Richard Branson told "stay out of space business" Virgin Galactic has been urged to "give up" on its commercial space-flight project following the test flight crash in which a pilot died. Claims emerged yesterday that safety warnings issued several years before SpaceShipTwo crashed in the Mojave desert in California on Friday were ignored. Meanwhile, the pilot who survived the crash which killed his colleague was yesterday "alert and talking," his employer said. Peter Siebold, the director of flight operations at Scaled Composites, was piloting SpaceShipTwo when it crashed in the Mojave desert in California on Friday. His co-pilot Michael Alsbury was killed when the craft suffered what the firm called a "serious anomaly." Carolynne Campbell-Knight, co-partner of engineering project Knights Arrow and an expert on rocket propulsion, said that she had warned those involved in the project about the dangers of using nitrous oxide fuel around four years ago. "They should stop, give up, go away and do something they might be good at like selling mobile phones - they should stay out of the space business," she said. She claimed she had contacted engineers working on the Virgin Galactic shuttle in around 2009 or 2010. This came after an explosion in 2007 during testing for the development of a rocket motor killed three workers. She said nitrous oxide can "go bang in a very unpredictable way," adding: "My view is from my own engineering experience which I shared with them; they obviously took the position that they knew better." Mrs Campbell-Knight stressed it was not yet clear what caused the latest incident, adding: "There are any number of things that could have brought it down." Describing her response to the crash, she said: "My initial reaction was shock but not surprise." Virgin Galactic said it is working with an independent safety investigation to determine the cause of the crash of SpaceShipTwo, which had been under development at the Mojave Air and Spaceport. Christopher Hart, of the US National Transportation Safety Board (NTSB), said the investigation at the scene - which spans five miles - could take between four and seven days. He added that six cameras were on board the aircraft, although he could not say whether all had been recovered. Mr Hart said the NTSB has "extensive data" available to them as test flights are "heavily documented" in ways other flights are not. He confirmed one parachute was discovered near where the surviving pilot was found, while the other had remained "undeployed." The overall investigation is expected to take up to 12 months, he said, adding that interviews have already begun. Mr Hart confirmed the probe will not stop Virgin Galactic from carrying out operations but said the NTSB can and will issue recommendations during its probe if it feels that is necessary. A statement released by Scaled Composites - Virgin's partner in the venture - said Mr Siebold, 43, has been communicating with medical staff and his family. It said: "The Scaled Composites family lost a respected and devoted colleague yesterday, Michael Alsbury, who was the co-pilot for the test flight of SpaceShipTwo. Peter Siebold, the director of flight operations at Scaled Composites, was piloting SpaceShip Two. He is alert and talking with his family and doctors. We remain focused on supporting the families of the two pilots and all of our employees, as well as the agencies investigating the accident. Mr Alsbury, 39, from Tehachapi, California, had worked for Scaled Composites in Mojave for 13 years. A biography, posted online in July last year, said he had recently been the co-pilot for both SpaceShipTwo's first glide and first powered flight. Mr Alsbury's experience was said to span preliminary aircraft design, manufacturing, flight test planning and flight test support as a flight test engineer and test pilot. Sir Richard Branson, the billionaire tycoon behind the Virgin Galactic space programme, yesterday said it will continue after the fatal crash, adding that millions of people "would one day love the chance to go to space." Sir Richard said he was determined to help authorities find out what caused the crash but likened the incident to the early days of flight. He said: "We owe it to our test pilots to find out exactly what went wrong and once we have found out what went wrong, if we can overcome it, we will make absolutely certain the dream lives on." Virgin Galactic said it was "not permitted" to comment on the accident pending the investigation.