Editor’s note, Feb. 6, 2024: NASA and SpaceX stood down from PACE’s Feb. 6 launch attempt due to unfavorable weather conditions. Launch is now targeted for 1:33 a.m. EST Wednesday, Feb. 7.
Editor’s note, Feb. 7, 2024: NASA and SpaceX stood down from PACE’s Feb. 7 launch attempt due to unfavorable weather conditions. Launch is now targeted for 1:33 a.m. EST Wednesday, Feb. 8.
There’s a good reason why NASA’s PACE satellite is launching in the early morning hours. Late tonight, I’ll venture out in the chilly Merritt Island air to catch a glimpse of a historic sight. At 1:33 a.m., February 6, NASA is slated to launch the Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) satellite atop SpaceX’s Falcon 9 rocket.
Why so early in the morning? The launch is timed to accommodate the satellite’s orbit around Earth.
PACE will be in a Sun-synchronous orbit, meaning it’s synced to always maintain the same position relative to the Sun. This also means it will cross Earth’s equator at the same local time for each orbit, and the angle at which the sun illuminates Earth will be consistent for each image that it takes. This allows scientists to collect consistent data.
“An Earth-observing satellite generally wants the Sun well overhead during observations,” said Scott Patano, flight dynamics system development lead for PACE at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
To get this level of lighting during its orbit, PACE wants the Sun to be almost behind it as it observes the Earth. Though if the Sun happens to be directly behind the satellite, there may be glare or reflections off the ocean, which isn’t ideal, especially considering one of its main purposes is to collect ocean data. To prevent glare, PACE will be slightly offset – not directly in front of the Sun. If you imagine the Sun is at the 12:00 angle, PACE will orbit at 1:00.
So why the 1:33 a.m. launch? The best answer to that question is… math. Really cool math. By launching south out of Florida on the dark side of the Earth, the math works out perfectly to get the satellite right into place on the approaching India as it crosses the equator for the first time on the daylight side of the Earth by 1:00 p.m. local time.
A previous night launch at NASA’s Kennedy Space Center in Florida. A SpaceX Falcon 9 rocket launches with NASA’s Imaging X-ray Polarimetry Explorer (IXPE) spacecraft onboard from Launch Complex 39A, Thursday, Dec. 9, 2021. Launch occurred at 1:00 a.m. EST. Photo Credit: (NASA/Joel Kowsky)
While some satellites launch first into a temporary orbit, before moving into their permanent position, PACE will be directly injected into its final orbit, “an effectively instantaneous launch,” said Joel Parker, flight dynamics lead for PACE at Goddard.
This leaves little wiggle room for the launch time: a mere 90-second window for the launch to proceed. A tense minute and a half for years of striking data.
So while I’ll be prescribing a late afternoon nap for myself, I know that when I wake up, I’ll be getting ready to see PACE rocketed up to its new home – where it will provide a stunning new view of ours.
Header image caption: The dark water of the turn basin at NASA’s Kennedy Space Center mirrors the night lights and the Vehicle Assembly Building and Launch Control Center, silhouetted against the post-sunset sky. Photo credit: NASA/Kim Shiflett
By Erica McNamee, Science Writer at NASA’s Goddard Space Flight Center
Kirk Knobelspiesse is an atmospheric scientist and the project science team polarimeter lead for PACE at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. He is also the polarimeter instrument scientist for the Atmosphere Observing System (AOS) constellation.
Kirk Knobelspiesse hiking sand dunes near Swakopmund, Namibia, during the ORACLEs field campaign. Image Credit: Michal Segal-Rozenhaimer
What is your favorite atmospheric or ocean related book or movie?
There was a series on Netflix called “Connected” that had an episode called “Dust.” The general idea is that everything in the world is connected, so it started with dust that was generated in the Sahara Desert, specifically the Bodélé Depression. And that dust – which is really from a dry lakebed – gets lofted into the atmosphere and goes out over the oceans, and in the process interacts with clouds and potentially fertilizes the ocean. That dust makes it all the way to the Amazon basin where it may also be an important source of nutrients.
What is your background?
I am a photographer who got really into imaging of all kinds, which led me to remote sensing. I ended up doing work on remote sensing of Earth from space and worked on SeaWiFs, which was an early ocean color mission. I decided I need to go back to grad school and get a more quantitative education, so I got an applied math degree at Columbia University.
What are you most looking forward to during launch?
Earlier in my career I worked on a satellite that had a launch failure (Glory in 2011). So, during launch, I am going to shut myself in a closet and not learn any news until somebody tells me it’s all over. Because it makes me so nervous. A lot of people want to go and see the launch and that kind of thing. Not me, I’m going to stay away. Somebody will tell me when it’s all over.
What are you most looking forward to post-launch?
Kirk Knobelspiesse in his office at NASA’s Goddard Space Flight Center in Greenbelt, Md. Image Credit: Kirk Knobelspiesse
I have a list of all the Science and Nature papers we’re hoping to write with PACE data. It’s ambitious, a little bit. But there are new types of observations that we will be making, that no other satellite will have done so far, at least not at a global scale. One aspect I’m interested in is just exploring the data, looking for basic things that will be useful for our understanding of aerosols and clouds and the climate in general.
I have some pet projects that I’ve always been interested in, for example a specific situation when aerosols are lofted above clouds. Aerosols are generally something that cools the climate because they reflect light. But if you have, say, a dark smoke aerosol on top of the cloud, it actually warms the climate, because it absorbs some of the energy that would have otherwise been reflected into space. So that’s something we’ll be able to do with PACE that we don’t really have great observations of now.
What is your favorite color and why?
I have a 10-year-old daughter, and favorite colors are very important to her and her friends. They’re always asking me what my favorite color is, and I say I can never answer them because how can you like one color without liking all the others?
Do you have a favorite type of cloud or weird atmospheric phenomena?
There’s also an optical phenomenon called glory. If you’re floating above a cloud and the Sun is behind, you look down at your shadow and you will see your shadow with a glory around it, which is like a circular rainbow around yourself. That’s one of my favorite optical phenomena.
What’s a fun fact about yourself? Something that a lot of people might not know about you?
Kirk Knobelspiesse working on the NASA P-3 during the ORACLES field campaign in São Tomé, São Tomé and Príncipe. Image Credit: Andrzej Wasilewski
I’ve been to latitude zero, longitude zero, the point in the South Atlantic Ocean where the equator and prime meridian intersect. It was part of the ORACLES field campaign. There’s nothing special there. It’s just ocean – and I don’t mean to offend my oceanographer friends by saying it’s nothing special – but there was no pillar of fire or something like that.
What advice would you give to aspiring scientists looking to get where you are today?
Don’t pigeonhole yourself into one discipline or one topic of study. Not just computer science or physics or oceanography. They’re human constructs, sociological constructs, and they don’t have anything to do with nature, other than how we have organized ourselves. A lot of where I’ve found interesting and productive things to do have been at the boundary between disciplines, or learning from one discipline and applying that approach to another discipline. So, don’t tell yourself, “I can’t do something because I’m not trained to do that.” You can learn and you can train yourself, and don’t be afraid to go out on a limb and do something you don’t really know how to do.
What is one catch-all statement describing the importance of PACE?
We will be making use of things that people cannot see – the nature of light – to understand things that we can’t otherwise observe.
Header image caption: Kirk Knobelspiesse hiking at Rachel Carson Conservation Park in Brookeville, Md. Image Credit: Barbara Balestra
By Erica McNamee, Science Writer at NASA’s Goddard Space Flight Center
With the towering structure of the spacecraft just behind clear plastic curtains, engineers, scientists, and others who worked on the Plankton, Aerosol, Cloud, ocean Ecosystem mission recently had the chance to see the result of their hard work.
“Your dad does amazing stuff for us. He goes and puts out fires all the time,” Juli Lander, the PACE deputy project manager, said to a teenager waiting with his family to take a picture in front of the satellite.
The spacecraft and its instruments are the culmination of more than eight years of hard work, late nights, and early mornings, she said, and this was their chance to see the finished product right before it traveled to Florida to prep for launch.
“It’s really important for us to let everyone see the great work that their family members have been doing,” Lander said. “Everybody who’s coming through is very excited, even if they’ve been here before.”
At one of the stops on the PACE Friends and Family Day tour at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, guests saw the thermal vacuum chamber where the spacecraft was tested to ensure it could survive in the harsh environment of space. Image Credit: NASA/Kate Ramsayer
More than 550 people came to the PACE Friends and Family day Oct. 28, 2023, at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, where the spacecraft and its Ocean Color Instrument (OCI) were built. They toured the cleanroom where PACE was assembled and tested, including the giant thermal vacuum chamber where it was subjected to the temperature and pressure extremes of space.
They heard from scientists about what insights the satellite will provide about the ocean, atmosphere, and climate, and got to peer through a microscope to see some of the tiny phytoplankton that PACE will study from space.
“We’re showing off the science that we’re doing with PACE,” said Carina Poulin, a scientist and outreach specialist who was helping with hands-on activities during the event. There were puzzles of colorful ocean waters, a PACE-themed card matching game, cultures of green and yellow and pink phytoplankton and more.
The visitors were asking lots of great questions, Poulin said. “They all know someone who works with PACE, so they’re excited.”
Sabrina Sharmin, who started with the PACE team almost seven years ago and is now a systems engineer with OCI, introduced her enthusiastic guests to coworkers, and pointed out highlights of the cleanroom facility.
“This remarkable spacecraft is a result of countless hours of collaborative effort by the entire team, and I am so proud of all of us,” Sharmin said. “It’s a momentous occasion, being able to showcase the project to friends and family.
Header image caption: PACE engineer Sabrina Sharmin, in center in brown shirt, brought friends and family to see the spacecraft at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “The anticipation and excitement within our team for launch is unparalleled,” she said. Image Credit: NASA/Kate Ramsayer
Kate Ramsayer, Strategic Communications Lead for Earth Science Missions at NASA’s Goddard Space Flight Center
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.”
An overview of the PACE satellite entering a thermal vacuum chamber. Before the doors closed, the whole observatory was run through additional testing. Image Credit: NASA’s Goddard Space Flight Center/Denny Henry
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.
Gary Davis, the missions systems engineer for PACE, examines the observatory before critical testing. Image Credit: NASA’s Goddard Space Flight Center/Denny Henry
“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.
Members of the PACE team continue testing in Goddard’s TVAC chamber. Image Credit: NASA’s Goddard Space Flight Center/Denny Henry
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.
Chaves is preparing to conduct scientific research while onboard. He worked around the clock to collect samples that will help check the accuracy of satellite data. Image Credit: NASA/Joaquin Chaves
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.”
Chaves conducting field experiments and validation. Credit: NASA/Joaquin Chaves
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
Whether in plants or animals, greenhouse gases or smoke, carbon atoms exist in various compounds as they move through a multitude of pathways within Earth’s system. That’s why NASA’s Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission – scheduled to launch in January 2024 – was designed to peer down at Earth from space to see those many forms of carbon in a way no other satellite has done before by measuring colors not yet seen from the vantage point of space.
“PACE is standing on the shoulders of some giants, but previous and current satellites are limited in how many colors of the rainbow they can actually see,” said Jeremy Werdell, project scientist for the PACE mission at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
Although one of the primary goals of the mission is to measure the colors on the ocean surface, in the 420 miles (676.5 kilometers) between PACE in orbit and sea level are parts of the complex carbon web that the satellite will also be able to monitor.
The connection between major wildfires and the subsequent explosion of phytoplankton production is an example of the events NASA’s upcoming Plankton, Aerosols, Clouds, and ocean Ecosystem (PACE) mission will help investigate. PACE’s suite of instruments will allow scientists to get a clearer picture of carbon as it links land use and fires, atmospheric aerosols and marine communities. Credit: NASA’s Goddard Space Flight Center
Atmosphere
From PACE’s location in space, one of the nearest forms of carbon to detect could be the wispy plumes of smoke and ash rising into the atmosphere from fires. Carbon is a key building block of much life on Earth, including plant life. When burned, the vegetation’s carbon-based molecules transform into other compounds, some of which end up as ash in these plumes.
The instruments on PACE will be able to monitor these smoky clouds, as well as other atmospheric aerosol particles, measuring their characteristics including the relative amount of smoke in different places. Combinations of these measurements made by PACE’s two companion polarimeter instruments, SPEXone and the Hyper-Angular Rainbow Polarimeter-2 (HARP2), and the detailed color measurements of the smoke made by the Ocean Color Instrument (OCI) will also help scientists identify what was burnt.
“Each instrument brings something different,” said Andy Sayer, PACE’s project science lead for atmospheres at NASA Goddard. “Putting them all together though, you’re getting the most information.” Sayer is also a senior research scientist for the University of Maryland Baltimore County.
These measurements help scientists understand more about the balance between the incoming energy from the Sun, the outgoing energy from Earth, and where it may be absorbed in between by things in the atmosphere like these smoke plumes. Even at a local level, PACE can provide information about how smoke affects air quality, impacting communities that may be near fires.
Land
Peering through the smoke particles and other aerosols, PACE can also tell us about the health of terrestrial plants and trees. Even after a devastating wildfire, fresh green plant life begins to grow and thrive. With more spectral bands and colors to see from the upcoming satellite, scientists will be able to understand what kinds of plants are recovering from fires over the years.
“In a time where we’re experiencing unprecedented climate change, we need to be able to understand how global vegetation responds to its environment,” said Fred Huemmrich, research associate professor at the University of Maryland, Baltimore County, and a member of the PACE science and applications team.
PACE will be able to monitor the different shades of colors in vegetation, and plant color can be an indicator of health. Just as house plants begin to fade to yellow if they haven’t been watered enough, plant life around the globe changes color as it experiences stress. Healthy plants take up carbon in the form of carbon dioxide as part of photosynthesis, while unhealthy plants that can’t complete photosynthesis leave the carbon dioxide roaming around the atmosphere. Given that carbon dioxide is a greenhouse gas, these measurements also play a significant role in understanding climate change in greater detail.
By measuring a full spectrum of color, PACE will view tiny changes in pigment to detect how plants are responding to stressors, helping scientists learn whether they are utilizing the surrounding carbon or not. Previously, these colors were primarily viewed in field studies of specific areas. Stressors like droughts were inferred using weather data, but covering large expanses was difficult.
“For the first time, we’ll really be able to look at changes in the health of plants over the globe,” Huemmrich said. “It will dramatically improve our understanding of how ecosystems function and how they respond to stress.”
Ocean
From plants on land to organisms in the ocean, PACE will view the expanses of water on Earth to measure phytoplankton – the P in its name. With its ability to measure a wide spectrum of colors, PACE will now not only be able to see more across the surface of the ocean but will also help scientists differentiate between phytoplankton species.
“It’s like you were making a painting with really coarse brushes, and now you have thin, fine brushes that help explain so much more in greater detail,” said Ivona Cetinić, an oceanographer in the Ocean Ecology Lab at NASA Goddard.
Phytoplankton, small organisms that live on the surface of the ocean, play a critical role in the food chain and the global carbon cycle. Each type of phytoplankton provides a different pathway in that expansive web of routes that carbon can take, all depending on the characteristics of the plankton. One pathway may lead to the carbon becoming food for a larger species, while another may lead to carbon becoming waste, sinking deeper into the ocean.
Scientists conducting field work have found that types of phytoplankton vary slightly in color and have identified these phytoplankton on small scales. PACE’s ability to measure a full spectrum of color will help scientists tell the difference between phytoplankton on a global scale by seeing more of these colors, deepening the understanding of carbon pathways and quantities.
Though one of PACE’s key goals is to view the ocean, its line of sight looks over the atmosphere and land as well. With these expansive observations, and the massive quantities of data collected, PACE provides the ability to see in what ways the atmosphere, land, and ocean are connected, including with the complex web of carbon pathways.
“I’m energized for this opportunity for discovery that this observatory is offering,” Werdell said. “I have every expectation the world is going to do great things with these data.”
By Erica McNamee, Science Writer 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.
