← INDEX — FIG. 00 — APOLLO 11 ENTRY, 36,194 FT/S, −6.48°
6.56 g · 286 BTU/ft²/s
ENTRY
HEAT SHIELDS AND ATMOSPHERIC ENTRY
Coming home from space means shedding almost all the rocket's energy.
BEGIN — CHAPTER 01 →CH.01 / 07 — LET THE AIR TAKE THE HEAT
Most of the energy must never reach the vehicle
A lunar return carries about 60 MJ per kilogram.
Allen and Eggers: blunt shapes put heat into the air.
CH.02 / 07 — PEAK g DOES NOT CARE ABOUT MASS
Only speed and angle decide the worst moment
Peak deceleration depends only on speed and angle.
Try Apollo 11's entry.
ALLEN–EGGERS BALLISTIC ENTRY
V = VE exp[ −ρ₀H e−h/H / (2β sin γ) ] · amax = VE² sin γ / (2eH) · h* = H ln[ρ₀H / (β sin γ)]
Gravity and lift neglected.
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Presets from Apollo by the Numbers and Desai et al.
CH.03 / 07 — A CAPSULE THAT FLIES
From 36 g to 6.6 g with a little lift
Apollo had a lift-to-drag ratio of about 0.3.
Orion's skip entry.
CH.04 / 07 — WHY BLUNT IS BETTER
Heating grows as speed cubed, and falls with nose size
Sutton–Graves: q ∝ √(ρ/rn) v³.
Apollo 11: 3.2 MW/m² peak.
STAGNATION-POINT CONVECTIVE HEATING (SUTTON–GRAVES)
q̇ = k √(ρ / rn) V³ · Q = ∫ q̇ dt
k ≈ 1.74 × 10⁻⁴.
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Uses the trajectory above.
CH.05 / 07 — SHIELDS THAT BURN AWAY ON PURPOSE
From Stardust's record to Orion's cracked char
Stardust: 12.9 km/s with a PICA shield.
Orion's Avcoat char loss and the Artemis II result.
CH.06 / 07 — SEVENTY YEARS OF COMING BACK
The blunt-body idea, tested again and again
Not a better material but a worse shape.
CH.07 / 07 — REFERENCES