Value chain · CLM-0977
In plain terms
In 1978 Boeing worked out how the timing reference should fan out across the kilometre-wide transmitter. The choice of how many branching levels to use was tied to how big each controlled patch of antenna could be and how tightly each level had to hold its timing: bigger patches need more levels controlled down to the individual tube, and each level then gets only two degrees of timing error at the reference frequency.
The claim as recorded
The 1978 Boeing briefing traded the reference-phase distribution tree directly against subarray size and per-level phase budget: a nine-node tree "suffers from poor reliability, poor phase randomization"; a four-node tree "may be a viable candidate if 10 m x 10 m subarrays are retained and phase control is exercised down to the klystron level"; a three-node tree "may be possible if phase control is exercised at the subarray level only, and subarray size is reduced to 5 m x 5 m"; and "even with 4 m x 4 m subarray, the 4-level system will require a total (1 GHz) phase accuracy of 2 degrees per level to achieve a 96% efficiency including tilt". The layout adopted for reliability analysis is a four-layer tree with 20, 19 and 19-way dividers at sector, group and subarray, 7,220 subarrays, triple redundancy at the first layer and double at the second.
Evidence behind this: T3-contractor briefing, a design trade stated with its numbers; attributed by the document itself to the LinCom report (SRC-462).
Scope and limits
A BRIEFING CHART SERIES; THE TRADE IS STATED, NOT DERIVED HERE. The numbers are design candidates in December 1978, superseded in detail by the 1979 Phase II budget (CLM-0978). The 96 per cent figure includes tilt and is not the same quantity as LinCom's 96 per cent at 6 degrees (CLM-0980).
What it assumes
The 2 degrees per level is stated at 1 GHz, the reference distribution frequency of that design, not at the 2.45 GHz power frequency.
Where it comes from
PDF p.119, "POTENTIAL PHASE DISTRIBUTION TREE LAYOUTS", raw and normalised: the nine-node, four-node and three-node sentences and "Even with 4 m x 4 m subarray, the 4-level system will require a total (1 GHz) phase accuracy of 2 degrees per level to achieve a 96% efficiency including tilt. This will require stringent design criteria. A possible 3 m x 3 m subarray could be accommodated by a 32 x 16 x 16 x 8 four node distribution system." PDF p.189: "The phase distribution network is a four layer tree. The first, second and third layers have 20, 19 and 19 way power dividers respectively at the nodes of the network. The first layer is called sector, the second group, the third unit, the fourth subarray." PDF p.121: "20 triply redundant sections at the first level, 19 doubly redundant paths at the second level, and 19 non-redundant paths (cable and electronics) at the third level (i.e., 7220 subarrays)." PDF p.108: "Lincom Inc., the designer of the baseline phase control system"; a fibre-optic cabling study "yielding a potential 20:1 reduction in phase error due to cable temperature fluctuations".
Basis: tree nodes; subarray side in metres; degrees of phase accuracy per level at 1 GHz
Related records
- Answers question
- QST-013 not published in this release
Cite this
energyaperture.com/c/clm-0977
CLM-0977, Energy Aperture, as of 1978-12.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-456
- CLM-0979The three designs disagreed about what the guide signal from the ground should look like. One used a pair of tones either side of the...CLM-0981Smaller patches tolerate more bending: halving the patch from 10 m to 5 m doubles the allowed tilt for the same half-per-cent loss. A...CLM-0995The whole ten-kilometre satellite was designed to sway once every fourteen minutes, and the antenna was required to be at least as stiff as...CLM-0998With the top of a five-kilometre section of the satellite two hundred degrees Fahrenheit hotter than the bottom, the estimate has its free...