Small satellites for big science: the challenges of high-density design in the DLR Kompaktsatellit AsteroidFinder/SSB

Abstract

The design of small satellites requires a paradigm shift in the thinking of satellite designers as well as mission scientists, payload users, and programme management - in brief, everyone involved. In a conventional approach, spacecraft design evolves in a mostly linear fashion from mission requirements by well-defined procedures through a series of reviews into a design space that is essentially not limited by constraints other than programmatic. The mission defines a pallet of instruments, their needs then shape the spacecraft bus, and the integrated spacecraft is finally mated to a dedicated launch, to be placed into an orbit carefully custom-tailored by mission analysis and continuously trimmed by on-board propulsion. Components are manufactured to spec, one-off plus spares, and painstaking testing has to iron out the many space firsts and compromises made in an arduous and protracted design process. Small satellite design reverses this comfortable line of thinking. It begins with hard, and not just programmatic constraints on most of the essential parameters that define a satellite. Launch as a secondary payload is the choice, not just for budgetary reasons, but due to the lack of viable dedicated launchers. It requires a small stowed envelope and a tightly limited mass budget. This results in limited surface area for solar panels and radiators. Small project volume enables a high flight cadence which makes re-use of designs and components desirable and feasible, in a self-catalyzing cycle. Re-use and constraints force the system perspective on every participant in a quick succession of sometimes diverging but generally converging iterations that lends itself to the Concurrent Engineering approach. There is simply no space left in a small satellite project for boxes to think in. To exploit the technological convergence that has created powerful and miniaturized science instruments and satellite components, the DLR research and development programme has initiated the Kompaktsatellit line of development. It is intended to enable dedicated missions for science projects that would earlier have resulted in one full-scale scientific instrument among many sharing a ride on a large platform without the perspective of follow-on within an academic career lifetime. In an internal competition, the AsteroidFinder instrument dedicated to the search for small bodies orbiting the Sun interior to Earth’s orbit has been selected as the payload to fly first on a Kompaktsatellit. Alongside, the Standard Satellite Bus kit, /SSB, is being developed, based on extensive re-use of experience, concepts, and components of the DLR satellites BIRD and TET. It is designed to avoid the overhead carried by pre-defined standard bus concepts while allowing for seamless integration of the payload into an organic spacecraft design. Challenges encountered and solutions found across the subsystems of AsteroidFinder/SSB will be presented.