Overview: Mission Development

The launch of Aquarius/SAC-D was the culmination of a decades-long journey that began with the idea that salinity could be measured remotely....

First global map of the salinity of Earth's ocean surface
From 1872 to 1876, the H.M.S. Challenger sampled the global ocean - including salinity measurements at depth - heralding the beginning of oceanography as a science discipline. Source: Wikipedia Commons
Although ocean salinity had been measured for centuries from ships and buoys, measuring changes in the saltiness of Earth's vast ocean demanded the use of satellite technology. During the late 1940s and early 1950s, several laboratory experiments were conducted to quantify the relationship between the salinity and "brightness temperature," the amount of energy that is naturally being emitted by the ocean surface at a fixed temperature, for various microwave frequencies. Based on this theoretical work, the first attempt to measure ocean surface salinity from space occurred in 1973 on Skylab at the frequency of 1.4 GHz, which would eventually be used by Aquarius.

Initially approved as a NASA Earth System Science Pathfinder program in 2001, Aquarius was confirmed as a mission in September 2005. To achieve that milestone, the project was reviewed on its mission requirements, design and costs. Key to the success of this early phase of mission development were promising results from an Aquarius prototype, the Passive-Active L- and S-band (PALS) sensor. A controlled investigation conducted at the Jet Propulsion Laboratory (JPL) in Pasadena, California confirmed that PALS could successfully measure brightness temperature with the accuracy required by the oceanographic research community. In 2003, Aquarius took its "next step towards space" when PALS was flown aboard a C-130 airplane while in-water salinity was measured beneath the aircraft's flight path. This exercise yielded an important discovery: retrieval of the natural salinity signal was dominated by sea surface roughness. As a result, the Aquarius instrument was redesigned to include a scatterometer to correct for wind-blown conditions at the ocean surface.

In January 2008, the NASA Goddard Space Flight Center (GSFC), based in Greenbelt, Maryland, delivered the Aquarius radiometer to JPL. Over the next 16 months, the radiometer was integrated with the Aquarius instrument at JPL, including the JPL-built and tested scatterometer and antenna. In June 2009, Aquarius traveled about 9600 kilometers (6000 miles) to Bariloche, Argentina for a year-long integration with the SAC-D service platform at the INVAP facility, a technology spinoff company. The Aquarius/SAC-D satellite successfully passed the last stage of environmental testing at the Laboratório de Integração e Testes of the National Institute for Space Research (INPE) in Sao Jose dos Campos, Brazil. In March 2011, the observatory was ready for the final "earthbound" leg of its journey: the last 10,000 kilometers (6200 miles) to the launch facility at Vandenberg Air Force Base, California where it launched on June 10th.

The history of Aquarius was covered in a webinar featuring Aquarius Principal Investigator (PI), Dr. Gary Lagerloef and Deputy PI, Dr. David Le Vine. Photographs of the major phases of Aquarius development are posted in our gallery. Click here to download a PDF of Aquarius: A Brief (Recent) History of an International Effort.

When Did the Partnership Between NASA and
CONAE Begin?
In 1994, CONAE released high-level goals for Argentina's space program that included developing and applying advanced technological knowledge; enhancing economic and human resources; and fostering international cooperation. A major initiative is the SAC satellite series, the fourth of which is Aquarius/SAC-D. For each mission, NASA has provided launch operations and launch vehicles: Space Shuttle (SAC-A), Pegasus (SAC-B), and Delta II (SAC-C and SAC-D). Each satellite was conceived by CONAE and built by the technology company, INVAP, S.E., located in Bariloche. Ground control operations for each mission have been conducted in Córdoba.

SAC-A, launched by Endeavour in 1998, characterized the performance of equipment and technologies for future missions. SAC-B was designed to study solar physics and astrophysics using science instruments from CONAE, NASA, and the Italian Space Agency (Agenzia Spaziale Italiana, ASI). Launched in November 2000, SAC-C focuses on Earth observations such as monitoring Argentina's soil conditions and marine ecosystems.
The First Light Image
After a brief commissioning period, the Aquarius instrument was switched into mission mode on August 25, 2011. The first-light global image was released on September 22, 2011, and featured the first sea-surface salinity data ever collected by NASA. (In this image, red and orange indicate relatively high salinity [equivalent to higher than 37 parts per thousand]; blues indicate relatively low salinity [equivalent to less than 34 parts per thousand].) This map demonstrated Aquarius' ability to detect large-scale salinity patterns clearly and with sharp contrast. About one month later, NASA Administrator Charles Bolden Jr. met with Argentine President Cristina Fernandez de Kirchner to witness the signing of a Framework Agreement on Cooperation in the Peaceful Use of Outer Space between the U.S. and Argentinian governments.

The post-launch assessment review process for Aquarius was completed on December 1, 2011, marking both the beginning of the science operations phase and transition of the Aquarius Project Office from JPL to GSFC. Aquarius/SAC-D mission operations were conducted at the CONAE ground station in Córdoba, Argentina. A ground control station of Argentina's space agency, Comisión Nacional de Actividades Espaciales (CONAE), transmitted raw Aquarius data to the ground system at NASA GSFC, where the data were processed and instrument operations managed. The Aquarius data processing system generated salinity products which are disseminated by and archived at NASA's Physical Oceanography Distributed Active Archive Center (PO.DAAC) at JPL.