What are are NASA's current goals, and what missions do they have planned within the next decade?
NASA's current major goals are:

1. Return humans to the Moon by 2024 through the Artemis program. The goal of Artemis is to eventually send humans to Mars. Planned Artemis missions in the next decade include:

- Artemis 3: First crewed flight of the Orion spacecraft around the Moon in 2023.

- Artemis 4: Crewed flight around the Moon and potential lunar landing in 2024.

2. Continue scientific discovery about the solar system and universe through robotic space probes and telescopes. Planned missions include:

- Perseverance rover mission to Mars in 2020 to search for signs of ancient life.

- Europa Clipper mission to study Jupiter's moon Europa and its potential habitability in the 2020s.

- James Webb Space Telescope to be launched in 2021 to study the earliest periods of the universe and peer inside dust clouds where stars and planetary systems are being born.

3. Develop new technologies for space exploration like advanced propulsion and habitats. This includes programs like the Next Space Technologies for Exploration Partnerships.

4. Study Earth and climate change via spacecraft and satellites. Planned missions include new Earth-observing satellites to monitor factors like sea level rise, extreme weather events, and climate patterns.

Those are the major goals and planned missions within the next decade according to NASA's current plans. Of course, these plans could change or be delayed due to budgetary or technical constraints.
What budgetary constraints has NASA had to face in the past?
NASA, like most federal agencies, has to operate within budgetary constraints imposed on it by the federal government.

As a result NASA has faced serious budgetary constraints in the past. In the 1970s NASA had to deal with the cancellation of the Apollo program. Despite achieving its goal of landing astronauts on the moon the program was cancelled due to budgetary constraints and public indifference to the program. 

In the 1980s the Regan administration cut NASA's budget which then resulted in many programs being cancelled, including the space shuttles development and testing. In 1986 the budget was restored but they still had to operate with less funding for a time which resulted in a hindered ability to achieve its mission directives. 

In more recent times NASA's budgetary constraints have more to do with changing political priorities and competition for federal funding. NASA's budget has fluctuated and some programs have faced cuts or cancellations. This includes the cancellation of the constellation program in 2010, which was intended to replace the Space Shuttle program.
What things has NASA had to cancel?
NASA has had to cancel or delay many projects over the years due to various reasons, including budget constraints, technical difficulties, and safety concerns. Some notable cancellations include:

Constellation Program (2004-2010): NASA's program to send humans back to the moon and eventually to Mars was cancelled due to budget constraints.

Europa Clipper Mission (2020): A mission to explore Jupiter's moon Europa was cancelled due to budget cuts.

Asteroid Redirect Mission (2017): A plan to redirect a small asteroid into lunar orbit for exploration and study was cancelled due to budget constraints.

Wide Field Infrared Survey Telescope (2011-2018): A space telescope designed to study dark energy and exoplanets was cancelled due to budget constraints.

Mars Sample Return Mission (2013-2018): A mission to bring Martian rock samples back to Earth for analysis was cancelled due to budget constraints.

Lunar Prospector (1997): A mission to map the moon's surface and study its resources was cancelled due to technical difficulties.

Mars Observer (1993): A mission to study Mars' atmosphere, surface, and climate was lost during its approach to the planet due to technical difficulties.

These are just a few examples, as NASA has had to cancel or delay many other projects over the years.