The Molniya orbit, a type of highly elliptical orbit (HEO), was the focus of the last HEO post. And it was noted that the Molniya is an orbit perfectly suited to communication. But what other missions and satellites use the HEO?
Believe it or not, the US has organizations that use the HEO for a few missions. The most recent launch of the NROL-33 “spy satellite” is kind of related to the HEO, in that it’s part of a possible satellite communications and data constellation using a combination of HEO and geosynchronous (GEO) satellites called the Space Data Segment (SDS).
In the illustration above, they call this particular combination of HEO and GEO satellites the “SDS-3 Constellation.” Does anyone really know what’s on these satellites, aside from the people working with them? One observation: realize the government likes to maximize on their investments with additional payloads on satellites. Just look at what NASA has done with their satellites and payloads to get an idea. There’s nothing to prevent the installation of some kind of extra monitoring payloads on any of these satellites. As discussed before regarding why the Russians use this kind of orbit, the view of areas that might be interesting to the US is pretty good. Only the people working with this constellation really know what it’s all for, though.
A few more HEO birds owned by the US are the overpriced Space Based InfraRed System (SBIRS) HEO satellites. There are currently two in orbit, with a third theoretically on the way. This system is a little more straightforward in purpose, as it’s part of the early warning system for missile launch detection. Why would the US want two to three missile launch detection satellites in highly elliptical orbit? The Russians/Soviets also did and still do use satellites in HEO for early warning. But the SDS, SBIRS, and OKO (Russian) satellites have to do with terrestrial activities and likely are trying to give their corresponding militaries an edge on terrestrial battlefields.
The most interesting mission using the HEO is one that’s coming up and has nothing to do with human activities on Earth: NASA’s Magnetospheric MultiScale mission (MMS). The focus of this two-phase mission isn’t necessarily the Earth, but the Earth’s magnetic field. And not just the Earth’s magnetic field, but the Sun’s, too, and observing the interplay (NASA say the connecting and disconnecting of the fields) between the two fields. The mission uses four satellites that will be “flying” in formation and placed in a “low-inclination” elliptical orbit of 28 degrees. This means the orbit’s tilt is at a 28 degree angle to the Earth’s Equator.
During phase 1, the satellites will have a perigee (point of orbit closest to the Earth) of 7,645 kilometers (4,750 miles) and an apogee (point of orbit furthest away from the Earth) of 76,452 kilometers (47,505 miles–at least I think NASA means apogee—on their website they say perigee twice). During Phase 2, the perigee’s the same, but apogee increases to 159,274 kilometers (a little over 98,968 miles). Seems like that’s pretty far, but believe it or not, the Moon is still further away, at over 238,857 miles average distance from Earth.
The two different orbits are designed to pass through the reconnection points of the magnetic fields of the Earth and the Sun. So they are necessarily big. But such an orbit also allows the satellites to “sample” different portions of the magnetic fields. And they fly in a pyramid formation to help map out the reconnection events in 3-D. Why go through all of this just to observe these reconnection events? The reconnection events tend to release energy, and the energy can impact the electronics here on Earth and on the satellites orbiting around it. There’s more to the science of these satellites on the MMS website. As a side note, the MMS satellites will be controlled out of the Laboratory for Atmospheric and Space Physics (LASP) in Boulder, Colorado (same place the Kepler mission is run out of). Worth visiting, if only just to walk around the campus in Spring.
And while you’re in Boulder, enjoy the offerings of the Avery Brewing Company, which has a terrific Belgian Wheat (White Rascal) beer and a tasty Imperial Oktoberfest (The Kaiser) beer. Sadly, there are no beers for HEO—which means we are now at the empty bottle part of the lesson.