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Balloons/Aerobots for Planetary Exploration

Task Objective

Balloon on Earth
Zero Pressure
Balloon on Mars
Super-pressure -- Mars (artist's rendition)
Balloon on Titan
Zero-pressure -- Titan (artist's rendition)
Super-pressure (pumpkin) (artist's rendition)
Artist concept of a ballon near Jupiter
IR Mongolfier -- Jupiter (artist's rendition)
Artist's concept of a balloon near Venus
Zero-pressure -- Venus (artist's rendition)
The exploration of the solar system has advanced from fly-bys and static landers to sophisticated orbiters, landers,  rovers, and other advanced exploratory vehicles. The possibility of using robotically-controlled balloons (also called "Aerobots") in missions for science exploration has tremendous promise for two reasons: (1) The nearness to the surface allows the use of relatively inexpensive imaging equipment, and (2) The mobility of the balloon allows us to explore a large area.

The goal of this research is to show how moderate vertical mobility can be used with improved wind models to achieve the horizontal mobility necessary to perform target-focused science missions with formations of balloons.

The near-term benefits of this research are quite simple: No one knows how to fly a single aerobot or a formation of aerobots to move from one place to another---much less how to maintain a formation during flight. This research will allow consideration of formations of aerobots for focused planetary science missions. Formations of balloons  will increase usable science data returned as well as allow for some redundancy of science exploration vehicles.

The long-term goal of this line of research is to convincingly demonstrate that aerobots or formations of aerobots can be highly useful for the scientific exploration of our solar system, including the earth.

Task Description

We have designed and implemented software for simulating multiple aerobots/balloons incorporating complete balloon thermodynamic models for high simulation fidelity. This is the first flexible simulation software to allow simulation of multiple balloons of various types. The object-oriented software in C++ simplifies implementation of new types of balloons, ballast control systems, motion controllers, and environments. The software incorporates new concepts for balloon flight train mechanics based on multi-body dynamics inward-outward recursion. The software also allows visualization of planetary wind fields as shown in the following figures:

Earth wind fields Mars wind fields
Earth wind fields
Mars wind fields

This wind field visualization software was used to visualize the trajectories that balloons might follow in a planets winds with a specified vertical trajectory. See the following figure for an example trajectory at Mars:

Mars balloon trajectory
Mars balloon trajectory

The key questions that the research has attempted to address is whether a balloon can move to desired locations with only limited vertical control by using the planet's wind structure. These questions can be divided into two separate issues:Reachability and Path Planning. Reachability is answering the question of whether it is even possible for an aerobot to move from on location to another desired location. Assuming that a path can be achieved (the target is reachable), then the second issue is how do we plan and execute a path that reaches the target. These two issues can also be further divided by regional extent involved.First, the winds in a relatively small region can be treated as being constant or varying linearly across the region.Obviously, as the region gets larger and reaches any significant portion of the globe, such simplifications about wind are unlikely to be valid and different techniques and approaches will be necessary.

These software tools were also used to visualize cones of reachability from a starting point with various vertical trajectories. The following figure shows the the reachable areas for a variety of vertical control decisions in a specific non-constant wind field.

Reachable trajectories
Wind field in rectangular volume with reachable volume illustrated.

Dr. Ranjan Mukherjee of Michigan State University implemented C-based simulation of single hot-air balloon for path planning research. They demonstrated bang-bang altitude control algorithms. This enables testing and demonstration of path planning concepts in wind fields of limted extent. Optimal control algorithms were developed and demonstrated optimal control of balloon motions in linear velocity fields. This research proved that optimal paths involve minimal number of vertical motion reversals.  These results greatly enhance our ability to plan and execute balloon paths in localized regions.

An eary phase of this research address the issue of pointing instruments from balloon platforms to enable high-resolution surface imagery/sensing from single and multiple balloon gondolas for planetary exploration by developing improved pointing and stabilization algorithms and technology.

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Updated: August 14, 2012