ALBERT

Description: The present study considers direct ballistic entries into the atmosphere of Venus using a 45deg sphere-cone rigid aeroshell, a legacy shape that has been used successfully in the past in the Pioneer Venus Multiprobe Mission. For a number of entry mass and heatshield diameter combinations (i.e., various ballistic coefficients) and entry velocities, the trajectory space in terms of entry flight path angles between skip out and -30deg is explored with a 3DoF trajectory code, TRAJ. From these trajectories, the viable entry flight path angle space is determined through the use of mechanical and thermal performance limits on the thermal protection material and science payload; the thermal protection material of choice is entry-grade carbon phenolic, for which a material thermal response model is available. For mechanical performance, a 200 g limit is placed on the peak deceleration load experienced by the science instruments, and 10 bar is assumed as the pressure limit for entry-grade carbon-phenolic material. For thermal performance, inflection points in the total heat load distribution are used as cut off criteria. Analysis of the results shows the existence of a range of critical ballistic coefficients beyond which the steepest possible entries are determined by the pressure limit of the material rather than the deceleration load limit.

Description: Atmospheric probes have been successfully flown to planets and moons in the solar system to conduct in-situ measurements. They include the Pioneer Venus multi-probes, the Galileo Jupiter probe, and Huygens probe. Probe mission concepts to five destinations, including Venus, Jupiter, Saturn, Uranus, and Neptune, have all utilized similar-shaped aeroshells and concept of operations, namely a 45 deg sphere cone shape with high density heatshield material and parachute system for extracting the descent vehicle from the aeroshell. Each concept designed its probe to meet specific mission requirements and to optimize mass, volume, and cost. At the 2017 IPPW, NASA Headquarters postulated that a common aero-shell design could be used successfully for multiple destinations and missions. This "common probe" design could even be assembled with multiple copies, properly stored, and made available for future NASA missions, potentially realizing savings in cost and schedule and reducing the risk of losing technologies and skills difficult to sustain over decades. Thus the NASA Planetary Science Division funded a study to investigate whether a common probe design could meet most, if not all, mission needs to the five planetary destinations with extreme entry environments. The Common Probe study involved four NASA Centers and addressed these issues, including constraints and inefficiencies that occur in specifying a common design.Study methodology: First, a notional payload of instruments for each destination was defined based on priority measurements from the Planetary Science Decadal Survey. Steep and shallow entry flight path angles (EFPA) were defined for each planet based on qualification and operational g-load limits for current, state-of-the-art instruments. Interplanetary trajectories were then identified for a bounding range of EFPA. Next, 3-DoF simulations for entry trajectories were run using the entry state vectors from the interplanetary trajectories. Aeroheating correlations were used to generate stagnation point convective and radiative heat flux profiles for several aeroshell shapes and entry masses. High fidelity thermal response models for various TPS materials were used to size stagnation point thicknesses, with margins based on previous studies. Backshell TPS masses were assumed based on scaled heat fluxes from the heatshield and also from previous mission concepts.

Description: Atmospheric probes have been successfully flown to planets and moons in the solar system to conduct in situ measurements. They include the Pioneer Venus multi-probes, the Galileo Jupiter probe, and Huygens probe. Probe mission concepts to five destinations, including Venus, Jupiter, Saturn, Uranus, and Neptune, have all utilized similar-shaped aeroshells and concept of operations, namely a 45 sphere cone shape with high density heatshield material and parachute system for extracting the descent vehicle from the aeroshell. The current paradigm is to design a probe to meet specific mission requirements and to optimize mass, volume, and cost for a single mission. However, this methodology means repeated efforts to design an aeroshell for different destinations with minor differences. A new paradigm has been explored that has a common probe design that could be flown at these different destinations and could be assembled in advance with multiple copies, properly stored, and made available for future NASA missions. Not having to re-design and rebuild an aeroshell could potentially result in cost and schedule savings and reduce the risk of losing technologies and skills difficult to sustain over decades.

Description: Exploration of Saturn atmospheric entry trajectory space using a 45 sphere-cone rigid aeroshell.

Description: Flight proven entry system and TPS technologies are critical for the successful execution of in-situ science missions at Venus. Emerging new technologies point to new possibilities and offer innovative approaches to delivering small satellites for orbital science. Venus entry can be very demanding and there are only a few flight proven TPS, some developed by Industry and others by NASA, capable of meeting the mission needs. NASA developed TPS has predominately been transferred to Industry and it is assumed industry will maintain the fabrication capability. However, lack of mission needs may result in obsolence of TSP fabrication capability if there is no money and no motivation. Even within NASA, its' expertise could be diverted to higher priority objectives and thereby the readiness for particular material systems can be impacted or lost. Atrophy of capabilities can come about in other ways as well such as changes to raw materials. Even small manufacturing process changes can demand requalification and TRL may be degraded. Carbon-Phenolic is a text book example. After a long period of absence of US Venus missions, VEXG and the Science community is making the case for future missions. It is insufficient to assume the TSP technologies will be there in 5 or 10 years without active and continual planning and assessment. After Galileo, Carbon-Phenolic materials and fabrication skills were allowed to atrophy. Then when missions needed it, in early 2000, it was no longer possible to make the heritage Carbon-Phenolic. What do we need to do? The first step is to advocate for the establishment of TPS readiness assess-ment. The assessment will involve understanding threats and opportunities, and the development of risk mitigation strategies. VEXAG needs to advocate for such an active monitoring of the needed capabilities, assessment of emerging risks and development of risk mitigation strategies with implementation plans. Such an approach reduces the threat of material obsolence and helps maintain the availability of entry system and TPS technology capabilities, both old and new. Venus probes, landers, balloons and other variable altitude missions, and skimmer missions such as "Cu-pid's Arrow" as well as aerocapture missions to deliver small spacecraft require qualified entry systems and ablative TPS. VEXAG advocated for HEEET in 2013/2014 and the community is well versed with the need to sustain it. But, other TPS that need to be sustained may not be apparent to VEXAG community. The following figure summarizes the ablative TPS capabilities vs Venus mission needs for both primary heatshield and backshell.