SMART 1

Spacecraft design

SMART-1 was about one metre across, and lightweight in comparison to other probes. Its launch mass was 367 kg or 809 pounds, of which 287 kg (633 lb) was non-propellant.

It was propelled by a solar-powered Hall effect thruster (Snecma PPS-1350-G) using xenon propellant, of which there was 82 kg (50 litres by volume at a pressure of 150 bar) at launch. The thrusters used an electrostatic field to ionize the xenon and accelerate the ions to a high speed. This ion engine setup achieved a specific impulse of 16.1 kN·s/kg (1,640 seconds), more than three times the maximum for chemical rockets. Therefore, 1 kg of propellant (1/350 to 1/300 of the total mass of the spacecraft) produced a delta-v of about 45 m/s. The electric propulsion subsystem had a weight of 29 kg with a peak power consumption of 1,200 watts. SMART-1 is the first in the program of ESA's Small Missions for Advanced Research and Technology.

The solar arrays made 1,190 W available for powering the thruster, giving a nominal thrust of 68 mN, hence an acceleration of 0.2 mm/s² or 0.7 m/s per hour (i.e., just under 0.00002 g of acceleration). As with all ion-engine powered craft, orbital maneuvers were not carried out in short bursts but very gradually. The particular trajectory taken by SMART-1 to the Moon required thrusting for about one third to one half of every orbit. When spiralling away from the Earth thrusting was done on the perigee part of the orbit. At the end of the mission, the thruster had demonstrated the following capability:

As part of the European Space Agency's strategy to build very inexpensive and relatively small spaceships, the total cost of SMART-1 was a relatively small 110 million euros (about 170 million U.S. dollars). SMART-1 was designed and developed by the Swedish Space Corporation on behalf of ESA. Assembly of the spacecraft was carried out by Saab Space in Linköping. Tests of the spacecraft were directed by Swedish Space Corporation and executed by Saab Space. The project manager at ESA was Giuseppe Racca and the project manager at the Swedish Space Corporation was Peter Rathsman; the Principal Project Scientist was Bernard Foing.

AMIE

The Advanced Moon micro-Imager Experiment was a miniature colour camera for lunar imaging. The CCD camera with three filters of 750, 900 and 950 nm was able to take images with an average pixel resolution of 80 m (about 260 ft). The camera weighed 2.1 kg (about 4.5 lb) and had a power consumption of 9 watts.

D-CIXS

The Demonstration of a Compact X-ray Spectrometer was an X-ray telescope for the identification of chemical elements on the lunar surface. It detected the x-ray fluorescence (XRF) of crystal compounds created through the interaction of the electron shell with the solar wind particles to measure the abundance of the three main components: magnesium, silicon and aluminium. The detection of iron, calcium and titanium depended on the solar activity. The detection range for x-rays was 0.5 to 10 keV. The spectrometer and XSM (described below) together weighed 5.2 kg and had a power consumption of 18 watts.

XSM

The X-ray solar monitor studied the solar variability to complement D-CIXS measurements.

SIR

The Smart-1 Infrared Spectrometer was an infrared spectrometer for the identification of mineral spectra of olivine and pyroxene. It detected wavelengths from 0.93 to 2.4 µm with 256 channels. The package weighed 2.3 kg and had a power consumption of 4.1 watts.

EPDP

The Electric Propulsion Diagnostic Package was to acquire data on the new propulsion system on SMART-1. The package weighed 0.8 kg and had a power consumption of 1.8 watts.

SPEDE

The Spacecraft Potential, Electron and Dust Experiment. The experiment weighed 0.8 kg and had a power consumption of 1.8 watts. Its function was to measure the properties and density of the plasma around the spacecraft, either as a Langmuir probe or as an electric field probe. SPEDE observed the emission of the spacecraft's ion engine and the "wake" the Moon leaves to the solar wind. Unlike most other instruments that have to be shut down to prevent damage, SPEDE could keep measuring inside radiation belts and in solar storms, such as the Halloween solar storms, 2003. It was built by Finnish Meteorological Institute and its name was intentionally chosen so that its acronym is the same as the nickname of Spede Pasanen, famous Finnish movie actor, movie producer and inventor. The algorithms developed for SPEDE were later used in the ESA lander Philae.

KATE

K_a band TT&C (telemetry, tracking and control) Experiment. The experiment weighed 6.2 kg and had a power consumption of 26 watts.

Flight

SMART-1 was launched September 27, 2003 together with Insat 3E and eBird 1, by an Ariane 5 rocket from the Guiana Space Centre in French Guiana. After 42 minutes it was released into a geostationary transfer orbit of 7,035 × 42,223 km. From there it used its Solar Electric Primary Propulsion (SEPP) to gradually spiral out during thirteen months.

The orbit can be seen up to October 26, 2004 at spaceref.com, when the orbit was 179,718 × 305,214 km. On that date, after the 289th engine pulse, the SEPP had accumulated a total on-time of nearly 3,648 hours out of a total flight time of 8,000 hours, hence a little less than half of its total mission. It consumed about 58.8 kg of xenon and produced a delta-v of 2,737 m/s (46.5 m/s per kg xenon, 0.75 m/s per hour on-time). It was powered on again on November 15 for a planned burn of 4.5 days to enter fully into lunar orbit. It took until February 2005 using the electric thruster to decelerate into the final orbit 300-3,000 km above the Moon's surface. The end of mission performance demonstrated by the propulsion system is stated above.

After its last perigee on November 2, on November 11, 2004 it passed through the L₁ Lagrangian Point and into the area dominated by the Moon's gravitational influence, and at 1748 UT on November 15 passed the first periselene of its lunar orbit. The osculating orbit on that date was 6,704 × 53,208 km, with an orbital period of 129 hours, although the actual orbit was accomplished in only 89 hours. This illustrates the significant impact that the engine burns have on the orbit and marks the meaning of the osculating orbit, which is the orbit that would be travelled by the spacecraft if at that instant all perturbations, including thrust, would cease.

ESA announced on February 15, 2005, the endorsement of a proposal to extend the mission of SMART-1 by one year until August 2006. This date was later shifted to September 3, 2006, to enable scientific observations from Earth.

Lunar impact

SMART-1 impacted the Moon's surface as planned, on September 3, 2006 at 05:42:22 UTC, ending its mission. Moving at approximately 2,000 m/s (4,500 mph), SMART-1 created an impact visible with ground telescopes from Earth. It is hoped that not only will this provide some data simulating a meteor impact, but also that it might expose materials in the ground, like water ice, to spectroscopic analysis.

ESA estimated that impact occurred at 34°24′S 46°12′W. These numbers can be entered into NASA's World Wind, to see where on the Moon it crashed. At the time of impact, the Moon was visible in North and South America, and places in the Pacific Ocean, but not Europe, Africa, or western Asia.

This project has generated data and know-how that will be used for other missions, such as the ESA's BepiColombo mission to Mercury.

The Committee on Space Research has established rules to protect planets and moons from possible contamination by spacecraft. In response to concerns of SMART-1 contaminating the Moon, ESA claims that "every chemical element present on SMART-1 and in its instruments exists naturally on the Moon". This is despite the fact that no such criticisms were made of the American Ranger program which had the primary objective of crashing probes on the Moon, nor of the many other crashed and landed probes, etc..

Important events and discoveries