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End of an era: Landsat 7 mission takes final images
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Re: End of an era: Landsat 7 mission takes final images
#12Dang, 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.)
Re: End of an era: Landsat 7 mission takes final images
#13It 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…
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.
Re: End of an era: Landsat 7 mission takes final images
#14It 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…
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.
Re: End of an era: Landsat 7 mission takes final images
#15Earlier quoted context omitted.
I'm more intrigued at the increased green of the landscape at large, did the water supply actually improve to encourage more plant growth?
The diminishing quantities of blue stuff got put on the brown stuff to turn it into green stuff.
By people, in case that isn’t clear.
Re: End of an era: Landsat 7 mission takes final images
#16It 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…
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.
Re: End of an era: Landsat 7 mission takes final images
#17It 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…
> I can see lots of failures - space stuff is hard - but why so many things exceeding it?
The design lifetime is treated as a minimum acceptable value; a vehicle which was designed to last 10 years but has a critical component fail at 9.5 would be considered a failure, for instance. This means that the average lifespan of the vehicle gets pushed out a lot further to ensure it meets its goals.
With that being said, it's not uncommon for space vehicles to reach end-of-life for reasons other than a system failure - one common one being that a satellite or space probe runs out of propellant. Since the underlying mechanism there is predictable, rather than a random failure, there's much less margin needed.
Re: End of an era: Landsat 7 mission takes final images
#18It 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…
all hardware is subject to the bathtub curve
Re: End of an era: Landsat 7 mission takes final images
#19A lot of my undergrad and grad school involved using ETM+ imagery. Gosh does that sink in how long ago that was.