Daniel Cosgrove

Lunar magnetic field measurements with a cubesat

We have developed a mission concept that uses 3-unit cubesats to perform new measurements of lunar magnetic fields, less than 100 meters above the Moon’s surface. The mission calls for sending the cubesats on impact trajectories to strongly magnetic regions on the surface, and transmitting measurements in real-time to a nearby spacecraft, or directly to the Earth, up until milliseconds before impact. The cubesats and their instruments are partly based on the NSF-funded CINEMA cubesat now in Earth orbit. Two methods of reaching the Moon as a secondary payload are discussed: 1) After launching into geostationary transfer orbit with a communication satellite, a small mother-ship travels into lunar orbit and releases the cubesats on impact trajectories, and 2) The cubesats travel to the Moon using their own propulsion after release into geosynchronous orbit. This latter version would also enable other near-Earth missions, such as constellations for studying magnetospheric processes, and observations of close-approaching asteroids.

Ground Systems and Flight Operations of the THEMIS Constellation Mission

THEMIS, a five-spacecraft constellation mission to study magnetospheric phenomena leading to auroral outbursts was launched on February 17, 2007 on a single Delta II rocket into a 31.4-hour, low-inclination insertion orbit. After an initial on-orbit check-out and science instrument commissioning period, the five spacecraft called probes were maintained in temporary coast phase orbits to control orbital dispersions. Beginning in early September 2007, four of the five probes were maneuvered into their highly elliptical, synchronized mission orbits with 1, 2 and 4-day periods in preparation for the primary winter observing season. The fifth probe, acting as an on-orbit spare, was maneuvered into its 4/5-day period orbit, once the four primary probes were completely deployed. This paper describes the concept of constellation operations including a description of the flight and ground systems, as well as mission, science and flight dynamics operations, and discusses challenges encountered and lessons learned during the first year of on-orbit operations.

Multi-Mission Flight Operations at UC Berkeley - Experiences and Lessons Learned

The University of California, Berkeley has conducted flight operations for multiple NASA-funded spacecraft from its multi-mission operations center at Space Sciences Laboratory for more than a decade. All ground systems were designed and implemented by members of the multi-mission operations team who are involved in all phases of mission life cycles from the early proposal stages through mission design and development, integration, launch and on-orbit operations. Operational task areas include mission and science operations, mission design and navigation, ground station operations, and hardware and software systems support. Team members are trained across missions and across support disciplines to provide a breadth of knowledge and redundancy within the team. This paper describes the ground system design and summarizes experiences, challenges, and lessons learned with conducting complex multi-mission spacecraft operations in an academic environment.

Navigating THEMIS to the ARTEMIS Low-Energy Lunar Transfer Trajectory

THEMIS – a NASA Medium Explorer (MIDEX) mission – is a five-spacecraft constellation launched in February 2007 to study magnetospheric phenomena leading to the aurora borealis. During the primary mission phase, completed in the summer of 2009, all five spacecraft collected science data in synchronized, highly elliptical Earth orbits. Both mission design and efficient navigation and flight operations during the primary mission resulted in appreciable fuel reserves. Therefore, an ambitious mission extension, ARTEMIS, became feasible. ARTEMIS involves transferring the outer two spacecraft from Earth to lunar orbits where they will conduct measurements of the Moon’s interaction with the solar wind and its crustal magnetic fields. Earth departure of these two spacecraft is accomplished by successively raising the apogees of their orbits until lunar perturbations become the dominant forces significantly altering their trajectories. This orbit raise sequence requires over forty maneuvering events, with multiple lunar approaches and fly-bys, before setting the two spacecraft on low-energy transfer trajectories to lunar orbit in February and March 2010. This paper addresses overcoming the navigation and operational challenges presented by the ARTEMIS mission, consisting of two spacecraft that were not designed to leave Earth orbits.

THEMIS Mission Networks Expansion - Adding the Deep Space Network for the ARTEMIS Lunar Mission Phase

THEMIS is a five-spacecraft constellation launched in 2007 to study magnetospheric phenomena leading to the aurora borealis. During the primary mission phase, completed in the fall of 2009, all five spacecraft collected science data in synchronized, highly elliptical Earth orbits. For an ambitious mission extension, the Project proposed to split the constellation into two parts - THEMIS-Low and ARTEMIS. THEMIS-Low includes the three spacecraft on the inner orbits with approximately one-day periods, continuing their study of the magnetosphere in a tighter formation. ARTEMIS involves transferring the outer two spacecraft from their Earth orbits with two and four-day periods into lunar orbits to conduct measurements of the interaction of the Moon with the solar wind and of crustal magnetic fields. This transfer was initiated on July 21, 2009 and follows low-energy trajectories with Earth and lunar gravity assists. The THEMIS mission is controlled from the highly automated multi-mission operations center at the University of California, Berkeley and was originally designed to be supported by 11-m class ground stations and NASAs Space Network. To increase the telemetry bandwidth for science data return at lunar distances, the mission network was expanded to also include the 34-m subnet of NASAs Deep Space Network (DSN). This paper discusses all aspects of the process to seamlessly integrate the new DSN interfaces into the THEMIS/ARTEMIS mission control network, and describes challenges and lessons learned with the implementation of real-time telemetry and command data transfer using the CCSDS Space Link Extension protocol. It also includes on-orbit characterization of the transponder ranging channels, orbit determination results using two-way Doppler and range data from a combination of conventional ground stations and DSN stations, as well as pass scheduling via the DSN Resource Allocation Planning Service and via automated, electronic data exchanges. All of these tasks were accomplished within a compressed schedule of one year, with very limited staffing resources, and on a tight budget.

Calibration of In-flight Maneuver Performance for the THEMIS and ARTEMIS Mission Spacecraft

We describe the development and details of in-flight calibration techniques used to obtain the required degree of accuracy for mission-required, small-scale trajectory adjustments. Using the dynamics data gathered from dozens of orbital-adjustment maneuvers previously conducted on the ARTEMIS and THEMIS spacecraft, the Space Sciences Laboratory (SSL) Flight Dynamics group has systematized a calibration process employing hill-climbing and grid searches for single segment and multi-segment maneuvers, respectively. This effort has resulted in the characterization of a nonlinear function of thruster performance scale factors and offsets to use in NASA Goddard’s GMAN software package for maneuver planning and reconstruction. To date, use of these factors has greatly reduced deviations between predicted and observed orbital state vector solutions and spinrate changes following a sequence of orbit-raising maneuvers intended to result in a lunar gravitational capture of the ARTEMIS probes in early 2010.

On-Orbit Propellant Estimation, Management, and Conditioning for the THEMIS Spacecraft Constellation

Proper propellant usage is vital to ensure successful completion of initial spacecraft mission goals and to create viable mission extension options. Opportunities exist for spacecraft operators to contribute in this area through the methods that they use to estimate fuel mass, manage its distribution throughout the propellant tanks, and thermally condition it for desiredV performance. In this paper, on-orbit propellant estimation, management, and conditioning are described for the THEMIS spacecraft constellation, which investigates magnetospheric phenomena leading to the aurora borealis. THEMIS is a NASA Medium- class Explorer mission comprised of five spacecraft currently making use of fuel reserves left over from its primary mission to execute an ambitious two part mission extension— THEMIS-Low and ARTEMIS. THEMIS-Low comprises the continuation of the original THEMIS mission with the inner three spacecraft flying in a closer formation, while ARTEMIS includes low energy transfers of two of the spacecraft into lunar orbit via two Earth-Moon libration points. Current results are provided from an ongoing nonlinear regression analysis to estimate the fuel mass through the fuels thermal response to tank heaters. Additionally, propellant management operations for all spacecraft are summarized and the authors evaluate the potential for improvedV performance through propellant thermal conditioning. Finally, lessons learned from nominal and extended THEMIS mission operations are highlighted with an emphasis on improving on-orbit propellant estimation, management, and conditioning in future spacecraft operations.

Operations planning and mission readiness testing for the THEMIS spacecraft constellation

THEMIS - a five-spacecraft constellation - is a NASA Medium Explorer mission that was launched in 2007 and maneuvered into synchronized, highly elliptical Earth orbits to study magnetospheric physics leading to the appearance of the aurora borealis. THEMIS operations are conducted from the multi-mission control center at the University of California, Berkeley. After a successful completion of the prime mission phase in fall of 2009, all five spacecraft and the ground systems are still performing very well. The excellent flight and ground systems performance can in part be traced back to a carefully designed and meticulously executed mission readiness test program, as well as operations planning and extensive operator training. This paper describes the methodology of the mission readiness test program, its organization from box level to full systems level end-to-end testing, and includes lessons learned that may be directly applicable towards future missions. 1 2

ARTEMIS operations - Experiences and lessons learned

THEMIS, a constellation of five spacecraft, referred to as probes, was launched in 2007 to study the physical processes leading to the aurora. In 2009, THEMIS successfully completed its primary mission phase. As an ambitious mission extension, the constellation was then split into two new missions - THEMIS-Low and ARTEMIS. THEMIS-Low refers to three of the five probes that continued magnetospheric observations in Earth orbits while the remaining two probes started a new lunar mission called ARTEMIS. The two ARTEMIS probes were transferred from Earth to lunar orbits via low-energy trajectories with Earth and lunar gravity assists. The complex mission design and navigation operations took the two probes on trajectories along weak stability boundary manifolds, venturing out as far as 1,500,000 km and 1,200,000 km from Earth, respectively. Upon arrival in the lunar environment, both probes were first inserted into libration point orbits where they spent up to ten months collecting science data. Periodic stationkeeping maneuvers were executed to ensure the two probes would not be ejected from these unstable orbits. In 2011, both probes were successfully inserted into stable, retrograde and prograde lunar orbits, respectively. We report on the challenges with executing the complex navigation plans, discuss experiences and lessons learned from operating two spacecraft in lunar libration point orbits for the first time ever, and finally cover mission planning and science operations in the lunar environment.

Collision Avoidance Operations in a Multi-Mission Environment

With the increasing number of manmade object orbiting Earth, the probability for close encounters or on-orbit collisions is of great concern to spacecraft operators. The presence of debris clouds from various disintegration events amplifies these concerns, especially in lowEarth orbits. The University of California, Berkeley currently operates seven NASA spacecraft in various orbit regimes around the Earth and the Moon, and actively participates in collision avoidance operations. NASA Goddard Space Flight Center and the Jet Propulsion Laboratory provide conjunction analyses. In two cases, collision avoidance operations were executed to reduce the risks of on-orbit collisions. With one of the Earth orbiting THEMIS spacecraft, a small thrust maneuver was executed to increase the miss distance for a predicted close conjunction. For the NuSTAR observatory, an attitude maneuver was executed to minimize the cross section with respect to a particular conjunction geometry. Operations for these two events are presented as case studies. A number of experiences and lessons learned are included.