Tomorrow-S12 and S13, and the Road to DeepSky

On October 1, two more Tomorrow.io microwave sounders, Tomorrow-S12 and S13, launched aboard SpaceX’s Transporter-18 from Vandenberg Space Force Base. They joined the fleet that reached a 60-minute global revisit in January and today runs well below it. This is how we got here, why that hour matters, and what comes next.

Nine rides to orbit

Every satellite we have flown went up as a rideshare on a SpaceX Falcon 9, sharing the ride with other spacecraft. The first two, in 2023, were pathfinders that operated precipitation radar from a small satellite. Since August 2024, every launch has carried microwave sounders: instruments that read the temperature and moisture of the atmosphere through cloud.

Why revisit is the number we chase

A satellite in low Earth orbit passes over any one place only a few times a day. The atmosphere doesn’t wait that long: a storm can form, deepen and reach land between two passes. Revisit is the time a place waits between looks, and it sets how fresh a forecast’s starting picture can be.

Each satellite we added shortened that wait. In January, our 10th and 11th sounders brought the constellation to a 60-minute global revisit, the cadence Sky 1 runs on to rebuild the global atmospheric picture every hour. Today, our global revisit runs well below 60 minutes.

Keeping Gen-1 fresh

Before this launch, eleven Gen-1 microwave sounders were active in low Earth orbit. Tomorrow-S12 and S13 are Gen-1 sounders too. With them, the work turned from building the constellation to keeping it fresh: adding satellites so the hourly picture keeps its hour as the fleet ages.

What comes next: DeepSky

DeepSky is our next generation, now being built. Each DeepSky spacecraft will carry five instruments: Gen-2 hyperspectral microwave sounders, GNSS radio occultation, GNSS reflectometry, infrared and visible imaging, and precipitation radar. All five fly on the same spacecraft at the same time, so they read the same column of atmosphere together.

It is aimed at the places where warning arrives late. Roughly 71 percent of Earth is ocean with virtually no ground-based weather radar, and more than five billion people live outside radar coverage entirely.

DeepSky · Tomorrow.io

DeepSky: The Early Warning Constellation, and the Five Instruments It Will Carry

What each of the five instruments reads, and why all five have to fly on the same spacecraft.

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From the instrument to the decision

We design and build the instruments, test them end to end before they fly, operate them in orbit, validate what they measure, model the data, and deliver it into the operations of the people who depend on it.

We made contact with it only an hour later and were able to start getting data down. That is very much a culmination of all your effort, wrapped up into one moment. — Jack Dalimore, Technical Program Manager, Tomorrow.io, 2025

Governments build on it too. In June, NOAA’s National Environmental Satellite, Data, and Information Service awarded us a contract to provide microwave sounder observations under its Microwave Sounder Data Buy. In September, NASA’s Commercial Satellite Data Acquisition program began a formal evaluation of our sounder data.

And the forecasts reach the field. In Kenya, a two-year pilot with TomorrowNow.org and One Acre Fund sent our forecasts by SMS to nearly 10,000 smallholder farmers, and their yields rose 12% relative to a control group. With TomorrowNow, our forecasts now reach millions of farmers in East Africa.

The team behind it

Behind every launch in the timeline above are years of work that come down to a single launch window. Engineers designed and built instruments small enough to share a rocket. Test teams ran the satellites end to end through a “Day in the Life” on the ground before they flew. Operators waited for first contact after deployment, and scientists turned the first readings into forecasts. Launch dates move and pads need turning around; the work keeps going.

To the team: thank you. Fifteen satellites in, we’re just getting warmed up.