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It would be the same blimp on Earth, except with some modifications like anti-corrosion coating. The blimp will use helium as the gas to keep it aloft. Would it last long enough to be useful?

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So far, we have only two actual examples of balloons deployed into Venusian atmosphere, the two Vega program balloons from June 1985. They were identical in design, 3.4 m diameter helium filled balloons made of teflon cloth matrix coated with teflon film, each with a gondola suspended on a 13 m long tether. You can read more about them on Goddard Space Flight Center pages: Vega 1 Balloon and Vega 2 Balloon.

Both released to near-equatorial latitudes into night side of Venus, Vega 1 Balloon was active for 46 hours and 32 minutes and traversed distance of 11,600 km, of which 3,100 km in Venusian day side. Vega 2 Balloon, released 4 Earth days later, was active for roughly 60 hours (GSFC page quotes same final transmission time as for Vega 1 Balloon, but that seems to be an error), and traveled in total of 11,100 km, 3,700 km of that in the day side. Both of their westward paths were tracked by 20 ground radars using Very Long Baseline Interferometry (VLBI) technique:

   Diagram of the paths of the two Vega balloons

   Diagram of the paths the two Vega balloons took in Venusian atmosphere. Source: The Venus Balloon Project (PDF)

It is unclear for how long balloons themselves lasted, since VLBI requires a radio source which were housed in the balloons' gondolas, but we know that both maintained average flight altitude of 53 to 54 km with variation of ~ 3 km (likely due to lee waves) and stable latitude, mean environmental pressure of 535 mbar (0.53 atm) and temperature range of 300 to 316 Kelvin (~ 27 to 43 °C).

So we know that relatively stable flight of aerostat dirigibles is possible on Venus at altitudes within the layers of sulfuric acid clouds and above most of them, and this flight can last for days with over 30 years old technology and design based on just as old knowledge about the atmosphere of Venus. We could probably, we should, do a lot better nowadays;

One proposed design is the use of Phase Change Balloons for Venus which could navigate at altitudes between 38 and 64 km, if filled with water/ammonia and helium mixture:

                                                     Phase Change Balloons for Venus

                  Phase Change Balloons for Venus. Image source and credit: Dr. Ronald Ross, JPL

Such design could be stabilized (in liberal interpretation of the word, extreme altitudes would be quite stable, but it would still oscillate up and down in altitudes between gas to liquid and vice versa phase change temperatures) to higher average flight altitudes by using dark, heat absorbing layer solar balloons beneath the transparent teflon-coated and sulfuric acid resistant surface, and then depending on the sun to heat up the phase-transitioning water/ammonia mixture faster to gaseous phase at higher altitudes, where there's higher solar flux on Venusian day side. It would still depend on heat from the atmosphere alone on the dark side of Venus, but one good thing about such design is that water and ammonia are much larger molecules than helium and will escape the balloon of same basic materials much slower, so technically the balloon part of the setup could last longer. Lowest altitude could be increased by increasing ammonia to water ratio of the mixture.

Another design is simply improving on the Vega balloons, like e.g. ILC Dover and NASA Wallops were doing back in 2007:

   enter image description here

This is an 18 ft (5.5 m) diameter balloon that is also teflon covered and helium filled, but includes a more reflective aluminum layer, a layer of mylar to prevent helium from escaping it, and a Vectran inner layer with polyurethane coating for structural strength and adhesion. They were designed to coast at about 56 km altitude, stable to under ±1 km.

And there are a couple of other balloon designs on the table for exploration of Venus and at various Technology Readiness Levels, like e.g. Venus In Situ Explorer that is in fierce competition for selection under the New Frontiers Program (see more in e.g. 2008 Opening New Frontiers in Space: Choices for the Next New Frontiers Announcement of Opportunity or VEXAG documentation) like this one, but those are low altitude balloons and don't directly apply to your question.

So, in conclusion, we can say with some confidence that days long flights at altitudes above most sulfuric acid clouds with small and in atmosphere deployable balloons is possible, and with smart design learning from past experience, they could last a whole lot longer. The NASA Wallops design above was meant to last for several circumnavigations of Venus, each taking approximately four days to complete. It then depends on the choice of your mission objectives and their prioritization how successful you would consider such a mission and what you can do with its science return. But there are designs, some materialized and being tested, others still having to achieve that, that would enable all kinds of flight profiles, from selection of injection latitudes to vertical and zonal ranges.

For some more information on the environment you'll be dealing with and references linked therein, also see:

And other questions tagged as and (link to questions including both tags).

Other references:

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