Issue 96

The next two articles examine Russian and Chinese space operations in what is called Very Low Earth Orbit (VLEO). VLEO describes the orbit of any spacecraft with a semi-major axis (SMA) or altitude of 300km or less. I asked Jack Anthony to take a look at VLEO operations and he (as always) was nice enough to oblige! How Low Can You Go? by Jack Anthony Operating at lower altitudes, especially those lower than 300km, gives operators a big focus item-atmospheric drag. Check out my “It’s a Drag” article in last issue for a good review. Attentiveness to orbit state and just how fast the atmosphere is reeling in a satellite is the norm of operators who must activate propulsive capability to raise perigee via delta V’s at apogee. There are benefits to being a lot closer to the Earth, distance reduced and thus maximum imagery resolution. In the 1960’s when the US began space-based reconnaissance the Corona satellite program operated by military and contractor crews at Sunnyvale California mastered VLEO operating as their spacecraft swooped as low as 90 miles (145 Km) altitude in a slightly non-circular 90 x 120 mi orbit. Corona satellites would send 2 “buckets” of film to earth to be caught by C-119 and then C-130 aircraft and then scurried off to be examined in mostly time critical situations. Around 1963 the Corona’s added a propulsive capability that would help operators beat the tug of atmospheric drag and keep perigee from perilous demise. If you want to learn more about Corona and other early satellite reconnaissance programs, check out the NRO History Corona web page. While operating satellites at <300kms doesn’t happen often, it isn’t completely novel. There have been several space missions in the past 10-15 years that operated in VLEO. The European Space Agency’s Gravity Field and Steady-State Ocean Circulation Explorer was operational from March 2009 to November 2013. It needed to be close to the Earth to achieve its gravity mapping endeavor and orbited the Earth at 255km. In 2017, the Japan Space Agency flew its Super Low Altitude Test satellite for 2 years starting at 271km and then working their way down to 167km. They used an ion thruster and some traditional propulsion to manage their darn low orbit! They even got a Guiness Book of Records accolade for the 167km orbit, lowest ever. Way to go Japan…Guiness record! I will share that the 90 x 120-mile orbit I mentioned (145 X 195km) orbit had a mean altitude of 170km. Currently underway is an ESA sponsored mission called Skimsat, how bout that cool name? Skimsat is being built by Thales Athena Space and Redwire and will have a high-specific impulse thruster capability as well as use the aerodynamic forces presented by the upper atmosphere to “skim” and fight off decay. Now that’s going to be a cool mission to watch in operation as it “skims” and “puffs with Xenon” in VLEO.