The BOOST (BOOst Symmetry Test) mission has been proposed as a future DLR small satellite mission. It aims to test the foundations of special relativity by conducting a modern Kennedy-Thorndike (KT) experiment, which will investigate the possible dependency of the speed of light on the speed of the source. The research aims to investigate the validity of Einstein's special theory of relativity – with measured deviations, new effects could be discovered within the fundamental theories of physics.
BOOST addresses the following issues:
Although somewhat speculative, placing known theories under scrutiny in this way could open new and exciting avenues for physics to explore. Many areas of fundamental physics (such as theories that explain the Big Bang, exponential expansion and quantum field theory) are influenced by experimental tests on the validity of special relativity.
With regard to satellite payload, two different optical frequency references are being used for BOOST: an absolute reference based on a molecular iodine, and a length-based frequency reference employing an optical resonator. The beat frequency between the two references contains the scientific signal, and this is what will be measured. By using clocks with a 10-15 frequency instability over an orbital period of approximately 90 minutes, and with integration over 5000 orbits (over a two year period with a 50 percent duty cycle of the mission), the measuring of the KT coefficient will be improved by at least two orders of magnitude compared to the best tests conducted on Earth so far.
For this, BOOST draws on current and successful developments in space-compatible optical frequency references from the department of System Enabling Technologies (SET) at the DLR Institute of Space Systems in Bremen. Working with the Centre of Applied Space Technology and Microgravity (ZARM) at Bremen University, and Humboldt-Universität zu Berlin, a laser frequency stabilized to a hyperfine transition of molecular iodine was realised and characterised. With this setup on Engineering Model (EM) level, a frequency instability of 4*10-15 at integration times of several thousand seconds was demonstrated. In a collaboration between ZARM and the Leibniz Universität Hannover, a long-term stable optical resonator on Elegant Breadboard (EBB) level is currently realised. The DLR compact satellite bus is currently under development at the DLR Institute in Bremen as part of the Eu:CROPIS mission (scheduled for launch in 2017).
In addition to being a scientific mission, BOOST is also a technology demonstrator. Key technologies required for a variety of future satellite missions in the field of science, Earth observation and navigation and ranging are verified there in space. The development of optical frequency references and the corresponding assembly-integration technologies used on satellites has a direct influence on missions such as eLISA (Evolved Laser Interferometer Space Antenna), NGGM (Next Generation Gravity Mission) and MAQRO (Macroscopic Quantum Resonators).
A similar mission concept is in place for the mSTAR project (mini SpaceTime Asymmetry Research). In cooperation with Stanford University (USA), NASA AMES Research Center (USA) and Kingabdulaziz City for Science and Technology (Saudi Arabia), a German team from the Centre of Applied Space Technology and Microgravity (ZARM, Bremen), Humboldt-Universität zu Berlin and the DLR Institute of Space Systems (Bremen) showed the principle feasibility of a Kennedy Thorndike experiment using the SaudiSat-4 satellite bus. The German contribution to mSTAR included the development of the iodine-based frequency reference, payload integration and involvement in the analysis of the data gathered.
The technology development projects ‘iodine EBB’, ‘iodine EM’ and ‘cavity EBB’ are supported by the DLR Space Administration with funds from by the Federal Ministry for Economic Affairs and Technology under the funding codes 50QT1102, 50QT1201 and 50QT1401.