[sparkman55]

For a long time, public satellite imagery came from satellites flown by the US Geological Survey (USGS). They came in two flavors: geostationary and low-earth orbit.

The geostationary satellites are perched very high above the earth, and take frequent pictures of the 'full disk' of earth. This is invaluable for weather forecasting, as we can see what clouds are doing in real time. However, they are so far away that you need big, expensive satellites and big, expensive launches, and the resulting resolution is quite poor (like one pixel per 5km depending on latitude, and worse at high latitudes).

On the other hand, the low-earth orbit satellites fly just above the atmosphere, and can take pictures at much higher (spatial) resolution, but may only fly over a particular spot of land once per day. So you trade temporal resolution for spatial resolution.

With miniaturization, advances in imaging and related technology, and decreasing launch costs, it should be possible to deploy a constellation of small low-earth-orbit satellites, to provide good temporal AND spatial resolution. That enables a whole bunch of new applications.

However, I'd be a bit concerned that long-lived airborne drones flying at high altitudes might do the same thing (good spatial AND temporal resolution), but at a lower price point and in a more efficient way (since you only fly where you want to look, instead of covering the entire globe).

Perhaps I'm missing something?

[ebildsten]

Satellites in LEO (including ours) travel at about 17,000 mph — drones can get nowhere close to that, which affects total coverage area possible per aircraft / spacecraft, which in turn will affect costs and operations.

To get a sense of what 17,000 mph ground speed looks like from a satellite's point of view: https://www.planet.com/pulse/la-to-vegas-in-52-seconds/

[sparkman55]

Ground speed doesn't seem like a feature to me - after all, the ideal is an unblinking 'eye in the sky' that provides high-resolution video for large regions a la ARGUS. A stationary observer seems like it would provide more valuable information than an orbiting one.

With orbiting satellites, most of the time the birds are over the ocean and empty stretches of land that most people don't care about. You're wasting most of your bandwidth and storage on places that someone might be interested in one day...

Don't get me wrong, the work you're doing is very cool, and global data sets are really fun! Unfortunately, I've found that the 'value density' of these global data sets isn't great.

[branchan]

You cannot keep a stationary drone in the sky for long stretches of time. Their field of view is also going to be massively smaller than a satellite. You would need a lot of them just to keep the same amount of coverage.

How do you know nobody is interested in the 'ocean and empty stretches of land'? It could provide a lot of meteorological and geological data for scientists for example.

[sparkman55]

Funny you should mention meteorological use cases. At a previous startup, we built global historical weather data sets (at 5km resolution, 30+ year hourly time series), accessible via a metered API. This took HPC, storage, and engineering investment about an order of magnitude less than Planet. We also had a whole room of tapes filled with satellite imagery from the world's governmental Met offices...

Our main use case was for wind and solar renewable energy, but we also entertained other uses, like architecture and agriculture. These data sets turned out to be difficult to monetize; while the continental US data set may have broken even, the rest of the globe never recouped the cost of storage, let alone the supercomputer time. It's not that people around the world weren't interested in the data, they just couldn't justify paying for it.

[Thrymr]

> but may only fly over a particular spot of land once per day.

Even less frequent: Landsat 8 repeats every 16 days: http://www.usgs.gov/blogs/features/usgs_top_story/landsat-8-...

[andygates]

Drones have to worry about airspace rules, which satellites do not.

One advantage they're keen to promote is that a 15-year lifespan sat has, by the end of its life, a 15-year-old camera. Technology marches on, and small cheap (nearly disposable!) satellites can just roll improvements into their replacement cycle in a way that the big boys can't.

[Already__Taken]

Since we're talking of comparing drones though, that camera argument doesn't work out since you can just land the drone and bolt a new one on.

Do airspace laws still go all the way up to if you can fly at say 60-80,00ft? I guess they must, we're talking about private spy planes aren't we.

[unchocked]

If you assume UAVs will improve while space launch costs stay flat, you probably have a point. If space launch keeps getting cheaper (thanks Elon!) then the persistence of satellites will give UAV swarms a run for their money.