Athul Pradeepkumar Girija

Since the beginning of robotic exploration nearly six decades ago, successful planetary probe entry has been accomplished at Venus, Earth, Mars, Jupiter, and Saturns moon Titan. More probe missions are under implementation or planned to Venus, Titan, and Uranus in the next decade. During entry, the probe is subject to rapid deceleration and aerothermal loads which the vehicle must be designed for, to deliver the robotic instruments inside the atmosphere. The design of planetary probes and their mission architecture is complex, and involves various engineering constraints such as peak deceleration, heating rate, heating load, and communications. These must be satisfied within the budget and schedule of cost constrained mission opportunities. Engineering design and flight data from previous probe missions serve as an invaluable reference for future missions. The present study compiles a historical entry probe dataset spanning a wide range of planets, performs a comparative analysis of the entry conditions, and provides engineering rules of thumb for design of future missions. Using the dataset, the study proposes a new empirical relationship which aims to more accurately predict the thermal protection system mass fraction for high heat load conditions during entry and aerocapture at Uranus and Neptune.

The Cassini-Huygens mission transformed our understanding of Titan from a hazy veiled moon to a place surprisingly like the Earth, with terrestrial physical processes such as wind, erosion, and rainfall shaping the an alien landscape, but with entirely different chemistry at low temperatures. Dragonfly, a single element mission which fits within the New Frontiers cost cap will arrive at Titan in 2034, and perform detailed in-situ investigations of the materials on the surface. However, its exploration will be limited to regions within its short flight range of the equatorial landing site. The big gaps in our understanding of Titan’s global topography, climate, polar regions, and upper atmospheric chemistry which can only be investigated from an orbiter around Titan will remain to be addressed by a future orbiter mission. Due to the challenges of attaining orbit, past Titan orbiter concepts have been beyond the New Frontiers cost cap. The present study explores the use of drag modulation aerocapture for a Titan Orbiter which fits within New Frontiers. The study shows how a Dragonfly-like lander, and a Titan orbiter which each individually fit within the New Frontiers cost cap, when combined together can provide the science data return equivalent to a Flagship-class mission.

Aerocapture is the technique of using the planet's atmosphere to decelerate a spacecraft in a single pass to achieve almost propellant-free orbit insertion. The technique has been extensively studied since the 1980s but has never been flown yet despite all the system-level technologies being considered ready for an operational mission. The entry conditions encountered during the maneuver are strongly destination dependent, as is the performance benefit offered by aerocapture. Aerocapture is applicable to all atmosphere-bearing destinations, with the exception of Jupiter and Saturn, whose extreme aerothermal conditions make it infeasible. There are two main classes of missions for which aerocapture has been most studied in recent works, one for small satellite missions to Mars and Venus, and the other for large Flagship-class missions to the outer Solar System including Titan, Uranus, and Neptune. The report compiles a list of design reference missions at Venus, Earth, Mars, Titan, Uranus, and Neptune. These reference missions can provide an initial assessment of the feasibility of aerocapture for a proposed mission and provide initial baseline values for more detailed system studies.

Aerocapture offers an efficient and near-propellantless method of orbit insertion at almost all atmosphere-bearing planetary destinations. Compared to propulsive insertion, aerocapture offers considerable savings in propellant mass which could be used to accommodate more scientific payload. Aerocapture is particularly attractive for low-cost interplanetary small satellite mission concepts. As with any space mission, aerocapture involves multiple disciplines and analyses: science, mission design, interplanetary trajectory, atmospheric guidance, navigation, and control, vehicle and spacecraft design, thermal protection system design, atmospheric models, satellite tour design, as well as programmatic, cost, and risk considerations. This report provides recommendations for developments in each of these disciplines and aims to inform space technology policy in prioritizing investments in the development of aerocapture technology for future science missions.

The identification of trajectories and promising mission architectures that enable planetary missions or significantly reduce their cost is a highly valuable asset for the planetary science and mission engineering community. The 2023-2032 Planetary Science Decadal Survey underscored the importance of programs to bridge opportunity gaps by increasing access to information about mission concept formulation, development, and proposals for future NASA missions. The high-level objective of this work is to create a proof-of-concept easy-to-use mission design suite aims to fill this gap, by providing the community with a new state-of-the-art mission design suite to enable rapid, early-stage end-to-end planning for NASA’s future planetary science missions. In this report, the work done in the pilot phase of Planetary Science Mission Architecture (PLASMA) Exploration Tool, its current capabilities, and technical details are discussed.

At the far reaches of the outer Solar System, the ice giants remain the last class of planets yet to be studied using orbiters. The 2023-2032 Planetary Science Decadal Survey has underscored the importance of the ice giants in understanding the origin, formation, and evolution of our Solar System. The enormous heliocentric distance of Uranus presents considerable mission design challenges, the most important being able to reach Uranus within a reasonable time. The present study presents two examples of aerocapture enabled short flight time, fast trajectories for Uranus orbiter missions, and highlights the enormous benefits provided by aerocapture. The first is an EEJU trajectory with a launch opportunity in July 2031 with a flight time of 8 years. The second is an EJU trajectory with a launch opportunity in June 2034 with a flight time of only 5 years. Using the Falcon Heavy Expendable, the available launch capability is 4950 kg and 1400 kg respectively for the two trajectories. Both trajectories have a high arrival speed of 20 km/s, which provides sufficient corridor width for aerocapture. Compared to propulsive insertion architectures which take 13 to 15 years, the fast trajectories offer significant reduction in the flight time.

The choice of the launch vehicle is an important consideration during the preliminary planning of interplanetary missions. The launch vehicle must be highly reliable, capable of imparting sufficient energy to the spacecraft to inject it on to an Earth-escape trajectory, and must fit within the cost constraints of the mission. Over the recent past, the most commonly used launchers for interplanetary missions include the Atlas V401, Atlas V551, Delta IVH, and Falcon Heavy expendable version. The NASA Launch Vehicle Performance website maintains a tool to help mission planners evaluate various launch vehicles during mission studies. However, there is no comprehensive dataset which can be used to quickly compare the launch performance and launch cost of various options. The present study compiles a dataset of the high energy performance of existing and planned launchers from open-source data and performs a quantitative comparison of the launch performance and the launch cost per kg. The Falcon Heavy expendable offers the lowest cost-per-kg for high-energy launches, with only $0.075M per kg. The Vulcan Centaur offers comparable performance to the Falcon Heavy. The results indicate Falcon Heavy Expendable and the Vulcan Centaur will be the likely choice for several future missions.

NASA has recognized the potential of small low-cost missions to perform focused planetary science investigations at Mars and Venus. EscaPADE, part of the NASA SIMPLEx program will deliver two small spacecraft to elliptical orbits around Mars using the Photon spacecraft. Orbit insertion, particularly to low-circular orbits requires significant propellant, taking up a substantial fraction of the Photon wet mass and present a significant challenge for small missions. The large ΔV requirements for low-circular orbit make it difficult to insert small satellites into these orbits even with the highly capable Photon, as the total ΔV for Earth escape and orbit insertion exceeds its propulsive capability. Aerocapture offers a promising alternative, using the atmospheric drag to obtain the large ΔV. The study shows how the Photon when combined with drag modulation aerocapture can deliver small orbiters to low-circular orbits, enabling a wide range of small orbiter missions. Aerocapture eliminates the need for Photon to provide 2 to 3.5 km/s of ΔV for orbit insertion, which translate into significant mass and cost savings, and can enable frequent low-cost small orbiters and satellite constellations at Mars and Venus in the near future.

With advancements in low-cost launchers and small interplanetary spacecraft, NASA has recognized the potential of small missions to perform focused planetary science investigations at Mars and Venus. The EscaPADE, part of the NASA SIMPLEx program will deliver two small spacecraft to elliptical orbits around Mars using the Photon spacecraft. Orbit insertion, particularly to low-circular orbits requires significant propellant, taking up a substantial fraction of the Photon wet mass and present a significant challenge for small missions. The large $Δ$V requirements for low-circular orbit make it difficult to insert small satellites into these orbits even with the highly capable Photon, as the total $Δ$V for Earth escape and orbit insertion exceeds its capability. Drag modulation aerocapture offers a promising alternative, using the atmospheric drag to obtain the large $Δ$V. The study shows how the Photon when combined with drag modulation aerocapture can deliver small orbiters to low-circular orbits, enabling a wide range of small orbiter missions. Aerocapture eliminates the need for Photon to provide 2 to 3.5 km/s of $Δ$V for orbit insertion, which translate into mass and cost savings, and can enable frequent low-cost small orbiters and small satellite constellations at Mars and Venus in the near future.