Aerocapture Performance Analysis for a Neptune-Triton Exploration Mission

Abstract

A systems analysis has been conducted for a Neptune-Triton Exploration Mission in which aerocapture is used to capture a spacecraft at Neptune. Aerocapture uses aerodynamic drag instead of propulsion to decelerate from the interplanetary approach trajectory to a captured orbit during a single pass through the atmosphere. After capture, propulsion is used to move the spacecraft from the initial captured orbit to the desired science orbit. A preliminary assessment identified that a spacecraft with a lift to drag ratio of 0.8 was required for aerocapture. Performance analyses of the 0.8 L/D vehicle were performed using a high fidelity flight simulation within a Monte Carlo executive to determine mission success statistics. The simulation was the Program to Optimize Simulated Trajectories (POST) modified to include Neptune specific atmospheric and planet models, spacecraft aerodynamic characteristics, and interplanetary trajectory models. To these were added autonomous guidance and pseudo flight controller models. The Monte Carlo analyses incorporated approach trajectory delivery errors, aerodynamic characteristics uncertainties, and atmospheric density variations. Monte Carlo analyses were performed for a reference set of uncertainties and sets of uncertainties modified to produce increased and reduced atmospheric variability. For the reference uncertainties, the 0.8 L/D flatbottom ellipsled vehicle achieves 100% successful capture and has a 99.87 probability of attaining the science orbit with a 360 m/s V budget for apoapsis and periapsis adjustment. Monte Carlo analyses were also performed for a guidance system that modulates both bank angle and angle of attack with the reference set of uncertainties. An alpha and bank modulation guidance system reduces the 99.87 percentile V 173 m/s (48%) to 187 m/s for the reference set of uncertainties.

Feasibility and Performance Analysis of Neptune Aerocapture Using Heritage Blunt Body Aeroshells (Pre-print)

“…Aerocapture studies have historically used a mid lift-to-drag ( / ) vehicle with / of 0.6-0.8 to accommodate the large navigation and atmospheric uncertainties at Uranus and Neptune [15][16][17][18][19]. Aerocapture at Jupiter and Saturn is considered a long-term goal due to the extreme aerothermal conditions during the atmospheric pass.…”

Aerocapture Performance Analysis for a Neptune Mission Using a Heritage Blunt-Body Aeroshell

“…4,[11][12][13][14] Aerocapture studies have historically used a mid lift-to-drag (L/D) vehicle with L/D of 0.6-0.8 to accommodate the large navigation and other uncertainties at Neptune. 15,16 Planetary entry vehicles flown to date are low-L/D vehicles with L/D less than 0.4. The non-availability of a mid-L/D vehicle is a major hindrance to Neptune aerocapture, as development and testing of new entry vehicle is an expensive, time-consuming endeavour with significant programmatic risk.…”

Neptune Aerocapture Systems Analysis

“…10,8 Angle of attack modulation provides increased responsiveness to high frequency density perturbations and may assist with uncertainties in trim angle of attack. Angle of attack control could be provided with movement of an internal ballast or possibly with an aerodynamic control surface.…”

“…The reference concept performance is simulated in a Monte Carlo simulation 8 and includes each of the uncertainties and dispersions as described above. Fig.…”