Don Eyles is a retired

computer engineer Computer engineering (CoE or CpE) is a branch of electrical engineering and computer science that integrates several fields of computer science and electronic engineering required to develop computer hardware and computer software, software. C ...

who worked on the computer systems in the Apollo Lunar Module vehicle. As a young engineer during the lunar landing on Lunar Module ''Eagle'' on 20 July 1969 he assisted with a series of computer alarms caused by data overflow from the radar, which could have caused the mission to be aborted.

Apollo missions

Eyles was educated at

Boston University Boston University (BU) is a Private university, private research university in Boston, Massachusetts. The university is nonsectarian, but has a historical affiliation with the United Methodist Church. It was founded in 1839 by Methodists with ...

where he earned a bachelor of science in mathematics. In 1966, at age 23, Eyles was hired by

Draper Laboratory Draper Laboratory is an American non-profit research and development organization, headquartered in Cambridge, Massachusetts; its official name is The Charles Stark Draper Laboratory, Inc (sometimes abbreviated as CSDL). The laboratory specialize ...

. He helped program the onboard computer for the Apollo Guidance Program Section where he worked with

MIT The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the m ...

, and other researchers, on the Apollo Guidance Computer. During the

Apollo Apollo, grc, Ἀπόλλωνος, Apóllōnos, label=genitive , ; , grc-dor, Ἀπέλλων, Apéllōn, ; grc, Ἀπείλων, Apeílōn, label= Arcadocypriot Greek, ; grc-aeo, Ἄπλουν, Áploun, la, Apollō, la, Apollinis, label ...

missions Eyles worked on the computer systems, programming for

Jack Garman John Royer "Jack" Garman (September 11, 1944 – September 20, 2016) was a computer engineer, former senior NASA executive and noted key figure of the Apollo 11 lunar landing. As a young specialist on duty during the final descent stage on 20 July ...

, advising

flight controller Flight controllers are personnel who aid space flight by working in such Mission Control Centers as NASA's Mission Control Center or ESA's European Space Operations Centre. Flight controllers work at computer consoles and use telemetry to ...

s in Mission Control on the operation of spacecraft computer systems and prior to the

Apollo 11 Apollo 11 (July 16–24, 1969) was the American spaceflight that first landed humans on the Moon. Commander Neil Armstrong and lunar module pilot Buzz Aldrin landed the Apollo Lunar Module ''Eagle'' on July 20, 1969, at 20:17 UTC, ...

mission he helped program operations for how flight controllers could react to a computer error code. There were a number of errors with the computer system during the mission. One was diagnosed as the rendezvous radar being on (which was correct according to the checklist), causing the computer to process data from both the rendezvous and landing radars at the same time. Eyles concluded in a 2005 Guidance and Control Conference paper that the problem was due to a hardware design bug previously seen during testing of the first uncrewed LM in

Apollo 5 Apollo 5 (launched January 22, 1968), also known as AS-204, was the uncrewed first flight of the Apollo Lunar Module (LM) that would later carry astronauts to the surface of the Moon. The Saturn IB rocket bearing the LM lifted off from C ...

. Having the rendezvous radar on (so that it was warmed up in case of an emergency landing abort) should have been irrelevant to the computer, but an electrical phasing mismatch between two parts of the rendezvous radar system could cause the stationary antenna to appear to the computer as dithering back and forth between two positions, depending upon how the hardware randomly powered up. The extra spurious cycle stealing, as the rendezvous radar updated an involuntary counter, caused the computer alarms. During the Apollo 14 mission, Eyles assisted when a faulty switch could have sent a spurious command to the onboard computer. According to a ''Rolling Stone'' article published in 1971 "The switch tells the on-board computer to reverse the engines — blasting the Module away from the moon, back into orbit. On the Apollo 14 flight, the switch accidentally jammed and would have told the computer to reverse the Module's course despite the fact that the astronauts wanted to complete the descent. "We had to write a new program that would make the computer not see the switch," said Eyles.''Don Eyles: Extra! Weird-Looking Freak Saves Apollo 14!''
rollingstone.com; accessed July 17, 2019.

References

External links

Oral Histories
{{DEFAULTSORT:Eyles, Don Living people 1940s births Year of birth missing (living people) NASA people Apollo 11 Apollo 14