Spacecraft Design Services

Spacecraft Design Background

Spacecraft are vulnerable to Space Weather. They are exposed to a multitude of environments that are not present at the surface of the Earth, including micrometeoroids and orbital debris, UV irradiation, neutral particles, cold and hot plasma, and particle radiation. Interaction with these environments cause degradation of materials, thermal changes, contamination, excitation, spacecraft glow, charging, radiation damage and induced background interference. Variations (temporal and spatial) in the constituency and density of the environments, result in effects depending on the position and attitude of the spacecraft. Analysis of the hazardous space environment and its impacts on the spacecraft systems is therefore an important task during space mission design.

Most modifications for space environment effects include component selection and testing, subsystem design, shielding requirements, grounding, error detection and correction, and estimates of observation loss. To determine the survivability of the components and the level of tolerated error mitigation, worst case levels of the space-environment are needed. There are a variety of hazards and risks to nominal operation that must be considered during the design stage. These are summarised pictorially in the Figure below, which is presented roughly as a function of energy.

There is an increasingly diverse and sophisticated body of software becoming available to study particular radiation effects on materials, and such effects tools may be used in conjunction with environment tools to construct a realistic representation of a piece of hardware intended for in-orbit operations. This could be a new technology detector or solar panel, for instance, and furthermore such an object can be encased within and surrounded by other objects and constructs to accurately represent either a single instrument or whole satellite. Such techniques are not restricted to radiation effects, and the effects on material due to interactions with space plasma and electric and magnetic field are readily studied. Having parametrised the orbit using the orbit generator, the hardware mock-up can then effectively 'be flown' for various epochs of the nominal mission, and the effects of the environment upon it quantified and analysed.

Such methods have been used extensively by ESA within the overall framework of the Galileo global navigation system. The Galileo fleet will operate at an altitude of ~23,200km, above both the GPS and GLONASS fleets by necessity. This places it further into the outer, mainly electron, trapped radiation belt, and therefore in a very different and more hostile operating environment. Indeed, this is the first time that a complex and safety-critical mission providing a range of service level agreement-bound services will have to be operated in that environment which raises particular challenges. Data taken by the pair of testbed satellites GIOVE-A and -B have been used along with representative geometries and materials to predict the long-term effects (each Galileo satellite will be expected to operate for up to 12 years) and optimise the design of the Galileo IOV satellites. A similar approach is anticipated for the Galileo FOC fleet. The traditional alternative at this stage is to heavily over-engineer the operational satellites as they are built, with correspondingly large cost overheads.

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