The document discusses how using JSR-385 could have prevented the loss of the Mars Climate Orbiter spacecraft. It describes how the orbiter was launched in 1998 to study the Martian climate but was lost due to a failure to convert between metric and imperial units. Had JSR-385 been used to define physical quantities with consistent units, as it does now, this error may have been caught during development. The document then provides an overview of JSR-385 and how it can help define quantities, units, and perform unit conversions to prevent such errors.

1. How JSR 385 could have Saved the Mars
Climate Orbiter
Zürich IoT Day 2021 Virtual Meetup
Werner Keil

2. @wernerkeil
https://hobbylark.com/party-games/1999-Fun-Facts-Trivia-and-News
@UnitAPI

3. https://youtu.be/v1Zst19VWvo
Life on Mars 1999
https://youtu.be/2CZl7ysDKOI https://youtu.be/EdLdL-Su_fo
@thodorisbais
@wernerkeil

4. Mars Climate
Orbiter
• Launched on 11
December 1998
• 338 kilograms
• $125 millions
• To study Martian
climate, atmosphere
and surface changes
@wernerkeil @thodorisbais

5. @thodorisbais
@wernerkeil

6. What went wrong
@thodorisbais
@wernerkeil
lbf·s N·s
4.45

7. Mars Climate Orbiter
“The problem here was not the error; it was the
failure of NASA’s systems engineering, and the
checks and balances in our process, to detect the
error. That’s why we lost the spacecraft.”
Edward Weiler
NASA associate administrator of space science,
IEEE Spectrum: Why the Mars Probe went off course
@thodorisbais
@wernerkeil

8. Lessons Learned
@thodorisbais
@wernerkeil
• Read the software specifications
• Use JSR-385 instead of primitives
• Fail-fast

9. @thodorisbais
@wernerkeil

10. What is the Fundamental Problem?
Primitive (Java) types are primitive types
• static final double C = 1079252849;
• static final double SPEED_OF_LIGHT = 1079252849;
• static final double SPEED_OF_LIGHT_IN_KM_PER_H = 1079252849;
@thodorisbais
@wernerkeil
static final Quantity<Speed> SPEED_OF_LIGHT =
Quantities.getQuantity(1079252849, Units.KILOMETRE_PER_HOUR);

11. Rolling your Own Library
• Development
• Maintenance
• Upgrades & extensions
@thodorisbais
@wernerkeil

12. Werner Keil Thodoris Bais
Maintenance Lead JSR-385
Expert Group Member JSR-385
Let’s meet
@thodorisbais
@wernerkeil

13. @thodorisbais
@wernerkeil
JSR-385: Units of
Measurement API 2.0
JSR-275 Modularity
Support Java SE >=8
JSR-363

14. JSR-385 Basic Concepts
• Dimensions
• Units
• Quantities
• Prefixes
• Converters
• Formats
• Systems of units
@thodorisbais
@wernerkeil

15. Setting up a project
<dependencies>
<dependency>
<groupId>tech.units</groupId>
<artifactId>indriya</artifactId>
<version>2.1.2</version>
</dependency>
</dependencies>
@thodorisbais
@wernerkeil

16. –Wikipedia
“A physical quantity is a physical property of a phenomenon, body, or
substance, that can be quantified by measurement.”
Definition of a Physical Quantity
@thodorisbais
@wernerkeil

17. Speed of Light
c = 299,792,458 m/s
= 1,079,252,849 km/h
@thodorisbais
@wernerkeil
Value Unit

18. Base Units
@wernerkeil @UnitAPI

19. Derived Units
@wernerkeil @UnitAPI

20. Multiples
• km
• ms
• Mm?
• ks?
@thodorisbais
@wernerkeil

21. Dimensions
@thodorisbais
@wernerkeil

22. Systems of Unit
Systems of Units
• Metric System
• Imperial System
• US customary units
• Roman units of measurement
• Swiss units of measurement
@thodorisbais
@wernerkeil

23. Doing the Math
@thodorisbais
@wernerkeil

24. Equality and Equivalence
• kΩ ≠ mHz
• kΩ ≠ mΩ
• kΩ ≡ kΩ
• N ≅ kg·m·s-2
• kg·m-2 ≅ mg·mm-2
• 1 kΩ ≠ 1 mHz
• 1 kΩ ≠ 1 mΩ
• 1 kΩ ≡ 1 kΩ
• 1 N ≅ 1 kg·m·s-2
• 1 kg·m-2 ≅ 1 mg·mm-2
• 1 kΩ ≅ 1,000 Ω
Units Quantities
@thodorisbais
@wernerkeil

25. Quantity Addition
• 1 Ω + 1 Ω = 2 Ω
• 1 Ω + 1 mΩ = 1.001 Ω
• 1 mΩ + 1 Ω = 1,001 mΩ
• 1 Ω + 1 m “does not compile”
@thodorisbais
@wernerkeil

26. How much is 0 °C + 0 °C?
Answer
@thodorisbais
@wernerkeil
IoT Day Math Exam

27. Demo Time
@thodorisbais
@wernerkeil

28. Write a program to calculate the BMI of a person
Exercise description
@thodorisbais
@wernerkeil

29. 1. Define two quantities
a. A mass
b. A length
2. Print them out
Useful classes:
•tech.units.indriya.quantity.Quantities
•getQuantity(java.lang.Number value, javax.measure.Unit unit)
•tech.units.indriya.unit.Units
•javax.measure.Quantity
•javax.measure.quantity.Mass
Exercise 1
@thodorisbais
@wernerkeil

30. • Divide the mass by the square of the height
• Print out the result
Exercise 2
@thodorisbais
@wernerkeil

31. a. Parse mass and height from a String
b. Read mass and height from the command line
Exercise 3
@thodorisbais
@wernerkeil

32. a. Define a BMI quantity
b. Define a BMI unit
c. Convert the quantity to the BMI unit before printing it out
Exercise 4
@thodorisbais
@wernerkeil

33. • Autodetect which argument has mass dimension and which one
has length
Exercise 5
@thodorisbais
@wernerkeil

34. JSR-385 Links
• JCP page
• https://jcp.org/en/jsr/detail?id=385
• GitHub pages
• https://unitsofmeasurement.github.io/
• https://github.com/unitsofmeasurement
• http://www.uom.si
• http://www.uom.systems
• Twitter
• @UnitAPI
@thodorisbais
@wernerkeil

35. @thodorisbais
@wernerkeil