![]() ![]() Again an antenna could have several beams and several feeds. You've correctly identified that it could come from a phased array or otherwise and so you already understand a beam doesn't have to associate 1 to 1 with a feed, though it could do.Īntenna = usually the overall assembly of a reflector and feeds, or just feeds if it is a direct radiating antenna. The answer may not be as clear cut as you are hoping, firstly because of terminology and then because of the architecture possibilities on a communications payload.įeed = feed horn, as you've correctly identified in the first photo with numbersīeam = a coherent rf field. From Spacelfight 101.Ībove: Screen shot from Inmarsat-5: Overview Brief for ArcticĪug 2014, pre F4, but showing layout of individual beams. Original image is huge!Ībove: Inmarsat-5 Coverage Map – Credit: Inmarsat. From Spaceflight 101Ībove: Inmarsat-5 F1 & F2 – Photo: Boeing. Is this done the good ole' fashioned way? Is it done using articulated, movable feed horns, or perhaps tilting dishes?Ībove x2: cropped from Spaceflight 101 Boeing images below:Ībove: Inmarsat 5-F1 (F4 Identical) – Photo: Boeing. Question 2: I don't see any evidence of phased arrays (though that doesn't mean they aren't there) so I'm wondering how the six steerable spot beams are generated! Is one uplink and the other downlink? If not, how does the arithmetic work? Question 1: I thought I could get 89 transponders by counting the feed horns on one side, but there are suggestions that there is a symmetric array on the other side. The high-capacity spot beams are fed by twelve 130-Watt traveling-wave tube amplifiers while the regular communication beams use bent-pipe repeaters and 60:48 TWTAs. Inmarsat 5-F4 hosts two transmit and two receive apertures, and six steerable spot beams deliver a high-degree of flexibility to respond to changing demands and direct additional capacity where it is needed. If you look at the next image, it seems to suggest a second set of 3 dishes, with perhaps dozens of more transponders:Ībove: Artist’s concept of a Global Xpress satellite. The problem with my arithmetic is that there is a little bit of a dish peeking out at the bottom, and I don't know what to do with it. Here's my arithmetic:Ībove x2: Photo: Inmarsat from Spaceflight 101.Ībove: Cropped, from this found at Defense Talk. And when I look at illustrations of the fully deployed satellite and estimate the geometry, the width divided by distance to dish is a similar ratio to the diameter of the earth divided by the GEO distance. I think I can get to approximately 89 Ka-Band transponders by adding up all of the feed horns arranged as focal plane arrays for the three side-mounted dish reflectors. Based on Boeing’s BSS-702HP satellite platform, each weighs in at around 6,100 Kilograms and hosts 89 Ka-Band transponders, supporting high user download speeds of 50Mbps and uplink of 5Mbps. The four Inmarsat-5 satellites are essentially carbon copies, using the same satellite platform and featuring identical payloads. Spaceflight 101's article Inmarsat 5-F4 Satellite Overview contains a lot of helpful discussion and excellent images. I've included many images in order to save the time of readers each doing their own image search. In this case I think it really needs to be since the question is a bit complex I'm trying to understand how all these components interact. ![]() Note: This is an old-style question meaning that it is a bit on the long side.
0 Comments
Leave a Reply. |