Self-Assessment Quiz: Nuclear and Advanced Propulsion

Twenty questions to check your grasp of nuclear thermal, nuclear electric, and nuclear pulse propulsion, solar sails, beamed propulsion, and antimatter — and, above all, of the discipline of separating demonstrated technology from theory. Answer each before opening the key. Aim for 16 or more. Use $g_0 = 9.81\ \text{m/s}^2$ and $c = 2.998\times10^{8}\ \text{m/s}$.

Question 1

The single idea that organizes every engine in this chapter is:

A) using more powerful fuels than kerosene B) separating the energy source from the reaction mass C) eliminating the nozzle D) flying only in deep space

Question 2

A nuclear thermal rocket roughly doubles chemical specific impulse mainly because:

A) its reactor runs far hotter than a chemical flame B) it uses pure hydrogen, whose low molecular weight raises $v_e \propto \sqrt{T_c/\mathcal{M}}$ C) it has no nozzle losses D) it carries no reaction mass

Question 3

Compared with a hydrogen–oxygen flame, a NERVA-class reactor heats its propellant to a temperature that is:

A) much higher B) about the same or somewhat lower C) ten times higher D) near absolute zero

Question 4

A 1-MW nuclear-electric system driving thrusters at $I_{sp} = 5{,}000\ \text{s}$ ($\eta = 0.6$) produces a thrust of roughly:

A) 25 mN B) 25 N C) 2,500 N D) 250,000 N

Question 5

For a fixed electrical power, using $F = 2\eta P/v_e$, raising the exhaust velocity (specific impulse):

A) raises the thrust B) lowers the thrust C) leaves the thrust unchanged D) makes the thrust infinite

Question 6

The defining engineering challenge of a nuclear-electric spacecraft — the thing that makes its radiators the largest structure aboard — is:

A) storing hydrogen B) rejecting waste heat, since space offers only radiation to shed it C) shielding the crew from sunlight D) avoiding the solar wind

Question 7

Project Orion (nuclear pulse propulsion) was ended primarily by:

A) a fatal flaw in the physics B) the 1963 Partial Test Ban Treaty (plus fallout concerns) C) the inability to build a pusher plate D) running out of uranium

Question 8

Orion can deliver both high thrust and high specific impulse at once because a nuclear explosion supplies enormous:

A) exhaust molecular weight B) power (energy per second) C) nozzle area D) mass ratio

Question 9

The radiation pressure of sunlight on a perfectly reflecting surface at 1 AU is about:

A) $9\ \text{Pa}$ B) $9\ \text{mPa}$ C) $9\ \mu\text{Pa}$ D) $9\ \text{kPa}$

Question 10

A reflecting sail feels twice the force of an absorbing sail because a reflected photon:

A) has twice the energy B) reverses its momentum, changing it by $2p$ instead of $p$ C) travels twice as fast D) is absorbed and re-emitted at half the wavelength

Question 11

The lightness number $\beta$ of a solar sail is the same at Saturn as at Earth because:

A) sunlight does not weaken with distance B) both the radiation-pressure force and solar gravity fall off as $1/r^2$, so their ratio is constant C) the sail speeds up to compensate D) Saturn's gravity cancels the Sun's

Question 12

Which of these has actually flown and demonstrated its principle in space?

A) an antimatter engine B) a nuclear-electric propulsion system (integrated) C) a solar sail (IKAROS, LightSail-2) D) a Project-Orion vehicle

Question 13

The central advantage of beamed propulsion over a solar sail is that:

A) it needs no reflective surface B) the energy source stays off the vehicle and the beam can be made intense and kept focused over great distances C) it violates conservation of momentum D) it carries its own reactor

Question 14

Per kilogram of fuel, matter–antimatter annihilation releases roughly how much more energy than chemical combustion?

A) 100 times B) 1 million times C) 7 billion times D) they are comparable

Question 15

The principal barrier to antimatter propulsion is best described as:

A) a violation of the conservation of energy B) an engineering barrier (production, storage, and use), not a physics barrier C) the absence of any way to release the energy D) the fact that antimatter does not exist

Question 16 (True/False, justify)

"A nuclear thermal rocket could detonate like a nuclear bomb if it malfunctioned." True or false? Justify in one sentence.

Question 17 (True/False, justify)

"A solar sail's achievable delta-v is not limited by the rocket equation's mass ratio." True or false? Explain briefly.

Question 18 (True/False, justify)

"Nuclear electric propulsion has already flown as a complete, integrated system." True or false? Say what has flown.

Question 19 (Short answer)

Give two reasons a nuclear thermal rocket is used as an in-space stage rather than as a launch (liftoff) engine.

Question 20 (Short answer)

In one or two sentences, state the difference between "physically possible" and "engineering-ready," using one example from this chapter.

Answer Key

Topics to review by question