BR-232 SMART-1. Technology records from ESA s small genius en route to the Moon ESA ACHIEVEMENTS

Transcription

1 BR-232 SMART-1 Technology records from ESA s small genius en route to the Moon ESA ACHIEVEMENTS

2 Card 1 The experiments that make up the SMART-1 payload, weighing only 19 kilograms in total, were tested during the 13-month cruise phase between the spacecraft s launch at the end of September 2003 and its arrival at the Moon in mid- November Major mission goals are to: 1 Conduct the first European in-flight test of a solar-electrically powered ion engine as the main spacecraft propulsion system, instead of the chemical propulsion commonly used today, and monitor the effects of using such an engine on the spacecraft s environment and performance at system level (SPEDE and EPDP experiments). In addition, test the response of an ion-enginepropelled spacecraft when subjected to gravityassist manoeuvres, a technique currently used by interplanetary missions to gain acceleration from celestial objects (e.g. planets) in order to reach their final target, thereby saving fuel. 2. Test future deep-space communication techniques for spacecraft (KaTE, RSIS and laser link experiments). 3 Test techniques for eventually achieving autonomous spacecraft navigation (OBAN experiment). 4 Begin testing the performance of miniaturised scientific instrumentation (AMIE micro-camera, SIR infrared spectrometer, D-CIXS X-ray camera and XSM X-ray instrument). AOES Medialab ESA

3 Card 1 The SMART philosophy How do we explore the planets, stars, galaxies and delve into their mysteries to unveil the secrets and laws of the Universe, while providing answers that advance today s understanding of nature? How do we optimise know-how, resources and technological investment versus scientific return? How do we design a spacecraft that is lighter, highly reliable, and can be operated more flexibly? How do we make European industrial technological competitiveness and independence grow? Ultimately, how do we look far into the future and think about the next generation of scientific space missions? One sensible answer to such questions is to develop a long-term scientific programme, in which any single step that is undertaken takes into account the current scientific challenges, balances the prevailing priorities in space research, and makes optimal use of the available know-how in science and technology. This is a programme able to look forward, to imagine space exploration the way we would like to see it in 10 to 20 years from now, and even beyond, and to invest in it. They are aimed at developing, testing and demonstrating new space technologies to be used operationally on future deep-space spacecraft. The SMART concept was accepted and included in the ESA Scientific Programme in the second half of the 1990 s, and the first such mission, SMART-1, was designed in The ESA Technology Research Programme was also heavily involved and ESA s ESOC ground control teams made an exceptioanl contribution to the design and operation of the SMART-1 mission. SMART-1 is a very small and light spacecraft 1 cubic metre in size and weighing just 370 kilograms designed to perform in-flight technology demonstrations to support a number of ESA s future scientific missions (the BepiColombo mission to Mercury, the Solar Orbiter mission to the Sun, LISA to detect gravitational waves, and other general applications). SMART-1 will also make scientific investigations once at the Moon and during the cruise to reach it. The experiments onboard are the result of a trade-off between the best possible scientific return and the technologydemonstration goals. Building on these principles and mixing these ingredients resulted in ESA s current Cosmic Vision scientific programme, which is based on a tradition of innovative thinking that now spans more than three decades. One of the tools for achieving this is to invest in key new space technologies that pave the way for future missions and make it possible to reach scientific goals not previously achievable. This is the concept behind the ESA SMART mission series - Small Missions for Advanced Research and Technology.

4 Card 2 The spacecraft s novel route to the Moon SMART-1 has not travelled to the Moon in the conventional way, in that it was not placed by the launcher on a direct lunar transfer trajectory towards the Moon Instead, after launch on 27 September 2003, SMART-1 was put by the Ariane-5 vehicle into a so-called Geostationary Transfer Orbit (GTO), with a perigee 650 km above the Earth, and an apogee of km. This is a standard parking orbit for telecommunications satellites, from which, with a single boost, they can easily reach their final circular (geosynchronous) orbit around the Earth. From GTO, SMART-1 instead set out on a long spiralling trajectory of ever-increasing orbits around the Earth. These took the small spacecraft closer and closer to the Moon, until it was captured by the gravitational attraction of Earth s only natural satellite and began orbiting it in mid- November In January 2005, SMART-1 will begin a global study of the lunar surface that will help scientists to understand exactly how the Moon was formed. The main reason for taking such an unusual route to the Moon was the low thrust that the electric propulsion provides. This long journey also provided SMART-1 with the opportunity to conduct the first European test of solar-electric propulsion ( ion engine ) as the main spacecraft thrusting system over a distance comparable to an interplanetary cruise. SMART-1 actually travelled 84 million kilometres during its journey to the Moon: an impressive detour considering that the Moon is only about km from Earth! During its long spiralling trip, during which it clocked up 332 orbits around Earth, SMART-1 was subject to an intensive set of operations and technology-demonstration tests and also had to face some thrilling moments Transiting the Earth s radiation belts. At the beginning of its journey (October-November 2003), SMART-1 periodically passed through the Earth s radiation belts (best described as two doughnut-shaped belts of charged particles interacting with Earth s magnetic field, which extend from 800 to 6000 km and from 3000 to km above the Earth s surface). One element of the SMART-1 experiments was to analyse the reactions of the ion engine and the spacecraft during this transit. In addition, at the end of October, an exceptional degree of solar activity caused extreme geomagnetic storms which adversely affected SMART-1 s ion engine. It switched off unexpectedly several times, during a delicate phase of the mission in which the engine had to perform almost continuously. Successful corrective measures were taken and the spacecraft could proceed on its journey. The spacecraft s two star trackers were also affected: because of the heavy bombardment from charged particles like protons, they saw many more stars than were actually visible. This caused some problems in determining the orientation of the spacecraft. Extremely clever software modifications, needed to distinguish the real stars from the false ones, eventually solved the problem. The solar arrays, upon which SMART-1 s ion engine relies for its power supply, proved very resilient during this bombardment phase. The long spacecraft eclipse. On 13 March 2004, SMART-1 was in eclipse, passing through Earth s shadow as planned. Orbital considerations meant that this eclipse would last 15 minutes longer than originally foreseen (2 hours and 15 minutes instead of 2 hours). This raised concerns about the spacecraft s thermal-control management and the power supply for its electric propulsion from the solar arrays). The length of this eclipse could have been shortened at the expense of using more fuel, but in the end, given the very good performance of the thermal control and power subsystems up to that point of the mission, the team decided to let the spacecraft go through the longer eclipse. It responded very well, showing no untoward effects, confirming the soundness of SMART-1 s design.

5 Card 2 Lunar resonance manoeuvres. In approaching the Moon, SMART-1 tested gravity-assist manoeuvres with a spacecraft driven only by an ion engine for the first time. Three manoeuvres of this kind were successfully performed while in orbit around the Earth. Cleverly, the period of the orbit was adjusted to ensure that the spacecraft was near the Moon at the time of the three Earth apocentre passes on 19 August, 15 September and 12 October The spacecraft was therefore able to make use of the Moon s gravitational pull, through lunar resonance manoeuvres, to accelerate it towards its destination. Such manoeuvres are pretty delicate: a problem with any one of them would have both delayed SMART-1 s arrival at the Moon by one month, and made the spaccecraft consume extra fuel. Last major ion-engine thrust. In all, SMART-1 fired its engine 289 times during the cruise phase, logging over 3700 hours of operation. The engine s last and decisive thrust in Earth orbit took place from 10 to 14 October 2004, pushing the spacecraft towards the Moon capture point, which it reached about one month later. Just a few minor trajectory corrections were needed before the spacecraft went into orbit around the Moon. Transition through the Moon capture point. On 13 November 2004, SMART reached the so-called Moon capture point, km from the lunar surface. This is a small region of gravitational equilibrium between the Earth and the Moon (also called the first Earth-Moon Lagrangian point). Once a spacecraft passes this point, it is no longer dominated by the Earth s gravitational pull and it enters into the sphere of influence of the Moon. SMART-1 crossed this point smoothly with the push of the last ion-engine thrust one month earlier and began its first lunar orbit. This phase was not considered critical because of the ion engine s inherent flexibility, which allows manoeuvres to be easily re-programmed if anything should go wrong. This represents a huge advantage compared with planetary orbit insertions for chemically-propelled spacecraft, which can fire their engines only a limited number of times. Then, if the manoeuvre goes wrong, insertion into the planetary orbit may be missed and there may be no other chance to recover the mission. Speeding towards the first perilune to reach final lunar orbit. On 15 November 2004, in the course of its first orbit around the Moon, SMART-1 reached its closest point to the lunar surface so far - its first perilune - at about 5000 km altitude. Starting just few hours before the first perilune, SMART-1 continuously fired its ion engine for its first major thrust in lunar orbit, which lasted about five days. This, and the following smaller thrusts, will allow SMART-1 to reach a stable lunar orbit by making ever-decreasing loops around the Moon. It will reach its final orbit, ranging between 300 km (over the lunar south pole) and 3000 km (over the lunar north pole) in altitude, in mid-january The spacecraft will then begin its scientific observations. The Moon s face as SMART-1 will see it during the first perilune passage on 15 November 2004, ESA The Moon as seen by SMART-1 at the first resonance approach in August 2004

6 Card 3 The ion engine at work The testing of the ion engine on SMART-1, together with the instruments to monitor its effects on the spacecraft, was the major technological demonstration goal of the mission. Solar-electric propulsion is being used as the main propulsion system on a European space mission for the first time, instead of the commonly used chemical boosters. Solar-electric ion engines are able to generate a low but continuous thrust using electricity provided by solar panels to produce a beam of charged particles that pushes the spacecraft relentlessly towards its destination. The SMART-1 ion engine is fuelled with xenon gas. The SMART-1 ion engine, known technically as a stationary plasma engine, has been tested over 13 months in space, being fired for the first time on 30 September 2003, until October 2004, when the demonstration phase was declared complete and successful. It pushed the spacecraft along everincreasing spiral orbits around Earth that eventually brought it to the capture point for lunar orbit. This long spiralling trajectory to reach the Moon, which is 84 million kilometres from Earth, was designed to allow the ion engine to be tested over a distance comparable to that of an interplanetary mission. The engine then continued to function to inject SMART-1 into a stable orbit around the Moon in November 2004, and will be used for another two months to reduce the spacecraft s altitude and prepare for the lunar science observation phase (starting in mid-january 2005). It will also be used to boost the spacecraft, after a natural orbit degradation, back into a stable orbit, after six months of operations around the Moon (in June 2005), if the scientific mission is extended. With SMART-1, Europe is making its first in-flight test of an ion engine as main propulsion system, ESA AOES Medialab, ESA

7 Objectives of the demonstration To demonstrate Europe s ability to fly a spacecraft using only an ion engine as its main propulsion system. To demonstrate new manoeuvring techniques that couple the ion engine s thrust with gravityassist manoeuvres. To demonstrate, using diagnostic tools to monitor the ion engine s performance and its effects on the spacecraft systems and instrumentation, that solar-electric propulsion is suitable for future missions. To increase European know-how in the science of ion engines, in the design of electrically propelled spacecraft, and in strategies to best optimise future missions that will make use of such engines, by building up flight-experience and confidence in the use of solar-electric propulsion. Advantages of ion engines Ion engines produce a low thrust, but a very high specific impulse (impulse per unit mass of fuel used), allowing a spacecraft to increase its velocity very efficiently over a longer period, thereby reaching its destination in less time. As the need to save fuel is less relevant with ion engines than with chemical engines, a space journey can be designed with fewer gravity-assist manoeuvres, allowing a more direct trajectory to be chosen and therefore resulting in a shorter trip. Solar-electric propulsion is particularly suited for missions to the inner Solar System, where the Sun can easily power the spacecraft, e.g. ESA s BepiColombo mission to Mercury and the Solar Orbiter mission to the Sun. Ion engines produce a gentle thrust, so special types of such engines tailored specifically for attitude control are optimal candidates for missions that need a very accurate spacecraft attitude and very low thrusts for complex or very precise manoeuvres within strong gravitational fields, e.g. missions that orbit close to the Earth like LISA, ESA s gravitational-wave detector. Because of their manoeuvrability, ion engines can also achieve and maintain lower orbits around target planets, favouring scientific observations in an environment where the planetary atmospheric drag obliges the spacecraft to undergo frequent orbital correction manoeuvres. Ion engines produce up to ten times as much impulse per kilogram of propellant used compared with chemical engines. The mass so saved can be made available for more onboard instrumentation or to save on launch costs, or in some cases to increase the spacecraft s operational lifetime. Ion engines can be switched on and off and their thrust can be modulated very easily. This means that a spacecraft s trajectory can easily be corrected if a manoeuvre should go wrong for any reason, giving a strong mission-recovery capability. This can be an important asset during delicate gravityassist manoeuvres, for example, when a spacecraft is making use of the pull of celestial objects (or of gravitational instabilities) to gain acceleration to reach the final target and save fuel.

8 Card 3 Performance & lessons learnt During the 13-month test phase, the SMART-1 ion engine was switched on and off 289 times, operating for a total of about 3700 hours and propelling the spacecraft over a distance of 84 million kilometres. Only 59 kg of xenon propellant were used (82 kg were available). Overall, the engine s performance was extremely good, allowing the spacecraft to reach the Moon quicker than initially expected. Fuel spared. Because of the engine s good performance, a considerable amount of fuel was saved. This allowed two originally planned lunar gravity-assist manoeuvres (fly-bys) to be dropped from the mission, so bringing forward the arrival at the Moon by two months. The extra fuel available also allowed the mission designers to significantly reduce the altitude of the final orbit around the Moon, which now ranges from 300 to 3000 km over the lunar poles, while the initially expected apolune (maximum distance from the Moon during lunar orbit) was km. This closer proximity to the surface will be even more favourable for the science observations that will start in January Need for greater navigational autonomy in the future. The possibility of these occasional interruptions in an ion engine s operation imply that it is not realistic to plan the mission s scientific observations in the traditional way (i.e. with a pre-planned schedule), because the spacecraft may not be at exactly the right place at the time foreseen. The solution is to invest in greater spacecraft and navigational autonomy and perhaps also to apply a different strategy in planning the observations. This would involve developing the spacecraft s ability to self-assess variations in its engine s performance and intervene accordingly, for instance by re-starting its engine autonomously. Experts identify the need to continue investing in new technologies that will allow a spacecraft to autonomously assess its position in space with respect to a target to be observed and then adjust its attitude to make the scientific observations. The implementation of such strategies would also reduce the work for ground tracking teams, thereby also reducing costs. Heavy radiation bombardment from the Sun, ESA Space radiation requires attention. Some components of the ion engine proved to be sensitive to bombardment by high radiation, for example during the transition through Earth s radiation belt and when the spacecraft was exposed to heavy radiation from violent solar activity during the first phase of the mission. In particular, one of the engine s electronic components reacted to the radiation by sending a signal to the on-board computer that was interpreted as a command to switch off the engine. Twenty-two events of this kind occurred. Ground teams must be flexible. Once this engine shut-down situation had been analysed by the ground engineers, the spacecraft s on-board software was adapted to switch-on the engine again autonomously whenever an anomalous shutdown occurred. This clever modification allowed the problem to be overcome and saved on expensive ground monitoring and intervention. SMART-1 passing through the Earth s radiation belt, AOES Medialab ESA

9 Self-monitoring. SMART-1 was equipped with two instruments to monitor the side-effects of solar electric propulsion on the ion engine itself and on the spacecraft: EPDP and SPEDE. The Electric Propulsion Diagnostic Package (EPDP) performed excellently. It monitored the engine s plume, the beam of charged particle that streams out at about 16 km/s to provide the thrust. Using sensors positioned on the spacecraft, it also monitored the variation in electrical potential on the engine, on the spacecraft and on its instruments. Oscillations in spacecraft voltage were recorded, but had no serious electrical effects on any instrumentation. EPDP was also able to observe the eroding effects of the engine s plume within its chamber. The side products of this erosion formed a cloud of particles that were deposited on parts of the spacecraft, but no damage was observed. The Spacecraft Potential, Electron and Dust Experiment (SPEDE) consists of two sensors mounted at the end of two 60-cm booms fixed to the outside of the spacecraft, and in addition to its scientific measurement goals it complements the EPDP s diagnostic function. It monitored the sideeffects of solar-electric propulsion, especially the distribution of plasma (gas of charged particles) around the spacecraft and the way it which it interacts with the electric and magnetic phenomena of the space environment. SPEDE was used to check valve operations for the engine, and to investigate some plasma oscillations around the spacecraft while the ion engine was firing. SPEDE is sufficiently sensitive to measure the natural plasma around the spacecraft in the absence of propulsion. SPEDE will also be used during the lunar observation phase, to measure the effect of the plasma on the spacecraft in the Moon s environment. The data collected by EPDP are fundamental for the design of future electrically-propelled missions. In fact the ion engine is a steady source of electrical potential that can even protect the spacecraft by serving as a shield against the bombardment of electrically charged particles coming from the space environment. This must be taken into consideration, however, when choosing the onboard instruments and experiments, which must still work correctly with such a variation in potential. EPDP also measured the effects on the engine plume itself, which is slightly modified in direction and intensity by the flow of electrically charged particles after a period of functioning. These small variations must also be taken into account in the design and the navigation profiles of future missions, especially for those that need high attitude accuracy and therefore rely on the precision and reliability of micro-thrusting.

10 Card 4 Performances & lessons learnt The KaTE radio link was tested between October 2003 and November 2004, using ESA s Villafranca tracking station near Madrid (E), which was upgraded for the purpose in terms of new hardware and signal-coding techniques. Villafranca successfully received Ka-band radio waves from SMART-1 carrying telemetry information. The technology to support Ka transmission, tested at Villafranca for the first time with SMART-1, will be transferred later to ESA s new tracking station at Cebreros, also near Madrid, which forms part of the ESA ESTRACK network. The campaign to collect and analyse data from KaTE will continue as long as SMART-1 is operational. The knowledge acquired is allowing European industry to test its Ka-band technology, including the necessary ground infrastructure. It is also providing ESA s ground controllers at ESOC in Darmstadt (D) with a real flight opportunity to consolidate their knowhow and fully master this technology, which represents the future for interplanetary radio transmissions. Using KaTE, RSIS collected more than 20 hours of data in One of NASA s Deep Space Network (DSN) antennas at Goldstone in California was used for the transmissions to and from the spacecraft. A rehearsal of the experiment to measure the Moon s libration, to be performed at a later stage in the mission, was successfully carried out on 8 October Data gathered to monitor variations in the motion of SMART-1 with high precision, to obtain indications of the engine s thrust conditions and performance, and to check the stability of the Ka-band space link, are currently being analysed. The laser link experiment was performed eleven times during the cruise, with SMART-1 s distance from the Tenerife ground station in the Canary Islands (E) ranging from to kilometres. The optical telescope on Tenerife used its highly sensitive camera to detect SMART-1 by means of the sunlight it reflected, and to direct a continuous laser beam towards the spacecraft. New alignment techniques had to be developed at the ground station to perform this task with the high precision required. The laser beam was detected by SMART-1 s AMIE camera, and the beam s power and the fluctuations in its intensity as received at AMIE provided important information for characterising the link. The laser link experiment and the data collected are important steps to establish and refine deep-space pointing strategies, and to be able to design the next generation of communication systems based on laser techniques. Future deep-space communications may use laser connections to transfer large amounts of scientific data to Earth. The ground station receiving these data will have to provide a laser beacon to be used by the spacecraft to point accurately at the ground terminal. SMART-1 has demonstrated that accurate pointing strategies from Earth are feasible, and that a laser beam sent from the ground can be reliably detected by a spacecraft flying at deepspace distances. The next spacecraft generation will make use of high-frequency radio transmissions, ESA/Remy van Haarlem AMIE spots the laser beam sent from Earth, ESA/Space-X Institute AOES Medialab ESA

11 Card 4 The future face of deepspace communications As scientific space missions become ever more ambitious in terms of their scientific goals, the capacity of their instruments, and the complexity of their journeys, deep-space communication techniques must keep pace with the need to transfer ever-increasing volumes of scientific data more efficiently and to have fast and reliable transmission of information between Earth and spacecraft. Such technologies can also be applied to determine the satellite s position in space, and in scientific experiments to learn about celestial targets during future missions. This is the goal of the SMART-1 deep-space communication tests, with the KaTE, RSIS and laser link experiments. Objectives of the demonstration KaTE (X/Ka-band Telemetry and Telecommand Experiment): To demonstrate, for the first time for Europe on a scientific mission, the next generation of radio links between Earth and a distant spacecraft, by using radio waves at frequencies higher than those commonly used for deep-space communications; to test new data coding techniques; and to validate and eventually upgrade the corresponding groundbased infrastructures needed to receive these kinds of signals. RSIS (Radio-Science Investigations): To make use of the KaTE radio waves to measure with high accuracy small changes in SMART-1 s motion and to determine the precise thrust delivered by the ion engine; this is achieved by analysis of the so-called Doppler effect, whereby the spacecraft s speed alters the wavelength of the radio waves. To demonstrate, as a scientific goal, a method of measuring the libration of the Moon (slight oscillation about its axis) with high precision, in order to derive information about the distribution of the Moon s mass and its rotational properties. To monitor the stability of the KaTE radio link in space, which is very important for radio-science measurements. Laser Link: To demonstrate the use both of a continuous laser beam to point a spacecraft from Earth and of mathematical models to track the spacecraft, for future communication purposes. To study the effects of atmospheric turbulence on the laser link. SMART-1 s onboard mini-camera, AMIE, is used in this experiment, with the addition of a laser filter (weighing only a couple of grams) to separate optical signals coming from Earth from the laser beam. The AMIE camera is used to spot the laser beam transmitted from the Tenerife (Spain) optical ground station. So far, the laser-link technology, in which Europe is a leader, has been applied to telecommunications satellites (geostationary, and therefore positioned in a fixed place in the sky with respect to Earth), to establish laser connections with other satellites in low Earth orbit, and bi-directionally with Earth. In addition, SMART-1 s laser link is demonstrating the feasibility of a laser connection between Earth and a spacecraft travelling at deep-space distances. Advantages for future missions Radio transmission in the so-called Ka band (very high frequency microwaves) represents the next generation of deep-space radio links. Use of the Ka band will allow future spacecraft to transmit information more efficiently compared with the frequencies traditionally used. The Ka-band information transmitted by the spacecraft s antennas travels in narrow beams and is less sensitive to radio disturbances in deep space. This technology is proposed for use on ESA s BepiColombo and Solar Orbiter which, travelling very close to the Sun, will be exposed to a great deal of radio noise caused by the solar corona. Ka-band communications may find applications on many other planetary missions where huge amounts of scientific data are to be gathered (e.g. missions to Mars). The high accuracy of Ka-band transmissions can also be exploited to accurately determine a spacecraft s position with respect to its planned orbit. The same high accuracy will also allow the motion properties of celestial bodies to be measured with high precision, which is important for future science experiments. The big advantage of laser communications for future spacecraft is that a laser beam is much more direct than a radio link and can thus cover greater distances; it can also carry a greater amount of information in the same time.

12 Card 5 Performances & lessons learnt SMART-1 provided a unique opportunity to test the OBAN concept under realistic operating conditions, with a real camera working in the harsh environment of space. The image-acquisition campaign began in the second half of 2004 and ended in November. About ten sequences of images of the Earth and the Moon (whose position in space is well known) were taken for this purpose. One pair of images of two different objects is necessary for the OBAN software to determine the spacecraft s position using a geometrical technique called triangulation. Two pairs of images of the same object taken in sequence are needed to also determine the spacecraft s velocity. Based on the OBAN experience, experts see the next step as the development of more intelligent software that includes not only the ability to understand where the spacecraft is at any given moment and how fast it is moving (by comparing the objects seen by the camera with the onboard catalogues), but is also able to calculate how the spacecraft has to move to look for objects when they are not yet visible. The OBAN simulation campaign using SMART-1 s images will be concluded by the beginning of 2005 and the results will be compared with the real navigation data acquired by the ESOC tracking station. The current projection is that OBAN may be able to determine SMART-1 s position with an accuracy of about 40 kilometres around the actual position of the spacecraft. More accurate positioning can be achieved in the future by using high-resolution cameras specially suited for navigation. Better accuracies are also expected in deep space, when a spacecraft is far way from strong gravitational fields like those of the Earth and the Moon. Asteroids, for example, which have low masses, can be used as a reference to determine the spacecraft s position. On future spacecraft, the images that they take will have to be compared by the onboard computers with catalogues, also stored onboard, of celestial objects whose positions are already well known. With SMART-1 images of two close space objects whose position is known, OBAN determined the spacecraft s position and velocity ESA/Remy van Haarlem ESA/Space-X Institute

13 Card 5 One step closer to autonomous spacecraft navigation Mission designers have a vision of future spacecraft that are intelligent enough to compute exactly where they are in space, to know how to search for their targets, and to be able to get there autonomously. Robotic spacecraft that have such independence, requiring a minimum of intervention from ground-control teams, will save on costs and on the allocation of ground-control resources. The SMART-1 OBAN experiment, which was tested during the long cruise to the Moon, was designed to take the first step in this direction. Objectives of the demonstration Advantages for future missions Implementing a tool like OBAN onboard a spacecraft with the necessary refinements will allow future satellite missions to determine their precise position in space with only limited tracking from ground stations, both during interplanetary travel and for encounters with celestial bodies. OBAN (On-board Autonomous Navigation) is an off-line experiment that consists of running navigation software on ground computers, using images of celestial objects (stars, asteroids, Earth and the Moon) taken by the AMIE camera on SMART-1. The purpose of the OBAN demonstration is to use these images as a reference in space to determine the exact position and velocity of the spacecraft, and so determine its actual orbit. There is previous experience of determining a spacecraft s orbit from the ground by using images taken from the spacecraft ( image navigation method), but the purpose of OBAN is to test this method using calculation techniques that are suitable for future application onboard the spacecraft itself. Such algorithms must not take up too much hard memory on the spacecraft, while still having a high calculation capability. Future spacecraft will apply the OBAN concept for orbit determination using images of space objects ESA/Remy van Haarlem

14 Card 6 Performances & lessons learnt The AMIE camera was operated throughout SMART-1 s cruise phase to the Moon. It took more than 1000 pictures, which include images of Earth, the Moon, the stars and a remarkable sequences of two total lunar eclipses, on 4 May and 28 October AMIE was designed to take series of four consecutive shots, separated by just a few seconds. Thanks to a control unit containing an innovative microprocessor, these images can be downloaded to the spacecraft memory within a few minutes, for later transmission to Earth. During the cruise phase, new command sequences have been uploaded to AMIE that, once at the Moon, will allow the camera to take eight consecutive shots instead of four. This upgrade will facilitate the imaging of the lunar surface and allow areas of it to be photographed before illumination conditions change as the Moon naturally rotates below SMART-1. AMIE was also used to spot the laser beam sent from Earth in the context of the Laser Link experiment. The last laser shot during the cruise was taken by AMIE on 6 October 2004, when the spacecraft was kilometres from Earth. This confirmed the excellent pointing capabilities of both the spacecraft and the ESA ground station that fired the laser beam towards it. AMIE images of the Earth and Moon were also taken for the OBAN experiments, to demonstrate a technique that uses images of celestial object to calculate the exact position and velocity of a spacecraft. XSM s observations of absorption lines from solar iron seem to indicate that some heating precedes solar eruptions. The combined data may also provide a better understanding of the Sun as a star, and will be compared with ESA XMM-Newton s studies of solar-like stars. The SIR infrared spectrometer was used during the cruise phase to make test observations of the Moon. More than 1000 lunar spectra were acquired, and changes in the spectral absorption lines across the lunar surface reflect the varying chemical composition of the soil that SIR will study in detail once SMART-1 arrives at the Moon (including the polar areas and the far-side). For the test, SIR was also pointed at Earth, but as expected only very weak infrared signals were received. In fact, the water present in the Earth s atmosphere absorbs almost all infrared radiation in the spectral range that SIR observed. This is why infrared studies of the Moon can only be made from space, that is from beyond the Earth s atmosphere. D-CIXS observed the X-ray fluorescence (red line) from Earth s atmosphere, induced by the Sun. This is confirmed by the match with the green line, representing the X-ray light curve of the Sun ESA/Remy van Haarlem/ D-CIXS team On 24 May 2004, XSM recorded a solar flare that lasted 1 hour, with the Sun 10 times more luminous in X-rays than before ESA/XSM team/soho EIT During the cruise phase, the X-ray instruments D-CIXS and XSM were successfully tested to prepare for the science phase at the Moon. The X-ray target Scorpius X-1 (the brightest detected X-ray source in the sky) was observed for 15 hours. Binary stars in the NGC6624 and X stellar systems were also observed. D-CIXS was also used to take test images of Earth, where it could see the argon present in Earth s atmosphere thanks to the fluorescence it produces in X-rays. The XSM solar monitor collected data in May and June 2004, when it could observe tens of solar flares in X-rays. By combining XSM data with data obtained by other solar observers, methods may be developed to calculate the size of solar flares on other stars also. Total lunar eclipse seen by SMART-1 from space on 28 October 2004 ESA/Space-X Institute

15 Card 6 Mini instruments for maxi results The high cost of launches and the need for spacecraft to carry as many instruments as possible, to maximise the scientific return from the mission, place important limitations on the mass and dimensions of the experiments that make up the payload. Today s spacecraft designers are therefore working extremely hard on miniaturisation techniques for scientific instruments. SMART-1 carries four such miniaturised instruments, which are being tested for the first time in space: AMIE, D-CIXS and XSM, and SIR. Objectives of the demonstration AMIE: To demonstrate the use of an ultracompact and ultra-light camera, weighing less than 500 grams, for scientific imaging of the Earth and the Moon. AMIE is the smallest scientific camera ever flown in space. Thanks to its colour filters, its images of the lunar surface will also provide mineralogical information. The camera s telephoto lens provides higher resolution colour images (40 metres, from an altitude of 300 kilometres) than previous lunar missions. During SMART-1 s six-month nominal mission, AMIE will be able to provide the first global map of all of the lunar areas that are in permanent shadow. AMIE also provides the images needed to support the OBAN and the Laser Link experiments. D-CIXS and XSM: To test for the first time ever in space D-CIXS, an ultra-compact X-ray camera (a toaster-sized cube just 15 centimetres wide and weighing less than 5 kilograms) able to work at very high temperatures and highly tolerant to radiation damage (D-CIXS is the first X-ray spectrometer ever flown in space with sufficient spectral resolution to separate signals coming from different chemical elements). To test the X-ray camera on a number of X-ray celestial sources like stars, the Moon, the Galactic Centre, and the Earth. To test the use of XSM, a compact and miniaturised X-ray instrument complementing D-CIXS, to monitor the X-rays emitted from the Sun ( solar monitor ), and so enable experts to distinguish and separate the solar X-rays from those emitted by the Moon and the other targets observed by D-CIXS. SIR: To demonstrate the use of a small and selfcontained infrared spectrometer (first of its kind ever built and the first infrared spectrometer to be used around the Moon) designed to chart the Moon s minerals. Advantages for future missions Using high-performance miniaturised scientific instrumentation will allow future interplanetary missions to use lighter spacecraft or to carry more instruments onboard. A camera based on the AMIE concept is being flown on the Rosetta lander, and is a candidate for ESA s ambitious BepiColombo mission to Mercury. SMART-1 tested its instruments to prepare for X-ray and infrared studies of the Moon in 2005 ESA AMIE sees Europe in its first picture of Earth on 21 May 2004 ESA/Space-X Institute On 14 August 2004, SMART-1 photographed Kourou, from which it was launched in September 2003 ESA/Space-X Institute First quarter of the Moon imaged by AMIE on 29 January 2004 ESA/Space-X Institute

16 Contents Card 1. Card 2. Card 3. Card 4. Card 5. Card 6. The SMART philosophy The spacecraft s novel route to the Moon The ion engine at work The future face of deep-space communications One step closer to autonomous spacecraft navigation Mini instruments for maxi results Prepared by: ESA Science Programme Communication Service Written by: Monica Talevi Published by: ESA Publications Division ESTEC, PO Box AG Noordwijk The Netherlands Editors: Bruce Battrick & Carl Walker Design and Layout: Leigh Edwards Copyright: 2004 European Space Agency ISSN No.: ISBN No.: Price: 7 Euros Printed in The Netherlands For further information on the ESA Science Programme, please contact the Science Programme Communication Service on (tel.) ; (fax) More information can also be obtained via the ESA Science Web Site at: