One Day to Go for Beagle 2

This time of year, I usually wind things down at Universe Today since the various news sources are all on holiday and there isn’t much to report. This year; however, it’s an entirely different story. The British-built Beagle 2 lander will be touching down on Mars on December 25. Stardust reaches Comet Wild 2 on January 2, and the Mars Exploration Rover arrives on January 3. Things couldn’t be busier.

So, first up… Beagle 2 and Mars Express. The lander is expected to arrive at 0254 UTC on December 25 (9:54 pm EST December 24). We won’t know if Beagle 2 arrived safely for another four hours or so, when Mars Express enters orbit – data won’t arrive back on Earth until 0700 UTC (2:00am EST). Keep your fingers crossed.

The European Space Agency has said they’ll be broadcasting information about the landing live on television, but I haven’t been able to find a link on the web for it (if you know of one, let me know). You can visit their special coverage of the landing and Mars Express arrival here. Or go straight to the Beagle 2 website, where they’ll just be focused on the lander. As I find cool stuff on the web, I’ll let you know.

And make sure you come visit the Universe Today forum and share your thoughts and ideas about the missions with the rest of our community.

Have a happy and safe holiday. See you on Mars!

Fraser Cain
Publisher
Universe Today

Beagle 2 Separates from Mars Express

Image credit: ESA

The European Space Agency’s Mars Express spacecraft successfully released the British-built Beagle 2 lander this morning, completing a major milestone on its trip to Mars. Mars Express fired a pyrotechnic device which slowly released a spring and separated the two spacecraft. Since Beagle 2 has no propulsion system, controllers have no way of fine-tuning the lander’s flight path. If everything goes as planned, Beagle 2 will enter the planet’s atmosphere on December 25.

This morning, ESA’s Mars Express flawlessly released the Beagle 2 lander that it has been carrying since its launch on 2 June this year. Beagle 2 is now on its journey towards the surface of Mars, where it is expected to land early in the morning of 25 December. Mars Express, Europe’s first mission to Mars, has passed another challenging milestone on its way towards its final destination.

At 9:31 CET, the crucial sequence started to separate the Beagle 2 lander from Mars Express. As data from Mars Express confirm, the pyrotechnic device was fired to slowly release a loaded spring, which gently pushed Beagle 2 away from the mother spacecraft. An image from the on-board visual monitoring camera (VMC) showing the lander drifting away is expected to be available later today.

Since the Beagle 2 lander has no propulsion system of its own, it had to be put on the correct course for its descent before it was released. For this reason, on 16 December, the trajectory of the whole Mars Express spacecraft had to be adjusted to ensure that Beagle 2 would be on course to enter the atmosphere of Mars. This manoeuvre, called ‘retargeting’, was critical: if the entry angle is too steep, the lander could overheat and burn up in the atmosphere; if the angle is too shallow, the lander might skim like a pebble on the surface of a lake and miss its target.

This fine targeting and today’s release were crucial manoeuvres for which ESA’s Ground Control Team at ESOC (European Space Operations Centre) had trained over the past several months. The next major milestone for Mars Express will be the manoeuvre to enter into orbit around Mars. This will happen at 2:52 CET on Christmas morning, when Beagle 2 is expected to land on the surface of Mars.

“Good teamwork by everybody – ESA, industry and the Beagle 2 team – has got one more critical step accomplished. Mars, here comes Europe!” said David Southwood, ESA Director of Science.

Original Source: ESA News Release

SMART-1 at Full Speed

Image credit: ESA

The European Space Agency’s SMART-1 spacecraft is continuing to function well on its long roundabout mission to the Moon. The spacecraft recently completed its 139th orbit and everything seems to be functioning properly, despite the recent solar storms that damaged a few other satellites. It’s running its solar-powered ion drive full time now, and incrementally raising its distance with each orbit around the Earth. SMART-1 will reach its final orbit around the Moon in March 2005.

The spacecraft is now in its 139th orbit, in good operational status and with all functions performing nominally. As previously, the spacecraft was operated in electric propulsion mode almost continuously.

This week we had no flame-outs, probably due to the adopted strategy not to thrust when the orbital altitude is less than 10 000 km. The procedure to automatically re-start the engine after a flame-out will be uploaded to the on-board software this week. Once this is in place, the thrust phase will no longer be interrupted.

The total cumulated thrust time is now more than 946 hours and SMART-1 has consumed almost 15 kg of Xenon. Even with such a low fuel consumption the electric propulsion engine has so far provided a velocity increment of about 665 ms-1 (equivalent to about 2400 km per hour). The electric propulsion engine’s performance, periodically monitored from telemetry data and by ground stations tracking, continues to show a small over performance in thrust, varying from 1.1% to 1.5% over the last week.

The newly adopted strategy to thrust in a direction perpendicular to the position vector in the orbital plane has produced a large perigee increase in the last week of more than 1200 kilometres (see orbital elements and orbit picture).

The degradation of the electrical power produced by the solar arrays is now slowing down considerably. As a matter of fact the available power has remained more or less constant in the last 15 days. This means that the degradation by radiation has matched the increase of solar irradiance due to the nearing of the Earth’s perihelion, so that the net effect is zero. This is explained by the fact that no direct proton radiation from solar activity was experienced and the fact that the spacecraft now stays outside of the radiation belts for a considerable part of its orbit.

The communication, data handling and on-board software subsystems have been performing very well in the last week.

The thermal subsystem continues to perform well and all the temperatures are as expected. The temperature of the optical head on star tracker #1 is now lower than before. This is due to the changed thrust attitude which reduces the exposure to the Sun of the ?Z side of the spacecraft. Other attitudes are being considered in order to test the dependence of the star tracker’s temperature upon the spacecraft’s attitude.

Orbital/Trajectory information
The SMART-1 orbit is continuously modified by the effects of the electric propulsion low thrust. The osculating orbital elements are periodically computed by the ESOC specialists. These elements define the so called osculating orbit which would be travelled by the spacecraft if at that instant all perturbations, including EP thrust, would cease. So it is an image of the situation at that epoch. In reality the path travelled by the spacecraft is a continuous spiral leading from one orbit to another. The most recent osculating elements are as follows:

From the start, the electric propulsion system has managed to increase the semi-major axis of the orbit by 6750 km, increasing the perigee altitude from the original 656 km to 7012 km and the orbital period by more than four and a half hours, from the initial 10 hours 41 minutes to the present 15 hours 22 minutes.

Original Source: ESA News Release

Pluto Mission Will Study Jupiter Too

Image credit: SWRI

Although the main goal of the NASA’s New Horizons mission will be to send a spacecraft to Pluto, the mission designers figure they can examine Jupiter on the way out as well – and get a valuable gravity boost that would shave years off the mission. If all goes as planned, New Horizons would launch in 2006, and pass Jupiter in early 2007 (probably three times closer than Cassini did in 2000); it will reach the Pluto-Charon system in 2015. After Pluto, New Horizons would then be re-targeted to fly past a Kuiper Belt Object.

The main goal of NASA’s New Horizons mission may be to explore Pluto-Charon and the Kuiper belt beginning in 2015, but first the mission plans to fly by the solar system’s largest planet, Jupiter, during February-March 2007. The Jupiter flyby would be used by New Horizons to provide a gravitational assist that shaves years off the trip time to Pluto-Charon and the Kuiper belt.

During the flyby, plans call for New Horizons to use its instrument payload, consisting of cameras, spectrometers, radiometers, and space plasma and dust sensors, to make a variety of scientific observations. Toward that end, the New Horizons team has formally kicked off its planning of the Jupiter flyby science observations. Southwest Research Institute? (SwRI?) and the Johns Hopkins University Applied Physics Laboratory (APL) lead the mission. Major partners include Ball Aerospace, Lockheed-Martin, Boeing, NASA Goddard Space Flight Center and the California Institute of Technology Jet Propulsion Laboratory.

“Every spacecraft must check out its instruments and pointing capabilities in flight prior to reaching its target,” says mission project scientist Dr. Hal Weaver of the Johns Hopkins University Applied Physics Laboratory. “By virtue of the gravity assist maneuver at Jupiter, New Horizons has a unique opportunity to do its check out on a very worthy and exciting scientific target.”

“New Horizons presents NASA’s next opportunity to study the complex and fascinating Jupiter system,” says Dr. Alan Stern, principal investigator of the New Horizons mission and director of the SwRI Space Studies Department. “To accomplish its gravity-assist maneuver on the way to Pluto-Charon, our spacecraft will venture at least three times closer to Jupiter than the Cassini spacecraft did in late 2000 when it used Jupiter for a gravity assist on the way to Saturn.

“Astronomically speaking, we will fly just outside of the edge of Jupiter’s large, planet-sized Galilean moon, Callisto.” From its closer range, New Horizons will perform a number of Jupiter system studies not possible from Cassini’s greater flyby distance.

Science planning is going forward to ready the mission for its planned 2006 launch, at the same time that required environmental and safety reviews are also being done. Through the summer of 2004, the New Horizons science team will prioritize its Jupiter science activities from objectives provided by team members as well as interested scientists from around the world. To accomplish this objective, Stern has appointed mission co-investigator and imaging team lead Dr. Jeff Moore of the NASA Ames Research Center to lead the New Horizons Jupiter Encounter Sequencing Team (JEST).

“New Horizons will be the next mission to Jupiter, and it is carrying a sophisticated instrument complement,” says Moore. “We intend to cull and then schedule the most critical needs for scientific observations of Jupiter, its satellites, its magnetosphere and its rings.

“Following that,” Moore continued, “the mission team will design and implement a five-month-long sequence of observations of the Jupiter system to be made from late 2006 through early 2007 as the spacecraft approaches and then recedes from Jupiter.”

“Exploring the Jupiter system is a coveted scientific bonus for New Horizons,” adds Weaver. “It also provides us with a valuable opportunity to check out the instrument payload and many of the flyby procedures we will later use at Pluto-Charon.”

New Horizons is proceeding toward a January 2006 launch, with a planned arrival at Pluto and its moon, Charon, in the summer of 2015. The 465-kilogram (1,025-pound) spacecraft will characterize the global geology and geomorphology of Pluto and Charon, map the surface compositions and temperatures of these worlds, and study Pluto’s atmospheric composition and structure. It will then visit one or more of the icy, primordial bodies in the Kuiper belt where it will make similar investigations.

In July 2002, the National Research Council’s Decadal Survey for Planetary Science ranked the reconnaissance of Pluto-Charon and the Kuiper belt as its highest priority for a new start mission in planetary science, citing the fundamental scientific importance of these bodies to advancing understanding of our solar system.

Original Source: SWRI News Release

NASA Tests a New Ion Engine

Image credit: NASA

NASA has tested a new high-power ion engine which could give future spacecraft significantly more thrust to accomplish exploration of the solar system. The High Power Electric Propulsion (HiPEP) ion engine should eventually be 10 times as powerful as NASA’s Deep Space 1 ion engine which was tested a few years ago. An engine like this will probably power the JIMO probe allowing it to go into and out of orbit around several of Jupiter’s moons and map them in great detail.

NASA’s Project Prometheus recently reached an important milestone with the first successful test of an engine that could lead to revolutionary propulsion capabilities for space exploration missions throughout the solar system and beyond.

The test involved a High Power Electric Propulsion (HiPEP) ion engine. The event marked the first in a series of performance tests to demonstrate new high-velocity and high-power thrust needed for use in nuclear electric propulsion (NEP) applications.

“The initial test went extremely well,” said Dr. John Foster, the primary investigator of the HiPEP ion engine at NASA’s Glenn Research Center (GRC), Cleveland. “The test involved the largest microwave ion thruster ever built. The use of microwaves for ionization would enable very long-life thrusters for probing the universe,” he said.

The test was conducted in a vacuum chamber at GRC. The HiPEP ion engine was operated at power levels up to 12 kilowatts and over an equivalent range of exhaust velocities from 60,000 to 80,000 meters per second. The thruster is being designed to provide seven-to-ten-year lifetimes at high fuel efficiencies of more than 6,000-seconds specific impulse; a measure of how much thrust is generated per pound of fuel. This is a contrast to Space Shuttle main engines, which have a specific impulse of 460 seconds.

The HiPEP thruster operates by ionizing xenon gas with microwaves. At the rear of the engine is a pair of rectangular metal grids that are charged with 6,000 volts of electric potential. The force of this electric field exerts a strong electrostatic pull on the xenon ions, accelerating them and producing the thrust that propels the spacecraft. The rectangular shape, a departure from the cylindrical ion thrusters used before, was designed to allow for an increase in engine power and performance by means of stretching the engine. The use of microwaves should provide much longer life and ion-production capability compared to current state-of-the-art technologies.

This new class of NEP thrusters will offer substantial performance advantages over the ion engine flown on Deep Space 1 in 1999. Overall improvements include up to a factor of 10 or more in power; a factor of two to three in fuel efficiency; a factor of four to five in grid voltage; a factor of five to eight in thruster lifetime; and a 30 percent improvement in overall thruster efficiency. GRC engineers will continue testing and development of this particular thruster model, culminating in performance tests at full power levels of 25 kilowatts.

“This test represents a huge leap in demonstrating the potential for advanced ion technologies, which could propel flagship space exploration missions throughout the solar system and beyond,” said Alan Newhouse, Director, Project Prometheus. “We commend the work of Glenn and the other NASA Centers supporting this ambitious program.”

HiPEP is one of several candidate propulsion technologies under study by Project Prometheus for possible use on the first proposed flight mission, the Jupiter Icy Moons Orbiter (JIMO). Powered by a small nuclear reactor, electric thrusters would propel the JIMO spacecraft as it conducts close-range observations of Jupiter’s three icy moons, Ganymede, Callisto and Europa. The three moons could contain water, and where there is water, there is the possibility of life.

Development of the HiPEP ion engine is being carried out by a team of engineers from GRC; Aerojet, Redmond, Wash.; Boeing Electron Dynamic Devices, Torrance, Calif.; Ohio Aerospace Institute, Cleveland; University of Michigan, Ann Arbor, Mich.; Colorado State University, Fort Collins, Colo.; and the University of Wisconsin, Madison, Wis.

A print quality photograph of the HiPEP ion engine is at:
http://www.grc.nasa.gov/WWW/PAO/pressrel/2003/03-079addm.html

For information about NASA on the Internet, visit:
http://www.nasa.gov

For more information about NASA’s Glenn Research Center, visit:
http://www.grc.nasa.gov

For more information about Project Prometheus on the Internet, visit:
http://spacescience.nasa.gov/missions/prometheus.htm

Information about JIMO is available on the Internet at:
http://spacescience.nasa.gov/missions/JIMO.pdf

Original Source: NASA News Release

Gravity Probe B Launch Delayed

Image credit: NASA

NASA has decided to push back the launch of its mission to test Einstein’s theory of general relativity, Gravity Probe B, until December 6. During recent tests, engineers noticed electronic noise coming from the sensor attached to one of the spacecraft’s gyros, so they’ve extended the launch date to find time to fix it. Once it does launch, Gravity Probe B will detect any distortions on its four spinning gyroscopes to detect the Earth’s distortion of spacetime around it – as predicted by Einstein.

After a review of test data, a decision has been made to reschedule the launch of Gravity Probe B (GP-B). The launch had been scheduled for Dec. 6 from Vandenberg Air Force Base in California.

Data obtained during spacecraft prelaunch testing shows electronic noise on an output channel associated with the No. 1 experiment gyro. This could compromise the quality of data received from it. The problem has been isolated to a component in the spacecraft?s experiment control unit (ECU). While there is a second available output channel for this gyro, a postponement of the launch will allow time for a repair. This precaution will restore full redundancy to the experiment and provide the greatest chance for success over the planned 16-month life of the mission.

At Space Launch Complex 2, the rocket has successfully completed the scheduled prelaunch preparations up to this time, and there are no issues or concerns with the Delta II. The current plans are for it to remain at the pad enclosed within the gantry-like mobile service tower until the spacecraft arrives.

The length of the postponement will not be known for about a week until a course of action has been developed to address the GP-B problem.

Original Source: NASA News Release

ESA Cancels Eddington

Image credit: ESA

The European Space Agency announced this week that it has canceled Eddington, a space-based observatory designed to search for extrasolar planets. They’re also going to be scaling back the BepiColombo mission to Mercury by removing the lander that was supposed to accompany the spacecraft. The agency blamed the cuts on budget overruns with other missions, such as Rosetta. One new mission was announced, however. The LISA Pathfinder will serve as a prototype to help search for gravity waves.

Today, at its 105th meeting, ESA’s Science Programme Committee (SPC) has made important decisions concerning the Cosmic Vision programme. Due to the current financial exigencies and an outlook with no budget increase or other relief, the SPC was forced to cancel the Eddington mission and rescope the BepiColombo mission.

Eddington had two aims, both remarkable and very pertinent to front-line astronomical interests. The first aim was to look for Earth-like planets outside our solar system – one of the key goals in the search to understand how life came to be, how we came to live where we do in the universe and whether there are other potential life supporting environments ‘out there’. At the same time it was going to follow on the path blazed by the ESA-NASA mission SOHO had taken with the Sun of using astroseismology to look ‘inside’ stars. In the longer term, the loss of this one mission will not stop us pursuing the grand quests for which it is a step.

The loss of the BepiColombo lander is also scientifically hard to take. ESA, in conjunction with the Japanese space agency, JAXA, will still put two orbiters around Mercury but the ?ground truth? provided by the lander is a big loss. However, to land on a planet so near the Sun is no small matter and was a bridge too far in present circumstances, and this chance for Europe to be first has probably been lost.

The origins of the problems were recognized at the ESA Council, held in June 2003. Several sudden demands on finance occurred in the spring, the most obvious and public being the unforeseen Ariane 5 grounding in January. A loan of 100 million Euro was temporarily granted, that must be paid back out of present resources by the end of 2006.

ESA’s SPC were therefore caught in a vice. Immediate mission starts had to be severely limited and the overall envelope of the programme kept down.

By making today’s decision, the SPC has brought down the scope of the Cosmic Vision programme to a level that necessarily reflects the financial conditions rather than the ambitions of the scientific community.

A long and painful discussion during the SPC meeting resulted in the conclusion that only one new mission can be started at this time, namely LISA Pathfinder. The mission is the technical precursor to the world?s first gravitational wave astronomical observatory, LISA. The LISA mission itself (to be made in cooperation with the United States) is scheduled for launch in 2012.

ESA’s Cosmic Vision, set to last until 2012, is a living programme. It has to be able to constantly adapt to to the available funding as well as respond to the expectations of the scientific community, to technological developments. Within these boundaries, the decisions made by the SPC try to maximize the outcome of Cosmic Vision across disciplines, keeping it at the same time challenging and affordable. Nonetheless, there are many European scientists with ambitions that exceed the programme?s ability to respond.

Original Source: ESA News Release

SMART-1 Update: One Month in Orbit

Image credit: ESA

The European Space Agency’s SMART-1 spacecraft has been orbiting the Earth for a full month now, and has made 64 complete orbits. Engineers have been wary this week about firing its ion engine with the increased solar activity. There have been a few problems: the engine unexpectedly turned off, but worked fine on the next firing; its star tracker had difficulty orienting the spacecraft but upgrades to the software resolved that. It’s still on track to reach the Moon by March 2005.

The spacecraft is now in its 64th orbit and has been flying in space for one month! The main activity of the last week was to continue the thrust firings of the electric propulsion engine in order to boost the spacecraft orbit. This operation was limited due to problems with the local radiation environment as a result of the recent, high intensity solar activity. The engine has now generated thrust for a total cumulated time of about 300 hours.

Despite the rather short thrusting phase, the electric propulsion engine performance has been periodically monitored as usual by means of the telemetry data transmitted by the spacecraft and by radio-tracking by the ground stations. We noticed that the EP performance is still improving. From the original expected underperformance of about 3%, we went to last week?s slight over-performance of about 0.5% and we now have an engine that gives about 1% higher thrust than expected. This confirms our confidence in the excellent conditions of the electric propulsion system.

In this period we have also experienced an autonomous shut-down, or flame-out, of the engine. This happened on 26 October 2003 at 19:23 UTC, a few hours before a scheduled switch-off. The engine then re-ignited autonomously at the next scheduled thrusting restart without problems. The experts are investigating the problems. One curious coincidence is that at exactly the same time the radiation monitors on two ESA scientific spacecraft in highly elliptical orbits (XMM and Integral) had detected considerable radiation coming probably from a solar flare. This event was so large and potentially dangerous that one instrument on board Integral stopped operations and switched itself in to safe mode.

The electric power provided by the solar arrays has been according to predictions – about 1850 W for this phase of the mission. The power degradation, due to the radiation environment, was also less than expected at 1-1.5 Watts per day. Recently however, starting from October 20, we noticed a sharper degradation of the power, probably due to the increased radiation environment.

The communication, data handling and on-board software subsystems have been performing according to expectations so far. We are also detecting signs of an increase in the local radiation environment. An onboard counter records the number of hits produced by charged particles, like protons or ions, which cause a single bit in the digital circuits of the computer memory to change state, known as a Single Event Upset. We noticed a sharp increase in the count rate from 23 October onwards. This is currently attributed to the increased solar activity.

The thermal subsystem continues to perform well and all the temperatures are as expected. During the last period the spacecraft systems coped very well with a partial lunar eclipse, where the Moon obscured about 70% of the solar disk for around 80 minutes. Although the average spacecraft equipment temperature has not changed much during the mission, some equipment is experiencing temperature fluctuations due to changes in both the spacecraft’s attitude along its orbit and the Sun’s position. The angle between the Sun direction and the orbit line of apses (the line joining the perigee and the apogee) has changed considerably during the mission. It has varied from about 16 degrees at the beginning of the mission to a current value of 35 degrees. This change could be responsible for the increase of the star tracker optical head temperature during part of the orbit. As the Sun gets further away from the line of apses, this effect should be attenuated and the star tracker conditions should improve.

The attitude control subsystem continues to work, in general, very well. The main area of concern in this period has been the star tracker. This advanced autonomous star mapper has failed in the last two weeks to provide good attitude information in a few cases during different parts of the orbit. We have now found the explanation for all cases. It is due to a combination of several effects. The dominant effect is the increased background radiation level, especially protons to which the star tracker CCD is sensitive. This effect, combined with the temperature increase of the star tracker optical head in some parts of the orbit, created ‘hot spots’ in the CCD which were mistakenly interpreted as stars. This problem has been corrected by a software change uploaded to the star tracker computer.

Another problem was caused by the high star richness of some areas of the galaxy where the star tracker is pointing during part of the orbit. Too many stars require a computer processing time in excess of the allocated slot and cause ‘drops’ of attitude determination. The third problem was the blinding that the Earth disk produces to the optical head. These problems have been corrected by modifications to the software of the star tracker, which has been successfully updated onboard. Since these corrections have been made, the star tracker has been working very well and no further drops in attitude determination have been observed.

Original Source: ESA News Release

SMART-1 is Doing Well

Image credit: ESA

The European Space Agency’s SMART-1 spacecraft has completed its 50th orbit of the Earth; operating its ion engine for more than 560 hours. The engine can only fire for half of the orbit because the spacecraft needs to raise its orbit until it reaches the Moon. ESA controllers have performed a series of tests on the spacecraft, and almost everything seems to be working perfectly – there’s a minor problem with its star-tracker. The spacecraft is expected to reach the Moon by March 2005, when it will begin mapping surface minerals and ice.

The spacecraft is now completing its 50th orbit and has completed more than 560 hours in space. The main actvity of the last week has been to repeatedly use the electric propulsion engine to gradually alter the spacecraft’s orbit. This is limited to around 15 hours a day based on whether the spacecraft is in eclipse. So far the engine has generated thrust for an accumulated time of about 240 hours.

The electric propulsion engine performance has been periodically monitored by means of telemetry data transmitted by the spacecraft and by radio-tracking at the ground stations. The EP performance has been constantly improving, as expected, during the thrusting phase. During the first firing we measured an underperformance of about 3%, as expected in the early operations of the engine in its first use. Today we have a slight over-performance of about 0.5% which gives us confidence in the excellent conditions of the electric propulsion system.

The electric power provided by the solar arrays is nominal. The expected degradation due to the radiation environment is less severe then the worst case scenario. We can, therefore, assume that we shall be able to thrust at full power for quite some time.

The thermal subsystem is performing very well: all the temperatures are as expected and the heater power consumption is lower than estimated. This is a comfortable situation and gives us confidence that the system will be able to cope well with the long eclipse seasons in the spring of next year.

The communication, data handling and on-board software subsystems have been performing nominally so far. The attitude control subsystem has, in general, been working very well and the controller performance during the thrusting phase has been so smooth and accurate that there has been no need to use the hydrazine thrusters to desaturate the small reaction wheels used as main actuators.

The main area of concern is the star tracker performance. This advanced autonomous star mapper has recently failed to provide good attitude information in a few cases around perigee and eclipse periods. Although the attitude control system can cope with these occasional problems, the spacecraft planned operations are disturbed by these events. The operation team at ESOC is obliged to reschedule the operations to take into account these events. In the meantime the ESTEC project and industry teams are busy trying to find an explanation to these anomalies. Despite this inconvenience the thrusting periods are maintained. More on the subject will be provided in future reports.

Orbital/Trajectory information
The SMART-1 orbit is continuously modified by the effects of the electric propulsion low thrust. The osculating orbital elements are periodically computed by the ESOC specialists. These elements define the so called ‘osculating orbit’ which would be travelled by the spacecraft if at that instant all perturbations, including EP thrust, would cease. So it is an image of the situation at that moment. In reality the path travelled by the spacecraft is a continuous spiral leading from one orbit to another.

In this diagram the GTO, the osculating orbits at launch and at different times are plotted. The large orbit, marked ‘final’, is the one we expect to achieve at the end of the radiation belt escape in about two months.

From the start, the electric propulsion system has managed to increase the semi-major axis of the orbit by 1555 km, increasing the perigee altitude from the original 656 km to 2035 km and the orbital period by more than one hour, from the initial 10 hours 41 minutes to the present 11 hours 42 minutes.

Original Source: ESA News Release

Cassini Confirms General Relativity

Image credit: NASA/JPL

The Cassini spacecraft has provided a group of Italian researchers with data that confirms Einstein’s general theory of relativity with 50 times more accuracy than before. They measured the frequency shift of radio waves traveling to and from the spacecraft as they went by the Sun. They measured how much the Sun’s gravity bent the radio signals and increased their travel times. Precise measurements are important because there might be a point at which general relativity stops predicting the interactions of gravity. Cassini is expected to reach Saturn on July 1, 2004.

An experiment by Italian scientists using data from NASA’s Cassini spacecraft, currently en route to Saturn, confirms Einstein’s theory of general relativity with a precision that is 50 times greater than previous measurements.

The findings appear in the Sept. 25 issue of the journal Nature. They are part of a scientific collaboration between NASA and the Italian Space Agency. The experiment took place in the summer of 2002, when the spacecraft and Earth were on opposite sides of the Sun separated by a distance of more than 1 billion kilometers (approximately 621 million miles).

Researchers observed the frequency shift of radio waves to and from the spacecraft as the waves passed near the Sun. They precisely measured the change in the round-trip light time of the radio signal as it traveled close to the Sun. The round-trip light time is the time it takes the signal transmitted from the Deep Space Network station in Goldstone Calif., to the spacecraft on the other side of the Sun and back traveling at the speed of light.

“The scientific significance of these results is the important confirmation of the theory of general relativity and the agreement with Einstein’s formulations to an unprecedented experimental accuracy,” said Sami Asmar, manager of the Radio Science Group, which acquired the data for this experiment at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “The technological significance of the experiment is the ability to overcome the harsh solar environment on radio links.”

The researchers measured how much the Sun’s gravity bent an electromagnetic beam, in this case the radio signal transmitted by the spacecraft and received by the ground stations.

According to the theory of general relativity, a massive object like the Sun causes space-time to curve, and a beam of radio waves (or light) that passes by the Sun has to travel further because of the curvature. The extra distance that the radio waves travel from Cassini past the Sun to the Earth delays their arrival; the amount of the delay provides a sensitive test of the predictions of Einstein’s theory. Although deviations from general relativity are expected in some cosmological models, none were found in this experiment.

Tests of general relativity have important cosmological implications. The question is not whether general relativity is true or false, but at which level of accuracy it ceases to describe gravity in a realistic way.

Past tests of general relativity confirmed Einstein’s prediction to an accuracy of one part per thousand. This accuracy was achieved back in 1979 using the Viking landers on Mars. The Cassini experiment confirmed it to an accuracy of 20 parts per million. The key to this improvement has been the adoption of novel technologies in space telecommunications.

The experiment could not have been conducted to this level of accuracy in the past because of noise on the radio link introduced by the solar corona. With the Cassini experiment, this hindrance was overcome by fitting the spacecraft communication system with multiple links at different frequencies. This new capability on the Cassini spacecraft and on the 34-meter (112 foot) diameter antenna at Goldstone, allowed scientists to remove the effects of the interplanetary and solar plasma from the radio data. In addition, the noise from Earth’s atmosphere was strongly reduced by special equipment installed at the Goldstone complex. These technological breakthroughs developed for the Cassini mission have led to unprecedented accuracies in the velocity measurements with benefits for future scientific experiments as well as deep space navigation.

The experiments are part of a series of radio science experiments planned for the cruise phase of the mission, including the search for low frequency gravitational waves.

Cassini will begin orbiting Saturn on July 1, 2004, and release its piggybacked Huygens probe about six months later for descent through the thick atmosphere of the moon Titan.

Cassini-Huygens is a cooperative mission of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of Caltech, manages the mission for NASA’s Office of Space Science, Washington, D.C. Authors of the Nature paper, “A New Test of General Relativity With the Cassini Space Mission,” are Dr. Bruno Bertotti of the University of Pavia, Italy; Dr Luciano Iess of the University of Rome “La Sapienza”, Italy; and Dr. Paolo Tortora of the University of Bologna, Italy.

Original Source: NASA/JPL News Release