TWINS (Two Wide-angle Imaging Neutral-atom Spectrometers) is a Mission of Opportunity under NASA's Small Explorer (SMEX) program. TWINS-1 and TWINS-2 are the designations for NASA-sponsored instruments flying on unspecified non-NASA U.S. government spacecraft.The TWINS-1 instrument high voltages were turned on in April 2007 and the TWINS-2 high voltages in May 2008; the exact launchdates are not available. The data (including both science data and spacecraft ephemeris/attitude information) from the two NASA-funded science instruments are publicly available to the scientific research community. TWINS instrumentation includes an energetic neutral atom (ENA) imager to capture charge-exchange-produced neutral atoms over a broad energy range (approximately 1-100 keV) and a Lyman-alpha detector to measure the density of the neutral hydrogen geocorona needed for extraction of magnetospheric ion fluxes from neutral atom data. The TWINS-1 and TWINS-2 instruments are identical.