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On September 23, 1999, the Mars Climate Orbiter disintegrated in the atmosphere of the planet and was never heard from again – a preventable disaster, given the right tools for the job.
After 10 long months of space travel, a team of exhausted NASA engineers and scientists eagerly awaited the opportunity to celebrate the successful insertion of the Mars Climate Orbiter spacecraft into Martian orbit. However, the mission soon became known as the mission that failed due to confusion between units of measurement and cost US taxpayers more than $125 million USD.
In a joint effort to better understand Mars, NASA and subcontractors designed the Orbiter program as one in a series of missions. The unmanned spacecraft was to collect data on the planet’s climate and serve as a communication relay between mission control and future spacecraft in the program.
On its journey, the Orbiter approached the planet following a precisely calculated flight path. The spacecraft was to enter Martian orbit at a specific altitude that would prevent it from breaching the upper atmosphere and encountering catastrophic atmospheric stresses. As NASA engineers stood by, communication with the Orbiter was suddenly lost and never established again. The Orbiter never successfully transmitted data from the red planet, except for a single grainy picture of Mars taken at a distance of about 4.5 million km. The mission was a total failure.
A Completely Avoidable Root Cause
The intended trajectory of the spacecraft would have resulted in an orbiting altitude of 226 km above the surface of the planet, far above the dangerous conditions of Mars’ upper atmosphere. However, a NASA investigation found that the actual Orbiter approach trajectory brought the spacecraft within 57 km of the planet’s surface – even though the Orbiter was thought to be able to survive only at altitudes greater than 80 km. The extreme environmental conditions of Mars’ upper atmosphere destroyed the spacecraft within seconds.
Further analysis concluded that human error caused the discrepancy in trajectories: the flight system software onboard the Orbiter was written to calculate thruster performance in metric Newtons (N), but mission control on Earth was inputting course corrections using the Imperial measure, pound-force (lbf).
“People sometimes make errors,” said Dr. Edward Weiler, NASA associate administrator for space science. “The problem here was not the error, it was the failure of NASA's systems engineering, and the checks and balances in our processes to detect the error. That’s why we lost the spacecraft.”1
Figure 1. Due to confusion between measurement units for a vital spacecraft operation, the actual trajectory taken was far closer to the planet than intended.
Industry Trends Demand Smarter Tools
With the advances of communication technology in the last decade, global development teams can work together like never before. Multinational corporations often design products in one geographical location, send prototypes for validation testing to another location, and perform end-of-line tests at manufacturing sites located in completely different countries. Furthermore, today’s complex designs often include components from globally diverse suppliers, and entire aspects of a project may be delegated to subcontractors.
For teams that collaborate across borders, the difference in measurement unit standards (International System of Units (SI) versus Imperial) is only part of the challenge. Given any quantity, there are multiple ways to represent the same measurement.
For example, miles per hour – a common representation of speed in the United States – can be represented as mph, mi/h, mi/hr, and more depending on personal preference.
These discrepancies with measurement units are ripe for human error. Engineers need smarter data-processing tools that account for units and help avoid catastrophe before the next instance of unit confusion leads to loss of life.
The Right Tool for the Job
Most data-processing software options, including spreadsheets designed for accountants’ financial use, completely ignore measurement units. As the disaster surrounding the Mars Climate Orbiter showed, units can make all the difference. Data without context is nothing more than a series of numbers.
To overcome today’s challenges and prevent mistakes caused by human error, NI DIAdem software adds context to data by associating descriptive property information with raw measurement data. The integrated Units Catalog in DIAdem provides five distinct benefits over alternative data analysis and reporting tools:
1.DIAdem sees all data as a measurement quantity, complete with units. Engineers can instantly convert measurement data between units with one mouse click.
2.The Units Catalog features unit aliases. Engineers can identify different symbolic representations that specify the same measurement unit.
3.All analysis calculations take units into account. If a calculation is performed using conflicting measurement units, DIAdem handles the internal conversion to maintain the integrity of the result.
4.All report graphs specify a measurement unit. If data with a differing unit is graphed, DIAdem handles the internal conversion necessary to maintain the unit quantity represented by the graph.
5.Engineers can process data using the units they prefer while ensuring conversion to an alternate established standard in the end.
Figure 2. DIAdem features a Units Catalog, complete with aliases, that directly integrates with various functionality in the environment.
DIAdem is a dedicated visualization, analysis, and reporting tool that is designed to process measurement data sets stored in any format. It includes many features, such as the Units Catalog, that help engineers gain efficiency and overcome today’s data-processing challenges.
Derrick Snyder is a product manager for DIAdem and data management software at National Instruments. In his spare time, Derrick is a marathon runner and uses DIAdem to correlate and synchronize the playback of the GPS, elevation, and pace information to improve run times.
1 “NASA’s Metric Confusion Caused Mars Orbiter Loss,” last modified September 30, 1999,http://articles.cnn.com/1999-09-30/tech/9909_30_mars.metric_1_mars-orbiter-climate-orbiter-spacecraft-team?_s=PM:TECH.
This article first appeared in the Q2 2011 issue of Instrumentation Newsletter.
Reader Comments | Submit a comment »
Imperial is fine for people who don't
have calculators, or are not lazy.
Anyone can add another zero to a
number or divide or muliple by 2, and
pretend that metric is better...
Metric is good for very rough
calculations, but it makes no difference
when doing accurate calculations.. how
can it?
10 doesn't divide evenly by anything but
2 and 5.
How is that the best system?
People only say otherwise because they
are dumbed down by the modern
education system.
The problem with the mars probe is not
a problem with units, its the same as the
Hubble disaster, it's "intelligent" people
so clouded by their own "intellect" that
they don't even double check their work...
you would think that would be a no
brainer.. especially considering a billion
dollars was at stake.
- Nov 15, 2011
Confusion
Some years ago I had a research project in
the US. I was surprised again and again, that
the colleagues could and where handling
metric units within the lab, but would switch
to imperial (and seem to be unable to use
metric units) outside the lab. So they used
m, m², l etc. inside the lab and ft, sqft,
gal outside.
Looks unbelievable for a continental European...
- Uwe Frenz, getemed AG. u.frenz@getemed.de - Jun 29, 2011
Silly mistake
It is a good thing that NI develops tools
for making the units used clear.
However, I believe that the metric system
should be used throughout science,
engineering, and industry, and that
strong laws in all countries should
enforce the use of the metric system as it
is the case in Europe and Japan. Only for
a few countries, do we need to live with
awkward and obsolete units such as the
imperial ones. I am sorry to be
somewhat bitter, but I live in Canada, and
unfortunately, both systems are still
used, which brings a lot of confusion. It is
really a mess. Officially, the country is
metric, but because of the industry and
economic partners, we also need to live
with the imperial system.
- Jun 21, 2011
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