Earth and Moon Missions

It is still easiest to study our planet and its closest neighbor than sending a probe elsewhere. This page talks about the important missions that study Earth and the moon that have occurred so far this century ... which so far is only one.

SMART - 1 SMART-1, Europe's first science spacecraft sent to orbit Earth's moon, was launched at 23:14 GMT on September 27, 2003, aboard Ariane Flight 162, launched from the Guiana Space Center in Kourou, French Guiana. It achieved its initial Earth orbit within the next hour. The 368 kg (811 lb) craft entered orbit of the moon on November 15, 2004. Its mission has been extended once so far to end in August 2006.

As the first mission in the new series of Small Missions for Advanced Research in Technology, SMART-1 is mainly designed to demonstrate innovative and key technologies for future deep space science missions. However, it is also a remote sensing probe with the goal of making the first comprehensive inventory of key chemical elements in the lunar surface. It will also try to gather evidence to support or refute the theory that the moon was formed in a violent collision of a small, Mars-sized planet with Earth early in our history.

The first technology to be demonstrated on SMART-1 was the Solar Electric Primary Propulsion (SEPP), a highly efficient and lightweight propulsion system that is ideal for long-duration deep space missions in and beyond our solar system. SMART-1's propulsion system consists in a single ion engine fuelled by 82 kg (181 lb) of xenon gas and pure solar energy. This plasma thruster relies on the "Hall Effect" to accelerate xenon ions to speed up to 16,000 km/hour (10,000 mph). It is able to deliver 70 mN of thrust with a specific impulse (the ratio between thrust and propellant consumption) 5 to 10 times better than traditional chemical thrusters and for much longer durations (months or even years, compared to the few minutes' operating times typical of traditional chemical engines).

The ion engine was scheduled to go into action on September 30, 2003. At first, fired almost continuously - stopping only when the spacecraft was in the Earth's shadow - to raise the altitude of its perigee (the lowest point of its orbit) from 750 to 20,000 km (450 to 12,500 miles). This maneuver took about 80 days to complete and placed the spacecraft safely above the radiation belts that surround the Earth.

Once at a safe distance from Earth, SMART-1 fired its thruster for periods of several days to progressively raise its apogee (the maximum altitude of its orbit) to the orbit of the moon. At 200,000 km (125,000 miles) from Earth, it began receiving significant tugs from the moon as it passed by. It then performed gravity-assist maneuvers while flying by the moon. Eventually, SMART-1 was "captured" and entered a near-polar elliptical lunar orbit. SMART-1 then used its thruster to reduce the altitude and eccentricity of this orbit.

During this transfer phase, the solar-electric primary propulsion's performance, and its interactions with the spacecraft and its environment, will were closely monitored by the Spacecraft Potential, Electron & Dust Experiment (SPEDE) and the Electric Propulsion Diagnostic Package (EPDP) to detect possible side-effects or interactions with natural electric and magnetic phenomena in nearby space. A promising technology, Solar Electric Primary Propulsion could be applied to numerous interplanetary missions in the solar system, reducing the size and cost of propulsion systems while increasing maneuvering flexibility and the mass available for scientific instrumentation.

In addition to Solar Electric Primary Propulsion, SMART-1 demonstrated a wide range of new technologies like a Li-Ion modular battery package; new-generation high-data-rate deep space communications in X and Ka bands with the X/Ka-band Telemetry and Telecommand Experiment (KaTE); and a computer technique enabling spacecraft to determine their position autonomously in space, which is the first step towards fully autonomous spacecraft navigation.

In early 2005, SMART-1 began the second phase of its mission, due to end in August 2005 but extended an extra year to August 2006, and dedicated to the study of the moon from a near polar orbit. For more than 40 years, the moon has been visited by automated space probes and by nine manned expeditions, six of which landed on its surface. Nevertheless, much remains to be learnt about our closest neighbor, and SMART-1's payload will conduct observations never performed before in such detail.

The Advanced/Moon Micro-Imaging Experiment (AMIE) miniaturized CCD camera will provide high-resolution and high-sensitivity imagery of the surface, even in poorly lit polar areas. The highly compact SIR infrared spectrometer will map lunar materials and look for water and carbon dioxide ice in permanently shadowed craters. The Demonstration Compact Imaging X-ray Spectrometer (D-CIXS) will provide the first global chemical map of the Moon and the X-ray Solar Monitor (XSM) will perform spectrometric observations of the sun and provide calibration data to D-CIXS to compensate for solar variability.

The SPEDE experiment used to monitor Solar Electric Primary Propulsion interactions with the environment will also study how the solar wind affects the Moon. The overall data collected by SMART-1 will provide new inputs for studies of the evolution of the moon, its chemical composition and its geophysical processes, and also for comparative planetology in general.

In addition to valuable lunar science, SMART-1's payload will be involved in the mission's technology demonstrations to prepare for future-generation deep space missions. For instance, the AMIE camera will be used to validate the On-Board Autonomous Navigation (OBAN) algorithm, which correlates data from sensors and star trackers to provide navigational data. It will also participate in a laser communication link experiment with ESA's optical ground station at the Teide Observatory in Tenerife, Canary Islands, trying to detect an incoming laser beam from the ground.

Using both AMIE and KaTE hardware, the Radio Science Investigation System (RSIS) experiment will demonstrate a new way of gauging the interiors of planets and their moons by detecting the well-known tilting motion of the Moon. This technology can be used later by ESA planetary missions.