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50TH ANNIVERSARY OF OF THE MOON LANDING 50TH ANNIVERSARY THE MOON LANDING

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MARGARET HAMILTON: APOLLO ON THE WAY SOFTWARE ENGINEER, AWARDED TO THE MOON: PRESIDENTIAL MEDAL OF FREEDOM LUNAR SCIENCE ANNOUNCED The primary goal of the first Moon landing mission was to demonstrate that the Apollo spacecraft systems could safely land two astronauts on the surface and return them safely to Earth. During the first lunar surface Extravehicular Activity (EVA), the crew were to spend about two hours outside the Lunar Module (LM). In addition to collecting rock and soil samples for return to Earth, the astronauts would also conduct science. On November 19, 1968, NASA announced that when Apollo astronauts first land on the Moon, possibly as early as during the Apollo 11 mission in the summer of 1969, they would deploy three scientific experiments – a passive seismometer, a laser ranging retro-reflector, and a solar wind composition experiment. The passive seismometer experiment was a self-contained 100-pound seismic station to detect any Moonquakes. The experiment was solar-powered and had its own communications capability so that it transmitted its results back to Earth after the astronauts departed the lunar surface. If the Moon is seismically active, the instrument could provide information about its internal structure and possibly yield clues about its formation. The Principal Investigator for this experiment was Gary Latham of Columbia University’s Lamont Geological Observatory in Palisades, New York.

Left: A mockup of the laser ranging retro-reflector. Right: Astronauts training to deploy the laser ranging retro-reflector before their mission.

The laser ranging retro-reflector was a passive experiment weighing about 70 pounds. It consisted of an array of precision optical reflectors to serve as a target for Earth-based lasers. By precisely measuring the time it takes a laser beam to travel from Earth and bounce back from the retro-reflector, scientists calculated the Earth-Moon distance to an accuracy of eight centimeters. Measurements taken over time and from different stations on Earth helped determine fluctuations in Earth’s rotation and also recorded continental drift. The Principal Investigators for the seismic experiment were Carroll Alley of the University of Maryland in College Park, Maryland, and Donald Eckhardt of the Air Force Cambridge Research Laboratory in Cambridge, Massachusetts. The solar wind composition experiment consisted of a sheet of aluminum to trap particles of the solar wind, in particular the noble gases helium, neon, argon, krypton, and xenon. The astronauts unfurled the aluminum foil collector near the beginning of their EVA and then rolled it up and returned it to Earth for laboratory analysis. The Swiss government sponsored the one-pound experiment. The Principal Investigator was Johannes Geiss of the University of Bern in Switzerland. During their flight from Earth, the experiments were stowed in the Scientific Equipment Bay of the LM’s Descent Stage. The crew manually retrieved the packages once on the lunar surface and deployed the experiments within 60 feet of the LM. Beginning with the second Moon landing, astronauts deployed more sophisticated experiments as part of the Apollo Lunar Surface Experiments Package (ALSEP) and conducted more extensive geological surveys around their landing sites. n

Fifty years ago, humans first set foot on the Moon during the Apollo 11 mission. That success would not have been possible if not for the team of 400,000 people who worked to ensure the success of the mission and the safety of astronauts Neil Armstrong, Buzz Aldrin and Michael Collins. One of those 400,000 people was Margaret Hamilton. On November 22, 2016, President Barack Obama awarded Hamilton the Presidential Medal of Freedom for her contribution that led to Apollo 11’s successful landing. The very first contract NASA issued for the Apollo program (in August 1961) was with the Massachusetts Institute of Technology to develop the guidance and navigation system for the Apollo spacecraft. Hamilton, a computer programmer, would wind up leading the Software Engineering Division of the MIT Instrumentation Laboratory (now Draper Labs). Computer science, as we now know it, was just coming into existence at the time. Hamilton led the team that developed the building blocks of software engineering – a term that she coined herself. Her systems approach to the Apollo software development and insistence on rigorous testing was critical to the success of Apollo. As she noted, “There was no second chance. We all knew that.” Her approach proved itself on July 20, 1969, when minutes before Armstrong and Aldrin landed on the Moon, the software overrode a command to switch the flight computer’s priority system to a radar system. The override was announced by a “1202 alarm” which let everyone know that the guidance computer was

shedding less important tasks (like rendezvous radar) to focus on steering the descent engine and providing landing information to the crew. Armstrong and Aldrin landed on the Moon, rather than aborting the approach due to computer problems. In fact, the Apollo guidance software was so robust that no software bugs were found on any crewed Apollo missions, and it was adapted for use in Skylab, the Space Shuttle, and the first digital fly-by-wire systems in aircraft. Hamilton was honored by NASA in 2003, when she was presented a special award recognizing the value of her innovations in the Apollo software development. The award included the largest financial award that NASA had ever presented to any individual up to that point. Today, Margaret Hamilton is being honored again – this time at the White House. President Obama has selected her as a recipient of the Presidential Medal of Freedom. The highest civilian award of the United States, it is awarded to those who have made an especially meritorious contribution to the security or national interests of the United States, to world peace, or to cultural or other significant public or private endeavors. n

Profile for HJ Special Sections

50th Anniversary: The First Man on the Moon  

A comprehensive look back on the historic U.S. flight and landing on the Moon 50 years ago on July, 20, 1969.

50th Anniversary: The First Man on the Moon  

A comprehensive look back on the historic U.S. flight and landing on the Moon 50 years ago on July, 20, 1969.

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