None of the five prospects invited to camp Monday have a realistic chance to make the Opening Day roster, but Luhnow said they were invited to get a taste of Major League camp. Contractual obligations also played into the decision.
"This is about the opportunity for them to get exposed to the Major League staff and veteran players," Luhnow said. "For all those guys, it's more about getting experience and getting a taste of it."
Springer, 22, was the Astros' top pick in the 2011 First-Year Player Draft after earning Big East Player of the Year honors at the University of Connecticut, where he hit .343 with 12 home runs and 77 RBIs in 66 games. After signing with Houston, Springer appeared in eight games at short-season Class A Tri-City.
"I would assume there would be some nerves, but ultimately I'm going to go out there and play and play as hard as I can, and whatever happens, happens," Springer told MLB.com. "The game is hard enough, and you can't let it get harder. I'm going to go out and have fun and enjoy this experience."
Ruggiano, who was born in Austin and attended Texas A&M University, has a .295 career average in parts of eight Minor League seasons, with 103 home runs, hitting a career-high 20 homers for Durham in 2007. He has stolen 20 or more bases in a season five times, and he finished third in the International League in outfield assists with 10 in 2010 while at Durham.
Ruggiano, 29, has spent parts of three seasons in the Major Leagues, all with the Tampa Bay Rays, and split the 2011 season between Tampa Bay and Triple-A Durham. In 46 games for the Rays, Ruggiano hit .248 with four homers and 13 RBIs, batting .391 with runners in scoring position.
"You have to fill out an outfield in the big leagues and an outfield at Oklahoma City, so the more options you have to mix and match at this point is good," Luhnow said.
Singleton, acquired by the Astros from the Phillies last July, is ranked as the club's top prospect by MLB.com. Springer is ranked as the club's third-best prospect, behind Singleton and pitcher Jarred Cosart. DeShields was drafted in the first round in 2010.
DeShields, 19, got his first taste of pro ball last year and had 17 doubles, nine home runs and 48 RBIs in 119 games at Class A Lexington. He also led the club in stolen bases (30) and runs scored (73) while batting .220.
Goebbert, 24, played at three levels in 2011, hitting a combined .290 with 27 doubles, four triples, 12 home runs, 67 RBIs and 42 walks in 132 games at Class A Lancaster, Double-A Corpus Christi and Triple-A Oklahoma City.
Singleton, 20, hit .333 in 35 games at Lancaster, with nine doubles, four home runs, 16 RBIs and 14 walks after being acquired from the Phillies last July as part of the Hunter Pence trade.
The left-handed-hitting Singleton posted a .405 on-base percentage and a .512 slugging percentage for Lancaster. He hit .298 in a combined 128 games at Class A Clearwater and Lancaster, with 23 doubles, 13 home runs, 63 RBIs and 70 walks.
Villar, 20, played in a combined 130 games (all at shortstop) in 2011 at Lancaster and Corpus Christi, hitting .241 with 23 doubles, six triples, 14 home runs, 52 RBIs and 34 stolen bases. Villar was acquired by the Astros from the Phillies in July 2010 in the Roy Oswalt trade.