Emergency ejection of CM during the launch phase.

[Chew]

I believe it's so the astronauts are oriented with the right way.

They flew heads down. Or did you mean the right way is upside-down?

000:00:16 Collins: Roger.

    [The Flight Plan calls for Frank to report to Mission Control the accomplishment of many of the events that occur during ascent. He has already reported lift-off and like many other commanders, has not reported the yaw maneuver. Frank does report the initiation of the roll and pitch program.]

    [Clear of all the pad's ironwork, the rocket can safely rotate around its longitudinal axis by 17.876° from its launch roll angle of 90 ° to its flight azimuth of 72.124°. With the roll completed, it will begin pitching over to fly along this bearing with the crew in a heads-down attitude. ^Link

[smartcooky]

OK, understood guys, thanks

I guess it must have been too much to expect them to have built Pads 39A & B to launch the astronauts already in the right positions. I can imagine all sorts of engineering issues might have been involved including roll-out from the VAB, fuel lines and crew entry.

Another issue might have been (and I don't know how important this would have been for Apollo) the orbital inclination required for TLI.

The Moon's orbit is inclined by about 5° w.r.t. the ecliptic (which is itself inclined to the earth's axis of rotation by about 23°). The point (or node) where the Moon's orbit intersects the ecliptic precesses over a period of about 18.6 years (known as the Saros Cycle) so the Moon's maximum declination (north or south of the ecliptic) for any given month can vary from about 18° to 28°. This could mean that the orbital inclination for TLI may have been a quite different for each mission.

It would be interesting to compare the Moon's declination on each launch date for all the Apollo missions that actually went to the Moon to see if the Moon's declination figure was taken into account when calculating the launch window; i.e. did they pick dates at which the declination of the Moon was close to zero?

[Chew]

It would be interesting to compare the Moon's declination on each launch date for all the Apollo missions that actually went to the Moon to see if the Moon's declination figure was taken into account when calculating the launch window; i.e. did they pick dates at which the declination of the Moon was close to zero?

Everything was taken into account.

Launch info here: http://apollohoax.proboards.com/index.cgi?board=apollo&action=display&thread=1356

Moon info here: http://ephemeris.com/ephemeris.php

[ka9q]

Apollo lunar launch azimuths, and hence the resulting orbital inclinations, varied as a function of time during each launch window. Since the launch pad didn't rotate, the launcher had to perform a variable roll after liftoff.

The IMU on the CM had only 3 gimbals. During launch, the reference direction (REFSMAAT) was oriented so that the gimbal lock positions (think of the poles of a globe) coincided with 90 degrees of out-of-plane yaw. So as long as you rolled so that the spacecraft Z axis (running parallel to the astronauts in their couches) was in the orbit plane, yaw was kept small and there was no risk of gimbal lock.

Another reason (often the main one, in fact) to roll a launcher after liftoff is to keep various antennas pointing in the right directions. The Saturn V had probably a dozen VHF telemetry transmitters. It also had UHF range safety (destruct) receivers, but those had multiple antennas since you couldn't depend on them facing in the right direction when you needed to send the command.

[BazBear]

Something I'd like to know about a similar thing that led up to Apollo, is:

Just how amazing (or otherwise) was Wally Schirra's non-pulling of the "chicken ring" during the first attempted launch of Gemini 6?

Gemini used ejection seats, didn't it (like the early STS flights)? I think I'd have hung in there as long as possible too; punching out from the top a Titan II sitting on the pad seems a bit iffy to me

[ka9q]

Yes, Gemini had ejection seats. They were never used, and I've always wondered if they would have worked.

[Allan F]

Wasn't the stack too short for a parachute to work before flight? Not a good idea to fall down next to an exploding rocket, by the way.

[ka9q]

I don't know that much about ejector seats, but it's my understanding that they can be designed for zero-zero operation, i.e., you could eject from a plane sitting on the runway and survive. The rockets take the pilot high enough that his parachute has time to open.

[Zakalwe]

I don't know that much about ejector seats, but it's my understanding that they can be designed for zero-zero operation, i.e., you could eject from a plane sitting on the runway and survive. The rockets take the pilot high enough that his parachute has time to open.

AFAIK, some seats are rated as "zero, -20" as they can be ejected even if the aircraft is under water.

http://www.ejectionsite.com/eunderh2o.htm

Martin Baker seats were developed to use a compressed air system if the seat ejection was initiated, as the normal explosive charges could kill the pilots if fired underwater.
http://www.ejectorseats.co.uk/underwater_ejection.htm

[Allan F]

Appears from that site as the Gemini escape system was designed to fire the astronauts away from the pad fast enough to outrun a fuel explosion.

[BazBear]

Appears from that site as the Gemini escape system was designed to fire the astronauts away from the pad fast enough to outrun a fuel explosion.

I'm sure, but it still sounds a lot dicier to me than leaving in the protection of a capsule.

[DataCable]

I don't know that much about ejector seats, but it's my understanding that they can be designed for zero-zero operation, i.e., you could eject from a plane sitting on the runway and survive. The rockets take the pilot high enough that his parachute has time to open.

But wouldn't Gemini ejection seats launch horizontally?

[Obviousman]

This might be useful:

[ka9q]

Would the astronaut's oxygen supply remain isolated after ejection? In the explosion of a Titan II rocket there would be large amounts of unburned fuel (Aerozine-50) and oxidizer (nitrogen tetroxide) that are quite toxic in even small amounts.

The brown clouds visible in the recent explosion of the Proton rocket are nitrogen tetroxide.

[Obviousman]

Absolutely.

I haven't seen details of the seat (I'll check, though) but all modern ejection seats have a 5 min O2 supply. This is normally disconnected during seat seperation but in light of the booster fuel and the fact they are wearing a pressure suit with helmet, I'd imagine that it remains connected.