How JSR 385 could have Saved the Mars Climate Orbiter - Zurich IoT Day 2021
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Werner KeilFolgen
9. Apr 2021•0 gefällt mir•184 views
How JSR 385 could have Saved the Mars Climate Orbiter - Zurich IoT Day 2021
9. Apr 2021•0 gefällt mir•184 views
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In 1999, NASA lost the $125 million Mars Climate Orbiter as it went into orbital insertion. Due to a mismatch between US customary and SI units of measurements in one of the APIs, the spacecraft came too close to the planet, passed through the upper atmosphere and disintegrated. Sadly, this hasn’t been the only instance where a mismatch between units of measurements had catastrophic consequences, but it’s certainly one of the most spectacular and expensive ones. How could this happen? The bad news: if you use primitive types to handle quantities in your code, due to the same practice at best, you’ve codified the unit in a variable name or database field, e.g. calling it lengthInMetres. Otherwise, you’re only relying on convention, just like Lockheed Martin and NASA did. Join this compact version of our talk for IoT Day 2021 to learn how JSR 385 can help you avoid $125 million mistakes, how it applied the 2019 redefinition of SI base units, and discover the immeasurable world of dimensions, units and quantities.
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How JSR 385 could have Saved the Mars Climate Orbiter - Zurich IoT Day 2021
- 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
Hinweis der Redaktion
- Software engineers
- Launched on the 19th of December 1998 at 18:45 UTC. It was launched from Cape Canaveral aboard a delta to launch the eco. the complete burn sequence lasted 42’ and brought the spacecraft into a so called human transform orbit from earth to Mars. The orbit is 669million kilometers long and takes 9.5 months to complete > over a pregnancy Primary science objectives of the mission: determine the distribution of water in Mars monitor the daily atmospheric conditions record changes of the Martian surface (due to wind) determine temperature profiles in the atmosphere look for evidence of past climate change So that was a whole set of things the MCO was supposed to do
- into a trajectory above 226km above the surface of Mars It probably got disintegrated in the atmosphere and disappeared. Minimum altitude to survive was 80km
- A piece of software provided by Lockheed Martin produced results for the total impulse by the thruster firing in pound force seconds, whereas the trajectory calculation software provided by NASA expected it to be in Newton seconds. The software specification said it should have been in Newton seconds so Luckheed Martin clearly made a mistake
- if Lockheed Martin had done a good job, it would have never happened Use JSR-385 instead of primitives Fail fast <== don’t rely on the checksum balancer to discover problems
- Mars 2020 Rover contains components from multiple different countries (most of them use the Metric System)
- using a primitive to represent a quantity is fundamentally conflicting with OOP and DDD, cuz you’re using a type representing just a number to represent a quantity which has a unit —- built in into the property and it contains both the value and the unit —- No way to misinterpret the SPEED of light at the bottom as that number in km/h
- wanna do it properly? define ur own library how difficult can it be? it’s just a value and a unit lot of work —> many units meter, time units, electrical resistance , TEMPERATURES?, divide & multiply Are you a UoM domain expert? so even if you use the SI system every day do you really understand how it works? TBH I didn’t even answer that question to myself. I would be surprised if you know all the peculiarities around SI. There is a number of strange things, even though it is designed as the rational system as compared to some other systems.
- This JSR is a major evolution of the Unit API 1.0 (JSR 363) specification. Focussed 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.
- Dimensions: length Unit: metre Quantity: 5 metres prefixes: kilo, milli, etc. converters: km/h —> m/s or mph formatting: print out the quantity and parse the quantity of the unit systems of units: metric, imperial and handle them in a good way
- It doesn’t do some kinds of optimisations that one could think it would be nice to have
- Yesterday I travelled 1.6Mm??? 1hour = 3.6ks, but “come back in 1ks”???
- Yesterday I travelled 1.6Mm??? 1hour = 3.6ks, but “come back in 1ks”???
- Yesterday I travelled 1.6Mm??? 1hour = 3.6ks, but “come back in 1ks”???
- Metre, kilogram, second, ampere… Foot, ounce, pound, gallon, Fahrenheit, horsepower Foot, ounce, pound, gallon, Fahrenheit, gallon, … Pes, uncia, libra, … Fot, favn, mål, tønne, snes, …
- Should you have functions to normalize expressions into what could be closer to the base unit That’s something you could consider, and also for quantities for example that 1 mg per mm-2 is automatically normalized to 1kg m-2 Special paint for small devices It’s not just about comparing the values and the units you have to convert to one unit and do the comparison in one reference unit
- We use the 1st unit if we can If it leads to an overflow, we can fall back to the second unit Otherwise, if it leads to an overflow in both units, we just throw an overflow error
- All 3 answers are correct depending on the situation. absolute or relative quantity? We hadn’t modelled this. So, again, are you a domain expert in ur system? Do you really know the SI system so that you can write a library to handle this stuff? Why are we using degrees celsius. Undoubtedly, it’s easy (0-100 degrees), but degrees celsius is not such a good unit to measure temperature. JavaZone example with Time (i.e. day light, saving time, etc., formatting problem with US month – dd - yyyy, countries using F and celsius)
- kg/m^2 a thing that matters for the BMI index is to express the units as kilograms and meters and not cm for example. We’ll see as we go through th exercise that we can handle that in a good way
- So you see? this is not difficult to do, so instead of defining an Integer to hold 75 as the mass, that’s not much of simplification compared to this