Solar and Space Weather Missions Ready for Launch

NASA’s IMAP mission is set to launch on September 24, 2025, aboard a SpaceX Falcon 9 rocket. This launch brings 3 separate missions to the Earth-Sun L1 Lagrange point: IMAP, the Carruthers Geocorona Observatory, and NOAA’s SWFO-L1. L1 offers an unspoiled vantage point on the sun and the solar environment near to Earth without magnetic interference, which has made it a popular destination for heliophysics research since the 1970s.

The history of satellite-based space weather observation dates back over 50 years. The IMP-8 spacecraft, launched in 1973, was the first to directly measure the solar wind for long periods over many years. ISEE-3 in 1978 was the first spacecraft to orbit the Earth-Sun L1 Lagrange point and for 4 years continuously studied the solar wind and its interactions with Earth. Wind followed in 1994 (at L1 since 2004)  and is still in operation today, joined by the Advanced Composition Explorer (ACE) in 1997 and the Solar and Heliospheric Observatory (SOHO) in 1995. All of these missions were distinguished by being heliophysics science missions that were also able to provide data to space weather forecasts once those began in the late 1990s. The Deep Space Climate Observatory (DSCOVR, 2015) is a hybrid between this and a dedicated observatory. It has both Earth and Sun-focused instruments but is primarily used as an operational space weather sensor by NOAA, to provide data continuity due to the aging out of ACE.

DSCOVR is rapidly approaching the end of its design life, as are ACE and SOHO. NOAA wants a dedicated space weather spacecraft and needs a new coronagraph, as the only current deep space coronagraphs are on SOHO and STEREO-B (launched 2007). While SOHO, ACE, and DSCOVR are all still fully operational, it remains important to have an observatory within its design life to protect data continuity. NOAA and its industrial partners arrived at a solution in the form of the SWFO-L1 mission.

While the solar research observatories historically and presently located at L1 provide a wealth of data useful to both researchers and space weather forecasters, the operational focus on research means that timely delivery of the data is not a primary concern. Forecasters desire relevant measurements as soon as possible after collection, to maximize time for ground based model runs and forecaster discussion and to enable the largest possible watch and warning lead times for affected groups. Scientists, meanwhile, do not need their data as urgently and can happily wait hours or days for downlinks to the ground. SOHO’s coronagraph, for example, has a general lead time from data collection to download of roughly 8 hours. SWFO imagery will be on the ground within 30 minutes, while numerical data on plasma, ions, and magnetic fields will be transmitted within five. Infrequent downlinks often place a much greater emphasis on the onboard storage capacity of the spacecraft, which must all be able to operate continuously for years in the radiation-filled and electromagnetically harsh deep space environment.

The IMAP mission is primarily tasked with observing the boundaries of the Heliosphere via numerous particle detectors, but as the boundary is strongly influenced by both the Solar Wind and the Sun’s magnetic field, measuring those is also critical to contextualize the more direct information. Those local solar environment measurements are also relevant to space weather forecasting, so portions of relevant data will be downlinked in near-real time via the IMAP Active Link for Real-Time (I-ALiRT) system while the rest will be transmitted every few days.

One primary focus of the IMAP mission is studying the outer reaches of the Heliosphere via Energetic Neutral Atom (ENA) imaging. The magnetic field and interstellar medium-solar wind interactions at the edge of the Solar System do not generate light, but they do generate ENAs. ENAs are uncharged atoms that are traveling extremely quickly, generated when charged particles from the solar wind interact with atoms in the Local Interstellar Medium (ISM). Some of these fast-moving atoms travel towards Earth and can have their direction of origin and energy level measured via special detectors. As ENAs are unaffected by magnetic and electric fields, they can be used to build maps of activity where the LISM and Solar Wind meet. They also tell us what the ISM is made of.

NASA’s first mission dedicated to exploring the interstellar boundary via ENAs was the Interstellar Boundary Explorer (IBEX), launched on October 18, 2008 on a Pegasus XL rocket and still in operation today. Designed as the first mission dedicated to mapping the boundary of the heliosphere, IBEX data could create 3d maps of the termination shock (the boundary zone where the solar wind becomes subsonic) and even provide information about how the solar wind behaves beyond the shock.

Among the most startling discoveries made by IBEX was a bright “ribbon” in its maps of ENA emissions that no prior model or theory had predicted. New theories emerged but for over a decade no real consensus emerged as to what caused the ribbon, with at least 11 serious candidates as late as 2014. Part of the problem in getting consensus is the low resolution of IBEX data, which is the primary purpose of IMAP.

With the combination of IMAP and SWFO-L1, our understanding of the Sun’s influence and our ability to respond to its unpredictable nature will be transformed. NOAA will, for the first time, gain large amounts of near real-time information on the Sun’s activity and current conditions, doing for space weather forecasting what the GOES-R program has done for terrestrial weather forecasting since 2016. The increased resolution and warning time will open more options for satellite operators, terrestrial utilities, and other vulnerable groups to protect their systems from space weather events and ultimately reduce societal impact. IMAP will tackle one of the biggest recent mysteries in our understanding of the heliosphere, and due to the lack of extant data and abundance of theories, no matter what it discovers will revolutionize our understanding. For now, all eyes are on the launch, so good luck IMAP, SWFO-L1 and Falcon 9.

Acronyms:

ENA – Energetic Neutral Atom

IBEX – Interstellar Boundary Explorer

IMAP – Interstellar Mapping and Acceleration Probe

SWFO-L1 – Space Weather Follow-On – L1