Metric Conversion Practice: Fill & Download for Free

The Mars Climate Observer was lost on 23 September, 1999, because of errors resulting from Lockheed Martin data being in pounds force and the JPL team assuming the data was in Newtons.The data was related to small thruster firings done routinely by the spacecraft. The information was used by JPL flight controllers to understand the state vector of the vehicle. The errors were in software on the ground, not on the vehicle itself.The mistake resulted in small errors that accumulated over time into a 100 km error in the knowledge of the vehicle's position. This led to the vehicle receiving inappropriate steering commands from the ground and entering the atmosphere and being destroyed.It is common practice for large US aviation/aerospace companies to do their work in English units because they have a century of empirical data in those units.

NASA hasn’t fully switched to metric, but the impetus was government direction.The Metric Conversion Act of 1975 directed Federal Agencies to use the metric system wherever it was practical and not of undue financial burden. This was amended by the Omnibus Trade and Competitiveness Act of 1988, which gave the responsibility for directing and coordinating this effort to the Secretary of Commerce.NASA’s implementation of that order is documented in NASA Policy Directive 7120.4E, which states:(8) Metric System of Measurement. Use the International System of Units (commonly known as the Systeme Internationale (SI) or metric system of measurement) for all new space flight projects and programs, especially in cooperative efforts with International Partners. 15 United States Code (U.S.C.) §205b and EO 12770 provide relief from use of SI if it is found that obtaining components in SI units would result in a significant increase in cost or delays in schedule. Each program and project will perform and document an assessment to determine an approach that maximizes the use of SI and document the approach in the Program or Project Plan in accordance with the governing NPR. This assessment will document an integration strategy if both SI and U.S. customary units are used in a project or program.For an existing program like the Space Shuttle, it made no sense at all to attempt to switch to the metric system. For other programs, it is determined on a practicality and cost basis. If the program utilizes significant legacy systems, it isn’t practical to use metric. If the program doesn’t, it may be practical, particularly for programs that involve international partners.

The slide rule.The slide rule has 4 centuries of history with Gunter’s rule as its antecesor, use to calculate all sort of useful things. This is a Gunter’s rule for carpenters:But there were Gunter rules for navigating and many other practical purposes.There were many different makers and models, as the circular ones:Or the Otis King Cylindrical slide rules (thanks Philip Talmage for letting me know of their existence):The HP35 calculator killed the slide rule but it was around 1975, what means that man engineered planes, the radar, ships, tanks,… even went to the moon using the slide rule, with other tools and human calculators. Actually, the Apollo 11 astronauts Armstrong, Aldrin and Collins took each one to the moon, the aluminum pocket of their choice slide rule Pickett 600-T Dual base Lol Log (source “The Oughtred Society”).The HP35 was sold then for $295, a lot of money at that time, $3000 in today’s money (The Oughtred Society).The accuracy of the slide rule was limited to 3 or no more than 4 decimals and it did not give you the point between integers and decimals, but once you learned how to use it, it was very useful.I only learned about the slide rule recently. When I worked on my thesis, I had to calculate where the graph crossed 0 and infinite. These points where so close that the differentiation started on the 40th significant digit and beyond. The slide rule would not have been of much help but most scientific calculators would not have given me so many digits either.Now it is more for collectors and a toy for math enthusiasts, as it is my case, though in my opinion it should not have been dropped as educational aid from schools as it is great to master logarithm and learn intuitively maths.If you would like to try one, there are digital slide rules or simulators :Digital Slide Rule - Apps on Google PlayVirtual Pickett N909-ES SIMPLEX TRIG RULE with METRIC CONVERSION Slide RuleEdits: I have included a picture of the Otis King Cylindrical slide rule after Philip Talmage let me know about them and I have included also the exact model that the Apollo 11 took with them to the moon and other interesting data, obtained from this interesting document about the slide rule from The Oughtred Society.https://www.sliderulemuseum.com/SR_Class/OS-ISRM_SlideRuleSeminar.pdfThanks for all your contributions, in particular to Mario Collado for the digital slide rule links.