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13

A few months before Cassini made its mission-ending dive into Saturn's atmosphere, it skirted the region between Saturn's atmosphere and the innermost ring. From NASA Spacecraft Dives Between Saturn and Its Rings, emphasis mine, The gap between the rings and the top of Saturn's atmosphere is about 1,500 miles (2,000 kilometers) wide. The best models for the ...


11

The "radio frequency" system draws up to 111.7 W (PDF on Voyager design, table 2 on page 10). This is purely the power amplifier, modulation/demodulation is listed separately at another 11 W. Note that this has nothing to do with the dish. Those 23 W is what comes out of the antenna as radio waves. The dish reflects pretty much 100% of this.


11

We're working on it. You do need a little telescope on the spacecraft to serve as the antenna. You can have two-way laser communications. It may in fact be essential to achieve the required pointing accuracy. There are many modulation schemes -- that's not an issue. Pulse position modulation is a front runner. The upside is much higher data rates with ...


6

I haven't made an exhaustive survey, but I checked the major outer-planets missions. The Galileo spacecraft was designed with a 4.6-meter diameter high-gain folding dish antenna which was supposed to deploy somewhat like a folding umbrella; however, it jammed and didn't deploy fully, and the mission had to rely on a smaller antenna. I believe this is the ...


6

That antenna is a Cassegrain horn (or 'casshorn'). This is an evolution of the earlier horn-reflector antenna (paper that describes the design), where a horn radiates into a parabolic surface: The Cassegrain horn reduces the antenna size (long distance between the horn and parabolic dish) by introducing a hyperbolic reflector: The feed is now at position ...


4

Yes, Venera-4 had a radiator-cooler in the center of its dish. From https://www.laspace.ru/projects/planets/venera-4/ Передача информации со скоростью 64 бита в секунду осуществлялась через параболическую остронаправленную антенну (ОНА) диаметром ~2,3 метра. ОНА состояла из жесткой центральной части, в которую был встроен радиатор–охладитель, и раскрываемой ...


2

I'll add a little bit to Hobbes' excellent answer and detective work. I looked up a physical copy of the book linked there; Practical Conic Sections: The Geometrical Properties of Ellipses, Parabolas and Hyperbolas by J. W. Downs, Dover, NY, 1993 and found it a short but incredibly interesting and informative little book, if you like reading about conic ...


1

You modulate the signal for a comms laser the same way you do for radio antenna (effectively) so this isn't the issue. The problems are: Powerful lasers are heavy They require a fair bit of power They are not very robust, compared to a dish antenna, which can take a fair amount of damage from fast moving particles and just suffer incremental loss of ...


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