Hello dear student

• Mechanical engineer can also apply for RAC post in isro. After clearing the exam you have to give a isro interview.
• In interview there is no weightage of marks obtained in written exam. Interview is the only thing that can give you a job in isro as scientific officer.
• And if you want to apply DRDO Than you should appear the set examination. For the SET exam, you have to apply online through the official website of DRDO .
• Step 2: To fill the DRDO online application form candidates have to click on the advertisement tab.
• Step 3: Candidates have to enter their Email Id and Password
• . Step 4: Candidates need to click on the recruitment .

For more information please visit the link.

https://engineering.careers360.com/articles/isro-drdo-barc-dae-how-work-here/amp

Hope that's helpful

Best of luck