Aerocapture

Schematic showing the various phases of the aerocapture maneuver. Atmospheric height is greatly exaggerated for clarity.

Aerocapture is an orbital transfer maneuver in which a spacecraft uses aerodynamic drag force from a single pass through a planetary atmosphere to decelerate and achieve orbit insertion.

Aerocapture uses a planet's or moon's atmosphere to accomplish a quick, near-propellantless orbit insertion maneuver to place a spacecraft in its science orbit. The aerocapture maneuver starts as the spacecraft enters the atmosphere of the target body from an interplanetary approach trajectory. The aerodynamic drag generated as the vehicle descends into the atmosphere slows the spacecraft. After the spacecraft slows enough to be captured by the planet, it exits the atmosphere and executes a small propulsive burn at the first apoapsis to raise the periapsis outside the atmosphere. Additional small burns may be required to correct apoapsis and inclination targeting errors before the initial science orbit is established.

Compared to conventional propulsive orbit insertion, this nearly fuel-free method of deceleration could significantly reduce the mass of an interplanetary spacecraft, as a substantial fraction of the spacecraft mass is often propellant used for the orbit insertion burn. The saving in propellant mass allows for more science instrumentation to be added to the mission, or allows for a smaller and less-expensive spacecraft, and, potentially, a smaller, less-expensive launch vehicle.[1]

Because of the aerodynamic heating encountered during the atmospheric pass, the spacecraft must be packaged inside an aeroshell (or a deployable entry system) with a thermal protection system. The vehicle also requires autonomous closed-loop guidance during the maneuver to enable the vehicle to target the desired capture orbit and command the vehicle to exit the atmosphere when sufficient energy has been dissipated. Ensuring that the vehicle has enough control authority to prevent the spacecraft penetrating too deep into the atmosphere or exiting prematurely without dissipating enough energy requires either the use of a lifting aeroshell, or a drag-modulation system, which can change the vehicle's drag-producing area during flight.[2][3]

Aerocapture has been shown to be feasible at Venus, Earth, Mars, and Titan using existing entry vehicles and thermal protection system materials.[4] Until recently, mid-L/D (lift-to-drag) vehicles were considered essential for aerocapture at Uranus and Neptune, due to the large uncertainties in entry state and atmospheric density profiles.[5] However, advances in interplanetary navigation and atmospheric guidance techniques have shown that heritage low-L/D aeroshells such as Apollo offer sufficient control authority for aerocapture at Neptune.[6][7] Aerocapture at Jupiter and Saturn is considered a long-term goal, as their huge gravity wells result in very high entry speeds and harsh aerothermal environments, making aerocapture a less attractive, and, perhaps, infeasible option at these destinations.[4] However, it is possible to use an aerogravity assist at Titan to insert a spacecraft around Saturn.[8]

  1. ^ NASAfacts, "Aerocapture Technology." [1] . 12 September 2007
  2. ^ Cruz, MI (May 8–10, 1979). "The aerocapture vehicle mission design concept". Technical Papers.(A79-34701 14–12). Conference on Advanced Technology for Future Space Systems, Hampton, Va. Vol. 1. New York: American Institute of Aeronautics and Astronautics. pp. 195–201. Bibcode:1979atfs.conf..195C.
  3. ^ Girija, AP; et al. (2020). "Feasibility and Mass-Benefit Analysis of Aerocapture for Missions to Venus". Journal of Spacecraft and Rockets. 57 (1). American Institute of Aeronautics and Astronautics: 58–73. Bibcode:2020JSpRo..57...58G. doi:10.2514/1.A34529. S2CID 213497903.
  4. ^ a b Spilker, Thomas R.; Adler, Mark (2019). "Qualitative Assessment of Aerocapture and Applications to Future Missions". Journal of Spacecraft and Rockets. 56 (2). American Institute of Aeronautics and Astronautics: 536–545. Bibcode:2019JSpRo..56..536S. doi:10.2514/1.A34056.
  5. ^ Saikia, S. J.; et al. (2021). "Aerocapture Assessment for NASA Ice Giants Pre-Decadal Survey Mission Study". Journal of Spacecraft and Rockets. 58 (2). American Institute of Aeronautics and Astronautics: 505–515. Bibcode:2021JSpRo..58..505S. doi:10.2514/1.A34703. S2CID 233976308.
  6. ^ Girija, A.P.; et al. (2020). "Feasibility and Performance Analysis of Neptune Aerocapture Using Heritage Blunt-Body Aeroshells". Journal of Spacecraft and Rockets. 57 (6). American Institute of Aeronautics and Astronautics: 1186–1203. Bibcode:2020JSpRo..57.1186G. doi:10.2514/1.A34719.
  7. ^ Deshmukh, R.G.; et al. (2020). "Investigation of direct force control for aerocapture at Neptune". Acta Astronautica. 175. Elsevier: 375–386. Bibcode:2020AcAau.175..375D. doi:10.1016/j.actaastro.2020.05.047. S2CID 224848526.
  8. ^ Lu, Ye; et al. (2020). "Titan aerogravity-assist maneuvers for Saturn/Enceladus missions". Acta Astronautica. 176. Elsevier: 262–275. Bibcode:2020AcAau.176..262L. doi:10.1016/j.actaastro.2020.06.001. S2CID 219911419.