Europa Surface Science Package Feasibility Assessment

JPL D30050
Europa Surface Science Package Feasibility Assessment
Prepared for
Dr. Curt Niebur, Program Scientist, Jupiter Icy Moons Orbiter, NASA Headquarters, Washington, DC by
Dr. Tibor S. Balint, Study Lead, Deputy Program Manager, Outer Planets Advanced Studies (Office 618)
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA

September 22, 2004

Executive Summary

The National Academy of Sciences identified Jupiter as a critical region of our solar system to search for life’s origins and to understand planetary evolution [NRC03]. The proposed Jupiter Icy Moons Orbiter (JIMO) mission was envisioned to enable the exploration of Jupiter’s Galilean moons, Callisto, Ganymede and Europa [NAS04].

The JIMO Science Definition Team (SDT) strongly recommended that a surface science package for Europa be incorporated into the JIMO mission design [GJ04]. It was also suggested that this Europa Surface Science Package (ESSP) could utilize up to 25% of JIMO’s payload mass allocation. The current predecisional conceptual design for the proposed mission would accommodate a payload of 1500 kg. Consequently, an ESSP could use up to 375 kg mass from JIMO’s payload allocation envelope. According to the SDT recommendations, the instruments on the ESSP should target key science objectives by performing astrobiology, geo physics and geological compositional measurements [GJ04].

In order to understand the trade space for an ESSP, Dr. Curt Niebur, the Program Scientist for the Jupiter Icy Moons Orbiter at NASA HQ, requested an initial study to be performed at the Jet Propulsion Laboratory [Nie04]. Guidelines were given on the scope to identify design drivers and constraints for an ESSP. The study inputs and assumptions included initial mass allocation, mission duration on the surface, and science payload objectives. However, cost, planetary protection & surface contamination issues were not addressed in this trade space exploration. Assessments, such as this one, are based on a number of assumptions, which in turn could significantly influence the findings. Parametric scaling relies of system level assumptions, derived from empirical data of previous design studies. Detailed concept designs can provide higher fidelity results and when cross-referenced with the parametric study, they can aid the former by increasing the confidence level in the predictions. Red team reviews of a study allows for independent checking of the findings from the first team. For the present trade space exploration study all three methods were used to address the questions posed by NASA HQ, thus aiding the process to evaluate the feasibility of an ESSP.

The combination of parametric scaling relationships, firmed up by point concepts and cross referenced by an independent team helped to identify the key drivers influencing an ESSP design. Based on the provided guidelines, a fast turnaround study was performed at JPL, lead by Dr. Tibor Balint, Deputy Program Manager for Outer Planets Advanced Mission Studies (Office618), using three concurrent design teams from the recently formed Team of Teams. MBED (Model Based En gineering Design) provided the parametric scaling relationships, Team X assessed a preliminary concept design, while NPDT (Next Generation Product Develop ment Team) gave an independent “red team” review of the Team X study and further advanced the concept.

In the mission design it was assumed that an ESSP would cruise to Europa on the proposed JIMO spacecraft. After the initial mapping of the surface the ESSP would be deployed for its 3, 7 or 14day surface mission. The landing location would be influenced by the assumed 100 km altitude JIMO orbit, the propulsion system option to deorbit the ESSP, and the landing method. Additional assump tions included dual string design, 1 MRad radiation tolerance for the electronic components and 30% contingency on mass and power, required by design princi ples.

Two sets of science instruments were assessed through detailed concept stud ies to demonstrate the flexibility of the options, where both could achieve the science objectives defined by the SDT. The first set included a GC/MS, a micro seismometer, a magnetometer, an imager and radiation sensors. Wet chemistry and Raman spectroscopy instruments were left out due to mass limitations. The second set included an organic detector connected to a minimass spectrometer, a seismometer, a magnetometer, a radiation sensor and a panoramic camera. These instruments were only defined for mass, power and system sizing purposes, with out trying to influence instrument choices on future landing concepts. It is also expected that any of the heritage instruments must be modified for the Europa environment.

It is concluded that the three key drivers bounding the trade space for an ESSP design are (1) the initial constraints imposed by the mission (e.g., mass limit,

TRL cutoff date by 2012); (2) the radiation environment potentially exposing JIMO and the ESSP up to 60 MRad of total ionizing radiation dose, which must be mitigated at a significant shielding mass penalty; and (3) the landing, which according to the rocket equation, would require about half of the mass allocation for the propulsion system, including propellant and propulsion dry mass. Three landing methods were assessed and compared. Regardless of the propul sion system, during landing on Europa a Delta v of ~1.5 km/s must be removed. Soft landing with advanced propulsion and throttled engines would provide the largest landed payload mass on the surface. With a “stop and drop” landing method most of the velocity would be removed propulsively then letting the ESSP free fall from ~ 1 to 2 km. Landing could be achieved with either airbags or with crushable materials, depending on the free fall altitude. The propellant savings for these latter methods would be less than the mass penalty from implement ing a secondary landing systems. Therefore, airbag and crushable material based landing would further constrain the already mass limited mission.

Parametric scaling results – firmed up by detailed concept studies – indicated that an ESSP mission with 150 kg or 300 kg would not be feasible based on the initial assumptions of this assessment. Hard landing with airbags or rough landing with crushable materials would also exceed the allocated mass limit. These methods were found to be less mass efficient than soft landing on planetary surfaces with out atmospheres.

It was found, however, that an ESSP with a mass allocation of 375 kg could be achieved using either targeted or untargeted soft landing methods. For a 3 day surface operation a battery powered lander should be able to meet all science objectives identified by the SDT. For 7 or 14day missions the increased battery size would scale the lander beyond the mass allocation limit, but a small Radioiso tope Power System based lander would be feasible. The mass cross over between battery and RPS powered landers is expected to be around 3 to 4 days of surface operation.

In light of the findings, it is recommended to follow up this assessment with a high fidelity point design, which could reduce the large margins inherent in The information contained within this document is predecisional and for discussion purposes only parametric studies. Such a point design should utilize a soft landing configuration and address all of the trades in addition to unexplored parameters, including cost and planetary protection issues. Results from a point design could benefit NASA HQ and the SDT to determine whether or not an ESSP should be considered for the proposed JIMO mission.

The information contained within this document is pre-decisional and for discussion purposes only

JPL D-30050