The search for TNOs requires deep surveys (i.e. large apertures) and, in order to establish a reasonable orbit, in average around 16 months of observation is needed (in case of OSSOS [20]). TESS data, being a mission dedicated to exoplanet search and research, have been successfully demonstrated to be used for the search of TNOs down to about V = 21...22 mag [21], [22]. This situation will change drastically with the operation of the Vera C. Rubin Observatory, formerly Large Synoptic Survey Telescope (LSST), scheduled to enter into full science operation in mid 2022. It is predicted that about 40,000-60,000 TNOs/SDOs/CENs will be discovered during the nominal 10 years operation [23], including precise orbits due to high precision astrometry (σ ~10 mas) over years. This much larger observed population will enable us to proof and refine dynamical models, reveal interactions and will increase the number of objects to be studied individually, also by stellar occultations.

The James Webb Space Telescope (JWST), planned to be launched end of this year, will open another window on TNOs, especially for radiometric measurements [24], [25]. 

Beside ground-based and space-based observatories the third option to explore trans-Neptunian objects are spacecraft encounters and flybys. After the successful flyby of the New Horizons mission at dwarf planet Pluto in 2015 and TNO (486958) Arrokoth = 2014 MU69 (nickname ‘Ultima Thule’) in 2019 (distance
to Earth = 44.3 au at time of flyby), the next opportunity to study this kind of objects in-situ will be the Lucy space probe, a 12 year NASA Discovery Program mission to six Jupiter Trojans. Lucy is scheduled to launch in October 2021. After flying by the inner main-belt asteroid (52246) Donaldjohanson in 2025, Lucy will
arrive in 2027 at the L4 Trojan cloud. 

Another mission, though still a concept, is the Interstellar Probe, a multi-generation NASA Heliophysics Division mission proposal to leave the solar system in a 50-years prime mission to study the heliosphere and the interstellar medium (goal is to go beyond ~350 au within these 50 years, depending on the propulsion technology). On its way there are opportunities to explore trans-Neptunian objects (TNOs) during a flyby. 2002 MS4, Quaoar, Pluto, Ixion, and Gonggong are reasonable targets for spacecraft outbound trajectories within +/- 20° heliocentric ecliptic latitude [26]. Launch could be in the 2030s, the spacecraft speed depends on the technology, currently the concept states about 7 to 8 au per year.