The pyramids of ancient Egypt were colossal machines intended to carry powerful rulers to the stars.
The modern one was the same.

In the mid 2100s, Earth is in decline. Colonies and mining around distant stars are needed to deal with resource shortages and population growth. But those require faster-than-light travel. A Nobel-winning physicist and a maverick mathematician have argued that FTL travel is a theoretical possibility, but only by using the mysterious superheavy element 126, ‘mahabhavium’. It is being created atom by atom in vast accelerators, but not in useful quantities.
Everything changes when mahabhavium is discovered spectroscopically in gas clouds surrounding a neutron star 400 light years away. The Star Pyramid project is born. A pyramid-shaped starship travelling just below the speed of light, Star Pyramid can reach the gas clouds in around 400 years – 98 years from the perspective of the crew, who will spend most of the trip in suspended animation anyway. It will harvest mahabhavium and use a small fraction to return to Earth immediately.
A massive concerted global effort provides the resources needed for Star Pyramid to launch in 2169, but not without critics on Earth and potential saboteurs on board.
What could possibly go wrong?