Falcon 9 launches PACE science satellite for NASA

by Justin Davenport

After a record-setting month featuring 10 launches, SpaceX is gearing up for a busy February. One of the launches this month is the Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) ocean science satellite, which flew aboard a Falcon 9 in a rare polar corridor launch from Florida.

PACE launched from Space Launch Complex 40 at the Cape Canaveral Space Force Station on Thursday, Feb. 8, at 1:33 AM EST (06:33 UTC), during an instantaneous launch window. The flight was previously scheduled for Feb. 6 and then Feb. 7 but in both cases was delayed due to unfavorable weather conditions. Falcon 9 took a southbound trajectory to a Sun-synchronous polar orbit, which allows for the satellite to see a given spot on Earth at the same time every day.

After stage separation, Falcon booster B1081-4 conducted a boostback burn with its Merlin engines, followed by a return-to-launch-site landing onto the concrete pad at Landing Zone 1, while the fairings splashed down in the ocean to be retrieved by SpaceX’s support ship Bob.

The second stage took PACE to a circular orbit of 676.5 kilometers at a 98-degree orbital inclination, with spacecraft separation occurring roughly 13 minutes after launch. 

B1081 has three prior flights to its name. This booster, one of the newer ones in the SpaceX Falcon fleet, started its flight career by lofting Crew-7 to orbit on Aug. 26, 2023. Afterward, B1081 flew the CRS-29 cargo mission and the Starlink 6-34 mission. The turnaround between Starlink 6-34 and PACE is 49 days.

Artist’s impression of the PACE satellite on orbit. (Credit: NASA)

The PACE spacecraft masses 1,694 kilograms and measures 1.5 meters by 1.5 meters by 3.2 meters. With one kilowatt of power available to it from a single solar panel, the spacecraft is designed for a three-year mission but with orbit maintenance capability for 10 years. As with many NASA spacecraft, if PACE successfully completes its primary mission and is still in acceptable condition, PACE could be offered extended missions to continue working.

In order to achieve its mission of measuring ocean color and the effect of aerosols on the ocean and atmosphere, PACE is equipped with three science instruments — the Ocean Color Instrument (OCI), the Spectro-polarimeter for Planetary Exploration (SPEXone), and the Hyper Angular Research Polarimeter (HARP2).

The OCI, built by the Goddard Space Flight Center along with the satellite bus, is designed to observe the world’s oceans in a hyperspectral manner, covering the ultraviolet, visible, and near-infrared spectrum with a finer resolution than prior ocean color measurements. This instrument observes the spectrum from 350 to 885 nanometers at intervals of five nanometers, as opposed to older multispectral instruments that only collected data at a few selected wavelengths.

PACE is designed to observe the ocean in ultraviolet, visible light, and near infrared wavelengths. (Credit: NASA)

The color of an ocean is influenced by how sunlight reacts with substances like chlorophyll, a pigment found in phytoplankton — a critical pillar of the marine food web and a consumer of carbon from the atmosphere. The first satellite to study ocean color was launched in 1978, and PACE is intended to extend humanity’s record of these observations at a higher resolution than ever before.

While the OCI spectrometer is measuring the color of the world’s oceans, the SPEXone and HARP2 instruments will work together to measure aerosols and clouds using complementary methods of spectral and angular sampling as well as differently-sized swaths of ocean coverage. 

SPEXone and HARP2 are polarimeters, which measure how the oscillation of sunlight within a geometric plane — polarization — is altered when passing through things like clouds, aerosols, and the ocean. Scientists expect to learn more than ever before about human impacts on clouds, how aerosols impact phytoplankton, forecasting harmful algal blooms, and much more about how the ocean and atmosphere interact.

As PACE project scientist Jeremy Wardell stated during an interview with NSF’s Julia Bergeron, “There are thousands and thousands of unique pieces of information for every pixel on Earth we’re going to collect. It’s going to be a lot, and the innovation has really begun in terms of how you start using machine learning and other computer data science tools and toolboxes to manage all of this information.” Data is expected to be available to the public 60 days after collection.

The PACE satellite seen connected to the Falcon 9 payload adapter before fairing encapsulation. (Credit: NASA)

PACE almost did not make it to the launch pad. The project, authorized in 2015, was once marked for cancellation in the Trump Administration’s Fiscal Year 2018 NASA budget, but Congress restored these funds. Additional challenges with parts failures on the HARP2 instrument, as well as the worldwide COVID pandemic, had to be overcome.

The NASA Launch Services Program turned to SpaceX to launch PACE, managed by the Goddard Space Flight Center and cost capped at $805 million, in a similar manner as it had done for other NASA payloads to use the Falcon family. These include the TESS exoplanet hunter, the Jason-3 and SWOT ocean observation missions, Psyche, IXPE, DART, and other spacecraft. The launch price for NASA was set at $80.4 million, or roughly 10 percent of the mission’s cost cap.

Vandenberg Space Force Base has historically been used to launch missions that required a Sun-synchronous polar orbit, while these launches were long forbidden from Cape Canaveral after an incident in the 1960s involving rocket debris falling on Cuba. However, the introduction of the Autonomous Flight Safety System (AFSS) along with the use of a “dogleg” trajectory to avoid overflying Florida coastal areas has allowed polar flights to resume from Florida if the launch vehicle is equipped with AFSS, which the Falcon family is.

Falcon 9 launches the Transporter-1 mission on a polar orbit trajectory from Florida. (Credit: SpaceX)

SpaceX had taken advantage of this capability to fly 11 polar missions from Florida, most of these Transporter rideshare missions with many small satellites. PACE is now the 12th and the first polar mission procured by NASA to fly from Florida. Although there is at least one additional polar orbit mission from Florida this year, Cape Canaveral is not intended to replace Vandenberg as the preferred site for polar launches.

PACE is the 11th mission for SpaceX and Falcon 9 this year and the first SpaceX launch of February, taking off before the Starlink 7-13 mission from California which had been delayed several times. So far, SpaceX is on pace to fly up to 120 Falcon missions this year, though they are targeting up to 148 flights for 2024. Regardless, if no anomalous events occur, Falcon 9 is in position to become the first rocket to fly 100 times in one calendar year.

(Lead image: PACE on Falcon 9 ahead of launch. Credit: Max Evans)

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