The lunar module from the Apollo missions is so familiar that it is hard to imagine other ways of landing on the Moon. Surely that spindly, fragile lander, and the command module in orbit with its lonely pilot are the way that these things are done.

But this way of landing on the Moon was not inevitable: in the early days of Apollo, it was not even seen as an option worthy of consideration. The original plans were for a single craft, capable of landing on the Moon, taking off again and flying all the way home on its own. Such a craft would have no need for a docking manoeuvre in Lunar orbit, which was seen as unnecessary and risky.

And, once we shed our preconceptions based on decades of images, this approach seems intuitively simpler. The Moon missions would already involve many dangerous firsts: why complicate things further by splitting the landing craft and command module, and attempting a docking manoeuvre a quarter of a million miles from home?

Of course, we now know that there are many good reasons to take the approach which we are familiar with, known as Lunar Orbit Rendezvous (LOR), not least that it dramatically reduces the weight of the lunar landing craft. But these reasons would not have been recognised without the persistent intervention of one person: John Houbolt.

Houbolt was an engineer who believed wholly in the value of LOR, and who also believed that it was not being taken seriously. He believed this so much, but met so much resistance, that he circumvented the hierarchy and wrote a famous and notoriously forthright letter to NASA Associate Administrator, Robert Seamans, advocating for LOR and criticising the way that decisions were being made. He was so persuasive that LOR was considered as a serious option, was eventually selected, and resulted in millions of models of lunar landers in museums and bedrooms around the world.

There are lessons (especially for technology architects) to draw from Houbolt, most obviously about persistence, courage and communication.

However, if we go to the text of the letter (which can be found from page 55 of this document), then I think that there are three further lessons we can learn.

First, Houbolt is clear and urgent about objectives. The most striking sentence in his letter is: ‘Do we want to get to the moon or not?’ When we are in the middle of the details of technical arguments, it can be easy to forget why we are having those arguments. Houbolt was clear (we’re going to the Moon!): we should make sure that we are clear too.

Second, Houbolt challenges artificial constraints placed on thinking: what were known as the ‘ground rules’ in the early days of Apollo planning. For example, one of the ground rules was the mission should allow a crew of three to land on the Moon: this rule determined the minimum size of the craft, with knock on effects on the size of the rocket system, on fuel and so on. Houbolt asked: if the job can be done by two people, why not do it with two people (leaving one person free to fly the command module)? We should make sure that we identify our own ‘ground rules’ and ask whether they really need to be rules.

Third, the final section of Houbolt’s letter begins, ‘It is one thing to gripe, another to offer constructive criticism. Thus, in making a few final remarks I would like to offer what I feel would be a sound integrated overall program.’ However, despite the tone of much of his letter, Houbolt hardly needed to make this assertion: it is clear throughout that he is an advocate rather than a critic, and has been moved to write because he believes in what he says. We should make sure that we are just as clear about what we are advocating for as we are about what we are arguing against.

Few, if any, people reading this will have the privilege to work on an endeavour such as the Apollo missions. But we all work on our own endeavours, and we all face criticism and challenge. Houbolt’s letter - and the success of that letter - remind us that passionate, persistent, expert advocacy, focused on the goals of the mission and unbound by needless rules, can change the world.