This summer, the PACE spacecraft (short for Plankton, Aerosol, Cloud, ocean Ecosystem) completed a critical phase of its launch journey: the thermal vacuum test (TVAC), where it was subjected to extreme temperatures and pressures in a specialized chamber at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
The objective? To verify the performance of the satellite once it’s launched and operational.
“This is the best way to simulate what PACE will experience in space,” said Craig Stevens, spacecraft systems lead. “Space is a vacuum, and the observatory is exposed to extreme temperatures. We must make sure PACE is ready for that environment.”
After months of round-the-clock shifts, numerous protocols, and a lot of team synergy, the mission completed its environmental testing in August, making it one step closer to launching in early January 2024.
“This proves the PACE observatory can withstand the rigorous thermal environment once it is launched and inserted into its operational environment,” said Mark Voyton, the mission project manager. “Completing the TVAC test is extremely significant, as it represents the last environmental test in our six-month environmental test campaign.”
Getting to this final test was a challenge for team members given the time and resources TVAC can take.
Before things could begin, the satellite was placed in the thermal chamber for a week earlier in June at NASA Goddard for setup.
Before the door for testing was closed, each team that had worked on PACE verified their part of the observatory was in working order, said Daniel Powers, PACE’s thermal product development lead. Members of the control room were also standing by to ensure that when the power for thermal testing went on, things worked properly.
Once the chamber door closed, official testing lasted about 33 days.
“This is the final verification that everything is working on the spacecraft as expected. We take it to temperature extremes as well,” said Powers. “By taking it to the expected extreme environments we will see on orbit, we can see that we have everything setup and designed properly from a thermal perspective.”
The team worked three shifts – covering 24 hours each day, every day – to ensure operations ran on a strict timetable.
“You have a full marching army, and it’s all hands-on deck,” Powers said.
PACE now has two more tests at ambient temperature and pressure, which complete the observatory’s post-environmental testing. Then the team begins preparing for the spacecraft’s journey to Florida and its launchpad.
Header image caption: The PACE observatory enters a thermal vacuum chamber at NASA’s Goddard Space Flight Center in Greenbelt, Md. It stayed in the chamber for 33 days of testing. Image Credit: NASA’s Goddard Space Flight Center/Denny Henry
By Sara Blumberg, NASA Oceans Communications Lead at NASA’s Goddard Space Flight Center
NASA researcher Joaquin Chaves calls it “ground truthing,” even though land is nowhere in sight.
This spring, Chaves boarded the Atlantic Meridional Transect (AMT) research cruise for six weeks of sampling water and taking measurements as the ship traversed the Atlantic Ocean. His team, based at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, uses that information gathered at sea to verify and improve ocean data from an array of Earth-observing satellites and instruments in orbit.
Upcoming satellites like the PACE, or Plankton, Aerosol, Cloud, ocean Ecosystem, mission launching in early 2024, will also use field campaigns like this one to help validate their sensors.
These sensors start collecting data soon after launch, but it takes time to ensure that those observations are accurate and reflect what is happening back on Earth. One of the best ways to do this is to send scientists like Chaves into the field.
On the spring cruise, Chaves was joined by another NASA Goddard scientist, Harrison Smith.
“It was a lot of work, always intense,” Chaves said. “Even before you sail, you’re setting up. Every day is a work day, there are no Saturdays or Sundays.”
During their time on the cruise, the NASA team collected two types of data to build mathematical models to validate satellite data. Validation is the practice of checking the accuracy of data before it’s processed and used by NASA and its partners.
The first data type was the optical properties of water.
“Ocean color satellites measure visible light,” Chaves said. “We must try to replicate what they measure.”
In addition to the optical measurements, the NASA scientists also gathered water samples to measure the abundance of phytoplankton pigments and various forms of carbon.
By the end of the campaign, Chaves had collected 700 samples to process, which he is now analyzing back at Goddard.
Chaves and Smith were just two of the research cruise’s passengers, which also included 25 scientists based in the UK, Europe, Africa, and Latin America. Chaves said it was one of the best field campaigns he’s been on. The researchers connected with others and talked of future collaborations.
“It’s hard work,” he said. “It remains one of my best experiences at sea because of how modern the ship was, well trained the crew were and the officers are and willing to help.”
The AMT program, which started in 1995, allows researchers from all over the world to study the ocean’s biogeochemistry, ecology, and physical properties during voyages between the United Kingdom and the South Atlantic.
Although PACE was formally authorized in 2015, its concept has been on the minds of NASA Earth scientists for over 21 years.
In 2023, that concept is now an assembled spacecraft at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
This past month, the PACE (Plankton, Aerosol, Cloud, ocean Ecosystem) mission advanced closer to launch, passing a critical review demonstrating final tests for its readiness for observatory integration and testing. PACE will continue preparations for its move to NASA’s Kennedy Space Center in Florida, where it is scheduled to launch in January 2024.
“It’s an absolutely huge achievement for the team after having conceived the PACE system architecture, completed the design, implemented and built all the hardware and software systems,” said Mark Voyton, PACE’s Project Manager.
PACE’s solar array deploying in the Goddard cleanroom. Video by Denny Henry, NASA
Once in orbit, PACE will view the atmosphere and ocean surface from space. It will help scientists learn more about the relationships between phytoplankton and the surrounding environment by measuring how light reflects off the ocean and through the atmosphere.
Before any NASA mission can launch, however, it must go through a series of immersive reviews, called key decision points, to show it can operate in space. Getting to this moment has been a long time coming for the team.
Since its inception, PACE has faced many challenges. Last year, for example, one of PACE’s polarimeters, HARP2, experienced parts failures during testing, forcing the team to reevaluate several of its design concepts. Budget-wise, the mission also experienced hurdles related to the global Covid-19 pandemic.
Testing and moving the PACE spacecraft. Image by: Denny Henry, NASA
“It is somewhat difficult to wrap my head around being fewer than 300 days from launch. All the ideas and concepts from the past decade have been turned into reality! It’s been a long strange trip, but one we don’t regret pursuing,” said PACE lead scientist Jeremy Werdell.
PACE team members have remained busy in their preparations. Late last year, the team integrated all three of its scientific instruments onto the spacecraft, thus forming the PACE observatory. The mission most recently also completed testing the deployment of PACE’s solar array.
Next steps for the team will focus on final integration and testing activities at Goddard. This includes vibration and acoustics tests that simulate the launch environment, as well as several months of thermal vacuum tests that simulate the environment of space.
“Once these activities are complete, the observatory will be trucked to Kennedy for additional testing and integration onto the launch vehicle,” Werdell said.
Header image caption: PACE tech Jean Arnett is cleaning the Aronson table. The Aronson table is used to tilt the spacecraft over like in the photo below. Image by: Denny Henry, NASA
By Sara Blumberg, NASA Oceans Communications Lead at NASA’s Goddard Space Flight Center
The Ocean Color Instrument (OCI) is integrated onto the PACE spacecraft in the cleanroom at Goddard Space Flight Center. Credit: NASA’s Goddard Space Flight Center.
The PACE satellite now has all three of its scientific instruments attached to the spacecraft, as the integration crew bolted the Ocean Color Instrument into place with its two polarimeter neighbors.
With the assembly completed Nov. 21 at NASA’s Goddard Space Flight Center, the team will now be working on the electronic and other connections between the different components of the satellite, then putting the complete observatory through tests to make sure it can work in the harsh environment of space.
By Kate Ramsayer, Science Writer at NASA’s Goddard Space Flight Center
NASA’s PACE mission, which will provide a major boost to scientists studying Earth’s atmosphere and ocean health, completed a milestone test in October at the agency’s Goddard Space Flight Center in Greenbelt, Maryland.
The Ocean Color Instrument (OCI) on the Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission passed thermal vacuum tests to ensure it can withstand the harsh space environments.
As we prepare the Plankton, Aerosol, and cloud Ecosystem satellite for launch, we’re gathering all the ingredients, um…instruments, and baking ourselves a fresh new satellite. Credit: NASA’s Goddard Space Flight Center/Scientific Visualization Studio. Video descriptions available.
PACE will view the atmosphere and ocean surface from space. While highly useful for studying atmospheric aerosols, OCI is specifically designed to look for small aquatic organisms called phytoplankton that can be so numerous they influence the colors of the ocean. Phytoplankton play a large role in the ocean ecosystem — not only are they food sources for larger species, but they also convert carbon dioxide into organic matter through photosynthesis, playing an active role in moving carbon from the atmosphere into the ocean.
The PACE mission will help scientists learn more about the relationships between phytoplankton and the surrounding environment by measuring how light reflects off the ocean and through the atmosphere. Scientists can see these organisms in the ocean using satellites, but currently can’t differentiate the phytoplankton by type easily. Identifying types of phytoplankton help scientists to detangle some of the complex ecological systems in the oceans.
“When you look down at the ocean, you can see phytoplankton there and for the first time, with PACE, the scientists will be able to see what type of phytoplankton there are from space,” said Gary Davis, mission systems engineer at Goddard for the PACE mission. “Hopefully this mission will be able to communicate the importance of ocean health and the health of plankton to the whole world.”
To ensure the satellite is ready to gather this data, engineers put the satellite through, well, its paces. The thermal vacuum test that was just completed reduces atmospheric pressure as close to the vacuum of space as possible and then cycles through a wide range of temperatures. During the sunlit part of a spacecraft’s orbit, it can get very hot, up to approximately 50 degrees Celsius (122 degrees Fahrenheit); at other parts of the orbit, zero solar exposure means extremely low temperatures, as low as -90 degrees Celsius (-130 degrees Fahrenheit).
OCI, which was built at Goddard, can measure light in a multitude of colors, far more than previous satellites that share its frequent global coverage. Light variation by wavelength, the character of light by which it is defined, provides the color we see. OCI can detect a continuous spectrum of different wavelengths of light, and can even see colors beyond what the human eye can detect. By detecting more wavelengths, the instrument will allow scientists to tell the difference between types of phytoplankton from space. This is helpful in understanding the pathways of the carbon cycle in the atmosphere, land, and ocean, and characterizing the phytoplankton as harmful or helpful.
“OCI is really a stretch of the state of the art of what we can do right now,” said Davis. “It’s probably the most advanced thing we have on the observatory.”
Former ocean-observing satellites had the ability to measure light at a small set of wavelengths through the development of multi-spectral instruments. OCI has the ability to measure color continuosly at many ultraviolet, visible, and near infrared wavelengths, also known as hyperspectral imaging.
The previous missions can be imagined as a regular 8-color box of crayons, said Jeremy Werdell, project scientist for the PACE mission. Though still highly valuable for creating a complete picture, there are gaps in between the shades of colors. For PACE, OCI can be imagined as a 128-color box of crayons, filling in those gaps using smaller and continuous intervals of wavelengths.
“With all of the colors of the rainbow here, most of us don’t know what we’re going to discover, because we’ve never had that chance on global scales,” Werdell said. “It’s the only mission planned at NASA or elsewhere that provide global hyperspectral, full colors of the rainbow everywhere, everyday.”
When light from the sun reflects off the ocean, that light has already traveled from the sun, through the atmosphere – clouds and aerosols that compose Earth’s atmosphere – and water before it reaches the plankton in the ocean. The light then bounces off the plankton and travels back through the water and atmosphere again. The light that makes its way through all those stages can tell a story through color but still needs to be analyzed and accounted for any atmospheric effects, which is where the polarimeters on PACE come into play.
The Hyper-Angular Rainbow Polarimeter 2 (HARP2) also recently completed TVAC testing, earlier in September. The instrument is one of two multi-angle polarimeters on PACE, which act as polarized sunglasses for the spacecraft, measuring how light bends as it travels through the water droplets, clouds, and aerosols in Earth’s atmosphere, informing scientists more about their physical properties, as well as providing another source of color measurements. HARP2 was built at the University of Maryland, Baltimore County.
SPEXone, the other multi-angle polarimeter, was built in the Netherlands by engineers from SRON Netherlands Institute for Space Research, Airbus Netherlands and NASA. Each of the three instruments will be integrated into the spacecraft as they complete their individual tests – and in fact, OCI was just lifted onto the spacecraft on November 21.
“We have an observatory!” said Werdell.
As the timeline of events for PACE ticks on, the days are being counted down, all leading to the launch scheduled for early 2024.