Freddy Pranajaya

Experiments in distributed microsatellite space systems

Distributed space systems are often cited as a means of enabling vast performance increases ranging from enhanced mission capabilities to radical reductions in operations cost. To explore this concept, Stanford University and Santa Clara University have initiated development of a simple, low cost, two-satellite mission known as Emerald. Funded through the AFOSR/DARPA University Nanosatellite Program, the Emerald mission will involve several studies involving the design and operation of distributed space systems. First, “low-level” inter-satellite navigation techniques will be explored. Second, “high-level” multi-satellite health and payload operations will be demonstrated. Third, system validation will be attempted by assessing how these capabilities improve a baseline scientific investigation involving lightning-induced atmospheric phenomena. The Emerald bus design is based on a heritage Stanford University design, a 15-kilogram, modular hexagonal vehicle relying heavily on commercial off-the-shelf components. This paper will discuss the Emerald mission’s focus on distributed space system technologies as well as the design of the two spacecraft and the distributed ground segment.

The Generic Nanosatellite Bus: From Space Astronomy to Formation Flying Demo to Responsive Space

With the increasing number of services on the Internet, it has become a great challenge to help users find services according to their demands. Personalized recommendation technology is an effective way to solve the problem. Existing service recommendation approaches make recommendations among services with same or similar functionalities to meet the non-functional requirements of users, while the functional requirements for service are seldom taken into account and new services that satisfy the needs of users are difficult to be recommended. Therefore, in this paper, we introduce social tags to the process of service recommendation and build service functionality oriented social tags model to describe user preference for service functionality, then we present a personalized service recommendation algorithm for service functionality (PSR-SF). The proposed algorithm first discovers the neighbors of a target user according to services use frequency of users, and then clusters services that have been used by the target user and his neighborhoods by using the functional characteristic vector of services which based on service functionality oriented social tags model. Finally, target user preference for service classes are generated by using service functionality tags use information of users to make recommendations. The experiment results show that the performance of PSR-SF algorithm is better than those existing recommendation algorithms in terms of service recommendation precision, recall and F values.In many pervasive applications like the intelligent bookshelves in libraries, it is essential to accurately locate the items to provide the location-based service, e.g., the average localization error should be smaller than 50 cm and the localization delay should be within several seconds. Conventional indoor-localization schemes cannot provide such accurate localization results. In this paper, we design an adaptive, accurate indoor-localization scheme using passive RFID systems. We propose two adaptive solutions, i.e., the adaptive power stepping and the adaptive calibration, which can adaptively adjust the critical parameters and leverage the feedbacks to improve the localization accuracy. The realistic experiment results indicate that, our adaptive localization scheme can achieve an accuracy of 31 cm within 2.6 seconds on average.The Space Flight Laboratory (SFL) at the University of Toronto Institute for Aerospace Studies develops missions using spacecraft measuring 20 by 20 cm in its cross section and up to 40 cm in length. Each spacecraft can weigh up to 15 kg with up to 9 kg of payload. One of the three SFL operational missions uses the Generic Nanosatellite Bus (GNB) form factor and was conceived, built, and delivered into orbit within seven months from project inception. This nanosatellite precedes an operational 75 kg microsatellite mission by demonstrating the payload technology. Other technologies currently in orbit include reaction wheels and propulsion system, which will be used in follow up missions. Of the five nanosatellites currently under construction at SFL, two are intended for performing astrophysics investigation, two are intended for carrying out formation flying technology demonstration, and one is intended for performing preoperational duties as a way to fast track the readiness of new technologies that are slated for larger, operational missions; the latter is currently slated for launch in Q3 2009. In addition, SFL is also providing a number of critical subsystems for an operational microsatellite mission. These spacecraft build upon a set of common components and technologies that are shared across multiple missions and implement an architecture that is directly expandable to larger, operational missions. The development of these missions follows the microspace approach for managing risks and ensuring rapid development, which maintains cost-effectiveness and responsiveness to new missions. Typically each spacecraft implements multiple on-board computers, high data rate radios, sensors and actuators. The system implements a number of redundancies to mitigate failures. The subsystem complement and the complexity of the spacecraft can be tailored to meet various mission needs, from a passively stabilized spacecraft using permanent magnets to a three-axis stabilized platform with reaction wheels with optional propulsion system. The spacecraft can also accommodate fixed appendages such as booms, antennas, and additional solar panels. SFL also builds its own separation systems called “XPODs” and arranges, on a regular basis, shared launches for nanosatellite developers worldwide through its Nanosatellite Launch Service (NLS) program.