Editing Aerobot (section)

==JPL aerobot experiments==
By this time, the [[Jet Propulsion Laboratory]] (JPL) of the US [[National Aeronautics and Space Administration]] (NASA) had become interested in the idea of planetary aerobots, and in fact a team under Jim Cutts of JPL had been working on concepts for planetary aerobots for several years, as well as performing experiments to validate aerobot technology.

The first such experiments focused on a series of reversible-fluid balloons, under the project name ALICE, for "Altitude Control Experiment". The first such balloon, ALICE 1, flew in 1993, with other flights through ALICE 8 in 1997.

Related work included the characterization of materials for a Venus balloon envelope, and two balloon flights in 1996 to test instrument payloads under the name BARBE, for "Balloon Assisted Radiation Budget Equipment".

By 1996, JPL was working on a full-fledged aerobot experiment named PAT, for "Planetary Aerobot Testbed", which was intended to demonstrate a complete planetary aerobot through flights into Earth's atmosphere. PAT concepts envisioned a reversible-fluid balloon with a 10-kilogram payload that would include navigation and camera systems, and eventually would operate under autonomous control. The project turned out to be too ambitious, and was cancelled in 1997. JPL continued to work on a more focused, low-cost experiments to lead to a Mars aerobot, under the name MABVAP, for "Mars Aerobot Validation Program". MABVAP experiments included drops of balloon systems from hot-air balloons and helicopters to validate the tricky deployment phase of a planetary aerobot mission, and development of envelopes for superpressure balloons with materials and structures suited to a long-duration Mars mission.

JPL also provided a set of atmospheric and navigation sensors for the Solo Spirit round-the-world manned balloon flights, both to support the balloon missions and to validate technologies for planetary aerobots.

While these tests and experiments were going on, JPL performed a number of speculative studies for planetary aerobot missions to [[Mars]], [[Venus]], [[Saturn]]'s moon [[Titan (moon)|Titan]], and the [[outer planet]]s.

=== Mars ===
JPL's MABVAP technology experiments were intended to lead to an actual Mars aerobot mission, named MABTEX, for "Mars Aerobot Technology Experiment". As its name implies, MABTEX was primarily intended to be an operational technology experiment as a precursor to a more ambitious efforts. MABTEX was envisioned as a small [[superpressure balloon]], carried to Mars on a "microprobe" weighing no more than {{convert|40|kg|lb}}. Once inserted, the operational balloon would have a total mass of no more than {{convert|10|kg|lb}} and would remain operational for a week. The small gondola would have navigational and control electronics, along with a [[stereo imaging]] system, as well as a [[spectrometer]] and [[magnetometer]].

Plans envisioned a follow-on to MABTEX as a much more sophisticated aerobot named MGA, for "Mars Geoscience Aerobot". Design concepts for MGA envisioned a superpressure balloon system very much like that of MABTEX, but much larger. MGA would carry a payload ten times larger than that of MABTEX, and would remain aloft for up to three months, circling Mars more than 25&nbsp;times and covering over {{convert|500000|km|mi}}. The payload would include sophisticated equipment, such as an ultrahigh resolution stereo imager, along with oblique imaging capabilities; a [[radar]] sounder to search for [[subsurface water]]; an [[infrared spectroscopy]] system to search for important minerals; a magnetometer; and weather and atmospheric instruments. MABTEX might be followed in turn by a small solar-powered blimp named MASEPA, for "Mars Solar Electric Propelled Aerobot".

=== Venus ===
JPL has also pursued similar studies on Venus aerobots. A Venus Aerobot Technology Experiment (VEBTEX) has been considered as a technology validation experiment, but the focus appears to have been more on full operational missions. One mission concept, the Venus Aerobot Multisonde (VAMS), envisions an aerobot operating at altitudes above {{convert|50|km|mi}} that would drop surface probes, or "sondes", onto specific surface targets. The balloon would then relay information from the sondes directly to Earth, and would also collect planetary magnetic field data and other information. VAMS would require no fundamentally new technology, and may be appropriate for a NASA low-cost [[Discovery Program|Discovery planetary science mission]].
 
Significant work has been performed on a more ambitious concept, the Venus Geoscience Aerobot (VGA). Designs for the VGA envision a relatively large reversible-fluid balloon, filled with helium and water, that could descend to the surface of Venus to sample surface sites, and then rise again to high altitudes and cool off.

Developing an aerobot that can withstand the high pressures and temperatures (up to 480 degrees Celsius, or almost 900 degrees Fahrenheit) on the surface of Venus, as well as passage through sulfuric acid clouds, will require new technologies. As of 2002, VGA was not expected to be ready until late in the following decade. Prototype balloon envelopes have been fabricated from [[polybenzoxazole]], a polymer that exhibits high strength, resistance to heat, and low leakage for light gases. A gold coating is applied to allow the polymer film to resist corrosion from acid clouds.

Work has also been done on a VGA gondola weighing about {{convert|30|kg|lb}}. In this design, most instruments are contained in a spherical pressure vessel with an outer shell of [[titanium]] and an inner shell of [[stainless steel]]. The vessel contains a solid-state camera and other instruments, as well as communications and flight control systems. The vessel is designed to tolerate pressures of up to a hundred atmospheres and maintain internal temperatures below {{convert|30|C|F}} even on the surface of Venus. The vessel is set at the bottom of a hexagonal "basket" of solar panels that in turn provide tether connections to the balloon system above, and is surrounded by a ring of pipes acting as a heat exchanger. An [[S-band]] communications antenna is mounted on the rim of the basket, and a radar antenna for surface studies extends out of the vessel on a mast.

The [[Venus Atmospheric Maneuverable Platform]] (VAMP) is a mission concept by the aerospace companies [[Northrop Grumman]] and [[LGarde]] for a powered, long endurance, semi-buoyant inflatable aircraft that would explore the upper atmosphere of Venus for [[biosignature]]s<ref>[http://earthsky.org/space/new-study-ponders-possible-life-adrift-in-venus-clouds Astronomers ponder possible life adrift in Venus' clouds]. Deborah Byrd, ''Earth & Sky''. 31 March 2018.</ref><ref>[https://www.inquisitr.com/4850106/scientists-explore-the-possibility-of-life-hidden-inside-the-clouds-of-venus/ Scientists Explore The Possibility Of Life Hidden Inside The Clouds Of Venus]. Kritine Moore, ''The Inquisitr''. 1 April 2018.</ref> as well as perform atmospheric measurements.<ref name='Devitt 2018'>[https://www.sciencedaily.com/releases/2018/03/180330171302.htm Is there life adrift in the clouds of Venus?]. Terry Devitt, ''Science Daily''. 30 March 2018.</ref>

In April 2021 it was reported that NASA allocated work to design and test robotic balloons for future [[Observations and explorations of Venus|exploration of Venus]].<ref>{{cite news |title=Robotic Balloons To Explore Venus? This Northwest Company Is Working On It |url=https://www.nwpb.org/2021/04/10/robotic-balloons-to-explore-venus-this-northwest-company-is-working-on-it/ |access-date=9 May 2021 |work=Northwest Public Broadcasting |date=11 April 2021}}</ref>

=== Titan ===
[[Titan (moon)|Titan]], the largest moon of [[Saturn]], is an attractive target for aerobot exploration, as it has a nitrogen atmosphere five times as dense as that of Earth's that contains a smog of organic photochemicals, hiding the moon's surface from view by visual sensors. An aerobot would be able to penetrate this haze to study the moon's mysterious surface and search for complex organic molecules. NASA has outlined a number of different aerobot mission concepts for Titan, under the general name of Titan Biologic Explorer.

One concept, known as the Titan Aerobot Multisite mission, involves a reversible-fluid balloon filled with argon that could descend from high altitude to the surface of the moon, perform measurements, and then rise again to high altitude to perform measurements and move to a different site. Another concept, the Titan Aerobot Singlesite mission, would use a superpressure balloon that would select a single site, vent much of its gas, and then survey that site in detail.

An ingenious variation on this scheme, the Titan Aerover, combines aerobot and rover. This vehicle features a triangular frame that connects three balloons, each about {{convert|2|m|ft|abbr=off|sp=us|spell=in}} in diameter. After entry into Titan's atmosphere, the aerover would float until it found an interesting site, then vent helium to descend to the surface. The three balloons would then serve as floats or wheels as necessary. JPL has built a simple prototype that looks like three beachballs on a tubular frame.

No matter what form the Titan Biologic Explorer mission takes, the system would likely require an atomic-powered [[radioisotope thermoelectric generator]] module for power. Solar power would not be possible at Saturn's distance and under Titan's smog, and batteries would not give adequate mission endurance. The aerobot would also carry a miniaturized chemical lab to search for complicated organic chemicals.

Outside of JPL, other mission studies of Titan aerobot concepts have included studies of airships by MIT<ref>John Duffner, Michael Liu, Christophe Mandy, Robert Panish, and Geoffrey Landis, "Conceptual Design of an Airship Mission to Titan," paper AIAA 2007-6265, AIAA Space-2007 Conference and Exhibition, Long Beach, CA, 18–20 Sept. 2007 ([http://arc.aiaa.org/doi/abs/10.2514/6.2007-6265 paper] on AIAA meeting papers site retrieved 13 May 2015)</ref> and NASA Glenn,<ref>R. Heller, G. Landis, A. Hepp, and A. Colozza, "Heated-Atmosphere Airship for the Titan Environment: Thermal Analysis," {{doi|10.1061/9780784412190.047}}, ''Earth and Space 2012,'' pp. 425–433. (paper at [http://ascelibrary.org/doi/abs/10.1061/9780784412190.047 ASCE library], retrieved 13 May 2015; [https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20120012527.pdf pdf at NASA NTRS site, retrieved 13 May 2015)</ref> and a proposed Titan airplane proposed by NASA Ames.<ref name="Aviatr">J. W. Barnes, C. McKay, L. Lemke, R. A. Beyer, J. Radebaugh, and D. Atkinson, "AVIATR: Aerial Vehicle for In-Situ and Airborne Titan Reconnaissance," 41st Lunar and Planetary Science Conference, March 1–5, 2010, The Woodlands, TX; LPI Contribution No. 1533, p.2551 ([http://adsabs.harvard.edu/abs/2010LPI....41.2551B abstract] at smithsonian database, retrieved 13 May 2015)</ref>

=== Jupiter ===
Finally, aerobots might be used to explore the atmosphere of Jupiter and possibly the other gaseous [[outer planet]]s. As the atmospheres of these planets are largely composed of hydrogen, and since there is no lighter gas than hydrogen, such an aerobot would have to be a [[Montgolfiere]]. As sunlight is weak at such distances, the aerobot would obtain most of its heating from infrared energy radiated by the planet below.<ref>Jack A. Jones and Matt Heun [Montgolfiere Balloon Aerobots for Jupiter’s Atmosphere (Abstract)]  Jet Propulsion Laboratory, California Institute of Technology</ref>

A Jupiter aerobot might operate at altitudes where the air pressure ranges from one to ten atmospheres, occasionally dropping lower for detailed studies. It would make atmospheric measurements and return imagery and [[remote sensing]] of weather phenomena, such as Jupiter's [[Great Red Spot]]. A Jupiter aerobot might also drop sondes deep into the atmosphere and relay their data back to an orbiter until the sondes are destroyed by temperature and pressure.