End of an era: Landsat 7 mission takes final images

[bmsan]

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.)

[is_true]

What did you do with the pvc pipe?

[bargle0]

Yeah, the scan line corrector broke. Landsat 7 images had these “whiskers” of missing data running perpendicular to the path. For a while there it was just old Landsat 5 and broken Landsat 7.

[Yawrehto]

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?

[duskwuff]

> 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.

[wongarsu]

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]

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]

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.

[userbinator]

Space is still a relative unknown, so overbuilding and conservative estimates are far preferred to aggressive cost-cutting and thin margins. You see the same thing with other technologies like cars and appliances -- early versions were mostly very overbuilt.

[noisy_boy]

When smart and dedicated people are allowed time to think, plan and execute instead of being constantly forced to sacrifice everything at the altar of next-quarter results, the quality of the output tends to be better.

[mmooss]

Basic consulting: Underpromise, overdeliver. Nobody knows how long a Mars rover should last; NASA perhaps picks a number so low that they can't fail, and then have another narrative about the amazing little robot that kept going, and which makes the investment look great for taxpayers.

[conception]

The engineering to get it to last a year probably isn’t significantly different from five years, etc.

[bwy]

Lindy effect?

If something is built to last 10 years, it makes it likelier that it can survive another 10.

[callmeal]

>government-owned space things last a lot longer than they're made for

Don't forget that once upon a time, commercial-owned things lasted a lot longer too. Unfortunately the mba's took over and planned obsolescence became a thing.

[Palomides]

all hardware is subject to the bathtub curve

[tiffanyh]

In the Las Vegas slider, the Lake Mead before/after difference is startling.

[trhway]

Aral Sea (https://earthobservatory.nasa.gov/world-of-change/AralSea - notice the 1960 outline in pale yellow before starting the 2000-2018 playback) and Lake Chad i'd say even more startling.

[syncsynchalt]

The after photo is actually _up_ substantially from 2022.

[whimsicalism]

you can also see a massive solar plant in red in the bottom right

(and maybe also wind - although why they would both be red is beyond me)

[Dalewyn]

I'm more intrigued at the increased green of the landscape at large, did the water supply actually improve to encourage more plant growth?

[foolfoolz]

this is because we siphon water from rivers, mostly for agriculture

[antman]

History of Landsat is very interesting https://www.space.com/19665-landsat.html

[Waterluvian]

A lot of my undergrad and grad school involved using ETM+ imagery. Gosh does that sink in how long ago that was.

[littlestymaar]

The two different pictures of Las Vegas in 1999 and 2024 shows the environmental tragedy unfolding: the city doubled in size, and Lake Mead shrank.

[helpfulclippy]

The overwhelming majority of the water does not go to Las Vegas (https://en.m.wikipedia.org/wiki/Colorado_River_Compact) — Nevada is only allocated 4% of the total water drawn from the Lower Colorado River. Las Vegas gets blamed due to its proximity to Lake Mead and the fact that it is in a desert, but it’s actually adopted aggressive water control measures over the years (see https://www.snwa.com/conservation/understand-laws-ordinances... for recent examples).

Also worth noting that while the colorizations of these satellite photos tend to paint the city in green, it is NOT very green at all. Clark County deprecated lawns ages ago by banning new ones and paying people to remove their existing lawns to replace with desert landscaping.

But that can only help mitigate the overdraw of the Colorado so much when 96% of the water is going to places that have much less stringent water conservation policy.

[tetris11]

It looks like it's 20% smaller bounds-wise, but that's the top layer of the lake: the volume reduction must be at around 40-50%...

[maxclark]

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

[sdmike1]

I can't seem to find a reason for shutting it down in the article. Does anyone have info on this? Was it for budget reasons or was their a failure on orbit?

[kragen]

perhaps the most important news to me here is that landsat 9 was launched in 02021. landsat 8 is also still alive and kicking!

[Mistletoe]

Frightening how much smaller Lake Mead is now.

> How long does Lake Mead have left? Lake Mead has been facing a water crisis for many years. The water level in the lake has been dropping due to the increasing demand for water and the decreasing supply. If the trend continues, the lake could run out of water in the next 10 to 15 years.

Great…I was in Vegas last weekend, I guess they’ll just run it until it’s dry. Humans are ridiculous.

[kibwen]

The city of Vegas is among the best and most proactive in the country at water preservation and reclamation. Sadly, it still might not be enough. In the 90s they started paying people to tear up their lawns, and more recently they outlawed lawns and started tearing some up forcefully, and last I checked watering grass still accounted for a double-digit percentage of their water budget.

[ks2048]

Amazing what a rounding error in the federal budget can do for humanity. More please.

[mmooss]

Are you volunteering to pay more taxes?

[edm0nd]

My thoughts exactly

[beginnings]

did somebody pop its balloon?

nasa running low on helium?