Value chain · CLM-0954
In plain terms
The 1975 designers worked out how much their kilometre-wide antenna would bend, precisely so they could decide how good the beam-steering correction had to be. The biggest bend came from building it slightly wrong in the first place - roughly three quarters of a metre to a metre and a half at the edge, depending on how the stated angle is read - and that does not move. Heat bending could be held to a few centimetres if the top and bottom of the truss were kept within four degrees of each other.
The claim as recorded
The 1975 MPTS study carried out a thermal and structural analysis of its 1 km, 40 m deep transmit antenna specifically to set the requirements for phase front control, and it found the largest deformation to be static. Transcribed from the render, Vol III p.28: "A thermal/structural analysis has been carried out to determine deformations to be used in establishment of requirements for phase front control." Result: "The assembly tolerances were found to be the largest source of deformation with a worst case tip deflection of 0.17 degree. Deflections due to thermal bending can be kept below 1 arc-min if thermal gradients between the upper and lower primary structural caps can be controlled to less than 4 K. Deflections due to loads were found to be insignificant." On a 500 m half-span, 0.17 degree is 1.48 m if read as a straight line from the centre, or 0.74 m if read as the tip slope of a uniform bow, the reading under which 1 arc-min is 7.3 cm (CALC-109); the page does not say which.
Evidence behind this: T3-primary-report. The design study's own structural analysis of its own antenna, which is the only place such a figure could come from for this design.
Scope and limits
A 1975 PRELIMINARY DESIGN, AND AMPLITUDES ONLY. The modal shapes and modal frequencies CLM-0907 records as missing are still missing: this gives deformation amplitudes and their causes, not modes, and the static assembly error it identifies as largest is exactly the kind a phase-control system calibrates out rather than tracks. No dynamic amplitude is given anywhere in it. The thermal figure is conditional on a 4 K cap-to-cap gradient the document sets as a requirement rather than demonstrates as achieved. None of it transfers to a different geometry without its stiffness: the helical CASSIOPeiA design has no stiffness data in the register, so this record bounds the 1975 planar truss and nothing else.
What it assumes
No assumptions are recorded against this claim.
Where it comes from
This is the project's own working, shown in full:
All spans from SRC-451 Vol III. The phase-front-control sentence and the 0.17 degree result are at PDF p.28; "The MPTS antenna is 1 km in diameter by 40 meters deep" at p.34, matching at the normalised level; the bay dimensions at p.39; and p.25 states the electronic control system is "shown to desensitize the tolerance on structural assembly accuracy". The text layer of Vol III is letterspaced on p.28, so those two sentences were read from the render and confirmed present by a squashed-text match, which is the only match level that reaches a letterspaced page; they are reported as transcribed, not quoted raw. CALC-109 reproduces the document's 1 arc-min figure from the stated 4 K gradient with a physically sensible coefficient of thermal expansion, 5.8e-6/K.
Related records
- Answers question
- QST-013 not published in this release
- Contradicts
- CLM-0907 No source held here gives a computed model of how a kilometre-scale structure of this kind... in part - its statement that no deformation amplitudes for a kilometre-class deployable are held; that record is narrowed rather than withdrawn since its modal half stands
Cite this
energyaperture.com/c/clm-0954
CLM-0954, Energy Aperture, as of 1975.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-451
- CLM-0959The original 1975 calculation found the satellite's radio noise would be fine for ordinary and troposcatter radio links and a problem only...CLM-0960The 1975 study found the satellite's harmonics - the multiples of its transmit frequency - would trouble radio astronomy at the second and...CLM-0961Everything in the 1975 interference analysis is for one satellite. The study itself says that a hundred of them would raise the noise and...CLM-0965In 1973 an astronaut on Skylab put together two long poles from short sections in just over two hours, about six minutes per join. A 1975...CLM-0966In 1975 the antenna alone was expected to take one to two years to assemble in orbit with about fifty people, and robot arms were judged...CLM-0968The 1975 antenna study worked out how hot the middle of the transmitter gets depending on how efficient the tubes are and how tightly they...CLM-0969If the tubes are only 70 per cent efficient, the transmitter's own face is not big enough to get rid of the heat they make, even spread...CLM-0972If you take a 1975 estimate of how fast people could build structure in space, checked against one Skylab task, and apply it to the 1978...More on the source page.