Tech it to space: Why do we always need to wait for ‘launch windows’ to get a rocket to space?

tech.hindustantimes.com:

Earlier this week, the Artemis I Moon mission was scrubbed again; now we have to wait for a new launch window.

Just 40 minutes before the Space Launch System rocket was set to take off from Kennedy Space Centre in Florida on September 3, a leaking fuel line caused engineers to scrub the launch.

So what is a launch window, and why can't a rocket go up at any time? And what does it mean to “scrub” it?

A launch window is like waiting for the stars to align. The rocket will be “thrown” off the surface of Earth. This toss must be timed perfectly so the craft's resulting path through space sends it – and everything it's carrying – towards the intended location at the right time.

For Artemis I – a mission to send the Orion capsule into orbit around the Moon – the “right time” means waiting for the Moon to be as close to Earth as possible (known as “perigee”) during its 28-day cycle. Hence why we'll now be waiting roughly four weeks for the next moonshot.

With much of the flight path relying on gravity assists (a “swing-by” that uses the momentum of a large body to increase or decrease the speed of a passing craft) from both Earth and the Moon, and because we want the Orion capsule to come back safely, the timing is crucial.

Orion must slingshot past the Moon, not crash into it, so the positions of the rocket launcher, Earth, Moon and lunar capsule must all be known precisely at all times.

It was a similar story with the launch of the James Webb Space Telescope. In this case, mission controllers were making sure it didn't hit the Moon on its way to Lagrange Point 2 – a gravitationally balanced spot between Earth and the Sun. The launch of the telescope was scrubbed a couple of times to avoid bad weather; it eventually launched from