Isro Placement Papers 2026

Meta Description: Prepare for ISRO Scientist/Engineer 'SC' 2026 with exam pattern, technical MCQs, aptitude questions, interview tips & salary details. Start your space career now!

Introduction

The Indian Space Research Organisation (ISRO) stands as the crown jewel of India’s scientific and technological ecosystem. As one of the world’s premier space agencies, ISRO has consistently delivered groundbreaking missions including Chandrayaan-3, Mangalyaan, Aditya-L1, and the upcoming Gaganyaan human spaceflight program. For Indian engineers, securing a position at ISRO is not merely a career milestone; it is a national service opportunity that places you at the forefront of aerospace engineering, satellite systems, propulsion technology, and space applications engineering.

Recruitment for the coveted Scientist/Engineer ‘SC’ position is conducted annually by the ISRO Centralised Recruitment Board (ICRB). Unlike PSU giants that rely heavily on GATE scores, ISRO designs and administers its own highly competitive written examination, followed by a rigorous technical interview. Each recruitment cycle typically offers 200–300 vacancies across core engineering disciplines: Electronics & Communication, Computer Science & Engineering, Mechanical Engineering, and Electrical Engineering. The selection ratio is exceptionally tight, with lakhs of applications funnelled into a few hundred seats, making conceptual clarity, speed, and domain-specific precision absolute necessities.

Engineers aspire to join ISRO for unparalleled exposure to mission-critical R&D, state-of-the-art testing facilities like the ISRO Propulsion Complex and Space Applications Centre, and the chance to contribute directly to India’s self-reliance in space technology. The organisation fosters a culture of continuous learning, interdisciplinary collaboration, and long-term project ownership, offering job stability, intellectual fulfillment, and the unique pride of contributing to national strategic capabilities.

Recruitment Process 2026

The ICRB follows a streamlined, transparent, and highly structured selection pipeline for Scientist/Engineer ‘SC’ recruitment. Candidates must carefully track official notifications on isro.gov.in and icrb.gov.in.

1. Official Notification Release: ICRB publishes discipline-wise vacancy details, eligibility criteria, and application timelines. Minimum qualification is BE/B.Tech with 65% marks or 6.5 CGPA in aggregate.
2. Online Application & Fee Payment: Candidates register, fill academic/professional details, upload documents, and pay the examination fee. SC/ST/PwD candidates receive fee concessions as per government policy.
3. Admit Card Generation: Roll numbers and exam centre details are released 7–10 days before the test. Hall tickets must be printed in A4 format.
4. Written Examination (Computer-Based or OMR): Conducted simultaneously across major Indian cities. The test evaluates core engineering fundamentals, analytical reasoning, and applied problem-solving under strict time constraints.
5. Result Declaration & Cut-Off Publication: ICRB releases discipline-wise cut-offs and shortlists candidates for the interview stage. Only top scorers (typically 10–15× the vacancy count) proceed.
6. Technical Interview & Document Verification: Shortlisted candidates appear before a subject-matter expert panel at ISRO centres (Bangalore, Ahmedabad, Thiruvananthapuram, etc.). The interview assesses conceptual depth, project work, and mission awareness.
7. Final Merit List & Offer Letter: Combined scores (Written 80% + Interview 20% or as per annual weighting) determine the final ranking. Successful candidates receive appointment letters with joining instructions.
8. Medical Examination & Onboarding: Standard government medical fitness checks precede induction into the Scientist/Engineer ‘SC’ cadre, followed by orientation at ISRO’s training academies.

Exam Pattern 2026

The ISRO Scientist ‘SC’ written examination is engineered to test engineering fundamentals rather than rote memorization. Speed, accuracy, and negative marking management are critical.

Section	Questions	Marks	Time
Technical (Discipline-Specific)	70	210	Integrated 90 Minutes
General Aptitude & Reasoning	10	30	Integrated 90 Minutes
Total	80	240	90 Minutes

• Marking Scheme: +3 for correct answers, -1/3 for wrong answers. Unattempted questions carry zero penalty.
• Language: English only.
• Difficulty Level: Moderate to High. Questions are concept-heavy, often requiring multi-step derivations or rapid numerical evaluation.
• Discipline Weightage: Technical section strictly follows your applied branch (ECE, CSE, ME, or EE). Cross-disciplinary overlap is minimal but foundational topics (Signals, Control, Thermodynamics, Data Structures) appear universally.

Technical Questions

The following 12 MCQs simulate the depth, domain coverage, and analytical rigor expected in the ISRO 2026 exam. Each includes a concise technical explanation.

1. [ECE/Digital Communications] In a coherent BPSK system operating over an AWGN channel, if the bit error rate (BER) is 10^-5, what happens to the BER when the received signal-to-noise ratio (Eb/N0) is increased by 3 dB? A) Decreases by half B) Decreases quadratically C) Improves exponentially D) Remains unchanged Answer: C Explanation: BER for coherent BPSK is Q(√(2Eb/N0)). The Q-function decays exponentially with argument increase. A 3 dB boost doubles Eb/N0, significantly improving BER due to the exponential tail of the Gaussian distribution.

2. [Space Tech/Orbital Mechanics] For a satellite in a circular Low Earth Orbit (LEO) at 400 km altitude, the orbital velocity is approximately: A) 5.6 km/s B) 7.68 km/s C) 11.2 km/s D) 3.1 km/s Answer: B Explanation: v = √(GM/(R+h)). Earth’s GM ≈ 3.986×10^14 m³/s², R ≈ 6371 km, h = 400 km. Substituting yields ~7.68 km/s. 11.2 km/s is escape velocity; 5.6 km/s is typical for MEO.

3. [Electronics/Analog Circuits] In an inverting op-amp configuration with Rf = 100 kΩ and Rin = 10 kΩ, introducing a compensation capacitor across Rf primarily addresses: A) DC offset voltage B) Input bias current C) High-frequency oscillation & phase margin D) Slew rate limitation Answer: C Explanation: The feedback capacitor creates a dominant pole, reducing gain at high frequencies, improving phase margin, and preventing parasitic oscillations due to op-amp internal pole interactions.

4. [Embedded Systems] In an ARM Cortex-M microcontroller, nesting interrupts with the same priority level is managed using: A) PendSV exception B) Tail-chaining optimization C) Priority grouping & subpriority D) Hardware stack pointer switching Answer: C Explanation: Cortex-M NVIC supports priority grouping, splitting bits into group priority (preemption) and subpriority (ordering within same group). True nesting requires different group priorities; same-level uses subpriority and tail-chaining.

5. [Control Systems] For a unity feedback system with open-loop transfer function G(s) = K/(s(s+2)(s+5)), the range of K for stability using Routh-Hurwitz criterion is: A) 0 < K < 10 B) 0 < K < 70 C) 0 < K < 50 D) K > 0 always stable Answer: B Explanation: Characteristic eq: s³ + 7s² + 10s + K = 0. Routh array: s³: 1, 10 | s²: 7, K | s¹: (70-K)/7 | s⁰: K. For stability: K>0 & 70-K>0 → 0<K<70.

6. [Mechanical/Aerospace Propulsion] The specific impulse (Isp) of a chemical rocket engine is primarily dependent on: A) Combustion chamber pressure only B) Nozzle exit area to throat ratio C) Exhaust velocity and gravitational constant D) Propellant tank material strength Answer: C Explanation: Isp = Ve/g0, where Ve is effective exhaust velocity and g0 is standard gravity. Higher Isp indicates efficient propellant utilization, directly tied to combustion temperature, molecular weight of exhaust, and nozzle expansion.

7. [CS/Data Structures] In ISRO’s real-time telemetry processing, which data structure ensures O(1) average time for insertion, deletion, and lookup of sensor packet IDs? A) Balanced BST B) Min-Heap C) Hash Table with chaining/open addressing D) Doubly Linked List Answer: C Explanation: Hash tables provide O(1) average-case complexity for key-based operations, critical for high-throughput telemetry packet routing. Collisions are managed via chaining or probing, maintaining efficiency.

8. [Electrical/Machines] A 3-phase induction motor running at 4% slip has rotor copper losses of 400 W. The gross mechanical power developed is approximately: A) 9600 W B) 4000 W C) 10000 W D) 8000 W Answer: A Explanation: Rotor copper loss = s × Rotor input. Rotor input = 400/0.04 = 10000 W. Gross mechanical power = (1-s) × Rotor input = 0.96 × 10000 = 9600 W.

9. [CS/Computer Architecture] In a 5-stage pipelined processor executing a loop with a backward branch, pipeline stalls due to control hazards are minimized using: A) Write-back forwarding B) Branch prediction & delayed branch slots C) Cache associativity increase D) Out-of-order execution hardware Answer: B Explanation: Control hazards from branches cause fetch uncertainty. Static/dynamic branch prediction reduces misprediction penalty, while delayed branch slots (RISC architecture) fill subsequent cycles with independent instructions.

10. [Signals & Systems] The Laplace transform of a time-domain function multiplied by t (t·f(t)) is equivalent to: A) dF(s)/ds B) -dF(s)/ds C) F(s)/s D) e^(-as)F(s) Answer: B Explanation: Frequency differentiation property: L{t·f(t)} = -d/ds [F(s)]. The negative sign arises from the integral definition differentiation under the integral sign with respect to ‘s’.

11. [Mechanical/Thermodynamics] In a cryogenic rocket stage using liquid oxygen and liquid hydrogen, the primary thermodynamic advantage over storable propellants is: A) Higher density impulse B) Lower molecular weight of exhaust gases C) Simpler thermal insulation requirements D) Higher ignition reliability Answer: B Explanation: LH2/LOX produces H2O as primary exhaust with molecular weight ~18 g/mol. Lower exhaust molecular weight at given temperature yields higher exhaust velocity (Ve ∝ √(T/M)), directly boosting specific impulse and efficiency.

12. [ECE/Antenna Theory] For a parabolic reflector antenna used in deep-space communication, the gain increases with: A) Decrease in operating frequency B) Increase in aperture efficiency and diameter²/λ² ratio C) Reduction in feed horn directivity D) Use of lossy dielectric radomes Answer: B Explanation: Gain G = η(πD/λ)², where η is aperture efficiency, D is diameter, λ is wavelength. Higher D/λ² and better illumination efficiency maximize gain, critical for long-range telemetry downlinks.

Aptitude & Reasoning Questions

ISRO’s aptitude section tests quantitative agility, logical deduction, and data interpretation under time pressure.

1. Time & Work: A takes 12 days, B takes 18 days to complete a telemetry module calibration. They work together for 4 days, then A leaves. How many more days will B need? Solution: A’s rate = 1/12, B’s = 1/18. Combined = 5/36/day. Work in 4 days = 20/36 = 5/9. Remaining = 4/9. B’s time = (4/9)/(1/18) = 8 days.

2. Probability: A batch of 15 resistors contains 3 defective units. If 4 are randomly selected, what’s the probability exactly 1 is defective? Solution: P = [C(3,1)×C(12,3)]/C(15,4) = (3×220)/1365 = 660/1365 ≈ 0.483.

3. Number Series: 2, 6, 14, 30, 62, ? Solution: Pattern: ×2 + 2. 62×2+2 = 126.

4. Syllogism: All satellites are payloads. Some payloads are reusable. Conclusion: I. Some reusable are satellites. II. Some payloads are not satellites. Solution: Neither follows. “Some reusable” may belong only to non-satellite payloads. Venn diagram shows undistributed middle term.

5. Speed-Distance: A signal travels through fiber at 2×10^8 m/s. Round-trip latency to a ground station 30,000 km away? Solution: One-way time = 30×10^6 / 2×10^8 = 0.15s. Round-trip = 0.3s = 300 ms.

6. Ratio & Mixture: Alloy A has Cu:Zn = 3:2. Alloy B has Cu:Zn = 1:4. Mixed 2kg A + 3kg B. New Cu%? Solution: Cu in A = 2×(3/5)=1.2kg. Cu in B = 3×(1/5)=0.6kg. Total Cu = 1.8kg in 5kg → 36%.

7. Data Interpretation: ISRO test: Tech 70 Qs, 210 marks; Apt 10 Qs, 30 marks. Cut-off 85. If candidate scores 180 in Tech and 18 in Apt, overall %? Solution: Total = 198/240 = 82.5%. Fails to clear 85% cut-off despite high aptitude.

8. Coding-Decoding: LAUNCH → NCLWQJ (each letter shifted +2). ISRO → ? Solution: I→K, S→U, R→T, O→Q. Answer: KUTQ.

Previous Year Questions Pattern

ISRO’s question paper consistently emphasizes fundamental clarity, dimensional analysis, and multi-concept integration. Unlike university exams, ISRO avoids lengthy derivations but demands rapid application of core formulas. Questions frequently blend analog/digital circuits, control stability, thermodynamic cycles, and algorithmic complexity. Numerical answers often require approximation or elimination strategies due to calculator restrictions.

Sample PYQ-Style Questions:

1. Mechanical/Fluid: A Venturi meter shows ΔP = 20 kPa for fluid ρ=1000 kg/m³. Inlet dia 50mm, throat 25mm. Flow rate?
   Ans: ~0.012 m³/s using Bernoulli & continuity.
2. ECE/Signals: System H(s) = s/(s²+4s+13). Natural frequency ωn?
   Ans: √13 ≈ 3.6 rad/s.
3. CS/OS: In demand paging, page fault rate decreases with increase in:
   Ans: Frame allocation & locality of reference.
4. Electrical/Power: 3-phase star load, line voltage 400V, phase impedance 10∠30°Ω. Total power?
   Ans: √3×V_L×I_L×cosφ = √3×400×(400/√3/10)×0.866 ≈ 24 kW.
5. Space/Orbits: Geostationary orbit altitude is ~35,786 km because orbital period equals Earth’s:
   Ans: Sidereal rotation period (23h 56m 4s).

Pattern reveals heavy weightage on circuit analysis, control stability, thermodynamics, data structures, and orbital parameters. ISRO rarely asks direct definitions; instead, it tests parameter relationships and physical intuition.

Interview Tips

1. Defend Your B.Tech Project Rigorously: Interviewers probe design choices, failure modes, component selection, and your specific contribution. Prepare block diagrams, mathematical models, and validation results.
2. Master Core Subject Fundamentals: Expect rapid-fire questions from 3–4 core subjects (e.g., Signals, Control, Analog/Digital, OS/Architecture, Thermodynamics, Strength of Materials). Clarity > memorization.
3. Demonstrate ISRO Mission Awareness: Study Chandrayaan-3 landing sequence, PSLV/GSLV architecture, NVS navigation satellites, and Gaganyaan life support systems. Relate your discipline to mission subsystems.
4. Show Structured Problem-Solving: When given a numerical or theoretical problem, verbalize your approach: assumptions → governing