Space Weather Follow On at Lagrange Point L1 (SWFO-L1)

Quick facts

Overview

Summary

Mission Capabilities

SWFO-L1 carries four instruments: the Compact Coronagraph (CCOR), Magnetometer (MAG), Suprathermal Ion Sensor (STIS), and Solar Wind Plasma Sensor (SWiPS). CCOR observes the density structure of the white-light solar corona to detect coronal mass ejections and determine their direction, speed, and estimate time of arrival at Earth. MAG measures the three vector components of the interplanetary magnetic field carried by solar wind, enabling the study of magnetic structures directed towards Earth.  STIS measures suprathermal ions and electrons across a wide energy range, providing real-time, continuous observation for early warning of space weather phenomena.  SWiPS measures solar wind ion velocity, density, and temperature providing in situ, real-time, continuous observations of plasma structures directed towards the Earth.

Performance Specifications

CCOR has a spatial resolution of 65 arcsec, with a 3.0 - 23.5 Rsun field of view (FOV). MAG has a +/- 440 nT range, with a cadence of 8 Hz. STIS has an ion energy range of 25-6000 keV, with an electron energy range of 25-250 keV and a cadence of 16 seconds. Finally, SWiPS has a measurable velocity range of 200-2500 km/s, with a FOV spanning 90° about the sensor cylinder azimuth and 45° about the sensor cylinder elevation centerline.

The spacecraft operates in a Lissajous orbit around the unstable Sun-Earth Lagrangian point L1, where the gravitational pull of the sun and Earth precisely equals the centripetal force required to move with them.

Space and Hardware Components

SWFO-L1 uses the BAE Systems Evolve Platform, with four onboard 5 N thrusters for course correction, positioning and orbital insertion. Payload data is downlinked in X-band to the global SWFO Antenna Network (SAN), and command and control transmissions are uplinked in S-band from the Wallops Command and Data Acquisition Station (WCDAS) in Virginia, U.S.

Overview

Space Weather Follow-On at Lagrange-1 (SWFO-L1) is the satellite component of the National Oceanic and Atmospheric Administration (NOAA) SWFO program. The mission aims to provide data continuity for existing space weather monitoring programs, such as the Deep Space Climate Observatory (DSCOVR), Advanced Composition Explorer (ACE), and the Solar and Heliospheric Observatory (SOHO). SWFO-L1 continues solar wind observations and coronal imaging from the Lagrange One (L1) orbit line, as well as making real time thermal plasma and magnetic field measurements. In addition to this satellite, the SWFO program includes a compact coronagraph instrument, carried by the Geostationary Operational Environmental Satellite U (GOES-19) mission which was launched in June 2024. The L1 point is the space between the Earth and the sun where their respective gravitational forces precisely equals the centripetal force required to move between them. Due to its location, satellites placed in orbit around L1 have an uninterrupted view of the sun. 1) 2)

The real time solar measurements from SWFO-L1 are highly valuable in monitoring Earth’s space weather, the physical state of the natural space surrounding the Earth, and its interactions with Earth’s magnetosphere, ionosphere, and atmosphere. The primary source of Earth’s space weather is the sun, through solar flares or coronal mass ejections (CMEs) and the corresponding geomagnetic storms experienced on Earth. Additionally, the speed and density of solar wind, the constant emission of charged particles from the sun’s corona, are key components of Earth’s space weather. 1) 2) 3)

Space weather events can have a range of damaging effects on both in-orbit and ground-based infrastructure. Phenomena such as CMEs or solar flares increase the levels of energetic particles in the near-Earth space environment, increasing the risk of satellites experiencing dielectric discharge or single event upset events which can cause loss of data or satellite control. Additionally, during magnetospheric and ionospheric storms, the upper atmosphere is heated and expands, increasing drag on low earth orbit (LEO) satellite systems. Geomagnetic storms also cause short term variations in Earth’s magnetic field, resulting in an electric field which can drive currents, known as geomagnetically induced currents (GICs), through long, grounded conductors, such as power grids. GICs can interfere with high-voltage power transformers, resulting in power restrictions and outages in severe circumstances. 3) 4) 5)

Space weather also interrupts communication, navigation and positioning systems. One of the largest sources of global positioning system (GPS) error is from satellite signals passing through the dense electron environment of the upper atmosphere. While this is usually resolved by correction models, during space weather events, these correction models may not be accurate, making GPS and similar precision positioning systems more vulnerable to errors during ionospheric storms. Finally, space weather also impacts high frequency radio communications. Solar flare or CME extreme ultraviolet (EUV) or x-ray emissions produce ionisation of the Earth’s atmosphere at lower altitudes, causing increased absorption of high frequency radio signals and communications blackouts. 3) 4) 5)

Due to its ‘upstream’ location at Lagrange point L1, SWFO-L1 can measure solar wind before it reaches Earth, providing valuable time for warnings. These in situ solar wind observations are fundamental for CME Earth impact intensity estimates. Its position also enables coronal observations uninterrupted by eclipses. 6)

Spacecraft

The SWFO-L1 spacecraft bus has been provided by BAE Systems. It is a three-axis stabilised, sun pointing satellite, built on the BAE Evolve platform. The bus includes a monopropellant propulsion system consisting of four thrusters, each canted 10° with respect to the spacecraft primary centre line. Each thruster provides up to 5N of force, and all four draw from a single fuel tank with hydrazine (N2H4) propellant and gaseous nitrogen (GN2) pressurant, with 72 kg of fuel carried in total.

The mission uses X-band for mission data and housekeeping telemetry downlinks and S-band for command uplink and housekeeping telemetry downlink. The spacecraft mission data and housekeeping telemetry downlink provide an equivalent isotropic radiated power (EIRP) of at least 43 dbW, in the X-band 8400 - 8450 MHz. The housekeeping telemetry downlink provides an EIRP of 18 dbW in the S-band 2290 - 2300 MHz, while the command and ranging uplink have a minimum antenna gain to noise temperature of -18 db/Hz, in the S-band 2050 - 2110 MHz. The SWFO-L1 bus supports continuous operation of both S- and X-band uplinks and downlinks. 6) 7) 8)

Launch

SWFO-L1 was successfully launched aboard a SpaceX Falcon 9 rideshare mission on September 24, 2025. SWFO-L1 operates in a Lissajous orbit around the Sun-Earth Lagrange point L1.

Lagrange points are positions in space where the gravitational pull of two masses precisely equals the centripetal force required to move with them. L1 provides uninterrupted viewing of the sun, and therefore has a history of space weather and solar observation satellite missions. However, L1 is an unstable Lagrange point, meaning objects there are highly susceptible to any gravitational disturbance, and maintaining satellites in position there requires regular adjustments and fuel use. For this reason, SWFO-L1 is placed in Lissajous orbit, around L1. A Lissajous orbit is a quasi-periodic orbital trajectory that an object can follow around a Lagrangian point of a three body system, requiring minimal propulsion. In this orbit, SWFO-L1 will maintain a Sun-Earth-Vehicle (SEV) angle between 13° and 4°, with a period of roughly seven months. 6)

Mission Status

• September 24, 2025: SWFO-L1 was successfully launched from the Kennedy Space Centre in Florida at 7:30 am EDT. It was launched aboard a SpaceX Falcon 9 rideshare mission, and is planned to reach L1 after approximately four months. 19)
• June 25, 2024: GOES-19 was successfully launched from the Kennedy Space Centre at 5:26 pm EDT. GOES-19 carries the SWFO CCOR instrument, and was launched aboard a SpaceX Falcon Heavy rocket. 20)
• February 16, 2024: British multinational aerospace company, BAE Systems, has acquired Ball Aerospace and Technologies, inheriting the SWFO-L1 bus construction contract. 21)
• November 9, 2020: NASA awarded the delivery order for the SWFO-L1 spacecraft bus to Ball Aerospace & Technologies of Boulder, Colorado, on behalf of NOAA. The contract is a firm fixed-price delivery order, worth USD 96.9 million, with the contact term running until March 31, 2025. 22)

Sensor Complement

Compact Coronagraph

The SFWO Compact Coronagraph (CCOR) consists of two different models of coronagraph. CCOR-1 is carried by the geostationary GOES-19 mission, while CCOR-2 is carried by SWFO-L1 at Lagrange point L1. Both instruments observe the density structure of the white-light solar corona, to detect coronal mass ejections (CMEs), in particular halo CMEs, those directed towards or directly away from the Earth, resolving as a ‘halo’ on coronagraph images. Based on existing models, these observations can determine the direction and speed of CMEs, as well as their mass and estimate time of arrival at Earth. CCOR also employs an onboard scrubbing algorithm to scrub energetic proton hits. This has been included due to the ‘snowstorm’ impacts of solar radiation storms that often coincide with the strongest CMEs, potentially blinding the instrument from seeing the CME. The differences between CCOR-1 and -2 are field of view (FOV), spatial resolution, and eclipses. CCOR-2 provides a larger FOV, at the expense of spatial resolution. As CCOR-1 is carried by GOES-19, in geostationary orbit, it experiences an eclipse, resulting in one or more images missed on 42% of the days of the year. 9) 10) 11)

Magnetometer

The SWFO-L1 Magnetometer (MAG) consists of two tri-axial fluxgate sensors that measure the three vector components of the interplanetary magnetic field carried by solar wind. Measurement of solar wind components allows MAG to provide real-time, continuous observations of magnetic structures directed towards Earth. MAG uses an elongated racetrack shape, as opposed to a traditional ring-shaped magnetometer design. This elongated form reduces noise by focusing the magnetic field along its length, providing more definite orientation by aligning the magnetic and mechanical axes and improving thermal stability through more uniform heat distribution along each axis. The two MAG components, an inbound and outbound sensor, are located 3.946 m and 5.6 m away from the spacecraft bus, mounted on its 5.6 m boom to isolate the magnetometers from any spacecraft generated fields. 10) 12) 13)

Suprathermal Ion Sensor

The Suprathermal Ion Sensor (STIS) carried by SWFO-L1 is a solid-state spectrometer for the measurement of suprathermal ions and electrons across a wide energy range, providing real-time, continuous observation to allow early warning of various space weather phenomena. Suprathermal ions observed by STIS have higher energy than the bulk plasma of a CME, and are produced by a combination of local solar radiation and acceleration at a CME shock front. The in situ measurement of these ions by STIS provides an earlier warning of geomagnetic activity before the CME itself reaches the SWFO-L1 observatory. The instrument itself is a single sensor housing a pair of solid state telescopes. Each telescope consists of a stacked pair of doped silicon detectors, and each has two active regions. The first Active Region (AR1) is a small 0.1 cm2 pixel for high flux measurement, while AR2 is a larger 1.0 cm2 annular region surrounding AR1, providing anti-coincidence shielding and sufficient area for intervals of low particle flux. 10) 14) 15)

Solar Wind Plasma Sensor

SWFO-L1’s Solar Wind Plasma Sensor (SWiPS) consists of two identical electrostatic analysers, measuring velocity, density and temperature of solar wind ions, and providing in situ and real-time, continuous observations of plasma structures directed towards the Earth for early warnings of geomagnetic activity. The sensor contains two primary subsystems, an ion sensor and electronics box. The ion sensor component consists of the two identical back-to-back, top-hat electrostatic analyzer/microchannel plate/anode assemblies, which employ common deflectors to determine the solar wind ion parameters at a 1 minute time resolution. The SWiPS dual assembly design allows measurement from one assembly to be cross-calibrated with the other at regular intervals. The instrument provides three dimensional plasma distribution functions of solar thermal ions over an energy/charge range of 0.17 to 33 keV/q with a resolution of 0.08 eV/eV. From these distribution functions, the velocity, density, temperature and dynamic pressure of solar thermal ions, or solar wind, can be derived. These ions are collected through the instrument aperture, located at the centre of the sensor assembly, pointing along the solar line of sight. The sensor FOV spans 90° about the sensor cylinder azimuth and 45° about the sensor cylinder elevation centerline. 10) 16) 17)

Ground Segment

The SWFO ground segment consists of the SWFO Antenna Network (SAN) and mission operation centre (MOC). SAN is a globally distributed antenna network, allowing it to provide continuous coverage for SWFO-L1 data collection. The system has dual S- and X-band antennas at the Wallops Command and Data Acquisition Station (WCDAS) in Virginia, and at the Consolidated Backup (CBU) facility in Fairmont, West Virginia, with X-band only antennas located around the world to enable continuous downlink of space weather observation data. Command and control of the SWFO-L1 satellite is conducted from the NOAA Satellite Operations Facility (NSOF) in Suitland, Maryland, with primary uplink capability from WCDAS and secondary capacity at CBU. 18)

References  

1) NASA, “SWFO-L1”, URL: https://science.nasa.gov/mission/swfo-l1/

2) NOAA National Environmental Satellite, Data, and Information Service, “Space Weather Follow On L1 Mission”, URL: https://www.nesdis.noaa.gov/our-satellites/future-programs/swfo/space-weather-follow-l1-mission

3) World Meteorological Organization, “Space Weather”, URL: https://web.archive.org/web/20250822225453/https://community.wmo.int/en/activity-areas/wmo-space-programme-wsp/space-weather-introduction

4) Bureau of Meteorology, “What is Space Weather?” URL: https://www.sws.bom.gov.au/Products_and_Services/5/18

5) International Space Weather Initiative, “What is Space Weather?”, URL: https://iswi-secretariat.org/home-page/about-iswi/space-weather/

6) NASA Technical Reports Server, “The Space Weather Follow On – Lagrange 1 Mission”, URL: https://ntrs.nasa.gov/api/citations/20250000026/downloads/Space%20Weather%20Follow%20On%20L1%20Mission%20Preprint392.pdf

7) NOAA National Environmental Satellite, Data, and Information Service, “Space Weather Follow-On – Lagrange 1 (SWFO-L1) Antenna Network (SAN) Request for Information (RFI)”, URL: https://imlive.s3.amazonaws.com/Federal%20Government/ID232784663815825628625211204372105003354/Antenna%20RFI.pdf

8) BAE Systems, “SWFO-L1”, URL: https://www.baesystems.com/en/product/swfo-l1

9) NOAA National Environmental Satellite, Data, and Information Service, “Compact Coronagraph (CCOR)”, URL: https://www.nesdis.noaa.gov/s3/2025-01/4-ccor-specs_as_built.pptx

10) NOAA National Environmental Satellite, Data, and Information Service, “SWFO Instruments”, URL: https://www.nesdis.noaa.gov/our-satellites/future-programs/swfo/swfo-instruments

11) WMO OSCAR, “CCOR-2”, URL: https://space.oscar.wmo.int/instruments/view/ccor_2

12) NOAA National Environmental Satellite, Data, and Information Service, “Magnetometer (MAG)”, URL: https://www.nesdis.noaa.gov/s3/2025-01/4-mag-specs-21-Jan-2025.pptx

13) WMO OSCAR, “SWIS/MAG”, URL: https://space.oscar.wmo.int/instruments/view/swis_mag

14) NOAA National Environmental Satellite, Data, and Information Service, “Suprathermal Ion Sensor (STIS)”, URL: https://www.nesdis.noaa.gov/s3/2025-01/4-stis-specs.pptx

15) WMO OSCAR, “SWIS/STIS”, URL: https://space.oscar.wmo.int/instruments/view/swis_stis

16) NOAA National Environmental Satellite, Data, and Information Service, “Solar Wind Plasma Sensor (SWiPS)”, URL: https://www.nesdis.noaa.gov/s3/2025-05/4-swips-specs_updated_4_28_2025.pptx

17) WMO OSCAR, “SWIS/SWiPS”, URL: https://space.oscar.wmo.int/instruments/view/swis_swips

18) NOAA National Environmental Satellite, Data, and Information Service, “SWFO Ground Segment”, URL: https://www.nesdis.noaa.gov/next-generation/space-weather/swfo-ground-segment

19) NOAA, “NOAA’s SWFO-L1 observatory heads to orbit for groundbreaking mission”, URL: https://www.noaa.gov/news-release/noaas-swfo-l1-observatory-heads-to-orbit-for-groundbreaking-mission

20) NOAA, “NOAA’s GOES-U Heads To Orbit For Historic Mission”, URL: https://www.nesdis.noaa.gov/news/noaas-goes-u-heads-orbit-historic-mission

21) BAE Systems, “BAE Systems Completes Acquisition of Ball Aerospace”, URL: https://www.baesystems.com/en/article/bae-systems-completes-acquisition-of-ball--aerospace

22) NOAA, “NASA Awards NOAA’s Space Weather Follow On-Lagrange 1 Spacecraft”, URL: https://www.nesdis.noaa.gov/news/nasa-awards-noaas-space-weather-follow-lagrange-1-spacecraft