Sometimes you spend years preparing for a scientific mission, and things go wrong at the last second. Other times what you get is way better than you expect. The LISA Pathfinder mission is in the latter category.
The mission was launched in 2016 and its goal was to test the technology that will allow the European Space Agency (ESA) to launch the Laser Interferometer Space Antenna (LISA), the first space-based gravitational wave observatory. The first results were five times better than the minimum requirements for the mission and now the final results have improved on the first data by a factor of two. The whole system is literally 10 times better than what was expected.
“We were blown away by the results in the first weeks of the mission, but our final results using more and better data and a deeper understanding of our space laboratory LPF really are a sight to behold.” Professor Karsten Danzmann, Co-Principal Investigator of the LISA Technology Package, said in a statement. “LISA Pathfinder beautifully demonstrated the key technologies for LISA, the future gravitational-wave observatory in space: the perfect undisturbed free fall of two cubic test masses inside the spacecraft.”
LISA will have three independent spacecraft positioned on the vertices of an equilateral triangle 2.5 million kilometers (1.55 million miles) from each other. Like the Earth-bound gravitational wave observatories, LISA will work on the principle of interferometry, which requires the laser sent out to be exactly the same as when it comes back in. Any changes ideally would mean a detection, but even small movements of the devices could create false positives.
It would be impossible to keep three spacecraft in the same position in space so far apart, so researchers had to get creative. To measure the relative motion of the spacecraft they had to find a reference body, and there’s nothing better than comparing to something in free fall. But the free fall needs to be measured to a high degree of precision for this to work. And that was the goal of LISA Pathfinder’s mission.
Pathfinder provided an indication of how well we could take the motion into account. It was expected to demonstrate a noise-level more than 10 times worse than what’s been planned for LISA but it showed that LISA can do better as the technology is already there. In the last few years since the launch, the researchers were able to create a better vacuum in the spacecraft as well as improving their understanding and modeling of the various forces affecting the craft. This was key for the high precision achieved.
LISA received its clearance goal by ESA to fly in the 2030s and it is currently scheduled to launch in 2034.