The Einstein-Elevator at the Hannover Institute of Technology (HITec) is operated by the Institute of Transport and Automation Technology (ITA). With the help of this facility, it is possible to create a weightless state inside a capsule. Scientists at the ITA are conducting research in the field of additive manufacturing under space conditions, basic physics research and further development of the facility to simulate other space environmental conditions.
In order to make the integration of various experiments into the Einstein-Elevator as simple as possible, an experiment carrier is currently being developed for the Institute for Satellite Geodesy and Inertial Sensing of the German Aerospace Center (DLR-SI) that can be set up as flexibly as possible.
Mode of Operation of the Einstein-Elevator
The Einstein-Elevator simulates weightlessness through the free fall of the experiment carrier. For this purpose, the carrier first stands in the gondola of the Einstein-Elevator during the experiment and is accelerated upwards together with the gondola within 0.5 s at 5 times the acceleration due to gravity. The gondola is then briefly decelerated so that the carrier inside lifts of from the gondola floor. The drive then controls the distance between the gondola and the experiment carrier to a defined flight altitude and follows the experiment carrier, which now flies freely for up to 4 s. Since the carrier has no contact with the surrounding gondola during this time, no external forces act on it. It is then in a vertical parabolic flight, which is equated with weightlessness or microgravity. To additionally minimize the influence of vibrations due to noise (for example from the drives and the guides), the gondola can be evacuated to a pressure of 10-2 mbar during the experiment.
Experiments in the Einstein-Elevator
Additive manufacturing processes, such as laser cladding, are being investigated under various gravitational conditions. In the future, the process may be used to generate and repair components during long space missions.
In other additive manufacturing projects, scientists are researching 3D printing with lunar dust (regolith). This should, for example, save the expensive transport of building materials to the moon for the construction of future lunar stations.
Experiments in the field of basic physics research are also currently being prepared. Among other things, compact atom interferometers are being developed and the search is on for indications of dark energy. Such quantum sensor experiments in particular place very high demands on the experiment environment.
Requirements for the experiment carrier
A key quality characteristic of facilities for research under microgravity conditions is residual acceleration. Drives, acoustics, or experiment hardware can induce vibrations that cause accelerations in the experiment during the weightless phase. The lower the amplitude of this residual acceleration, the better the quality of the system is evaluated.
In order to achieve such low residual accelerations, it is necessary that the experiment carrier is as little susceptible as possible to vibrations or that these decay within a very short time. The experiment carrier is therefore designed to be as stiff as possible and thus to allow only natural vibration with a high frequency. At the same time, however, the construction must not be too heavy, since the Einstein-Elevator can carry a maximum permissible mass of 1,000 kg inside the gondola. Furthermore, the maximum volume of 1.7 m in diameter and 2 m in height should still be available for experiments.
Experiments in the field of fundamental physics in particular place high demands on the residual acceleration, as well as rotations and magnetic fields that occur. To reduce magnetic influences, the carrier should be made exclusively of non-magnetic materials. Rotations can be reduced by precisely centering the center of gravity or by active mechanisms, such as control nozzles or reaction wheels.
Construction of the experiment carrier
The experiment carrier consists essentially of three components: The carrier base, the pressure tight shell, and the payload (see Figure 1).
The carrier base is the lower element of the carrier (see Figure 2). This component is designed as a pressure vessel. Inside is all the hardware used to control the carrier and record sensor data. The experiment hardware can be connected to the carrier base via various interfaces. Those provide a cooling system, various power supplies, network connectivity, and control signals for experiments.
Above the base, the payload (the experiment) of the experimenters is placed. The respective experiments are mounted on special payload levels. If possible, the payload should be as rigid as possible. For this purpose, stiffening elements can be used, which are bolted between two levels and give them additional stiffness. The payload is then bolted to the base as “one package”.
The entire payload can optionally be enclosed in a pressure tight shell. This places the experiment in a normal atmosphere, while a vacuum outside the carrier decouples acoustic influences. In this way, there is no need to consider vacuum suitability when setting up the experiment. Alternatively, it is possible to operate the carrier without the pressure tight shell and use vacuum-capable experiment hardware, such as when testing satellites that must be designed to be vacuum-capable for their final operation anyway.
The carrier is currently being fabricated (see Figure 3). Aluminum is used for the welded individual components, as this both reduces magnetic influences and keeps the weight of the structure low. Some parts of the carrier have already been completed (see Figure 4).
Completion of the entire girder system is scheduled for the end of 2022. After that, the system will be evaluated together with the new experiment carrier and the first experiments can be performed with the new system.