code: def generate_nasa_l1b_filename(prefix):
      """Generate a filename that follows NASA MODIS L1b convention."""
      now = datetime.now()
      return f"{prefix}_A{now:%y%j_%H%M%S}_{now:%Y%j%H%M%S}.hdf"
  
imports: from __future__ import annotations
  from datetime import datetime, timedelta
  from typing import Optional
  import numpy
  import pytest
  from pyhdf.SD import SD, SDC
label_desc: Use image node_id 11 for calling a global function with example usage: generate_nasa_l1b_filename(prefix) and returns: prefix, str, now, str, now, str