Pros
Fantastic work-life balance, probably the best. Never expected to work overtime and if so, you'll always be compensated, whether with cash or comp time. Can sometimes get away with not working the full 40 hours, depending on team and if you get your work done.
Work is super easy. All you do is sustain old software.
Despite being a contractor, you're basically a full-time employee in terms of stability. Once contract ends, everyone moves to the new contract. NASA wants to keep employees familiar with the software.
Contractors are the last people to go without pay, so government shutdowns don't affect us at all like it does for civil servants. On that note, it's probably the most stable job out there.
Cons
Pay and benefits are lacking.
Depending on team, you may be expected to do on-site mission support, which occur in odd hours of the night. This is expressed to you during the interview process.
Work is not challenging at all and really old, outdated tools and software are used. Your skills as an engineer will dull at this job, but it's a stable first job.
Not easy to move up or switch positions. They expect you to do the work of transitioning yourself to any new position you want with the same pay and title rather than handing opportunities to you.
Strictly on-site. For now everyone is remote because of COVID, but there is intent to move back on-site and it appears to be a change to fully on-site.