by Douglas Messier
A Franco-American mission to measure global surface water levels from space continues to hold to its budget and an April 2022 launch date despite the late arrival of its main scientific instrument, according to a new assessment by the Government Accountability Office (GAO).
The $754.9 million Surface Water and Ocean Topography (SWOT) mission had been working toward a September 2021 launch date, which would have been seven months ahead of schedule.
However, the project experienced a six-month delay in delivery of the Ka-Band Radar Interferometer (KaRIn) instrument’s radio frequency unit from CNES, the French space agency.
Despite the delay, NASA expects to meet the original April 2022 launch date. SWOT will be launched aboard a SpaceX Falcon 9 booster from Vandenberg Air Force Base in California.
Data returned by the SWOT satellite “will make it possible to estimate water discharge into rivers more accurately, and help improve flood prediction,” GAO said. “It will also provide global measurements of ocean surface topography and variations in ocean currents, which will help improve weather and climate predictions.”
The Canadian Space Agency and the UK Space Agency are also partners in the SWOT mission.
GAO’s assessment of the SWOT mission follows.
NASA: Assessments of Major Projects
Report to Congressional Committees
Government Accountability Office
Surface Water and Ocean Topography
The Surface Water and Ocean Topography (SWOT) mission will use its wide-swath radar altimetry technology to take repeated high-resolution measurements of the world’s oceans and freshwater bodies to develop a global survey.
This survey will make it possible to estimate water discharge into rivers more accurately, and help improve flood prediction. It will also provide global measurements of ocean surface topography and variations in ocean currents, which will help improve weather and climate predictions.
SWOT is a joint project between NASA and the French space agency—the Centre National d’Etudes Spatiales (CNES).
The SWOT project is still operating within its cost and schedule baselines despite delays with its primary instrument, the Ka-Band Radar Interferometer (KaRIn). The project was working toward a September 2021 launch date, but is reviewing this schedule after a 6-month delivery delay for the KaRIn instrument’s radio frequency unit.
The project has since integrated the radio frequency unit onto KaRIn and started testing. The project is preparing a schedule replan for approval by NASA because of these delays, but project officials expect the project will still launch by its April 2022 committed launch readiness date.
In addition to challenges with the KaRIn instrument the project identified the likely root cause of an issue with the structure that supports the deployable antenna and has started testing its repair. The project is investigating an issue with the failure of bonds in joints of the structure that supports the spacecraft’s deployable antennas.
Finally, the project is refining its approach to calibrating and validating the measurements from the KaRIn instrument using an airborne sensor, Light Detection and Ranging, and other technologies.
Cost and Schedule Status
The SWOT project is still operating within its cost and
schedule baselines, but is reviewing its internal launch
readiness date due to delays with its primary instrument. The project had been working towards a September 2021 launch date, which is 7 months earlier than its committed launch readiness date of April 2022.
However, project officials stated that component delivery delays for the Ka-Band Radar Interferometer (KaRIn)—the project’s most complicated technology development effort—have put this date at risk.
As of January 2020, the project had consumed all payload schedule margin due to these delays. Additionally, the project is preparing a schedule replan for approval by NASA, but the project still expects to launch prior to its committed launch readiness date.
The project received the KaRIn instrument’s radio
frequency unit from CNES in August 2019, 6 months later than planned. This delay was due to issues with one of the unit’s electrical components, which had to be replaced as a result of parts reliability concerns discovered on other projects and issues that we reported in 2019 related to the unit’s digital assembly and power supply.
The project has since integrated the radio frequency unit onto KaRIn and performed basic functional testing. The project plans to perform environmental testing, including thermal vacuum testing, on the KaRIn instrument ahead of the system integration review.
In addition to challenges with the KaRIn instrument
electrical systems, the project is repairing four joints of the structure that supports the KaRIn instrument’s deployable antennas, which failed during static testing on more than 100 joints. The project identified surface contaminants as the likely root cause of the joint failure and has started thermal and static load testing on the repaired joints.
Other Issues to Be Monitored
The project continues to refine its approach to calibrating and validating the measurements from the KaRIn instrument. The project plans to use an airborne sensor as well as a combination of Light Detection and Ranging (LIDAR), gliders, and moorings.
The airborne sensor will help calibrate and validate measurements for inland waters, whereas the LIDAR, gliders, and moorings will help the project calibrate and validate measurements for ocean waters as the airborne sensor is not effective for oceans due to heavy wave activity.
The project completed a LIDAR validation campaign off the coast of California in April 2019, and is conducting additional experiments at the California site with a glider and three moorings.
Project Office Comments
In commenting on a draft of this assessment, project officials stated that SWOT is a challenging mission making a first-of-a-kind measurement of global surface water.
Officials also noted that the project has made significant progress completing the heritage (Nadir) payload, and delivered key KaRIn radar electrical sub-systems to enable completion of the electrical portion of the KaRIn radar.
The KaRIn radar testing shows excellent performance, according to officials, and the project is now focused on completing the mechanical subsystems and preparing for the integration of the complete payload module.
Officials also provided technical comments on a draft of this assessment, which were incorporated as appropriate.