Self-Assessment Quiz: SpaceX and the Reusability Revolution

Twenty questions to check your grasp of iterative development, propulsive-landing economics, the cost of reuse, Starship, and Raptor. Answer each before opening the key. Aim for 16 or more. Every figure is approximate and version-dependent (Tier 2); watch the reasoning, not the last digit.

Question 1

SpaceX's development philosophy — build, fly, fail, fix, repeat — is best described as:

A) exhaustive up-front analysis with a single perfect flight B) iterative, hardware-rich development that treats failures as cheap information C) avoiding all test flights to save money D) flying crew as early as possible to prove safety

Question 2

Why did SpaceX begin with the small Falcon 1 rather than an orbital-class booster?

A) it had higher payload B) small vehicles are cheaper to lose, so the team could iterate through failures C) Falcon 1 was reusable D) regulations required it

Question 3

The "9" in Falcon 9 refers to:

A) nine stages B) the ninth block upgrade C) nine first-stage Merlin engines D) a 9-tonne payload

Question 4

A block upgrade is:

A) a launch delay B) a numbered revision bundling improvements while keeping the vehicle broadly similar C) a stack of satellites D) the concrete pad a rocket launches from

Question 5

Recovering a first stage reduces payload primarily because:

A) the booster is heavier after landing B) reserved landing propellant raises the burnout mass, lowering ascent delta-v C) the second stage must be discarded D) grid fins add drag on the way up

Question 6

A return-to-launch-site (RTLS) recovery costs more payload than a droneship landing because it:

A) needs a bigger heat shield B) requires a large boostback burn to cancel downrange velocity, reserving more propellant C) uses more engines D) flies to a higher orbit

Question 7

In the reuse cost model $C_{\text{reuse}}(N) = M/N + R + F$, the cost per flight as $N \to \infty$ approaches:

A) zero (just propellant) B) $M$ C) $R + F$ D) $M + F$

Question 8

For Falcon 9, the fixed cost $F$ that reuse never recovers is dominated by:

A) the recovered first stage B) the expended second stage plus operations C) the landing legs D) propellant

Question 9

Roughly how does Falcon 9's cost per kilogram to LEO compare with the Space Shuttle's?

A) about the same B) about 2× cheaper C) about 20× cheaper D) about 1000× cheaper

Question 10

Starship is built of stainless steel primarily because steel:

A) is the lightest available material B) stays strong at high temperature (so it needs less heat shield) and is cheap and weldable C) is transparent to radar D) cannot be welded, forcing a stronger design

Question 11

Starship burns methane (methalox) in part because methane:

A) has the highest specific impulse of any fuel B) can be manufactured on Mars from CO2 and water C) is not cryogenic D) requires no oxidizer

Question 12

A fully reusable upper stage needs on-orbit refueling to go beyond LEO because:

A) it has no engines B) carrying a heat shield, flaps, and landing propellant ruins its mass ratio, leaving it nearly empty at LEO C) methane cannot reach LEO D) refueling is required by law

Question 13

Super Heavy's booster is recovered by:

A) parachutes into the ocean B) landing legs on a droneship C) being caught in mid-air by the launch tower's arms D) gliding back on wings

Question 14

Raptor's engine cycle is:

A) gas-generator B) expander C) pressure-fed D) full-flow staged combustion

Question 15

One advantage full-flow staged combustion gives Raptor for reuse specifically is:

A) it dumps turbine exhaust overboard B) each turbine handles one propellant type, eliminating the interpropellant seal C) it burns liquids directly for higher thrust D) it needs no turbopumps

Question 16 (True/False, justify)

"Reusing a rocket is essentially free, since the vehicle comes back." True or false? Justify in one sentence.

Question 17 (True/False, justify)

"The very first flight of a reusable-design booster is cheaper than an equivalent expendable one." True or false? Explain briefly.

Question 18 (Short answer)

A first stage burns out at $3{,}860\ \text{m/s}$ expended. Reserving landing propellant raises its burnout mass so its mass ratio drops from $3.90$ to $3.02$. With $v_e = 2{,}840\ \text{m/s}$, compute the reusable ascent delta-v and the delta-v lost to recovery.

Question 19 (Short answer)

Explain in one or two sentences why "price per kilogram" is a soft number, giving one reason it can mislead.

Question 20 (Short answer)

In your own words, why is reusing both stages (Starship) needed to get past the cost floor that reusing one stage (Falcon 9) reaches?

Answer Key

Q Ans Note
1 B Iterate on cheap, uncrewed, instrumented hardware; failures buy information.
2 B A small vehicle can be lost without ending the company, enabling iteration.
3 C Nine Merlin engines in the first stage (the "octaweb" in later blocks).
4 B A numbered revision (v1.0 → v1.1 → Full Thrust → Block 5) capturing accumulated lessons.
5 B Reserved propellant stays attached → higher $m_f$ → lower mass ratio → less ascent delta-v.
6 B Boostback to cancel downrange velocity reserves extra propellant, costing more payload.
7 C $M/N \to 0$, leaving the floor $R+F$.
8 B The new-every-flight second stage plus operations set the floor.
9 C ~$2,700/kg vs ~$54,500/kg is roughly a 20× drop (Tier 2).
10 B Strong-when-hot → less thermal protection; also cheap, weldable, strong at cryo.
11 B Sabatier-made methane enables Mars refueling; also clean-burning and mid-density.
12 B Full reuse's dead mass (TPS, flaps, landing propellant) wrecks the upper-stage mass ratio.
13 C The tower "chopsticks" catch it (first achieved Oct 2024), saving landing-leg mass.
14 D Full-flow staged combustion — the first ever to fly (2019).
15 B No interpropellant seal (a historic failure point); also gas–gas burns and cooler turbines.
16 False Recovery costs ~25% of payload (reserved propellant) plus refurbishment and a still-expended upper stage; it is a trade, not a free lunch.
17 False The first flight pays for legs, grid fins, and lost payload with no amortization yet, so it costs more than expendable; reuse pays off only on later flights.
18 — $\Delta v = 2{,}840\times\ln(3.02) = 2{,}840\times1.105 = 3{,}138\ \text{m/s}$; lost $\approx 3{,}860 - 3{,}138 = 722\ \text{m/s}$.
19 — It assumes the rocket is filled to capacity and mixes price with cost; a half-empty launch or a full-program accounting changes it by a large factor.
20 — Reusing one stage bottoms out at the cost of the expended second stage + ops; only recovering both stages (plus cutting operations) removes that floor.

Topics to review by question

Questions Topic Section
1, 2 Iterative development §38.1
3, 4 Falcon 9 and block upgrades §38.2
5, 6, 18 The delta-v/payload cost of reuse §38.3
7, 8, 9, 16, 17, 19, 20 Reusability economics & cost floor §38.4
10, 11, 12, 13 Starship's design choices §38.5
14, 15 Raptor & full-flow staged combustion §38.6