The 37-year-old and husband Ned Rocknroll are expecting their first child together - Winslet's third - later this year and British business tycoon Branson, Rocknroll's uncle, has promised to give the unborn tot a free flight when the child is old enough, reported Sun Online.
"Richard told Kate and Ned they can go up any time and the same goes for their new arrival," a source said. The couple have already secured a seat on the first trip into space, which is due to happen this Christmas day.
A ticket on the Virgin Galactic flight costs USD 200,000 and a host of star-gazing celebrities have already purchased seats. Other confirmed famous passengers include 'Two and a Half Men' star Ashton Kutcher, Mila Kunis, Justin Bieber, Leonardo Dicaprio and Russell Brand, while Angelina Jolie and her fiance Brad Pitt, Katy Perry, scientist Steven Hawking and Tom Cruise have all expressed an interest.
The first ever two-hour flight in the planet's orbit will be boarded by Branson and his family and anyone who has paid a deposit guaranteeing them a place on it. Passengers will travel 62 miles in altitude - the internationally recognised boundary of outer space - and will experience weightlessness and an incredible view of the curve of the Earth.