How JSR 385 Could have Saved the Mars Climate Orbiter JCON September 2019

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

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

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

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

More unit mishaps
• The 12 October 1492 “mishap” 
• “Gimli Glider”, 1983 
• Air Canada ﬂight 143 
• Received less than half the fuel needed 
• Clarence the Tortoise, 2001 
• A whole set of medication dose errors

Problem Statement

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

What is the Fundamental Problem?
• 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

What is JSR-385?

JSR-385: Units of Measurement API 2.0
Description

This JSR is a major evolution of the Unit API 1.0 (JSR 363) specification. Focused
on the SI System redefinition, modularity and support for Java SE 8/9 and above.
JSR 363

This JSR specifies Java packages for modelling and working with measurement
values, quantities and their corresponding units.

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</version>
</dependency>
</dependencies>

Quantities

–Wikipedia
“A physical quantity is a physical property of a phenomenon, body,
or substance, that can be quantiﬁed by measurement.”
–Ibidem
“A physical quantity can be expressed as the combination of a
magnitude expressed by a number - usually a real umber - and a
unit.”
Deﬁnition of a Physical Quantity

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

–Wikipedia
“A physical quantity is a physical property of a phenomenon, body, or substance,
that can be quantiﬁed by measurement.”
“A physical quantity can be expressed as the combination of a magnitude
expressed by a number - usually a real umber - and a unit.”
Deﬁnition of a Physical Quantity
–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
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

•Read mass and height from the command line
Exercise Time

Units

Base Units

Derived Units

Multiples
• km

• ms

• Mm?

• ks?

1.Deﬁne a BMI unit

2.Convert the quantity to the BMI unit before printing it out
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 compute”

JCON School
September 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

JCON School
• 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

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

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

JCON 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

JCON 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
•

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

JCON 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
•

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 Unit
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?

JSR-385 Current Status
• JCP page

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

• GitHub repositories

• https://github.com/unitsofmeasurement

• Current status

• Final Release

–https://www.jcp.org/en/participation/overview
“The JCP gives you a chance to have your own work become an official component of
the Java platform and to offer suggestions for improving and growing the technology.
Either way, everyone in the Java community benefits from your participation. That's one
of the reasons the JCP is open to everyone.”
–https://www.jcp.org/en/participation/membership
“Membership in the JCP offers you a chance to become a permanent part of the Java
platform's history by contributing your work and recommendations to the various
standard specifications, and/or a chance of serving on the Executive Committee.”
The Java Community Process

Becoming a JCP Member

How JSR 385 Could have Saved the Mars Climate Orbiter JCON September 2019

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How JSR 385 Could have Saved the Mars Climate Orbiter JCON September 2019