The Case for Space by Robert Zubrin;

Author:Robert Zubrin;
Language: eng
Format: epub
ISBN: 9781633885356
Publisher: Penguin Random House LLC (Publisher Services)

SATURN EXPRESS

It seems to me that the Breakthrough Initiative needs a near-term mission that can act as a transition to its visionary goal of interstellar travel. I have a concept for this, which I call “Saturn Express.” The basic idea is to create an ultrafast sail craft that can enable near-term exploration of the outer solar system while demonstrating the potential for more advanced incarnations to go to 550 AU, and then the stars.

So consider: at 1 AU, solar light pressure is nine micronewtons per square meter. So a sail craft with an areal density of 1.5 g/m2 would experience an acceleration away from the sun of 0.006 m/s2, which is exactly the same as the gravitational acceleration exerted by the sun at 1 AU. These two forces would balance, at 1 AU and all other distances, since they both go down with the inverse square of the distance. Therefore, such a craft released with escape velocity from Earth would move out in a straight line along the tangent to Earth's orbit at the Earth's orbital speed, which is 30 km/s, or 6 AU/yr. It would thus be able to reach Jupiter in about 0.8 years, Saturn in 1.5 years, Uranus in 3.2 years, and Neptune in 5 years.

Saturn would be an excellent first target because it is of such great interest to exobiology. If we have a sail with an areal density of 1 g/m2 (one micron thick, which should be doable) and an area of one hundred square meters, it will have a mass of one hundred grams. This leaves fifty grams for the spacecraft. The configuration could be like a parachute, with the sail craft like the parachutist astern of the sail, which would be billowing out ahead of it. This would be passively stable, with the concave side of the parachute pointing toward the sun, which would also be toward the Earth once it was out far enough, providing a high gain reflector. The sail craft would mount a strobe light, blinking with a power of one hundred watts for one millisecond every one thousand seconds. It would have an average power consumption of 0.0001 watts, using up 0.88 watt-hours per year. By looking at it with Hubble or Webb, we could track its speed via its Doppler shift. If the craft could be targeted to fly behind Enceladus, we conceivably might be able to look for the spectrum of organic molecules launched into orbit by its plumes.

That's the basic idea. By leaving the multimegawatt laser for later, Breakthrough Starshot could have something flying soon, on a budget well within the means of Yuri Milner. It would be a profound demonstration of fast sail technology, directly traceable to more advanced versions with potential for interstellar missions.

I sent a write-up laying out this plan to the Breakthrough Starshot Foundation in 2018. Let's hope they go for it.

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