MISSION DESIGN

LAUNCH AND INSERTION :

The Mars Orbiter Mission is planned to launch on an Indian Polar Satellite Launch Vehicle flying in

its XL configuration. Mangalyaan does not use a direct injection in which the launch vehicle delivers the spacecraft to its Trans-Martian Trajectory. Instead, Mangalyaan is delivered to Earth orbit from where it uses its own propulsion system to insert itself into its TMI trajectory over a period of weeks. This design still requires the spacecraft to be launched within a narrow window that is only open for a few days every 26 months. The MOM launch window opens on October 28, 2013 and extends through November 19, 2013.

The Polar Satellite Launch Vehicle in its XL Version stands 44.5 meters tall, has a core diameter of 2.8 meters and a liftoff mass of 320,000 Kilograms. It is a four-stage rocket that uses a combination of solid rocket stages and liquid-fueled stages. The launcher can deliver payloads of up to 1,410 Kilograms to Geosynchronous Transfer Orbit and is not capable of delivering payloads of this weight-class to interplanetary trajectories – requiring a different approach to Lunar or Mars missions using PSLV.

The PSLV launcher consists of a large core stage that is 20.34 meters long and holds 138,000 Kilograms of solid propellant – making it one of the largest solid rocket stages ever flown. It provides a whopping thrust of 495,600 Kilograms. Clustered around the core are six Solid Rocket Boosters – each being 1 meter in diameter and 13.5 meters long holding 12,000 Kilograms of propellant. Each of the boosters provides 51,250 Kilograms of thrust.

The second stage of the launch vehicle uses storable propellants, Unsymmetrical Dimethylhydrazine fuel and Nitrogen Tetroxide oxidizer, that are consumed by a single Vikas 4 engine that provides 81,500kg of vacuum thrust. The stage is 12.8 meters long featuring a 40,700-Kilogram propellant load.

The PS3 stage of the PSLV launcher is solid-fueled, being 2.02 meters in diameter and 3.54 meters long holding 6,700 Kilograms of HTPB-based propellant. The third stage provides a total thrust of 24,900 Kilograms. Stacked atop the third stage is the PS4 Upper Stage that again uses hypergolic propellants – Monomethylhydrazine fuel and Mixed Oxides of Nitrogen – consumed by two L-2-5 engines. The stage is 2.02 meters in diameter and 2.6 meters long featuring a fuel load of 2,920 Kilograms. Upper stage thrust is 1,500 Kilograms.

LAUNCH SEQUENCE:

Following the completion of a 56.5-hour countdown, PSLV will launch with the Mangalyaan spacecraft hidden under its 3.2 by 8.3-meter payload fairing. The rocket will basically follow a standard mission profile to a Geosynchronous Transfer Orbit type orbit from where the MOM spacecraft begins its long journey to Mars. PSLV launches from the Satish Dhawan Space Center located on India’s East Coast.

At the moment of T-0, the PS1 Stage is ignited followed 0.5 seconds later by Boosters 1&2 and another 0.2 seconds later by Boosters 3&4 to create a total launch thrust of 700,600 Kilograms. Blasting off at a thrust to weight ratio of 2.18, initial ascent is very quick as PSLV races into the sky, starting a Pitch and Roll maneuver to align itself with a pre-planned ascent trajectory taking it south-east across the Indian Ocean.

The remaining Boosters (5&6) are ignited at T+25 seconds when the vehicle is already 2.5 Kilometers in altitude. Each of the Boosters burns for 49.5 seconds. The four ground-lit boosters are separated at T+1 minute and 10 seconds and fall into the Ocean. The air-lit boosters are jettisoned 22 seconds later enabling the PS1 stage to continue ascent on its own.

Throughout the booster phase and PS1 burn, three axis control is provided by a Secondary Injection Thrust Vector Control (SITVC) for yaw and pitch and two radially mounted thrusters for roll.

When the first stage has burned out, it separates from the second stage at T+1:53 followed by PS2 ignition an instant later. Staging occurs at approximately 58 Kilometers in altitude. During the second stage burn, the launch vehicle departs the dense atmosphere – allowing the vehicle to jettison its payload fairing at T+3:22 at an altitude of 113 Kilometers, exposing the MOM spacecraft for the remainder of the ascent as aerodynamic forces can no longer damage the vehicle. Vehicle control during second stage flight is provided by engine gimbaling for pitch and yaw and a roll reaction control system.

The second stage burns for about two minutes and 35 seconds before separating from the third stage that then ignites and assumes control of the flight at T+4:26. The solid-fueled third stage burns for 112 seconds to boost the stack to a sub-orbital trajectory. It uses the fourth stage Reaction Control System for three-axis control. After burnout of the PS3 stage, the stack begins a coast phase – initially holding onto the spent third stage before separating it at T+9:43 and continuing to coast uphill.

This coast phase allows the vehicle to fly uphill so that the fourth stage burn can increase the apogee altitude and also put a few Kilometers onto the perigee to place the stack in a stable orbit. MOM is targeting a higher Argument of Perigee than all previous ISRO mission into GTO in order to minimize the energy required from the GTO-type orbit to the interplanetary trajectory. Therefore, the coast between the 3rd and 4th stage burns is extended to 25 minutes.

The long coasting necessitated specific modifications to the coast phase guidance algorithm, on-board battery capacity augmentation, assessment on the performance of inertial systems for extended flight duration and deployment of two tracking ships to acquire the critical telemetry data during 4th stage flight and MOM separation.

Once the stack reaches its desired altitude, the two L-2-5 engines of the fourth stage ignite at T+35 minutes on a burn of about 8.5 minutes to boost the stack into its Transfer Orbit.

The Mars Orbiter Mission targets an injection orbit of 250 by 23,500 Kilometers at an inclination of 19.2 degrees. MOM separation takes place 44 minutes and 16 seconds after launch.