It sounds as crazy as the space elevator, but the physics work: a group of engineers want to build a slingshot-like machine to launch payloads to space at 1/100 the cost of rockets. The acceleration would be so high that it could only launch fuel and building materials, which is crucial for interplanetary travel.
https://gizmodo.com/japan-will-have-a-space-elevator-by-2050-5887210
https://gizmodo.com/these-guys-want-you-to-crowdfund-their-space-railroad-966678435
