Homes Away From Home: Map III
Homes Away from Home: Map III
The exploration of our solar system is founded upon the pursuit of three simple yet profound questions:Where do we come from? Where are we going? Are we alone?
This three-part series, "Homes Away from Home," highlights what is known today, and hoped to be discovered, about our solar neighborhood. The story of life elsewhere is told beginning with the very large and distant places, as they might have seeded what today is very small and near. Our solar system began to take shape about 4.6 billion years ago, as the primordial solar nebula of dust and gas began to coalesce around the infant Sun. Within the first billion years or so, the planets formed and life began to emerge on Earth — and perhaps elsewhere.
Heavens on Earth
At present there are fourteen NASA solar system exploration missions, including five Mars missions, either in flight or in full-scale development.
|Explorer to the Moon’s South Pole, and potentially lunar basin ice.|
MESSENGER is being prepared for launch in 2004. As the first Mercury orbiter, it will provide unprecedented insight into the composition, structure, and history of the innermost planet. In July 2004, the international Cassini-Huygens mission will arrive at Saturn to begin its four-year mission. A major focus will be Titan, whose atmosphere may be a prebiotic analog to that of the early Earth. The Huygens probe will descend through Titan’s clouds in January 2005.
The first two deep space sample return missions, Genesis and Stardust, are in flight now as a part of NASA’s Discovery Program. They will return their small yet tremendously valuable samples to Earth in 2004 and 2006, respectively. During a high-speed encounter, Stardust will capture samples of dust and gas from the tail of a comet and return them to Earth. Genesis will acquire and return to Earth samples of the solar wind, a continuous stream of small particles ejected from the outer regions of the Sun. The image above shows the Sun as seen in ultraviolet light.
The first planned New Frontiers mission, New Horizons, would be launched in 2006 to conduct the first reconnaissance of the Pluto-Charon system and possibly other Kuiper objects.
The top priority (non-Mars) flagship mission objective is intensive exploration of potential subsurface oceans on Jupiter’s large icy satellites. The Galileo mission has provided strong indications that a liquid ocean may exist beneath the ice crust of Europa, and perhaps beneath the surfaces of Ganymede and Callisto as well. Examples of high-priority missions that would represent major scientific advances include:
* A Titan Explorer that would build on the results of the Cassini-Huygens mission by performing a detailed in situ exploration of Titan.
* A Neptune Orbiter with Probes that would perform the first detailed exploration of this ice giant planet and its major moon, Triton.
* A Venus Sample Return that would provide insight into the causes and effects of the apparent global climate change that Venus experienced in the distant past. At the surface of Venus and at the depths we must explore on Jupiter, the convergence of temperature and pressure conditions limits the lifetime of systems built with present technology to just minutes. Improved pressure vessels, thermal control, temperature-tolerant electronics, and low-power systems are needed to prolong the lives of these vehicles.
Using highly efficient nuclear electric propulsion, a single mission could successively orbit Callisto, Ganymede, and Europa. This Jupiter Icy Moons Orbiter would represent a major step in our understanding of the nature and extent of habitable environments in the solar system. In addition, as the first application of nuclear electric propulsion, this mission would open a pathway for use of this revolutionary technology throughout the solar system. The large propulsive capability will enable high-energy missions that are otherwise impossible, and the fission power supply allows increased data return as well as fundamentally new types of scientific measurements. NASA is studying the Jupiter Icy Moons Orbiter for a possible launch early in the next decade.
Follow the Water
The Mars’ exploration strategy is characterized by the increasingly refined search for sites that show evidence of past or present liquid water, and for materials that may preserve either biosignatures or paleo-environmental records.
|Orbital, surface and sub-surface explorers for Mars.|
The Mars Exploration Rovers are sophisticated mobile explorers that will roam Mars for three months or more, searching for and studying evidence of past liquid water and martian climatic evolution. Each rover can travel up to 100 meters per day and can take microscopic images as well as broad panoramas. The MERs are more than ten times the size of the Sojourner rover that fascinated the world in 1997. . The Mars Reconnaissance Orbiter, to be launched in 2005, will observe the martian surface with unprecedented precision. By resolving features as small as 8-12 inches across, it will allow us to follow the tantalizing hints of water wherever they lead.
NASA’s first Mars Scout will be selected in 2003 for the 2007 Mars launch opportunity. It is anticipated that Mars Scout missions will be launched at every other Mars opportunity, or about once every four years. One Mars exploration "pathway" might focus on exploration of extinct hydrothermal vent systems in the search for evidence of life below the surface.
The year 2009 will represent another quantum leap in Mars exploration when the Mars Science Laboratory (MSL) is planned to be launched. The overall objective of MSL is to address issues of martian habitability, which we define as the potential of the planet to have supported life at some time in its history. To accomplish this, MSL would be designed as a mobile platform for suites of instruments that enable it to function as a sophisticated in situ scientific laboratory. Included will be a "contact suite" of instruments that require physical contact with rocks or soil, a "remote sensing suite" for more distant observations, and, most importantly, an "analytical suite" to take in and analyze samples of martian materials. It would incorporate precision landing, by which it can land within a few kilometers of sites of targets of scientific interest, hazard detection and avoidance, and long-range mobility that will allow us to explore specific sites up to several kilometers away in a single mission. MSL may also incorporate a new radioisotope power system that will provide it with an operational lifetime of a year or more, dramatically increasing the scientific capability of this advanced robotic explorer.
In order to maximize the science return from our spacecraft operating on and around Mars, NASA is planning to place a communications relay satellite — a Mars Telesat — into orbit around Mars in 2009. This satellite will be designed for a lifetime of at least six years, with a goal of ten years, and will be placed into a high Mars orbit that will enable it to cover a large fraction of the martian surface every few hours. The Telesat will not only substantially increase the total volume of data that can be returned from Mars, it will also provide essential telemetry relay during critical events such as Mars landings, orbital entries, and the launch of samples from the martian surface.
Progress in solar system exploration over the past forty years has required major improvements in deep space telecommunications. The most recent advance is the implementation of communications systems operating at Ka-band. This capability, to be fully demonstrated on the 2005 Mars Reconnaissance Orbiter, will provide a data rate from Mars of more than 2 megabits/second. In addition to its role as a relay at various radio frequencies, the Telesat will carry the first deep space optical communications payload. This revolutionary technology utilizes laser light instead of radio waves to dramatically expand the data "pipeline" to Earth. As the first operational test of optical communications for planetary missions, this experiment on the Mars Telesat will help to alleviate one of the fundamental constraints on solar system exploration.
Getting There vs. Being There
Many of the more energy-intensive missions planned for the future, however, would be severely constrained by chemical propulsion technology, which is approaching the limit of its capabilities for reasonable flight times. A major step forward in interplanetary transportation technology occurred in 2001 with completion of the space validation of solar electric propulsion (SEP) by the New Millennium Program’s DS-1 spacecraft. This technology can reduce the propellant required to reach certain planetary destinations by a factor of 10 or more, and can significantly reduce flight times for high-energy missions.
|Highly efficient ion engine nozzle, driven by an exhaust of charged particles.|
The first planned application of SEP on a science mission will be Dawn, a multi-asteroid orbiter, under development for launch in 2007. Significant improvements in the efficiency and performance of SEP are underway, and the resulting systems may provide substantial benefits to planned missions to small bodies and the inner planets. When coupled with aerocapture (rapid aerodynamic braking within a planetary atmosphere), SEP may also enable rapid and cost-effective delivery of orbital payloads to the outer solar system, as well as the ability to deliver much larger payloads into orbit around Mars and Venus.
Mid- and far-term flagship missions to the outer solar system, such as the Jupiter Icy Moons Orbiter, will require a propulsive capability that far exceeds the potential of chemical propulsion or SEP. For these high-priority missions, nuclear electric propulsion (NEP) is an enabling technology. This requires the development of a compact and efficient fission power source coupled to advanced electric propulsion systems.
To meet the needs of the next generation of highly capable planetary explorers, NASA is developing new, safe, reliable power and propulsion systems based on nuclear technologies. Project Prometheus has two primary near-term objectives. First, it will develop a new, more efficient radioisotope power system (RPS) to provide spacecraft electrical power for surface and deep space applications. The first use of this new RPS may be on the Mars Science Laboratory, to be launched in 2009. Project Prometheus is also developing a compact fission reactor that would provide power of up to 100 kilowatts to support nuclear electric propulsion. This technology would revolutionize solar system exploration by enabling high-energy missions that cannot be accomplished using conventional power and propulsion technology. The first utilization of fission power and propulsion would be on the Jupiter Icy Moons Orbiter, which is under study for possible launch early in the next decade.
In spacecraft design, smaller is almost always better. The payoff from miniaturization of planetary instruments is significant, since the cost of delivering 1 kilogram of payload to a planetary destination may be anywhere from five to thirty times the cost of delivering a comparable amount of payload to Earth orbit. The NASA-developed thermopile detectors to be used on the Mars Reconnaissance Orbiter, for example, reduced the mass of the instrument by 35 kilograms, providing a major benefit to the mission. Reducing landed mass is even more critical due to the additional propulsion and shielding required to place systems on planetary surfaces.