Laser Relativity Satellite 2 was launched on 13 July 2022 from the European Space Agency's (ESA) spaceport in Kourou, French Guiana. LARES-2 was built by the Italian Space Agency (ASI) for around 10 million euros and lifted off on the maiden flight of an improved version of the European Vega rocket.
The Vega-C's performance was "spectacular," says the head of the mission, Ignazio Ciufolini, a physicist at the Universitá del Salento in Lecce, Italy. "ESA and ASI have put the satellite into orbit with an accuracy of only 400 meters." This precise positioning will help to improve the quality of the researchers' measurements, adds Ciufolini.
"This is a great progress for measuring the effect," says Clifford Will, a theoretical physicist at the University of Florida in Gainesville.
Space is rocked by a reflective ball.
Lares-2 is a metal ball that is covered with 303 reflectors and has no electronics or navigation control on board. The design of the disco ball is similar to that of its predecessor Lares, an experiment on general relativity theory, which started in 2012, and a probe called Lageos, which NASA used in the 1970s primarily to investigate the gravity of the earth.
With Lares-2, there is about 295 kilograms of material in a ball of less than 50 centimeters in diameter.
Its density minimizes the effects of phenomena such as the radiation pressure of the sunlight or the weak air resistance of the earth's atmosphere at high heights, says space engineer Antonio Paolozzi from the University of La Sapienza in Rome.
After experiments with tailor -made materials of high density, the team chose a commercially available nickel government.
This had an acceptable density and made it possible to qualify Lares-2 without expensive flight certification tests for Vega-C first flight.
Ciufolini and his colleagues plan to track the orbit of LARES-2 over several years using an existing global network of laser measuring stations. This type of probe can provide data for decades. "You can just sit back and send laser beams to her," says Will. "As far as costs are concerned, that's a cheap and good thing."
According to Newton's gravity, an object that circles a perfectly spherical planet should run through the same ellipse again and again. But in 1913 Albert Einstein and his employee Michele Besso based on a preliminary version of the general theory of relativity pointed out that a rotating planet would have to cause a slight shift in the satellite track. The exact mathematical calculation of the effect was carried out in 1918 by the Austrian physicists Josef Lense and Hans Thirring. Modern calculations predict that the lens-thirring effect, a kind of relativistic "frame dragging", should lead to the level of the orbit around the earth's axis by 8.6 millionth degrees a year.
In practice, the Earth itself is not a perfect sphere, but "shaped like a potato, " says Ciufolini. The resulting irregularities in the gravitational field of the Earth – exactly what LAGEOS was supposed to measure – lead to an additional precession of the orbit, which can complicate the measurement of the relativistic effect. However, by comparing the orbits of two satellites, these irregularities can be compensated for.
Ciufolini, who has been working on the concept of the Lares mission since his doctoral thesis in 1984, applied this principle for the first time in 2004 to measure the rail shift by comparing the lanes of Lageos and Lageos-2-a similar probe that started by ASI. He and his colleague Erricos Pavlis from the University of Maryland, Baltimore County, claimed to have determined the effect with an accuracy of 10 percent.
Although the result was still very inaccurate, the team managed to thwart a NASA experiment costing the equivalent of about 785 million euros, which wanted to measure the frame displacement using a different technique. The highly complex Gravity Probe B mission, launched in 2004, measured not the changes in the spacecraft's trajectory, but the inclination of four rotating spheres that shifted by a tiny fraction of a degree per year. Unforeseen complications led to the fact that Gravity Probe B was able to achieve an accuracy of only 20 percent, far from the original goal of 1 percent.
Lares-2 is at an optimal height of 5900 kilometers
Ciufolini and his team then improved their earlier result to an accuracy of 2 percent with LARES, the first probe specifically designed for this type of experiment. However, due to the limitations of the launcher – the former Vega – LARES could only reach an altitude of 1450 kilometers. LARES-2 is now at an optimal altitude of 5900 kilometers, where the irregularities of the Earth's gravity field are damped, but the influence of the frame is still strong.
The aim of the mission is to achieve an accuracy of 0.2 percent. With the precise orbital injection, this goal is likely to be within reach, says Ciufolini. The team could thus determine whether the general theory of relativity is gaining the upper hand over alternative space-time theories, he adds.
Thibault Damour, a theoretical physicist at the Institute for Advanced Scientific Studies (IHES) near Paris, praises the low cost of the experiment. "If you find a deviation [from the theoretical prediction], that would be an important result," says Damour. However, he adds that there have already been more detailed reviews of the general theory of relativity in space; for example, a test of the Cassini mission.
The effects of frame dragging are only weak near the earth. But when two black holes circle and merge, they become gigantic. Gravitational wave observatories could already have started to discover such effects in the last orbits of some black-hole pairs: from the shape of the waves you can calculate how quickly the lighter black hole moved forward and how quickly the heavier black hole turned. With the discovery of gravitational waves, the understanding of frame dragging has "become of fundamental importance for astrophysics," says Ciufolini.
© 📓 🐠 1⃣ 0⃣ . 1⃣ 0⃣ 3⃣ 8⃣ /d 4⃣ 1⃣ 5⃣ 8⃣ 6⃣ -022-02034- ✖ , 2⃣ 0⃣ 2⃣ 1⃣
