12 Doves – Flock 2p

Photo: NASA
Photo: NASA

Riding into orbit aboard the PSLV C34 rocket are 12 Dove satellites operated by Planet Labs to make up the Flock 2p of the company’s Earth Observation Satellites.

Flock 1 & 2 is a satellite constellation of CubeSats dedicated to Earth Observations using a fleet of small satellites to generate high-resolution images of Earth achieving resolutions of three to five meters. The operational constellation began deployment in 2014 and uses a combination of shorter and longer lived orbits being launched from the International Space Station and different orbital launch vehicles.

The satellites are designed, developed, manufactured and operated by Planet Labs based in San Francisco that markets the Earth Observation data products to a range of customers for a variety of applications.

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Image: Planet Labs
Image: Planet Labs
Image: Planet Labs
Image: Planet Labs

The Flock 2 spacecraft are based on the three-unit CubeSat specification having a launch mass of about 5 Kilograms and being 100mm × 100mm × 340mm in size featuring body mounted solar panels and two deployable solar arrays with three panels each using triangular advanced solar cells.

The solar arrays are spring-loaded and deployed by burn-wires once the satellites are released into their independent orbits. Flock spacecraft contain Lithium-Ion batteries that provide power to the various systems. A power distribution unit delivers power to all subsystems. The load bearing satellite structure consists of three skeleton plates, with L rails along each corner edge. Laser etched side panels are used for the Flock satellites.

Attitude data is provided by three-axis magnetometers to accomplish three-axis stabilization via a reaction wheel system and magnetic torquers for momentum management. Fine pointing data is provided by a Star Camera. Flock 1 satellites use a single-board computer to control all spacecraft and payload functions with a watchdog board able to reboot the flight computer in the event of errors or radiation related upsets.

The satellites use an X-Band system for the downlink of acquired images and systems telemetry at data rates of up to 120Mbit/s. Primary command uplink is done via S-Band, although a low-speed Telemetry and Command System operating in the UHF band is also available and in use for early commissioning operations and as a backup.

Image: Planet Labs
Image: Planet Labs

The main payload of each satellite is an optical telescope of unknown specifications to acquire high-resolution images of Earth. The telescope has an aperture diameter of 90mm and is protected by an aperture cover that is deployed via springs. The optical axis is down the central axis of the satellite to achieve a maximum focal length.

The Flock satellites, also known as Doves, are going through constant modifications and improvements, even within a group of satellites, not all are necessarily identical. Variations that have been introduced include the use of improved detectors and infrared filters.