It’s been five years since the space shuttle program ended at NASA, eight years after the shuttle Columbia disintegrated over Texas and Louisiana as it reentered Earth’s atmosphere. But it wasn’t the disaster that doomed the space program: it was money.

NASA instructor and flight controller Robert Frost hopped onto Quora recently to explain why the space shuttle program was shut down despite there being no alternative launch vehicle. Frost told Forbes that NASA is an agency of the government that must abide by what the government says. The reality is, shuttles cost a lot of maintenance, and although no follow-on vehicle was lined up, the government ended up deciding it just wasn’t worth it as priorities shifted over the years.

Former president George W. Bush initiative the program’s cancellation back in 2004 as part of the Vision for Space Exploration, which involved helping to finish assembly on the International Space Station, with the shuttle to retire in 2010 after around 30 years in service. Instead, funding would be focused on a Crew Exploration Vehicle for going to the moon and eventually Mars.

Priorities changed again, with new president Barack Obama assuming the highest office in the land. The shuttle gained a little more time and the CEV became Orion and was delayed.