Nitpick time… on that JWST location-tracking page, there is a button to choose between “English” (degrees Fahrenheit, miles) and “metric” (degrees Celsius, kilometres) units.
Now, the “metric” units are almost certainly SI Metric. But “English”? Do they mean US Customary units, or Imperial units? If someone starts talking about “gallons”, there’s a good chance something will get mixed up.
This may seem a nitpick, especially if they don’t talk about anything other than distance and temperature, but this is frickin’ NASA fer Pete’s sake! They of all people ought to know about the necessity for clarity in describing measurements!
(And besides, where are the temperatures in kelvins?)
I just now noticed something else new on that page (or at least, something I wanted to see but didn’t see before): There are now buttons to select a “Time” view or a “Distance” view.
The default view on the timeline (until now, the only view) showed equi-spaces days on the timeline. Since the craft is slowing down, it follows that the distances are not shown to scale. In this view, it appears to be only about one third of the way there.
With the new Distance display, the timeline shows distances drawn to scale. In this view, it shows the telescope to be a little over half-way there.
Many of us lay consumers of NASA output probably think in terms of English versus Metric. Those are certainly the terms my internal voice bandies about when I’m trying to figure out what wrench to use.
I’m sure they appreciate the necessity for clarity. In fact, I’d bet the people working inside NASA would have been inclined to vote for the US going SI. But NASA’s public-facing pages are probably quite right to offer their entertainment in “English” for normal voters and “Metric” for offbeat voters in the US.
And I say this as a very pro-SI voter who actually did work for NASA in 1963.
When I was at the KSC recently, I noticed some (for lack of a better word) “sloppy” labeling on the descriptions in front of the rockets in the Rocket Garden. I don’t remember the exact quotes or numbers, but here is a made-up example of what I’m talking about:
This rocket weighs about 20,000 pounds (9,071.85 kg)
I found it odd that they provided the English measurement as an approximation, and the metric version with such precision. So I quickly went to my Google machine and typed in “20,000 pounds in kilograms”. Sure enough, the result was 9,071.847, which proves that the metric amount is false precision. To make it clear that it is an approximate number, they should just say “about 9,000 kg”, or “about 9,100 kg”.
Since NASA is an American institution, funded by the American government, it hardly seems like a stretch to assume that American units are intended. Your nitpick would make sense only if NASA were a joint American/British venture. Do you go around asking highway departments if they mean statute miles or nautical miles?
NASA is entirely American, but the JWST is not. It’s a joint venture between NASA, the European Space Agency (ESA) and the Canadian Space Agency (CSA). ESA was notably responsible for the launch and accurately setting it on its trajectory to L2 orbit, while CSA provided some of the most important instrumentation.
Back on topic, we are past due on some updates about the sun shield tensioning. It’s obviously working as the cold side is now impressively chilly, but although tensioning is supposed to take about two days, “start” and “completion” are two separate milestones. Hope all is well.
The temperature popup has more information, but no more clarity:
UNITS
By default the page loads and displays distances in miles, temperatures in Fahrenheit, ie English/US units (also known as Imperial or USCS system units). If you wish to have the page load and display in kilometers and temperatures in Celsius, ie metric system units use the urls below to select your preferred units.
So, they recognize that USCS is a name for a system that uses miles and degrees Fahrenheit, but make no further distinction between English/Imperial/USCS. But on the other hand, as long as they stick to lengths and temperatures (and avoid fluid measures specifically), there’s not really any potential for ambiguity.
For terrestrial navigation everybody uses nautical miles, and, besides those, in the US alone there are also survey miles and statute miles and who knows what else, so for anyone who is not already familiar with old-school NASA work, “What’s a mile?” seems like a legitimate question, not just being cute.
International vs. survey miles is an important distinction if you’re actually building things at a large scale, but the difference (at the time I wrote this) is between a distance of 518038.1 mi vs. 518037.0 mi. Unimportant for a public-facing page like this. Nautical miles are a more significant difference, but they’d have been specified if used.
The page uses metric internally. I found this bit of Javascript: _0x5a8556(0x138)]=Number(g['tempCoolSide1C']*(0x9/0x5)+0x20
Also, looking through the code–although the temperatures are dynamic and come from a state page, it looks like the distances are hard-coded. There’s a table in the page with fixed distances based on the “deployment index”, and I believe they just get interpolated based on the current time. At any rate, all the distances in the table are in kilometers and get converted to miles by multiplying by 0.621371.
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