Constellation Operations Lessons Learned For Future Exploration

The Earth Science Afternoon Constellation Constellation Operations Lessons Learned For Future Exploration Space Operations 2006 Conference Rome, Italy June 2006 Angelita C. Kelly / NASA Goddard Space Flight Center Warren F. Case / SGT, Inc.

Topics • Purpose • Earth Observing Constellations • Morning Constellation • Afternoon Constellation (“A-Train”) • Unique Challenges • Lessons Learned • Summary

Purpose Describe the lessons learned by flying the first 5 missions of the Afternoon Constellation.

Earth Observing ConstellationsWhy Fly Constellations? The Earth science community has long advocated placing numerous instruments in space to study the Earth and its environment. • Constellations provide the opportunity to makecoincident, co-registered, and near simultaneous science measurements. • The satellites align their orbital positions so their instrument fields of views overlap. • Earth science data from one satellite’s instrument can be correlated with data from another. The whole is greater than the sum of its parts

Earth Observing ConstellationsMorning Constellation • Four members with descending equator crossing near 10:00 Mean Local Time (MLT). • All 4 satellites are currently on-orbit. • Landsat-7 nominal • Terra nominal • EO-1 lowering its orbit to satisfy re-entry requirements • SAC-C raised its orbit to avoid a close approach with EO-1 and Landsat-7 in 2005, extending it’s lifetime in the process

Earth Observing ConstellationsAfternoon Constellation • All 7 members have ascending equator crossing times near 13:30 MLT. • All but Glory and OCO are on-orbit (these due in 2008)

Earth Observing ConstellationsAfternoon Constellation Phasing

Earth Observing ConstellationsUnique Challenges • The Earth Observing Constellations are unlike other satellite constellations. • They present a number of unique challenges.

Earth Observing Constellations Unique Challenges (cont’d) The Earth Observing Constellations are not a homogenous mix of identical satellites. They comprise several satellites with diverse instruments that provide complementary observations. Aura CALIPSO OCO Aqua Glory CloudSat PARASOL OCO - CO2 column OMI - Cloud heights OMI & HIRLDS – Aerosols MLS& TES - H2O & temp profiles MLS & HIRDLS – Cirrus clouds CALIPSO- Aerosol and cloud heights Cloudsat - cloud droplets PARASOL - aerosol and cloud polarization OCO - CO2 MODIS/ CERES IR Properties of Clouds AIRS Temperature and H2O Sounding (from M. Schoeberl)

6x7 km POLDER 1. 4 km Cloudsat 0.5 km MODIS Band 3-7 0.09 km CALIPSO Cloud 13.5 km AIRS IR; AMSU & HSB m wave OCO 1x1.5 km 5.3 x 8.5 km TES Washington DC USGS Map The Afternoon Constellation observational “footprints” vary greatly

Earth Observing Constellations Unique Challenges (cont’d) Terra SAC-C EO-1 Landsat Most constellations are spaced around the Earth to provide instantaneous, global coverage (e.g., GPS, communications, satellite radio, weather). GPS Constellation In contrast, the Earth Science Constellation satellites orbit in close proximity so that observations occur at about the same time over approximately the same region. Due to the relative closeness of the satellites (as small as 10 seconds), safety is an issue. Morning and Afternoon Constellations

Earth Observing Constellations Unique Challenges (cont’d) • The independent operations of the Afternoon Constellation are managed by multiple organizations (both U.S. and International Partners) • The Control Centers are at widely distributed locations

Constellation Management and Coordination Needed Based on these challenges . . . There was a clear need for Constellation management and coordination. We need to keep the constellation safe, thus enabling constellation science.

Mission Operations Working Group (MOWG) In response . . . • The Afternoon Constellation Mission Operations Working Group (MOWG) was formed with representatives from each mission • The MOWG has been effective at addressing constellation management and coordination concerns • Agreed on basic constellation operations philosophy: • Agreed on basic orbital configuration • Agreed on WHEN and HOW we need to coordinate (during special/critical events, anomalies) • Agreed on process for handling changes and conflict resolution Each mission operates independently, but all missions are committed to keeping the constellation safe

Mission Operations Working Group (MOWG) (cont’d) • For the past 3 years we have learned a lot working together as a "constellation team” • Aqua, Aura, and PARASOL provided a learning experience, exercising some of the agreed-upon interfaces and procedures • Preparing for the launch and early orbit phase of CALIPSO and CloudSat provided recent lessons.

Constellation Operations Lessons Learned • Science teams need to communicate their constellation requirements early. • Ensure all missions are willing to coordinate constellation requirements with each other. • Start constellation discussions early enough to incorporate constellation requirements into the mission operations concept and spacecraft design. • Analyze each mission’s maneuver capabilities and strategy. • Implement a coordination system. • Minimize number and complexity of constellation interfaces. • Thoroughly test all constellation interfaces. • Be prepared for changes in planned mission order of launches. • Analyze each mission’s ascent plan. • Analyze constellation contingency scenarios. • Set up a mechanism to authorize constellation configuration changes and resolve conflicts. • Coordinate end-of-mission plans. • Maintain communications between teams.

AQUA AURA Lessons Learned #1Science teams need to communicate their Constellation requirements early. • Science requirements drive the operations concepts for both the mission and the constellation design. • To do coordinated observations, science teams must ensure their requirements are understood by the mission design team. Example: Science requirement: Aura’s Microwave Limb Sounder (MLS) instrument needs to view the same air mass on the horizon that Aqua observed 8 minutes earlier by looking down. Solution: Aura orbits 8-15 minutes behind Aqua, offset 215 km West.

Lessons Learned #2Ensure all missions are willing to coordinate constellation requirements with each other • The benefits derived from flying in close proximity to other satellites come at a cost. • Mission teams must understand that coordination with other teams will be required. • In nominal operations, little interaction is required • It is usually only during special activities (e.g., inclination adjust maneuvers) and contingency operations that teams must coordinate. • Agreements must be reached with all teams prior to a satellite’s entry into the constellation.

Lessons Learned #3Start constellation discussions early • Start discussions early enough to incorporate constellation requirements into the mission’s operations concept and spacecraft design. • Fuel allocations • Staffing • Glint constraints (relative to science requirements) • “What-if” scenarios. • Example: • Constellation-flying requires more fuel than free-flying. • Formation flying with another constellation satellite requires even more fuel. CloudSat has enough fuel to do formation flying with CALIPSO.

Lessons Learned #4Analyze maneuver capabilities and strategy • Evaluate the on-orbit maneuver philosophy for each mission • Each mission needs to evaluate its on-orbit maneuver philosophy. • A maneuver plan that works for a free-flying satellite may not be appropriate in a constellation environment. • Example: • CloudSat must match CALIPSO’s maneuvers in order to maintain their formation. • A dangerous situation can occur if a scheduled CALIPSO maneuver is delayed. CloudSat must react immediately. • CloudSat changed its maneuver strategy to schedule an automatic “undo” maneuver in case CALIPSO’s maneuver is delayed. Once CALIPSO has maneuvered successfully, CloudSat’s “undo” maneuver is cancelled.

Mission 1 Mission 1 5 interfaces 1 interface versus Mission 6 Mission 6 Mission 2 Mission 2 Mission 3 Mission 3 Mission 5 Mission 5 Mission 4 Mission 4 Lessons Learned #5 Implement a Coordination System • Develop a centralized coordination system to automate routine functions • Orbital product exchanges • Event notifications • Ephemeris displays • One centralized system relieves all organizations from developing multiple systems performing similar functions and redundant interfaces • Example: • For both the Morning and Afternoon Constellations, NASA GSFC developed the Centralized Coordination System (CCS) to fulfill this requirement.

Example: Some product transfers require 2 “hops”, when 1 hop could have sufficed. This increases the likelihood of facility or network problems. Products for CNES Products for CNES NASA Goddard NASA Langley CNES Products for Goddard Products for Goddard Lessons Learned #6 Minimize number and complexity of constellation interfaces • Fewer interfacesLess coordination when problems occur, so minimize the number of interfaces. • Standardize formats as much as possible (e.g., STK). Example: Some of our products require format conversions, increasing the complexity of the task and introducing a potential source of error. • Get “buy-in” and review from all interfacing organizations. Interface agreements must be reviewed and agreed-to by both management and operations organization. Example: An ICD, signed by management, was not reviewed sufficiently by the people building and operating the system. This caused late-breaking changes to operational systems.

Lessons Learned #7 Thoroughly test all constellation interfaces • Allocate time to conduct thorough interface testing prior to launch to identify any problems early. • Where possible, incorporate constellation testing into existing mission testing to reduce additional impact to the mission. • Agree on needed stand-alone constellation testing and simulations. • These verify that agreed-upon constellation procedures are workable. Example: Pre-mission simulations for CloudSat and CALIPSO identified some incompatible formats.

Projected Launch Dates CALIPSO/ CloudSat 2006 Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug PARASOL Launched 2004 2005 Lessons Learned #8 Be prepared for changes in the planned mission order of launches • Mission B may launch before Mission A, even though Mission A was to launch first. This may have consequences. • Example: • CALIPSO/CloudSat were to launch before PARASOL, so they received more attention from the Constellation MOWG. CALIPSO/CloudSat’s launch was delayed, so some Constellation testing with PARASOL did not happen. • Fortunately, • The Constellation entry risk for PARASOL was lower since CALIPSO/CloudSat were not yet on-orbit • PARASOL did not have any constellation-related anomalies during ascent, and • CNES did an excellent job of keeping the other mission teams informed. • Application: • We benefit in preparing for the Glory and Orbiting Carbon Observatory (OCO) missions in 2008

Lessons Learned #9Analyze each mission’s ascent plan • Analyze each mission’s ascent plan in relation to rest of Constellation to ensure safety. • The most risk to the Constellation occurs for the final injection burns, although the entire ascent (including contingencies) needs examination. • Have a third party evaluate ascent plans • This was done for the CALIPSO and CloudSat ascents • Conduct ascent simulations, including recovery from an anomalous situation. • Example: • Ascent simulations showed the need for teams to coordinate more via telecons during the launch and early orbit (L&EO) phase. • Application: • Glory and OCO ascents will be analyzed and coordinated with the rest of the constellation teams.

Lessons Learned #10Analyze constellation contingency scenarios • Each mission team performs contingency analysis for their own satellite, but not those involving other satellites. “Credible” constellation contingency scenarios must be analyzed • Identify the most likely contingencies. • Analyze the ability of each mission to react to contingencies • Develop procedures to mitigate the risks. • Get all teams to signoff on the procedures • Simulate the contingency procedures to verify their efficacy. • If and when contingencies do occur, the response and resolution will be timely, efficient, and effective. • Example: • If one satellite goes into safe-hold and starts drifting, it eventually could threaten another Constellation satellite. A collision between the two could create a debris field that could threaten all missions. Contingency procedures were developed and signed off by all teams so there will be no confusion over a mission’s actions in a contingency situation.

Coordination Process Mission Teams Notices sent to affected missions Constellation Executive Board Aqua Conflict not resolved Conflict resolved Aura Not resolved Resolved Conflict CloudSat Analysis Start Orbit data NASA HQ CNES HQ No conflicts CALIPSO No action required Resolved PARASOL Updated Orbit data Resolution decisions OCO Glory KEY: Unresolved conflict No conflict • Provide orbit data • Analyze conflicts • Resolve conflicts • Implement resolution decisions Data flow Lessons Learned #11Set up a mechanisms to authorize constellation configuration changes and resolve conflicts • Establish an approval process for planned constellation configuration changes. • Establish a process to resolve conflicts. • Examples: • Aqua’s original ground track control requirement was ±20 km. • CloudSat and CALIPSO science teams asked Aqua to change this to ±10 km to improve the science. • 2. To maintain its mean local time (MLT) requirement, Aqua originally planned to conduct inclination adjust maneuvers in Spring 2005. • CloudSat and CALIPSO mission teams asked that Aqua perform these maneuvers earlier in order to save fuel for their missions. • In both cases, Aqua was able to accommodate the requests.

Lessons Learned #12Coordinate End-Of-Mission Plans • A mission must ensure that its exit from the constellation does not present a close approach risk to nearby satellites. • The end of mission plan must be reviewed by the other constellation members several months before the mission begins exiting the constellation.

Lessons Learned #13Maintain Communications Between Teams • Facilitate and encourage communication between the mission teams throughout the mission life cycle. • Example: • Remember also that Points of Contact usually change after launch. Be sure to identify points of contact for both the planning/development phase and the on-orbit phase, then involve both groups in the communications flow. • Issue periodic updates based on personnel changes.

Summary • Start early. Talk with science teams. Develop an operations concept for a constellation of diverse satellites and organizations. • Understand individual mission capabilities. • Get the mission teams to communicate and work together as one constellation team. • Get signed agreements for coordination, especially for the handling of contingencies. • Develop a coordination system to exchange data. • Minimize complexities, but always be prepared for changes and contingency situations. We hope that these lessons prove useful for other constellations.

Constellation Operations Lessons Learned For Future Exploration