The Spaceflight Now article DigitalGlobe books two launches with SpaceX for Earth-imaging fleet goes beyond describing the two launches to talk about DigitalGlobe's future plans.
Fitted with imaging telescopes and detectors built by Raytheon, the WorldView Legion satellites will capture panchromatic, or black-and-white, images with spatial resolution of around 1 foot, or 30 centimeters. That is comparable to the imaging resolution offered by DigitalGlobe’s newest satellites, WorldView 3 and WorldView 4.
DigitalGlobe says the WorldView Legion fleet will double the company’s ability to capture the highest-resolution 30-centimeter-class imagery, and triple capacity over the parts of the planet with the highest imaging demands. The development, construction and launch of the new Earth observation fleet is expected to cost around half of the WorldView 1, WorldView 2 and GeoEye 1 missions it will replace.
The combination of DigitalGlobe’s existing satellites, the Scout network and WorldView Legion will be able to observe “the most rapidly changing areas on Earth as frequently as every 20 to 30 minutes, from sunrise to sundown,” the company said in a statement.
Am I misunderstanding the article, or is there a suggestion that ~30cm resolution would be available "as frequently as every 20 to 30 minutes" (daytime) for the world's most rapidly changing areas?
Question: Assuming agile, state-of-the-art ADCS, how many satellites would be necessary to to re-image a specific equatorial or mid-latitude area at even medium to high resolution (if not ~30 cm) "as frequently as every 20 to 30 minutes"?
Are we talking hundreds, or thousands? The article mentions Planet Labs and about 200 Doves for once-daily coverage per site as reference, but if I understand correctly those are generally nadir-fixed and use the constellation's pattern to rescan, whereas DigitalGlobe's satellites might be targetting a specific site for higher cadence.
I'm interested in understanding DigitalGlobe's plans and how the "as frequently as every 20 to 30 minutes" statement stacks up to their plans; maybe I'm just reading it wrong?