NASA is big with many parts, many locations, many missions. Many of these have their own web sites. Navigation of all of this is not easy. The main NASA site is a good start.
NASA main site [link]
Another good start is the NASA science site. There might be a link to this science site on the main NASA site, but I have not found it.
NASA science site [link]
The "Missions" link on this NASA science site is especially useful. The list there can be sorted be any of the headers; for example, by the mission type. Near the bottom is "WISE" which is the source for the NASA Disc Detective citizen science project.
NASA science missions site [link]
On the top navigation bar of NASA science sites are buttons to link to the major kinds of NASA science missions. The four mission areas are Earth, Heliophysics (Sun physics), Planets, Astrophysics.
For example, the scienceNASA Earth site [link]
In the left box there the "Missions" link is again especially useful. Again, this list can be sorted by any of the headers. Sorting by the phase header shows what missions are operating.
NASA science Earth science missions site [link]
On these NASA science sites the "NASA science for . . ." header (on the narrow dark navigation bar near the top) has a "Citizen Scientists" component. There you can find links to the "Disc Detective" citizen science project which our group is now test driving.
NASA science citizen scientists site [link]
In the top navigation bar there is a "Big Questions" link which is especially interesting. It has many links to more information about those big questions. The Earth part is being revised.
NASA science Big Questions page [link]