As astrophysicist Neil DeGrasse Tyson bemoans the loss of NASA’s space shuttle program, two billionaires say they’re inching closer to the launch of spaceships that can (commercially) fill the void.

An artist’s rendering of a Space X rocket. (AP)

Another billionaire mogul, Virgin Group head Richard Branson, also made an announcement Tuesday about his Virgin Galactic sub-orbital spaceflights planned for 2013, saying that actor Ashton Kutcher would be his 500th passenger.

Despite the void Musk is filling for astronauts and Branson for wannabe space tourists, not everyone is on board with their plans, so to speak.

In testimony before Congress, prominent space heroes Neil Armstrong and Gene Cernan both said they were worried that commercializing space could lead to safety issues, according to Daily Tech.

Many are also worried about the costs. Musk says he hopes in several years to provide rides to the space station for American astronauts, who have been hitching rides on Russian Soyuz rockets for about $60 million a ride. It is unclear what it would cost them to ride on Musk’s Space X Dragon Capsule.

As for Branson’s future space travelers, the trip 68 miles above the Earth (a typical transatlantic flight is just 6.6 miles up) will set passengers back about $200,000.

Both billionaires have also been criticized for their prior inexperience with space. Musk’s degrees are in business and physics, not aerospace, and Branson never graduated from college.

“Although the private space industry is growing, it’s far from viable, or proven,” Popular Mechanics wrote last year of Virgin Galactic and Space X. “Buckle up.”