The SWOT satellite observatory is being jointly built by NASA and Centre National D'Études Spatiales (CNES). It consists of a Payload Module and Spacecraft Bus whose assembly is being led by the NASA Jet Propulsion Laboratory (JPL) and CNES, respectively.

The Payload has components contributed by NASA, CNES, and CSA. The primary payload is the Ka-band Radar Interferometer (KaRIn) that is being developed by JPL. The Canadian Space Agency will provide a high-power assembly component for KaRIn. CNES will build the Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) Antenna and Nadir Altimeter. JPL will also provide a Global Positioning System (GPS) science receiver, a Laser Retroreflector and two-beam Microwave Radiometer.

The boom between SWOT's radar interferometer antennas will be 10 meters (32.8 feet) apart. Radar pulses will be transmitted by one antenna and received by both for interferometry, creating two parallel swaths of data.

Payload

SWOT's payload is comprised of the following instruments:
  • KaRIn
    • Using JPL-developed instrument technology, radar interferometry, KaRIn will measure ocean and surface water levels over a 120-km (75-mi) wide swath with a ~20 km (~12 mi) gap along nadir. It will operate in two modes:
      • Low-Resolution over the ocean with significant onboard processing to reduce data volume.
      • High-Resolution over broad, primarily continental, regions defined by the SWOT Science Team, focusing on hydrology studies.
  • Jason-class Altimeter will collect data in the gap between the KaRIn swaths. It will send and receive signals that travel straight up and down. Each pulse's round-trip travel time will be used to determine Sea Surface height.
  • DORIS Antenna will pick up signals from 50-60 ground-based radio beacons, equally distributed over Earth to ensure good coverage.
  • Microwave Radiometer will measure the amount of water vapor between SWOT and Earth's surface. More water vapor means slower radar signals.
  • X-band Antenna will be used for high-rate data downlink.
  • Laser Reflector Assembly is an array of mirrors that will provide a target for laser tracking measurements from the ground.
  • Global Positioning System (GPS) Receiver will pick up tracking signals from the constellation of GPS satellites.

Spacecraft Bus

Mounted below the Payload Module, the Spacecraft Bus is a multi-purpose platform housing many of the electronics required for the observatory to function:
  • S-band antenna will be used to communicate with Earth using a radio transmitter and receiver.
  • Command and data handler will manage the observatory's communication links and perform various tasks (e.g., data storage) using a centralized processor.
  • Electrical power subsystem is where all of the spacecraft’s power is generated, stored, and distributed.
  • Thermal control is a subsystem responsible for maintaining the temperatures of each component on the observatory within its allowable limits.
  • Solar arrays will be deployed from opposite sides of the Spacecraft Bus while SWOT is in orbit, using small drive motors to keep them pointed at the Sun.
  • Attitude control system will determine the observatory's orientation using star trackers. The satellite's attitude will be carried out by magnetic torquer bars and reaction wheels.
  • Propulsion will be used to adjust SWOT's orbit by firing a combination of its onboard thrusters. This subsystem also includes a propellant tank.

Resources

How SWOT Will Work [e-brochure]
[2017] This e-brochure explains how interferometry - the study of how waves interfere - will be used by SWOT to measure water levels with extraordinary accuracy across the globe.
Solar Panel Deployment [video]
[2016] The deployment of SWOT's solar panels is featured in this animation.
Deployment of Interferometer Antennas [video]
[2016] This animation shows the various stages of boom deployment for the interferometer antennas.
SWOT Data Collection Over Florida [video]
[2016] This animation shows the collection of data over the state of Florida, which is rich with rivers, lakes and wetlands.