Deployment of dual reflector systems

A method and system for deploying a multi-reflector antenna system (10). The antenna system (10) includes an antenna structure (12) mounted to a satellite (14), where an antenna feed array (16) is mounted to the antenna structure (12). A single articulated antenna arm assembly (26) is mounted to the antenna structure (12) by a first spring loaded hinge (28). The arm assembly (26) includes a first arm (30) on which is mounted a first reflector (38), and a second arm (32) on which is mounted a second reflector (40). The first and second arms (30, 32) are connected to each other by a second spring loaded hinge (34) such that the reflectors (38, 40) directly oppose each other and are substantially parallel when the arm assembly (26) is in the stowed position. A plurality of launch locks (44, 46, 50, 54) hold the arm assembly (26) in the stowed position against the bias of the hinges (28, 34) prior to deployment. When the antenna system (10) is ready to be deployed, the launch locks (44, 46, 50, 54) are released in a predetermined sequence such that the arm assembly (26) first moves away from the feed array (16) under the bias of the first hinge (28), and then the second arm (32) moves away from the first arm (30) under the bias of the second hinge (34). When the antenna system (10) is in the fully deployed state, the feed array (16) and the first and second reflectors (38, 40) are oriented relative to each other to define a side-fed geometry.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to a system and method for the deployment 
of dual reflectors and, more particularly, to a system and method for the 
deployment of a side-fed dual reflector system used in connection with a 
Ka band satellite. 
2. Discussion of the Related Art 
Various communication systems, such as certain telephone systems, 
television broadcast systems, internet systems, military communication 
systems, etc., make use of satellites orbiting the Earth in a 
geosynchronous orbit, where the satellites are maintained at the same 
location relative to the Earth or non-geosynchronous orbit, where the 
satellites do not maintain the same relative position. A satellite uplink 
communications signal is transmitted to the satellite from one or more 
ground stations, and then re-transmitted by the satellite to the Earth as 
a downlink communications signal to cover a desirable reception area 
depending on the particular use. The uplink and downlink signals are 
transmitted at a particular frequency bandwidth, such as the Ka frequency 
bandwidth, and are frequently coded. The satellite is equipped with 
antenna system(s) including a plurality of antenna feeds that receive the 
uplink signals and direct the downlink signals to the Earth. The 
configuration of the antenna feeds and associated antenna optics of the 
antenna system is designed to provide coverage over a specifically defined 
area on the Earth, such as the continental United States, although 
coverage could also be global. 
Certain antenna system designs make use of multiple reflectors to direct 
the downlink signals from the antenna feeds to the Earth, or the uplink 
signals from the Earth to the antenna feeds. For example, a downlink 
antenna feed array including a plurality of antenna feeds may be 
positioned relative to a sub-reflector and main reflector, where the 
sub-reflector receives the beams from the feeds and directs the beams 
towards the main reflector to be directed towards the Earth. The 
orientation of the feed array, sub-reflector and main reflector can take 
various geometries and configurations depending on a particular design. 
These designs require that the sub-reflector and main reflector be 
positioned at select locations and orientations relative to the feed array 
depending on the focal lengths of the design. 
Serious considerations are given to the design of an antenna system of the 
type discussed herein apart from the actual geometry of the antenna system 
for providing the desired Earth coverage area. Particularly, the feed 
array and reflectors need to be mounted on a supporting structure in a 
manner that minimizes use of the available real estate on the satellite. 
Further, the antenna system must be compact and lightweight, but be strong 
enough to survive the satellite launch and space environment, as well as 
fit within the launch vehicle fairing. Typically, these designs require 
that the reflectors be at least partially stowed in a folded position 
during launch, and later deployed once the satellite is in orbit. Known 
deployment strategies would either deploy each reflector of a dual 
reflector antenna system on a separate boom or arm, or deploy one of the 
reflectors on a movable arm and maintain the other reflector fixed to a 
bus or antenna structure. These designs typically take up significant 
space to satisfy the launch and deployment requirements. Modern dual 
reflector antenna systems sometimes have relatively long focal lengths and 
may require that both reflectors be stowed in a folded position. 
What is needed is an improved deployment strategy for deploying multiple 
reflectors associated with a multiple reflector antenna system. It is 
therefore an object of the present invention to provide such a strategy. 
SUMMARY OF THE INVENTION 
In accordance with the teachings of the present invention, a method and 
system for deploying a multiple reflector antenna system is disclosed. The 
antenna system includes an antenna structure mounted to a satellite, where 
an antenna feed array is mounted to the antenna structure. A single 
articulated antenna arm assembly is mounted to the antenna structure by a 
first deployment device, such as spring loaded hinge. The arm assembly 
includes a first arm on which is mounted a first reflector, and a second 
arm on which is mounted a second reflector. The first and second arms are 
connected to each other by a second deployment device, such as a spring 
loaded hinge, such that the reflectors oppose each other when the arm 
assembly is in the stowed position. A plurality of launch locks hold the 
arm assembly in the stowed position against the bias of the hinges prior 
to deployment. 
When the satellite is in space and the antenna system is ready to be 
deployed, the launch locks are released in a predetermined sequence such 
that the arm assembly first moves away from the feed array under the bias 
of the first hinge, and then the second arm moves away from the first arm 
under the bias of the second hinge. In one embodiment, when the antenna 
system is in the fully deployed state, the feed array and the first and 
second reflectors are oriented relative to each other in a side-fed 
geometry. 
Additional objects, advantages, and features of the present invention will 
become apparent from the following description and appended claims, taken 
in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The following description of the preferred embodiments directed to a 
strategy and apparatus for deploying a multi-reflector antenna system from 
a satellite is merely exemplary in nature, and is in no way intended to 
limit the invention or its applications or uses. Particularly, the 
discussion below concerns deploying a side-fed multi-reflector antenna 
system used in connection with a satellite. However, the deployment 
strategy of the present invention has other uses for deploying multiple 
reflectors other than side-fed reflectors for satellites. 
FIG. 1 shows a side plan view of a multi-reflector antenna system 10 
including an integrated antenna mounting structure 12 secured to a 
satellite platform or bus 14 (partially shown herein) at a strategic 
location, such as the nadir facing portion of the satellite, depending on 
the particular design requirements of the antenna and satellite system. In 
a practical application, the antenna system 10 is one of a plurality of 
similar antenna systems mounted to the bus 14. A feed array 16 including a 
plurality of antenna feed horns 18 is secured to a mounting plate 20 so 
that the horns 18 are arranged along a predetermined contour consistent 
with the antenna design. The mounting plate 20 is mounted to the antenna 
structure 12 so that the feed array 16 is positioned at a particular 
location and orientation that is also consistent with the antenna design. 
A notional supporting bracket 22 is connected to the plate 20 and the 
structure 12 as shown. 
A single articulated antenna arm assembly 26 is connected to the antenna 
structure 12 by a first spring-biased deployment hinge 28. The deployment 
hinge 28 is in a spring loaded condition when the assembly 26 is in the 
stowed position. The bias of the deployment hinge 28 provides a force such 
that when the antenna system 10 is deployed, the arm assembly 26 will move 
away from the satellite at a predetermined rate and force. The antenna arm 
assembly 26 includes a first antenna arm 30 and a second antenna arm 32 
connected together by a second spring-biased deployment hinge 34. The 
deployment hinges 28 and 34 can be any deployment hinge or mechanism 
available in the art suitable for the purposes of the present invention as 
described herein. The arms 30 and 32 can be made of any suitable material 
or alloy, such as a graphite composite, that will satisfy the 
environmental requirements. A main reflector 38 is mounted to the arm 30 
and a sub-reflector 40 is mounted to the arm 32 so that the reflectors 38 
and 40 directly oppose each other and are substantially parallel in the 
stowed state. The reflectors 38 and 40 can be made of any suitable 
reflector material known in the art, such as a graphite composite, and be 
mounted to the respective arm 30 or 32 in any suitable manner consistent 
with the discussion herein, such as by a lightweight mechanical 
connection. 
The antenna system 10 includes a plurality of launch locks that maintain 
the antenna arm assembly 26 in the stowed position against the bias of the 
hinges 28 and 34 prior to being deployed. In one design, the antenna 
system 10 incorporates five launch locks for suitable stowage. In one 
example, each launch lock includes an electrical device that receives an 
electrical signal that disengages a mechanical connection. Of course, any 
launch lock suitable for the purposes described herein can be used. In the 
embodiment shown herein, a reflector forward launch lock 44 is connected 
to the antenna feed mounting plate 20 and the arm 32 as shown. 
Additionally, two aft reflector launch locks 46 (nearside and farside) are 
mounted to the reflectors (38, 40). Launch locks 46 connect the reflectors 
to launch lock support structure 48, for example, consisting of three 
support struts that are connected to the antenna structure 12, as shown. 
Further, a reflector internal launch lock 50 connects the main reflector 
38 and subreflector 40. A structure launch lock 54 is provided to connect 
the antenna structure 12 to the satellite bus 14. 
In the stowed position, all of the launch locks 44, 46, 50, and 54 are 
restrained (locked), and the hinges 28 and 34 are under spring tension. 
When the antenna system 10 is to be deployed, the launch locks 44 and 46 
are first released from the arm 32, and reflectors 38, 40 so that the 
spring bias of the hinge 28 causes the arm assembly 26 to move away from 
the feed array 16, as shown in the partially deployed state in FIG. 2. As 
is apparent, the launch lock 50 has not yet been released because when the 
assembly 26 is proximate to the feed array 16 in the stowed position, the 
arm 32 would contact the feed array 16 if it were released. Once the arm 
assembly 26 has moved far enough away from the feed array 16, the launch 
lock 50 is released so that the arm 32 is deployed by the bias of the 
hinge 34. This launch lock (50) function can also be achieved through 
deployment rate control of the hinges. Additionally, the structure launch 
lock 54 is also released. 
FIG. 3 shows the antenna system 10 when all of the launch locks 44, 46, 50, 
and 54 have been released and the arm assembly 26 fully deployed. The 
launch locks 44, 46, 50, and 54 and the launch lock support structure 48 
are not shown in this figure for clarity purposes. In this configuration, 
the orientation of the feed array 16, the sub-reflector 40, and the main 
reflector 38 are in a side-fed geometry. In the case of a downlink 
antenna, where the sub-reflector 40 receives the beams from the feed horns 
18, and directs the beams toward the main reflector 38 in a manner which 
satisfies the focal length of the reflector 38. The main reflector 38 
directs the beams towards the Earth over the desired coverage area. In 
this side-fed design, the sub-reflector 40 has a hyperbolic contour and 
the main reflector 38 has a parabolic contour. A more detailed discussion 
of a side-fed antenna system can be found in U.S. patent application Ser. 
No. 09/232,452, titled Side-Fed Dual Reflector System for Cellular 
Coverage, filed Jan. 15, 1999. Of course, other antenna configurations and 
designs can be provided within the scope of the present invention. 
The foregoing discussion discloses and describes merely exemplary 
embodiments of the present invention. One skilled in the art will readily 
recognize from such discussion, and from the accompanying drawings and 
claims, that various, changes, modifications and variations can be made 
therein without departing from the spirit and scope of the invention as 
defined in the following claims.