THOUSAND OAKS, Calif.-- At 18, Bernard Moon was looking at a bright future. A charismatic high school honors student and athlete, he had been accepted at elite universities.

But his life was cut short this week by the blast of a homemade rocket -- a failed nighttime science experiment on the tarmac of a Southern California elementary school.

A homemade chemical rocket attached to a skateboard blew up Monday night, mortally injuring Moon, who died at a hospital. His 17-year-old friend suffered minor injuries.

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The rocket was about a foot long and three-quarters of an inch in diameter, Ventura County sheriff's Capt. Garo Kuredjian said.

"It wasn't meant to go up into the sky," he said of the rocket. "It was meant to go horizontally to propel a skateboard."

The blast appeared to be a tragic accident, he said.

It was unclear whether anyone was trying to ride the skateboard at the time, he said.

Both teens attended Thousand Oaks High School in Ventura County.

"Our hearts are broken," said a posting on the school's Twitter site. "The bonds of faculty, staff, & students will bring healing."

The blast occurred on a courtyard at Madrona Elementary School. The experiment at the elementary campus wasn't sanctioned by any school, and the victims likely were using the courtyard because it's an open space, Kuredjian said.

The Conejo Valley Unified School District released a written statement that reads in part: "Our sympathies go out to the families involved. We are thankful for the quick actions and support of emergency response personnel."

"We don't suspect any more danger," added Kuredjian. "This was a tragic event [and it was] nothing sinister."

High school students dressed in all black Tuesday to pay their respects to Moon.

"He was just a cool kid. He was a nice person to around. He could make you laugh. He was just the kind of person that you would want to interact with," student Ken Zhou said to CBS Los Angeles.

Alissa Drucker had known Moon since elementary school and had just learned about her friend's death Tuesday morning. "He was in a scientific research class, which only a few people really get into at the school. And he loved science really," she said.

Investigators did not immediately confirm reports that Moon may have been working on a project for the April 20 Ventura County science fair.

He had placed in the 2014 and 2015 fairs.

It wouldn't have been out of character for Moon, a high school varsity tennis player and honors student who took advanced science classes. He had been accepted to both the University of California, Berkeley and Brown University, friends said.

William Kim, 18, of Irvine, met Moon last summer at Boys State in Sacramento, a weeklong camp where one standout student from each California high school gathers to set up a mock government.

Moon overwhelmingly was elected to head his fictional party, Kim said in a telephone interview.

Moon was outgoing, friendly, charismatic, ambitious, well-versed in politics and could think on his feet, Kim said.

He was the kind of leader "that made people laugh and feel comfortable," he added.

"I still can't believe that I've just had a meal with him a month ago, talking as if nothing like this was ever going to happen," Kim wrote on Facebook.

Madrona Elementary School in California was closed Tuesday in order for officials to ensure the safety of the campus, CBS Los Angeles reported. The school reopened Wednesday morning.