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CL 01-0574



3CS unseparated

The Three Corner Satellite (3CS) project is a mission being developed jointly by Arizona State University, University of Colorado at Boulder, and New Mexico State University. 3CS consists of three coordinated satellites that will be deployed in a stack configuration from the Space Shuttle and will then separate to form a "virtual formation". The constellation will orbit at approximately 380 km with a 40-degree angle of inclination. The mission lifetime is estimated to be 2-4 months. The goals of the 3CS mission include the demonstration of stereo imaging, formation flying and innovative command and data handling.

The principal instrument on 3CS are digital cameras onboard each of the three spacecrafts. A total of twelve cameras (resolution 640 x 480) reside within the 3CS constellation, four onboard each spacecraft. It takes on the order of 1/30th of a second to take each image. Images will only be collected during daylight periods. Nominally we expect to collect 24 images per orbit resulting in 2.4 MB of image data per orbit. The storage capacity for the images is still being determined, but the current plan is to allow for onboard storage of 3 orbits worth of images. 3CS will utilize a PowerPC 750 flight processor.

AI Technology

3CS individual 3CS will be demonstrating a number of autonomy technologies.
Robust execution management software
using the Spacecraft Command Language (SCL) package to enable event-driven processing and low-level autonomy
Continuous Activity Scheduling Planning Execution and Replanning (CASPER) software
to respond to mission anomalies as well as validate science data onboard.
Context-sensitive anomaly detection software
using the SELMON monitoring system

The onboard execution software SCL has been flow previously by Colorado Spacegrant on the DATA-CHASER shuttle payload and was used for automation of Clementine and FUSE as well as other missions. SCL provides a rule and script-based procedural language for encoding robust execution procedures as well as basic coordination constructs (locking, blocking, and run-time resource management).

The onboard planning system CASPER is a soft, real-time version of the ASPEN planning system. Rather than considering planning a batch process in which a planner is presented with goals and an initial state, CASPER has a current goal set, a current state and projections into the future, and a current plan. At any time an incremental update to the goals or current state (an unexpected event or simply time progressing forward) may update the planner process. The planner is then responsible for maintaining a consistent, satisficing plan for the most current information. Incremental changes to the goals, initial state, or executed activities trigger iterative repair to resolve conflicts with the plan.

Within the 3CS mission parameters, CASPER will be able to respond to activity and state updates on the 10 second timescale. This will enable more up to date information regarding the execution status of activities as well as monitored state and resource values to influence planning. For the 3CS mission, CASPER will be managing the onboard execution including: engineering activities (such as communications, calibration, power and other resources), science imaging activities (including data validation, prioritization for downlink), as well as interacting with downlink activities. CASPER will be integrated with the SCL execution system allowing for tight feedback from SCL rules and scripts to be reflected and acted upon within the CASPER plans.


Operating spacecraft in a ground-based mode prevents rapid response to science opportunities or anomalies due to transmission delays, contact schedules, and limited commuications bandwidth.


Onboard decision-making enables rapid response to science events to improve science, anomalies to reduce downtime. Onboard processing also enables low priority science data to be discarded, meaning that limited downlink can be more effectively used.


3CS critical design review scheduled for March 2001. CASPER is currently being integrated with the remainder of the 3CS flight software. Hardware is due for integration in the Fall of 2001, with software delivered later. Nominal launch date for the 3CS mission is Fall 2002.


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Dr. Steve Chien
Steve.Chien at

Project Team

JPL: Steve Chien
Rob Sherwood
Gregg Rabideau
Daniel Tran
Barbara Engelhardt


The 3CS flight demonstration of CASPER is sponsored by the Thinking Systems Thrust Area of the Cross Enterprise Technology Development Program and the JPL Telecommunications and Mission Operations Technology Program.