The in situ measurements of particles and CME transients (IMPACT) investigation on the twin STEREO spacecraft focuses on the solar energetic particle, solar wind and suprathermal electron, and magnetic field measurements needed to address STEREO’s goals. IMPACT will provide regular, identical, in situ multipoint measurements bracketing Earth as each spacecraft separates from it at a rate of ∼22°/yr along Earth’s orbit. Combined with the PLASTIC and SWAVES investigations, IMPACT fills a critical role in the STEREO quest to connect SECCHI’s 3D coronal images to their interplanetary consequences.
