The launch was initially scheduled for 21 March 2015 .
This was delayed to study a problem with a helium pressurisation system on the Falcon 9 rocket , and a new launch date was set for no earlier than 24 April 2015 .
The launch was initially scheduled for 21 March 2015 but this was delayed to study a problem with a helium pressurisation system on the Falcon 9 rocket , and a new launch date was set for no earlier than 24 April 2015 .