5 ms·

At least it wasn't a unit-conversion problem. It would be really shameful for an _European_ lander to mix up an altitude reading between feet and meters. But i

by Fiahil 10y ago

At least it wasn't a unit-conversion problem. It would be really shameful for an _European_ lander to mix up an altitude reading between feet and meters. But it's not the case, isn't it?

etatoby 10y ago
It may very well be. Maybe they used an US-developed microcontroller library and screwed up the unit setting.
- cordite 10y ago
  How realistic is a dry run via an earth simulation from high aptitude to make sure units are sane?
  - hguant 10y ago
    Given that Mar's atmosphere masses about 25 terratonnes compared to Earth's 5148 terratonnes, and Mar's atmospheric pressure is about 1% that of Earth's sea level, you'd need to do high altitude testing at about 30 miles up, which is about 5 Mount Everests. Much simpler to test fire the engines in a lab somewhere to make sure they run, and test the software in a simulation of the landing. It'll probably come out in the next year or so that there was either just a flat error in the code, or that the simulation was incorrect in some way.
zymhan 10y ago
Surely in 2016 no one is using imperial units as a default for anything even remotely related to aerospace programming.
- deleted 10y ago
  [deleted]
- rootbear 10y ago
  I work at NASA and sadly, we do still use Imperial units for many things. It's a travesty.
  - logfromblammo 10y ago
    In military aviation mission planning, it's even worse. We have to support any damn-fool unit some random major might want to see on the printed reports. A length might need to display in feet, yards, meters, kilometers, statute miles, nautical miles, US flight level (hundreds of feet by barometer reading), AGL vs. MSL, etc. Sometimes, people mix customary, nautical, and SI units, such as by showing distances in km, altitudes in feet, and speed in knots (NM/h). If I were ever to somehow become absolute tyrant over the entire Earth, my first edict would make open and notorious use of non-SI units a capital crime, then I'd go live in my imperial hermit shack on a remote mountainside (paradoxically, one with a >1 Gb/s network connection) until my minions finished mopping up the last of the blood.
    - TylerH 10y ago
      I enjoy the literary irony here of you imposing a ban on Imperial units and yet you'd go live in an Imperial shack.
  - witty_username 10y ago
    Does the software store unit information and calculates with units (like say 1 m / 1 s = 1 m/s) or does it directly operate on the numerical value (so just 1/1 = 1)? I think the first way should be fast enough with today's processors (but IIRC the processors on the Rovers are slower).
  - Fiahil 10y ago
    .. I don't understand how you guys can get something up in space. That's amazing. It's either a remarkable feat of engineering or an gigantic 42 gallons barrel of liquid luck.
  - zymhan 10y ago
    :(
3chelon 10y ago
That seems exceedingly unlikely. No-one in Europe would even consider using anything other than metric units even for buying their groceries, let alone a critical engineering task. That said, _if_ there were any US companies involved then perhaps there might have been complications. Many years ago I worked on guidance software for tunnelling machines and we had a US client who insisted that we reprogrammed the entire system for them to work in "centifeet", i.e. 100th of a foot or approx 3mm. I well remember the chaos and arguments caused by adopting such a ridiculous chimera of a unit, and was struck by how resistant some people are to adopting something as universal and transferrable as SI units.
- PLenz 10y ago
  10ths (and hundredths of an inch) are completely standard in US surveying. For example: https://www.amazon.com/Lufkin-FE200D-Engineers-Fiberglass-Measure/dp/B001R1UFP6/ https://www.amazon.com/Lufkin-FE200D-Engineers-Fiberglass-Me...
  - 3chelon 10y ago
    Interesting to know - 100th of an inch is extremely small - certainly not visible with my eyesight! Seems odd to need that for surveying.
- sethrin 10y ago
  There are actually a fair few problems with SI units. The candela is fairly ridiculous, the kilogram needs to not depend on a physical object (it's also a little silly to have a prefixed base unit). The ampere is not practical to measure with its current definition, and apparently with the current definitions of Hz and radians, 1 Hz = 1/s = 1 radians/second. Other people take issue with the mole, as well. SI is an improvement but it is not quite perfect. As long as we have a choice of imperfect systems, we have to pick which is most convenient.
  - 3chelon 10y ago
    > it's also a little silly to have a prefixed base unit I somewhat agree with that - I had the exact same conversation with my kids very recently. Re. physical object: well, whatever physical reference artefact is used, to all intents and purposes the physical stuff is water, with the basically sensible equivalence 1L = 1kg = 1000cc. As you point out, it's not perfect because of the somewhat arbitrary scales (kg, cc), and it gets worse when you bring temperature into it (I believe it's supposed to be measured at 4 degrees C, but I'm not totally sure of that). You're right in that it is not perfect, but at least it is a fair attempt at coherence.

by Fiahil 10y ago

At least it wasn't a unit-conversion problem. It would be really shameful for an _European_ lander to mix up an altitude reading between feet and meters. But it's not the case, isn't it?

etatoby 10y ago

It may very well be. Maybe they used an US-developed microcontroller library and screwed up the unit setting.

cordite 10y ago
How realistic is a dry run via an earth simulation from high aptitude to make sure units are sane?
- hguant 10y ago
  Given that Mar's atmosphere masses about 25 terratonnes compared to Earth's 5148 terratonnes, and Mar's atmospheric pressure is about 1% that of Earth's sea level, you'd need to do high altitude testing at about 30 miles up, which is about 5 Mount Everests. Much simpler to test fire the engines in a lab somewhere to make sure they run, and test the software in a simulation of the landing. It'll probably come out in the next year or so that there was either just a flat error in the code, or that the simulation was incorrect in some way.

zymhan 10y ago

Surely in 2016 no one is using imperial units as a default for anything even remotely related to aerospace programming.

deleted 10y ago
[deleted]
rootbear 10y ago
I work at NASA and sadly, we do still use Imperial units for many things. It's a travesty.
- logfromblammo 10y ago
  In military aviation mission planning, it's even worse. We have to support any damn-fool unit some random major might want to see on the printed reports. A length might need to display in feet, yards, meters, kilometers, statute miles, nautical miles, US flight level (hundreds of feet by barometer reading), AGL vs. MSL, etc. Sometimes, people mix customary, nautical, and SI units, such as by showing distances in km, altitudes in feet, and speed in knots (NM/h). If I were ever to somehow become absolute tyrant over the entire Earth, my first edict would make open and notorious use of non-SI units a capital crime, then I'd go live in my imperial hermit shack on a remote mountainside (paradoxically, one with a >1 Gb/s network connection) until my minions finished mopping up the last of the blood.
  - TylerH 10y ago
    I enjoy the literary irony here of you imposing a ban on Imperial units and yet you'd go live in an Imperial shack.
- witty_username 10y ago
  Does the software store unit information and calculates with units (like say 1 m / 1 s = 1 m/s) or does it directly operate on the numerical value (so just 1/1 = 1)? I think the first way should be fast enough with today's processors (but IIRC the processors on the Rovers are slower).
- Fiahil 10y ago
  .. I don't understand how you guys can get something up in space. That's amazing. It's either a remarkable feat of engineering or an gigantic 42 gallons barrel of liquid luck.
- zymhan 10y ago
  :(

3chelon 10y ago

That seems exceedingly unlikely. No-one in Europe would even consider using anything other than metric units even for buying their groceries, let alone a critical engineering task. That said, _if_ there were any US companies involved then perhaps there might have been complications. Many years ago I worked on guidance software for tunnelling machines and we had a US client who insisted that we reprogrammed the entire system for them to work in "centifeet", i.e. 100th of a foot or approx 3mm. I well remember the chaos and arguments caused by adopting such a ridiculous chimera of a unit, and was struck by how resistant some people are to adopting something as universal and transferrable as SI units.

PLenz 10y ago
10ths (and hundredths of an inch) are completely standard in US surveying. For example: https://www.amazon.com/Lufkin-FE200D-Engineers-Fiberglass-Measure/dp/B001R1UFP6/ https://www.amazon.com/Lufkin-FE200D-Engineers-Fiberglass-Me...
- 3chelon 10y ago
  Interesting to know - 100th of an inch is extremely small - certainly not visible with my eyesight! Seems odd to need that for surveying.
sethrin 10y ago
There are actually a fair few problems with SI units. The candela is fairly ridiculous, the kilogram needs to not depend on a physical object (it's also a little silly to have a prefixed base unit). The ampere is not practical to measure with its current definition, and apparently with the current definitions of Hz and radians, 1 Hz = 1/s = 1 radians/second. Other people take issue with the mole, as well. SI is an improvement but it is not quite perfect. As long as we have a choice of imperfect systems, we have to pick which is most convenient.
- 3chelon 10y ago
  > it's also a little silly to have a prefixed base unit I somewhat agree with that - I had the exact same conversation with my kids very recently. Re. physical object: well, whatever physical reference artefact is used, to all intents and purposes the physical stuff is water, with the basically sensible equivalence 1L = 1kg = 1000cc. As you point out, it's not perfect because of the somewhat arbitrary scales (kg, cc), and it gets worse when you bring temperature into it (I believe it's supposed to be measured at 4 degrees C, but I'm not totally sure of that). You're right in that it is not perfect, but at least it is a fair attempt at coherence.