Аэрозахват: Маневр орбитального перевода с использованием атмосферного торможения.

Orbital transfer maneuver

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. 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. Aerocapture has been shown to be feasible at Venus, Earth, Mars, and Titan using existing entry vehicles and thermal protection system materials. 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. 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. 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. However, it is possible to use an aerogravity assist at Titan to insert a spacecraft around Saturn.

NASA technologists are developing ways to place robotic space vehicles into long duration scientific orbits around distant Solar System destinations without the need for the heavy fuel loads that have historically limited vehicle performance, mission duration, and mass available for science payloads. A study showed that using aerocapture over the next best method (propellant burn and aerobraking) would allow for a significant increase in scientific payload for missions ranging from Venus (79% increase) to Titan (280% increase) and Neptune (832% increase). Additionally, the study showed that using aerocapture technology could enable scientifically useful missions to Jupiter and Saturn. Aerocapture technology has also been evaluated for use in crewed Mars missions and found to offer significant mass benefits. For this application, however, the trajectory must be constrained to avoid excessive deceleration loads on the crew. Although there are similar constraints on trajectories for robotic missions, the human limits are typically more stringent, especially in light of the effects of prolonged microgravity on acceleration tolerances.

To perform aerocapture, the vehicle must enter the atmosphere within the aerocapture theoretical entry corridor. Entering too steep will result in the vehicle failing to exit the atmosphere. Entering too shallow will result in the vehicle exiting the atmosphere without depleting enough energy. Entering within the corridor allows the vehicle guidance scheme to achieve the desired exit conditions for a capture orbit around the planet. The aerocapture maneuver can be accomplished with three basic types of systems. The spacecraft can be enclosed by a structure covered with thermal protection material also known as the rigid aeroshell design. Similarly another option is for the vehicle to deploy an aerocapture device, such as an inflatable heat shield, known as the inflatable aeroshell design or a mechanically deployed drag skirt. The third major design option is of an inflatable, trailing ballute—a combination balloon and parachute made of thin, durable material towed behind the vehicle after deployment in the vacuum of space.

The blunt body, rigid aeroshell system encases a spacecraft in a protective shell. This shell acts as an aerodynamic surface, providing lift and drag, and provides protection from the intense heating experienced during high speed atmospheric flight. Once the spacecraft is captured into orbit, the aeroshell is jettisoned. NASA has used blunt aeroshell systems in the past for atmospheric entry missions. The most recent example is the Mars Exploration Rovers, Spirit and Opportunity, which launched in June and July 2003, and landed on the Martian surface in January 2004. Another example is the Apollo Command Module. The module was used for six uncrewed space flights from February 1966 to April 1968 and eleven crewed missions from Apollo 7 in October 1968 through the final crewed Apollo 17 lunar mission in December 1972. Because of its extensive heritage, the aeroshell system design is well understood. Adaptation of the aeroshell from atmospheric entry to aerocapture requires mission specific customization of the thermal protection material to accommodate the different heating environments of aerocapture. Also, higher temperature adhesives and lightweight, high temperature structures are desired to minimize the mass of the aerocapture system. but later changed to aerobraking for reasons of cost and commonality with other missions. Aerocapture has been proposed and analyzed for arrival at Saturn's moon Titan.

Aerocapture within fiction can be read in Arthur C. Clarke's novel 2010: Odyssey Two, in which two spacecraft (one Russian, one Chinese) both use aerocapture in Jupiter's atmosphere to shed their excess velocity and position themselves for exploring Jupiter's satellites. This can be seen as a special effect in the movie version in which only a Russian spacecraft undergoes aerocapture (in the film incorrectly called aerobraking). Players of the video game Kerbal Space Program often employ aerocapture, particularly when exploring the satellites of Jool (a gas giant that serves as the game's Jupiter analogue). In the television serial Stargate Universe, the ship Destiny's autopilot employs aerocapture within the atmosphere of a gas giant at the edge of a star system. This puts the ship on a direct heading into the star at the center of the system. In the sci fi novel Delta v, asteroid miners use a purpose built aerocapture ship in a desperate attempt to return to Earth from the asteroid Ryugu.

Aerocapture Mission Analysis Tool (AMAT) provides rapid mission analysis capability for aerocapture and Entry, Descent, and Landing (EDL) mission concepts to atmosphere bearing destinations in the Solar System.