U. S. citizens tend to think of NASA when the topic turns to space exploration. But the European Space Agency (ESA), established in 1975 to combine the efforts of 19 European nations, has its own ideas for advancing space technology. Among the most interesting efforts with which ESA is involved is one aimed at extending Internet connections to spacecraft. Though its annual budget is about $5.2 billion compared to NASA’s $18 billion, ESA is making important strides in fundamental space research.
Nanosats to test software
Engineers and technicians at ESA today control satellites and space experiments using Packet Utilisation Standards, a software suite that dates to 1994. There have been upgrades since then, but the stumbling block to moving to newer software is that space scientists and the organizations that fund them must ensure the software, including operating systems, languages, and interfaces, is fit for space.
“No one wants to use new and possibly problematic software on a multimillion-euro mission in space,” says Mario Merri, head of the Mission Data Systems Div. at ESA operations center.
Unfortunately, the only real way to prove software is fit is to take it into space and run it through its paces.
To lower the cost of validating software, and to ensure no missions are endangered, ESA researchers developed Operations Satellites, dubbed Op-Sats. The 30 × 10 × 10-cm satellites’ mission is to test and validate critical onboard and ground software. The spacecraft is outfitted with off-the-shelf processors that have more computing power than a satellite usually carries. It’s also designed to recover easily and quickly from “buggy” software. Researchers on Earth can replace the entire onboard software suite with new and fresh code daily, letting developers troubleshoot their work in a real, but safe, environment.
The first Op-Sats could launch next year.
Spinning an interplanetary Web
People increasingly take reliable and fast Internet access for granted. Now space scientists want to extend the same simplicity and reliability of the Web to astronauts on the Moon or Mars. The first goal will be to let astronauts communicate among themselves, with control centers on Earth, and with spaceships and bases. But who knows; someday top-level Internet domains may include such names as .moon, .mars, or .sstation.
To this end, ESA, NASA, and other major space organizations and industrial partners have been working together as part of the Consultative Committee for Space Data Systems. They have developed standards for hardware and data exchange that should pay off even in the short term for commercial space-flight businesses, satellite manufacturers, and space agencies.
Satellites have already been used for links between Earth and mission spacecraft. In 2008, for example, ESA’s Mars Express acted as a data-relay node between NASA technicians on Earth and their Phoenix Lander during decent and landing on Mars, It will repeat that task in August this year with NASA’s Mars Science Laboratory.
And last December, ESA’s worldwide tracking station network handled contact between Russian controllers and that country’s Phobos-Grunt mission to Mars. Then, in October of this year, an astronaut on the International Space Station will practice at remotely controlling a planetary rover at ESA’s operations center, simulating orbiterrover communication links on a planet like Mars.
“Establishing technical standards and communication architectures isn’t the most high-profile part of space exploration, but it’s absolutely vital for ensuring that the more-exciting efforts, like sending an astronaut to Mars, will work when that time comes,” says Nestor Peccia, the person responsible for ground software development at ESA’s German operations center.
Tech transfer for piezo foil
Back in the early 1990s, a German engineer was developing a new type of pressure sensor that would coat the wings of Hermes, a reusable mannedshuttle that would be launched into space atop an Ariane 5 rocket and then return to Earth on it own, much like the Space Shuttle. The sensor had to be light and thin so it would not add bulk or drag to the airfoil. The engineer turned to piezoelectric foil to do the job. Like other piezo materials, the thin foil (30-microns thick) converts vibrations and pressures into electrical pulses that can be measured and interpreted.
The foil sensors were successfully tested in a hypersonic wind tunnel, but the Hermes project was cancelled. So over the years, ESA has been looking for civilian uses for the piezo sensors. One of the earlier applications was converting the foil to paint and putting it on a human molar. Scientists used this ”instrumented” tooth to measure forces a toothbrush puts on teeth.
But just recently, Volkswagen saw the sensor demonstrated at the Hannover Fair at a booth set up by ESA’s Technology Transfer Programme Office. They quickly decided to use the piezo sensors on crash-test vehicles. Traditional sensors do well at recording pressure up to the point of impact, then they are too often destroyed in the crash. The foil versions, however, survive the crash, sending pressure data to the researchers through the entire crash event.
The original ESA engineer worked to convert the foil into a strip of about 50 individual sensors, each about a square centimeter. At the end of each strip is a flexible printed-circuit board with a 50-channel amplifier. When it is attached to a fender or bumper, it lets test engineers know how fast that metal is bending, as well as whether it is bending 20° in one direction or 60° in the other.
VW has now used the sensor in several crash tests and it has contributed to changes that make the cars safer, according to VW managers.
A Swarm heads for space
Three identical Swarm satellites will launch from Russia’s Plesetsk Cosmodrome next month on a four-year mission to explore the Earth’s magnetic field. This is the first time a team of satellites has been deployed on a single, dedicated mission. Two of the satellites will travel side by side in a near-polar orbit about 305 miles above the Earth. The third Swarm orbits slightly higher, 330 miles, and about 40° off axis from the other two. During the four-year mission, this third Swarm will drift to 90° off axis from the other two. The 1,100-lb satellites will circle the Earth 15 times each day.
A single rocket will carry all three Swarms into space, and it will take about three months to get them in their final orbits and check out all subsystems and payloads. The satellites each measure about 30-ft long, but half that length is taken up by a tail which will extend back from the satellite during the check-out phase. A pair of magnetometers mount on the tail, isolating them magnetically from any interference from the satellites and its electronics.
For simplicity, the Swarms do not carry or extend solar arrays. Instead the two sides of each triangular-hulled satellite that face outer space will be covered with GaAs solar panels that deliver 608 W of power at the outset of the mission. The cells will charge a set of 48 A-hr lithium-ion batteries for power when the satellites are not in the sun.
The satellites will record and transmit to Earth high-precision, high-resolution measurements of the Earth’s magnetic field strength, direction, and variation. They will also provide accurate navigation data tied to magnetic and electric-field measurements, all of which are needed to map the geomagnetic field.
Having three satellites in two different orbits will improve sampling in terms of space and time, letting scientists distinguish between the effects of different sources of magnetism.
It is hoped the data gained will give scientists insights into the dynamics of the Earth’s liquid-metal core and crust, as well as into their interactions with Earth’s protective shield in the ionosphere and magnetosphere.
Catching a comet
Eight years ago, the Rosetta probe was launched on an 11-year convoluted journey to chase down the comet 67P⁄Churyumov-Gerasimenko. The spacecraft has already made three swingbys of Earth and one of Mars, and managed to fly by a pair of asteroids, 2,867 Steins, and 21 Lutetia, and circle the sun four times. Currently, it’s traveling at about 2,600 fps and is on schedule for a May 2014 rendezvous with Comet 67P.
Rosetta weighs in at 6,750 lb, but carries 3,200 lb of fuel. It measures 9 × 7 × 6 ft, but the twin solar panels deployed once Rosetta was in space give the space probe a 104-ft “wingspan.”
Rosetta took some measurements and images when close to the asteroids and Mars during the trip, but for the most part, it is hibernating, with most electrical systems shut down except for thermal control, radio receivers, and computers.
Several challenges have made it difficult for ESA controllers to keep Rosetta on track and healthy. For example, at some points in its journey, it has taken 100 min for signals to travel to Rosetta and for receivers to get a response. And communications have been constrained by an 8-bps rate for data and relatively little power available, compared to other satellites. This is the first solar-powered spacecraft to fly farther than 3.1 astronomical units (288.3 million miles) from the sun.
Eventually, Rosetta must brake to match its speed to the comet’s as they both head toward the sun. Once within a few miles of the comet, Rosetta will begin observing it with its onboard instruments. They include a UV spectrometer, ion-mass analyzer, impact analyzer and accumulator, and an imaging system. These last three are designed to examine cometary dust.
Once established in orbit above the moving comet, Rosetta will release Philae, a 220-lb lander, and it will become the first spacecraft ever to make a soft landing on a comet. It is made mostly of carbon fiber with a hood of solar cells.
While Philae and its suite of 10 instruments investigates the comet from ground level, Rosetta will orbit and study it for a year as it continues to its perihelion or closest approach to the sun. Rosetta will then remain with the comet for another six months as the comet heads towards the orbit of Jupiter, ending its mission in December 2015.
On the comet, Philae will be sending data to Earth relayed through the Rosetta orbiter. Its instruments will detect alpha particles and X-rays to determine the comet’s composition. Cameras will take high-resolution images of the descent and surroundings of the landing area. Gas analyzers should identify organic molecules and isotropic ratios of light elements. Another set of sensors be will measuring the density, thermal, and mechanical properties of the soil on the surface. And a drill will go up to 8-in. deep to collect geological samples that will be dried onboard Philae and examined microscopically.
The main objective of the 1-billion-Euro mission is to make the most detailed observations of a comet’s icy nucleus, surface, and tail. According to astronomers, comets represent a relatively unchanged environment from 4.6 billion years ago. So a close examination will give scientists a snapshot of what the solar system was like when planets were first forming.