🚨 Decision Point #3

Turn Around or Free-Return?

GET 61:29:43 | Post-Explosion Crisis

⚠️ The Situation

Oxygen tank explosion 6 hours ago at 200,000 miles from Earth
Still coasting toward the Moon at a few thousand mph — Earth's gravity has been slowing the climb the whole way out
Service Module damaged — its main engine (the SPS) may be broken, and no one can tell
Fuel cells offline, running on limited backup batteries
Must decide route home NOW: direct reversal or loop around Moon

🔄 TURN AROUND

Blast retrograde to stop and reverse direction

✓ Advantages

Fastest route home (shortest total time)
Direct path back to Earth
Familiar trajectory calculations
No need to wait for Moon flyby

✕ Disadvantages

Requires a massive burn from the Service Module's big SPS engine — the engine sitting right next to the explosion damage, and nobody knows if it still works
To get enough thrust, the crew would have to jettison the Lunar Module — throwing away their only lifeboat
If the damaged engine failed or blew up mid-burn, there would be no backup and no LM to retreat to
May damage weakened spacecraft structure further

🌙 FREE-RETURN

Use Moon's gravity to slingshot back

✓ Advantages

Safer for damaged systems
Uses significantly less fuel
Proven orbital mechanics (tested on Apollo 8, 10)
Uses undamaged LM descent engine
Conserves resources for course corrections

✕ Disadvantages

Takes much longer (must loop around Moon first)
Crew must survive nearly 4 more days in a crippled spacecraft
More time for additional systems to fail
Psychological stress of waiting
More consumables needed (oxygen, water, power)

🤔 WHAT SHOULD THE CREW DO?

👆 Choose one of the options above 👆

NASA's Decision

✓ FREE-RETURN TRAJECTORY

At GET 61:29:43, the crew fired the Lunar Module descent engine for about 34 seconds to put Apollo 13 back on a free-return trajectory - a path that would loop behind the Moon and use lunar gravity to slingshot them back to Earth.

Why NASA chose FREE-RETURN:

Safer approach that wouldn't stress already damaged systems
Used the undamaged LM descent engine instead of the Service Module's SPS engine, which sat right next to the explosion damage
Kept the LM lifeboat — a direct abort would have meant jettisoning it and betting everything on the possibly damaged SPS
Conserved critical fuel for later course corrections
Proven technique from previous Apollo missions
Required patience, but minimized risk of catastrophic failure

"Let's solve the problem, but let's not make it any worse by guessing." — Gene Kranz, Flight Director, to his controllers on the night of the accident

Outcome: The free-return trajectory worked perfectly. Apollo 13 swung around the Moon and headed back toward Earth, giving the crew a chance at survival. The conservative choice saved lives.

📚 Sources for Skeptics

Would you have gambled on the fast way home? Arguing with the answer is exactly what good engineers do. Check the mission record yourself:

Apollo 13 Flight Journal — every radio call between the crew and Houston, annotated day by day, with photos and audio
Apollo 13 in Real Time — replay the whole mission with real Mission Control audio, synced to the second
Apollo 13 Mission Report (PDF) — NASA's official engineering report: what broke, and exactly how they got home