SpaceX launched 21 Starlink internet satellites into low-earth orbit on a Falcon 9 rocket on Friday, Sept. 20. With the right night-time weather conditions, it's possible to see a few satellites in this mega-constellation. 

Soon after deployment, some SpaceX launches appear as a "Starlink satellite train” which is only visible at low orbit.

SpaceX has recently had frequent launches. This includes sending five Bluebird smartphone satellites to orbit for AST SpaceMobile on Wednesday.

 It also returned the crew of the Polaris Dawn private mission back to Earth on Sept. 10.

SpaceX launched more than 90 missions to space this year.

Starlink Mega-Constellation

The latest launch included 13 satellites equipped with Direct to Cell technology.

Some other SpaceX missions for this booster have included a couple of Transporter launches, which send satellites for multiple clients to space at the same time, as well as national security missions for the National Reconnaissance Office.

More than 6,300 Starlink satellites are currently in-orbit and operational, according to the Harvard-Smithsonian Center for Astrophysics which tracks space launches.

The Starlink Equation

According to the online NASA Spaceflight website the mega-constellation developed by the private space agency is currently planning to put up to 42,000 satellites in orbit.

The vast fleet of Starlink satellites which orbits Earth, provides internet coverage on a global scale. 

The satellites climb to their optimum operating altitude of 340 miles (550 kilometers).

Starlink satellites travel very quickly. They complete one orbit of Earth every 90 minutes which means it can be possible for sightings every two hours.

The ever-increasing numbers of satellites from SpaceX and other private companies, such as OneWeb, have the potential to create light pollution and space debris stemming from these mega-constellations.

 Space advocates have called for greater regulations from government agencies. 

Recent technology advances have brought the development of some stargazing apps to the phone screen. If you want to view Starlink satellites, there are several apps avail that allow you to “test before you invest.” And there are also some free versions available.