[HN Gopher] End of an era: Landsat 7 mission takes final images
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End of an era: Landsat 7 mission takes final images
Author : Qqqwxs
Score : 76 points
Date : 2024-09-26 21:13 UTC (1 hours ago)
(HTM) web link (www.usgs.gov)
(TXT) w3m dump (www.usgs.gov)
| tiffanyh wrote:
| In the Las Vegas slider, the Lake Mead before/after difference is
| startling.
| Dalewyn wrote:
| I'm more intrigued at the increased green of the landscape at
| large, did the water supply actually improve to encourage more
| plant growth?
| stouset wrote:
| The diminishing quantities of blue stuff got put on the brown
| stuff to turn it into green stuff.
| eep_social wrote:
| By people, in case that isn't clear.
| Yawrehto wrote:
| It seems like a lot of these government-owned space things last a
| lot longer than they're made for. There's Landsat, Spirit,
| Opportunity, Hubble, the Voyagers, et cetera. It seems to be a
| pretty steep curve - either they fail on launch or landing or
| very early, or they far outlast expectations. There seems to be
| little that meets expectations. I can see lots of failures -
| space stuff is hard - but why so many things exceeding it?
| conception wrote:
| The engineering to get it to last a year probably isn't
| significantly different from five years, etc.
| wongarsu wrote:
| They build and design everything in a way that ensures a 99%
| chance that after successful launch and deployment it will last
| for the mission duration in a harsh and still somewhat
| unfamiliar environment. That happens to translate into a very
| high chance that it will still work after twice the mission
| duration, or ten times the mission duration.
|
| Part of this is cultural, part of it is political: nobody wants
| a failed mission, it's better for the image of the agency and
| the involved politician to spend a bit more money and
| underestimate the lifetime. Higher chance of success, and
| nobody complains if the mission can be extended afterwards.
| bmsan wrote:
| For this particular satellite, I think it's actually both. One
| of the components of the imaging system failed relatively early
| on[1], but they've worked around the issue for the past 20
| years.
|
| 1: https://landsat.gsfc.nasa.gov/satellites/landsat-7/
| beerandt wrote:
| Because you set a min life, but statistics aside, the design
| for that minimum life isn't usually something that can be
| tweaked on a continuous scale, but ends up being binned by
| design constraints.
|
| Eg, you need an industrial road with a 5-year lifespan over a
| swamp. To meet this minimum you actually have to build a
| bridge, which when built to industry standards, might start at
| lifespans of 20-30 yrs.
|
| Space is a bit different because of budgeting for ongoing
| operations, so you frontload the cap-x, knowing that asking for
| addl op-x funds later to extend the program will seem like a
| no-brainer deal.
|
| Plus sometimes it's as simple as: if you design something to
| statistically survive space launch, it results in something
| that is overdesigned to just sit in orbit for years (given that
| it survives that initial launch).
|
| It's similar to human lifespan statistics- if you get over the
| historical infant mortality hump, every adult seems
| 'overdesigned' compared to the historical expected lifespan.
| maxclark wrote:
| Life expectancy is statistical probability
|
| The mission targets a length of time, then the engineering
| matches for the design and build
|
| Reality is usually much longer
| bmsan wrote:
| Dang, hits home. When I was a senior in high school, I was lucky
| to able to volunteer under Dr. Eric Brown De Colstoun at NASA
| Goddard, checking error rates for tree cover estimates using
| Landsat data^. Many hours that fall spent trudging around parks
| and forests, looking at the sky through a PVC pipe. It still kind
| of blows my mind at how much is able to be gained from images
| where each pixel is 15mx15m of ground-level area (and, I believe,
| with an important component of Landsat 7's imaging system broken
| for most of its lifespan).
|
| I also wasn't aware that Landsat program imagery had been made
| free to access a few years later. Nice.
|
| ^(A massive thank you to him, since I wouldn't have graduated
| without being able to participate in that project. And a massive
| apology for going on to get a fine arts degree.)
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