Interview experience
ISRO Interview Questions and Answers (2026)
Overview
Section titled “Overview”ISRO’s main fresher engineering hire - Scientist/Engineer ‘SC’ - runs almost entirely on your GATE score: there’s no separate ISRO written exam, just GATE-based shortlisting followed by a single Personal Interview.
ISRO interview process at a glance
Section titled “ISRO interview process at a glance”| Round | Duration | What it tests |
|---|---|---|
| GATE score shortlisting | - | Valid GATE score in the matching engineering discipline, shortlisted ~1:7 against vacancies |
| Personal Interview | 30-45 min | Technical/academic depth (40), specialisation awareness (20), communication (20), comprehension (10), academic record (10) |
| Document verification & medical | - | Eligibility documents, category certificates, physical fitness |
GATE score shortlisting
Section titled “GATE score shortlisting”There’s no ISRO-conducted written exam for the Scientist/Engineer ‘SC’ post - your GATE score in the relevant paper is the only filter before the interview. Shortlisting is relative (roughly 1:7 candidates per vacancy), so the effective cutoff shifts every year with vacancy count and applicant volume.
Common questions
- N/A - this stage is a pure score-based shortlist, not a test with questions
Personal Interview
Section titled “Personal Interview”A single 100-mark interview does all the technical and behavioural evaluation. Panels lean hard on your GATE-syllabus subjects and expect you to explain your final-year project clearly and in depth, since Comprehension and Presentation/Communication are scored as separate criteria alongside raw technical knowledge.
Common questions
- Core subject questions from your GATE discipline (e.g. control systems, thermodynamics, structures, VLSI, depending on branch)
- General-awareness questions on ISRO’s current missions and programmes relevant to your specialisation
- Detailed walkthrough of your final-year project or thesis - methodology, results, and what you’d change
- Why ISRO, and which centre or work area interests you
- Basic questions probing clarity of explanation, since communication is scored separately from technical content
Sample answer frameworks for the interview are on the ISRO HR interview questions page.
Why there’s no written exam or GD at ISRO
Section titled “Why there’s no written exam or GD at ISRO”Unlike IOCL or NTPC, which sometimes add a Group Discussion, or apprentice-style PSU entries that run their own computer-based test, ISRO’s Scientist/Engineer ‘SC’ recruitment (via ICRB) has stripped the pipeline down to GATE score plus interview. That means your prep timeline is compressed into two things: getting a competitive GATE score in your discipline, and then treating the single interview as carrying the entire evaluation - there’s no second technical round to recover a weak interview performance.
Common technical interview questions and answers
Section titled “Common technical interview questions and answers”Q: What does negative feedback do to a control system, and how do you check stability?
Negative feedback subtracts a measured output from the reference input, so the controller acts on the error. That reduces sensitivity to plant parameter variation and disturbances, widens bandwidth and improves linearity, at the cost of reduced overall gain and a risk of instability if the loop phase shift approaches 180 degrees while the loop gain is still above unity. For a linear time-invariant system, stability means every closed-loop pole lies in the left half of the s-plane. You test this without factoring the characteristic polynomial using the Routh-Hurwitz criterion - the number of sign changes in the first column of the Routh array equals the number of right-half-plane poles - or graphically with gain and phase margins on a Bode plot.
Q: State the sampling theorem and explain aliasing.
The Nyquist-Shannon sampling theorem says a signal band-limited to a maximum frequency fm can be reconstructed exactly from samples taken at a rate greater than 2fm; that threshold, 2fm, is the Nyquist rate. If you sample slower, frequency components above half the sampling rate fold back and appear as lower frequencies that are indistinguishable from genuine ones - that is aliasing, and no processing afterwards can undo it. The fix is an analogue anti-aliasing low-pass filter before the ADC, which is why every real telemetry or imaging chain places the filter ahead of the sampler rather than after it.
Q: What are setup time and hold time in a digital circuit?
Setup time is the interval before the active clock edge during which the data input must already be stable; hold time is the interval after the edge during which it must stay stable. Violate either and the flip-flop can go metastable, settling to an unpredictable value after an unbounded delay. A setup violation means the data path is too slow, so you fix it by shortening combinational logic, pipelining, or lowering the clock frequency. A hold violation means the path is too fast and is independent of clock period, so you fix it by adding buffer delay in the data path. Crossing clock domains needs a synchroniser, typically two cascaded flip-flops.
Q: State the first and second laws of thermodynamics and explain Carnot efficiency.
The first law is conservation of energy for a system: the heat added equals the change in internal energy plus the work done, or dQ = dU + dW. It says energy cannot be created or destroyed but places no limit on direction. The second law supplies that direction - entropy of an isolated system never decreases, and no engine can convert heat entirely into work while operating in a cycle. The Carnot cycle sets the upper bound on efficiency between two reservoirs: efficiency = 1 minus T_cold divided by T_hot, with temperatures in kelvin. So an engine between 800 K and 300 K cannot exceed 62.5 percent, no matter how it is built - a real engine is always lower because of irreversibilities.
Q: What is the difference between stress and strain, and what does the stress-strain curve tell you?
Stress is internal force per unit area (N/m squared, or pascal); strain is the resulting fractional deformation, change in length over original length, and is dimensionless. In the initial linear region they follow Hooke’s law, stress = E times strain, where E is Young’s modulus - the slope, a measure of stiffness. The curve then passes the proportional limit and yield point, after which deformation is plastic and permanent, rises to the ultimate tensile strength, and ends at fracture. A ductile material like mild steel shows a long plastic region and necking before failure, while a brittle material like cast iron fractures with almost no plastic warning - which is why launch-vehicle structures are designed with yield and ultimate factors of safety against limit loads.
Q: What is the rocket equation, and what does specific impulse mean?
Tsiolkovsky’s rocket equation gives the velocity change a rocket stage can produce: delta-v = Ve times the natural log of initial mass divided by final mass, where Ve is the effective exhaust velocity. Because the mass ratio sits inside a logarithm, propellant requirement grows exponentially with the required delta-v - the reason launch vehicles like PSLV and LVM3 are staged, dropping empty tanks to keep the mass ratio favourable. Specific impulse, Isp, is thrust per unit weight flow rate of propellant, measured in seconds, and relates to exhaust velocity as Ve = Isp times g0. Solid boosters sit near 250-290 s, storable liquids near 300 s, and cryogenic LOX-LH2 engines near 440 s in vacuum, which is why cryogenic upper stages matter for heavy GTO missions.
Q: Why is a geostationary orbit at about 36,000 km, and how does a sun-synchronous orbit differ?
A geostationary satellite must complete one orbit in exactly one sidereal day (23 h 56 m) so it appears fixed over a point on the equator. Equating gravitational and centripetal acceleration gives an orbital radius of about 42,164 km from Earth’s centre, which is roughly 35,786 km of altitude, and the orbit must be equatorial with near-zero inclination - that is where communication satellites such as the GSAT series sit. A sun-synchronous orbit is a low, near-polar orbit at roughly 600 to 900 km with an inclination near 98 degrees, slightly retrograde. Earth’s equatorial bulge (the J2 term) precesses its orbital plane by about one degree per day, matching Earth’s motion around the Sun, so the satellite crosses every latitude at the same local solar time - giving the consistent lighting that remote-sensing missions like Cartosat and Resourcesat need.
Q: What is escape velocity, and how does it relate to orbital velocity?
Escape velocity is the speed at which an object’s kinetic energy equals the magnitude of its gravitational potential energy, so it can leave a body’s gravitational influence with zero residual speed: Ve = square root of 2GM divided by r, which is about 11.2 km/s at Earth’s surface. Orbital velocity for a circular orbit is Vo = square root of GM divided by r, about 7.9 km/s near the surface and around 7.8 km/s in low Earth orbit. So escape velocity is exactly root-two times circular orbital velocity at the same radius - roughly 41 percent more speed. Note it is a speed, not a direction, and it ignores atmospheric drag, which is why real launch profiles pitch over and gain altitude before accelerating hard.
Frequently asked questions about ISRO interviews
Section titled “Frequently asked questions about ISRO interviews”What is the ISRO interview process for freshers?
ISRO hires Scientist/Engineer ‘SC’ - its main fresher engineering entry - through the ISRO Centralised Recruitment Board (ICRB) using a GATE-score route: 1. Candidates are shortlisted purely on their valid GATE score in the matching discipline, in roughly a 1:7 ratio against vacancies - there is no separate ISRO written exam for this route. 2. A single Personal Interview (100 marks: Technical/Academic Knowledge 40, General Awareness in your specialisation 20, Presentation and Communication 20, Comprehension 10, Academic Achievements 10). 3. Document verification and medical examination. The full cycle from GATE score release to offer typically runs a few months.
Is there a written test for ISRO recruitment, or is it only GATE-based?
For the Scientist/Engineer ‘SC’ post - ISRO’s main fresher engineering hire - there is no separate written exam; shortlisting is done entirely on your GATE score, followed by an interview. ISRO also occasionally runs direct recruitment drives (e.g. for Technical Assistant or other non-GATE posts) that do use their own written/computer-based test, but for degree-engineer hiring the GATE route is the dominant path today.
What questions are asked in the ISRO interview?
The ISRO Personal Interview is discipline-heavy: expect deep technical/academic questions from your core engineering subjects (as covered in your GATE syllabus), general-awareness questions tied to your specialisation and ISRO’s mission areas, and questions built around your final-year project or thesis. Communication and comprehension are scored separately, so panels also probe how clearly you explain technical ideas.
How many rounds are there in the ISRO interview?
Just two effective stages for the GATE route: GATE-score shortlisting (no written exam) and a single Personal Interview. That’s a shorter pipeline than most PSUs, which often add a Group Discussion - ISRO’s SC recruitment skips that entirely and puts all the weight on the interview.
How should I prepare for ISRO interviews?
Score well in GATE first - your rank inside the shortlisting ratio determines whether you get an interview call at all. For the interview itself, revise your GATE-syllabus subjects at depth (that’s 40 of the 100 marks), read up on ISRO’s current missions and programmes relevant to your discipline, and prepare a clear, well-rehearsed walkthrough of your final-year project since panels probe it in detail.
What GATE score or rank does ISRO require for Scientist/Engineer ‘SC’?
ISRO doesn’t publish a fixed minimum GATE score - shortlisting is relative, done in roughly a 1:7 ratio of candidates to vacancies for each discipline, based on your GATE score (not raw marks or All-India Rank) in that year’s exam. The effective cutoff therefore moves every year depending on vacancy count and the applicant pool for each engineering discipline.