FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1962
1962 - 2081.PDF
464 Missiles and Spaceflight (continued from page 432) COMSAT COMMENTS THIS discussion of the communication satellite design study carried out by the Royal Aircraft Establishment for the GPO, first details of which were published in our August 16 issue, has been contributed by Dr W. F. Hilton, formerly head of the astronautics section of the advanced projects group of Hawker Siddeley Aviation. WHILE one may applaud the RAE's thorough if somewhat belated statement of British communication satellite policy, there appear to be several inconsistencies in the proposed scheme which earlier publication might have modified. Orbit and lifetime Two statements in the first column of the article ("Britain's Comsat Plans," page 245, August 16 issue) are contradictory. First: "It had been suggested that elliptical orbits were preferable on the grounds of increased payload at greater heights for much of the orbital period: this appeared valid if the launch vehicle could not place a reasonable payload into a sufficiently high circular orbit, but did not apply for the ELDO vehicle." By contrast, we read: "With the launch vehicle as envisaged (with an HTP/kerosine third stage), RAE con clude that the full communications requirements cannot be met." In fact an anticipated traffic requirement for 1,000 telephone circuits is pared down to several hundred by the choice of orbit. Thus Britain would be faced with two alternatives shortly after launching its equatorial comsat system: (a) Premature scrapping and replacement with satellites of a new and larger type, and hence no need for the original small ones to have a five-year life, or (b) Additional satellites of the existing small type, together with duplication, triplication or even worse of Goonhilly-type ground stations all round the world. Why not launch the desired 1,000-circuit satellite into an inclined elliptical orbit to start with? True, the orbit corrections will use up the available propane supplies in perhaps one year instead of five, but what magical radio output device would RAE propose which would last five years? The travelling wave tube is the only trustworthy output stage, and has a one-year life at the present time. New devices and improvements must not be trusted in inaccessible communications links of the cable and satellite type. It is entirely a question of balancing the lifetime probability of control in the proposed orbit against the lifetime of the electronics. The best design at any moment must give equal weight to the appropriate laws of Nature, and the properties and reliability of the various items of hardware. It is indeed unfortunate in this respect that five branches of the Government (Ministries of Defence, Aviation, Air, Science and the GPO) all have an interest in space, and that the communication satellite is divided between two of these. A single design team would yield a better balanced design. GPO Requirement. The GPO demand a 24-hour service, even with one satellite "out." While the need for 24-hour service can be questioned, the problem of "outage" must always be met in com munications. The circular orbit has to employ double the number of satellites to eliminate outage. The 63° inclined ellipse with apogee at 20°N can give continuous service in the northern hemisphere, even with one of its nine satellites out, although it will give predictable gaps in the service to the southern hemisphere. This is probably accept able, as little revenue arises from this region, and calls can be stock piled for an hour or so in a region where no alternative service exists. While the North Atlantic is the most lucrative space-phone link, we have little hope in 1967 of dislodging American interests from the lead they have already started to build up in this region. Our attention should be directed towards the smaller cities of the British Commonwealth, and their interconnection. This demands a some- FLIGHT International, 13 September 1%2 what different type of satellite from Telstar; the 1,000 circuits need to be broken down into smaller units, say eight of 60 circuits and four of 120 circuits each. Complication on the ground in backward countries is thereby balanced against sophistication in the satellite. True, the transatlantic use would be slightly more complex, particularly for TV relay purposes, but I for one am not convinced of the British need for extensive relaying of American television to the United Kingdom. Turning now to the 24-hour requirement, the USA will have provided this service before Britain enters the field at all. The article does not mention the possibility of supplementing their service by a "daylight only" service. The US having scooped the whole 24 hours of the lucrative geographical links, we might scoop the equally lucrative peak periods in less advanced parts of the world. A 12-hour service can be given with half the number of satellites needed for a 24-hour service. Indeed, it is true to say that an orbit can be tailored to cover any specified set of places and times. The GPO could be more imaginative in their specification of requirement, particularly as they have a much wider experience of world communications than have our American friends. Satellite layout The fifth design factor is quoted as: "Layout of the satellite must be such that the minimum of shadowing of the solar cells by other parts of the satellite occurs." Surely the novel cruciform arrangement is bad in this respect? Solar cells on a square or polygonal satellite would be better. Equatorial launch site and relay stations Although the equatorial orbit plane has the advantages mentioned in the article, the need for an equatorial launching site is not unduly stressed. The £20m cost of building an equatorial "Woomera" is mentioned, but the recruitment of suitable technical staff would be a stumbling block. Apart from the cost of equatorial sites, the inclined ellipse is more economical in the number of satellites needed. Using the basis of the article for costing, we find:— Initial capital cost im Three guidance stations .. .. .. .. .. 4.5 16 communications ground stations .. .. .. 24.0 (9 + 5 dud) satellites 3.0 (9 + 5 dud) satellite launchings 21.0 Total 52.5 This represents a saving of £32m on the proposed capital cost. Each satellite gives more than twice the number of phone circuits, matching the anticipated demand, but has somewhat less than half the expectation of life. In addition to supporting Woomera, we must remember that Australia is politically more stable than most equatorial countries and islands, and its defence is already arranged. Conclusion If Britain is to go into space at all, surely communica tion satellites are our natural first interest, unlike the USA and USSR. Finally, as a martyr to the comsat cause, could I make a plea for a more vigorous policy, and earlier deadlines? TITAN III AUTHORIZED The US Department of Defense announced on August 20 the selection of the Martin-Marietta Corporation as systems integra tion contractor for the Air Force Titan HI system. The Titan III, for which the DOD requested and received $204m in fiscal year 1963, is to be a standardized launch vehicle. It will be capable of a first-stage thrust of over 2m lb, and will be able to perform a wide range of manned and unmanned space missions during this decade. It will form a part of the national launch vehicle programme meeting requirements in the 5,000 to 25,0001b—payload bracket for relatively low orbits. The Titan HI system, designated Standard Space Launch System 624A, is based upon technology and hardware developed in the liquid and solid ICBM programme. It is the first launch vehicle to be developed by the DOD from the outset as a space booster. (Current military space boosters are all TRBMs or ICBMs
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
