If a chemical rocket has a jet power of 18 MW, inert mass of 50 kg, a propellant mass of 1000 kg, then what is its specific power?

8.91 kW/kg

17.14 kW/kg

25.43 kW/kg

34.28 kW/kg

Correct Answer : 17.14 kW/kg

Explanation : Specific power is jet power divided by the total mass of that the propulsion system prior to its launch. It is lower for electric propulsion system when compared to chemical rockets. This is because of the heavier and relatively inefficient power source that it has to carry.
P_spec = P_jet / m_total
m_total = m_inert + m_prop
= 50 + 1000 = 1050 kg
∴ P_spec = 18 x 10⁶ / 1050
= 17.14 kW/kg.

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In which of the propulsion systems is the maximum temperature achieved?

Nuclear

Chemical

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Solar heating

Correct Answer : Option (C) : Arc heating

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.

What is the propulsion duration of resistojets?

Few weeks

Few days

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Correct Answer : Option (B) : Few days

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.

Which of the following engines can achieve the maximum specific impulse of 5000 s?

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Correct Answer : Option (B) : Ion-electrostatic

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.