THEMIS Reaction Control System: From I and T Through Early Mission Operations

Sholl, Michael; Leeds, Michael; Holbrook, Jamie

doi:10.2514/6.2007-5579

Cited by 10 publications

(3 citation statements)

References 2 publications

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“…Main RCS components, shown in Figure 3, included two spherical propellant tanks, a pyro-actuated repressurization tank, two latch valves, and four 4.5-N thrusters (Aerojet MR-111C). [7] Two of the four thrusters were mounted parallel to the spin axis, and were hence referred to as axial thrusters (A1, A2). The other two thrusters were mounted in the spin plane and were termed tangential thrusters (T1, T2).…”

Section: Navigation Capabilities and Constraintsmentioning

confidence: 99%

ARTEMIS operations - Experiences and lessons learned

Bester

Cosgrove

Frey

et al. 2014

2014 IEEE Aerospace Conference

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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.

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Section: Navigation Capabilities and Constraintsmentioning

confidence: 99%

ARTEMIS operations - Experiences and lessons learned

Bester

Cosgrove

Frey

et al. 2014

2014 IEEE Aerospace Conference

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“…10, and corresponding orbital elements of the constellation are summarized in Table 3. Early maneuvers in the orbit placement sequence were very difficult to plan in terms of magnitude and timing, as the mission design team had to work with a rather narrow window of opportunity in the blow-down pressure profile for fuel tank repressurization (Frey et al 2008;Sholl et al 2007). Tank repressurization had to be coordinated with the fuel consumption on each probe in such a way that neither firing of the thrusters at too low an Note: Total V includes targeted V maneuvers plus contributions imparted by attitude precession and spin rate change maneuvers inlet pressure, nor over-pressurization of the fuel tanks could occur.…”

Section: Coast Phasementioning

confidence: 99%

THEMIS Operations

et al. 2008

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THEMIS-a five-spacecraft constellation to study magnetospheric events leading to auroral outbursts-launched on February 17, 2007. All aspects of operations are conducted at the Mission Operations Center at the University of California at Berkeley. Activities of the multi-mission operations team include mission and science operations, flight dynamics and ground station operations. Communications with the constellation are primarily established via the Berkeley Ground Station, while NASA's Ground Network provides secondary pass coverage. In addition, NASA's Space Network supports maneuver operations near perigee. Following a successful launch campaign, the operations team performed on-orbit probe bus and instrument check-out and commissioning tasks, and placed the constellation initially into a coast phase orbit configuration to control orbit dispersion and conduct initial science operations during the summer of 2007. Mission orbit placement was completed in the fall of 2007, in time for the first winter observing season in the Earth's magnetospheric tail. Over the course of the first 18 months of on-orbit constellation operations, procedures for instrument configuration, science data acquisition and navigation were refined, and software systems were enhanced. Overall, the implemented ground systems at the Mission Operations Center proved to be very successful and completely adequate to support reliable and efficient constellation operations. A high degree of systems automation is employed to support lights-out operations during off-hours.

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“…The THEMIS RCS (Sholl et al 2007) is a complex design of a blow-down hydrazine system of two spherical tanks, a pyro-activated helium gas repressurization system, and four 4.5 N thrusters. Allocating 4 kg of fuel for attitude control, the fuel load at launch of 49 kg provides the equivalent of approximately 930 m/s of the total delta V capacity for each probe.…”

Section: Placement Phasementioning

confidence: 99%

Orbit Design for the THEMIS Mission

Frey

Angelopoulos²,

Bester

et al. 2008

Space Sci Rev

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THEMIS, NASA's fifth Medium Class Explorer (MIDEX) mission will monitor the onset and macro-scale evolution of magnetospheric substorms. It is a fleet of 5 small satellites (probes) measuring in situ the magnetospheric particles and fields while a network of 20 ground based observatories (GBOs) monitor auroral brightening over Northern America. Three inner probes (∼1 day period, 10 R E apogee) monitor current disruption and two outer probes (∼2 day and ∼4 day period, 20 R E and 30 R E apogees respectively) monitor lobe flux dissipation. In order to time and localize substorm onsets, THEMIS utilizes SunEarth aligned conjunctions between the probes when the ground-based observatories are on the nightside. To maintain high recurrence of conjunctions the outer orbits have to be actively adjusted during each observation season. Orbit maintenance is required to rearrange the inner probes for dayside observations and also inject the probes into their science orbits after near-simultaneous release from a common launch vehicle.We present an overview of the orbit strategy, which is primarily driven by the scientific goals of the mission but also represents a compromise between the probe thermal constraints and fuel capabilities. We outline the process of orbit design, describe the mission profile and explain how mission requirements are targeted and evaluated. Mission-specific tools, based on high-fidelity orbit prediction and common magnetospheric models, are also presented. The planning results have been verified by in-flight data from launch through the end of the first primary science seasons and have been used for mission adjustments subject to the early scientific results from the coast phase and first tail season.

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THEMIS Reaction Control System: From I and T Through Early Mission Operations

Cited by 10 publications

References 2 publications

ARTEMIS operations - Experiences and lessons learned

ARTEMIS operations - Experiences and lessons learned

THEMIS Operations

Orbit Design for the THEMIS Mission

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