"lfk f; \"A Lt. - Airborne Systems

drogue and starts the timer which operates :m an
independent battery or :he vehicle power saurcs.
if1e control functions fo low in a preset sequence.
A variation of th s s,:oquence could be uutCJined by
lIsin\) Lwo timers and placing a baroswitch in series
with the drogue interval timers. Then above a preset
max imu m 01 ti tu de desi red for main parachute deployrrent,
disconnect of the drogue wll be delayed until
the system has descended to the: altitude. The
second timer would then be started by the main ceployment
signD (and dr8gLe disccnnect) to seCLlence
the desired fu nctions after the mai'l aaraehlte is fL lIy
inflated.
\ more complex contrcl/actuation subsystem , a
multi-mode eonccj:t to prcvi:e for sevel al in-fligrit
abort possibilities. is showr by the diagram of Figure
2. fr.e example applies to a lifting body shaped
one-man escape capsule fram a design study226 The
total spacecraft was ' ntended for leunc:, to a 20D-mile
ocbit and return with normal landing on airstrips
without deployment of the emergency system.
Conditions cOfl3;dered in tt-,e cesign of :he escape and
recovery system were the following ebort modes:
A. eff-pad and early boo
B. du ring boos: cbove 50 000 ft
du ring late I aunch phase
escape from orbit
after deorbi, retrofi r8
F. during reentry, and
G/H at low altitude during glide and landing
Control Components
Componen ts requ ired t:J :Jr:Jvide control fu ncti ons
may include power sources; event times, and acce' erfJ:lnn
and pressure switches. Switching releys , diodes
and fuses He also incorpocated in llany electrically
operatea recovery conc.rol subsystems.
Power Sources. Electrical power availability in
mil itary aircraft, drenes, missiles anc spacecraft varies
in type and power factors. Twenty-eight volt
BC or de
systems are usually avail8ble. Items requiri:lg heating
or energizing may require an indeperdent source of
power, particularly if tho :)ayload bein recovered
sep8rates frcm the primc:ry j:OW6r SOJ r::e or as a backup
source i' the e'Jent of primary power failures.
Batteries of various types and sizes have been used,
depending upon the cu rrent cequirements and the
duration of demand. OthEr considerations including
the ope'ating temperature range and the length of
ti me from i nstai lati 011 of the charged battery to '.5e
witilOUt recharging may hfluence the choice of a
battery type.
113
Storage Batteries, High efflcloncy torage batteries
using alkaline electrolytes have been used as inde.
pendent power SOJrces for mClny recovery systens,
Two basic types are available: nickel-cadmium batteries
and silver-z' nc :)(Jtteries. Both types have the
characteristics of hi h current discharge capabiiity.
:Jperation at temperatures down to - , leak-proof
sealed cases. and long life. TI-e individual cell votage
is nomhally 1. 2 volts for the nickel-cadmium type
and 1. 5 for the silvw- zinc type.
Reserve Cells. For certain Llses, shelf.life of ma'lY
years without iTairtenance, followed by a short-term
Jsage ::ycle dictates use of a power sou cce known as 2
reserve cell or thermcl battery In this type of bat-
/ the plates are pre-charged 8nd the electrolyte is
stored separately in an internal breakable capsule.
Upcm actuation (ge1erally by larYi)rd pull , e pyrotechnic
cartridge vvi th i n the cell fires, breaki ng tile
electrolyte capsLle, dispensing t1e elec- rolyte throughout
the Gell and heating the cell to a high temj:erature
(above 200 F).
Because of the r, igh temperature, a small battery
Jt this type generates a high volta 2 And current
capacity until it cools down. The relative high cost of
the reserve cell when compared to tht: larger rechargeable
alkaline storage batteries has inhibited videspraad
use of the reserve cell.
Salt Water Batteries. Payloads which touch
down at sea otten require power to operate post.
I andi ng recovery/I acati on/retrieval devices. Sa t water
switches and solt water batteries are used to close
electrical circuits. power pa:achute disconnects, initiate
in'flation of flotat' on gear and power radio or
fl ash ing I igh t beacons. Sal t water batteries consist of
two 0' more rretal plates , slightly separated in a case
with pons to p' ovide free flow of sea water.
After several hours of operation , salt water batter-
ies mal, decrease thei r outpu t because of an aCCL! mulaliurl
of gas b..:bbles 01- a layer of chemical deposit or
the plates. Soecial pr::JVisions must be made to prevent
such an accumulation if more tr,an a few hours
of operation are needed-
Timing Devices. A " timer" is any device wh icr
con:rols the elapsed time between a start sigral and
an cction such as 2 switch closure or mechanical displacement
to iritate an eve r. t. A common type of
timer is electro-mechiJnical , a switch bank drivel by
clock spring or electric motor. Thermal delay switches
are another type of timer which, when electric
currert is CJpr;lied, operate on the :Jimetal spring
principle to close after an claj:sed inte'Val. Stil