NASA, the US's publicly-funded space programme, has said that Elon Musk's rockets aren't big enough for its missions.
What it means: Elon Musk, the multi-billionaire Tesla businessman has started his own space exploration company. A few months back, he launched Falcon Heavy, the world's most powerful rocket. For a lot of people, it signals a kind of changing of the guard: rather than government funded, space exploration would be dominated by businesses – sometimes called 'commercial interests'.
NASA has been reluctant to work with Space X, and lots of people think it should be using Musk's technology for launches, rather than investing loads and loads of money in building its own. NASA's excuse: the rocket just isn't big enough.