Launch Window

Author: Tianjiang Shuo

Website: https://cislunarspace.cn

Definition

The launch window is the set of launch times that satisfy mission requirements, including the selection of launch date and launch time. The launch window is jointly determined by orbital inclination, right ascension of the ascending node, launch site location, and target orbit requirements.

Core Elements

Launch Site Constraints

Let the geocentric latitude of the launch site be φI\varphi_I, the geocentric longitude be λI\lambda_I, and the azimuth be AIA_I. Then the orbital inclination satisfies:

i=arccos⁡(cos⁡φIsin⁡AI)i = \arccos(\cos\varphi_I \sin A_I)

From this we obtain:

φI≤i≤π−φI\varphi_I \leq i \leq \pi - \varphi_I

The closer the launch site is to the equator, the wider the range of orbital inclinations achievable without orbital maneuvers.

Relationship Between RAAN and Launch Time

Ω=S‾(tI)+λI−arctan⁡(tan⁡φIcos⁡icos⁡AI)\Omega = \overline{S}(t_I) + \lambda_I - \arctan\left(\frac{\tan\varphi_I \cos i}{\cos A_I}\right)

where S‾(tI)\overline{S}(t_I) is the Greenwich mean sidereal time at the launch moment.

Launch Direction and Orbit Type

Azimuth RangeOrbit TypeDescription
0<AI<π0 < A_I < \piPrograde Orbit0<i<π/20 < i < \pi/2
π<AI<2π\pi < A_I < 2\piRetrograde Orbitπ/2<i<π\pi/2 < i < \pi
AI=π/2A_I = \pi/2Eastward Launchi=imin⁡=φIi = i_{\min} = \varphi_I
AI=3π/2A_I = 3\pi/2Westward Launchi=imax⁡=π−φIi = i_{\max} = \pi - \varphi_I

Determining the Launch Window

If the target orbit's inclination ii and right ascension of the ascending node Ω\Omega are fixed, the launch time tIt_I is determined accordingly. If the inclination ii and orbit insertion time tIt_I are fixed, the right ascension of the ascending node Ω\Omega can be determined.

Application Value

The selection of the launch window is a critical step in space mission planning. The launch window is constrained by multiple factors, including target orbit parameters, launch site geographic location, ground tracking and telemetry coverage, illumination conditions, and the space environment. Proper selection of the launch window can reduce launch energy consumption, improve orbit insertion accuracy, and meet special mission requirements for illumination and coverage.

References

  • 郑伟, 安雪滢, 周祥, 何睿智. 空天飞行力学[M]. 国防科技大学, 2026.
  • 贾沛然, 陈克俊, 等. 远程火箭弹道学[M]. 国防科技大学出版社.