INFO 22-1998: Hurry along please, for the Mars Express
19 June 1998
Any scientists wanting to send instruments to the surface of the planet Mars have until 3 July to offer a small lander that might be carried aboard the European Space Agency mission Mars Express. The selection of a lander, if any, will then be the last stage in defining the scientific payload of Mars Express, which is intended to go into orbit around the Red Planet at the end of 2003. The choice of instruments for the orbiting spacecraft was recently ratified by ESA's Science Programme Committee. This month ESA is inviting tenders to build the spacecraft from three industrial competitors, Alenia/Aerospatiale, Dornier and Matra-Marconi, who have already studied the mission. The project must be fully defined in time for the Science Programme Committee to finally confirm Mars Express.Why the hurry? The deadline is set in the form of a favourable launch opportunity just five years from now. The positions of Earth and Mars in their orbits at that time will mean that a spacecraft can reach Mars more quickly, carrying a greater weight of instruments, than from any other launch date in the next decade. A decision to proceed taken towards the end of 1998 would leave less than five years to create, test and launch a complex spacecraft and meet that deadline. Most judgements about Mars Express and its instruments have therefore to be made in advance if the engineers and scientists are to make sure that everything is ready for lift-off in June 2003.
The brisk pace is also fitting for the prototype of a new class of Flexi (flexible) missions. Mars Express is the first of what should become a series of relatively inexpensive and quick projects introduced into ESA's space science, to seize special opportunities to broaden the programme. At about one-quarter of the cost of the major Cornerstone missions, which have long lead-times, the Flexi missions replace the previous class of Medium missions, in ESA's forward planning. Streamlined management procedures for the Flexi missions help to keep down the costs to ESA while placing more responsibility on the industrial contractors and the participating scientists.
Space scientists advising ESA recognized the special opportunity for Mars Express after the failure of the Russian Mars 96 mission, in November 1996. It left a gap in the international programme for the exploration of Mars, and some of the key instruments which fell into the Pacific Ocean with Mars 96 had been devised by space scientists in ESA member states. The strong scientific interest in Mars within Europe, and the predicted advantage of the mid-2003 launch, led to the proposal to add Mars Express to ESA's programme.
A distinctive role in exploring Mars
The search for water is one of the main tasks foreseen for Mars Express. The discovery of reservoirs of frozen or liquid water beneath the martian surface would greatly improve the practical possibilities for human ventures to the Red Planet. It would shed light on the chemical history of Mars and on whether conditions were ever right for life to appear there. And the chief motive for all of ESA's deep-space missions is to understand the Earth better. The fate of water on Mars is one of the salient questions about why the planet is very different from the Earth, although it is a near neighbour in the Solar System.
A team led by the University of Rome will contribute the Subsurface Sounding Radar/Altimeter on Mars Express. This instrument will map the distribution of ice and liquid water with radar pulses penetrating the martian surface. It will chart the topography of the surface too, and the observed effects of the martian ionosphere on the radar waves will show how the solar wind influences the state of the atmosphere. The link between the solar wind and the fate of water on Mars is the concern of the Swedish Institute of Space Physics in Kiruna, and the ASPERA experiment lead. Mars may have lost most of its water by solar effects destroying water vapour in the atmosphere. By sensing neutral and charged atomic particles in the planet's vicinity, ASPERA will shed light on any such mechanism for dehydrating Mars.
The escape of gas from Mars will also be seen by SPICAM UV, which is the special responsibility of the Service d'Aéronomie at Verrières near Paris. The instrument will examine the martian atmosphere by ultraviolet light. A major aim of SPICAM UV is to clarify the threat that solar ultraviolet rays and oxidizing chemicals (ozone and hydroxyl) may have posed to any life incipient on Mars.
Comprehensive observations of the martian atmosphere, and of its gases, dust and weather, will come from PFS, an infrared instrument provided by a team led by the Istituto di Fisica dello Spazio Interplanetario in Frascati. It measures the intensities of infrared rays at sharply defined wavelengths. PFS will also monitor temperature changes on the surface, and investigate the seasonal frost on Mars.
To provide minerological information about the surface of Mars is the job of the mapping spectrometer OMEGA, supervised by the Institut d'Astrophysique Spatiale at Orsay near Paris. It will observe the gases and dust in the atmosphere too, but the main aim of OMEGA is to use visible and infrared signatures to distinguish materials on the surface -- silicates, hydrated minerals, oxides and carbonates, organic frosts and ices.
Confirming Europe's chance to make a distinctive and original contribution to the study of Mars is a unique German instrument, the High Resolution Stereo Camera. It will provide unprecedented images in stereo and colour, showing details of the surface down to 12-15 metres, across huge areas. Its images will enable scientists to re-evaluate the the history of Mars and its volcanic and water-eroded features, as well as giving clearer impressions of dust storms, frost and other weather-related events. The principal investigator for the stereo camera is at the Institut für Planetenerkundung in Berlin.
A valuable addition to the science of Mars Express requires no special onboard equipment. The Radio Science Experiment, masterminded at the University of Cologne, will use the radio communications link between the spacecraft and the Earth to probe the martian atmosphere. Effects of the martian surface on radio signals reflected from it will give fresh clues to the surface composition, and the radio science observations will help to refine the measurements of heights and effects of gravity, made with the stereo camera.
Family resemblances between the experiments on Mars Express and those selected for the Rosetta mission to Comet Wirtanen show a coherence in ESA's approach to the science of the Solar System. Rosetta is due to fly a few months before Mars Express.
The lander option
In addition to the seven excellent experiments selected for the orbiter, a lander is also considered as an option, with a mass of about 60 kilograms. The Agency now expects proposals from the science community for this lander by July 3rd.
