GOLIAT is a CubeSat technology demonstration mission of the Bucharest University and Bucharest Polytechnic University under the coordination of the Romanian Space Agency (ROSA). The objective is imaging of Earth's surface using a digital camera and in-situ measurement of the radiation dose and the micrometeoroid flux.
The CubeSat project was started in 2005 and beside its scientific and technical objectives it was also meant as a means to educate a new generation of young professionals in the space applications development sector in Romania. At the core of the development team is a group of students from University of Bucharest and “Politehnica” University of Bucharest, who work under the supervision of experts from ROSA and the Romanian Institute for Space Sciences. 1) 2) 3) 4) 5)
Figure 1: Schematic view of the GOLIAT CubeSat (image credit: Bucharest University)
Educational objectives/requirements: The educational objectives were defined in such way that they clearly encourage the involvement of the students in the project. The students shall be involved in each stage of the projects development and they shall carry out the work with the supervision of their mentors. A special attention was accorded to the students training outside the universities by establishing collaborations with relevant research institutes and aerospace industry.
Scientific and technological objectives: The scientific and technological objectives were defined to increase the student interest in the project by establishing targets for each satellite subsystem and payload.
The GOLIAT spacecraft complies to the CubeSat standard of 10 cm sidelength and a mass of < 1.33 kg. The CubeSat structure is based on Pumpkin's CubeSat kit. It comprises the main structure together with the FM430 flight module (FM430 flight module with Texas Instruments single-chip 16-bit MSP430). The CubeSat kit is modified to adapt/accommodate two reaction wheels, the UHF and GPS antennas, and the antenna deployment system.
The ADCS (Attitude Determination and Control Subsystem) uses a 3-axis fluxgate magnetometer (Honeywell HMR 3400), and a 2-axis momentum wheel system. Each reaction wheel assembly consists of a micro-motor and a metal disc. The speed and the torque of each reaction wheel assembly can be controlled by the OBC. An experimental GPS receiver is integrated onboard GOLIAT for accurate determination of in orbit position.
Figure 2: Reaction wheels mounted inside the structure (image credit: GOLIAT consortium)
The magnetometer measurements are compared with the specific local values of the Earth magnetic field components taken by interrogation of the IGRF (International Geomagnetic Reference Field) database. The position of the satellite is determined using a SGP4 type orbit propagator.
EPS (Electrical Power Subsystem): EPS was developed by the GOLIAT team with the requirement to reduce the electrical noise in the regulated voltages lines. As such, the voltage regulation stage features only LDO (Low Drop Out) regulators, an inefficient solution imposed by the on board experiments. More so, under nominal operations, the voltage at the input of the LDO is sourced by a Li-ion battery pack, and a switching power supply is used only in the charging of the other battery pack. The average estimated power generation is 2 W.
The unique feature of the subsystem is represented by the ping-pong architecture. Due to the fact that micrometeorites detection experiment require a low noise power supply, the system was designed to charge one battery back from the solar panels, while the second battery pack is powering the satellite. The battery supports are manufactured through the 3D print technology, being designed to act as battery enclosures as well as inter-board separators.
Figure 3: Illustration of the battery support inside the CubeSat (image credit: GOLIAT consortium)
DHS (Data Handling Subsystem): The DHS consist in 3 different microcontrollers interconnected through the SPI (Serial Peripheral Interface) bus. In this architecture the satellite software can be updated on-orbit by sending the new software version via a ground station. The UHF transceiver writes the received information using the beacon microprocessor to the onboard SD card. Besides those three interconnected microprocessors, the electronic power supply system and the image acquisition system have dedicated microprocessors.
RF communications: A two transceiver architecture is selected for the communication system of the GOLIAT picosatellite (both transceivers operate independently):
• The S-band (2.4 GHz transceiver), a fully commercial product, is used for TT&C data transmission. Downlink for experimental data & detailed housekeeping and uplink for spacecraft control. The link provides an output power of up to 1 W. The data rate is programmable with an average bit rate of 9.6 kbit/s.
• In addition, a UHF beacon (70 cm radio amateur band) at 437.485 MHz (IARU coordinated) is used. The beacon data is downlinked at 1.2 kbit/s in AFSK packets.
The antenna deployment system represents a novelty in the CubeSat community. The original design consists in a DC gear motor with threaded shaft as a pushing mechanism for the deployment system. By comparing with the usual used nylon wire mechanism, the GOLIAT system offer a much better reliability and very short packing time.
Figure 4: Illustration of the GOLIAT UHF and S-band deployed antenna (image credit: GOLIAT consortium)
The multiple payload launch encompasses a primary payload of 400 kg called LARES (LAser RElativity Satellite), and CubeSats (educational payloads) as secondary payloads, whose launch is sponsored by ESA. The free launch of CubeSats was offered by the ESA Education Office in Oct. 2007 (Announcement Opportunity) in cooperation with the Vega program. 8)
CubeSat passenger payloads: Although ESA's Education Office is providing 9 CubeSat positions on the maiden flight of Vega, only 7 CubeSats are confirmed as of December 2011 (Ref. 9). Not all universities that were preselected for the launch opportunity in June 2008, were able to deliver their CubeSat and the requested documentation. Other CubeSat projects, like SwissCube and HiNCube, decided to be launched on commercial flights.
On December 22, 2011, Romania officially became ESA’s 19th Member State.
ALMASat, a microsatellite of the University of Bologna, is another secondary payload of the flight.
Use of P-POD (Poly Picosat Orbital Deployer) for the deployment of all CubeSats.
Orbit of secondary payloads: Elliptical orbit, altitude of 354 km x 1450 km, inclination = 69.5º, orbital period = 103 minutes (14 revolutions/day), eccentricity = 0.075. About 75% of the orbit is in sunlight.
Status of Goliat mission:
• March 2012: Communications with the Romanian Goliat have been intermittent, and the team is working to establish more regular contacts with the satellite. Telemetry from Goliat has been downloaded, and decoding of the satellite’s transmissions was achieved during a single pass. The team is now working to establish two-way communications, in order to determine the status of Goliat’s experiments and update the onboard software accordingly. 11)
Sensor complement (Ciclop, SAMIS, DOSE-N)
Ciclop (Earth Observation Camera):
Ciclop is a 3 MP digital camera equipped with a custom 57 mm focal length lens mount. Each snapshot image provides a observation area of 70 km x 50 km. The system is comprised of three distinctive components:
• Camera sensor board, up to 3MP high resolution color sensor in 4/3 image format
• Camera processor board; a powerful 600 MHz core, 64 MRAM digital signal processor capable of real time JPEG compression
• Custom lens mount system: in house, custom made system , 6º viewing angle.
• The spatial resolution of the image is 21 m x 28 m.
Figure 5: The Ciclop camera: CAD view (Top) photo of model (bottom), image credit: GOLIAT consortium
Figure 6: The Ciclop camera integrated in GOLIAT (image credit: GOLIAT consortium)
SAMIS (Micro Meteoroid Detector):
SAMIS is a detector for the fine particles typically found in Earth’s orbit. The device features a simple design having a piezo-electric film as a sensitive element. The material is a polyvinylidene fluoride (PVDF), a polarized fluoropolymer. The metallization of the electrodes is based on silver ink and the thickness of the PVDF film is 110 µm, while the metallization adds 12 µm.
Table 2: Typical specifications of the piezo film
As it can be observed in Table 2, the piezo-films have pyro-electric properties, which might be an issue when mounted on the outside of the satellite, due to the high absorption in the infrared range.
Figure 7: Illustration of a piezo film sheet (image credit: GOLIAT consortium)
Figure 8: Exploded view of the SAMIS assembly (image credit: GOLIAT consortium)
The SAMIS assembly is mounted on one side of the satellite, on top of the solar panel board. The maximum height, including the solar panel PCB (Printed Circuit Board), is 6.5 mm. The mechanical support for the experiment is shown in Figure 8. Each side of the piezo-film is glued to the metallization on a PCB by use of a conductive silver based epoxy. A frame is cut on the two PCBs so that it will not restrict the movement of the piezo-film and it will not obstruct incoming micrometeoroids. The two frame PCBs are mounted on top of an aluminum base plate and are kept in place by six screws. The signal from each of the two electrodes is collected on two pins that are connected to the solar panel PCB, where the detection electronic is situated.
The impact of a micrometeoroid produces the deformation of the sensor and an electrical signal is obtained. The amplitude of the signal depends on the deformation of the detector, therefore of the energy released at impact (the incident energy of the detector). The projected energy for the impact of micrometeoroids is presented in Table 3.
Table 3: Estimated energy of impact
A typical pulse shape is presented in Figure . The signal was obtained by a sphere with 1.25 mm in diameter from a height 380 mm. The energy of the impact (24 mJ) is equivalent to a micrometeoroid of 10 µm in diameter. The second pulse that can be observed is for the second impact of the particle that was bounced by the detector.
The experiments in the laboratory were conducted with millimeter sized projectiles with the equivalent energy of micrometeoroids. The projectiles were released from fixed heights and the signal shapes were collected of the voltage’s time dependence.
Figure 9: Typical pulse shape (image credit: GOLIAT consortium)
Figure 10: Photo of the SAMIS experiment integrated on GOLIAT (image credit: GOLIAT consortium)
DOSE-N is a total dose measurement experiment, the objective is the measurement of cosmic radiation. The system consists of a PIN photo diode, integrated with a solid state scintillator. The PIN diode and the solid state scintillator are selected to match. The scintillator material generates photons which are directly proportional with the total amount of cosmic radiation that passes through its volume. The photons are captured and converted to an electric signal. The scintillation material is covered on each face with a thin layer of TiN (Titanium Nitride) to obtain a reflective surface. The entire assembly is encapsulated in a block of black duramide plastic which gives much more mechanical strength and at the same time prevents the external light to reach the active aria of the PIN diode.
• A semiconductor sensor (PIN diode) and a scintillating material are used as a detector
• Measurements are made at regular time intervals
• Expected results: The total dose as a function of coordinates on LEO (latitude, longitude, altitude).
Two ground stations were installed for communicating with the spacecraft:
• A 437 MHz UHF station at the Physics’ Department of the University of Bucharest, near Bucharest.
• A 2.4 GHz S-band station at a remote location in the Carpathian Mountains, near Cluj-Napoca, Romania.
1) Romanian CubeSat Project GOLIAT,” 2008 Cubesat Summer Developer’s Workshop, August 9-10, 2008, Logan, UT, USA, URL: http://mstl.atl.calpoly.edu/~bklofas/Presentations/SummerWorks...
3) Marius Florin Trusculescu, Marius-Ioan Piso, Claudiu Gabriel Dragasanu, Mugurel Balan, Constantin Alexandru Pandele, “Scientific Experiments On Board The Goliat Cubesat,” Proceedings of IAC 2011 (62nd International Astronautical Congress), Cape Town, South Africa, Oct. 3-7, 2011, paper: IAC-11.B4.2.6
4) Mugurel Balan, Marius-Ioan Piso, Adrian Mihail Stoica, Claudiu Gabriel Dragasanu, Marius Florin Trusculescu, Corina Mihaela Dumitru, “GOLIAT Space Mission: Earth Observation and Near Earth Environment Monitoring Using Nanosatellites,”Proceedings of the 59th IAC (International Astronautical Congress), Glasgow, Scotland, UK, Sept. 29 to Oct. 3, 2008, URL: http://www.rosa.ro/index2.php?option=com_resource&task=download2&no_html=1&file=NV9JQUMtM
5) Mugurel Balan, Marius-Ioan Piso, Marius Florin Trusculescu, Claudiu Gabriel Dragasanu, Constantin Alexandru Pandele, “Past, present and future of the Romanian Nanosatellites program,” Proceedings of IAC 2011 (62nd International Astronautical Congress), Cape Town, South Africa, Oct. 3-7, 2011, paper: IAC-11.B4.1.8
6) “ESA’s new Vega launcher scores success on maiden flight,” ESA, Feb. 13, 2012, URL: http://www.esa.int/SPECIALS/Vega/SEMJ8LYXHYG_0.html
7) “Vega VV01 launch campaign,” ESA, URL: http://www.esa.int/SPECIALS/Vega/SEMY64BX9WG_mg_1.html
8) Jakob Fromm Pedersen, “CubeSat Educational Payload on the Vega Maiden Flight, Interface Control Document,” ESA/ESTEC, Feb. 13, 2009, URL: http://www.ies.univ-montp2.fr/robusta/satellite/IMG/pdf/SP_GN_2009.02.13_ICD.pdf
9) “ESA’s CubeSats ready for flight,” ESA, Dec. 16, 2011, URL: http://www.esa.int/SPECIALS/Education/SEMG1C8XZVG_0.html
10) “ESA Cubs delivered for first Vega flight,” ESA, Nov. 14, 2011, URL: http://www.esa.int/esaMI/Education/SEM3L0WWVUG_0.html
11) “CubeSats satellite operations update,” ESA, March 28, 2012, URL: http://www.esa.int/SPECIALS/Education/SEM2KRGY50H_0.html
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.