High Earth orbit

​, where $a$a is the semi-major axis of the orbit and $\mu$μ is Earth's standard gravitational parameter, $3.986 \times 10^{14}$3.986×1014 m³/s². For HEO with semi-major axes corresponding to perigee altitudes above 32,000 km, periods range from approximately 24 hours (for GEO at a ≈ 42,164 km) to multiple days or weeks for highly elliptical orbits with larger $a$a. This extended periodicity arises directly from the cubic dependence on $a$a, providing greater dwell times compared to lower orbits.^[8][9] Perturbations from Earth's oblateness, captured by the J₂ zonal harmonic (J₂ ≈ 1.0826 × 10⁻³), significantly impact HEO stability by inducing secular variations in orbital elements. The dominant effects include precession of the right ascension of the ascending node (RAAN) and the argument of perigee, with the averaged nodal precession rate expressed as $$\dot{\Omega}_{J_2} = -\frac{3}{2} n J_2 \left( \frac{R_e}{p} \right)^2 \cos i,$$Ω˙J2​​=−23​nJ2​(pRe​​)2cosi, where $n = \sqrt{\mu / a^3}$n=μ/a3

​ is the mean motion, $R_e$Re​ ≈ 6,378 km is Earth's equatorial radius, $p = a(1 - e^2)$p=a(1−e2) is the semi-latus rectum, and $i$i is the inclination. For inclined HEO (e.g., i > 0°), this results in RAAN regression rates of several degrees per year, depending on altitude and eccentricity, while apsidal precession $\dot{\omega}_{J_2} \approx \frac{3}{2} n J_2 (R_e / p)^2 (2 - \frac{5}{2} \sin^2 i)$ω˙J2​​≈23​nJ2​(Re​/p)2(2−25​sin2i) can cause perigee drift, potentially destabilizing the orbit over time without corrective maneuvers. These effects diminish with increasing altitude but remain relevant for long-duration missions in HEO.^[10] Satellites in HEO with sufficiently high perigee experience minimal exposure to the Van Allen radiation belts, which extend from altitudes of approximately 1,000 km to 60,000 km. The inner belt (L ≈ 1.2–3 Earth radii) is proton-dominated, with fluxes for energies >50 MeV reaching ~10⁴ protons/cm²/s/sr at peak intensities near L = 1.5–2.2, varying by up to a factor of 2 with geomagnetic activity. The outer belt (L ≈ 3–10) features relativistic electrons (0.5–5 MeV) with omnidirectional fluxes on the order of 10⁶–10⁸ electrons/cm²/s/sr, modulated by solar cycle and local time, posing risks to electronics and necessitating robust shielding for orbits passing through them.^[11] Achieving HEO from low Earth orbit demands additional delta-v of 2–4 km/s, accounting for transfer trajectory and final insertion; for instance, a Hohmann transfer from a 400 km circular LEO to geostationary orbit (a common HEO benchmark) requires approximately 4.2 km/s total delta-v, split between perigee and apogee burns. This budget increases for higher apogees in elliptical HEO but can be optimized through multi-impulse strategies.^[12]

Types of High Earth Orbits

Geostationary Orbits