Nirbhay is an all-weather, long-range subsonic cruise missile capable of carrying large variety of conventional and nuclear war heads. The missile has a range of more than 1000 km. The missile has a loitering capability, i.e., it can go round a target and perform several manoeuvres and then re-engage it. The missile is capable of flying at different altitudes ranging from 500 m to 4 km above the ground at speeds of 0.8 Mach and can also fly at low altitudes (like low tree level) to avoid detection by enemy radar.
The missile can carry warheads ranging between 300 kg and 400 kg and a total of 24 types of warheads can be attached based on mission requirements. It can be launched from multiple platforms including aircraft, land-based vehicles/launchers, ships and submarines and shall be inducted into Indian Navy, Army, and Air Force.
BRAHMOS is a two-stage missile with a solid propellant booster engine as its first stage which brings it to supersonic speed and then gets separated. The liquid ramjet or the second stage then takes the missile closer to 3 Mach speed in cruise phase. Stealth technology and guidance system with advanced embedded software provides the missile with special features.
Brahmos is one of the deadliest supersonic anti ship and land attack cruise missiles in the world. It’s not meant to have a long range as its for an entirely different purpose.
Brahmos is a supersonic cruise missile (2.8 mach-3.0mach). Nirbhay is subsonic missile (0.7mach), hence much slower.
Subsonic cruise missile is an entirely different technology than a supersonic cruise missile. The former uses a turbofan engine while the later uses a ramjet. The range is larger for nirbhay. Each of these capabilities bring with them their own challenges and overcoming them is part of the process.
Brahmos remains like a missile all the way (although it still is manoeuvrable) , however Nirbhay, after dropping its first stage rockets, opens the small wings with the gas turbine starting up, operates more like an aircraft. Way-points can be set-up for it, and then it would take a pre-set path, just like an aircraft.
Brahmos would hit the target with high speed and strong impact. Nirbhay is more tactical. It can circle around the target (waiting for the rigth time to attack) and deploy the multiple payloads that it might be carrying.
Once detected, it’s relatively easy to shoot down the Nirbhay with a decent Surface to Air Missile . But once detected, it’s nearly impossible to shoot down Brahmos unless you have top class anti missile systems like Aster or S400.
Both these missiles are very flexible and can be launched from any Indian Navy ship which carries the UVLS module.
Brahmos is a tactical weapon whereas Nirbhay is for strategic purposes. There payloads differ as well. Brahmos can carry only Conventional warheads but Nirbhay is a Nuclear capable. Eventually K-15 Missiles In S-2 (Arihant) will be replaced by Nirbhays.
Brahmos is more of a high impact missile, thanks to its very high speed. It has 32 times the on-cruise kinetic energy compared to Tomahawk missile. However Nirbhay is more of a clever weapon, as it can not only wait in air for the right time to strike, it can also carry about 24 difference types of payloads.
I imagine Brahmos to be used more on static, highly fortified targets. Nirbhay would be used for those far away targets which are are on the move, and are tactically well defended by anti-missile technology.