MAGIC (Mass-Change and Geosciences International Constellation)

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Overview

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Overview

The Mass-Change and Geosciences International Constellation (MAGIC) is a planned National Aeronautics and Space Administration (NASA) and European Space Agency (ESA) joint venture that will include six Earth observation satellites, with each agency providing three. MAGIC will measure fluctuations in Earth’s gravitational field, allowing the study of hydrological phenomena such as mass transport, as well as building on the success of previous missions in the field, such as the Gravity Recovery and Climate Experiment (GRACE), and its follow-on mission, GRACE-FO. MAGIC will provide data continuity for the mass transport time series from these missions, as well as improvements in the temporal and spatial resolution of gravitational field mapping. This greater resolution in mapping Earth’s gravitational field will also allow enhanced study of mass transport, the shift of water mass between phases of the global water cycle, as mass transport has a calculable impact on gravitational field fluctuations. MAGIC satellites will operate in pairs, using changes in relative position to calculate gravitational field strength across the orbit. 1) 2) 3) 4) 5) 9)

MAGIC will build upon ESA's successful history of gravity measurement from space, in the Gravity field and steady-state Ocean Circulation Explorer (GOCE) mission, which produced the most accurate model of Earth’s geoid to date, seen in Figure 1, as well as the joint US-German GRACE and GRACE-FO missions, which measured variations in gravity over time, revealing large scale mass transport. The MAGIC mission will operate in pairs in low Earth orbit (LEO), to maximise gravitational field strength, and will consist of two pairs, one in near-polar orbit (89° - 90°) and a second with an orbit inclination between 65° - 70°.

Spacecraft

Each satellite is planned to have a seven year lifetime, assuming a six-month commissioning period.

System design status and Phase A studies

The NGGM Phase A is currently running an “extension” phase (8 months) approaching the Delta - Preliminary Requirement Review of the satellite design proposed by two consortia in competition (A and B, shown in figure 2). Each satellite will carry three ultra-fine accelerometers (for redundancy and enhanced on board calibration capability) and a Laser Tracking Instrument (LTI), i.e. a Michelson interferometer in transponder configuration.
The proposed designs rely on a mono-propellant solution to enable drag-compensation, formation and attitude control system (i.e. DFAOCS), allowing the satellites to be three-axis stabilized and nadir pointing, to track each other, and to implement drag compensation to minimise the disturbances on the accelerometer instruments.
The actuators devoted to lateral/cross-track drag compensation and attitude control are proportional cold gas thrusters, and those devoted to drag compensation are based on electric propulsion, aiming to cover a lifetime up to 7.5 years.
Several baseline and back-up thruster options have been presented and are under evaluation.

The design of the spacecraft and dispenser were supported by detailed Finite Element Analyses. This allowed their verification for stiffness and strength, as well as the derivation of the dynamic environment of the payload units and the propulsion sub-system. The internal accommodation was verified by performing thermal analyses of the orbital environment, involving detailed Thermal Mathematical Models. These thermal analyses not only serve as reference for assessing the compatibility with the thermal specifications of the different units, but also provide the thermal maps employed on the prediction of the Thermo-Elastic Distortions (on-going), performed by Finite Element Analyses. 13) 14)

NGGM (P2) Mission Concept

NGGM consists of two identical spacecraft (the concept design is shown in figure 2), embarking each a MicroSTAR accelerometer and the LTI, flying in in-line formation.
The P2 pair will be launched on a Vega-C rocket into a quasi-circular orbit (397 km altitude, 70 degrees inclination) - this design also compatible to polar/quasi-polar orbit.
Orbit altitude is maintained and ground track is controlled in a box of +- 1 km wrt. 
Each satellite is enabled by hybrid propulsion (proportional cold gas plus electric propulsion), using the same propellant. Electric propulsion technologies are required to enable active drag compensation (1 dof or 3 dof).
The nominal intersatellite distance is 220 km and the nominal lifetime of each spacecraft is five years (after commissioning), designed and sized to embark consumable for a mission extension of at least two years.

Launch

Launch is targeted for no earlier than 2028.

Mission Status

• April 25, 2023: ESA announced that NGGM Phase A is currently running an extension phase (8 months) approaching the Delta Preliminary Requirement Review of the satellite design, proposed by two consortia in competition.
• October 13, 2022: ESA and NASA announced that their joint ‘Next Generation Gravity Mission’, is undergoing its initial phase design activities, within the Mass Change and Geoscience International Constellation.
• November 2020: ESA’s ministerial council decided to investigate a Next-Generation Gravity Mission (NGGM) in Phase A as a First Mission of Opportunity of the FutureEO program 2)

• October 1, 2021: ESA’s Next Generation Gravity Mission (NGGM) is a candidate Mission of Opportunity for ESA–NASA cooperation in the frame of the Mass Change and Geosciences International Constellation (MAGIC). The mission aims at enabling long-term monitoring of the temporal variations of Earth’s gravity field at relatively high temporal (down to 3 days) and increased spatial resolutions (up to 100 km) at longer time intervals. 9)

• May 24, 2022: ESA’s Living Planet Symposium, where ESA’s Pierluigi Silvestrin explained, “Indeed, as part of our FutureEO programme, we have actually already been working closely with NASA for over a decade to develop this joint mission, which would be a constellation of satellites, to measure gravity variations and monitor mass transport.” 2)

• November 23, 2022: The ESA Council at Ministerial level decided on an additional €2.7 billion to ESA’s Earth observation programme, and approved the commencement of the next ESA Earth Explorer, Harmony, and the MAGIC mission.

Sensor Complement

The MAGIC sensor complement will carry similar instruments to the GRACE and GRACE-FO missions, with the key instrument being a Microwave Instrument (MWI), which enables K-band ranging. 
This instrument will allow ultra-precise satellite to satellite tracking (SST). From this data, variations in orbit can be determined, allowing derivation of relative gravitational field strength across the orbit. MAGIC will utilise two satellite pairs, P1 and P2, providing greater temporal resolution through the orbital configuration shown in Figure 2, which depicts the ascending tracks of a circular orbit, selected due to the low altitude orbit that is preferable for gravity missions, where the gravitational field strength is highest. 7)

From this higher temporal resolution dataset, a greater understanding of mass transport processes within the Earth can be gained. Mass transport refers to the process of soil, regolith or rock being moved by ice or water. As such, detection of mass transport processes allows a greater understanding of the distribution of ice and water across the Earth, insights that are vital to future climate predictions and the understanding and prediction of global hydrological cycles. As mass transport shifts enormous amounts of the Earth’s crust, it can be detected in variations in Earth’s gravitational field, meaning the proposed MAGIC system will play a vital part in a future understanding of Earth’s hydrological processes.6) 8)

MicroSTAR Accelerometers

The MicroSTAR accelerometer is composed of three units:
The accelerometer Sensor Head (ASH), with the mechanical parts of the sensor, as the proof-mass and the electrode cage surrounding it.
The Front-End Electronic Unit (FEEU), which allows control of the proof-mass and to provide the acceleration measurement. Digital FEEU is baselined for NGGM.
The Interface and Control Unit (ICU), with the software for controlling the FEEU/ASH and for interfacing with the spacecraft, including the power conversion functionalities

Performance Requirements

The accelerometer has been designed to meet the top-level relative non-gravitational acceleration measurement error requirement (figure 5).

NGGM Technology Pre-Development Activity 

The activity focuses on the adaptation of the ONERA’s MicroSTAR accelerometer, to fulfil the NGGM’s needs and specifications.
Its main objectives are to consolidate and propose a detailed accelerometer design, based on heritage capable of meeting the NGGM. The requirements are to procure,   manufacture and test, in a representative environment, the units comprising the accelerometer design for NGGM.

Sensor Improvement

The objective is to obtain low-frequency noise of the accelerometer (below 1 mHz), and improved wrt GOCE.
The performance shall be identical along the three directions (three ultra-sensitive axis), but limited in the axis where the thin discharge wire is located -> cubic proof mass. The accelerometer will support three linear plus three angular drag compensation.
Proof mass translational and rotational measurements, are used for satellite attitude control.

Performance improvement

Several parameters can be adjusted, to improve the performance. 
This includes Increasing the gap between proof-mass and electrodes, changing the material and the stiffness property of the proof-mass grounding wire (for discharging purposes), read-out electronics re-design, for decoupling the measured translational and rotational motion of the proof-mass.
The performance along the three axes can be pushed closer to the 10^-13 m/s^1/2/Hz^-1/2  noise floor, with heavier and cubic proof-mass.

Laser Tracking Instrument LTI

The LTI consists of an Instrument Control Unit (ICU) that includes a phasemeter (ICU), also called Laser Ranging Processor (LRP) in case of US contribution, a Laser Head Unit consisting of a narrow linewidth NPRO laser at 1064 nm wavelength, and with control electronics (LHU), and a Laser Stabilization Unit (LSU), made of a very stable optical cavity (CAV) and associated coupling optics (optical arm), to stabilize the laser in frequency.
Other instruments included are an interferometer Optical Bench Assembly (OBA), to host the interferometer optics, with the associated Optical Bench Electronics (OBE), an off-axis Retro-Reflector Unit (RRU), to route the beam to the other spacecraft, a scale factor measurements system (SFMS) for the measurement of the absolute laser frequency (called scale factor unit (SFU/FSU). It will be part of the ICU).
Finally, also included is an Ultra Stable Oscillator (USO) for precise time tagging, traded off against the UCXO.

Performance Requirements 

Figure 7 above shows the amplitude spectral density, in the goal and threshold requirements of the inter-satellite distance variation (as reference, the performance @ 220 km inter-satellite distance is given on the left vertical axis).
The LTI has been designed to meet the top-level ranging measurement noise requirement above. The design is based on a trade-off between several former ESA development activities and the LaserRanging Interferometer (LRI), a US-German technology demonstrator embarked on GRACE-FO.

Propulsion Subsystem

The selection and definition of the NGGM propulsion technologies and system architectures, build on the heritage and lessons learned from the highly successful GOCE, and LISA Pathfinder missions. 
The propulsion system requirements fall into two categories, which are the spacecraft attitude and orbit control (jaw, pitch and roll control, correction of disturbance forces cross-track and radial to the orbital plane), and atmospheric drag compensation (compensation of atmospheric drag force tangential to the orbital plane (along the velocity vector)).

Propulsion System Requirements

The requirements are ultra-fine thrust control, resolution and low thrust noise, 1µN thrust knowledge and control resolution.

More requirements include wide throttling ranges of 1,000:1 for attitude, and 50:1 for drag compensation, and rapid throttling capability (>100µN. S-1) to compensate for localized atmospheric density variations, and swirling at higher frequencies.
Also, long lifetime (>70 khrs) and resilience to residual atmospheric constituents, e.g. ATOX, high specific impulse for ADC requirements (of the order of 2500s), and total impulse capability (of the order of 100kNs) for the relatively large drag compensation requirements, are needed.

Options and Design Status

For the relatively high thrust and total impulse requirements of drag compensation, efforts are focusing on the application of small electric propulsion (EP) thruster technology, specifically the miniaturised gridded ion thruster technology developed in Europe.

The neutralizer technologies under consideration for NGGM range from propellent-less (often referred as ‘dry’ thermionic electron emitters, to conventional hollow cathodes and RF neutralizer technologies. The latter two technologies also employ a flow of propellant and therefore impact the overall specific impulse of the system, although they are of a higher technology readiness level (TRL) .
The hollow cathode technology was successfully flown on the GOCE mission and is currently being developed for NGGM. Two examples of development neutralizers, immediately prior to diode emission, are presented below.
These devices have been manufactured and have a diameter of 32mm x 66 mm long and a mass of <350 g, including a thermal isolating mounting bracket. The devices have an inherently high emission current capability and hence provide a large growth capability for subsequent constellations that could employ multiple thrusters operating simultaneously.

For the relatively low thrust and low total impulse requirements of spacecraft attitude control, efforts are focusing on the application of more traditional, proportional cold gas thruster technology, such as the system flown on the LISA Pathfinder mission.
The relatively low Isp capability of this technology being offset by the lower total impulse requirements, power consumption and system complexity. 12)

Ground Segment

The MAGIC mission will deliver at least Level-1 and Level-2 data products to the science community. Its Level-1 products will be Low-Low satellite to satellite tracking (LL-SST) ranging for each pair, non-gravitational accelerations for each satellite, kinematic positions and velocities, attitude information, as well as other data such as temperature, satellite geometry model, surface characteristics, thrust, control and alignment information. The mission will also deliver two Level-1b products, de-aliasing products and tidal corrections. The Level-2 products of the MAGIC mission will be gravity field measurements, Level-2 de-aliasing products and precise science orbits. As well as these, Level-3 products, mass transport estimates for different areas and scales, will be selected. Most of the product processing processes are already well established due to the similarity in mission concepts between the MAGIC mission and the existing GRACE and GRACE-FO programs.

References  

1) Daras, Ilias. “ESA/NASA Mass change And Geosciences International Constellation (MAGIC) mission concept – science and application prospects.” Meeting Organizer, URL: https://meetingorganizer.copernicus.org/EGU23/EGU23-13535.html

2) ESA Earth and Mission Science Division. “Next generation gravity mission as a mass change and geosciences international constellation (MAGIC) a joint ESA/NASA double-pair mission based on NASA's MCDO and ESA's NGGM studies- Mission Requirements Document.” 30 October 2020, URL: https://esamultimedia.esa.int/docs/EarthObservation/MAGIC_NGGM_MCDO_MRD_v1_0-signed2.pdf

3) “ESA - It's a kind of MAGIC.” European Space Agency, 24 May 2022, URL: https://www.esa.int/Applications/Observing_the_Earth/FutureEO/It_s_a_kind_of_MAGIC

4) Haagmans, Roger, et al. “Next Generation Gravity Mission as a Masschange And Geosciences International Constellation (MAGIC)- Mission Requirements Document.” MAGIC MRD, 30 October 2020, URL: https://www.asi.it/wp-content/uploads/2021/03/MAGIC_NGGM_MCDO_MRD_v1_0-signed2.pdf

5) “Mass Change (MC) | Science Mission Directorate.” NASA Science, URL: https://science.nasa.gov/earth-science/decadal-mc

6) “Ministers back ESA's bold ambitions for space with record 17% rise.” European Space Agency, 23 November 2022, URL: https://www.esa.int/About_Us/Corporate_news/Ministers_back_ESA_s_bold_ambitions_for_space_with_record_17_rise

7) “Next Generation Gravity Mission Elements of the Mass Change and Geoscience International Constellation: From Orbit Selection to Instrument and Mission Design.” MDPI, URL: https://www.mdpi.com/2072-4292/13/19/3935

8) “SC 2.6: Gravity Inversion and Mass Transport in the Earth System - IAG.” Gravity Field, 2 October 2020, URL: https://com2.iag-aig.org/sub-commission-26

9) Technische Universität München, et al. “Simulation studies for a Mass change And Geosciences International Constellation (MAGIC).” TUM, URL: https://www.asg.ed.tum.de/fileadmin/w00cip/iapg/MAGIC/MAGIC_ExecutiveSummary.pdf

10) Wiehl, M., and M. Scheinert. “Mass Transport and Mass Distribution in the Earth System.” GFZpublic, URL: https://gfzpublic.gfz-potsdam.de/rest/items/item_231104_1/component/file_231103/content

11) Wiese, David. “Explore Earth- Mass Change Town Hall.” NASA Science, 13 December 2022, URL: https://science.nasa.gov/science-pink/s3fs-public/atoms/files/MC%20AGU%202022%20Slide%20Deck_221208%20Rev.pdf

12)  Massotti Luca, Bulit Alexandra, Daras Ilias, Carnicero Domínguez ernardo, Carraz Olivier, Hall Kevin, Hélière Arnaud, March Günther, Marchese Valentina, Martimort Philippe, Palmer Kyle, Rodrigues Gonçalo, Silvestrin Pierluigi, and Neil Wallace, “Next Generation Gravity Mission design activities within the MAGIC -Mass Change and Geoscience International Constellation”, ESA, EGU23, 14882, Vienna (virtual presentation), 25/04/2023, URL: https://presentations.copernicus.org/EGU23/EGU23-14482_presentation.pdf 

13) Massotti, L., Bulit, A., Daras, I., Carnicero Dominguez, B., Carraz, O., Hall, K., Heliere, A., March, G., Marchese, V., Martimort, P., Palmer, K., Rodrigues, G., Silvestrin, P., and Wallace, N.: Next Generation Gravity Mission design activities within the  MAGIC - MAss Change and Geoscience International - Constellation, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-14482, URL: https://doi.org/10.5194/egusphere-egu23-14482 

14) Massotti Luca, Caiazzo Antonio, Carnicero Dominguez Bernardo, “Next Generation Gravity Mission design activities within the Mass Change and Geoscience International Constellation”, October 13, 2022, Clean Space Industrial Days, ESA-ESTEC, URL: https://indico.esa.int/event/416/contributions/7507/attachments/4913/7529/Clean%20Space%20Industrial%20Days_NGGM%20w_video_v3.pdf  

The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (eoportal@symbios.space).