The trajectory, starting from Jovian insertion, is only conjectural. The extremely involved pointing and timing intricacies associated with the proposed GA's to slow Asterius while consuming as little propellant as possible was not touched upon. A much more detailed trajectory needs to be designed. Any changes in the trajectory will undoubtedly alter the proposed launch date and mission timeline.
In the process of spacecraft design, often many more questions are raised then are answered by the initial calculation process. Asterius' structure system is no different in this respect from any of its predecessors. The major issues that must be answered number four. Of course, there are actually an infinite amount of questions a design engineer would like answered but that is rarely possible. In this case the four issues that must be addressed are 1.) computational FEM models of Asterius while being loaded with the forces that the craft is expected to encounter during its mission. The FEM models would allow the structure to be strengthened where it is weak and made lighter where it is overdeveloped. 2.) Computational thermal models of the spacecraft and its various components while in operation. This area would definitely give us a better look at what is happening thermally to the structures and equipment that comprise Asterius in the various environments it will be in during its lifetime. With a more complete picture we would evidently be able to make the thermal system lighter and much more efficient. 3.) Access to advanced materials research that would allow us to substitute many of the materials on Asterius for cheaper, stronger, and lighter materials that are currently being introduced to the market. 4.) Tests of the probe's construction and how the probe would actually perform in a frozen environment with the above designed method of travel and experimental cooling/heating methods described above.
Outstanding issues that remain in the ACS subsystem are those that cannot be addressed until a more detailed design of Asterius is performed. The spacecraft dynamics have only been calculated regarding the spacecraft to be crudely modeled as a simple, homogenous cylinder. The current solid model renderings are based primarily on mission modules (i.e., OOM and SOM). Little consideration was given to exact placements of instruments and their consequential weight distributions. Hence, the center of mass and its magnitude is not yet definitive at this stage of development. It is expected that the spacecraft dynamics will go through several variations right up until the time of launch. Once a relatively constant dynamic model is attained, the RWA's may be sized and chosen accordingly.
As each spacecraft and its mission are unique, so are its needs. The integration of all of the ACS instruments will undoubtedly require additional hardware and software development.
Fine tuning of Asterius' propulsion system such as calculating the optimum amount of fuel needed for the descent to Europa as well as the exact volumes of fuels, oxidizer, and pressurants needed for the complete mission are just some of the outstanding issues that would need answered if Asterius were to go on to real time manufacturing and development. Making the propulsion system safer and more efficient is paramount to downsizing the mass of the spacecraft and would make considerable changes to the final mass. The propulsion systems are the most massive contributors to the spacecraft's total mass and when these systems are optimized the improvements are definitely noticeable and considerable.
A full study of the moments produced by the thrusters and engines as well as models predicting center of mass excursions due to slosh effects would also be paramount to understanding the spacecraft's dynamics while operating.
Since the WISP's data is the most important part of this mission the communication hardware on the WISP is also important. More specifics need to be found about the acoustic transducer such as: power requirements, mass, data transmission rates and dimensions. It is hoped that consultation with an experienced acoustic engineer will help resolve these issues.
The required resources of the computer and recorder have been determined, as has been the command and data handling architecture. What remains to be decided is the specifications and protocols used: the networking protocol used in the bus, the instruction set architecture of the computer, the programming language, the encoding, decoding, and compression algorithms, and several other details.
The power sources have been selected; details about how the power is distributed to the spacecraft components need to be decided.
The thermal estimates presented here are merely first-order. Better estimations of thermal balance need to be made. Also, almost no component-level thermal analysis has been made; this must be done.