A five-year-old Auckland boy has fulfilled a dream that would spark the envy of any rocket scientist.

Kiwi aerospace company Rocket Lab let him test-fire one of their top secret engines.

Arian has a highly aggressive brain tumour and the company is helping raise funds for a possible cure.

For the first time the world will see a test fire of the revolutionary engine, and the person in charge is five-year-old Arian.

Even CEO Peter Beck has been kicked out to watch from the hillside.

The Rutherford engine was designed and 3D-printed by Rocket Lab to power its electron rocket.

Arian was invited along because of his dream of going to space.

"It is one of his dreams, so for him to tick one of his dreams off, it's a blessing," says mother Sanaz Truter.

Arian has about nine months to live after being diagnosed with an aggressive brain tumour.

There is no cure, but clinical trials in Germany could help, so Arian's family is fundraising for $120,000 through Givealittle.

The response so far has been overwhelming.

"It just tears me up," says Ms Truter. "It's beautiful to see people who want to help because they are so kind."

That is including Rocket Lab, who could have just released the footage to the world, but instead gave Arian the experience and the publicity.

"We are trying to raise money for his Givealittle page so he can cram a whole life into the little time that he has left," says Mr Beck.

The rest of the tour was off-limits to Newshub, but Arian saw mission control and signed his name on the first electron rocket.

He may not see it, but Arian's dream of making it to space will come true.

Newshub.