This week will be one of contrasts for space exploration. Sunday at 7:36 p.m., a robotic device from Earth touched down on the northern plains of Mars to analyze the soil for water. Next Saturday, seven astronauts will lift off the surface of Earth in the next space shuttle mission, in which they will attach a science laboratory to the International Space Station. Man or machine? Which is best for space exploration?
Space is a hostile place. Humans need air, food, water and minimal exposure to ionizing radiation. Outer space provides none of these and, therefore, is fatal to humans without an enclosure providing an artificial living environment. Everything that is necessary for human existence must be brought along for the ride. That is an enormous amount of payload to be lifted into space that can be superfluous to the mission objectives.
All the equipment that creates and maintains this living environment must be constantly monitored. Such a commitment reduces the useful time that an astronaut has to perform experiments for scientific inquiry, whether on the space shuttle, space station or the future Crew Exploration Vehicle to the moon.
Human space flights are enormously expensive and their cost effectiveness is unclear. The average cost for a space shuttle flight is currently estimated to be around three-quarters of a billion dollars. Robotic explorers have been performing the important science in the background with little fanfare and relatively inexpensively.
Machines extend our reach into space significantly faster and farther than can be done with manned missions. For example, the two Voyager spacecraft, in space for more than 30 years, are several billion miles from the sun and are still sending back information. Launched in 1977 to explore the outer planets, these spacecraft are approaching the region where the influence of the sun ends — the true “edge” of our solar system. In the coming years, the Voyagers are expected to cross this boundary, leave the solar system, and become the first vehicles from Earth to enter the realm of interstellar space.
Other ongoing robotic missions include the Messenger mission to Mercury, which has just completed its first pass by the planet. This unmanned spacecraft will enter into a permanent orbit around Mercury in 2011. The New Horizons mission to Pluto is in transit, with an arrival time of 2015. Spirit and Opportunity, the current Mars rovers with their 90-day expected lifetime are still operating four years later. (And who can forget the endearing Mars Pathfinder microrover back in 1997?) The Cassini spacecraft has been swinging around Saturn since 2004 and is expected to do so for another two years; the Galileo mission orbited an unmanned planetary probe around Jupiter for eight years.
Multiyear unmanned missions, generally unheard of by the public, with obscure names such as COBE, WMAP, AXAF and SOHO, have given astronomers and physicists great insight into the nature and structure of stars, galaxies and the universe.
Separate roles to play
Robotic space missions serve a useful purpose as the trailblazers, the mechanized pioneers, investigating the path ahead. When it comes to survey missions, orbiters, landers and rovers produce impressive results. The long-term follow-up studies are where crewed missions do better.
Robots can only follow programmed instructions. Man, not machines, can initiate new paths of investigation — and on the spot. The remote interpretation of data from a probe can lead to ambiguous results without the ability to perform follow-up tests. Each unmanned mission is limited in scope and ability, primarily because of a minimized design. Such a trimmed-down version is essential because of the launch constraint of reducing the payload weight — these machines have to be “thrown” a long way!
Astronauts can maneuver a spacecraft to a desired location and calibrate their instruments on the spot. Robotic missions have to be placed and their instruments calibrated in advance. Machines have to be sturdy to survive the tumultuous vibrations of launch, so instrument sensitivity is compromised for ruggedness.
Humans can creatively solve problems on location, but robotic probes must rely on redundancy. Malfunctions and design flaws can be terminal. The Hubble Space Telescope originally had optical problems but it was repaired and upgraded several times by humans (and it will be again later this summer).
Robotic probes can miss important clues, while humans can quickly determine what to study. One “live” geologist on Mars could answer many questions after a few weeks of study that would take years for multiple robotic probes.
Public opinion is in favor of manned space flight. Humankind sees itself exploring space directly, not by proxy.
With the track record improving for landing machines on Mars, there is optimism that the Phoenix Mars Lander would successfully set down Sunday evening on the Red Planet. A far northern site was chosen because the Odyssey orbiter, circling Mars, has found evidence for frozen water in the northern soil.
Phoenix will dig into the ground and analyze these soil samples for water and carbon compounds. This lander is also equipped with cameras, microscopes and a weather station that will provide information about the ongoing atmospheric changes in Mars’ arctic region.
Back to the ISS
Space Shuttle Discovery is set for launch to the International Space Station at the end of this week. This is the second of three flights that will bring components of a Japanese science laboratory to the ISS and is Japan’s major contribution to the station. Called “Kibo,” meaning “hope,” it consists of a pressurized laboratory module and two robotic arms that are mounted on the exterior of the lab.
Discovery’s 14-day mission includes three space walks, two for working on the installation of Kibo and the third walk to replace a failed nitrogen tank attached to the outside of the station. This mission is the 26th flight to the Space Station and the 35th flight for Space Shuttle Discovery.