The requirements, design tradeoff, design, and performance of the Spacelab scientific airlock hatch latching mechanisms are described. At space side the hatch is closed and held against internal airlock/module pressure by 12 tangential overcenter hooks driven by a driver. At module side the hatch is held by 4 hooks driven by rollers running on a cammed driver

Terhaar, G. R.

English

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HATCH LATCH MECHANISM FOR SPACELAB SCIENTIFIC AIRLOCK ---__ -. ----~--- -~-- __- 
by Ir. G.R. ter EIaar 
Fokker-VFW Space Division 
ABSTRACT -~ 
This paper describes the requirements, design trade-off, design 
and performance of the Spacelab scientific airlock hatch latching 
mechanisms. 
At space side the hatch is closed and holded against internal air- 
lock/module pressure by 12 tangential overcentre hooks driven by 
a urivering. At mo'dule side the hatch is holded by 4 hooks driven 
by rollers running on a cammed drivering. Both mechanisms behaved 
well in tests. 
INTRODUCTION 
'~'ne Spacelab Scientific Airlock (see fig. 1) will be mounted in 
tne top of the Spacelab module as shown in figure 2. The main 
parts forming the airlock are: 
A 1 meter diameter and 1 meter long cylindrical shell 
with sealing and mounting flange 
A flat hatch on space side (Outer Hatch) with conical sealing 
flange, hinging as shown in fig. 2. 
-. A completely removable flat hatch on module side (Inner Hatch) 
with a flat sealing flange. 
A latticed table consisting of 3 parts moving an experiment 
upto 150 kg either into space or into the module. 'The air- 
lock provides power and data lines to the experiment. 
Manually operated mechanical controls to move, latch, 
lock and interlock the various mechanisms 
Housekeeping, signals, heating, etc. 
89 
https://ntrs.nasa.gov/search.jsp?R=19790013190 2020-03-22T00:02:14+00:00Z
Most of above parts are rather specific for this airlock. There- 
fore only the more general latch mechanism for both the inner and 
outer hatch will be described here. 
OUTER HATCH LATCHING MECHANISM 
REQUIREMENTS 
The main requirements which had to be fulfilled for the outer 
hatch latching mechanism are: 
Latching and holding of outer hatch against pressures up to 
1.1. bar as limit and 2.2 bar as ultimate 
Allowable leakage over seal < 1 gram/day 
No drive failure allowed when 400 N is applied on the drive 
handle at any jam of the system 
Unlatching has to be performed with only 1 operation 
DESIGN TRADE-OFF 
To meet above requirements several design solutions have been 
studied. Aechanisms compressing an O-seal represent state of 
the art techniques, with hardly any need for qualification. 
However, due to the high forces needed to compress the seal, 
and maintain the seal compression against the airlock pressure, 
the mechanisms will be relatively heavy and high transmission 
ratios will be needed. This especially results in jamming be- 
hind the transmission becoming a considerable design case, 
furthermore, the feeling for a jam is negligible which might 
cause undesired damage. When different types of seals are used 
qualification of the seals is deemed to be necessary with a 
relatively high development risk. Sliding of the hatch over a 
compressed seal is impossible without a separate mechanism 
because of the long moment arms involved and undesirable be- 
cause of increased wear. 
Table 1 shows the different mechanisms studied and a summary 
of the main advantages and disadvantages. The tangential hook 
design was chosen for the outer hatch latch mechanism because 
of its straight forward and state of the art sealing technique, 
90 
but also its flexibility for thermal and mechanical distortions 
and the possibility for opening the outer hatch at relative 
high pressure differences. 
DESCRIPTION OF CHOSEN DESIGN 
The latch mechanism consists of 12 latches on overcentre cranks 
driven via pushrods by a drive ring at the bottom of the airlock 
flange as shown in fig. 3. The drivering is activated by a manual- 
ly operated handle at module side driving a pinion running on a 
rack on the drivering. Wrong operations are prevented by interlocks. 
The hooks catch directly ontg spherical bearings attached to the 
hatch. The seal flange is 60 conical to keep vertical seal com- 
pression forces and variations in gap size as low as possible. 
The outer hatch is guided by guidepins and leveled by spring- 
loaded seats just above seal contact to provide proper hatch 
alignment. To allow for misalignments up to 1 mm in lateral di- 
rections the hooks are supported in teflon lined spherical 
bearings, and stabilized by two springs pushing the hook towards 
the hatch grippoint. During latching the latch hooks rotate for- 
ward until they touch the ball bearings on the outer hatch and 
then they pull the hatch downward until nominally 2 mm overcentring 
in the cranks is reached. At pressurization overcentring can in- 
crease until the hooks reach their individual stops in the hook 
brackets. Therefore the drivering position is not very critical 
and ample clearances can be allowed. such preventing jamming cases. 
Overloading of the mechanism inherent to overcentring devices is 
prevented by the curved shape of the hooks. 
TEST RESULTS 
During tests the mechanism behaved well. The characteristic 
force curve at the handle is shown in fig. 4. The peak value 
depends on seal hardness and system adjustments; at nominal ad- 
justment and a seal hardness of 75 shore a 100 N handle load 
was measured 
The only disadvantage of the current system is the fact that 
jamming behind the transmission can hardly be felt on the 
handle with the risk of causing damage. 
Leakage was always found to be far within the 1 gram/day require- 
ment, even with 1 hook failed. With 2 mating hooks failed an 
intermittent bleed-off at 600 millibars was found. Furthermore it 
was shown that the outer hatch can even be opened at 100 mBar 
91 
pressure difference without any chance for personnel injury, which 
reduces venting times tremendously. In practice opening will be 
allowed at about 30 mBar. 
INNER HATCH LATCHING MECHANISMS 
REQUIREMENTS 
The main requirements which are applicable to the inner hatch 
latching mechanism are: 
Keeping the inner hatch in place and providing initial 
sealing against shell until module pressure seals the 
hatch firmly against seal and shell flange when the air- 
lock is evacuated. 
Keeping inner hatch in place at repressurization, but 
allowing bleed-off when pressure difference airlock/ 
module exceeds 30 mBar and preventing a pressure differen- 
ce above 80 mBar at maximum supply (5 grams/set). 
At release under zero G the latches shall free the 
hatch without the possibility that the hatch starts flying 
around. 
At release under 1G conditions the latches shall retain 
the 18 kg hatch 
Release shall be effected by a single operation 
DESIGN TRADE-OFF 
To obtain initial sealing at least 4 hooks are required to 
keep the hatch edge member within reasonable dimensions. A 
single release operation can only be obtained when the 4 hooks 
are interconnected by a drive ring. Because of the relative 
low loads required during latching a cam roller design was 
chosen because of'its simplicity and resulting low mass. 
92 
DESIGN DESCRIPTION 
Fig. 5 shows the current design for the latch mechanism. The 
hooks have a roller,fitting in the hatch rim and enabling 
mounting of the hatch in every rotational position. The rollers 
which are running, springloaded downwards, on a cam of the 
drivering, move the hooks up and down. The hooks are guided 
by the two side-walls of the brackets and two guiding pins 
in a slot on the hooks. During release the hooks move downwards 
on the cam until the guide pins touch the end of slot, which 
starts rotation of the hooks away from the hatch. However, 
under 1 g conditions the hatch mass keeps the hookroller in the 
rim until the hatch is slightly lifted. In space the hooks only 
rotate so far away that some force is needed to pull the hatch 
out of the hookrollers. The best method of replacing the hatch 
is to push the hatch through the rollers onto its seat. Under 
lg conditions the hatch has to be hooked in into the rollers to 
avoid drop down. When latching, the hooks first move inwards and 
then upwards, giving enough pretension in the seal to obtain 
initial sealing. 
The tubular drivering, running all the way around the cylinder 
and supported by rollers, is driven by a crank handle system. 
Its rotational accuracy is kept to a minimum by a flat upper 
surface of the cam. Overloading of the system is prevented by 
the curved shape of the hook. 
TEST RESULTS 
During tests the mechanism behaved well. However, on some points 
minor deviations were found: 
At airlock overpressure bleed off via the hatch sealing 
did not occur at the required 30 mBar but already at 
20 mBar. It seemed possible to meet the 30 mBar requirement 
by change of adjustments, however, then the required handle 
forces became too high. 
When, under lg conditions, release is performed too quickly, 
the hatch might drop down due to slight sticking effects of 
the hatch to the seal, which allow the hooks to swing out 
during the unlatching operation 
Sometimes the hookrollers remained at the edge of the rim 
of the hatch, which might cause high hookstresses 
when the airlock has some overpressure. 
93 
CONCLUSIONS 
Both latching mechanisms described here were tested on detail 
models and recently on the first airlock model. Their functio- 
ning has proven to fulfill the requirements. In a few months 
time qualification of the mechanisms will be performed on the 
airlock qualification model. 
REFERENCE 
"Functional description of Scientific Airlock" 
Spacelab Program Technical Report TN-FO-11-063-77 d.d. 
19-09-77 
Authors : Benes/ter Haar/Setz 
Some copies will be available during the presentation. 
94 
- 
--+--7 : 
Fig. I. . Hard Mock-up model of Spacelab Scientific Airlock 
95 
Fig. 
2, 
Scientific 
Airlock 
m
ounted 
in 
S
pacelab 
96 
Tangential hooks 
al and thermal distortions 
ed unlatching at internal over- 
2. Radial hooks 
anical and thermal dis- 
- Direct load path 
- Simple design 
Disadvantages: 
- Well known operational problems 
- Many possible coldwelding areas 
- Reliability clamp release 
- Complex drive 
tional disadvantages: 
stem cannot apply high compression load: 
alternative sealing technqiue required 
ry sensitive for debris 
quired accuracy and similarity of cams 
ose of function at jam of 1 roller 
Coldweldin 
- Simple design 
- Direct structural load support 
Main disadvantages: 
- Drive power required to slide over seal -U 
soft seal design 
ent sealing 
quires additional pressure system 
aling design needs development and 
qualification 
Table 1 Design trade-off Outer Hatch latching mechanism 
97 
HATCH 
+---‘7”------~,-~--~ 
RACK ANO PINION 
FIGURE 3 
* 
.l 2 .3 .4 .5 .b .I .B .9 1 
STROKE + 
FIGURE 4 Operational force Curve 
v-fiiik HANDLE 
813 I i 
OPERATING 
SCHEHATII VIEW OF OPERATION -__ 
LATCH0 UNLATCHFO LPIOER 
l- (I CC?4OITION 
UNATfHEO UNDER 
O-G CONOITIM 
HALFWAY 
m!T. 5 Imer hatch latching mechanism 


Hatch latch mechanism for Spacelab scientific airlock

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