SORCE Daylight-Only Operations

The recent experience of the SORCE flight operations team offers an excellent example of innovative engineering using limited resources. The goal of this paper is to extend to the space operations community the lessons learned during this critical redesign in order to aid other missions facing equally daunting challenges. The end result is a mission extended well beyond its designed life continuing to return important data to the science community to extend the climate record

The Fully Automated and Self-Contained Operations Paradigm of the CSIM Mission

The Compact Spectral Irradiance Monitor (CSIM) CubeSat Mission has been collecting solar spectral irradiance (SSI) data for over two years, contributing to 40+ years of multi-mission SSI data collection. CSIM utilizes a fully automated and self-contained operations paradigm developed at the Laboratory for Atmospheric and Space Physics (LASP). LASP efficiently performs the entire operations workflow for CSIM, from planning through data processing, which nominally requires only 15 minutes of staffed operations support per week. Mission operations students at LASP are responsible for the entire planning process. They query for ground station contacts and solar observation times which are input into a suite of software tools to create the onboard stored command table and the weekly uplink plan. An automated ground station script then configures for the upcoming CSIM contacts by querying Space-Track for overflights. Within 2 minutes from the start of a pass, the script commands the UHF or S-Band antenna to point at the spacecraft, brings up the command-and-control software, and performs an initial health-and-safety check upon AOS (acquisition of signal). Automated command scripts then configure the spacecraft and upload the plan using command success logic checks. This ensures that all commands are sent and accepted by the spacecraft in-order, and without overwriting any non-expired scheduling slots. The week\u27s worth of commands is loaded within a few passes, and science collection typically starts soon after. Ground automation will detect major anomalies and notify the flight control team in real-time, allowing the operators to recover the spacecraft on the next contact and prepare a new activity plan for autonomous upload. Additionally, ground automation queries CSIM health and safety data and sends telemetry trends to the operations team for daily, weekly, and monthly health and safety checks. CSIM science data is downlinked during 1 or 2 passes per day via the S-band antenna. This data is processed twice per day via an automated data processing pipeline which requires no regular human intervention. The self-contained and automated nature of the data processing pipeline ensures that LASP scientists can access CSIM data within a few hours of being received on the ground. We discuss how this efficient single-mission, self-contained operations paradigm will be expanded to support multiple missions and external customers in the future

Estimation and Modeling of Enceladus Plume Jet Density Using Reaction Wheel Control Data

The Cassini spacecraft was launched on October 15, 1997 by a Titan 4B launch vehicle. After an interplanetary cruise of almost seven years, it arrived at Saturn on June 30, 2004. In 2005, Cassini completed three flybys of Enceladus, a small, icy satellite of Saturn. Observations made during these flybys confirmed the existence of a water vapor plume in the south polar region of Enceladus. Five additional low-altitude flybys of Enceladus were successfully executed in 2008-9 to better characterize these watery plumes. The first of these flybys was the 50-km Enceladus-3 (E3) flyby executed on March 12, 2008. During the E3 flyby, the spacecraft attitude was controlled by a set of three reaction wheels. During the flyby, multiple plume jets imparted disturbance torque on the spacecraft resulting in small but visible attitude control errors. Using the known and unique transfer function between the disturbance torque and the attitude control error, the collected attitude control error telemetry could be used to estimate the disturbance torque. The effectiveness of this methodology is confirmed using the E3 telemetry data. Given good estimates of spacecraft's projected area, center of pressure location, and spacecraft velocity, the time history of the Enceladus plume density is reconstructed accordingly. The 1 sigma uncertainty of the estimated density is 7.7%. Next, we modeled the density due to each plume jet as a function of both the radial and angular distances of the spacecraft from the plume source. We also conjecture that the total plume density experienced by the spacecraft is the sum of the component plume densities. By comparing the time history of the reconstructed E3 plume density with that predicted by the plume model, values of the plume model parameters are determined. Results obtained are compared with those determined by other Cassini science instruments