Device for use in descending spacecraft as altitude sensor for actuating deceleration retrorocket

Campbell, C. C., Jr.

Chandler, J. A.

Grubbs, T. M.

English

NASA Technical Reports Server

Feb. 7, 1967 C. C. CAMPBELL, JR.. ETAL 3,303,304 
DISCRETE ?,I '. L ALTITUDE SENSING DEVICE 
F,~ed  Dec. 23, 1965 
 car///^ /P C. Comph ~ / d  . 
Joseph A. C h ~ n d / e r  
7c/o/ncrs M. GruAAs 
I \ v1-i I 01's 
https://ntrs.nasa.gov/search.jsp?R=19700032496 2020-03-17T02:11:44+00:00Z
United States Patent 
3,303,304 
DISCRETE LOCAL ALTITUDE SENSING DEVICE 
Carlisle C. Caanpbell, Jr., 212 Confederate Way, Sea- 
bro0k9 Tex. 77586; Joseph A. Charadlea; 3030 Long- 
wood, Dirkinnson, Tex. 77539; and Thomas M. ' 
Gmbbs, 9905 Tiltree, Hoaastow, Tew. 97934 
Pi'iled Dee. 23,1965, Ser. No. 516,159 
3 Claims. (CP. 200-68.45) 
The invention described herein may be manufactured 10 
and used by or for the Government of the United States 
of America for governmental purposes without the pay. 
ment of any royalties thereon or therefor. 
This invention relates to sensing devices in general but 
more particularly to  an altitude sensor for use with a 15 
space vehicle. 
The safe descent to a landing surface by a manned 
vehicle requires that its vertical component of velocity be 
reduced to approximately eight (8) to ten (10) ft.  per 
second, particularly if it is to descend on a hard surface 20 
such as land, rather than water. In order to reduce the 
descent velocity to within this general range, a system of 
parachutes, automatically released for deployment by a 
baro-switch or similar type device is generally used. 
However, with the advent of larger space vehicles it is 25 
desirable to have in addition to the parachutes, a braking 
system usable for land or water descents, which insures 
that impact forces upon landing will be within the known 
limits of safety. One of the systems proposed for this 
purpose employs a plurality of retrorockets affixed to the 30 
vehicle with the nozzles pointed toward the impact surface 
so that the rocket thrust vector acts opposite to that of the 
vehicle's velocity vector. Immediately prior to impact, 
the rockets may be actuated so as to reduce vehicle 
velocity thereby reducing impact forces to within the 35 
range endurable by its occupants or cargo. 
Of fundamental importance to the velocity deceleration 
solution described above is the device which senses and 
signals the retrorocket system prior to impact. Such a 
device must be extremely accurate, responsive, and of ob- 40 
vious high reliability. For example, a vehicle descending 
by parachute at the rate of 30 feet per second must, at an 
altitude of about ten (10) feet be braked by the retro- 
rocket system to about one third its velocity. The retro- 
rockets, which fire effectively for a period of less than one 45 
(1) second, therefore rnust reduce velocity of the vehicle 
to less than ten (10) feet per second before or at the time 
it comes in contact with the impact surface. It is ap- 
parent that a mere fraction of a second prematurity or 
delay in firing of the system easily spells the difference 50 
between success or failure of the landing. 
In view of the discussion above, the present invention 
is directed to a sensing mechanism capable of detecting a 
predetermined dicrete local altitude and of instantaneously 
transmitting a firing signal to  the vehicle retrorocket 55 
system. Upon receipt of the signal the rocket system is 
ignited and the thrust therefrom reduces vehicle velocity 
to within the desired range. Due to the positive contact 
design of the sensor, premature actuation of the rockets 
caused by vehicle oscillation or wind loads is substantially 60 
eliminated. In addition, a hemispherically shaped head 
is provided on the sensor which icsures instantaneous 
actuation at all angles of impact. Also, the impact force 
necessary to close the actuation switches may be varied, 
thus enabling use of the sensor on a variety of surface 65 
hardnesses such as land, water, or sand. Due to the 
simplicity of its construction and independence of all 
2 
external factors such as atmospheric pressure, initiating 
electrical signals, or human monitors, the sensor is reliable 
under the most adverse conditions. In addition lo those 
obvious advantages, it is light (weighing generally less 
than 5 Ibs.) and compact in size (approximately 4" x 4" 
x 6"), both of these factors making the device particularly 
adaptable for use on a spacecraft or other vehicle having 
stringent subsystem weight and size limitations. 
Other advantages and features of the invention, both 
as to its construction and mode of operation, will be read- 
ily appreciated as the same become better understood by 
reference to the following detailed description when con- 
sidered in connection with the accompanying drawings 
in which like reference numerals designate like parts 
throughout the figures, and wherein: 
FIG. 1 is a perspective view of the sensing device of 
the invention; 
FIG. 2 is a sectional view along the axis 2-2 of 
FIG. 1; and 
FIG. 3 is a sectional view along the axis 3-3 of 
FIG. 2, showing the switch frame and miniature snap 
action switches supported thereon. 
The altitude sensor of the invention includes, as best 
shown in FIGS. 1 and 2, the conicaI!y shaped switch 
frame 3, a cover member 5 which is asxed over the 
switch frame, and the bumper means 7 which is in opera- 
tive comn~unication with a plurality of switches 9 sup- 
ported on the switch frame. The bumper means 7 in- 
cludes a lower hemispherically shaped bumper element 11 
fixedly connected to the freely hanging inner cone mem- 
ber 13  by a series of round head machine screws 15 
which are in~erted through and recessed in the bumper 
element d l .  The inner cone member 13 is supported 
from switch frame 3 by means of the bolt 17 which ex- 
tends through circular chamfered hole 19 in the frame. 
The bolt is fitted through threaded aperture 23 in the 
upper horizontal section 25 of inner cone member 13. 
Lock nut 29 is threaded on the bolt within the inner cane 
member so as to thereby support the latter in hanging 
relation from the frame 3 while also permitting swinging 
movement therein. It  is thus apparent that the inner 
cone member and attached bumper element is movable 
not only in a vertical direction into engagement with 
the switch frame 3 but also is rotatable and angularly 
displaceable with respect thereto. It  will also be recog- 
nized that the distznce between the upper horizontal 
surfaces 25 of inner cone member 13  and lower horizontal 
surface 26 of switch frame 3 is critical since the miniature 
silap action switches 9 wo~tld be constantly tripped if the 
distance was too small. Conversely they would not trip 
at all if the distance were too great since member 13 
would likely engage switch frame 3 without contacting a 
switch. By use of the threaded connection between bolt 
17, aperture 23, and lock nut 27, this distance may be 
adjusted to vary the amount of movement by bumper 
element 11 necessary to close the actuator arms 37 of 
the switches. It may be desirable for example, if the 
vehicle is to land on water to shorten the distance, thus 
making the device more sensitive to the softer landing 
surface. Also. in this regard the bumper means 7 is 
generally made of relatively lightweight material, such 
as aluminum, by con~parison to switch frame 3 since 
impact on a softer surface such as water or h e  porous 
sand may not otherwise raise the former into immediate 
contact with a switch. By contrast the switch frame 
3 is generally made of a heavier material, such as stain- 
less steel, so that descent onto a surface would more 
3,303,3 
3 
quickly bring it down on the bumper element thereby 
closing at least one o f  the switches 9. 
Fixedly connected to switch frame 3 is a plurality o f  
conventional miniature snap action switches 9. The 
switches, which are preferably six in number, are cir- 5 
cumferentially spaced thereabout and are affured each to 
extending upwardly directed flanges 33 which are integral 
with the switch frame (see FIG. 3 ) .  Adjacent to each 
o f  the flanges is a rectangularly shaped aperture 35 over 
which the switches lie and through which each switch 10 
actuator arm 37 extends (F IG .  2. Force on any one o f  
the arms by the bumper element will compress a contact 
button 39 which closes the circuit thereby allowing trans- 
mission o f  a current which ignites the retrorocket system. 
In order to dampen vibrations occurring during descent 15 
which might prematurely close a switch, a resilient damp- 
ening body 65, such as soft rubber or other appropriate 
material, may be affixed to the frame adjacent each 
switch. By equidistant circumferential spacing o f  the 
switches, movement o f  the bumper element 11 in sub- 20 
stantially any direction would close a switch thereby 
transmitting the actuating electrical signal. The lead 
wires 41 from each switch are dressed-down along circum- 
ferential flange 43 o f  the switch frame and brought to 
the position o f  the common conduit 45. The common 25 
conduit extends through hole 47 i n  cover member 5 which 
is affixed, by round head screws 51, over the switches 
and associated circuitry to the switch frame. Since the 
conduit 45 acts also as the support for the sensor from 
the vehicle, it is looped through the pivoted horseshoe 30 
55 affixed to arms 53 on the switch frame. The conduit 
is taped as at 57 in the manner shown so that the forces 
o f  deployn~ent may not be transmitted to the lead wires 
41 and their connections to their respective switches. 
The sensor may be deployed from the vehicle at an 35 
appropriate time either automatically or manually after 
the parachutes have opened. This may be done by 
merely dropping it from beneath the vehicle and allow- 
ing deployment forces to be absorbed by the aforemen- 
tioned conduit. The particular length o f  the conduit 40 
will depend upon the altitude at which it is desired to 
actuate the retrorockets. Upon impact with the landing 
surface the bumper element 11 will, as previously ex- 
plained, depress at least one or several o f  the switches 
thus closing the circuit and transmitting a signal to ignite 45 
the retrorockets. 
It should be understood that the foregoing disclosure 
relates only to a preferred embodiment o f  the invention, 
and that it is intended to cover all changes and modifica- 
tions o f  the examples o f  the invention herein chosen for 50 
the purpose o f  the disclosure which do not constitute de- 
partures from the spirit and scope o f  the invention. 
What is claimed and desired to be secured by Letters 
Patent is: 
I. An  altitude sensing device for energizing a braking 55 
system on a descending vehicle at a discrete local altitude 
above an impact surface, said device comprising: 
a frame member having electrical switch means aEixed 
thereto in normally open condition hut in operative 
association with the braking system and with a 60 
bumper element; 
a bumper element for closing said normally open 
switch means upon contact o f  said element with the 
impact surface; and 
means movably affixing said bumper element to said 65 
frame member in adjacent relation to said switch 
means so that impact force on said bumper element 
causes it to close said switch means thereby actuat- 
ing the braking system, 
said switch means having an extended actuator arm 70 
aflTxed thereto; 
an aperture in said frame member for receiving the 
actuator arm o f  said switch means therethrough; and 
said bumper element disposed on the side o f  the aper- 
tured frame member through which said actuator 75 
:04 
4 
arm extends and in adjacent relationship to said ex- 
tending arm so that impact force on said bumper 
clement moves it azainst said actuator arm, thereby 
closing the switch. 
2. An altitude sensing device for energizing a braking 
system on a descending vehicle at a discrete local altitude 
above an impact surface, said device comprising: 
a frame member having electrical switch means affixed 
thereto in normally open condition but in  operative 
association with the braking system and with a 
bumper element; 
a bumper element for closing said normally open 
switch means upon contact o f  said element with the 
impact surface; 
means movably affixing said bumper element to said 
frame member in adjacent relation to said switch 
means so that impact force on said bumper element 
causes it to  close said switch means thereby actuat- 
ing the braking system, said frame member having 
a sloped surface for receiving said bumper element 
and guiding it into closing contact with said nor- 
mally opened switch means; 
said bumper element having a sloped surface substan- 
tially complementary to the sloped surface o f  said 
Game member but in adjacent spaced relation there- 
to so that pressure on said bumper element from any 
o f  substantially an infinite number o f  angles causes 
said switch means to close; 
said switch means including a plurality o f  switches, 
each said switches having an extending actuator arm 
thereon; 
said sloped surface o f  said frame member having a plu- 
rality o f  spaced apertures, each for receiving a 
switch actuator arm therethrough; and 
said bumper element disposed on the side of  said aper- 
tured frame member through which said actuator 
arms extend and in adjacent relationship thereto so 
that impact forces on said bumper element moves it 
against at least one o f  said actuator arms, thereby 
closing at least one o f  said switches. 
3. An  altitude sensing device for energizing a braking 
system on a descending vehicle at a discrete local altitude 
above an impact surface, said device comprising: 
a frame member having electrical switch means affixed 
thereto in normally open condition but in operative 
association with the braking system and with a 
bumper element; 
a bumper element for closing said normally open switch 
means upon contact o f  said element with the impact 
surface; 
means movably af^nxing said bumper element to said 
frame member in adjacent relation to said switch 
means so that impact force on said bnmper element 
causes it to close said switch means thereby actuat- 
ing the braking system; 
said frame member having a sloped surface for receiv- 
ing said bumper element and guiding it into closing 
contact with said normally open switch means; 
said bumper element having a sloped surface substan- 
tially complementary to the sloped surface o f  said 
frame member but in adjacent spaced relation there- 
to so that preasure or? said bumper element from any 
o f  substantially an infinite number o f  angles causes 
said switch means to close; 
said switch means including a plnrality o f  switches, 
each said switches having an extending actuator arm 
thereon; 
said slo~ed surface o f  said frame member having a 
plurality o f  spaced apertures for receiving each 
switch actuator arm therethrough; 
said bumper element disposed on the side o f  said aper- 
lured frame member through which said actuator 
arms extend and in adjacent relationship thereto so 
that impact forces on said bumper element moves it 
- - 
against at least lone of said actuator arms thereby References Cited by the Applicant 
closing at least one of said switches; 
said bumper element including first and second por- UNITED STATES PATENTS 
tions, said first portion disposed adjacent said switch 2,055,153 3/19 13 Ferguson. 
frame and adapted to contact said plurality of  g 2,352,692 7/1944 Dann. 
switches, and said second portion having a convex 2,507,986 5/1950 Liss. 
external surface so as to positively receive angularly 2,916,287 12/1959 Davey. 
directed impact forces. 2,930,549 3/1960 Ernst. 
References Cited by the Examiner 
UNITED STATES PATENTS 
3,128,970 4/1964 Tinajero. 
10 3,154,265 10/1964 Hendrix et al. 
Re. 25,764 4/1965 Robinson --------- 200-61.44 BERNARD L. GILHEANY, Primary Examirzer. 
2,492,501 1211949 Robins ,----------- 244--138 J. J. BAKER, Assistant Examiner. 


Discrete local altitude sensing device Patent

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