Thinking clearly · Chapter 7
Why did Mars Climate Orbiter fail?
Ground software supplied thruster impulse data in pound-seconds where navigation expected newton-seconds. The mismatch distorted the trajectory calculation. Checks and communication also failed to catch the error.1
A handoff is part of the engineering
NASA identified the failure to use metric units in the Small Forces software as the root cause. The interface documentation specified the required units, but the delivered data did not match them. The report also identifies contributing operational and process failures.1
The loss therefore cannot be understood as a solitary arithmetic slip. What was delivered, what was assumed and how the discrepancy was checked all mattered.
The lesson is not just use metric
Chapter 7 distinguishes experience from learning. 'Be careful with units' leaves the same handoff vulnerable. My response is to make the interface testable: name the unit, check a known value and confirm what the receiving team actually used.
A cost, date, coordinate or design load can suffer a similar problem. Agreement about a label is not enough when the data beneath it means something different.
A check you can use
- State units, conventions and reference conditions in the data.
- Run a known-value test through the whole handoff.
- Have the receiver confirm interpretation, not only receipt.
Did Mars Climate Orbiter crash?
It was lost during its attempted arrival at Mars. The established explanation is the trajectory error. The word 'crash' should not imply that a witnessed impact or recovered wreck supplied the diagnosis.1
Zafar Alam is a civil engineer and Chartered Construction Manager with about 12 years on major projects. He is the author of What Are We Missing? How to Think More Clearly Before You Decide, planned for 13 February 2027.
Keep thinking
How do you make decisions with incomplete information?Chapter 9 · What the Room Does With What It HearsWhat questions should you ask before making a decision?Chapter 11 · Integrated Decision ArchitectureUse this on a real decision
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