tle2mer.rb

if ARGV[0]
  tle = File.open(ARGV[0]).read
  tle_line_1 = tle.lines[0]
  tle_line_2 = tle.lines[1]
else
  print 'Line 1 > '
  tle_line_1 = gets.chomp
  print 'Line 2 > '
  tle_line_2 = gets.chomp
end

# Converts TLE scientific notation to a float:
#   sci_to_f('-412-6') # => -0.000412
#
def sci_to_f(input)
  if input[0] == '-'
    components = input[1..-1].split('-').map(&:to_f)
    components[0] = -components[0]
  else
    components = input.split('-').map(&:to_f)
  end

  components[0] * 10 ** -components[1]
end

mean_elements = {
  "Element set epoch"                => tle_line_1[18..31],
  "First derivative of mean motion"  => tle_line_1[33..42],
  "Second derivative of mean motion" => sci_to_f(tle_line_1[44..51]),
  "BSTAR"                            => sci_to_f(tle_line_1[53..60]),

  "Inclination"                      => tle_line_2[8..15],
  "RAAN"                             => tle_line_2[17..24],
  "Eccentricity"                     => tle_line_2[26..32],
  "Argument of perigee"              => tle_line_2[34..41],
  "Mean anomaly"                     => tle_line_2[43..50],
  "Mean motion"                      => tle_line_2[52..62]
}

mean_elements.each_pair do |key, value|
  puts '', "#{key}:"
  puts "%f" % value.to_f
end