The Orbital ATK Cygnus, just snatched up for docking with the ISS by the station’s Canadarm2. Image from NASA.
Sometime in the past few days, new objects showed up in the satellite tracking database published by Space-Track.org. This is nothing new. Space-Track.org is supposed to do this every day. It’s their job: tracking and identifying objects orbiting the Earth, primarily for the United States Department of Defense, and as an ancillary service to the public and commercial organizations.
However, what was different about these objects was when and how they were deployed in orbit. Space-Track gave numbers to the objects associating them with the launch of a ULA rocket with an Orbital ATK Cygnus International Space Station (ISS) resupply capsule that occurred in March 2016. These objects showed up in late June, after the Cygnus capsule had departed from the ISS. Orbital ATK noted that five cubesats would be deployed before the Cygnus re-entered the Earth’s atmosphere. Space-Track identified the objects as cubesats belonging to Spire Global.
As near as I can tell, this is the first time this sort of satellite deployment has happened. What basically happened was the cubesats hitched a ride up on the Cygnus to dock with the ISS. Then stayed aboard the Cygnus while it was docked with the ISS for three months or so until the Cygnus left the ISS. Once Cygnus left, the cubesats were deployed in the desired orbit. Initially, this doesn’t sound much different from cubesats deploying from a deployer during a rocket’s ascent to orbit. That kind of rideshare has been occurring for some time now. And it might not sound much different from cubesats deploying from the ISS, which is on track this year to deploy even more cubesats than in 2015.
But there are some possible differences that makes this kind of post-ISS deployment desirable. What immediately comes to mind is deploying the cubesats that way gives the owners more flexibility in what low Earth orbit (LEO) the satellites can be placed in. Depending on whether the Cygnus has power left over after it’s ascent to the ISS, the orbital inclination (the angle of an orbit as it goes across the Earth’s equator) might be different than that of the ISS. There’s also the possibility of using a Cygnus-like dedicated cubesat deployer to deploy more than five cubesats. Imagine an entire constellation, maybe 50 or more cubesats belonging to one company, being deployed this way.
A bigger, dedicated deployment spacecraft is not too far from reality. SpaceX keeps pushing back the launch of Formosat 5, which unfortunately, is also tied with Sherpa. A Falcon 9 will be conducting a launch of the two spacecraft sometime during the third quarter of 2016…unless they postpone it again. Formosat 5 isn’t that interesting. It’s an optical Earth observation satellite, one of many orbiting the Earth. Sherpa, however, is more interesting.
Sherpa has been called a space tug. Sherpa is designed, by the folks at Spaceflight Services, to deploy cubesats. A LOT of cubesats. When it launches with Formosat 5, it will eventually deploy 87 cubesats. A Dnepr cluster mission launched in 2014, which deployed the most types of small satellites so far, 37 (don’t let their advertised number of 33 fool you–there was s a satellite that deployed more satellites on board the Dnepr), doesn’t even approach half of Sherpa’s projected deployments. Of course Sherpa needs to be launched first.
There seem to be many different ideas for how to place small satellites in orbit. The weight and size standards set for cubesats in particular, seem to be encouraging people to be creative. The post-ISS Cygnus deployments and Sherpa tug both seem to indicate that no matter which way is offered, there is someone willing to fund a cubesat.
Spire Global, in the case of the Cygnus deployments, has been busy populating low Earth orbits with their own imagery/Earth observation constellation, which might be called Lemur. They’ve also had a few cubesats deployed from the ISS Nanoracks CubeSat Deployment system this last May.