---------- Forwarded message ----------
Date: Fri, 9 Mar 2001 12:35:29 -0600 (CST)
From: Gene Mechtly <[EMAIL PROTECTED]>
To: "W. Brian Keegan, Chief Engineer, NASA" <[EMAIL PROTECTED]>,
"Righard H. Weinstein, Technical Stds." <[EMAIL PROTECTED]>,
"Paul J. Shawcross, Leader, G-00-021" <[EMAIL PROTECTED]>
Subject: SI at NASA
Dear Mr. Keegan:
I recently downloaded and printed the Inspector General's Report
"Assessment of NASA's Use of the Metric System, G-00-021" of 2001 Feb 20,
and would like to make the following comments and recommendation.
My direct experience with NASA has been ten years as an employee
at the MSFC (including the ABMA, and the GMDD of the AOML in Huntsville).
While there, I wrote "The International System of Units, Physical Constants
and Conversion Factors" which was first published in 1964 by the NASA
Scientific and Technical Information Division as NASA SP-7012.
Recommendation 1 of the Assessment, with the support of your
concurrence on Feb 8, calls upon you, as NASA Chief Engineer, to
"... develop a new approach for the Agency's conversion to SI."
The present approach is vertical; SI for each NASA program,
project, or Center; or not-SI by waivers, project by project.
Here is a proposal for a new approach: *Metricate Horizontally*
across program, project, and Center boundaries. Begin with flight
performance variables about which there is *no* cost penalty, great
promise of uniformity, and little potential for dispute.
For example, the SI Unit of acceleration is meter per second
squated (m/s^2). It shall be used. Waivers for exceptions shall be
difficult to obtain. SI prefixes may be applied to scale numerical values
up or down. e.g. km/s^2 is an accepted multiple in SI.
Another example, the SI Unit of pressure is the pascal (Pa).
It shall be used. Waivers for exceptions (e.g. inclusion of psi after
Pa, in parentheses) shall be difficult to obtain. As always, SI prefixes
may be applied. e.g. mPa, kPa, and MPa may be used to form submultiples
or multiples of the pascal.
Replacement of non-millimeter hardware (e.g. fasteners, pipes,
tubes, valves, couplers, and connectors) shall *not be required* until
new and improved millimeter designs are widely adopted in private sector
industry. However, reasonable efforts shall be made to write millimeter
specifications for existing and proven standard hardware items.
Please make clear distinctions between software conversions to SI
(easy) and conversion of hardware specifications to SI (more difficult)
when you write new directives to implement preferential use of SI for
within NASA and for its contractors. Introduction of *new hardware designs*
in millimeters would be last on the list of priorities because of the
high cost of premature replacements of proven items of hardware.
I hope that you and your staff are persuaded that movement
toward preferential use of SI, *horizontally* across program, project,
and Center boundaries, *SI Unit by SI Unit*, is a feasible "new approach"
to metrication throughout NASA.
Sincerely,
Eugene A. Mechtly, College of Engineering
University of Illinois at Urbana-Champaign (uiuc)
cc: U.S. Metric Association
