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This case has been updated. Compatible choices are kept; revisit the evidence before drawing your conclusion.
01 / The briefing
Begin with the question.
Mars Climate Orbiter was intended to study Mars and relay communications. It launched in December 1998 and approached the planet in September 1999, but contact was lost during arrival. The investigation traced a critical discrepancy to information about small thruster impulses. One ground system supplied values in pound-force seconds while navigation software expected newton-seconds. The file could be read; its numbers were not random or visibly corrupt. They simply meant something different to the producer and consumer. Your job is to connect that quiet interface mismatch to a growing navigation error, then ask why other defenses failed to expose it. Do not stop at naming the units: the board also examined communication, staffing, training and verification weaknesses.
The timeline
Mars Climate Orbiter launches.
Small-force data are supplied for navigation modeling.
Contact is lost during the Mars arrival sequence.
The small-force unit discrepancy is identified.
The Phase I mishap report is issued.
A researched reconstruction for learning. These reasoning steps simplify a complex record; no score can capture the full history.
02 / The evidence
What does the record show?
Read each exhibit before settling on an explanation. The numbered source links below every exhibit lead to the record behind it.
The interface contract
The ground-software interface specified impulse data in newton-seconds; the delivered small-force data used pound-force seconds.
Source record [s1]
A factor, not random noise
One pound-force is about 4.45 newtons. Reading the same numeric impulse in the wrong unit systematically understates the modeled effect.
Source record [s1]
The dangerous accumulation
Repeated momentum-management events made the small-force modeling error matter over the cruise, rather than requiring one spectacular bad command.
Source record [s1]
Defenses beyond conversion
The board identified contributing weaknesses in navigation staffing, team communication, training and verification of interfaces.
Source record [s1]
03 / Your reasoning
Follow the strongest explanation.
Choose an interpretation, then compare it with the evidence. You can revise your choice. The goal is understanding, not a perfect score.
04 / The findings
The chain behind the outcome.
The board identified the failure to use the specified metric units in the small-force ground file as the root cause. Its effect was not that Mars used a different measurement system, nor that the spacecraft suddenly forgot how to steer. The navigation process underestimated accumulated forces and the spacecraft approached far lower than intended. The report also described missed opportunities to recognize and resolve trajectory discrepancies. This makes the case an interface investigation as much as a conversion exercise. A number becomes a useful measurement only when its units, reference frame and meaning survive every handoff. The preventive lesson is therefore layered: express units explicitly, test the complete data path with physical examples, and give anomalous observations a route to resolution. The spacecraft’s exact final fate was inferred after loss of contact; the critical navigation failure is better established than a frame-by-frame reconstruction of its destruction.
Take the method with you
- A valid number can carry invalid meaning.
- Test interfaces with physical examples, not only file formats.
- Treat unexplained discrepancies as evidence, not administrative noise.
You can read findings at any time. Exploring every reasoning step marks this case as complete in your notebook.
The open record
Sources & further reading
Read the original record and its scope before relying on a conclusion. Source references support the exhibit summaries; Faultory’s reasoning prompts are editorial reconstructions.
- s1NASA — MCO Phase I mishap report
discovery.larc.nasa.gov
- s2NASA/JPL — Team finds likely cause of loss
www.jpl.nasa.gov
- s3NASA — Mission overview
science.nasa.gov
Written and curated for Faultory by Yunus Emre Vurgun, with AI-assisted research and drafting. Sources and interpretations can need correction. Read our editorial standards or report an issue.