In 1996-1997, I became extremely enthusiastic about the space exploration prospects for aerobot technology. There seem to be at least 10 celestial bodies suitable for aerobot deployments: Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Enceladus, Europa, & Titan. I even published my master's thesis on the subject.

At the time, Kerry Nock was leading a group of scientists at JPL who were studying the subject with institutional funding. They did several experiments and published some of their results:

  • ALtItude Control Experiments (ALICE)
  • Balloon Experiment at Venus & Venus Flyer Robot (BEV & VFR)

But in the nearly two decades since that time, there have been no aerobot missions (that I know of) and I've read very little about even proposed aerobot missions. Of those few I have encountered, they seem to get a little funding for study and then get abandoned in favor of more difficult missions.

I think an airborne aerobot on Titan must be one of the single most promising (in terms of discovering exobiology) and technologically feasible missions imaginable for the near future.

Why has this idea apparently been abandoned?

Are there scientific or engineering problems that make it impractical or too expensive? I have been unable to find any such issues myself. Or is it a political thing?

If DEPTHX (which strikes me as a kind of aerobot floating in water instead of air) got funded by NASA with the goal of developing technology that can explore the oceans of Jupiter's moon Europa (which first requires getting through miles of ice; no mean task), then why have there been no (or few) NASA or ESA funded projects for aerobots in less challenging environments like Titan or the upper atmosphere of Venus?

  • $\begingroup$ See also: space.stackexchange.com/questions/104/…. $\endgroup$ – gerrit Jul 17 '13 at 16:21
  • $\begingroup$ You include Earth. There's been plenty of in-situ research going on in the Earth atmosphere (: $\endgroup$ – gerrit Jul 17 '13 at 16:22
  • $\begingroup$ @gerrit thanks for your comment, and I suppose that's true, but there's been not much (that I know of) using what I think are some of the best ideas like reversible fluids for passive altitude control. $\endgroup$ – Osteoboon Jul 17 '13 at 16:25
  • $\begingroup$ Does "aerobot" in this usage mean buoyant crafts? Does it include planes like the one proposed to Mars? marsairplane.larc.nasa.gov $\endgroup$ – AlanSE Jul 17 '13 at 16:35
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    $\begingroup$ @RoryAlsop that's a good point. I think the best driver may be the search for exobiology. Many planetologists agree that Titan is one of the most promising bodies yet found that might harbor life. $\endgroup$ – Osteoboon Jul 17 '13 at 16:49

Aerobots occupy an intermediate position between landers and orbiters. Turns out they cannot do well some things that these two are capable of.

  • No ability to do geological studies. A big objection if you remember the main drive in planetary exploration today - the search for life, present or extant, or at least habitable conditions. You simply cannot have a second look at this piece of what might be clay over there. You can't grab it and put into SAM.

  • No predictability of a polar orbiter mission: you cannot plan a revisit cycle to spot changes in successive images (one of the reasons people are extremely enthusiastic about HiRISE). Neither can you set up regular relay links if you've got a rover or two down there.

Yes, there are many things you can do with aerobots, but most of them are about weather and the atmosphere. It would be fantastic to combine wide-area exploration (aerosols, magnetic field, chemistry analysis, vertical atmospheric profiles) by aerobots with landers and orbiters, but...

...money matters.

First, missions are de-scoped all the time in favor of modes with greater potential for results.

Second, planetary destinations are juggled around so that bodies where aerobots would be ideal are moved to the back of the queue. Why? Because in the present conditions Mars is our best bet to find (possibly extant) life. Look at Discovery where Titan Mare Explorer failed to score - and TiME was much more promising in terms of science payload than a venusian aerobot.

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    $\begingroup$ There may also be some psychological reasons that landing is preferred. Even if all the science could be done from orbit, the public perception would seem to be that one has not really "visited" a body until one has put "boots on the ground" (and humans wearing the "boots" is an even more significant). Popular perception matters for funding. $\endgroup$ – Paul A. Clayton Jul 31 '13 at 14:13
  • $\begingroup$ Well @DeerHunter I suppose you could be right in this. No doubt that money matters, but I think that a convincing, evidence-based argument could be made that an aerobot could collect much more data than a ground-based rover could. But of course I doubt we'll see a definitive answer without a NASA administrator weighing in on the question. So thanks for your thoughts. $\endgroup$ – Osteoboon Aug 1 '13 at 1:05

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