The Danish company designed 26 toy astronaut figures bearing the logo for the European Space Agency (ESA) to accompany 38 year-old Andreas Mogensen aboard the Russian Soyuz rocket, which left from Kazakhstan yesterday.
The figures will be handed out to schoolchildren on their return as competition prizes.
Lego’s cosmic stunt came as the company reported an 18 per cent leap in first half sales to 14bn Danish kroner (£1.38bn) as ranges such as Lego City and Lego Star Wars continued to fly off the shelves.
The jump in sales means Lego has surpassed Barbie-maker Mattel as the world’s biggest toymaker.
Lego’s chief executive Jorgen Vig Knudstorp said the performance was particularly encouraging compared with 2014 when toys from the Lego Movie boosted sales.
“We are pleased that we have again been able to develop exciting and fun play experiences that really appeal to children all over the world. A strong performance across the entire product range enabled us to deliver a highly satisfactory result for the first half of 2015,” he said.