As the launch date approaches, NASA and CNES will begin SWOT testing.

The final spacecraft assembly of the Surface Water and Ocean Topography (SWOT) spacecraft is being completed by France's Centre National d'Etudes Spatiales (CNES) and NASA with less than a year until launch.

The Canadian Space Agency (CSA) and the United Kingdom Space Agency (UKSA) both contributed to the SWOT mission, which is a joint NASA-CNES mission.

The SWOT mission will be the first-ever global surveyor of all of Earth's water, with the goal of determining how bodies of water change over time.

SWOT will launch from Space Launch Complex 4 East (SLC-4E) at Vandenberg Space Force Base (VSFB) in California on a SpaceX Falcon 9.

The mission will launch no earlier than November 2022, according to the current schedule.

SWOT is the latest in a series of satellites developed by NASA and CNES to map Earth's waters.

The TOPEX/POSEIDON mission, launched on an Ariane 42P H10 launch vehicle in August 1992, was the start of this program.

Radio altimeters and precise orbit determination systems were used by the TOPEX/POSEIDON satellites to map the Earth's ocean surface topography as well as changing sea levels.

TOPEX/POSEIDON allowed for continuous observation of global ocean topography while tracking changes in sea levels and how heat is stored in upper-level waters while it was active.

TOPEX/POSEIDON was decommissioned in January 2006 due to the failure of its pitch reaction wheel.

TOPEX/POSEIDON lasted 13 years, far longer than the three years it was supposed to last.

Because of the success of TOPEX/POSEIDON, NASA and CNES decided to continue working together on the Jason satellite program.

The Jason program began as a dedicated program to carry on TOPEX/POSEIDON's mission, with the same goals as its predecessor but improved accuracy and the ability to operate with multiple satellites at the same time.

Jason-1, the first satellite, was launched in 2001.

Since then, in 2008 and 2016, two more missions bearing the Jason moniker have been launched.

Sentinel 6 Michael Freilich, the fifth satellite, will be launched in 2020.

It's based on the same technology, but it's called Sentinel because it's a collaboration with the European Space Agency.

Jason Continuity of Service (Jason-CS) is another name for the mission.

Sentinel 6B/Jason-CS B, the second mission, will launch in 2025.

With Jason 3 and Sentinel 6 still operational, the Jason program carries on the TOPEX/POSEIDON legacy.

SWOT was first proposed by the National Research Council Decadal Survey in 2007.

The mission is an offshoot of the Jason program, and it employs many of the same technologies.

The mission underwent conceptual studies and technological advancements from 2007 to 2015.

It started preliminary design and technology completion in 2015.

It was approved for implementation in 2016, and final design and fabrication began in 2017.

The payload suite and the satellite bus are the two main components of the SWOT spacecraft.

Thales Alenia Space (TAS) was chosen to build the satellite bus in 2015.

The SWOT bus is TAS's newest satellite bus, which complies with France's Space Operations Act.

This bill aims to reduce space debris and reduce the risk of reentry into the atmosphere over populated areas.

Any satellite using the new bus will be able to control itself during reentry to ensure a safe disposal.

Many components supporting the payload suite will be housed on the satellite bus.

When the construction is finished, the bus will be parked beneath the suite.

To allow radio communications between the spacecraft and ground stations, it will use an S-band antenna.

The spacecraft's communication and other tasks will be managed by a command and data handler.

Electrical power will be provided by two solar arrays.

The spacecraft's propulsion and attitude control system (ACS) will also be housed on the bus.

To control where the spacecraft is pointing, the ACS will use star trackers with magnetic torque rods and reaction wheels.

The spacecraft's orbit is controlled by eight 22-Newton hydrazine thrusters.

The payload suite is located on top of the satellite bus.

Six instruments, including an X-band antenna, will be housed in the suite to carry out SWOT's mission.

The suite was built at NASA's Jet Propulsion Laboratory in California, unlike the bus, which was made in France.

All four contributing space agencies have contributed instruments.

JPL provides and develops the primary instrument, the Ka-band Radar Interferometer (KaRIn).

Components for KaRIn will be provided by the CSA and the UKSA.

Interferometry will be used by KaRIn to measure ocean and surface water levels.

The instrument will use two antennas to monitor water levels, each with a 60-kilometer swath.

Between the two swaths, there will be a 20-meter gap.

It will have a low and high-resolution mode while in use.

Over oceans, the low resolution will be used with more onboard processing.

In broad, primarily continental, regions, high resolution will be used to focus on hydrology studies.

During launch, the two antennas will be enclosed.

The antennas will be deployed after the launch, allowing global water level observation.

CNES will provide two instruments to close the majority of the 20-meter gap.

The data between the KaRIn swaths gap will be collected using a Jason-class Nadir altimeter.

The Nadir altimeter will send signals to the sea surface and calculate the height based on the signal's round trip time.

The Nadir altimeter will be supported by a second instrument, the Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) antenna.

To determine SWOT's orbit, the DORIS antenna will pick up ground-based radio signals.

To gain precise orbit determination, a GPS receiver provided by JPL will be used in conjunction with the Nadir altimeter and DORIS antenna.

JPL will also provide two additional SWOT instruments.

For in-orbit tracking and orbit determination, the Laser Reflector Assembly provided by JPL will use mirrors and ground-based lasers.

A Microwave Radiometer is the final instrument, which is used to measure water vapor.

If the radiometer sends slow signals to the earth, there is more water vapor present.

On June 30, 2021, a US Air Force C-17 delivered the payload suite to TAS in France after it was completed.

TAS mated the suite on top of the satellites bus in August 2021, with the help of CNES and JPL teams.

"The best part has been seeing two complex systems built by different teams across the world come together and work," said Said Kaki, deputy project manager for SWOT at JPL.

TAS was able to complete the final assembly of the spacecraft after completing the primary spacecraft assembly.

This can include any additions to the spacecraft, such as electrical systems and hardware.

The SWOT spacecraft's final assembly may allow the TAS teams to begin final launch testing.

Testing will begin in the months leading up to SWOT's launch to see if the spacecraft can withstand the harsh environment of a launch and space.

The SWOT testing will be done in three stages.

The first step is to see if the spacecraft can withstand the launch environment.

The satellites will be attached to a shake table and then an acoustic chamber by the teams.

This enables the spacecraft to be shaken and bombarded with sounds in order to simulate a launch.

The spacecraft will then be placed in a thermal vacuum chamber, which will simulate the vacuum and extreme temperature changes it will encounter in space.

Electromagnetic interference will be checked in the final phase of testing.

Final hardware will be installed on the spacecraft after it passes testing before it is delivered to VSFB for launch.

"After that, we seal the spacecraft and transport it to the launch site," Kaki explained.

The team at Vandenberg will put the finishing touches on the satellite in order to get it ready for launch, which is set for November 2022.

SWOT's science team is also getting ready for when the spacecraft is in orbit.

The team is running simulations to make sure they'll be ready when SWOT launches into orbit to collect data.

Several space agencies from around the world have enlisted the help of the science team.

"Working with a large international research team with diverse interests and backgrounds in oceanography and hydrology is the best part of my job as the mission's project scientist," said Lee-Lueng Fu, the JPL project scientist for SWOT.

"Even after 40 years of dedication to Earth research, this experience has broadened the horizons of my scientific career."

NASA created the AirSWOT mission to support the SWOT mission.

AirSWOT is a NASA Armstrong Flight Research Center-operated airborne instrument based on the B2000 Super King Air aircraft.

AirSWOT collects two swaths of data on the ground using the Ka-Band SWOT Phenomenology Airborne Radar (KaSPAR).

The AirSWOT is used to collect data in order to better understand Earth's natural properties, as well as to better understand the data that will be collected by SWOT in the near future.

AirSWOT is currently being used and will continue to be used after the launch.

It can be used to help calibrate the data collected by the satellite and prepare the team for the data from SWOT.

The roughly 2,000 kg satellite will be launched into near-polar orbit by a SpaceX Falcon 9.

NASA's Launch Service Program (LSP) chose Falcon 9 as SWOT's launch vehicle in November 2016.

The satellites will be placed in an 857 km circular orbit with a 77.6 degree inclination in the beginning.

For the first six months after launch, the satellite will remain in this orbit to conduct "fast-sampling." After that, the satellite will begin on-orbit checkouts and begin its commissioning period.

The calibration of SWOT will begin in the next 90 days.

The satellite will spend a week after completion raising its orbit to the operational altitude.

SWOT will begin its three-year mission once it reaches its operational orbit of 891 kilometers.

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The spacecraft will take overlapping measurements of the ground with an average revisit time of 11 days.

The satellite will be operated jointly by NASA and CNES in orbit.

The spacecraft will be controlled and communicated with via S-Band communications, while payload data will be communicated via X-Band communications.

Every day, the satellite will communicate with ground stations 21 times.

The data will be processed and released within 60 days after NASA and CNES receive it from the satellite.

The payload and satellite bus are integrated together by Thales Alenia Space.

(Photo courtesy of Thales Alenia Space)

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