JPL and NASA News

Bill Wheaton, IPAC - 1999 May

The New Mars Program

Developments in the exploration of Mars have been so rapid during the past few months that it seems I could almost devote this entire column to Mars alone, every month, and still hardly keep up. At this moment Mars Global Surveyor (MGS) is in operation, finally in its proper mapping orbit (despite a problem with an antenna hinge, still being worked); the Mars Climate Orbiter (MCO) and the Mars Polar Lander (MPL, carrying also two Deep Space 2 micro-penetrator probes) are in transit and scheduled to arrive later this year. I have previously described these missions, most recently in the January 1999 and September 1998 issues. Exciting as they are, the most remarkable recent development is the suite of missions in preparation and planning, which includes landers and orbiters at virtually every two-year opportunity, and a simply bewildering array of rovers, sample-return missions, and even an aircraft.

Mars mission opportunities are timed about every two years, much like oppositions. To go to Mars efficiently, one must wait until a few months before opposition, and then depart from Earth by increasing one's orbital speed around the Sun. The transfer orbit is approximately tangent to the orbits of both Earth and Mars, with the Earth-Mars opposition somewhere between launch and arrival. Thus the current MCO and MPL missions departed in December 1998 and January 1999, and will arrive in September and December 1999, respectively, with opposition in April 1999 just past. Note that returns from Mars to Earth run on a rather similar schedule, centered on the oppositions: departing before, and arriving after. The mean interval between oppositions is 2.135 years, or 2 years and a little over 7 weeks, with substantial variations around the mean, mainly due to the large eccentricity of Mars's orbit. Based on such arithmetic, oppositions and hence opportunities occur on odd years, e.g. '01 ,'03, '05, '07, until late in the next decade.

Objectives of the program include characterization of the chemistry and composition of the surface and atmosphere, a search for evidence of present or past water, and of course the search for fossil life. It had originally been planned to launch an ambitious rover for the 2001 opportunity, which would gather and cache rocks for later return to Earth in 2005. Unfortunately cost and schedule problems with the rover and its elaborate instruments proved too much and forced a painful revision, completed last November. The original 2001 rover has been placed with a much simpler version, similar to that on Pathfinder in 1997, and the more complex sample-collecting rover delayed until 2003. The new plan, as summarized in the table, is greatly broadened and strengthened by major involvement of European partners, especially France and Italy. It is based on a sample return scheme in which US landers and rover combinations ('03, '05, '07, '09) collect and launch Martian samples (about 1 kg each) to low orbit using a solid-fuel Mars Ascent Vehicle (MAV). The samples are then collected in Mars orbit by orbiters, launched on an Ariane 5's, in 2005 (committed) and 2009 (planned), for final return by parachute to Utah.

This is certainly a very ambitious and exciting plan. It has the robustness advantage of being spread among a number of less-expensive missions, so no single failure would cause loss of the major objectives. The French contribution of at least one and possibly two Ariane 5 vehicles for the sample return is critical, as current US alternative launchers (only Titan IV is yet in operation) are too expensive considering the $300 million per year NASA plans to spend on the program.

In addition to the key missions shown above, a number of others, both NASA and non-US, are possible and at various stages of development. The Japanese Nozomi Mars orbiter is already launched, but will not arrive until early 2004 due to problems encountered in its on-board propulsion system. Putting all together, even if budget or technical problems result in some loss, the next decade should be extremely productive in advancing our knowledge of Mars. Administrator Dan Goldin and many others have expressed the belief that successful completion of the plan will permit the realistic consideration of human exploration missions in the 2010-2020 time frame.

Bill Wheaton
Waw@ipac.caltech.edu