Sequential Events Control System

7/29/2019 Sequential Events Control System

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Sequential Events Control System


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Sequential Events Control System (SECS)

This lesson will cover the Sequential Events Control System (SECS), whichis the Apollo spacecraft subsystem that controls the automaticallysequenced functions during the mission and during any aborts that could be

. ,

integration into and use of the spacecrafts other systems, and details onthe functions it is responsible for controlling during the mission.

Objectives:

The student will be able to understand the Systems Architecture

The student will be able to describe the major components in the System

The student will understand the major System Functions


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System Description

e equen a ven s on ro ys em s e po o spacecrasubsystem which controls the automatically sequenced functions duringascent, entry, and any mission aborts

Adapter Separation

Parachute Deployment

Tower

Jettison

C/M S/M SEP & S/M


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System Functional Diagram


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System Vehicle Interfaces

The SECS interfaces across several vehicle components which include:

Launch Escape Tower (LET)

Command Module(CM)

APEX Cover

SM/LM Adapter(SLA)

Service Module(SM)

Lunar ExcursionModule (LM)


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System Controllers

Contained within the SECS is the Master Events Sequence Controller(MESC), which is the master controller of the entire system. The MESCinterfaces with the following subsystem controllers:

SM J ettison Controller (SMJ C) Command Module (CM) Reaction Control System (RCS) controller

Earth Landing Sequence controller (ELSC)

Translation Controller

Feeding into these controllers are numerous relays, time delays, andbaroswitches that enable discrete events to occur in a prescribed order, atspecific times or altitudes.

All components inaccessible to the crew for maintenance purposes.Redundancy accomplished by having two identical systems, A and B, thatcan each accomplish all requirements.


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System Architecture


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MESC & ELSC Location in CM

Master Events Earth Landing

Controllers

ContVerif Box


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RCSC Location in CM

RCS

RCSC


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SECS Power Requirements

DC power provided by a total of 5 batteries on board CM

Batteries A, B provide Logic Bus power SECS A and B, respectively

Batteries A, B, and C combined provide three legs of logic power requiredor

All three batteries rechargeable in flight by spacecraft power buses

Two Pyro batteries supply power to Pyro Busses - not rechargeable

Main DC power supplied by uel cells in SM or CM RCSC

Two additional batteries in SM power SMJ C after CM/SM separation - not

rechargeable


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SMJC Locations

SMJC

SMJCBatteries


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SECS Additional Components

Various circuit breakers, switches, and indicators on main display andcontrol panel in CM

Powered by batteries A, B, and C

n aunc pa , ccep ance ec ou qupmen an use or

integrated system checkouts, via GSE Flyaway Umbilical


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SECS Functions

SECS armed one hour prior to launch and remains energized until afteradapter separation. (~3 hours GET)

Turned on again for CM/SM separation on pre-entry and remains energized

Nominal Functions include:

Launch Escape Tower (LET) J ettison

Spacecraft/LM Adapter (SLA) Separation-

SM J ettison

Parachute Deploy

ona or unc ons


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Nominal Ascent Events Profile

T + ~11:44

1. Lift-Off : EDS ENABLED

2. AUTO OXID DUMP OFFT + 3:19

AUTO RCS ENABLE - ARMED

3. MAX Q REGION

4. 2 ENG OUT AUTO ABORT & L/V56

7

T + 2:10

T + 2:41

T + 2:43

~200K ft. (60.96 km)

~ . .

RATES AUTO ABORT OFF

5. S-IB INBD ENG OFF

6. S-IB OUTBD ENG OFF

4:

~115K ft. (35.05 km)

7. S-IVB IGNITION AND STAGING8. LAUNCH ESCAPE TOWER

J ETTISON

-2

3

=

T + 61 sec

T + 1:26

~24K ft. (7.315 km)

~40K ft. (12.19 km

1


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Nominal Entry Events Profile

1. ARM MESC

2. PRESSURIZE CM RCS

1 23 thru 7 8 400K ft. (121.92 km)

.

4. CM/SM UMBILICAL DEADFACED5. RCS CONTROL TRANSFERRED

6. MAIN DC BUS TIED TO BATTERIES

7. CM/SM SEP

8. CM/SM SEP PRYO CUTOFF

9. ARM ELS-

9

.

11. CM RCS/SCS DISABLED

12. APEX COVER J ETTISONED

13. DROGUE CHUTES DEPLOYED

10, 11

12

13

24K ft.(7.315 km)

14. DROGUE CHUTES RELEASED/PILOTCHUTES DEPLOYED

15. BURN C/M RCS PROPELLANTS

16. MAIN CHUTES

1516

17

18

.(3.048 km)

TOUCHDOWN

17. PURGE CM RCS

18. RELEASE MAIN CHUTES


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A Quick Word on Aborts

Launch Escape System Aborts

Utilizing the Launch Escapeower o prov e crew

with an instantaneous meansof escape. Effective anytimewhile on the launch ad untilLET jettison (approximately3:19).


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A Quick Word on Aborts

Service Propulsion System Abort

Utilizes the SMs propulsion system. Initiated during powered flight, anytimebetween LET jettison and Adapter separation (nominally ~ 3 hours into

. - .


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Launch Escape Tower (LET) Jettison

LET is part of the Launch Escape System (LES) which provides the meansfor the crew to escape instantaneously from the launch vehicle in the eventof an abort, either while on the launch pad and anytime up until the end of

.

SECS acts as the controlling agent, via the MESC, for LET jettison.Function is manually initiated by the crew following first stage staging andignition of the second stage, and also during some aborts. During all LESaborts, the LET is jettisoned automatically by the MESC with the time ofjettison being controlled by the 24,000 foot ELS baroswitches.


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LET Jettison

APEX Cover


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LET Jettison


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Launch Escape System (LES)


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Spacecraft/Lunar Excursion Module/Adapter (SLA)Separation

SECS performs the nominal SLA separation task once initiated by the crew (~ 3 hoursinto mission)

Commander manually enables the CM RCS/SCS (RCS CMD ON)

Approximately 2-3 seconds later he will manually initiate adapter separation whichutilizes MESC components


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SLA Separation


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Spacecraft/LM Adapter (SLA) Separation

Emergency separation of the SLA is performed automatically following themanual initiation of an SPS abort anytime between nominal LET jettison andnominal SLA separation. During this abort, the following functions are

-BECO (Booster Engine Cut-off)

-

-Guidance and Navigation signaled of SPS abort

-Event Timer Reset

-

-SM RCS/SCS enabled for rate stabilization


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CM/SM Separation & SM Jettison

CM/SM separation is performed by MESC and occurs during entry followinga nominal end of mission or an SPS abort

Manually initiated command from the crew (Switches on Panel 02)

ame comman aso energzes e e son on ro er w c a ec s e

retrograde and roll-out maneuver of the SM away from the CM


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Separation function is performed automatically by the MESC on LES abort

After CM/SM separation, RCS control is transferred from the SM to the CMby two motor switches in the CM RCSC, being driven by a signal from the

Automatic backup switching power for tying the CM batteries to the MainDC Bus is directed across a set of contacts in each of these motor switches


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CM/SM Dead-facing

Part of the CM/SM separation process is the destruction of the CM to SMwiring umbilical. A prerequisite to this action is to open certain circuitsknown to be hot. To accomplish this, circuit interrupters are fired by the

-SM.

Also following the initiation of the CM/SM separation, whether in the nominalend of mission phase or subsequent to an SPS or LES abort, thepyrotechnic circuits for separating the CM from the SM are dead-faced byde-energizing the separation relays. This function prevents any possibility

of a high resistance short to ground within the separation system from

parachutes.


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CM/SM Umbilical Deadfacing

CM/SM Umbilical

Umbilical

CM UmbilicalFairing

SM UmbilicalFairin


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CM/SM Umbilical Deadfacing

Electrical Circuit Interrupters


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Earth Landing System (ELS)

The Earth Landing System (ELS) is utilized automatically by the SECSfollowing a nominal end of mission entry, or for subsequent functions to anLES or an SPS abort. The ELS includes the drogue, pilot, and main landing

.

The ELS Logic Bus is armed manually during a nominal entry or followingan SPS abort with return to earth prior to descending to an altitude ofapproximately 50,000 feet, but is not activated automatically until closure ofthe 24,000 foot baroswitch contained within the ELSC.

During all LES aborts, the ELS is armed automatically by the MESC

fourteen seconds after the initiation of the abort and activated with closure, w .

Subsequent functions of the ELS are dependent upon these 24,000 footbaroswitches, some 10,000 foot baroswitches and time delays.


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Parachute Deploy

Drogue parachutes are deployed automatically by the ELSC firing mortars1.6 seconds after the Apex Cover is jettisoned. Drogue chutes are released

,deployed by the ELSC firing mortars.

Main Landing parachutes are deployed by the use of these small Pilotarachutes. Durin a nominal descent the Pilot arachutes are de lo ed

when the 10,000 foot baroswitches close in the ELSC.

The ELSC also fires the parachute release mechanisms. The Main Landing

parachutes are released only after the crew initiates their release manuallyafter touchdown on the water.


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Parachute Deploy


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Emergency Detection System (EDS)

The Emergency Detection System (EDS) contained within the launchvehicle provides inputs to and interfaces with the SECS.

An EDS automatic abort may be voted within the Master Events Sequence

when this capability is automatically switched off, or until inhibited by thecrews switching functions.

The EDS automatic abort ca abilit is armed b the crew rior to launchbut is not enabled automatically by the MESC until lift-off.

An EDS automatic abort is initiated by abort voting relays within the MESC

when certain conditions are satisfied within the EDS.


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The Translation Controller provides the Commander (left side) with themeans to manually initiate an LES or an SPS abort.

LES abort may be manually initiated by the Commander while on the launch,

jettisoned.

After the LET is jettisoned, there is no longer any possibility for an EDSautomatic abort as reviousl stated and therefore an SPS abortmustbemanually initiated by the Commander.


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Additional SECS Functions

Resets Digital Events Timer Readout at Abort Upon initiation of an abortthe timer is reset to zero and restarted again to enable the crew to monitorfunctions during the abort and return to earth. The Digital Readout is

- .

Initiates Booster Engine Cut off at Abort The MESC contains relays whichinitiate the shutdown of the booster or LV at the initiation of aborts. Ran eSafety specifies that for a certain specified amount of time following liftoff,Booster Engine Cut-Off (BECO) will be inhibited. This is controlled by at

time delay in the Instrument Unit that will inhibit cutoff even though theu w .


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Pressurizes the CM RCS When an LES abort has been initiated, it is mandatorythat the CMs RCS be pressurized with helium, either for disposal of the propellantsor for utilizing the RCS for stabilization or orientation. The MESC handles thisfunction immediately upon abort initiation or when commanded manually before

- .

Commands CM RCS Oxidizer Dump If the 61 second timer in the CM RSCS that is

used for controlling automatic Oxidizer dumping has not timed out after beingenergized at lift-off, the CMs RCS Oxidizer will be dumped with the energizing of theOxidizer Dum rela s in the RCSC. When an LES abort has been initiated theserelays are energized by an output signal from the MESC. At the same time, theHelium and Oxidizer Interconnect Squib valves that are between the oxidizer supplytanks are fired by other relays within the RSCS to affect this operation thoroughly.

It is also desired to always dispose of the Helium, either by purging the RCS, as on anominal descent or aborts after 61 seconds from lift-off, or by dumping it directly fromthe supply tanks when time critical. For LES aborts from the pad up to 61 secondsfrom lift-off, when time is most critical, the helium will be dumped automatically 18seconds after the abort was initiated and the full fuel load will remain on board the

.

SECS during this type of abort, unless for back-up purposes. Every function isperformed completely automatically.


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CommandOxidizerDump

CommandOxidizerDum

Pressurizewith

Pressurizewith

quib Valves

Helium

Dump Path


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Controls CM RCS Propellant Disposal During nominal descents after mainlanding parachute deployment, the Commander will dispose of all remainingRCS propellants on board the CM by burning it off through the simultaneous

, .

For any LES abort after 61 seconds from lift-off, the full load of propellantsis dis osed of b burnin . For LES aborts fromthe launch ad or u until61 seconds from lift-off, however, the oxidizer is always dumpedautomatically in the first 11-12 seconds during the abort ascent phase.


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CM RCS Locations

ddi i l S CS i


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gn es oc e o ors or or mme a e y o owng einitiation of an LES abort, either from the pad or up until 61 seconds fromlift-off, the MESC ignites the Launch Escape and Pitch Control motorssimultaneously to propel the Launch Escape Vehicle (LEV) away from and

.from lift-off, however, the possibility for igniting the Pitch Control motor is

automatically switched out by the time-out of the 61 second automaticoxidizer dump time delays, thereby making it impossible for the PitchControl motor to be ignited in case of an LES abort between that time andtower jettison.

Deploys Canards The Canards are deployed automatically by the MESC

eleven seconds after the initiation of an LES abort.

J ettisons Apex Cover The Apex Cover is jettisoned automatically by theMESC, but dependent upon the 24,000 foot baroswitches in the ELSC. TheApex Cover is jettisoned 0.4 seconds after the LET is jettisoned at 14seconds after the initiation of an abort below 30,000 feet. For any abortabove 30,000 feet or for a nominal entry after a successful mission, theApex Cover is not jettisoned automatically until after descending toapproximately 24,000 feet


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Ignites LES Rocket Motors for Abort

PitchControl

o o

LES RocketMotor


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Deploy Canards

Canard DoorDeployed


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APEX Cover Jettison



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a n orma on own s e e prov es con one s gnas othe telemetry equipment through the Data Distribution Box so that certainvital information may be downlisted to the Manned Space Flight Network(MSFN). This vital information is events which take place from the time the

,personnel in determining the status of the mission.

Special Thanks


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Special Thanks

We would like to extend special thanks to theKansas Cosmosphere and Space Center forprov ng exce en p o ograp s o e pane s o

the Lunar Module Trainer, from which many of.

p: www.cosmo.org

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Sequential Events Control System

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