Imagine a heartfelt reunion with someone you never thought you'd hear from again.

That must have been what it felt like for NASA as a long-lost spacecraft finally re-established communications after nearly two years of being alone in outer space.

The space agency's 9-year-old STEREO-B spacecraft — short for Solar Terrestrial Relations Observatories — had drifted away somewhere in the vast expanse on Oct. 1, 2014. It had lost contact with our planet ever since.

For 22 months, however, NASA attempted to recover communications with the lost spacecraft through the monthly recovery operation known as Deep Space Network (DSN).

Their efforts weren't in vain. On Sunday, Aug. 21, NASA announced that it has contacted the solar observatory at long last.

Losing Contact With Earth

The STEREO-B spacecraft, the twin of another solar observatory named STEREO-A, was about 189 million miles away from Earth when it regained contact with NASA.

Both STEREO observatories, with "A" meaning ahead and "B" meaning behind, were launched in 2006. The spacecraft began orbiting the sun in slightly different Earth-like orbits. This was done so that scientists could observe the sun in different angles.

The $550-million STEREO-B project was supposed to end in 2008, but because it was successful, the space agency decided to keep it going. Unfortunately, trouble hit the mission on October 2014: STEREO-B had gone into a hard reset and lost contact with our planet.

Regaining Contact

Thanks to the DSN, which is designed to track and communicate with space missions, NASA has recovered contact with the spacecraft.

According to Karen Fox, a spokesperson from NASA, the DSN established a lock on the downlink carrier of STEREO-B at 6:27 p.m. EDT (6:27 a.m. EST).

The signal was then monitored by the STEREO Mission Operations team for several hours to determine the attitude of the spacecraft. The transmitter high voltage was lowered down to conserve battery power.

But although the feat is a cause for celebration, every scientist involved in the STEREO mission is on the edge of their seats, says STEREO Project Scientist Joe Gurman.

"The very hard and scary work is just beginning," Gurman tells Business Insider.

Gurman says the STEREO spacecraft was meant to be as autonomous as possible in case it runs into trouble. He says that if scientists could "turn on the computer" to get insight into what went wrong, they could fix the problem.

In a December 2015 article about recovery efforts, NASA mentioned that the spacecraft does not know if it's rotating and how fast. It's a huge problem for a robot that needs to aim its solar panels at the sun and charge its batteries. STEREO-B has barely been charging since the reset. Its batteries could quickly drain.

With that in mind, the Mission Operations team is planning to perform further recovery processes to evaluate the spacecraft's health, re-establish control of attitude and assess all instruments and subsystems. Scientists are taking their time to produce a brief set of rescue instructions to save the spacecraft.

The STEREO-A spacecraft continues to function normally.