Author Topic: What degree of manual control did the Apollo astronauts have prior to TLI?  (Read 2291 times)

Offline Apollo 957

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I'm aware that the Apollo astronauts, on trans-lunar coast, used the 'optics' (sextant) to determine position, compute course, and then apply correction.

To what extent did they have manual control prior to this? Was there any element of them actually 'steering' the craft at any point from launch to TLI?

I could spend a happy hour or two looking up the various documents, but I'm hoping someone who is certain of the answer already could summarise it in a short paragraph for me.

Offline JayUtah

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First of all, the optical assemblies were mostly about determining attitude.  Position was determined onboard by dead reckoning from periodic state vector updates from the ground.  The ground can obtain a very accurate position by observing the direction of the radio signal over precise intervals, whether in Earth orbit or in the translunar orbit.  The optics were rigidly aligned to the guidance reference platform by some extremely robust structure.  Hence the optics could tell you if the platform had drifted by even a small fraction of a degree.  With some math and careful observation, it would have been possible for the the crew to use the sextant to observe landmarks on Earth and reason about their position in orbit, but that was a contingency technique.

The extent to which the crew had manual control was simply the extent to which they wanted it.  They could configure the flight controls to give them manual control over the SPS and the RCS, the latter being capable both of rotations and low-impulse translation.  The system was fly-by-wire, but the control system could be configured to apply the hand-controller inputs in different ways.  For example, in one mode you could deflect the hand controller and the ship would rotate at a speed proportional to the amount of deflection until you released the controller, whereupon the ship would stop.  In another mode the rotational acceleration would be proportional to the degree of deflection, so that you could do things like set up a constant rotation rate.  Finally, in "hard over" mode, the hand controller would fire the appropriate jets directly -- bypassing the fly-by-wire -- if the controller is deflected all the way in any direction.

For ordinary attitude control it was simply easier to punch the pre-planned attitude values into the digital autopilot and let it do its thing.  But nothing prevented full manual control.
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Offline Willoughby

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Jay, it is my understanding that they didn't have any control prior to TLI since they are still attached to the third stage of the Saturn V.  I could see RCS, but using the SPS engine with the LM directly below it would have not been good.  Am I wrong about this?  Could you clarify what control they would have had before TLI and why they would have used the RCS of the service module while still attached to the S-IVB while the J-2 is burning?

Offline QuietElite

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Jay, it is my understanding that they didn't have any control prior to TLI since they are still attached to the third stage of the Saturn V.  I could see RCS, but using the SPS engine with the LM directly below it would have not been good.  Am I wrong about this?  Could you clarify what control they would have had before TLI and why they would have used the RCS of the service module while still attached to the S-IVB while the J-2 is burning?
The S-IVB stage had its own RCS system consisting of two hypergolic APS modules that could provide three-axis control during coast phases when the J-2 wasn't burning and therefore couldn't provide gimbal control.

Offline Glom

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So basically spam in a can until S-IVB separation.

Offline Willoughby

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Jay, it is my understanding that they didn't have any control prior to TLI since they are still attached to the third stage of the Saturn V.  I could see RCS, but using the SPS engine with the LM directly below it would have not been good.  Am I wrong about this?  Could you clarify what control they would have had before TLI and why they would have used the RCS of the service module while still attached to the S-IVB while the J-2 is burning?
The S-IVB stage had its own RCS system consisting of two hypergolic APS modules that could provide three-axis control during coast phases when the J-2 wasn't burning and therefore couldn't provide gimbal control.

Right Ok.  So, they don't have any access (nor would they want access) to the service module systems until separation, and the RCS on the S-IVB is not going to do any massive course corrections or anything - is that a safe assumption?

Offline JayUtah

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Whoops, I guess I misunderstood the implication of the question.

Yes, prior to TLI -- with the S-IVB attached -- the crew had very limited options for maneuvering.  It was all through the APS and all under LVDC control, and there wasn't any manual control of the LVDC from the CM except insofar as a clever person could put the LVDC into alternate steering mode (where the AGC was used as the brains) and then use the normal cockpit controls to generate flight control signals in the AGC which would then pass to the S-IVB.  The answer implied question, "Could the crew fly the S-IVB under manual control?" is a foggy "maybe, but probably not."  The normal control loop was via the Instrument Unit transceiver, which meant radio control from the ground, and generally only during powered flight.
"Facts are stubborn things." --John Adams

Offline bknight

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First of all, the optical assemblies were mostly about determining attitude.  Position was determined onboard by dead reckoning from periodic state vector updates from the ground.  The ground can obtain a very accurate position by observing the direction of the radio signal over precise intervals, whether in Earth orbit or in the translunar orbit.  The optics were rigidly aligned to the guidance reference platform by some extremely robust structure.  Hence the optics could tell you if the platform had drifted by even a small fraction of a degree.  With some math and careful observation, it would have been possible for the the crew to use the sextant to observe landmarks on Earth and reason about their position in orbit, but that was a contingency technique.
....

I thought I had read somewhere that a sextant wasn't that accurate in determining course?
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Offline JayUtah

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I thought I had read somewhere that a sextant wasn't that accurate in determining course?

It isn't during most flight modes.  In fact, nearly useless for that purposes.  But prior to TLI the spacecraft would be in Earth orbit, and some determination of the spacecraft position can be obtained by using the sextant to sight landmarks on Earth as the CSM/S-IVB stack passes over them.  This can translate into a set of observations that, taken together, could determine the spacecraft orbit if no other means were available.  This and related techniques require using the sextant as a "dumb" sighting device, not really in the way it was designed.
"Facts are stubborn things." --John Adams

Offline ajv

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Cernan in the ALSJ : "I could have flown that Saturn V to orbit"

Quote
The launches - both from the Earth and from the Moon - were the only truly automatic phases of the mission, but we could take over and fly it manually to orbit. Aborting during Earth launch was the last thing I wanted to do, so I trained and planned. It was a lot more difficult at night than in the daytime because you didn't have horizons and things to look at; you had to look at the stars. We had several modes of failure that could have degraded systems. The worst would have been for all the guidance to fail so that you literally had to fly it by the stars. Now, I can never prove that I could have done it. But I did it a lot of times in simulators and really did - and still do - believe that I could have flown that Saturn V to orbit. It's one of those things where you say 'I hope it never happens; but I dare you. I'll show you. If you do fail, you just watch.'

Offline ka9q

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Re: What degree of manual control did the Apollo astronauts have prior to TLI?
« Reply #10 on: January 27, 2017, 04:31:46 AM »
I always saw Cernan's claim of being able to pilot the Saturn V into orbit as a bit of a boast. Luckily, it never had to be tested.

The Apollo Guidance Computer on the CSM could determine position/trajectory in cislunar flight by having the crew sight the edge of the moon or earth. This was first tested during Apollo 8 with Jim Lovell as CMP, and his solutions essentially matched those produced by radio tracking from earth.

Offline bknight

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Re: What degree of manual control did the Apollo astronauts have prior to TLI?
« Reply #11 on: January 27, 2017, 10:46:19 AM »
I always saw Cernan's claim of being able to pilot the Saturn V into orbit as a bit of a boast. Luckily, it never had to be tested.

The Apollo Guidance Computer on the CSM could determine position/trajectory in cislunar flight by having the crew sight the edge of the moon or earth. This was first tested during Apollo 8 with Jim Lovell as CMP, and his solutions essentially matched those produced by radio tracking from earth.

Lovell had good experience that would be helpful in A13's trajectories, thrust to shorten the return and be within supplies in the spacecraft.  The Law of Unintended consequences.? :)
Truth needs no defense.  Nobody can take those footsteps I made on the surface of the moon away from me.
Eugene Cernan

Offline JayUtah

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Re: What degree of manual control did the Apollo astronauts have prior to TLI?
« Reply #12 on: January 27, 2017, 11:53:58 AM »
The Apollo Guidance Computer on the CSM could determine position/trajectory in cislunar flight by having the crew sight the edge of the moon or earth. This was first tested during Apollo 8 with Jim Lovell as CMP, and his solutions essentially matched those produced by radio tracking from earth.

Somewhere in my dead-tree library I have the paper that tested the degree of accuracy practically obtainable by this method.  As I recall, the limiting factor was the dispersion in the optics for detection the edge of a bright object like the Earth in comparison with a nearby star.  But yes, the bottom line is that a sextant is merely an object for measuring angles optically, and it can be put to a number of uses with enough imagination and mathematics.

Flying the Saturn V during powered flight is a much different animal than on-orbit maneuvers after SECO.  Giving pitch and yaw commands from a hand controller via alternate command mode still washes those commands through the IU flight computer for necessary rate-limiting filtration, so you have very limited control anyway.  The problem with rocketry in general is that it's extremely easy to exceed the structural limits for bending moments.  You steer a rocket gently, and if gently isn't enough then all heads turn to the range safety officer.  The bending moment measured on the Saturn V (and I want to say it was at one of the joints at the S-IC/S-II interstage) was well over 100 kN·m in normal flight.  The last thing you want to do with a very large launch vehicle is fly it manually.
"Facts are stubborn things." --John Adams

Offline bknight

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Re: What degree of manual control did the Apollo astronauts have prior to TLI?
« Reply #13 on: January 27, 2017, 02:02:18 PM »
How much, if any, torque is applied to the Saturn V from all the umbilicals being released?
Truth needs no defense.  Nobody can take those footsteps I made on the surface of the moon away from me.
Eugene Cernan

Offline JayUtah

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Re: What degree of manual control did the Apollo astronauts have prior to TLI?
« Reply #14 on: January 27, 2017, 02:08:57 PM »
How much, if any, torque is applied to the Saturn V from all the umbilicals being released?

Negligible.  The extraction force of some umbilical connectors can top 200 lbf on the Saturn V, but the connectors for launch vehicles always have some sort of stored-energy mechanism (spring, gas capsules, etc.) that provides the actual force.  There's nothing pulling at the vehicle.  All you have are incident forces from the separation actuators working.
"Facts are stubborn things." --John Adams