Exploring the Unknown - NASA's History Office

EXPLORING THE UNKNOWN 33
6. How can Hughes expect to do so much better than others? The answer does not
lie in any startling but questionable innovations, inventions or break-throughs. Rather, the
answer lies chiefly in application of the Hughes brand of System Engineering, plus exploiting
Hughes competence in low-noise reception and traveling-wave-tube development.
The starting point was to assume a quasi-stationary orbit (satellites held within about
5˚ angular limits of desired point on the stationary orbit), to be put there by a Scout booster.
The limited payload weight to 30 lbs on the basis of Chance-Vought performance predictions,
or to 25 lbs on derating the predicted velocity by 800 fps. This obviously limits
the satellite transmitting power, energized from solar cells, to a watt or so. [3]
Transmission at or near 2 kmc (the accepted optimum frequency for space communication)
favors high antenna gain and use of traveling-wave-tubes. The nearest to a breakthrough
was the assurance by Dr. J. T. Mandel of the feasibility of developing a 2.5 watt
periodic PM focused 2 kmc high efficiency traveling-wave-tube of one pound, including
its INDOX VI focusing magnets. The low satellite power is handled at the earth terminals
by low noise (cooled maser or parametric) reception and very high antenn [sic] gain
(58 db). In achieving the latter at reasonable costs, the quasi-stationary position of the
satellite avoids the need for full azimuth and elevation control which has been made even
80 ft steerable parabolas so expensive. At similar cost, the beam from a 150 ft truncated
parabola can be steered through a +5˚ range. Thus, the burden is put on the earthterminals,
where it belongs. The satellite antenna design is a compromise between using
an omni-directional antenna for maximum simplicity and using a 17˚ beam for maximum
gain. While either of these extremes could be fatal, the compromise of a spin-stabilized
doughnut pattern provides 6 to 9 db gain, with simplicity. Finally, with adequate design for
a 14 db S/N ratio, the addition of frequency modulation raises the S/N ration to a commercial
32 db.
7. Because of the importance of assessing feasibility of staying within the weight
capability of the Scout booster, Ed Felkel was named to the Task Force to analyze the
weight of the payload package. His report (attached in Appendix B) shows confidence of
keeping it safely within weight.
8. Putting the satellite in orbit and keeping it in position entails a sequence of individually-practicable
operations within today’s state of the art. Cumulatively, however, the
multiplicity of stages plus operations of velocity adjustment, de-spinning, re-spinning and
incremental orbit adjustment present a currently-indeterminable hazard to the success of
any one firing. It is believed that a combination of (a) careful and conservative engineering
with step-by-step pre-testing, (b) adequate training on analog simulators, (c) study of
any troubles in earlier NASA Scout firings, and (d) adequate determination of the cause
of any initial Hughes failure, will result in adequate probability of success within the programmed
three tries. Admittedly, there can never be certainty of success in only three
attempts. However, a fourth or subsequent firings should not increase the program cost
proportionately.
9. As might be expected, the Task Force study has resulted in significant system
improvements, by Dr. Rosen as well as by Task Force members and others. For example,
the payload configuration has been broadened to improve spin-stability and has been stiffened
by a central column. More important, perhaps, has been the swing away from design
primarily for television relaying, with additional narrower i-f channels for other communication
services, toward the simpler and more flexible and potentially rewarding
approach of coordinated use of a broad-band single-channel repeater simultaneously by
several earth-terminals. This mode of operation requires that earth-terminals equalize
their transmitting powers by monitoring the spectrum from the satellite, rather than
depending on AGC of separate i-f channels in the satellite to prevent a too-strong earthsignal
from weakening other retransmissions. Also, this mode of operation provides flexi-