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Aerocapture System Technology for Planetary Missions
Executive Summary
The Splinter Sessions Focused on the Following Technology Areas
– System and Performance Modeling
– Aerodynamics and Aerothermodynamics
– Thermal Protection Systems/Structure
– Guidance, Navigation, and Control (GN&C)
Session Topics
– Future space science mission needs
– Desired workshop products
– Technology splinter session discussions
– Needs/potential capabilities assessments
• Key Observations
– Aerocapture is applicable to all planetary destinations with suitable atmospheres (Venus, Earth, Mars, Jupiter, Saturn, Titan, Uranus, and Neptune)
– The primary advantage of aerocapture is propellant mass savings. The net vehicle mass savings range from 20-80% depending on the destination and can manifest themselves in terms of smaller, cheaper launch vehicles or increased payloads.
• Preliminary results indicate that some missions (e.g. Neptune Orbiter) cannot be done without aerocapture because they won't fit on the largest available launch vehicle (Delta IV heavy).
• Aerocapture can also reduce trip time (by allowing higher arrival speeds than chemical capture can feasibly accommodate), and enable new missions with increased flexibility
– Aerocapture is a systems technology in which most of the elements already exist due to development in other aeroentry applications. The critical next step is to assemble these elements into a prototype vehicle, fly it in the space environment and thereby validate the design, simulation and systems engineering tools and processes
• This need is very well matched to the NMP program objective that ST-9 be a systems level validation experiment
– ST-9 flight experiment is key to making aerocapture technology available to science missions
• Recommendations for ST-9 Flight Experiment
– ST-9 should validate the most mature and immediately useful vehicle configuration, which is the blunt body aeroshell
• Blunt body aeroshell systems provide robust performance for aerocapture at all “small body” destinations in the solar system (Mars, Titan, Venus, Earth)
• The validation will be directly relevant to other aeroshell geometries (as will be needed for the gas giants) for the guidance, simulation and systems engineering disciplines
– The ST-9 flight validation must demonstrate a drag delta-V of 2 km/s, in order to involve all of the essential physics of the problem and serve as an acceptable validation of aerocapture
• Although the ST-9 cost cap precludes a "true" aerocapture flight test involving a hyperbolic to elliptic orbit change effected by atmospheric drag, this objective can be accomplished with an elliptical-to-elliptical orbit change.
– The ST-9 flight test should include an autonomous periapse raise maneuver after the atmospheric portion of the flight
– The ST-9 vehicle should incorporate diagnostic instrumentation to the maximum extent possible under the cost cap
• The two priorities are to get information about the hypersonic flow field around the vehicle and to quantify the performance of the thermal protection material.
– The ST-9 vehicle should baseline mature TPS and structural materials to minimize risk
• However, it is recommended (if affordable given the cost cap) that the vehicle incorporate a test coupon of one or more new TPS materials that are candidates for future aerocapture and/or aeroentry missions at other planets. These coupons should be incorporated in such a way that their failure does not compromise the overall flight test experiment
Aerocapture Overview
What is it?
• Aerocapture is an orbit insertion flight maneuver executed upon arrival at a planet.
• Spacecraft flies through the atmosphere and uses drag to effect multi-km/s deceleration in one pass
• Requires minimal propellant for attitude control and a post-aerocapture periapse raise maneuver.
Benefits
• Significant reduction in propellant load; arrival mass can be reduced by 20-80% for the same payload mass depending on the mission
• Achieves the required orbit faster than with aerobraking or SEP alternatives (hours vs weeks/months)
• Can result in reduced flight times since arrival speeds can be higher than for propulsive capture
State of the Art
• Never been attempted before
• Considerable relevant experience from past aeroentry and aerobraking missions
• Sufficient technical maturity exists for a flight test experiment
Primary Technical Approach
• Spacecraft carried inside a protective aeroshell
• Aeroshell provides both thermal protection and aerodynamic surface functionality
• Aeroshell cutouts and feedthroughs enable full spacecraft functionality during cruise
• Automatic guided flight through atmosphere using specialized algorithms/software
• Aeroshell jettisoned after capture
Aerocapture is an Enabling Technology
• Aerocapture can save so much propellant mass that it enables missions that cannot otherwise be done
– Propulsive orbit insertion obeys the rocket equation: Mfuel ~ exp(DV)
– Aerocapture mass is predicted to scale almost linearly: MAC ~ DV
Aerocapture Technology Areas to be Addressed by ST-9
• Complete systems level test of a free-flying vehicle in order to validate the design, simulation, and systems engineering tools and processes.
• This validation will directly address flight mechanics, vehicle design, systems engineering and integration, no matter what the future planetary destination is.
• This validation will partially address aerothermodynamics and TPS, since the applicability to future missions is more limited because of the specialized needs of the different destinations.
Experiment Requirements
• In a single atmospheric pass, utilize bank angle modulation through an atmosphere to remove the necessary amount of delta V from the vehicle approach trajectory to achieve the target orbit.
– The delta V achieved during this maneuver must be on the order of 2 km/s to validate all phases of the guidance and achieve hypersonic continuum aerodynamics
• Validate a mature and immediately useful vehicle configuration
• Perform an autonomous periapse raise maneuver after the atmospheric portion of the flight
• Utilize diagnostic instrumentation to the maximum extent possible, to acquire information about the hypersonic flow field and quantify the performance of the thermal protection material.
– The information obtained will be the key to model validation and technology infusion
State of the Art
• Aerocapture has never been flown in space
• Elements of aerocapture have been flown
– Aeromaneuvering (lifting, guided and controlled) with low L/D aeroshell, lift vector modulation with low control authority
• Apollo, Gemini
– Atmospheric exit human rated for Apollo, but never flown
– Russian Zond 6 spacecraft performed loft on Lunar return, to reach U.S.S.R. in 1968 (using pre-programmed bank commands)
– Aeroassist demonstrated spacecraft with similar characteristics
• Viking – lifting, controlled, unguided Mars Entry, Descent and Landing
– Ballistic entries completed at
• Mars, Jupiter, Venus, Earth, Titan (Huygens Jan 05)
– Shuttle
• Trailing ballute never flown
• Russians built, launched, attempted re-entry of inflatable ballistic attached ballute