Spinworks > uPGRADE – miniaturized Prototype for GRavity field Assessment using Distributed Earth-orbiting assets

uPGRADE - miniaturized Prototype for GRavity field Assessment using Distributed Earth-orbiting assets

The main goal of the uPGRADE project is to develop and qualify for space operations a Gravity Recovery nanosatellite prototype.


uPGRADE – miniaturized Prototype for GRavity field Assessment using Distributed Earth-orbiting assets
Development through qualification of a gravity recovery nanosatellite prototype.
Norte, Centro e Lisboa
Spin.Works, Iberian Nanotechnology Laboratory – INL, Universidade do Minho, Instituto de Soldadura e Qualidade – ISQ
1.943.732,13 EUR
FEDER – 1.395.328,52 EUR


The uPGRADE mission will attempt to follow on the footsteps of the groundbreaking GRACE and GRACE-FO gravimetry missions with a small 6U Cubesat carrying a GPS sensor, a dual-head star tracker and a high accuracy accelerometer. The spacecraft has been under construction since 2020 and its’ space qualification is currently underway at ISQ test facilities, with the launch planned for 2024.

Consortium and Team Contributions

A US-Portugal consortium team is developing uPGRADE, with the scientific team led by the University of Texas at Austin’s Center for Space Research, and an industrial team led by Spin.Works in Portugal, with the support of INL, UMinho and ISQ
Spin.Works is also contributing with the spacecraft’s On Board Computer and Star Tracker, whereas INL and UMinho are developing a MEMS-based High Accuracy Accelerometer. ISQ is providing its’ test facilities for space qualification as well as with a Data Analysis Facility. 

Satellite Architecture

The uPGRADE satellite is a standard 6U with fixed solar panels. The structure is highly rigid with the sole deployable/flexible device being the UHF antenna, which has been separately tested to guarantee sufficient rigidity and avoid perturbing accelerometer measurements.

The avionics bay comprises the OBC, power conditioning and distribution unit, communications board, and star tracker processing board.

Other devices such as the S-Band antenna, GPS antenna and ADCS components (magnetometer + magnetorquer, sun sensors, IMU and inertia wheels) are placed such as to ensure a suitable field-of-view and avoid interference with the sensitive devices responsible for the science mission (GPS sensor, accelerometer and star tracker optical heads).

On Board Computer

The mission’s On Board Computer has been developed at Spin.Works and shares many of the functionalities and interfaces with another project (VIRIATO). The main processing device is an STM32H7-series with an ARM-Cortex-M4/M7 processor that provides high performance (about 1000DMIPS) at low power consumption (300mW avg, 1W peak), along with ample connectivity (I2C, UART, Quad SPI, CAN, USB, Ethernet) and storage (FRAM, NOR Flash and SD Card).

The OBC board connects to the Cubesat’s PC-104 stack and weighs g. It is effectively the brain of the mission, ensuring that all on board operations are executed just as planned, including the configuration, data handling and monitoring of each device in the spacecraft throughout the mission.


The on board software ensures that all peripherals, storage facilities and MCU functionalities are made available to the system user, and provides sufficient infrastructure to guarantee and monitor the operation of the spacecraft, using local and remote means. The generic part of the OBSW includes the system initialization routine, a set of configuration files, a suitable Hardware Abstraction Layer, the RTOS and corresponding file system, and the Middleware – a set of tasks, function libraries and other resources which implement lower-level functionalities required for proper operation of the applications.
Finally, the mission-specific (the Application layer) is the highest level of the software architecture. The OBC is developed with the premise that it must be a stand-alone product, which offers a set of standard functionalities and interfaces for use in different missions (involving a Cubesat or other vehicle types). The Core Appplications are applications which do not change from one mission to another (Command Manager, Configuration Controller, File System Manager, FDIR, Mission and Vehicle Manager and AIV Interface), while the Mission Applications are viewed as extensions to the OBC software that implement mission-specific functionalities (e.g. ADCS, Communications, Payload Management or Power System Handling functions).

The element that owns or contains each Mission Application is the associated subsystem. A few of those subsystems are described in more detail next.

Attitude Determination and Control System (ADCS)

The ADCS is one of the key elements developed by Spin.Works for uPGRADE. The several sensing and actuating units involved all connect to the mezzanine board attached to the OBC.
The system primarily uses magnetotorquers to keep the spacecraft oriented such that its’ solar panels continuously generate electrical power, while monitoring its’ own attitude relative to the sun and Earth using multiple sun sensors and a 3-axis magnetometer.
Most operational ADCS modes only require these 3 devices, including for nominal science operations where angular rates will essentially track the spacecraft orbital path. Communications sessions (especially those concerning TM/TC) will generally be carried out using a low-rate omnidirectional UHF antenna that does not require low attitude pointing errors. For higher S-band data rates, where a moderate degree of pointing accuracy is required, magnetorquers may be used when disturbances to the science measurements need to remain low, whereas for circumstances where pointing accuracy needs to be high, reaction wheels are preferred.


The payload on uPGRADE comprises three sensor types: a GNSS receiver (along with the respective antenna), a dual-head Star Tracker, and a high-accuracy accelerometer.
The only unit among these to be procured commercially is the GNSS, which will acquire ranging signals from several hundred channels from all available satellite navigation constellations. These signals will provide information on the total acceleration that the satellite is being subjected to.

Star Tracker

The dual-head star tracker will provide attitude measurements with an accuracy of a few arc-seconds.
The image sensors help determine attitude by correlating star field images collected in space with those stored in a priori star catalogs. The system field-of-view, image sensor and typical image exposure have been selected such as to ensure GRACE-like attitude knowledge performance with a sky coverage of >99%.
Attitude measurements are produced every second by the data processing unit (although the system can reach up to 10Hz), which for this application will be running at a comparatively low-power mode.
The entire dual-head system, which uses modified COTS lenses, fits within 1U and weighs less than 1kg including the data processing unit. The measurements are used to help derive both the aerodynamic and the radiation pressure contributions to the non-gravitational accelerations acting on the spacecraft.

High Accuracy Accelerometer

Developed at INL and University of Minho, this accelerometer attempts to use MEMS technology to measure nm/s2-level accelerations.
This is comparable with the sensitivity of seismometers, which means that it is difficult to test it on the ground, even under laboratory conditions. 

Given its extreme sensitivity, the device is far more suited for operating in orbit – or on the surface of other planetary and small bodies as a seismometer. 

The package enclosing the accelerometers and keeping in place the different components has been developed at Spin.Works.

Test Facilities

The different components, as well as the integrated uPGRADE spacecraft, have been tested and have been qualified to operate under conditions which are representative of the launch and orbital environments the mission will endure once it is launched in 2024.

The tests have taken place at ISQ in Castelo Branco (central Portugal), which is equipped with both a shaker, a thermo-vacuum chamber and final satellite integration facilities.


  1. Project Management and Planning
  2. Mission Conceptual Design
  3. Preliminary Design
  4. Detailed Design
  5. Development and Implementation
  6. Assembly, Integration, Testing and Verification
  7. Qualification
  8. Promotion and Dissemination of Results
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