San Francisco, June 8 : Elon Musk has told his SpaceX staff to make Starship spacecraft top priority and speed up progress on the super-heavy rocket which has seen some turbulent testing in recent months. In an internal email accessed by CNBC, Musk urged SpaceX employees to accelerate progress on its next-generation Starship rocket. Starship is the heaviest rocket for space tourism and long-distance trips and represents a truly reusable rocket with fast turnaround times that make spaceflight more accessible. But the Starship prototype has faced four failed tests since the project began late last year. "Please consider the top SpaceX priority (apart from anything that could reduce Dragon return risk) to be Starship," Musk wrote in the email over the weekend. Marking the beginning of a new era in the US space programme, the SpaceX Crew Dragon spacecraft carrying NASA astronauts Robert Behnken and Douglas Hurley successfully docked with the International Space Station (ISS) on May 31. SpaceX is developing Starship with the goal of launching as many as 100 people at a time on missions to the moon and Mars. "We need to accelerate Starship progress," Musk said. "For those considering moving, we will always offer a dedicated SpaceX aircraft to shuttle people," he added. In April, a prototype of Starship 'SN3' broke apart during a pressure test at the company's test site in Boca Chica, Texas. The explosion happened as liquid nitrogen was being poured into the rocket's propellant tanks. On November 20 last year, the Mk1 prototype blew its top during a cryogenic pressure test and on February 28, the SN2 prototype exploded at the base during a cryogenic pressurization test. Musk has hinted that many of these prototypes will be needed to perfect the Starship vehicle. /IANS