In 2014, two European Space Agency satellites, Galileo 5 and 6, were launched into space but experienced a thermal breach, causing them to enter highly elliptical orbits instead of the intended circular orbit. This turned out to be a fortunate accident, as scientists were able to use the satellites to test the gravitational redshift prediction of general relativity.
The satellites' atomic clocks were used to measure time dilation as they orbited the Earth, and the data collected over 1,000 days allowed scientists to reduce the uncertainty in the measurement by a factor of 5, setting a new record. While the results confirmed general relativity, scientists believe that further tests may reveal new aspects of nature, as general relativity and quantum mechanics have yet to be successfully merged, and dark energy and dark matter remain unexplained.
Here are the key facts extracted from the text:
1. On August 21, 2014, two satellites, Galileo Satellites 5 and 6, were launched by the European Space Agency.
2. The satellites were intended to become part of the Global Navigation Satellite System (GNSS).
3. The European GNSS is the European version of the American GPS system.
4. The satellites were launched with the Russian Soyuz rocket.
5. The final stage of the rocket was set to inject the satellites into circular orbit around 23,000 kilometers above the Earth.
6. A thermal breach occurred between a line of cold helium and a line of propellant, causing the propellant to freeze.
7. The failure of the altitude control thrusters resulted in the satellites being injected into highly elliptical orbits.
8. The satellites' orbits were not useful for navigation due to their elliptical shape.
9. The satellites experienced significant radiation exposure due to the Van Allen belts.
10. The satellites had propellant on board to allow for periodic course corrections over their planned 10-year lifespan.
11. The propellant was used to attempt to correct the satellites' orbits.
12. The satellites did not have enough propellant to completely turn their elliptical orbits into circular ones.
13. The satellites' elliptical orbits allowed for the testing of general relativity.
14. According to general relativity, clocks tick slower in stronger gravitational fields.
15. The satellites' clocks were expected to tick faster relative to those on Earth due to their weaker gravitational fields.
16. The satellites' clocks were atomic clocks, specifically passive hydrogen MASER clocks.
17. The MASER clock uses microwaves to interact with hydrogen atoms.
18. The clock's frequency is determined by the interaction between the microwaves and the hydrogen atoms.
19. The clock's stability allows it to keep track of time with incredible accuracy.
20. The scientists used the satellites to test the gravitational redshift predictions of general relativity.
21. The tests were not easy to carry out due to errors in the satellites' positions.
22. The positions of the satellites were affected by the power of sunlight.
23. Careful modeling and laser ranging to the satellites brought the orbital uncertainties down to an acceptable level.
24. Data was collected over more than 1,000 days (almost 3 years) to improve the statistics.
25. The results of the tests reduced the uncertainty in the measurement of the gravitational effect on time by a factor of 5.
26. The satellites' orbits were made more circular using the propellants on board, but they are still elliptical.
27. The navigation signals from the satellites have been tested and are within acceptable parameters.
28. The satellites are currently restricted to "test mode" awaiting new software and modifications on the ground.
29. A cold cesium atom clock is set to fly in the International Space Station to further test general relativity.
30. The clock aims to reduce the deviation by a further factor of 10.