How JSR 385 could have Saved the Mars Climate Orbiter Adorsys 2020

How JSR-385 could have
Saved the Mars Climate
Orbiter
Werner Keil & Thodoris Bais
@thodorisbais@wernerkeil

https://hobbylark.com/party-games/1999-Fun-Facts-Trivia-and-News

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

Result of the Mission

What went wrong
lbf·s N·s4.45

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

Lessons Learned
•Read the software speciﬁcations
•Use JSR-385 instead of primitives
•Fail-fast

More unit mishaps

Problem Statement

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;
static final Quantity<SPEED> SPEED_OF_LIGHT =
Quantities.getQuantity(1079252849, Units.KILOMETRE_PER_HOUR);

Rolling your Own Library
• Development
• Maintenance
• Upgrades & extensions

Werner Keil Thodoris Bais
Spec Lead JSR-385 Expert Group Member JSR-385
Let’s meet

What is JSR-385?

JSR-385: Units of
Measurement API 2.0
JSR-363 Modularity
Support Java SE >=8

JSR-385 Basic Concepts
• Dimensions

• Units

• Quantities

• Preﬁxes

• Converters

• Formats

• Systems of units

Exercise

Write a program to calculate the BMI of a person
Exercise description
BMI is a person's weight in kilograms (kg) divided by his or her height in meters squared

Setting up a project
<dependencies>
<dependency>
<groupId>tech.units</groupId>
<artifactId>indriya</artifactId>
<version>2.0.2</version>
</dependency>
</dependencies>

Quantities

–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

Speed of Light
c = 299,792,458 m/s
Value Unit

One more quote
–Ibidem
“The same physical quantity can be represented equivalently in many unit
systems.”

Speed of Light
c = 299,792,458 m/s
= 1,079,252,849 km/h

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 Time

• Divide the mass by the square of the height

• Print out the result
Exercise Time

• Parse mass and height from a String
Exercise Time

Units

Base Units

Derived Units

Multiples
• km

• ms

• Mm?

• ks?

1. Deﬁne a BMI quantity

2. Deﬁne a BMI unit

3. Convert the quantity to the BMI unit

4. Print out the result
Exercise Time

Dimensions

Dimensions
• L: length

• T: time

• M: mass

• I: electric current

• Θ: thermodynamic temperature

• N: amount of substance

• J: luminous intensity

• (1)
Force: L · M · T-2

•Autodetect which argument is the mass and which is the length
Exercise Time

Summary Table

Doing the Maths

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

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”

Adorsys School
January Exam on Maths
How much is 0 °C + 0 °C?
• 0 °C
• 0 °C
• 273.15 °C
Two absolute temperatures
0 °C + 0 °C = 273.15K + 273.15K
= 546.30K
= 273.15 °C

• 0 °C
• 0 °C
• 273.15 °C
An absolute temperature and a temperature change
0 °C + 0 °C = 273.15K + 0K
= 273.15K
= 0 °C
Adorsys School

• 0 °C
• 0 °C
• 273.15 °C
Two temperature changes
0 °C + 0 °C = 0K + 0K
= 0K
= 0 °C
Adorsys School

273.15 °C (546.30 K)
0 °C + 0 °C = 0 °C (273.15 K)
0 °C (0 K)
Answer
Adorsys School

Multiplication
Units
•kg × m = kg·m
•kg × mm = kg·mm
•g × km = g·km ≟ kg·m
•m × m = m2
•km × km = km2
•mm × km = mm·km ≟ m2
•µm × m = µm·m ≟ mm2
Quantities
•2 kg × 3 m = 6 kg·m
Adorsys School

Division
Units
•kg / m = kg·m-1
•kg / mm = kg·mm-1
•g / mm = g·mm-1 ≟ kg·m-1
•m2 / m = m
•m / m = 1
•km / km = 1
•km / m = km/m ≟ 1k
Quantities
• 3 kg / 2 m = 1.5 kg·m-1
Adorsys School

Powers
Units
•(m)2 = m2 
•(km)2 = km2
•(m2)2 = m4
Quantities
• (3 m)2 = 9 m2
•
Adorsys School

Celsius Revisited
Units
•(K)2 = K2 
•(°C)2 ≟ (K - 273.15)2
•m × °C ≟ m·(K - 273.15)
Quantities
•0 °C2 ≟ 74,610.9225 K2
•1 m°C ≟ 1 mK or 273.151K
Adorsys School

Parsing Units & Quantities

•299,792,458 m/s 
•299792458 m/s 
•299792.458 km/s 
•299,792.458 km/s 
•299,792,458 km*s-1 
• 299,792.458 km×s-1
•299,792.458 km·s-1 
•299,792.458 km·s⁻¹ 
•299,792.458 km*s^-1 
•1,079,252,849 km/h 
•1,079,252,849 km/t
• 670,616,629 mph
Speed of Light

Systems of UnitSystems of Unit
• Metric System
• Imperial System
• US customary units
• Roman units of measurement
•Norwegian Units of Measurement

Demo Time

What Was the Fundamental
Problem Again?
Primitive (Java) types are primitive types

JSR-385 Current Status
• JCP page

• https://jcp.org/en/jsr/detail?id=385

• GitHub repositories

• https://github.com/unitsofmeasurement

• https://github.com/thodorisbais/jsr385-examples

• Current status

• Final Release

Java Community Process

How JSR 385 could have Saved the Mars Climate Orbiter Adorsys 2020

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