2
$\begingroup$

What crosshairs were used to maintain an attitude during the famous manual trajectory correction burn during Apollo 13's return to Earth? What was their normal function?

This is all I can hear in the reenactment in the Apollo 13 movie:

Well Houston we’ve got one. If we can keep the Earth in the window flying manually, the (coax??) crosshairs right on its terminator, all I need to know is how long I need to burn the engine.

$\endgroup$
3
  • 3
    $\begingroup$ It's COAS Crew Optical Alignment Sight. hq.nasa.gov/alsj/coas.htm pronounced koh-azz $\endgroup$ Oct 27, 2020 at 13:08
  • 1
    $\begingroup$ @OrganicMarble do they use it for the ohms burns? $\endgroup$
    – uhoh
    Oct 27, 2020 at 13:11
  • 4
    $\begingroup$ Reminder that, while accurate in many aspects, the film departs from reality for the sake of simplicity and drama, and the transEarth midcourse correction burn is one of the most comically exaggerated aspects. The Apollo Flight Journals are an amazing source of factual historical information and their annotations will answer a lot of questions like this for you. $\endgroup$ Oct 27, 2020 at 19:43

1 Answer 1

3
$\begingroup$

Generally, they used the optical alignment sight to align the spacecraft when docking. https://www.hq.nasa.gov/alsj/coas.htm

The film may be referring to the landing point designator, or LPD found in the commanders window.

Edit: Fixed my acronyms! I apologize for my incorrectness.

$\endgroup$
2
  • 2
    $\begingroup$ Can you provide a reference showing that in the Apollo program, IMU alignments were routinely (you say "generally") done with the COAS, and not the sextant? You might want to read this question and its excellent answer: space.stackexchange.com/q/31279/6944 $\endgroup$ Oct 27, 2020 at 21:04
  • 1
    $\begingroup$ You are very correct, completely my fault. I’d incorrectly concluded that the COAS was used in IMU alignment. The optical alignment telescope was used for IMU realignment $\endgroup$
    – not_jc
    Oct 28, 2020 at 0:53

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.