# Powered swing-by using tether cutting

Tsubasa Yamasaki, Mai Bando, Shinji Hokamoto

### 抜粋

The swing-by maneuver is known as a method to change the velocity of a spacecraft by using the gravity force of the celestial body. The powered swing-by has been proposed and researched to enhance the velocity change during the swing-by maneuver, e.g. Prado (1996). The research reports that applying an impulse maneuver at periapsis maximizes the additional effect to the swing-by. However, such impulsive force requires additional propellant. On the other hand, Williams et al. (2003) researched to use a tether cutting maneuver for a planetary capture technique. This current paper studies another way of the powered swing-by using tether cutting, which does not require additional propellant consumption. A Tethered-satellite is composed of a mother satellite, a subsatellite and a tether connecting two satellites. In a swing-by trajectory, a gravity gradient force varies according to the position of the tethered-satellite, and consequently its attitude motion is induced; the tethered-satellite starts to liberate and rotate. Cutting the tether during the tethered-satellites' rotation can add the rotational energy into the orbital energy. In this research, since the gravity gradient effect on orbital motion is small, the orbit can be considered a hyperbolic orbit. Assuming that the tether length is constant, Eq. (1) describes the equation of the attitude motion of a tethered-satellite within the SOI (sphere of influence) of the secondary body. θ = 1/1+ e cos α {2e (θ' + 1) sin α - 3/2 sin 2θ} where e is an orbit eccentricity, α is a true anomaly, θ is an attitude angle and l is tether length. The prime means the derivative with α. The mother satellite and subsatellite can obtain not only the velocity change but the position change by the tether cutting; they are denoted as Δv and Δr, and described in Eqs. (2) and (3), respectively. Δv = -l1(α + θ) [-sin (α + θ) cos (α + θ)] Δr = -l1 [cos (α + θ) sin (α + θ)] where l1 is a distance between the center of gravity of the tethered-satellite and the mother satellite. Since α and θ are functions of time, Δv and Δr are also functions of time. This means that changing the tether cutting point can maximize the velocity change in this proposed powered swing-by maneuver. Furthermore, the optimum cutting point depends on the attitude and angular velocity when the tethered satellite enters the SOI. We propose a systematic design procedure to obtain the desired velocity change by optimizing the cutting point, the initial attitude and the initial angular velocity of the tethered satellites.

元の言語 英語 Proceedings of the International Astronautical Congress, IAC 出版済み - 1 1 2016 67th International Astronautical Congress, IAC 2016 - Guadalajara, メキシコ継続期間: 9 26 2016 → 9 30 2016

### All Science Journal Classification (ASJC) codes

• Aerospace Engineering
• Astronomy and Astrophysics
• Space and Planetary Science