Aborting would have dashed flamboyant billionaire Branson's hopes of beating rival Jeff Bezos, whose own flight to space was scheduled a few days later.
If successful, Jeff Bezos' Blue Origin programme plans two more passenger flights to space by this year's end.
Scientists are worried about the potential for longer term harm as the industry is poised for major growth, particularly impacts to the ozone layer in the still poorly understood upper atmosphere.
An incredible, life-changing experience to see Earth from Space: Indian-American astronaut Sirisha Bandla
Bandla, a 34-year-old aeronautical engineer joined British billionaire Richard Branson and four others on board Virgin Galactic's SpaceShipTwo Unity to make a journey to the edge of space.
Sirisha, who grew up in Houston since she was 5-year-old, became the third Indian origin woman and the first Telugu to fly into space after Kalpana Chawla and Sunita Williams.
The feat vaults the nearly 71-year-old Richard Branson past fellow billionaire and rival Jeff Bezos, who is planning to fly to space in a craft of his own nine days from now.
The spaceflight should take place at 8:30 am Mountain Time (1430 GMT), after overnight weather conditions forced a 90-minute delay. Virgin Galactic is livestreaming the launch on its website.
The winged rocket ship will soar from New Mexico — the first carrying a full crew of company employees. It will be only the fourth trip to space for Virgin Galactic.
Sirisha Bandla's zeal to learn more about space led her to pursue Bachelors of Science degree in aeronautical/astronautical engineering from Purdue.