Interview experience
DRDO Interview Questions and Answers (2026)
Overview
Section titled “Overview”DRDO runs two structurally different hiring pipelines - a GATE-based route for Scientist ‘B’ graduate/postgraduate entries via RAC, and a separate own-exam route for non-gazetted technical posts (STA-B, Technician-A) via CEPTAM.
DRDO interview process at a glance
Section titled “DRDO interview process at a glance”| Round | Duration | What it tests |
|---|---|---|
| GATE score shortlisting (Scientist ‘B’ / RAC route) | - | Valid GATE score in the matching discipline |
| Written/descriptive test (most disciplines, RAC route) | Varies | Core subject depth beyond GATE screening |
| Personal Interview (RAC route) | 30-45 min | Technical depth, defence-tech awareness, project discussion |
| Computer-Based Test - CBT (CEPTAM route, non-gazetted posts) | Multi-tier | General awareness, reasoning, quantitative aptitude, trade/technical knowledge |
| Trade/Skill Test (CEPTAM route) | Varies | Hands-on trade proficiency |
| Document verification & medical | - | Eligibility documents, category certificates, physical fitness |
GATE score shortlisting (Scientist ‘B’)
Section titled “GATE score shortlisting (Scientist ‘B’)”DRDO’s Scientist ‘B’ recruitment via RAC starts with shortlisting purely on your GATE score in the relevant engineering or science discipline - there’s no separate DRDO screening test at this stage.
Common questions
- N/A - this stage is a pure score-based shortlist, not a test with questions
Written/descriptive test (Scientist ‘B’, most disciplines)
Section titled “Written/descriptive test (Scientist ‘B’, most disciplines)”For most engineering disciplines, GATE-shortlisted candidates sit a written or descriptive test before the interview, going deeper into core subject fundamentals than GATE’s objective format allows. A few disciplines skip this and go straight to interview.
Common questions
- Descriptive/analytical questions on core subjects from your GATE discipline (e.g. mechanics, electronics, materials, depending on branch)
- Problem-solving questions that require worked derivations, not just multiple-choice recall
Personal Interview (Scientist ‘B’)
Section titled “Personal Interview (Scientist ‘B’)”The closing stage for RAC-route candidates: a panel interview covering core technical depth, awareness of DRDO’s programmes and defence-technology areas, and a detailed walkthrough of your final-year project or thesis.
Common questions
- Core-subject numericals and concept questions from your discipline
- Awareness of DRDO projects relevant to your field (missile systems, radar, materials research, electronics, etc.)
- Detailed project/thesis discussion - methodology, results, and design choices
- Why DRDO, and why defence R&D over a corporate or private-sector role
Sample answer frameworks are on the DRDO HR interview questions page.
Computer-Based Test and Trade/Skill Test (CEPTAM route)
Section titled “Computer-Based Test and Trade/Skill Test (CEPTAM route)”For non-gazetted technical posts like Senior Technical Assistant-B and Technician-A, CEPTAM runs its own Computer-Based Test - typically across multiple tiers - covering general awareness, reasoning, quantitative aptitude, and trade or technical knowledge specific to the post. Candidates who clear the CBT move to a hands-on Trade/Skill Test.
Common questions
- General awareness and current-affairs MCQs
- Quantitative aptitude and reasoning questions
- Trade/technical-knowledge questions specific to the post (e.g. electronics, mechanical, or ITI trade syllabus)
- Practical trade or skill demonstration relevant to the post applied for
RAC vs CEPTAM: why the recruitment route matters
Section titled “RAC vs CEPTAM: why the recruitment route matters”DRDO isn’t one hiring pipeline - it’s two, run by different internal bodies. RAC handles gazetted Scientist posts (Scientist ‘B’ and above) through GATE-based shortlisting, a discipline-dependent written test, and an interview. CEPTAM handles non-gazetted technical and support posts (STA-B, Technician-A, and similar) through its own Computer-Based Test and Trade/Skill Test, with no GATE requirement. Applying to the wrong prep track - say, GATE-focused prep for a CEPTAM CBT, or trade-syllabus prep for a Scientist ‘B’ interview - wastes real time, so confirm which recruitment body your target post falls under before you start.
Common technical interview questions and answers
Section titled “Common technical interview questions and answers”Q: What is the radar range equation, and why does detection range grow so slowly with transmitted power?
The monostatic radar range equation gives received power as Pr = Pt * G^2 * lambda^2 * sigma / ((4*pi)^3 * R^4), where Pt is transmitted power, G antenna gain, lambda wavelength, sigma the target radar cross section and R the range. Because the signal spreads on the way out and again on the way back, received power falls as the fourth power of range. Solving for maximum range at a fixed minimum detectable signal means R_max varies as the fourth root of Pt, so doubling transmitter power buys only about 19 percent more range. That is why radar designers prefer higher antenna gain, pulse compression and coherent integration over brute-force power.
Q: What is the difference between a ballistic missile and a cruise missile?
A ballistic missile is rocket-powered only during a short boost phase, after which it follows an unpowered ballistic trajectory shaped by gravity and drag, often leaving and re-entering the atmosphere; it flies high and fast and is used for long-range strike. A cruise missile uses an air-breathing engine such as a turbojet, turbofan or ramjet for the whole flight, stays within the atmosphere, and flies a low, terrain-following path with aerodynamic lift from wings. Cruise missiles are harder to detect because of that low flight profile and can manoeuvre and re-target in flight; ballistic missiles trade that for speed and range. BrahMos is a ramjet-powered supersonic cruise missile, while the Agni series is ballistic.
Q: What does an inertial navigation system do, and why is it usually combined with satellite navigation?
An INS uses accelerometers and gyroscopes to measure specific force and angular rate, then integrates them to propagate position, velocity and attitude from a known starting state. It is fully self-contained and cannot be jammed or spoofed, which matters for defence platforms, but sensor bias and noise are integrated too, so position error drifts and grows with time. Satellite navigation gives bounded absolute position error but is weak under jamming and has low update rates and outages. Fusing the two in a Kalman filter lets the satellite fix continuously estimate and correct INS bias and drift while the INS bridges outages, giving both short-term stability and long-term accuracy.
Q: Why are fibre-reinforced composites used instead of metals in aerospace and missile structures?
Carbon-fibre composites give very high specific strength and specific stiffness - strength and modulus divided by density - so a structure of equal load capacity weighs substantially less than an aluminium one, and every kilogram saved on a missile becomes range or payload. Their properties are anisotropic, so the laminate stack-up can be tailored to place fibres along the principal load paths. They also resist fatigue and corrosion far better than aluminium alloys. The trade-offs are poor through-thickness strength, vulnerability to barely visible impact damage and delamination, difficult non-destructive inspection, and much higher manufacturing cost.
Q: How is radar cross section reduced in a stealth aircraft?
Radar cross section is reduced mainly by shaping and by material choice. Shaping uses flat, canted surfaces and aligned planform edges to reflect incident energy away from the transmitter rather than back to it, and eliminates strong returns such as right-angle corner reflectors, exposed engine faces and external stores. Radar-absorbent materials add a lossy layer - typically ferrite or carbon-loaded - that converts incident energy into heat, and impedance-matched coatings cancel the surface reflection. Because monostatic detection range varies as the fourth root of RCS, cutting RCS by a factor of 10000 cuts detection range only by a factor of 10, which is still operationally decisive.
Q: What is the difference between engineering and true stress-strain, and what is the yield point?
Engineering stress is load divided by the original cross-sectional area and engineering strain is elongation divided by the original gauge length, while true stress and true strain use the instantaneous area and length. Up to yield the two curves are nearly identical, but after necking the engineering curve turns down because the area shrinks while the original area is still used in the denominator, whereas the true stress curve keeps rising. The yield point marks the end of elastic behaviour and the start of permanent plastic deformation; for materials without a sharp yield, the 0.2 percent offset proof stress is used instead. Static design is normally carried out against yield strength with a factor of safety, not against ultimate tensile strength.
Q: State the Nyquist sampling theorem and explain aliasing in a radar receiver.
The Nyquist-Shannon theorem states that a signal band-limited to B hertz can be reconstructed exactly from uniform samples taken at a rate strictly greater than 2B. If the sampling rate is lower, frequency components above half the sampling rate fold back into the baseband and appear as false lower-frequency components - aliasing - which is irreversible once it has happened. In a radar receiver this shows up as ambiguous Doppler or range measurements: a target whose Doppler shift exceeds half the pulse repetition frequency is reported at the wrong velocity. Remedies are an analogue anti-aliasing filter ahead of the ADC, a higher sampling or pulse repetition frequency, or deliberate PRF staggering to resolve the ambiguity.
Q: Compare solid and liquid propellant rocket motors.
A solid motor stores fuel and oxidiser pre-mixed in a cast grain inside the casing, so it is mechanically simple, storable for years and can be launched at very short notice - which is why tactical and strategic missiles favour it. Once ignited, though, it burns to completion: thrust is set by the grain geometry and cannot be throttled or shut down and restarted. A liquid engine feeds separate fuel and oxidiser through pumps or pressurised tanks into a combustion chamber, so it can be throttled, stopped and restarted and generally gives higher specific impulse, at the cost of turbopumps, valves, plumbing and cryogenic handling. Hybrid motors pair a solid fuel with a liquid or gaseous oxidiser to get partial throttling with less complexity.
Frequently asked questions about DRDO interviews
Section titled “Frequently asked questions about DRDO interviews”What is the DRDO interview process for freshers?
DRDO runs two very different recruitment routes depending on the post. For Scientist ‘B’ (the main entry for engineering/science graduates and postgraduates, via the Recruitment & Assessment Centre/RAC): 1. Shortlisting on your GATE score in the matching discipline. 2. For most disciplines, a written/descriptive test after shortlisting; for some disciplines DRDO skips the written test and goes straight from GATE score to interview. 3. A Personal Interview. For non-gazetted technical/admin posts like Senior Technical Assistant-B or Technician-A (via CEPTAM): DRDO’s own Computer-Based Test (CBT, often in two tiers), followed by a Trade/Skill Test, document verification, and medical exam - no GATE requirement at all.
Does DRDO recruit only through GATE, or does it also have its own exam?
Both, for different posts. Scientist ‘B’ - the main graduate-entry technical role - is recruited primarily through GATE score shortlisting via RAC, sometimes with an added written test depending on discipline. Non-gazetted technical and support posts (Senior Technical Assistant-B, Technician-A, and similar CEPTAM-recruited roles) don’t use GATE at all - they’re filled through DRDO’s own multi-tier Computer-Based Test plus a Trade/Skill Test.
What questions are asked in DRDO interviews?
For Scientist ‘B’ interviews: core subject questions from your GATE-syllabus discipline, defence-technology and DRDO-programme awareness questions, and detailed cross-questioning on your final-year project or thesis. For CEPTAM technical-post selection, the CBT covers general awareness, reasoning, quantitative aptitude, and trade/technical knowledge, followed by a hands-on trade or skill test relevant to the post.
How many rounds are there in the DRDO interview process?
For Scientist ‘B’ via RAC: GATE-score shortlisting, then (for most disciplines) a written test, then a Personal Interview - so two or three real stages depending on discipline. For CEPTAM technical/support posts: a multi-tier Computer-Based Test, a Trade/Skill Test, document verification, and a medical exam - with no GATE or scientist-style interview involved.
How should I prepare for DRDO interviews?
If you’re targeting Scientist ‘B’, prioritise a strong GATE score in your discipline first, then revise core subject fundamentals at GATE depth for the written test and interview, and prepare a clear narrative on your final-year project since panels probe it closely. If you’re applying for a CEPTAM technical post (STA-B, Technician-A), focus on general aptitude, reasoning, and your specific trade syllabus for the CBT, and practice the hands-on skill test relevant to your trade.
What is RAC and CEPTAM in DRDO recruitment?
RAC (Recruitment & Assessment Centre) handles DRDO’s gazetted Scientist posts - Scientist ‘B’ and above - largely through GATE score shortlisting. CEPTAM (Centre for Personnel Talent Management) handles non-gazetted technical and administrative posts like Senior Technical Assistant-B and Technician-A through DRDO’s own Computer-Based Test and trade/skill tests. They’re separate recruitment bodies with completely different selection processes, so check which one your target post falls under before you prep.