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Qqqwxs | 42 comments

bmsan|next|

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|parent|next|

What did you do with the pvc pipe?

MostlyStable|root|parent|next|

if I had to guess, they were going to randomly selected locations, looking at the sky through the PVC pipe (presumably straight up), and seeing if it was obstructed by tree canopy or not, and then comparing to whether or not the satellite said there was tree cover in that location

bargle0|parent|prev|next|

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|prev|next|

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|parent|next|

> 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|parent|prev|next|

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.


mmooss|parent|prev|next|

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.

userbinator|parent|prev|next|

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.

beerandt|parent|prev|next|

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.


bmsan|parent|prev|next|

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/


conception|parent|prev|next|

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

bwy|parent|prev|next|

Lindy effect?

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


Palomides|parent|prev|next|

all hardware is subject to the bathtub curve

tiffanyh|prev|next|

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

syncsynchalt|parent|next|

The after photo is actually _up_ substantially from 2022.

whimsicalism|parent|prev|next|

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)


foolfoolz|parent|prev|next|

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

Dalewyn|parent|prev|next|

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|root|parent|next|

The diminishing quantities of blue stuff got put on the brown stuff to turn it into green stuff.

eep_social|root|parent|next|

By people, in case that isn’t clear.

syncsynchalt|root|parent|prev|next|

May is much greener than July.

daamsie|root|parent|prev|next|

The photo from '99 was taken in May. The recent one was in July.

syncsynchalt|root|parent|next|

Other way 'round. That's why the after photo is so green, May is much greener than July.

littlestymaar|prev|next|

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.

antman|prev|next|

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

maxclark|prev|next|

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


Waterluvian|prev|next|

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

ks2048|prev|next|

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

mmooss|parent|next|

Are you volunteering to pay more taxes?

andrewinardeer|root|parent|next|

I would if I could choose which program the money was directed at.

i3o3o3o|prev|next|

Oooy4o3

IROROKROEO6383637


edm0nd|parent|next|

My thoughts exactly

Mistletoe|prev|next|

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|parent|next|

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.

beginnings|prev|

did somebody pop its balloon?

nasa running low on helium?