The heaviness of rockets, why it matters in space flight

Subject: Science and technology

Context-

The Indian Space Research Organisation (ISRO) crossed an important milestone with the successful launch of the LVM3 M2/One Web India-1 mission.
The LVM3 rocket carried almost 6 tonnes of payload into lower-earth orbit, the most that any ISRO mission has delivered into space to date.

Concept:

Increased capability of India-

Very few countries have the capability to launch satellites weighing more than 2 tonnes.
Until recently, even ISRO used to take the services of Ariane rockets of Europe to launch its heavy satellites.
The LVM3 rocket, which used to be called GSLV Mk-III earlier, is meant to end that dependence and also become the vehicle for the more ambitious parts of India’s space programmes — manned missions, Moon landings and deep space explorations — in the near future.

India’s rockets-

the Polar Satellite Launch Vehicle or PSLV, of which there are multiple versions;
the Geosynchronous Satellite Launch Vehicle or GSLV Mk-II;
the Launch Vehicle Mark-3 or LVM3 or GSLV MK-lll

The PSLV has been the most commonly used, having carried out as many as 53 successful missions since 1993.
Only two flights of PSLV have failed.
The GSLV-Mk-II rocket has been used in 14 missions, of which four have ended in failure, most recently in August last year.
The LVM3 has flown five times, including the Chandrayaan 2 mission, and has never disappointed.
ISRO has been working on a reusable launch vehicle (RLV).
Unlike other rockets, the RLV would not end up in space as waste.
Instead, it can be brought back and refurbished for use multiple times.

Heavier rockets-

LVM3 is the culmination of more than three decades of efforts to indigenously develop a rocket that can carry heavier payloads, or venture much deeper into space.
The passenger (or payload) comprises barely 2 to 4 per cent of the weight of the rocket.
Between 80 and 90 per cent of the launch-time weight of any space mission is the fuel, or the propellant.
This is because of the need to overcome the tremendous force of gravity.
The LMV3 rocket, for example, has a lift-off mass of 640 tonnes, and all it can carry to lower earth orbits (LEO) — about 200 km from the Earth’s surface— is a mere 8 tonnes.
To the geostationary transfer orbits (GTO) that lie farther ahead — up to about 35,000 km from Earth— it can carry much less, only about 4 tonnes.

Global comparison-

The LMV3 is not particularly weak when compared to the rockets being used by other countries or space companies for similar jobs.
The Ariane 5 rockets, frequently used by ISRO earlier for its heavy payloads, have a lift-off mass of 780 tonnes, and can carry 20- tonne payloads to lower earth orbits and 10 tonnes to GTO.
The Falcon Heavy rockets from SpaceX, supposed to be the most powerful modern launch vehicles, weigh over 1,400 tonnes at launch time and can carry payloads weighing only about 60 tonnes.

The constraints-

Most of a rocket’s energy is burnt in travelling to the lower earth orbit because the force of gravity is the strongest here.
It takes half as much energy for a rocket to travel to the Moon from the LEO (a journey of nearly 4 lakh km) compared to what it takes to travel to LEO from Earth (about 200 km).