36

A tea cozy keeps the tea in a teapot warmer longer by insulating it.

Why does the nose of the rocket shown in Apollo-era file footage used in this video (lower your volume before watching) have a thick cover that's pulled off about eight seconds before launch?

enter image description here

note: as in the video in the as-yet unanswered question Is this one coherent set of images or a mixture of several missions? it appears that the footage in the video is from mixed missions.

uhoh
  • 148,791
  • 53
  • 476
  • 1,473

1 Answers1

42

That video frame shows the top of the Apollo LES. The object under the cover is the Q-ball. The cover is removed at T - 9 s.

The Q-ball is an angle of attack sphere perched above the launch escape system,

The Q-ball is not unlike a pitot tube on an aircraft that measures airspeed. It consists of eight openings at the top of the Launch Escape Tower. These openings lead to instruments which gauge air pressure.

This paper has more information:

The Q-ball has eight static ports (openings) through which pressure changes are measured. The instru­ments use this information to determine aerody­namic incidence angle and dynamic pressure data. The instruments send information on the angle of attack to an indicator of the CM's main display console and to the launch vehicle guidance.

The pitch and yaw pressure-change signals are electronically summed in the Q-ball and dis­played on the indicator. The Q-ball information provides a basis for crew abort decision in the event of slow launch vehicle divergence.

Herorelics has photos and can tell us why there's a cover:

While on the pad, the Q-ball is protected by a cover to keep the ports free of dust and debris.

Q-ball

This is the LES with the cover on top:

enter image description here

Vintage Space has a video that explains the LES, the Q-ball and how the cover retraction mechanism worked. And the origin of the name: Q is the symbol used to indicate air pressure (think max-Q).

Community
  • 1
Hobbes
  • 127,529
  • 4
  • 396
  • 565
  • Excellent! Mystery solved. Following the links, that seems to be Apollo 15 (here's the video). Also this cropped section of a NASA photo from another link there shows the cover nicely. – uhoh Dec 07 '17 at 16:21
  • 4
    Thanks for posting this question and answer. At time in the past, I had wondered why the X-15 had a hydraulically powered Q-ball, and this reminded me of that. I found a good paper here https://www.nasa.gov/centers/dryden/pdf/87711main_H-374.pdf The Apollo q-ball is an obvious derivative if not the same device. It's an interesting approach to measuring alpha and beta. – Organic Marble Dec 07 '17 at 16:50
  • 15
    I much prefer "nose-cone cosy" to "Q-ball cover." – David Richerby Dec 07 '17 at 17:05
  • @OrganicMarble I'm trying to understand why the aircraft's Q-ball in your linked article is hydraulically actuated. Why does it move? Is it moved by the pilot or by some feedback loop? To measure AOA I would have thought that it remains fixed and some ratio is taken to estimate the angle. – uhoh Dec 07 '17 at 17:44
  • 3
    Another source of some information is a video by Vintage Space, https://www.youtube.com/watch?v=SDWEpNx05uA – PearsonArtPhoto Dec 07 '17 at 18:10
  • 1
    @uhoh it's a clever, mechanical/hydraulic system to measure the angles. Differential pressure causes the actuator to move the ball until the delta-p goes away. Then you can read the angles from the physical angle of the ball. Just a servomechanism, no computer needed. The schematic on page 5 of the pdf shows how it works. IDK if the Apollo ball moved (I doubt it was hydraulic even if it did). – Organic Marble Dec 07 '17 at 19:31
  • This paper https://www.hq.nasa.gov/alsj/CSM15_Launch_Escape_Subsystem_pp137-146.pdf makes it look like the Apollo q-ball didn't move. Rather, it just measured the differential pressures. – Organic Marble Dec 07 '17 at 19:37
  • 9
    I wonder why the cover needs to be removed in the very last seconds of the countdown. Surely, the chance of stuff getting stuck there right after launch is much larger than a couple of minutes before? That last-minute pull-off seems a rather unnecessary extra risk. – leftaroundabout Dec 07 '17 at 19:56
  • 1
    There's also a chance of wildlife inhabiting the Pitot tubes...https://en.wikipedia.org/wiki/Birgenair_Flight_301 ... among others – DJohnM Dec 07 '17 at 20:20
  • 3
    @leftaroundabout: go ahead and ask that as a new question. Quite a few things go on on the last minutes before launch, including the retraction of much larger structures than this bit of insulation. – Hobbes Dec 07 '17 at 20:41
  • 1
    @leftaroundabout I think that's a really good question with good answers - I'd encourage you post it as a new question. – uhoh Dec 08 '17 at 03:17
  • I note that the answer states that the cover is removed at T -15. But the video shows it happening at T -9. – Simba Dec 08 '17 at 15:12
  • @leftaroundabout A possibly related question would be whether the dust from lift-off rises high enough to interfere with it anyway and how that's countered. – Mast Dec 08 '17 at 15:48
  • 2
    I was the Q-Ball Cover Retraction engineer at KSC for Apollos 8 - 13. – David Shomper Apr 30 '19 at 16:54
  • @DavidShomper Tell us more! – Ingolifs Apr 30 '19 at 20:33