Jeff Thornburg, the man who helped build SpaceX's mighty Raptor engine, is now aiming for the skies once more. His startup, Portal Space Systems, has raised $50 million to develop solar thermal propulsion, promising to propel spacecraft at unprecedented speeds.

The technology, first investigated in NASA labs over two decades ago, could turn orbital manoeuvres from slow and cumbersome into swift and efficient affairs. With thousands of new satellites launched annually, the demand for quick and agile space vehicles is surging, especially as China tightens its grip on technological superiority.

Thornburg envisions a future where his 'fighter jet for orbit' allows satellite operators to navigate and manoeuvre their crafts with ease. The U.S. military sees potential in this technology too, investing $45 million to leverage Portal's capabilities in orbital warfare.

The path ahead is fraught but promising: first prototypes are launching soon, and a full-scale demonstration of the engine is expected by 2027. With recent advancements in additive manufacturing and materials science, Thornburg’s team stands on the brink of revolutionising space travel.

While nuclear-powered rockets remain tantalising possibilities, for now, solar thermal propulsion could be our stepping stone to a more dynamic space age.