The Skylab Trash Airlock (TAL) used throughout the Skylab mission to transfer trash materials that could support microbial growth from the pressurized cabin to the unpressurized waste tank is described. The TAL, which uses several basic mechanisms, was successfully operated daily for the 170 days of manned missions for a total of 637 cycles

Price, L. R.

English

NASA Technical Reports Server

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N76-19183E
11. SKYLAB TRASH AIRLOCK*
By Larry R. Price
McDonnell Douglas Astronautics Company
SUMMARY
The Skylab Trash Airlock (TAL) was used througho_'* the Skylab mission
to transfer trash materials that could support microbial _rowth from the
pressurized cabin to the unpressurized waste tank. The TAL, which uses
several basic mechanisms, was successfully operated daily for the 170 days
of manned missions for a total of 637 cycles.
TRASH MANAGEMENT APPROACH
Trash management for Skylabwas a challenging pro'blem. The expected
trash volume from three crewmen for a total of 140 days (actual duration of
manned mission was approximately 170 days) was predicted to be 36.8 m 3
(1300 cubic feet). This volume was more than could be conveniently stored
in the cabin. Also, much of this trash (wet -wipes, food containers, urine,
etc. ) could support microbial growth that could be a health hazard. In
addition, to avoid contamination of experiments and minimize general pollu-
tion of space, trash could not be ejected into the spacecraft environment.
The resulting approach was to collect trash in bags at specified locations
in the cabin. Trash was categorized and collected separately as biologically
active or not biologically active. At appropriate times, usually daily, the
biologically inactive trash bags were transferred to storage areas within the
pressurized volume, and the biologically active trash was transferrcd to an
unpressurized aft portion of the Orbital Workshop identified as the waste
tank. This tank was internally screened and vented so that only vapor would
escape from the Spacecraft. The general configuration is shown in Figure 1.
This approach required a highly reliable device that would allow
convenient and safe transfer of biologically active trash in closed but vented
bags from the pressurized cabin at 34. 5 kPa (5 psi) to the unpressurized
waste tank at a pressure ¢ff less than 0. 607 kPa (0. 088 psi).
The device designed and developed to meet those requirements was the
Trash Airiock Assembly, McDonnell Douglas Astronautics Company part
number IB81491-1. The airlockis mounted on the bulkhead between the cabin
and the waste tank at" the centerline of the spacecraft. Figure 2 shows the
TAL installed in the Skylab in its launch configuration.
"ThisworkdoneunaerthesponsmshipofNASA'sMarshallSpaceFlightCenterandJohnsonSpaceCenter,C,::ltractNAS9-6555
NASA'sU.S.PatentNo.3,807,656ontheSkylabTrashAirlock=savailableforhcensmgunderNASAP.,t, ,; '.=censmgRagul=e
t=ons14CFR1245.2bywrltlnyPatentCounsel,GeorgeC.MarshallSpaceFlightCenter,Alabama3581?
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FORWARDCOMPARTMENT
_'_"_, _ SLEEPCOMPARTMENT
WASTEMANAGEMENT
_,.....__ _ EXPERIMENT1 BAG
TRASH A IRLOCK COMPARTMENT
WASTE TANK-/ "_ "- ' f""
i
Figure 1. Trash DisposalSubsystem
F_gure2. Launch Configurat=on Trash A=rlock
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GENERAL DESCRIPTION AND OPERATION "
The trash disposal airlock assembly is a pass-through chamber built
into the waste tank common bulkhead and extending through the floor into
the cabin. Each side of the chamber is equipped with a hatch, forming an
airlock (Figure 3). The airlock is equipped with a pressurization valve
that ports the airlock to either the cabin or the waste tank, as required.
On orbit, the trash disposal airlock is normally vented to the waste tank.
The airlock body is spherical, approximately 610 mm (Z4 inches) in diam-
eter, and has a pressure gage for viewing by the crew. It is equipped
with a mechanical ejector to transfer the waste material to the waste tank.
The functional steps of the operation cycle of trash disposal from the
habitation area are as follows (see Figure 4):
1. Valve/outer door handle-pressure 34.5 kPa (5 psi) (verify).
Z. Lid-unlock and open.
3. Insert trash [_ag.
4. Lid-close and lock.
5. Valve/outer door handle-close and veut [verify 3.45 kPa
(0. s psi)].
6. Valve/outer door handle-open.
7. Ejector handle--eject return to close.
8. Valve/ouler door handle-close and vent.
9. Ejector handle- retract.
DESCRIPTION
The trash airlock is made up of the assemblies described below.
Lid Assembly (Figures 5 and 6)
The aluminum lid subassembly is the inboard door. it is a simple two-
hinge door with a third friction hinge to maintain the lid in the open position.
The lid contains a metal gasket with molded rubber seals on the top and
bottom, which is removable and may be replaced with an on-orbit spare.
The lid subassembly also houses the ejector mechanism.
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1976012084-151
)LID LOCI
LID LOCK-TO-
OUTER/DOOR EJECTORMECHANISM
HANDIF INTERLOCK (EXTENDED)
ROD
VALVE/OUTER CYLINDER
DOORHANDLE (EJECTORGUIDE)(OPENPOSITION)
PRE
VALVE
VACUUMSHUTOFF OUTERDOOR(OPEN|
VALVEHANDLE EJECTOR
VENTLINE
Figure3. TrashAirlo(:k
t LOADING/EQUALIZE PREUURE
TRASH BAG SEALED _-- -_'_...__ RUTDAINT TAll (3)
HEAD,FDRPLACEUENTt-_--<,_'_\_ /- EJECTORtHETRACTEO)
IN TRASH LOCK _ _ , _ ,, ,_,/) -- / ,,_.._---UECTOn HANOLE(R TRACT)
LID LOCK (UNLOCKED) --% _ 1 ,_ _'
VACUUM SHUTOFF _ _ _* _--, B
VALVE (DIqEN _k _\ ,D _ VAL
THROUGHOUT MISSION| ....... .X ,_ (_C _ i 0 , '
_"E_\.S_- _mo,.,,.,,
LID LOCK . WAnE TANI _ OUTER ODOR _ _'('_
,LD.D,-\"VEHTTDVACUU. ,CLD.D). / / ¢_/,II\\
DOOR HANDLE _ " -- 1 ' / _ O00 g _N / _ V " _ J_ '/_ J
-.,,,.,,
/_ //T II 1,1_._\ \ (NIETRAINIO IV TAGS) ELECTOR _ ',__.____,:_,-.,..
_I l_'2 IA_ ) =EC.,N..,/ _ _-_
TRAI_I SAG EICTED /
_-OUT DOOR (CLOiHLO)
FiOU_I4, OperationalSequqmcm
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LID_ ,., •
EJECTOR ..L- ._:'"'".: ,_,c_
,_.._/,s.... _ , °7, _-w_.. .
BAG RETAINER _" ;f;" "_,_'''/._'-__-_ _'_" '"" .F " , ,
LID-TO-LID .'
LOCK
INTERLOCK _'
LEVER-"_"'_ _.
CYLINDER../ASSEMBLY--"
Figure5. Lid and Ejector
LID-_ - n._,-_,..,
, ...--EJECTOR
EJECTOR__., HANDLE
LID
HINGE
frWO)_._ FRICI'IOI'_HINGE
_-----BAG RETAINER
LID LOCK_ t ., PIN (3)INTERLOCK ., _ ,.....SPHEREASSEMBLY
-
ROD_ ,* ....--VALVE/
/.i- OUTERDOOR
DOORCRANK----...." :'_p_,, HANDLE
PRESSURIZATION VALVE
PORT_____._. ASSEMBLY
f--- VENT
VACUUM SHUTOFF LINE
VALVEHANDLE---I'-"...... ""
Figure6. TrashAirlock Details
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Trash Ejector Mechanism (Figure 5)
The trash ejector mechanism is a rigid scissors extension device
operated by a crank arm with an overall mechan_.cal advantage of 0.5.
The mechanism is equipped with an ejection plate that pushes the trash
bag into the waste tank when the ejection handle is raised. The ejector
and scissors links are aluminum.
Sphere Assembly (Figure 6)
The aluminum sphere asse:nbly is a weldment that serves as the pres-
sure vessel and basic mounting structure for the mechanical system, which
makes up the trash disposal operating system. The sphere itself is com-
posed of six welded parts. The welds are made on an automatically
programmed welding me.chine.
Cylinder Assembly (Figure 5)
The alumir:am cylinder assembly is the compartment into which the trasn
bag is inserted before ejection into the waste tank. It is a smooth-walled
cylinder 351.0 mm (13.81 inches) in diameter and approximately 559.0 rnm
(ZZ inches) long. Three steel pegs at the inboard circumference of the
cylinder at 120 degrees hold the bag away from the outer door during opening.
Outer Door Assembly (Figure 7_
The aluminum outer door or "eyelid" forms the seal bet_,een the cabin
environment and the waste tank vacuum when trash is being inserted into the
airlock cylinder. Its seal is molded into the eyelid and cannot be replaced
on-orbit. The eyelid is operated by the valve/outer door handle through a
combination cam, crank, and over-center device that first retracts the
eyelid 10. _ mm (0.4 inch) and then rotates the door on the inside of the
airlock to clear the ejection port.
Valve/Outer Door Operator (Figures 8 and 9)
The door operator is a crank handle that operates both the valve and the
outer door by direct attachment to the valve spool and by a c_rn and cr--nk
mechanism to the outer door operator. The parts are stainless steel.
Pressurization Valve Assembly (Figure 10)
The valve is a two-way, two-position valve using a ro_ _ting cylinder
with O-rings to open and close ports. When _he valve/out • door handle is
in the PRESS position, the airlock is ported to the cabin. When the valve/
outer door handle is in the VENT position, the airlock is ported to the waste
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LID EJECTORMECH._NISM
PROTECTION
//-OUTER DOOR
EJECTOR-
COMMONEdLKHEAO SEAL(MOLDED)
Figure7. OuterDoor _d Ejec_r
DOORLIFT )OORLIFT
r'wo) CAMGUIDE
DOORLIFT ('TWO)
CAMROLLER
(TWOI
CRANK
PRESSURIZATION ,..- CAM
VALVEASSY _ GUIDE
.• /VALVE/OUTER DOOR
DOOR _ HANDIE
CRANK
LID LOCK
ASSY
F.,Me IL Trmh A_
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Figure 9. Door Lift Mecharl=sm (Without Door)
Figure 10, Operationll Trash Airlock
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([ tank. When the valve/outer door handle is rotated to the OPEN position, the
airlock is still ported to the waste tank. although partially closed relative to
the VENT position. The valve metal parts are stainless steel.
Absolute Pressure Gage (Figure I0)
The absolute pressure gale contains a bourdon tube pressure sensor
housed in a sealed stainless steel container evacuated to provide ",he refer-
ence vacuum. The bourdon tube drives the needle through an amplifying
linkage mechanism. The gage reads from zero to 103.4 kPa (15 psi) but will
take pressures up to 310_ Z kPa (45 psi) without degradation. The gage indi-
cates when the airlock has completed pressurizatioa or depressurization
The gage may also be used for trouble shooting for leaks by indicating pres-
sure decay or vacuum degradation.
Lid Lock (Figures 6, 8, and 10)
The stainless steel lid lock is an over-center cam device with a large
mechanical advantage. It performs the following:
1. Unlatches the lid, making it possible to raise the lid for inserting
trash.
2. Provides an over-center latch to compress the lid seal to ensure a
pressure seal when tl _ airlock is exposed to the waste tank vacuum.
Cabin pressure aids in compressing the seal further when the air-
lock is depressurized.
DESIGN FEATURES
The trash airlock is designed to perform normally in the 34.5 kPa
(5 psi) cabin environment. Its life is based on five operations a day for
140 days at cabin ambient temperatures. Its proof pressure is _pproxi-
mately 68.9 kPa (1O psi) differential ana is capable of withstanding a
launch malfunction differential pressure of 179.2 kPa (26 psi) in either
direction without damage.
The TAL includes the following safety interlocks:
I. Lid Lock-to-Valve/O_ter Door Handle (Figure 3) -- The valve/outer
door handle must be in the PRESS position before the lid lock can be
unlocked. This prevents opening the lid with the valve in the VENT
position or with the outer door open.
2. Lid-to-Lid Lock (Figure 5) - The lid must be ;losed before the lid
lock can be retracted. This prevents closing the lid lock with the
lid open, which would allow overricting the lid lock-to-valve/outer
door interlock.
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3. Ejector Handle-to-Lid Lock (Figure 3)- The ejector must be
retracted before the lid lock cz_n be unlocked. This prevents
unlocking and opening the lid with the ejector extended.
The following summarizes other signlficant features.
1. Total Gas Volume: 0. 1218 n_ 3 (4.3 ft3).
g. Transfer Tube Size: 350 mm (13.8 inches).
3. Trash Capacity: 350 mm dia. by457 rnm (13.8 inches dia. by
18 inches).
4. Overall Size: See Figure 11.
5. Weight: 71.7 Kgm (158 Ib).
6. Microbial Control: May be evacuated between operations.
FLIGHT EXPERIENCE
The trash airlock was used successfully throughout the three missions.
Although there were no malfunctions of the airlock, there were several
operational difficulties that were successfully resolved. Figure 12 shows
astronaut Gerald Carr operating the TAL in space.
There were two incidents of near jamming, which were attributed to
overfilled trash bags. Further problems were avoided by better control of
trash combinations during disposal.
It was noted during the iirst manned missiot_ that the valve handle could
be iuadvertently kicked into or left in an intermed,ate position between the
pressurize and vent positions, which caused a cabin atmosphere leakage of
as much as 1.5 Kgm/hr (3.3 lb/hr). This problem was overcome by strap-
ping the handle in the PRESS position between operations.
During the second mant,_d mission, an operating characteristic of the
airlock was highlighted. The manual force required to squeeze the lid during
the initial portion of the latching operation is high. This high force charac-
teristic is more significant in weightlessness because body restraint is
difficult. It was found that the high force of latching could be overcome by
proper technique or use of two crewmen.
Although the trash airlock was used to approximately 80% of the expected
on-orbit operation with no malfunction, there are two improvements recom-
mended for future use. First, a detent device should be added to the valve
handle to positively maintain the valve handle in the PRESS or VENT positions
between operations. Second, the squeeze force during latching should be re-
duced. This could be done by refining the h_nge gap adjustment by shimming
or changing to a softer rubber for the lid se_A.
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Figure 11. Overall Dimensions
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1976012084-159


Skylab Trash Airlock

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