Aerocapture is a precision orbit insertion maneuver aimed at placing space vehicles into long-duration orbits around planetary destinations by making a single pass through the atmosphere. The maneuver starts with an approach trajectory into a planet's or moon's atmosphere. As a spacecraft flies through the atmosphere, it uses drag force -- friction experienced by a craft as it flies through an atmosphere, used to assist in slowing the vehicle -- to decelerate and achieve a desired orbit.
Click here to view a graphic that shows a typical aerocapture mission sequence.
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Components of the Rigid Aeroshell System |
The great advantage of this approach is that the atmosphere does most of the work of slowing down the vehicle, rather than the spacecraft’s engines. Therefore, this nearly fuel-free method of slowing down a space vehicle and placing it into an orbit could significantly reduce the mass of planetary spacecraft. Aerocapture vehicles could have much smaller fuel loads and engines than traditional spacecraft that rely on chemical propellant for orbit insertion. This mass savings could translate into extra science payload, smaller (and less expensive) launch vehicles and, or reduced trip times. A recent cost-benefit analysis quantified the advantages of aerocapture technology for all destinations in the Solar System. This analysis also showed that some deep space
missions cannot, in fact, be done without this technology.
The aerocapture maneuver has never been flight-tested, even though the concept has been around since the early 1960s. Even so, because aerocapture is an inherently multidisciplinary technology -- consisting of traditional spacecraft elements and specialized aerospace disciplines -- many of the elements needed to accomplish the maneuver already exist or evolved from developments in other aeroentry applications. Aerospace disciplines, such as hypersonic aerodynamics, computational fluid dynamics, thermal protection materials and orbit insertion guidance algorithms, are largely shared by the atmospheric entry vehicles that have --for many years -- delivered probes and landers to other planets. In fact, aerocapture vehicles are often based on the same kinds of blunt body, rigid aeroshells used today for Mars atmospheric entry missions.
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Artists Rendition of Heatshield Testing |
In 2002, NASA’s New Millennium Program (NMP) sponsored a detailed design for an Earth aerocapture flight experiment. Shortly thereafter, the In-Space Propulsion (ISP) Technologies Program -- implemented by the In-Space Propulsion Technology Office at the Marshall Space Flight Center in Huntsville, Ala., on behalf of NASA's Science Mission Directorate in Washington -- sponsored a multi-NASA center team to perform a detailed design and mission analysis for Titan aerocapture, using the same vehicle concept as the NMP Earth flight design. The team concluded that aerocapture at Titan -- the planet Saturn's largest moon -- is viable. One challenge, however, is deciding which thermal protection material is best suited for the Titan application. This challenge is currently being investigated by ISP-funded subcontractors. The NASA Titan aerocapture study also produced a mission animation that can be viewed by clicking here.
Another ISP-funded study that focused on using aerocapture at Neptune -- the eighth planet from the Sun -- was done in 2003. The study concluded that additional technology development in the areas of medium lift aeroshells, fluid dynamic computer codes and thermal protection materials is required for this more challenging application. Detailed ISP-sponsored studies of aerocapture at Mars and Venus have been completed, as well, showing aerocapture’s viability and benefit for missions to these planets.
There are four key functional parts to an aerocapture maneuver, as listed below. Several links are provided to technical papers that provide example designs and methodologies taken from the NASA Titan aerocapture study:
- Approach navigation using Earth-based and onboard sensors to target the desired entry point in the planetary atmosphere. (Titan navigation paper.)
- Vehicle aerodynamics, and an automatic guidance and control system that modifies the atmospheric trajectory in such a way as to achieve the target orbit. (Titan guidance paper, Titan flight mechanics paper.)
- Protection for the spacecraft from the high temperature environment created by its high speed flight through the atmosphere. (Titan aeroheating paper #1, Titan aeroheating paper #2, Titan thermal protection materials paper.)
- Relatively small thruster firings after atmospheric flight to raise the orbital periapsis -- the point in an orbit closest to the body being orbited -- out of the atmosphere and adjust for aerocapture delivery errors.
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Aerocapture Mission Sequence.
Click on the photo to view a
larger labeled example. |
The In-Space Propulsion Technologies Program has also sponsored investigations into the use of aerocapture inflatable structures, such as ballutes -- balloon/parachutes -- or inflatable aeroshells. These technologies are less mature than the traditional rigid aeroshell designs, but preliminary studies indicate the potential for significant mass savings.
More information on aerocapture can be found by clicking on the following link which contains an extensive bibliography of published technical papers: Bibliography of published technical papers
Continue on to read about our Aerocapture Technologies including Rigid Aeroshells, Inflatable Deceleraters, Ballutes and Inflatable Aeroshells on the next page. |
