ISRO - Dreams do come true

Since 2017 , I have been reading the success stories of many ISRO aspirants of CSE from various source and always had dreamed about writing a success story. I guess the day has finally arrived. Failures have been my constant companion , but it laid the stones to my success finally. Let me give you a brief background about myself.

I am Sandeep Nithyanandan. I am 2016 graduated from Sreepathy Institute of Management and Technology , a private engineering college in Kerala . I completed my in Computational Linguistics , from GEC Palakkad in Kerala in 2019. I have been working since then in a private firm.

My Gate and ISRO exam details:
Gate 2016 - not cleared, ISRO 2016 - written not cleared

Gate 2017 - AIR 4497 , ISRO 2017 Dec - Written not cleared

Gate 2018- AIR 3039, ISRO 2018 - Written not cleared

Gate 2019 - AIR 1916, NO ISRO exam in 2019

Gate 2020 - AIR 1445 , ISRO 2020 (it is 2019 notification)- Written 108 marks and Cleared

Gate 2021- AIR 2297.

After seeing my performance you might be thinking is this guy mad. To be honest , I was never a bright student at all, my Gate score tells the same. But one thing which i did was I never gave up (being a Manchester United fan ). I kept on preparing for Gate even during my time as well as working time. Consistency really matters in the long run . I prepared every year and it helped me a lot even in the ISRO interview. The motivating factor to me was working in ISRO, that helped me a lot.

Now to the specific ISRO 2019 recruitment details:

OCT 2019 (Notification from ISRO)- 44 vaccany - This was a huge number and i was really happy. I thoght this is my best chance to get selected and I have my past experience to learn from. I started preparing seriously by solving ISRO previous years and mocks as well.

Jan 2020 - The day for the written exam. The pressure was at the highest , much more pressure to me than the Gate. I had given my everything for this ISRO recruitment. Even during my working hours I tried to find time to prepare for ISRO. After getting the question paper and seeing the first question , my confidence went down as i did not know the answer. But my past experiences helped me here. I moved on quickly to next question and answered it. The exam which you want to crack the most is the most difficult one for you and it turned out to be true. I messed up my easy questions , those questions which if asked to me in my sleep , i would have answered. Coming out of the exam hall , i felt very sad. I told my girlfriend(now my fiance) it went bad. She had also came to write the exam , just to give me the mental support. After seeing the response on different facebook group related to the exam , I thought it was bad for everyone. From that day onwards till the written result came. i constantly checked my answers and calculated my marks and it turned out to be 108 marks. This was the lowest marks of all my ISRO exams and felt i had doomed this one as well. Failures as I said was a constant with me and i thought it would be the same this time as well.

May 2020- I was working and saw a notification in Gateoverflow that isro has declared the result. As usual i thought , no hope this time also. 108 till that time was my lowest in all ISRO written exams and going by ISRO written exam trend i would not qualify. I opened the result pdf with not much hope and searched my roll number. But expect the unexpected , I found the search to be showing 1/1 and i was dumbstruck to see my roll number in the selected list. The joy i had could not be explained. I was now determined to utilise the chance i got to the fullest.

May 2020- March 2021- It was one of the most uncertain period in my life. Covid came in , Work from home had started and I had to prepare for Interview. I started reading standard text books, read many interview experiences and joined many groups and prepared. But there was an uncertainty about how the interview will be done , online or offline and when will it be.

March 20, 2021 - I had chosen VSSC Trivandrum as my center. I had faced a lot of hurdles on the past day. The hotel i booked did not register my booking properly and there were issues . It made my confidence go down. But then I remembered it is all part and parcel of the game. The funny part is i forgot to wear a mask when i came out of my hotel. I felt my interview will be doomed . But somehow i managed to get one mask from outside and felt a sense of relief.

My interview was schedule on 11 am . I reached around 9.30 am. I entered into VSSC , it gave me goosebumps . I felt this is the do or die situation. When i sat in the waiting room , a lot of things flashed into my memory . 4 years of my gate preparation and a lot of other things. They called me around 12 to go to interview hall. I was waiting outside the interview hall and at 12:30pm I was called.

The next 25-30 mins was the best minutes of my life.

I am sharing the detailed interview experience below:

The interview was online this time.
I was asked to introduce myself and asked to tell my work exp , educational background and favorite subject. I introduced and told my favorite subject as OS,TOC,DS,Algo,COA. My preferred programming language was asked and i told Python and C.

I am not remembering the proper order of questions , and might have missed some questions also. Please dont mind it.I was told first TOC would be asked.


1) What is language

I was stuck for one second. But explained "A language is a subset of sigma star".

2)What is Sigma


3)Define DFA

Explained the five tuple form.

4) If NFA and Epsilon NFA exist , why go for DFA.?

I told NFA and Epsilon NFA is easier to construct than DFA. Also we have algorithm to convert NFA to DFA.

5)What is recursive language?

Expalined it using Total Turing Machine concept. I guess this was a game changer. I thank Kiran Kumar Pasupuleti sir for the teaching the TTM concept.

6)What is recursive enumerable language?


7)What is NP hard?


8)What is NP Complete?


9)What is halting problem of Turing Machine?


10)What is decidable language?


11) What is A^n B^n C^n?

I told it is CSG. But he was expecting the machine which accept it. I told its LBA.


12)What is tree?

An acyclic graph which is connected.

13)What is forest?


14)How to make a stack using queue?


15)What is Binary Search tree?

16)What is AVL Tree?

17)What is threaded binary tree?.

I said i dont know about it.


18)Paging vs Segmentation?

19)What is Disk Scheduling algo?

I explained the FCFS, SSTF,SCAN, Elevator.

20)How can we avoid starvation.

I replied "increasing the priority of process".


22)Give example of Divide and Conquer, Greedy and Dynamic Programming algorithm

23)What is difference between Divide and Conquer , Dyamic Programming

25)What is inplace sorting algorithm and Not inplace sorting algorithm.

C programming

26)What is macros

27)What is inline function


28)What is pipelining?

29)What are hazards

30)What is locality of reference?

31)What is write back cache?

32)What is write through cache?


33)What are the layers of ISO/OSI?

34)Compare TCP and UDP?

35)In which port HTTP runs.

36)Example of UDP using Application layer protocol.

Machine Learning

37)What is Machine learning vs deep learning.

Expalined that ML need hand crafted features but DL extract features automatically. Explained some DL and ML algorithms

38)What is underfitting and overfitting.

39)What is k-crossfold validation

40)What is corelation vs covariance

(I replied i dont remember sir)

S/w Engg

41)Different stages of SDLC.

(Told me to just name them only)

42)What are different examples of testing.

43)What is regression testing

44)Good features of a s/w

They gave me hints. But I was not able to answer it


46)Different stages of compiler.

I replied saying pre-processing, compilation. But he helped me saying that "not this. there are some stages during a compilation". I understood my blunder. I replied with all the stages.

47)What are the different examples of Code optimization.

I answered with some examples. But it was not completely correct.


This was the last question. But since i did not prepare dbms i politely replied "I cannot recollect sir".

He said "OK . Thanks sandeep. Interview is over"


The whole interview went around 25-30 min i think.I felt it was like a rapid fire round. But in meantime they allowed me to drink some water. They tried to look at the breadth wise knowledge of my subjects. They asked questions even from outside of my favorite subject , but i answered it confidently. I guess this helped me a lot. My ML background also helped me i guess. After coming out of interview hall i felt i had given my best.


The next 5 months was very hard to pass by. The second wave came and our results were delayed.


Sept 3 2021- ISRO had given the tentative dates for the result as first week of September. Till evening 5 pm , result did not come. Around 6 , i got a telegram notification that result had come. My heart started raising and i opened the pdf. I started scrolling down from the bottom hoping that i might get at least a 44 rank. I kept on scrolling and reached the top. Then i thought i have not got selected. But then found my name on Top :)


Sandeep Nithyanandan - AIR 1 - Selected. My ISRO Dream has come true.


I literally cried after seeing this. All my years of effort has been finally approved. This was the Endgame for me and i succeeded. I would like to thank all my teachers who helped me in this journey.


I have met some very good friends.  Balaji Jegan  Mayank Raj Sajith Menon Akshay Kishore Parwateeswar Gollapalli. I would like to thank Habib Mohammad Khan Devesh Kumar Harshit Saxena Saurabh Shrivastava as they have helped and guided me a lot.

If you are determined and consistent , success will come. For me ISRO was my dream and i never gave up on it.
posted in Interview Experience 6 days ago



Heartiest congratulations Bhaiya!! It was really an extremely motivational read. May you bring pride to the nation one day!
Bhaya what an inspiring post , may Shiva always bless you

thank you for sharing this and inspiring aspirants like me
My interview was very similar to yours. But dont know why I was waitlisted. Anyway, so so happy for you as I am in your same boat- failure after failure for isro - I know ur pain before getting in. But I will not give up. Could u may be pm me ur number so that we can talk? I have some doubts.