LEO, MEO or GEO? Diversifying orbits is not a one-size-fits-all mission (Part 2 of 3)

  • Published
  • By Lisa Sodders, SSC Public Affairs
Sandwiched between Low Earth Orbit (LEO) and Geosynchronous Orbit (GEO) lies Medium Earth Orbit, also known as MEO. Less costly to reach compared to GEO and less fuel intensive to operate in compared to LEO, Medium Earth Orbit offers a blend of benefits not found in other orbital planes. It also presents unique challenges.

At  1,243 miles to 22,236 miles above earth, satellites in MEO require significantly less momentum to stay on course compared to their counterparts in LEO. Traveling at approximately 7,000 mph, satellites in MEO circle the globe once every 12 hours, or roughly twice per day. LEO, by comparison, requires satellite speeds of up to 17,500 mph to resist Earth’s gravity and stay in orbit.

It also takes less energy to keep satellites on course in MEO because there’s minimal gravitational pull from the Earth as well as less atmospheric drag.

“Station-keeping is easier in MEO versus LEO and requires less fuel,” notes Gregory Henning, a project leader who specializes in space debris simulations with the Aerospace Corporation.

In addition to lower fuel consumption, one of the main advantages of MEO is that satellites have a higher vantage point compared to LEO and this means it takes fewer satellites to provide full coverage of the Earth. This makes MEO ideal for navigation satellites. It is home to the U.S.’s Global Positioning Satellite System, as well as Galileo, GLONASS and BeiDou, the European, Russian and Chinese versions of GPS.

“If you were to try to do the GPS mission in LEO, the number of satellites you would need would be enormous,” says Henning.  Compared to the thousands of satellites in LEO, MEO contains under 200 satellites.

“The trade-off is, the further away from Earth that you go, the stronger your transmit power beam needs to be; thus, the larger your equipment and the bigger your satellite, so it (generally) costs more to launch (satellites into MEO compared to LEO),” notes Kerstyn Auman, a space situational awareness (SSA) analyst at the Aerospace Corporation.

Another trade-off that’s wholly unique to MEO involves the two zones of energy charged particles above the equator known as the Van Allen radiation belts. Satellites passing through these belts must have special shielding to avoid damage to their electronic systems.

Along with LEO, MEO is the target destination for a new missile warning, missile tracking and missile defense program under development at Space Systems Command. It will supplement the existing SBIRS (Space-Based Infrared) satellites in geosynchronous orbit and provide an overlapping layer of resiliency to the nation’s space sensing capabilities.

Col. Daniel T. Walter, senior materiel leader, Strategic Missile Warning Acquisition Delta at Space Systems Command, points out that space-sensing satellites in MEO offer a number of advantages not found in GEO or LEO.

For one, greater proximity to Earth reduces the size and complexity of the satellites and sensors needed to perform the new missile warning and tracking mission when compared to their counterparts in GEO.

For another, sensors orbiting in MEO have longer target area pass times and wider fields of view than LEO. As a result, “MEO sensors can maintain custody of missile tracks for longer periods of time (compared to LEO) because the higher altitude allows for a larger field of view,” says Walter.

“As we continue to innovate and enhance what systems are placed in each orbit and then create connections between orbits, we open up warfighting opportunities we have never seen before,” says Col. Heather Bogstie, senior materiel leader for the Resilient Missile Warning, Tracking, and Defense Acquisition Delta at SSC.  “Couple this with rapid commercial technical innovation and future allied systems, and we have emerging a truly robust sensing network.”

To learn more about SSC’s pivot to MEO for missile warning, tracking and defense, view this video. And stay tuned for All About Orbits: Part Three, which delves into the realm of Geostationary orbits.

Test Your Orbital Knowledge: Choose the answer that doesn’t fit.
  1. Medium Earth Orbit is:
    1. Located between LEO (Low Earth Orbit) and GEO (Geosynchronous Orbit)
    2. The most populated orbit in terms of satellites
    3. The orbit of choice for global navigation satellites.
  1. Satellites in Medium Earth Orbit:
    1. Travel faster than satellites in Low Earth Orbit
    2. Circle the globe approximately twice per day
    3. Reach speeds of approximately 7,000 miles per hour
  1. Sensors in Medium Earth Orbit:
    1. Have wider fields of view compared to Low Earth Orbit
    2. Have shorter area pass times than Geostationary Orbit
    3. Do not require special radiation shields
  1. B. Low Earth Orbit contains more satellites (thousands) versus Medium Earth Orbit (less than 200)
  2. B. Travel more slowly than satellites in Low Earth Orbit because they require less momentum to counteract drag
  3. C. Sensors in Medium Earth Orbit pass through the Van Allen Radiation Belts; therefore, they must be protected with shields