m00nwalk: Apollo 11 SSTV Slow-Scan Television Audio Demodulation
“Decode this message from the moon. Hints: How did pictures get sent back from the moon? What is the name of the Apollo 11 audio format?”
picoCTF{...}💡 THE INTUITIVE ANALOGY (Fax Machine from the Moon)
In 1969, NASA astronauts on the moon couldn't send high-definition digital videos. Instead, they used Slow-Scan Television (SSTV), which turns pictures into screeching audio tones (very similar to an old-school dial-up modem or fax machine). The pitch of the sound represents the brightness and color of each pixel row by row. If you play the audio into an SSTV receiver, it draws the original photograph right before your eyes!
1. 10-Second Smartphone Decode (Robot36)
- Install Robot36 - SSTV Image Decoder (Free on Android Google Play Store) or BlackCat SSTV on iOS.
- Play
message.wavon your PC speakers. - Hold your phone near the speaker: The app automatically detects the Scottie 1 sync pulse and draws the image line-by-line in real time!
2. Python SSTV Decoder Script (`solve.py`)
import sstv.common
import sstv.decode
from PIL import Image
# Suppress progress output
sstv.common.log_message = lambda *args, **kwargs: None
sstv.decode.log_message = lambda *args, **kwargs: None
sstv.common.progress_bar = lambda *args, **kwargs: None
sstv.decode.progress_bar = lambda *args, **kwargs: None
# Decode SSTV audio signal (Scottie 1 mode)
decoder = sstv.decode.SSTVDecoder('message.wav')
img = decoder.decode()
# Save rotated image for upright reading
img.rotate(180).save('result_rotated.png')
print("🎉 SSTV Decoded successfully! Check result_rotated.png")sstv -d message.wav -o result.png3. Decoded Flag
Extracted Secret Flag:
4. The Complete Investigation Path & Mental Roadmap
Listened to message.wav and identified rhythmic chirping characteristic of Slow-Scan Television (SSTV).
Decoded the audio waveform using Robot36 / Python sstv in Scottie 1 mode.
Read handwritten flag text from the rendered image: picoCTF{beep_boop_im_in_space}.