Robert L. Staehle

Exploration of Pluto

Abstract Pluto is the last known planet in our Solar System awaiting spacecraft reconnaissance. In its eccentric orbit taking it 50 AU from the Sun, Pluto presently has a thin atmosphere containing methane, which is projected to “collapse” back to the icy planets surface in about three decades, following Plutos 1989 perihelion pass at 30 AU. Based on ground and Earth-orbit-based observing capabilities limited by Plutos small size and extreme distance, present top-priority scientific questions for the first mission concern Pluto and Charons surface geology, morphology and composition, and Plutos neutral atmosphere composition. Budgetary realities preclude a large, many-instrument flyby spacecraft, while distance and launch energy requirements preclude any but the smallest orbiter using presently available launch vehicles and propulsion techniques. A NASA-sponsored Pluto Mission Development activity began this year. Two alternative cost-constrained mission implementations are described, based on which a primary implementation will be chosen. The Pluto Fast Flyby (PFF) mission utilizes an 83 kg (dry) spacecraft launched in 1998 aboard a Titan IV(SRMU)/Centaur for an ∼7 year direct trajectory to Pluto. Instruments described are an integrated CCD-imaging/ultraviolet spectrometer, with a possible integrated infrared spectrometer. The larger Pluto-350 spacecraft, ∼316 kg, carries a broader instrument set, greater redundancy, and requires > 11 year flight time launching in 2001 aboard a Delta or Atlas, toward Earth and Jupiter swingbys to provide the energy to reach Pluto. Launch by Proton is under consideration. Both mission implementations store data during the brief encounter, to be played back over several months. Cost is the primary design driver of both alternatives, with major tradeoffs between spacecraft development, launch services, radioisotope thermoelectric generator procurement and launch approval, and mission operations. Significant benefits are apparent from incorporating “microspacecraft” technologies from Earth orbiters.

Pluto express: Advanced technologies enable lower cost missions to the outer Solar System and beyond

Missions to Pluto and the outer Solar System are typically driven by factors which tend to increase cost, such as: long life, high radiation exposure, a large power source, high ΔV requirements, difficult telecommunications links, low solar illumination at the destination, and demanding science measurements. Advanced technology is a central part of responding to such challenges in a manner which permits the cost of development and operations to be an order of magnitude less than for prior outer planet missions. Managing the process of technology planning and advanced development versus the associated cost and mission risk is a formidable challenge. Outer Solar System/Europa/Pluto/Solar Probe development activities are leveraging the latest products from the industry, government lab and academia technology pipeline in the areas of software, low power integrated microelectronics, low mass, high efficiency radioisotope power if used, and telecommunications. This paper summarizes the current technology develo...

Ice & Fire: Missions to the most difficult solar system destinations… on a budget

Abstract Three radii from the surface of the Sun… more natural radiation around Jupiter than would be encountered immediately following a nuclear war… to the farthest planet and beyond… these challenges are faced by the three “Ice & Fire” missions: Solar Probe, Europa Orbiter, and PlutoKuiper Express. These three missions will be beneficiaries of the X2000 and related advanced technology development programs. Technology developments now in progress make these missions achievable at costs recently thought adequate only for missions of relatively short durations to “nearby” destinations. The next mission to Europa after Galileo will determine whether a global subsurface liquid water ocean is currently present, and will identify locations where the ocean, if it exists, may be most accessible to future missions. Pluto-Kuiper Express will complete the reconnaissance of the known planets in our Solar System with geological, compositional, and atmospheric mapping of Pluto and Charon while Pluto remains relatively near the Sun during its 248 year orbit. An extended mission to a Kuiper Disk object may be possible, depending on remaining sciencecraft resources. Using a unique combination of Sun shield/high gain antenna and quadrature encounter geometry, Solar Probe will deeply penetrate our nearest stars atmosphere to make local measurements of the birth of solar wind, and to remotely image features as small as 60 kilometers across on the Suns surface. Avionics technology, leading to integration of functions among a set of multichip modules with standard interfaces, will enable lower production costs, lower power and mass, and the ability to package with modest shielding to enable survival in orbit around Europa inside Jupiters intense radiation belts. The same avionics and software can be utilized on the other Ice & Fire missions. Each mission is characterized by a long cruise to its destination, facilitated by planetary flybys. The flight systems will represent a unique early integration of science “payload” and “spacecraft,” becoming a more integrated “sciencecraft.” To reduce operations and tracking costs, sciencecraft will be more autonomous. They will self-monitor and self-command, while sending a continuous beacon alerting ground receivers to general sciencecraft health and any need for immediate attention. Where solar power proves impractical for achieving mission goals, an advanced radioisotope power source may be utilized with a much smaller amount of fuel than on prior missions. The three missions described are to begin the Outer Planets/Solar Probe exploration program, as first proposed in the FY1998 Federal Budget. Sciencecraft, launch systems and mission operations must all fit within a single program, encouraging system- and program-wide tradeoffs to minimize costs. Some of the system and technological solutions utilized by these missions may find application in a variety of other science-driven missions.

Pluto express sciencecraft system design

Abstract A number of mission system architectures have been studied for a Pluto flyby mission, with the goal of achieving the most cost effective means of meeting a well defined set of science and technology objectives. The current Pluto Express approach at JPL incorporates emerging new technologies to reduce cost, mass, power, and volume, without sacrificing performance, science, or operations capability. The design has evolved through a number of option studies involving an extensive trade space which includes alternate power sources and various propulsion and trajectory options. The results of this trade study have been coupled with a new development implementation approach to create a highly integrated concurrently engineered mission system called a “sciencecraft.” The current approach results in a Sciencecraft Module with dry mass of less than 100 kg, power consumption of less than 100 watts, and functional simplicity to achieve high reliability, operability, and a low total mission cost.

A Fractionated Space Weather Base at L5 using CubeSats and Solar Sails

The Sun–Earth L5 Lagrange point is an ideal location for an operational space weather forecasting mission to provide early warning of Earth-directed solar storms (coronal mass ejections, shocks and associated solar energetic particles). Such storms can cause damage to power grids, spacecraft, communications systems and astronauts, but these effects can be mitigated if early warning is received. Space weather missions at L5 have been proposed using conventional spacecraft and chemical propulsion at costs of hundreds of millions of dollars. Here we describe a mission concept that could accomplish many of the goals at a much lower cost by dividing the payload among a cluster of interplanetary CubeSats that reach orbits around L5 using solar sails.

Methane on Mars and Habitability: Challenges and Responses.

Abstract Recent measurements of methane (CH4) by the Mars Science Laboratory (MSL) now confront us with robust data that demand interpretation. Thus far, the MSL data have revealed a baseline level of CH4 (∼0.4 parts per billion by volume [ppbv]), with seasonal variations, as well as greatly enhanced spikes of CH4 with peak abundances of ∼7 ppbv. What do these CH4 revelations with drastically different abundances and temporal signatures represent in terms of interior geochemical processes, or is martian CH4 a biosignature? Discerning how CH4 generation occurs on Mars may shed light on the potential habitability of Mars. There is no evidence of life on the surface of Mars today, but microbes might reside beneath the surface. In this case, the carbon flux represented by CH4 would serve as a link between a putative subterranean biosphere on Mars and what we can measure above the surface. Alternatively, CH4 records modern geochemical activity. Here we ask the fundamental question: how active is Mars, geochemically and/or biologically? In this article, we examine geological, geochemical, and biogeochemical processes related to our overarching question. The martian atmosphere and surface are an overwhelmingly oxidizing environment, and life requires pairing of electron donors and electron acceptors, that is, redox gradients, as an essential source of energy. Therefore, a fundamental and critical question regarding the possibility of life on Mars is, “Where can we find redox gradients as energy sources for life on Mars?” Hence, regardless of the pathway that generates CH4 on Mars, the presence of CH4, a reduced species in an oxidant-rich environment, suggests the possibility of redox gradients supporting life and habitability on Mars. Recent missions such as ExoMars Trace Gas Orbiter may provide mapping of the global distribution of CH4. To discriminate between abiotic and biotic sources of CH4 on Mars, future studies should use a series of diagnostic geochemical analyses, preferably performed below the ground or at the ground/atmosphere interface, including measurements of CH4 isotopes, methane/ethane ratios, H2 gas concentration, and species such as acetic acid. Advances in the fields of Mars exploration and instrumentation will be driven, augmented, and supported by an improved understanding of atmospheric chemistry and dynamics, deep subsurface biogeochemistry, astrobiology, planetary geology, and geophysics. Future Mars exploration programs will have to expand the integration of complementary areas of expertise to generate synergistic and innovative ideas to realize breakthroughs in advancing our understanding of the potential of life and habitable conditions having existed on Mars. In this spirit, we conducted a set of interdisciplinary workshops. From this series has emerged a vision of technological, theoretical, and methodological innovations to explore the martian subsurface and to enhance spatial tracking of key volatiles, such as CH4.