Astronomy

There are four ways to get admission in IIA : GATE, CSIR NET , JEST and IIAST.
You need minimum 96 percentile in GATE to get selected for the Interview round in IIA.
NET and JEST qualified students can also apply for IIA.
IIAST is a national level exam conducted by IIA. The forms for IIAST comes in September and the exams are in major cities across India on second Saturday of December.
There are two courses available Ph.D and Int. M.Tech- PhD.
For engineers, in the IIAST written exam,they basically ask basic astronomy, EMT, Signals, Digital & Analog electronics, Control systems, Optics and basic 12th standard physics.
Almost 4-5 students selected each year for M.Tech -PhD.
If you have qualified IIAST then you need not to qualify GATE or any other test. At the time of interview, it doesn't matter from which National level test you have come.
To know how to prepare for IIA Interview, you can ask any student of IIA Int. M.Tech-PhD programme. There email IDs are available on IIA website.

No, you can not get into NASA after D Pharma.
You can get into NASA as a Geologist!
I would like to quote legendary astronaut Dr. Sally K. Ride :
"The most important steps that I followed were studying math and Science in school. I was always interested in physics and astronomy and chemistry, and I continued to study those subjects through high school and college on into graduate school. That's what prepared me for being an astronaut; it actually gave me the qualifications to be selected to be an astronaut. I think the advice that I would give to any kids who want to be astronauts is to make sure that they realize that NASA is looking for people with a whole variety of backgrounds: they are looking for medical doctors, microbiologists, geologists, physicists, electrical engineers. So find something that you really like and then pursue it as far as you can and NASA is apt to be interested in that profession."
So yes if you are very much into Geology, you can definitely make your way to NASA.
But before that you should know that,
You need to have an American citizenship.
NASA gives preference to Educators.
So you'll need to plan accordingly.
Now coming to our Indian Space Research Organisation (ISRO)
Oh yes! They too recruit Geologist.
Indian Institute of Remote Sensing (IIRS), a unit of Indian Space Research Organisation (ISRO), is a premier institute for capacity building and research in the field of remote sensing and geoinformatics. The Institute has a multi-disciplinary and problem oriented research agenda focusing on developing land-ocean-atmosphere applications and understanding Earth's surface and subsurface processes using primarily the space-based technologies. The research programmes are intricately linked to overall goal of ISRO towards operationalisation of space-based services for national development.
You should definitely go through this link: Indian Space Research Organisation Recruitment 2015 - 39,100 Salary
It will for sure give you an idea about the requirements for getting into ISRO as a Geologist.
On a lighter note :)