The Origins Space Telescope (OST) is an initiative to develop a space telescope in the 8 to 15 diameter meter range, in an L2 orbit, to observe Infrared Wavelengths in the 5um to 1mm range, for launch roughly 2035. It is to aim at high Redshifts as well investigation of Solar System objects such as Comets, and Extra-Solar Planet observations.
At present, concepts are being developed, the first (now called Concept 1) for a 9.1m Primary Mirror, and instruments including camera(s), Spectrograph(s) and Polarimeter(s) covering 5 to 660 μm, with instruments cooled to 5K to reduce Thermal Noise, thus increase sensitivity. This wavelength-range is similar to Herschel Space Observatory but it would have far more sensitivity due to the cryogenic Temperature.
Concept 2 is for a less-ambitious project aiming for a smaller budget. One practical concern addressed is the launch size and weight, reducing its mass and dimensions so as to be launched by the SLS 8.4m-diameter launch rocket, currently in development. The telescope would cover the same wavelength range with similarly sensitive instruments cooled to 5K. The primary mirror size would match James Webb Space Telescope-size (6.5m) or would be somewhat smaller, but would be larger then Herschel (3.5m). The sensitivity offered by the 5K temperature is considered the primary advantage over earlier similar telescopes.