GB2430311A

GB2430311A - Satellite payload design enabling replacement of units in orbit

Info

Publication number: GB2430311A
Application number: GB0518874A
Authority: GB
Inventors: Christakis Nicolaou Fellas
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-09-15
Filing date: 2005-09-15
Publication date: 2007-03-21
Also published as: GB0518874D0

Abstract

This invention describes a novel design for a communications satellite payload that facilitates replacement of payload modules in orbit while utilising known established technology. The design describes a new architectural payload design based on modular blocks which are easily accessible and where thermal control design is implemented so as to avoid thermal control problems in orbit. The invention incorporates special designs of the mechanical, electrical and RF interfaces so as to make the replacement of modules easy while at the same time introducing the smallest possible changes to established and reliable technology.

Description

(* 2430311 Satellite Payload Design Enabling Replacement of Units in Orbit

Background to the Invention

Large Geostationary satellites have been providing a variety of telecommunication services for more than forty years. They are designed to withstand space radiation and severe environmental conditions for a time period of approximate fifteen years. Despite the use of high reliability components and substantial testing prior to launch, failures of units in orbit are quite common, leading to loss of services and subsequent expensive insurance claims.

Statement of Invention

This invention describes a novel design for a communications satellite payload, which facilitates replacement of payload modules in orbit. The design describes a new architectural payload design based on modular blocks which are easily accessible and where thermal control design is implemented so as to avoid thermal control problems in orbit. The invention incorporates special designs of the mechanical, electrical and RF interfaces so as to make the replacement of modules easy. It also includes designs of parts of the mechanical arms for replacement of the modules.

Introduction to Drawings

An example of the invention will now be described by referring to the accompanying drawings: * Figure 1 shows a schematic diagram of an example of a satellite payload with six end to end communication transponders.

* Figure 2 provides top and side views of a replaceable module design of a payload according to the invention.

* Figure 3 shows a structure that may be used to secure each module to the satellite external wall according to the invention.

* Figure 4 shows one end of the waveguide interface, where it is mounted to the wall according to the invention.

* Figure 5 shows the detailed interface on the satellite wall where the waveguide fits according to the invention.

* Figure 6 shows an example of a clamping device that may be used to demount and remount a payload module from the satellite.

* Figure 7 shows an example of a release device that may be used to declamp the waveguides from the panel as well as the DC harness connectors.

None of the drawings are to scale.

Detailed Description

Satellite Payload descriptions and how they work may be found in various textbooks. Figure 1 gives a simplified version of one such payload with six communications transponders. In this design the signal is received by the ( 2 antenna Ar and then fed to either receiver RI or receiver R2 by means of the redundancy switches (2). The signal is fed through the input waveguide manifold (3) to a row of six cavity filters (4a to 4f). The input waveguide manifold (3) and the filters (4) come normally as one assembly called IMUX (input multiplexer). It enables the six transponders to utilise one antenna and one receiver and functions so as to channel the six incoming carriers via waveguides (1) into their corresponding filters. From the output of each filter the signals are fed to frequency converters (5) using a waveguide (1) and then to an in-line amplifier (6) that has an adjustable by tele-command gain step. The signal is then fed to the T\NT (Travelling Wave Tube, (8)), which is powered by the EPC (Electronic Power Conditioner, (7)), the connection between EPC and T\NT not shown in the diagram. The EPC (7) and the TWT (8) normally are procured as one assembly called the TWTA (Travelling Wave Tube Amplifier). It functions so as to amplify the incoming signal by as much as 60 dB and the output power may be as high as 250 Watts or as low as 10 watts.

The output of the TWT is fed to a waveguide (1) to the output filter (9) via an isolator/circulator (not shown in the diagram). The six output filters (9a to 9f) combine all six output signals via the waveguide output manifold enabling transmission to a single transmitter antenna (At) . The six output filters (9) and the output manifold (4) normally come as one unit called OMUX (Output multiplexer). In this design the redundancy switches and the redundant units for converters (5), in-line amplifiers (6), and TVVTAs (6,7) were deliberately omitted. Units (5), (6), (7) and (8) are identical for all six transponders. The receiver redundancy (2:1) is standard design and it is retained here. With the exception of antennas payload units are attached on the inner side of the North and South panels. In this example TWTAs are used as high power amplifiers. Other payload designs, to which this invention equally applies, utilise SSPAs (Solid State Power Amplifiers) or linearisers instead of in-line gain step amplifiers.

The first change to normal payload design, introduced with this invention is the swapping of positions between the units mounted on the inner side of North and South walls with the units mounted on the inner surfaces of East/West panels. This change is made so as to have unimpeded access to the payload units that may be placed on the outer surfaces of the satellite and to avoid the solar array panels that are attached on the North/South walls.

The second change is to move the deployable Antenna hinges to the earth facing wall from the rear panel edge. This leaves the external * surfaces of the East/West panels free from any obstruction so that a service space vehicle may approach the East and west external surfaces of the satellite and replace units or modules.

As described above, figure 1 shows a simplified diagram of a six transponder payload. Frequency converter(5), in-line gain step amplifier(6), and TWTA (6) and (7) are the same in all six transponders. These four units may be built as one subassembly in order to minimise spares since one spare may replace any one subassembly which may fail from one of the six transponders.

The third change is to move all such subassemblies ( 5 to 8) to the outside of the panels, leaving the rest ie Receivers and Multiplexers on the inside. In figure 1 all units in the area ABB'A' are moved to the outside.

Figure 2 shows side view and top view of one subassembly (module), consisting of frequency converter (5), inline amplifier (6), EPC (7) and TWT (8) attached to the panel (10). The size of the boxes are such that they rest on the panel and are all of the same height. They may all be housed in one box or be interlinked so as to be one integral unit. The interlinking bars are not shown on the diagram. The mechanical and RF interfaces are via waveguides (1) going through the panel. The DC Harness (11) provides the electrical interfaces via two connectors (15) as shown in figure 2. Note that there is no electrical connection from the harness (11) to the TWT. The power to the TWT is provided via a bundle of cables (14). Also there is no RF interfaces with the EPC (7).

The waveguide connects the in-line amplifier (7) to the TWT (8), passing alongside the EPC.

The fourth change introduced here is to implement thermal control individually on each unit of the module (5) to (8). The units of each module are re-designed so as that the heat generating parts are closed to the surface facing space. This will allow heat to be conducted to that surface. Figure 2 side view shows how a layer of thermal conductive adhesive (13) is utilised in order to attach one or more second surface mirrors (12) to each unit to act as heat radiators. In figure 2 only one surface of each unit (space facing) is shown to be covered with second surface mirrors. In practice all surfaces may have thermal control mirrors attached. Such decision will depend on detail thermal analysis of the specific mission and the specific requirements imposed on each unit. The essence of this invention is that heat control is implemented on individual units and the design may be validated by thermal vacuum tests at module level. Each module must be tested with the tube at saturation for 12 hours monitoring temperatures throughout, in order to validate the design in each case.

The design of the module is such that when it is placed on the panel surface the two wavegu!de ends fit into position. Figure 3 shows a holddown structure, which is placed on the top and pushed into the panel. It is designed to hold down the module during the vibration phase experienced during launching of the satellite. The hold-down structure fits exactly onto the panel (10) and locks into position with standard locking mechanism (not part of this invention).

Figures 4 and 5 show details of the waveguide to waveguide interface as per this invention. The waveguide ends on both sides of the module have two attachments (15) that fit exactly to the recesses (16) on the panel (10) where the waveguide at the output of the filter (4) (not shown) is attached. When the module is pushed onto the panel (10) it locks into position with a standard locking mechanism (not shown, as not part of this invention) aligning the two pieces of waveguide, so as to minimise RF transmission losses due to mismatch.

Removal and Replacement of faulty Module In-Orbit If any one of the units (5), (6), (7) and (8) suffers a failure in orbit then the entire module is replaced. The faulty module is returned to earth where it is repaired so that may be used again, should another module fails. The replacement is performed in orbit either by a manned or unmanned spacecraft suitably equipped (such a spacecraft is not part of this invention). The spacecraft should be equipped with two robotic arms as per figures 6 and 7 to be able to perform this operation as per this invention.

Upon a failure of one of the units in the module, all units of the failed module are switched off. The robotic arm of figure 6 is first placed into position so that the clamp C' is attached to position E of figure 3 and clamp D' (figure 6) is attached to position F of figure 3. The standard locking mechanism (not part of this invention) which locks the 10 legs of the hold- down structure of figure 3, releases the hold upon pressure with the tip (17) of the robotic arm of figure 7. When the robotic arm of figure 3 is attached to the hold-down structure, each lock at the bottom of each leg is released in turn. The hold-down structure is then removed.

The same robotic arm of figure 6 is then attached to the module so as clamp C' is attached to position C (figure 2) on the waveguide and clamp D' (figure 6) is attached to the waveguide at D (figure 2). The tip (17) of the robotic arm of figure 7 is then used to release the locks of the DC connectors (15) of figure 2 and then the two locks of the waveguide ends attached to panel (10) of figure 2. Once all four locks are released, the module lifts from the panel.

The replacement procedure is then the reverse of the removal. The new module is held by the robotic arm of figure 6 at points C and D and pushed into position such that the waveguide ends fit onto the panel (10). The DC connectors (15) are then locked into position. The hold-down structure is then replaced so as all ten legs lock into position, completing the replacement of the faulty module.

Claims

Claims 1. A satellite design where the architecture is altered so as to

make payload units accessible by a visiting spacecraft.
2. A payload design, according to claim 1, without redundant units for frequency converters, in-line gain step amplifiers and T\i\ITAs
3. A payload design according to claim 1 where transponders are in groups (of any number of transponders) and the section of each transponder between IMUX output and OM.UX input is identical for all the transponders of the group.
4. A payload modular design, according to claims 1, 2 and 3, where the replaceable modules are on the outside wall of the satellite facing space, enabling replacement in orbit for any number of the identical modules of the group and the rest of the payload on the inside of the same wall.
5. A payload module interface design according to claim 4 where modules on the outside of the panel are removable and replaceable with the minimum performance degradation.
6. A thermal control method applicable to payload units placed on the outside surface of the satellite panel facing space.
7. A method for replacing payload modules in orbit.