Engineering Questions with Answers - Multiple Choice Questions
Rocket Propulsion – Definitions and Fundamentals – Typical Performance Values
1 - Question
Which of the following is not true about chemical rockets?
a) Relatively low values of specific impulse
b) Relatively light machinery
c) Very high thrust capability
d) Very low specific power
View Answer
Explanation: Chemical rockets have very high thrust capability. Because of this, chemical rockets have high specific power and high acceleration.
2 - Question
Which of the following vehicles is used where the flight time is long?
a) Electrical propulsion unit
b) Solid propulsion system
c) Liquid propulsion system
d) Hybrid propulsion system
View Answer
Explanation: Electrical propulsion units have low thrust values. This means that it is a less viable option during take-offs and landing. Because of its very low acceleration potential, it takes a long period of time to accelerate and hence is suited for missions that are time intensive.
3 - Question
What is a sensible specific impulse value for a nuclear fission type rocket engine among the given options?
a) 300 s
b) 600 s
c) 800 s
d) 2000 s
View Answer
Explanation: Chemical rocket engines have relatively lower values of specific impulse. Ion-electrostatic type of rocket engines have very high specific impulses, but they lag in their acceleration potential. Nuclear fission type rocket engines have typical values of the specific impulse around 600 s, while the arc-electro thermal ones have it around 800 s.
4 - Question
What is the typical order of magnitude of mass flow rate (in kg/s) for a chemical rocket engine?
a) 10
b) 0.1
c) 0.01
d) 1
View Answer
Explanation: Typical value of the mass flow rate for a chemical rocket engine is about 0.03. Nuclear fission and arc-electro thermal types of engines have it around the same order of magnitude.
5 - Question
Which of the following engines can achieve the maximum specific impulse of 5000 s?
a) Ion-electrostatic
b) Nuclear fission
c) Hall effect
d) Solar heating
View Answer
Explanation: Ion-electrostatic engine has a specific impulse of 1200-5000 s. Nuclear fission type engines have Isp of 500-860 s, while solar heating engines have it around 400-700 s.
6 - Question
What is the propulsion duration of resistojets?
a) Few seconds
b) Few minutes
c) Few days
d) Few weeks
View Answer
Explanation: Resistojets have a propulsion duration spanning a few days. The chemical rocket engines have a propulsion duration lasting a few seconds to a few minutes, while for ion-electrostatic engines, it lasts for months.
7 - Question
In which of the propulsion systems is the maximum temperature achieved?
a) Chemical
b) Nuclear
c) Arc heating
d) Solar heating
View Answer
Explanation: Arc heating can lead to temperatures of about 20,000 deg C. Chemical propulsion systems have a maximum temperature ranging from 2500-4100 deg C, while nuclear fission leads to temperatures of about 2700 deg C.
8 - Question
Which of the following types of engines use Xe as a typical working fluid?
a) Resistojets
b) Electro thermal
c) Hall effect
d) Nuclear fission
View Answer
Explanation: Hall effect type of rocket engines uses Xe as a typical working fluid. Resistojet rockets typically use H2 or N2H4 as working fluid, while nuclear fission uses H2 and electro thermal one uses NH3, N2H4 or H2.
9 - Question
Which of the following can typically achieve maximum effective exhaust velocity?
a) Electrostatic and electromagnetic
b) Arcjet
c) Solar heated H2
d) Nuclear fission
View Answer
Explanation: Electrostatic and electromagnetic type of propulsion system can achieve the maximum exhaust velocity out of the given options. It is typically of the order of 20,000 m/s.
10 - Question
A rocket engine moving at 500 m/s produces a total thrust of 9563 N, consuming propellants at the rate of 4.55 kg/s. The energy content of the propellants is 5.35 MJ/kg. Find the effective exhaust velocity.
a) 2100 m/s
b) 3936 m/s
c) 1555 m/s
d) 1400 m/s
View Answer
Explanation: Rocket thrust is the product of mass flow rate and effective exhaust velocity. Using this, ue = T/m = 9563/4.55 ≈ 2100 m/s.