIs, 31 stolen bases and a .786 OPS at Class AAA Oklahoma City. The switch hitter possesses a cannon of an arm and has smooth feet, and he could team up in the middle of the Astros’ infield with 23-year-old second baseman Jose Altuve until 2012 No. 1 overall pick Carlos Correa arrives in Houston.