JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II Year INTRODUCTION TO SPACE TECHNOLOGY Previous Question Paper (July/August - 2021 - R13)
Answer any Five Questions. All Questions Carry Equal Marks.
Main
What is the condition for the maximum thrust in a chemical rocket? Derive an expression for the same.
Answer
The thrust produced by a chemical rocket engine is defined by the equation:
where ṁ is the mass flow rate, ve is the exit velocity, pe is the exit pressure, pa is the ambient pressure, and Ae is the nozzle exit area. The condition for maximum thrust occurs when the exit pressure of the exhaust gases is equal to the ambient pressure, known as the optimum expansion condition, where pe = pa.
To derive this, consider the total thrust equation. If the nozzle is designed such that the exit pressure matches the ambient pressure, the pressure thrust term (pe - pa)Ae becomes zero. Under this condition, the thrust is purely momentum thrust:
If pe > pa, the nozzle is under-expanded, meaning the exhaust gases continue to expand outside the nozzle, wasting potential energy. If pe < pa, the nozzle is over-expanded, which can lead to flow separation and shock waves within the nozzle, reducing efficiency and potentially causing structural damage. Therefore, maximum thrust efficiency is achieved when the nozzle geometry is optimized such that the exit pressure exactly matches the ambient pressure at the operating altitude.
Discuss with suitable sketches, the three systems of electrodynamic rocket propulsion.
Answer
Electrodynamic rocket propulsion, or electric propulsion, accelerates propellant using electrical energy. The three primary systems are:
- Electrothermal Thrusters: These use electrical energy to heat a propellant gas (like hydrogen or ammonia) via an arc or resistor. The heated gas expands through a nozzle to produce thrust.
- Electrostatic Thrusters (Ion Thrusters): These utilize an electric field to accelerate ionized particles. Propellant is ionized, and the positive ions are accelerated by high-voltage grids, resulting in very high exhaust velocities and high specific impulse.
- Electromagnetic Thrusters (Plasma Thrusters): These use both electric and magnetic fields (Lorentz force) to accelerate plasma. Examples include Hall Effect Thrusters (HET) and Magnetoplasmadynamic (MPD) thrusters, which provide higher thrust densities than purely electrostatic systems.
What do you mean by sounding rocket? Explain the characteristics of mixture ratio.
Answer
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Explain the effects of heating on the trajectory of a re-entry space vehicle. Indicate the heating rate profiles for launch vehicles having various ballistic coefficient values in graphical form.
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Explain in brief about the re-entry launch vehicle configuration with neat sketch.
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Distinguish between circular and elliptical orbital motion of a body in a non rotating reference frame with its origin at another body.
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Consider a Hohmann transfer from a circular orbit of radius r1 to another coplanar circular orbit of radius r2. Let Δv be the sum of the two velocity increments required for the maneuver. Show that for a fixed gravitational parameter and radius r1, the maximum required Δv occurs for r2 = 15.58 r1.
Answer
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Compare Bi-elliptic transfer of orbit with Hohmann transfer of orbit principles.
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An earth orbiting S/C is observed to have a velocity of 10.7654 km/s at an altitude of 1500 km. The angle made by velocity vector with normal to radius is 23.174°. Show that the shape of the orbit is hyperbolic.
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Explain the features of mission characterization with examples.
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