Future Venus Missions Options

[Phil Stooke]

Oh well, might as well start that new topic since it's already well advanced in the Juno area...

My perspective on landers is as follows. All the landers we've had so far were dropped blind onto an essentially unknown surface. Any future landers can be targeted for specific terrains. It really is not true that we have had representative landings. Even a descent image or two, a panoramic photo plus a bit of surface composition, from a simple Venera-class lander just updated a bit, would be useful if we could put several down at well chosen targets. My choices would be:

Examples of the main plains units (smooth, fractured, ridged)

tesserae

high elevation radar-bright tesserae

large fresh lava flow unit ('fluctus')

crater dark parabola

crater ejecta outflow unit

dunes area.

And I have always assumed, rightly or wrongly, that it would be relatively easy to put these down, so they ought to be fairly inexpensive as planetary landers go.

Phil

[Gerald]

I was wondering whether any fiber is known to be strong and heat-resistant enough, and found aramids, e.g. M5, possible candidates. I'm just not sure whether thin fibers would also be sufficiently weathering resistant under the harsh environmental conditions in the Venus atmosphere.
This is before thinking about the dynamics of such a tether in a dense and stormy atmosphere.
In space in Earth orbit, at least, some tether experiments were already performed in the 1990s (SEDS-1 and SEDS-2).
(More space tether missions.)

[mcaplinger]

In space in Earth orbit, at least...

I've talked with people who worked on TSS-1 and -1R and they had quite a few stories about it. Let's just say that I don't think tether technology is quite ready for a Venus mission.

[JRehling]

Reading the afore-linked reports, I think I've been disabused of the notion that an idealized aerobot, allowing for mobility at the surface, would be implemented anytime soon. It's possible in principle, but isn't part of the VEXAG report, and the complexity of more modest aerobot concepts implies the greater complexity of surface-to-clouds-and-back aerobots.

One important pragmatic consideration: Descent is more expensive than ascent, requiring energy to compress the helium and generally being rate-limited, while ascent is comparatively cheap and easy. For hypothetical missions that would cool at height and then descend and operate quickly, this would be a problem because there would be substantial thermal load accumulating during the slow descent.

The most modest aerobot/balloon missions would be, like the Soviet Vega balloons, operating only at high altitude, studying only the "local" atmosphere with no surface science. A more ambitious option is to perform surface science from "afar", observing in IR from altitude, but here there's a tangle of tradeoffs as cooler temperatures keep the aerobot in the clouds. Operating below the clouds, for better surface visibility, means higher temperatures. The clouds themselves entail a harsh chemical environment. And altitude control entails engineering complexity with added mass and points of failure.

There are a variety of possible aerobot missions at Venus, but there isn't going to be a be-all end all option that can visit the surface multiple times anytime soon.

Airplanes create other options, with some of the same tradeoffs. One possibility, unique to Venus, is an airplane that would operate in perpetual sunlight, flying east against the atmosphere's rotation, as the planet rotates beneath it. The clouds, again, create the unfortunate tradeoff: You get solar radiation for solar power or a view of the surface, but not both.