Introduction and Objectives
The development risk of any future reentry vehicle can significantly be reduced by a preparatory technology demonstration flight program verifying and demonstrating the maturity of required technologies. At the Space Systems Institute (IRS) under contract with the German Space Agency (DARA) a semi-ballistic capsule COLIBRI (Concept of a Lifting Body for Reentry Investigations) has been conceived as testbed to perform autonomously scientific and technology experiments during the reentry flight with three primary goals:
The COLIBRI Mission
The mission profile of the COLIBRI capsule is illustrated in Fig. 1. A ``piggy-back''-flight opportunity on a Russian FOTON carrier-capsule is considered, that is launched into a low Earth orbit by a Soyuz rocket. Because the carrier capsule will perform the deorbit maneuver prior to separation of the COLIBRI vehicle, the experimental capsule needs not to be equipped with a deorbit propulsion module. The drawback associated with this low-coast approach is that entry conditions are defined by the ballistic FOTON capsule to be recovered in southern Russia and can not be selected independently. Thus, the recovery area of FOTON is at the lower end of the attainable landing area of the semi-ballistic COLIBRI vehicle as illustrated in Fig. 2. Though FOTON enters the atmosphere following a ballistic path, the reentry flight of COLIBRI will be autonomous and controlled. In order to ease the recovery of the vehicle a landing accuracy of 5 km is regarded as sufficient.
Figure 1: The COLIBRI Mission Profile
Figure 2: Ground Track and Attainable Landing Area
The COLIBRI Vehicle
The selection of the capsule shape was based on 3DOF trajectory simulations. For typical entry conditions and a representative set of vehicle parameters the flight performance and loads have been assessed. The selected concept consists of a sphere-cone configuration with a scarfed bottom surface and a split body flap as depicted in Figs. 3 and 4.
The dimensions of approximately 1.5 m in length and 1 m in maximum diameter are within the geometrical constraints of the payload fairing of the Russian Soyuz launch vehicle. This shape offers moderate lift-to-drag (L/D)-values of 0.5 to 0.75 at comparatively low angles of attack (10° to 20°). The overall vehicle mass amounts to 170 kg. The required center of mass of the capsule is trimmed for static aerodynamic stability by proper distribution of subsystem accommodation. The capsule can be trimmed to obtain longitudinal and directional aerodynamic stability at least in the hypersonic speed range.
The capsule yields enough lift to reduce deceleration loads below 3 g. Also, it offers sufficient maneuvering capabilities to support guidance and control experiments and to guide the vehicle to a designated recovery site with landing accuracies competitive with higher L/D designs. Attitude control will be achieved by the use of cold gas thrusters. Guidance of the vehicle is performed by a bank angle modulation, i.e. a rotation of the lift vector.
Figure 3: In-orbit configuration of COLIBRI as a ``piggy-back'' payload atop of the FOTON vehicle
Figure 4: Conceptual Design of the Experimental Reentry Capsule COLIBRI
The flight states (position, velocity, attitude, angular rates) of the vehicle are to be determined by a combination of an Inertial Navigation System (INS) and a GPS system, since GPS navigation is lost during the ``blackout'' phase, where aerodynamic control is highly effective.
Copyright: Space Systems Institute (IRS), Stuttgart University, 1997