In the United States, the federal executive agency that is supposed to support the environment is the Environmental Protection Agency. Each state has an agency with a similar responsibility and a different but similar name.
In other countries, the agency is often called something like "Ministry of the Environment."
The National Aeronautics and Space Administration is an executive agency.
In my experience the term 'executive agency' is for certain bureaus in the British government. Since NASA is a part of the US government it would not be an executive agency under this definition. If you mean, is it an agency falling under the US Executive Branch (under the President) then yes, it falls under the President.
Independent executive agency
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Trans-European Transport Network Executive Agency was created in 2006.
The Environment Act 1990
European Environment Agency was created in 1990.
National Environment Agency was created in 2002.
The Office of Management and Budget (OMB) helps the President prepare and administer the Federal Budget.