The First Moon Landing, Fifty Years On

  • What's next in the evolving space industry
  • Physics & Astronomy feature on aerospace research
  • Expert insights from a former Apollo engineer & specialist in aerospace design

Apollo 11 Nearly Landed on the Edge of a Deep Crater

We've asked Pat Norris, former Apollo engineer to share his experience on the spaceflight SPSN-Astronomy-Apollo © Springermission. He worked in the space and software business from 1964, until his retirement in 2018.  

Highlights include working on the Apollo moon landings in Houston in the 1960s (he received an award from Neil Armstrong in 1969), for the European Space Agency in the 1970s and then for software multinational CGI in the UK from 1980 until his retirement.  His third book has been published to coincide with the 50th anniversary of Apollo 11 and is called: Returning People to the Moon after Apollo: will it be another 50 years? (Springer-Praxis).

The level of interest in Apollo 11 is enormous, and the fact that I worked on the program in Houston seems to intrigue people of all ages.  In London, England, where I have lived since 1980, Primary School kids (grades 1 through 5) are especially inquisitive about what happened and when might it do so again. 

I worked at an aerospace company called TRW from 1968 to 1970 developing algorithms for NASA’s Mission Control to navigate Apollo to and from the Moon, and in orbit around the Moon. The latter proved especially difficult and errors in the information provided by Houston to the Lunar Module (the Eagle) two hours before the landing meant that Neil Armstrong had to manually fly the Eagle to a safe landing site away from where the guidance computer was planning to set them down. Mission Control back in Houston couldn’t see it in their low resolution TV images but Armstrong could see boulders the size of a bus strewn around the area and also could see that the Eagle was being steered by its computer to land perilously close to the rim of a deep crater.  The Houston experts were puzzled by Armstrong’s decision to take over manual control of the descent and some of them became quite frustrated – “Why doesn’t he land the G…….n thing” a voice was heard to cry out as Eagle’s fuel level got lower and lower.

The 5-minute long video called “Final Approach film by René and Jonathan Cantin” on NASA’s Apollo 11 Video Library website captures the drama of these moments brilliantly.  I have found that it gets the attention of kids and adults alike and serves as a brilliant introduction to the navigational challenges we faced back in 1969.

We knew at the time that the roughness of the Moon’s gravity field was a major source of these navigational errors. The dark circular areas on the face of the Moon were regions of especially strong gravity; it is thought that the asteroids that created these regions weakened the Moon so that heavier material rose from its centre close to the surface, thus increasing the gravity there. Although we knew this general principle, there simply wasn’t enough data from spacecraft orbiting the Moon to allow us to work out a detailed formula for the gravity field, so we relied on relatively simple approximations that left us a few miles off course every time a spacecraft went round the Moon.  I remember asking my NASA customer to see if the Soviets had any gravity model data we could use, and we did in fact get one such mathematical model from them, but it turned out to be even worse than the models we were using.

So Armstrong and Aldrin ended up overshooting the intended landing site by 4 miles (6 km)  or so.  Fortunately most of the error in predicting the Lunar Module’s trajectory one orbit ahead was an over- or under-shoot, that is to say along track as opposed to across track.  So for Apollo 12 in November 1969 the algorithm only needed a simple tweak to land them on the money.  As the Apollo 12 Lunar Module (Intrepid) appeared from behind the Moon on its way to the landing site Mission Control radioed them a single number, with the anonymous label “Noun 69” that was the over- or under-shoot distance based on how early or late they had emerged from behind the Moon.  The computer in Intrepid adjusted the location of the landing site by this much, and this brought them down bang on target.

Sometimes it pays not to over-complicate things.

© SpringerReturning People to the Moon After Apollo: Will It Be Another Fifty Years?

This book assesses the legacy of the Apollo missions based on several decades of space developments since the program’s end. The question of why we haven’t sent humans back to the Moon is explored through a multidisciplinary lens that weaves together technological and historical perspectives. The nine manned Apollo missions, including the six that landed on the Moon, are described here by an author who has 50 years of experience in the space industry and whose work spanned the Apollo 8–13 missions. The final section of the book provides a comprehensive assessment of today’s programs and current plans for sending humans to the Moon. Find out more

Pat Norris 

Pat Norris spent 50 years working on space projects including the Apollo Moon landings as a NASA contractor and the Hubble Space Telescope as a European Space Agency program manager. Since 1980, he has worked for the company CGI, and he is currently a part-time consultant to its Space Business Unit. Norris is the author of two books on space surveillance as well as many articles, book chapters and conference presentations on all aspects of space. He was awarded the Apollo Individual Achievement Award in 1969 and the Sir Arthur Clarke Lifetime Achievement Award in 2016.

For more on this topic visit our Apollo moon landing 50th anniversary page

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