Background of the Invention Small (micro) satellites have been known to be using the surplus payload capability of larger-sized launchers/launch vehicles in order to obtain cheap launches into space as secondary payloads.

A well-known example of a type of launch vehicle secondary payload carrier is shown in Figure 1. As shown in the Figure, the so-called"ASAP-5" installation structure 30 available for satellites on Ariane 5 ("ASAP"denotes Ariane structure for Auxiliary Payloads) comprises a number of microsatellites, each of up to 100 kg mass, which are in turn mounted on an annular platform beneath the main (primary) payload 35. It is to be noted that the space available 36 for the secondary satellite (s) is limited by the need to install it beneath the main payload 35 around the central payload adapter 37. Further, the mass available is limited by the load carrying capacity of the structure 38 beneath the attachment/release units 39, so that while in the shown example of ASAP-5 the complete structure can typically carry up to 800 kg mass of satellite (s) load, the individual attachment points can only typically carry less than 100 kg mass of satellite (s) load.

Objects and Summary of the Invention The present invention aims to overcome or at least substantially reduce some of the above-mentioned drawbacks.

It is the principal object of the present invention to provide an improved secondary payload satellite design which provides an increase in the available mass and volume for the spacecraft.

In broad terms, the present invention resides in the concept of providing an improved satellite design, carrying onboard propulsion, with bridging means which cleverly bridges two of more of the launch vehicle attachment

points/locations such as to permit the available mass and volume for the spacecraft to be increased.

According to the present invention there is provided a satellite comprising: an onboard propulsion system; an inner structural member; a plurality of outer structural members; said inner and outer structural members being mechanically coupled together to provide a multi-compartment facility; and wherein each said outer member is coupled to a different attachment point/location of a launch vehicle associated therewith to permit the different attachment points/locations to be mechanically bridged.

In accordance with an exemplary embodiment of the invention which will be described hereafter in detail, there is provided a central inner structural member and opposing sides of said central member are each attached to an outer structural member.

Conveniently, there may be two separate attachment points/locations for use in the invention. Additional attachment points/locations could be readily provided, if desired.

Advantageously, the inner structural member is arranged to provide a first structural compartment box and the outer structural members are arranged to provide a plurality of outer structural compartment boxes.

In this connection, it is to be appreciated that the first structural compartment box could be configured to carry a thruster and that the outer structural compartment boxes could each be configured to carry part of the onboard propulsion system, a propellant tank for example.

The proposed secondary payload satellite design is advantageously compact and simplified and it can be implemented at reasonable cost.

The above and further features of the present invention are set forth in the appended claims and, together with advantages thereof, will become more clear from consideration of the following detailed description of an exemplary embodiment of the invention given with reference to the accompanying drawings.

Brief Description of the Drawings Figure 1 is a schematic of the ASAP-5 structure which is an example of a known type of launch vehicle secondary payload carrier; and Figure 2 is a schematic plan view of a satellite embodying the present invention.

Detailed Description of an Exemplary Embodiment of the Invention Referring to Figure 2, there is shown therein a schematic plan view of a preferred satellite design 10 embodying the present invention. As shown in the Figure, the satellite design 10, carrying an onboard propulsion system 6, has a radial axis of symmetry (generally indicated in broken line). The satellite design 10, comprises three box structure compartments 1,2, 3 in the form of a central box structure compartment 1 and two outer box structure compartments 2,3.

As shown, the two outer box structure compartments 2,3 are preferably configured to contain main propellant tanks 6 of the propulsion system which are in turn located in the vicinity of/above the two launch vehicle attachment points/locations 4,5 to which they are appropriately connected by a rigid structural interface member (not shown). In this connection, it is to be also noted that the particular positioning of the two propellant tanks 6 above the two launch vehicle attachment points/locations 4,5 is such as to reduce/minimise the load paths for these heavy items. This consideration provides a definite advantage over known arrangements.

Thus, in the described embodiment, the three box structure compartments 1,2, 3 are so arranged to bridge mechanically the two separate attachment points/locations 4,5, permitting the available mass and volume for the spacecraft to be effectively increased.

As also shown in Figure 2, the central box structure compartment 1 is preferably configured to carry a central thruster 7 which is arranged to point outwards from the centre of the launch vehicle (not shown) for launch.

It is to be appreciated that the onboard propulsion system 6 may be a liquid propulsion system. Alternatively, the onboard propulsion system 6 could equally be in the form of a hybrid (liquid/solid) propulsion system.

Having thus described the present invention by reference to a preferred embodiment, it is to be appreciated that the embodiment is in all respects exemplary and that modifications and variations are possible without departure from the spirit and scope of the invention. For example, whilst in the described embodiment there are provided three box structure compartments for mechanically bridging two separate launch vehicle attachment points/locations, the arrangement could be readily modified to provide a multi-box structure compartment facility having four, five or more box structure compartments for mechanically bridging three or more separate attachment points/locations. The above-discussed arrangement could also be appropriately modified to carry additional thrusters and/or additional propellant tanks, if desired.