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Solar System Exploration Survey
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Missions
Posted:   01/02/04

Summary: Solar system exploration remains a compelling activity because it may provide answers to basic questions of profound interest: Are we alone? Where did we come from? What is our destiny? The National Research Council has surveyed expert opinion on how to go about asking these fundamental questions.

Solar System Exploration Survey

Space Studies Board of the National Research Council
The Senate Testimony of Dr. Michael J.S. Belton, Ph.D.
Chair, Solar System Exploration Survey Committee, National Research Council


A critical element of the charge to the Solar System Exploration Survey was to formulate a "big picture" of solar exploration - what it is, how it fits into other scientific endeavors, and why it is a compelling goal today.

Solar system exploration remains a compelling activity because it places within our grasp answers to basic questions of profound human interest: Are we alone? Where did we come from? What is our destiny?

UV_venus
Ultraviolet image of Venus obtained by Pioneer-1.
Image Credit: BNSC


Mars and icy satellite explorations may soon provide an answer to the first question; exploration of comets, primitive asteroids and Kuiper Belt objects may have much to say about the second; surveys of near-Earth objects will say something about the third.


Although the scientific goals of NASA's Solar System Exploration program have been quite stable, in recent years the emphasis has increased in two areas - the search for the existence of life, either past or extant, beyond Earth, and the development of detailed knowledge of the near-Earth environment in order to understand what potential hazards to the Earth may exist.

The field of astrobiology has become an important element in solar system exploration and there is an increasing interest in learning more about objects that could collide with the Earth at some future time. The Survey developed four integrating themes to guide solar system exploration in the coming decade:

· The First Billion Years of Solar System History. This formative period propelled the evolution of Earth and the other planets, including the emergence of life on Earth, yet this epoch in our Solar System's history is poorly known.
· Volatiles and Organics; The Stuff of Life. Life requires organic materials and volatiles, notably liquid water, originally condensed from the solar nebula and later delivered to the planets by organic-rich cometary and asteroidal debris.
· The Origin and Evolution of Habitable Worlds. Our concept of the "habitable zone" is being expanded by recent discoveries on Earth and elsewhere in the Solar System. Understanding our planetary neighborhood will help to trace the evolutionary paths of the planets and the fate of our own.
· Processes; How Planets Work. Understanding the operation of fundamental processes is the firm foundation of planetary science, providing insight to the evolution of worlds within our Solar System, and planets around other stars.

Frost and Viking 2 Lander
White patches of frost on the ground are visible behind the Viking 2 Lander. Click to enlarge.Credit: NASA.


With these four themes agreed to, the Survey was able to prioritize among the literally hundreds of scientific questions of interest to the community. The resulting set of twelve key questions with high scientific merit should guide the selection of flight missions over the next decade. We measure the scientific merit of a question by asking whether its answer has the possibility of creating or changing a paradigm, whether the new knowledge might have a pivotal effect on the direction of future research, and to what degree the knowledge that might be gained would substantially strengthen the factual basis of our understanding.

The First Billion Years of Solar System History.

The twelve key questions, grouped within the four themes, are:

1. What processes marked the initial stages of planet and satellite formation?
2. How long did it take the gas giant Jupiter to form, and how was the formation of the ice giants different from that of the gas giants?
3. What was the rate of decrease in the impactor flux throughout the solar system, and how did it affect the timing of the emergence of life? Volatiles and Organics; The Stuff of Life.
4. What is the history of volatile material; especially water, in our Solar System?
5. What is the nature and history of organic material in our Solar System?
6. What planetary processes affect the evolution of volatiles on planetary bodies? The Origin and Evolution of Habitable Worlds.
7. Where are the habitable zones for life in our Solar System, and what are the planetary processes responsible for producing and sustaining habitable worlds?
8. Does (or did) life exist beyond the Earth?
9. Why did the terrestrial planets diverge so dramatically in their evolution?
10. What hazards do Solar System objects present to Earth's biosphere? Processes; How Planets Work.
11. How do the processes that shape the contemporary character of planetary bodies operate and interact?
12. What does our solar system tell us about other solar systems, and vice versa?

To advance the subject these scientific themes and key questions must be addressed by a series of spaceflights of different sizes and complexities. Also, as resources are finite, these proposed new flight missions must be prioritized. It is important at this juncture to understand that the foundation on which the Survey's priorities rest must also be maintained and secured. The top-level programmatic priorities that are required to provide the foundation for productivity and continued excellence in solar system exploration are:

KT_hit
The painting titled "K/T Hit" by artist Donald E. Davis. This impact occured 65 million years ago, ending the reign of the dinosaurs.
Image Credit: Don Davis


· Continue approved Solar System Exploration programs, such as the Cassini-Huygens mission to Saturn and Titan, those in the Mars Exploration Program, the Discovery Program of low-cost missions, and ensure a level of funding that is adequate for both the successful operations and the analysis of the data and publication of the results of these missions.
· Assure adequate funding for fundamental research programs, follow-on data analysis programs and technology development programs that support these missions.
· Continue to support and upgrade the technical expertise and infrastructure in implementing organizations that provide vital services to enable and support Solar System exploration missions.
· Continue to encourage, facilitate and support international cooperation in its Solar System exploration flight programs.

Maintaining a mix of mission size is also important. For example, many aspects of the key science questions can be met through Discovery class missions (<$325 M), while other high-priority science issues will require larger, more expensive projects.

Particularly critical in our strategy is the New Frontiers line of missions ($325-650 M), which are Principal-Investigator (PI) led , medium class, competed missions. This line was proposed in the President's FY 2003 budget submission before the Survey was completed. The Survey strongly supported the proposal to establish a New Frontiers line of competitively procured flight missions with a total mission cost of approximately twice the Discovery cap. Experience has also shown that large missions that enable extended and scientifically multi-faceted experimentation are an essential element of the mission mix.

clementine
Lunar Clementine mission shows the South Pole of the Moon. The permanently shadowed region center shows evidence of meteor cratering and ice never exposed to direct sunlight.
Credit: NASA/DOD Clementine


The Survey recommended that the development and implementation of Flagship (>$650M) missions, comparable to Viking, Voyager, Galileo, and Cassini-Huygens, be at a rate of about one per decade to provide for the comprehensive exploration of science targets of extraordinarily high priority.

Within this structure the Survey recommended the following prioritized flight program of missions in general solar system exploration in the period 2003-2013. It must be emphasized that, at NASA's request, the prioritization was done within cost classes and not over the entire list. Also by NASA's request, the priorities for the Mars Exploration Program were kept separate from the priorities for the Solar System Exploration Division.

Small Class
1. Discovery missions (at a frequency of approximately 1 every 18 months)
2. Cassini Extended Mission

Medium Class
1. Kuiper Belt/Pluto
2. South Pole Aitkin Basin Sample Return
3. Jupiter Polar Orbiter with Probes
4. Venus In-situ Explorer
5. Comet Surface Sample Return

Large Class (at a frequency of approximately 1 every decade)
1. Europa Geophysical Explorer For the Mars exploration program the Survey recommended that in the coming decade the flight program should focus on missions that get down onto the surface of the planet with the ultimate goal of implementing Mars Sample Return missions in the period immediately following the current decade. It is believed that such samples are necessary to settle the question of the presence of life.

The Survey recommended the following flight mission priorities for Mars exploration in the period 2006 - 2013:

Small Class
1. Mars Scout line
2. Mars Upper Atmosphere Orbiter


Medium Class
1. Mars Smart Lander
2. Mars Long-lived Lander Network


Large Class
1. Mars Sample Return (Preparation for flight missions in the next decade)

In addition the Survey committee counseled that NASA should seek to engage international partners at an early stage in the planning and implementation of Mars Sample Return; that the Mars Smart Lander (MSL) while addressing high priority science goals, should take advantage of the opportunity to validate technologies required for sample return, and that the Scout program should be structured like the Discovery program, with PI leadership and competitive missions.

huygens
Huygens landing probe to Saturn's moon, Titan.
Image Credit: ESA


The Survey advocated that a Scout mission should be flown at every other Mars launch opportunity. This future program for solar system exploration laid out above clearly requires a mix of Medium and Large class missions to adequately challenge current scientific paradigms. It also requires that small missions whether Discovery class, Mars Scout, or mission extensions, provide focused ways of responding quickly to discoveries made or provide vehicles for entrepreneurial creativity and new scientific ideas.

Our proposed Kuiper Belt-Pluto mission may well be the last great reconnaissance mission within solar system exploration and, with it completed, we can expect that the program will rapidly enter a phase of large and medium class missions operating on the surfaces of planets or within their atmospheres and plasma environments.

These missions will utilize technologies, yet to be practically developed, that will enable long sojourns, power advanced instrumentation, and return samples to the Earth. The inclusion of Project Prometheus and the optical communications initiative in the President's FY 2004 budget submission are two excellent examples of the type of technology development that is needed to move solar system exploration forward. The Survey recognized that a significant investment in advanced technology development is needed in order for both the recommended flight missions to succeed and to provide a basis for increased science return from future missions.

The following list of future possible missions (unprioritized) with high science value was noted by the Survey and gives some idea of the technical challenges that lie ahead:

europa
Europa Orbiter.
Image Credit: JPL


Terrestrial Planet Geophysical Network
Trojan/Centaur Reconnaissance Flyby
Asteroid Rover/Sample Return
Io Observer
Ganymede Observer
Europa Lander
Titan Explorer
Neptune Orbiter with Probes
Neptune Orbiter/Triton Explorer
Uranus Orbiter with Probes
Saturn Ring Observer
Venus Sample Return
Mercury Sample Return
Comet Cryogenic Sample Return

The Survey identified the following areas in which we believe that technology development is appropriate:

Power: Advanced RTGs and in-space nuclear fission reactor power source
Propulsion: Nuclear electric propulsion, advanced ion engines, aerocapture
Communication: Ka band, large antenna arrays, and optical communication
Architecture: Autonomy, adaptability, lower mass, lower power
Avionics: Advanced packaging and miniaturization, standard operating system
Instrumentation: Miniaturization, environmental (Temperature, Pressure, radiation) tolerance
Entry to Landing: Autonomous entry, hazard avoidance, precision landing
In-Situ Ops: Sample gathering, handling and analysis, drilling, instrumentation
Mobility: Surface, aerial, subsurface, autonomy, hard-to-reach access
Contamination: Forward contamination avoidance
Earth Return: Ascent vehicles, in-space rendezvous and Earth return systems

These technology areas were not prioritized by the Survey. Nevertheless, I note that in-flight power and nuclear electric propulsion initiatives were included in the 2003 budget request and appear again in the 2004 request as Project Prometheus. Also, there are other elements of the above list that are, I believe, being actively considered for inclusion in a future mission in NASA's New Millennium program.

The road that leads to the future of any endeavor is usually well defined only at its start. And quickly, the future becomes obscured by latent uncertainties: the possibility of new discoveries, of changing paradigms, changes in national policy, blind alleys, and funding pleasures and disappointments. Solar system exploration is no exception and in the time since the Survey was completed and published I have felt great excitement and considerable pleasure as important elements of our strategic plan have been proposed to Congress and move, hopefully, towards reality.

The New Horizons mission, which I believe can fulfill our goals at the Kuiper belt and Pluto, is seeing strong support; the proposed Jupiter Icy Moons Mission will more than fulfill our goal of a flagship mission to further explore the subsurface oceans on Europa while simultaneously applying the new technologies that the Survey advocates as a basis for much of the future program.

The most important of these new technologies - in-flight power and nuclear electric propulsion - are adequately covered in the proposed Project Prometheus. The New Frontiers program is going ahead and we await details of how NASA intends to implement this program to include the flight priorities that we have advocated. Finally, the research infrastructure, which underlies the flight program, also appears to be drawing adequate support. The tragic Columbia accident will no doubt have effects on this program in ways that I cannot anticipate. Whether these effects will be positive or negative remains to be seen. However, I note the old proverb "much good can often come out of adversity."

nebula
Spectacular gas remnants from exploding star.
Image Credit: Hubble


Since the end of the Apollo Program, the human spaceflight program has served to enable a number of robotic missions (the Shuttle has been needed to launch important spacecraft such as the Ulysses, Magellan, and Galileo probes, and the Hubble Space Telescope), but has not played a direct role in the exploration of other solar system bodies. In the distant future I expect that this may change in some elements of the program. Human exploration of Mars is a long spoken of goal but faces major technical challenges.

A second area is the protection of the Earth from a potentially hazardous near-Earth object on a collision course. The role of humans, if any, in such an endeavor has not yet been satisfactorily worked out and, in my opinion, deserves attention. In conclusion, the future of solar system exploration appears to be very bright. NASA is taking the technological and programmatic steps necessary to support future missions that will explore our solar system in astounding detail.

Supported by the strategy laid out in the Survey, future solar system exploration will enable us to answer three fundamental human questions:

Are we alone?
Where did we come from?
What is our destiny?

What's Next

2004
- European Rosetta mission, to land a science probe on the surface of Comet Churyumov-Gerasimenko
- Mercury orbiter, MESSENGER, to look for water-ice on the closest planet to the Sun
- Comet rendezvous, Deep Impact, to fire a bullet into comet P/Tempel 1 and study the ejecta and crater
- Japanese Lunar-A, Lunar Mapping Orbiter and Penetrator, to fire two bullets 3 meters into the lunar soil near Apollo 12 and 14 sites

2005
- Mars Reconnaissance Orbiter (MRO) launch, Mars Orbiter to collect high-resolution, 1-meter, images in stereo-view of Mars
- European Venus Express, Venus Orbiter for two-year nominal mapping life [486 days, two Venus year]

2006
- New Horizons, Pluto and moon Charon flyby, mapping to outer solar system cometary fields and Kuiper Belt
- Dawn, Asteroid Ceres and Vesta rendezvous and orbiter, including investigations of asteroid water and influence on meteors
- Kepler, Extrasolar Terrestrial Planet Detection Mission, designed to look for transiting or earth-size planets that eclipse their parent stars [survey 100,000 stars]
- Europa Orbiter, planned Orbiter of Jupiters ice-covered moon, Europa, uses a radar sounder to bounce radio waves through the ice
- Japanese SELENE Lunar Orbiter and Lander, to probe the origin and evolution of the moon

2007
- Japanese Planet-C Venus Orbiter, to study the Venusian atmosphere, lightning, and volcanoes.
- Mars Scout mission, final selections August 2003 from four Scouts: SCIM, ARES, MARVEL and Phoenix
- French Mars Remote Sensing Orbiter and four small Netlanders, linked by Italian communications orbiter

2009
- BepiColumbo, European Mercury Orbiters and Lander, including Japanese collaborators, lander to operate for one week on surface
- Mars 2009, proposed long-range rover to demonstrate hazard avoidance and accurate landing dynamics


Dr. Michael Belton served as Chairman of the Solar System Exploration (Decadal) Survey for the Space Studies Board of the National Research Council. The NRC is the operating arm of the National Academy of Sciences, chartered by Congress in 1863 to advise the government on matters of science and technology. Dr. Belton is an Emeritus Astronomer at the National Optical Astronomy Observatory and President of Belton Space Exploration Initiatives, LLC, in Tucson, Arizona. He has been an investigator on several NASA flight missions including Mariner Venus-Mercury, Voyager, Galileo, Contour and Deep Impact. The Office of Space Science of the National Aeronautics and Space Administration sponsored the SSE Survey to chart a bold strategy for general solar system and Mars exploration over the next decade. The Survey reported its recommendations in July 2002.

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