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Launching to Cloud Nine: DoD’s Reference Orbits

Launching to Cloud Nine: DoD’s Reference Orbits

Space & Missile Systems Center Shield (Courtesy of  U.S. Air Force )

Space & Missile Systems Center Shield (Courtesy of U.S. Air Force)

I’m not going into infinity. I’m going into low earth orbit.
— Helen Sharman

While a successful space transportation company can market itself to a number of private customers, it must also be able to compete for public contracts. In the United States, the Department of Defense (“DoD”) spends billions of dollars annually on space-related programs. Therefore, it is a priority target for many U.S. centric space transportation companies such as SpaceX, Blue Origin, United Launch Alliance, and Orbital ATK.

In fact, the DoD’s 2019 proposed budget includes $9.3 billion for space-related projects. This figure contains $4.8 billion for satellites and $2.4 billion for launch platforms. Hence, landing one of these DoD’s space-related contracts can be a make-it-or-break-it moments for a space company’s bottom line.

The DoD’s most lucrative and competitive missions are those involving national security payloads. But, a space transportation company must satisfy many requirements before it’s certified to compete for any of these missions. This qualification process could be arduous and take a significant amount of time, energy, and expense. As a part of this certification process, one of DoD’s key criteria is the launch platform’s ability to carry payloads into certain orbits. In this post, I will explore these reference orbits (and additional reference orbits that the DoD is proposing for 2024).

Evolved Expendable Launch Vehicle

One central component of the DoD’s Space portfolio is the Evolved Expendable Launch Vehicle (“EELV”). The EELV is a United States Department of Defense Program managed by the Launch and Range Systems Directorate of the Space and Missiles Systems under the United States Air Force Space Command.

The main objective of the EELV program is to ensure that the DoD and other governmental agencies will continue to have reliable and affordable means of launching national security payloads into Outer Space. To that end, EELV was instrumental in the development of ULA’s Atlas V and the Delta IV rockets, the only two launch platforms that are certified for EELV missions. However, SpaceX’s Falcon 9 has been approved by United States Air Force to compete for EELV missions and is currently undergoing the certification process.

The Nine Reference Orbits

Under the EELV Program, one of the major criteria for selection is a launch platform’s ability to carry national security payloads into nine reference orbits around Earth.

Orbit No. 1: LEO

LEO, or Low-Earth Orbit, is a common orbit of operation for satellites and human space flight operations. So, it is with little surprise that one of EELV’s reference orbits is within LEO. For this orbit, the EELV requires a platform to reach an apogee, or highest, altitude of 500 nautical miles (“nmi”) and a perigee, or lowest, altitude of 500 nmi as well. With the same apogee and perigee altitudes, this is one of the EELV’s circular orbits. This reference orbit’s inclination, the angle of the orbit relative to the Earth’s equator, is 63.4 degrees. under EELV guidelines, a launch platform must be able to launch a payload of up to 15,000 pounds to this orbit with such payload fitting within either a 4-meter envelop (“Category A”) or a 5-meter envelop (“Category B”).

Orbits Nos. 2-3: Polar Orbit 1 and 2

EELV also has two reference orbits within the Polar Orbit. A satellite in the Polar Orbit would pass near both the North and South Poles. Since this would make the orbit almost exactly perpendicular to the Earth’s equator, such orbits’ inclination is usually around 90 degrees. In fact, EELV’s reference Polar Orbits have an inclination of 98.2 degrees. For these two circular reference orbits, EELV requires an apogee and perigee altitudes of 450 nmi.  A launch platform needs to be able to lift 15,000 pounds to these orbits, with Polar Orbit 1 requiring both Category A and Category B capabilities, while Polar Orbit 2 requiring the payload to fit within an extended 5-meter envelope (“Category C”).

Orbit Nos. 4-5: MEO Direct 1 and MEO Transfer 1

The next set of EELV reference orbits are within the Medium Earth Orbit (“MEO”). The MEO, sometimes called the intermediate circular orbit, is primarily used for navigation and communication satellites. The most common altitude within the MEO is about 10,907 nmi, which would yield an orbital period, how long it takes to complete one orbit, of 12 hours. The EELV circular reference orbit, MEO Direct 1, has both an apogee and perigee altitude requirement of 9,815 nmi with an inclination of 50 degrees. Meanwhile, the EELV elliptical reference orbit, MEO Transfer 1, has an apogee altitude of 10,998 nmi and a perigee altitude of 540 nmi with an inclination of 55 degrees. The difference between the two orbits is marked by the fact that the transfer orbit, with its elliptical shape, will be used to, as its name suggests, transfer a satellite from one orbit to another orbit in the same plane. EELV requires a launch platform to lift 11,700 pounds to MEO Direct 1 and only 9,000 pounds to MEO Transfer 1. However, both MEO reference orbits require Payload Category A and Payload Category B capabilities.

Orbit No. 6: GTO

GTO, or Geostationary transfer orbit, is an elliptical orbit that is commonly used to transfer a satellite from LEO to GSO, geosynchronous orbit. Because of its transfer function, the GTO is a type of Hohmann transfer orbit. The EELV reference orbit for the GTO has an apogee altitude of 19,323 nmi and a perigee of 100 nmi. The inclination for the GTO is 27 degree and the EELV expects that a launch platform will be able to carry a payload weighing 18,000 pound to such orbit, with Payload Category A and Payload Category B sizing requirements.

Orbit No. 7: Molniya

Molniya, the Russian word for Lightning, is also an elliptical orbit like the GTO. This orbit is named after Russian communications satellites that were the first to use such orbit. One of the most elliptical of EELV’s reference orbits, the Molniya Orbit has an apogee altitude of 21,150 nmi and a perigee of 650nmi with an inclination of 63.4 degrees. Launch platforms are expected to be able to carry both Category A and Category B payloads weighing up to 11,500 pounds payload into this orbit.

Orbit Nos. 8-9: GEO 1 and 2

GEO, or Geostationary Orbit, is one of the most important orbits around Earth. With an inclination of 0 degrees, the GEO is directly above the earth’s equator and is a special type of a Geosynchronous Orbit. What makes this orbit unique is that an object in GEO will appear to stay in a fixed position relative to a spot on earth. This is due to its orbital period of nearly 24 hours. The EELV has two circular reference orbits in the GEO, both having the same apogee and perigee altitudes of 19,323 nmi. For GEO 1, EELV requires launch platforms to have Category A and Category B capabilities for payloads of up to 5,000 pounds. While for GEO 2, a 14,500 pounds Category C payload capability is required.

Bonus: Two Additional Orbits for GPS Update in 2024

The EELV Program also introduced two additional reference orbits for purposes of updating the Global Positioning System in 2024. Both reference orbits are in the MEO, with an inclination of 55 degrees. Both reference orbits require Category A and Category B payload designs. The first, MEO Direct 2, is a circular orbit with apogee and perigee altitudes of 10,998 nmi and requires launch platforms to have a payload capability of 9,000 pounds. The second, MEO Transfer 2, is an elliptical orbit with an apogee of 10,998 nmi and a perigee of 540 nmi, and requires a payload capability of 11,200 pounds.


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