The 50-year exploration of the solar system by robotic spacecraft not only has been one of the great adventures in history, but also has transformed humankind’s understanding of the collection of objects orbiting the Sun. Mission after mission, new, stunning discoveries have been made, each in its turn altering our view of the nature of the solar system. The scientific harvest from these robotic missions has been sensational, but the extraordinary breadth and depth of these discoveries would not have been possible without the parallel technology developments that provided the necessary capabilities.
Ongoing missions underscore the value of past technology investments. For example, Dawn’s ion propulsion engine is the essential enabling component of its unique mission to investigate two of the largest asteroids. After a flight of nearly 4 years, Dawn will arrive at 4 Vesta to spend approximately a year, starting in the summer of 2011, making detailed observations of 4 Vesta, after which the spacecraft will cruise for another 3 years toward its second asteroid destination, 1 Ceres. At 1 Ceres in 2015-2016, Dawn will conduct another complete scientific investigation. Such a two-asteroid mission would not have been possible using classical chemical propulsion. Years ago, analytic studies showed that continuous-thrust, high-specific-impulse propulsion opened up many different mission opportunities, including missions with multiple targets. These studies triggered the technology development program that resulted in the ion engines that are currently propelling Dawn toward 4 Vesta.
The Mars Exploration Rovers, now in their seventh year conducting scientific observations while roaming the Red Planet, benefited immensely from significant precursor technological investments in both mobility systems and the scientific payload. The story is essentially the same for all pioneering robotic planetary missions: they would not have been possible, and would not have produced such extraordinary results, without the visionary technology developments that enabled or enhanced their capabilities.
Continued success of the NASA planetary exploration program depends on two major elements. It is axiomatic that the sequence of flight projects must be carefully selected so that the highest-priority questions in solar system science are addressed. But it is equally important that there be an ongoing, robust, stable technology development program that is aimed at the missions of the future, especially those missions that have great potential for
|Chapter 4 The Primitive Bodies||Chapter 5 The Inner Planets||Chapter 6 Mars||Chapter 7 The Giant Planets||Chapter 8 Satellites|
|Technology development||Continue technology developments in several areas including ASRG and thruster packaging and lifetime, thermal protection systems, remote sampling and coring devices, methods of determining that a sample contains ices and organic matter and of preserving it at low temperatures, and electric thrusters mated to advanced power systems.
Develop a program to bridge the TRL 4-6 development gap for flight instruments.
|Continue current initiatives.
Possibly expand incentives to include capabilities for surface access and survivability for challenging environments such as Venus’s surface and frigid polar craters on the Moon.
|Key technologies necessary to accomplish Mars Sample Return are Mars ascent vehicle, rendezvous and capture of orbiting sample return container, and planetary protection technologies.||Continue developments in ASRGs, thermal protection for atmospheric probes, aerocapture and/or nuclear-electric propulsion, and robust deep-space communications capabilities.||Develop the technology necessary to enable Jupiter Europa Orbiter.
Address technical readiness of orbital and in situ elements of Titan Saturn System Mission including balloon system, low-mass/low-power instruments, and cryogenic surface sampling systems.
discovery and are not within existing technology capabilities. Early investment in key technologies reduces the cost risk of complex projects, allowing them to be initiated with reduced uncertainty regarding their eventual total costs. Although the need for such a technology program seems obvious, in recent years investments in new planetary exploration technology have been sharply curtailed and monies originally allocated to it have been used to pay for flight project overruns. As already stressed in Chapter 9, it is vital to avoid such overruns, particularly in flagship projects.
In the truest sense, reallocating technology money to cover short-term financial problems is myopic. The long-term consequences of such a policy, if sustained, are almost certainly disastrous to future exploration. Metaphorically, reallocating technology money to cover tactical exigencies is tantamount to “eating the seed corn.” The committee unequivocally recommends that a substantial program of planetary exploration technology development should be reconstituted and carefully protected against all incursions that would deplete its resources. This program should be consistently funded at approximately 6 to 8 percent of the total NASA Planetary Science Division budget. The technology program should be targeted toward the planetary missions that NASA intends to fly, and should be competed whenever possible. This reconstituted technology element should aggregate related but currently uncoordinated NASA technology activities that support planetary exploration, and their tasks should be reprioritized and rebalanced to ensure that they contribute to the mission and science goals expressed in this report. The remainder of this chapter discusses the specific items that should be addressed by this reconstituted technology program.
From Laboratory to Spaceflight
Given an appropriate technology program budget, the way in which the monies are allocated to the different phases of technology development should be informed both by the lessons of past efforts at technology infusion, and by the guideline that any technology to be used on a flight mission should be at technology readiness level 6 prior to the project’s preliminary design review. The technology readiness level (TRL) is a widely used reference system for measuring the development maturity of a particular technology item. In general, a low TRL refers to technologies just beginning to be developed (TRL 1-3), and a mid-TRL covers the phases (TRL 4-6) that take an identified technology to a maturity at which it is ready to be applied to a flight project (Figure 11.1).
A primary deficiency in past NASA planetary exploration technology programs has been an overemphasis on TRLs 1-3 at the expense of the more costly but vital mid-level efforts necessary to bring the technology to flight readiness. Many important technological developments, therefore, have been abandoned, either permanently or temporarily, after they have reached TRL 3 or 4. This failure to continue to mature the technologies has resulted in a widespread “mid-TRL crisis” that has, in turn, created its own unique set of problems for flight projects. A new flight project that desires to use a specific technology must either complete the development itself, with the concomitant cost and schedule risk, or forgo the capability altogether. To properly complement the flight mission program, therefore, the committee recommends that the Planetary Science Division’s technology program should accept the responsibility, and assign the required funds, to continue the development of the most important technology items through TRL 6. Otherwise it will remain difficult, if not impossible, for flight projects to infuse these technologies without untoward cost and/or schedule risk.
Technology Infusion Initiatives
In recent competed mission solicitations, NASA provided incentives for infusion of new technological capabilities in the form of increases to the proposal cost cap. Specific technologies included as incentives were the following:
• Advanced solar-electric propulsion, NASA’s Evolutionary Xenon Thruster (NEXT),
• Advanced bipropellant engines, the Advanced Material Bipropellant Rocket (AMBR),
• Aerocapture for orbiters and landers, and
• A new radioisotope power system, the Advanced Stirling Radioisotope Generator (ASRG).
These technologies continue to be of high value to a wide variety of solar system missions. The committee recommends that NASA should continue to provide incentives for the technologies listed above until they are demonstrated in flight. Moreover, this incentive paradigm should be expanded to include advanced solar power (especially lightweight solar arrays) and optical communications, both of which would be of major benefit for planetary exploration.
The Need for Innovation
A significant concern with the current planetary exploration technology program is the apparent lack of innovation at the front end of the development pipeline. Truly innovative, breakthrough technologies appear to stand little chance of success in the competition for development money inside NASA, because, by their very nature, they are directed toward far-future objectives rather than specific near-term missions.
The committee hopes that the new NASA Office of the Chief Technologist formed in 2010 will reconstitute an activity similar to the previous NASA Institute for Advanced Concepts (NIAC) that will elicit an outpouring of innovative technological ideas, and that those concepts will be carefully examined so that the most promising can receive continued support. However, it is not yet clear exactly how future technological responsibilities will be split between the new NASA technology office and the individual mission directorates. Given the unique needs of planetary science, it is therefore essential that the Planetary Science Division develop its own balanced technology program, including plans both to encourage innovation and to resolve the existing mid-TRL crisis. These plans should be carefully coordinated with the NASA technology office to optimize their management and implementation.
Core Multi-Mission Technologies
Although the ingenuity of the nation’s scientists and engineers has made it appear almost routine, solar system exploration still represents one of the most audacious undertakings in human history. Any planetary spacecraft, regardless of its specific destination, must cope with the fundamental challenges of traveling long distances from Earth and the Sun, surviving and operating over the resulting long mission duration, and operating without real-time control from Earth and with limited data streams. These vehicles must be equipped to make a wide range of measurements while simultaneously dealing with the challenges of alien and frequently harsh environments. As future mission objectives evolve, meeting these challenges will require continued advances in several technology categories, including the following areas:
• Reduced mass and power requirements for spacecraft and their subsystems;
• Improved communications capabilities yielding higher data rates;
• Increased spacecraft autonomy;
• More efficient power and propulsion for all phases of the missions;
• More robust spacecraft for survival in extreme environments;
• New and improved sensors, instruments, and sampling and sample preservation systems; and
• Mission and trajectory design and optimization.
The Requirement for Power
Of all the multi-mission technologies that support future missions, none are more critical than high-efficiency power systems for use throughout the solar system. In particular, the committee notes the special significance of the new highly efficient ASRG, which enables up to a 75 percent reduction in the use of plutonium-238 compared to systems based on thermoelectric conversion. As discussed in Chapter 9, plutonium-238 is a limited and expensive resource, production of which is currently at a standstill, and future production plans are uncertain. Since more efficient use of the limited plutonium supply will help to ensure a robust and ongoing planetary program, the committee’s highest priority for near-term multi-mission technology investment is for the completion and validation of the Advanced Stirling Radioisotope Generator.
Progress in these core technology areas will benefit virtually all planetary missions, regardless of their specific mission profile or destination. The robust Discovery and New Frontiers programs envisioned by this report would be substantially enhanced by such a commitment to multi-mission technologies. For the coming decade, it is imperative that NASA expand its investment program in these fundamental technology areas, with the twin goals of reducing the cost of planetary missions and improving their scientific capability and reliability. Furthermore, while the requirements will vary from mission to mission, the scope of these challenges requires careful planning so that research and development can establish the proper technological foundation. To accomplish this goal, the committee recommends that NASA expand its program of regular future mission studies to identify as early as possible the technology drivers and common needs for likely future missions.
Capability-Driven Technology Investments
In structuring its multi-mission technology investment programs, it is important that NASA preserve its focus on fundamental system capabilities rather than concentrating solely on individual technology tasks. An example of such an integrated approach, which NASA is already pursuing, is the advancement of solar electric propulsion systems to enable a wide variety of new missions throughout the solar system. This integrated approach consists of linked investments in new thrusters, specifically the NEXT xenon thruster (Figure 11.2), plus new power processing, propellant feed system technology, and the systems engineering expertise that enables these elements to work together.
The committee recommends that NASA consider making equivalent systems investments in the advanced Ultraflex solar array technology that will provide higher power at greater efficiency, and an aerocapture to enable efficient orbit insertion around bodies with atmospheres.
Investing in these system capabilities will yield a quantum leap in the ability to explore the planets and especially the outer solar system and small bodies. Perhaps more importantly, the availability of these systems is imperative in order for NASA to meet its solar system exploration objectives within reasonable budgetary constraints.
Planning for Competed Missions in the Next Decade
Solar system exploration in the coming decade will include many missions selected through open competition. Discovery and New Frontiers missions would benefit substantially from enhanced technology investments in the multi-mission technology areas described above; however, two issues have yet to be overcome:
• The nature of the peer review and selection process effectively precludes reliance on new and “unproven” technology, since it increases the perceived risk and cost of new missions; and
• It is difficult to ensure that proposers have the intimate knowledge of new technologies required to effectively incorporate them into their proposals.
Left unchecked, these two issues will ultimately limit the scope and ingenuity of competed missions.
While expanding its investments in generic multi-mission technologies, NASA should encourage the intelligent use of new technologies in its competed missions. NASA should also put mechanisms in place to ensure that new capabilities are properly transferred to the scientific community for application to competed missions. One example of such a transfer mechanism is the development of a freely available technology database, customized with the information required by new proposals and populated by technologies that have been pre-screened by NASA to ensure that they can be infused at a manageable risk. This database should be accompanied by publication of the results of technology development tasks in free and open media; plans for such publication should be made a prerequisite to the award of technology funding. In this manner NASA can ensure that its technology resources are used to the benefit of the entire community of potential mission proposers.
Technology for Flagship Missions in the Next Decade
NASA’s comprehensive and costly flagship missions are strategic in nature and have historically been assigned to NASA centers rather than competed. They can benefit from, and in fact are enabled by, strategic technology investments. The following sections provide a brief summary of the technological needs for the five flagship mission candidates discussed in Chapter 9.
Mars Astrobiology Explorer-Cacher
MAX-C is the first component of the Mars Sample Return campaign. For the MAX-C sample caching rover, the most challenging technology is sample acquisition, processing, and encapsulation on Mars. For the later elements in the Mars Sample Return campaign, the two greatest technological challenges are the Mars Ascent Vehicle (MAV), which will carry the samples from the martian surface to Mars orbit, and the end-to-end planetary protection and sample containment system. These three high-priority technologies will each require major long lead investments if the overall Mars Sample Return campaign is to have an acceptably high probability of success. The estimated required investment to bring the MAV up to TRL 6, for example, is around $250 million. Additional technology developments may be required to enable precision landing by the Mars Sample Return lander, and autonomous rendezvous and guidance for the Mars Sample Return orbiter. During the decade of 2013-2022, NASA should establish an aggressive, focused technology development and validation initiative to provide the capabilities required to complete the challenging Mars Sample Return campaign. Along with other required developments of infrastructure capabilities, such as sample handling facilities and Mars telecommunications, these developments will enable an intensive Mars exploration program leading to return of samples from the planet’s surface.
Jupiter Europa Orbiter
The Jupiter Europa Orbiter (JEO) mission will have to contend with the challenge of Jupiter’s harsh radiation environment and the need to operate far from the Sun. Fortunately, because significant development has already been accomplished in many key technical areas, the JEO mission currently envisioned requires no fundamentally new technology in order to accomplish its objectives. However, the capability to design and package the science instruments, especially the detectors, so that they are able to acquire sufficiently meaningful data in the jovian radiation environment, has not yet been completely demonstrated. A supporting instrument technology program aimed specifically at the issue of acquiring meaningful scientific data in a high-radiation environment would be extremely valuable, both for JEO and for any other missions that will explore Jupiter and its moons in the future. Planetary protection requirements will provide additional challenges for both the JEO spacecraft and its instruments.
Uranus Orbiter and Probe
The major technological challenges of this mission are as follows:
• Long-lived, flight-qualified ASRGs, with lifetimes in excess of 15 years;
• Lightweight materials for the orbiter structure and subsystems; and
• Thermal protection systems for the probe.
Although the Uranus mission can be accomplished using chemical propulsion, the availability of a flight-tested, comparatively inexpensive solar-electric propulsion module would result in both a wider range of launch dates and more mass in orbit around Uranus. Aerocapture capability would enhance a Uranus orbiter mission. For a Neptune orbiter, the advantages of aerocapture are enormous.
The Enceladus Orbiter’s key scientific instruments are a mass spectrometer, a thermal mapping radiometer, a dust analyzer, an imaging camera, and a magnetometer. Other than improvements in the sensitivity and accuracy of the mass spectrometer and thermal mapping radiometer in particular, which would enhance the scientific mission, the major technological challenge is ensuring the reliability and lifetime of the ASRGs. The mission requires three ASRGs to deliver power throughout the Enceladus orbit phase, which lasts for at least a year beginning 12 years
after launch. Because of the potential habitability of Enceladus, planetary protection is an additional technological challenge for an orbiter mission.
Venus Climate Mission
The Venus Climate Mission (VCM) includes four distinct flight elements: the carrier spacecraft that becomes a Venus orbiter, a gondola and balloon system, a mini-probe, and dropsondes. The packaging of the mini-probe and the dropsondes, especially integration of a sophisticated neutral mass spectrometer in the mini-probe, is the key technological challenge of VCM. Although each of the components of the entry flight system, which contains the gondola and the balloon, is close to TRL 6, indicating technological maturity, the entry flight system itself still presents a significant design and development challenge. The management of the power, mass, and volume of this “Russian doll” vehicle throughout its design cycle could be viewed as a technology development in its own right.
Future Mission Capabilities: 2023-2032
During the decade 2013-2022, the missions recommended by this decadal survey will address the most compelling science objectives within the limited resources available to NASA. It is essential that the Planetary Science Division also invest in the technological capabilities that will enable missions in the decade beyond 2022. During the course of this decadal survey, a number of mission concepts have been studied to assess their cost, feasibility, and scientific value, and these studies provide the foundation for important technology investments. Table 11.2 summarizes these missions and their key technology drivers. The committee strongly recommends that NASA strive to achieve balance in its technology investment programs by addressing the near-term missions cited specifically in this report, as well as the longer-term missions that will be studied and prioritized in the future.
The instruments carried by planetary missions provide the data to address key science questions and test scientific hypotheses. Among the wide variety of missions are flybys, orbiters, atmospheric probes, landers, rovers, and sample returns. As would be expected, the range of science instruments that support these mission sets is also broad. At present there are significant technological needs across the entire range of instruments, including the improvement and/or adaptation of existing instruments and the development of completely new concepts.
Virtually all instruments can be improved by technological developments that reduce their mass and/or power and/or data transmission requirements. Increased instrument sensitivities and measurement accuracies dramatically expand the range of scientific hypotheses that can be addressed by a mission. Mass spectrometers are just one example of a family of instruments that would benefit significantly from a science instrument technology program aimed at improving basic instrument performance characteristics.
But improving and adapting existing instruments will not meet all the goals of future solar system missions. New concepts must also be supported and developed. Astrobiological exploration in particular is severely limited by a lack of flight-ready instruments that can address key questions regarding past or present life elsewhere in the solar system. The committee recommends that a broad-based, sustained program of science instrument technology development be undertaken, and that this development include new instrument concepts as well as improvements in existing instruments. This instrument technology program should include the funding of development through TRL 6 for those instruments with the highest potential for making new discoveries.
Survival in Extreme Environments
One of the biggest challenges of solar system exploration is the tremendous variety of environments that spacecraft encounter. Exploring the surface of Venus for any period longer than a few hours requires engineering
TABLE 11.2 Summary of Types of Missions That May Be Flown in the Years 2023-2033 and Their Potential Technology Requirements
|Objective: 2023-2032||Mission Architecture||Key Capabilities|
|Venus climate history||Atmospheric platform
Advanced chemical propulsion
|Venus/Mercury interior||Seismic networks||Advanced chemical propulsion
Long-duration high-temperature subsystems
|Lunar volatile inventory||Dark crater rover||Autonomy and mobility Cryogenic sampling and instruments|
|Habitability, geochemistry, and geologic evolution||Sample return||Ascent propulsion
Autonomy, precision landing
In situ instruments
|Giant Planets and Their Satellites|
|Titan chemistry and evolution||Coordinated platforms: orbiter, surface and/or lake landers, balloon||Atmospheric mobility
Remote sensing instruments
In situ instruments-cryogenic
|Uranus and Neptune/Triton||Orbiter, probe||Aerocapture
|Trojan and Kuiper belt object composition||Rendezvous||Advanced power/propulsion|
|Comet/asteroid origin and evolution||Sample return
Cryogenic sample return
|Advanced thermal protection
Verification of samples–ices, organics
Cryogenic sample preservation
Thermal control during entry, descent, and landing
systems and science instruments that can withstand intense heat and pressure. A spacecraft that dwells in the equatorial plane of Jupiter, or that orbits any of the inner Galilean satellites, must be designed to handle an extremely harsh radiation environment.
Systems or instruments designed for one planetary mission are rarely able to function properly in a different environment. Yet technological developments often are considered completed as soon as the specified technology demonstrates its functionality in a single environment. The committee recommends that, as part of a balanced portfolio, a significant percentage of the Planetary Science Division’s technology funding be set aside for expanding the environmental adaptability of existing engineering and science instrument capabilities.
In Situ Exploration
Future missions will emphasize in situ exploration in a variety of environments. These will include such extremes as the atmospheres of the giant planets; the surfaces and atmospheres of Venus, Mars, and planetary satellites; and the surfaces and subsurfaces of small bodies. Exploration of such diverse environments requires
a focused technology program element to prepare the required capabilities. Development of new and improved capabilities for entry and landing, mobility, sample acquisition and return, and planetary protection will help ensure progress toward the key objectives of the next and following decades.
Solar System Access and Other Core Technologies
The core multi-mission technologies described above provide the foundation for many of the missions that comprise the majority of planetary flight opportunities. It is essential that the Planetary Science Division continue to advance the state of the art in these technologies to benefit both the competed and the flagship mission programs. In addition, flexibility to respond to new discoveries should be a hallmark of technology programs for the next decade. The allocation of technology monies for discovery-driven elements will ensure the ability to react quickly to the new needs and opportunities that are certain to emerge.
Research and development in the fields of celestial mechanics, trajectory optimization, and mission design have paid substantial dividends in the recent past, identifying new and higher-performance opportunities for planetary missions. A future sustained effort in this technology area is essential, both to exploit fully the expanding range of possible mission modes (electric propulsion, aerocapture, etc.) and to continue to develop the automated software tools for searching rapidly for the “best” mission opportunities.
The future of solar system exploration depends on a well-conceived, robust, stable technology investment program. As recommended above, NASA’s Planetary Science Division should strive to set aside 6 to 8 percent of its mission budget for technology investments. It should also make certain that its technology program has a balanced portfolio, with significant investments in each of the key technology components. Table 11.3 presents an example of a technology investment profile that would have the appropriate balance.
TABLE 11.3 An Example of a Possible Technology Investment Profile That Would Be Appropriately Balanced for the Future Requirements for Solar System Exploration
|Technology Element||Percentage Allocation||Key Capabilities|
|Science instruments||35||Environmental adaptation
In situ sample analysis and age dating
|Extreme environments||15||Survivability under high temperature and pressure
Radiation tolerance (subsystems)
Survival and mobility in cryogenic conditions
|In situ exploration||25||Sample acquisition and handling
Descent and ascent propulsion systems
Thermal protection for entry and descent
Impactor and penetrator systems
Mobility on surfaces and in atmospheres
|Solar system access and core technologies||25||Reduced spacecraft mass and power
Improved interplanetary propulsion
Low-power, high-rate communications
Enhanced autonomy and computing
Improved power sources
Innovative mission and trajectory design