The Russian-U.S. Venera-D project is designed to conduct long-term studies of the surface and atmosphere of Venus . Under this project it is supposed to send a spacecraft (SC) to Venus, which will consist of an orbiter and a lander. The orbiter separates from the main spacecraft a few days before its approach to Venus in order to break in orbit about Venus, the parameters of the orbit are currently under development .
Essential part of the project «Venera-D» is to determine available landing sites on the surface of Venus [1–5]. First of all, this task appears because of impossibility to make a landing at any place on surface of Venus due to small length of launch window from Earth (about 2 weeks from optimal launch date), as well as limitation on maximum permissible overload. An additional factor that reduces the number of achievable landing sites is the low angular velocity of Venus' rotation. The simplest solution to the problem may be to extend the launch window from Earth, but this possibility is limited by the value of the characteristic velocity ΔV. Another method may be to use an intermediate near Venusian orbit for later descent to a desired location, or to use a lander that allows aerodynamic manoeuvring in the atmosphere of Venus and thereby landing at a desired location. However, all these methods require either high costs of characteristic velocity.
The feature of this study is the demonstration of a new technique for expanding the achievable areas of landing. Its essence is to use the gravitational field of Venus to transfer the spacecraft to the heliocentric orbit, resonant with the orbit of Venus with a ratio of periods of 1:1. The proposed study considers launch windows from 2029 to 2034. The application of the technique is shown on the specific example of landing in a given and inaccessible, using traditional approaches, the area on the surface of Venus (Imdr Regio). It is demonstrated that its application allows to achieve significant expansion of achievable landing areas (over 70 %) and in some cases to provide access to any point on the surface of Venus.
It should be noted that similar techniques are used for spacecraft control in the Jupiter system. For example, the Laplace-P project intends to use gravity manoeuvres near Ganymede and Callisto to switch to resonant orbits with Ganymede and subsequently reduce the relative velocity of the spacecraft near Ganymede. The Europa Clipper project involves moving to resonant orbits for the purpose of repeated encounters with Jupiter's moon Europa.