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Meeting	ACGS Committee Meeting 121 - Tucson, AZ - April 2018
Agenda Location	4 GENERAL COMMITTEE TECHNICAL SESSION 4.1 Government Agencies Summary Reports 4.1.2 NASA 4.1.2.4 Engineering & Safety Center
Title	Engineering & Safety Center
Presenter
Affiliation	Sanjay Garg
Available Downloads*	presentation
	Downloads are available to members who are logged in and either Active* or attended this meeting.
Abstract	The NESC GNC TDT continues to perform a number of independent technical assessments in support of NASA missions. The TDT also sponsors and performs multiple discipline advancing activities. The peer review of SLS GN&C System that was initiated in September 2017 is a good example of an independent technical assessment. The focus of this peer review was on the significant B1B Navigation architecture modifications that are needed to support the operation of the Extended Upper Stage (EUS). The EUS stage has 3 additional (relative to SLS Block 1) burns – ascent assist (to get to 100 circular orbit), apogee raise burn (ARB) to get to HEO (100 x ?), multiple pointing / steering / maneuver modes (deploy co-manifested payload, secondary payloads). It has pointing constraints, barbecue rolls, etc. which constitute a “complex attitude timeline”. The EUS has to be able to navigate itself while in its post-launch parking orbit prior to the Trans-Lunar Injection (TLI) burn. This has led to an enhanced B1B architecture that will use GPS/INS navigation not simply inertial navigation. We held a TIM in February to close out the multiple reviewer comments and recommendations. The NESC GNC TDT is also supporting the Lunar Reconnaissance Orbiter (LRO) mission. This work emerged out of similar study work done in support of a 2-wheel attitude control for the Kepler spacecraft. In this activity the NESC, in a collaboration with the LRO Program, is extending non-linear optimization algorithms and methods initially developed at the Naval Postgraduate School (NPS) and which previously were demonstrated in-space on the TRACE spacecraft by unlinking a series of ground determined commanded quaternions. The objective is to perform attitude slews more quickly to leave more time for science data collection. The current challenge is adapting and integrating these algorithms and methods to the real-world LRO mission operations constraints. The team is moving towards a proof-of-concept flight demonstration on an eventual path to routine LRO operational implementation. AS of today a proof-of-concept demo has been completed in the LRO high-fidelity ground-based flight system testbed and a flight demo in scheduled near future, most likely later this Summer. We have also highlighted here the NESC GNC TDT-sponsored work led by J. Russell Carpenter (GSFC) & Christopher N. D’Souza (JSC) to create a landmark Technical Report capturing the space navigation community’s knowledge gained over the past 50 years in the area of on-board navigation filtering. The slides shown on Chart 4 are the summary best practices as presented at the NESC- sponsored recent “Beyond the Textbook” short course presented at the AAS GN&C Conference in Breckenridge, CO, in February 2018. A short preliminary (first cut) study of the technical feasibility of using micro cold gas thrusters for spacecraft precision attitude control/LOS pointing and stabilization as alternative to reaction wheels was performed under NESC GNC TDT sponsorship in late 2017. This work was done by the Aerospace Corporation in El Segundo, CA. Chart 5 describes the specific tasks performed and provides a high-level summary of the results.