Xatcobeo CubeSat mission
The Xatcobeo CubeSat technology demonstration mission is a collaborative effort between the University of Vigo (with a campus at Vigo, Ourense and Pontevedra, Spain) and INTA (National Institute for Aerospace Technology), Madrid, Spain. The project is being realized with a multi-disciplinary team of students. Faculty members from Vigo and Ourense are on the team and supervising the project. Technical and management support is provided from INTA. The Xatcobeo project was initiated in response to an ESA AO (Announcement of Opportunity) in 2007 on the maiden flight of the Vega launch vehicle.
• Verification of a new system for measuring the amount of ionizing radiation (RDS)
• Development of a new SRAD (Software-defined Reconfigurable Radio) system
• Experimental solar PDM (Panel Deployment Mechanism) system
• Students' education and experience.
Background of the name Xatcobeo: Ano Santo Xacobeo in the Galician language (or Año Santo Jacobeo in Spanish) is the so-called holy year of St. James. It takes place in the year whenever the 25th of July (feast day of St. James the Apostle) is a Sunday. This happens within a fixed period of 6, 5, 6, and 11 years, which implies that there are 14 Años Santos Jacobeos in a century. 4)
During the St. James holy year, the catholics can get the “bula jubilar” or jubileo (jubilee indulgence) when visiting the cathedral of Santiago de Compostela in Galicia, Spain, where St. James the Apostle, is buried. Obviously, any “Ano Santo Xacobeo” is a special event for all the pellegrini (pilgrims) hiking on the “Camino de Santiago,” the most famous pilgrimage route in Europe. Millions of pilgrims participate in such events hiking long distances from all over Europe.
A long tradition (almost 900 years) goes along with the Ano Santo Xacobeo. The first Año Jubilar or Jubilee Year was granted by Pope Calixtus II, it took place in the year 1126. The most recent Jubilee Years were in 1993, 1999 and 2004. The next ones will be in 2010 and 2021.
The city of Vigo is located in the southwest corner of Galacia (Spain) just north of the border to Portugal and about 70 km south of Santiago de Compostela. The CubeSat project of the University of Vigo modified the famous name of Xacobeo somewhat in order to phonetically have similarity with “SAT” .... and finally came out with the name: XATCOBEO or Xatcobeo for the first CubeSat mission of the university.
Figure 1: Illustration of the Xatcobeo CubeSat (image credit: University of Vigo)
The Xatcobeo spacecraft complies to the CubeSat standard of 10 cm side length and a mass of ≤ 1 kg. The CubeSat structure is based on Pumpkin's CubeSat kit.
An ADCS (Attitude Determination and Control Subsystem) is not needed due to the absence of any pointing requirements for the mission. The mass saving is used for the extra shielding needed in the higher elliptical orbit.
The OBDH (On-Board Data Handling) subsystem is a distributed system consisting of an OBC (On-Boar Computer) based on a Virtex-II FPGA, and OBPIC (On-Board Programmable Interface Controller) used to regulate the payload power and to condition the bus system. The onboard data are communicated via I2C bus.
Figure 2: Illustration of the OBDH (image credit: University of Vigo)
EPS (Electrical Power Subsystem) is provided by Clyde Space (UK) providing ~ 3 W of power from triple-junction solar cells. The solar cells are provided by Spectrolab and are referred to as UTJ (Ultra Triple Junction). The Li-ion battery has a capacity of 1250 mAh.
RF communications: Use of UHF (437 MHz) bands with transmissions in the the downlink and VHF (145 MHz) in the uplink. Use of a TNC (Terminal Node Controller) and 4 monopole (turnstile) antennas with omnidirectional radiation capability. The transponder works in half-duplex fashion using Manchester pulses (SP-L) for the downlink, and a phase with data subcarrier (PM/PBSK) for the uplink. Use of the CCSDS protocols for frame and channel coding. A data rate of 1.2 kbit/s is used in the downlink (although the system can provide up to 9.6 kbit/s).
Figure 3: Photo of the Xatcobeo CubeSat (image credit: University of Vigo, INTA)
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. 7)
Use of P-POD (Poly Picosat Orbital Deployer) for the deployment of all CubeSats. The expected lifetime of Xatcobeo is 6 months to 1 year.
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. 8). 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.
ALMASat, a microsatellite of the University of Bologna, is another secondary payload of the flight.
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 mission:
• March 2012: Xatcobeo is sending back regular telemetry data to its ground station at University of Vigo, Spain, even though its operations are disturbed by unexpected tumbling. The spacecraft is nearing completion of its commissioning phase, with all systems performing well. The communications link is expected to improve once the spacecraft slows its spinning rate. 10)
• First signals of Xatcobeo were received a few hours after launch during its first pass over the University of Vigo’s ground station, and its signal was also tracked by many radio amateurs. The data showed that the satellite’s batteries were properly charged and that telemetry and telecommand systems worked well. 11)
Experiment compliment: (SRAD, PDM, RDS)
SRAD (Software-defined Reconfigurable Radio):
The objective of SRAD is to demonstrate and evaluate a reconfigurable and programmable logic device on flight.
Figure 4: Functional block diagram of SRAD (image credit: University of Vigo)
PDM ( Panel Deployment Mechanism):
Power is the prime resource for any CubeSat mission; it is normally available in very limited power budgets. Hence, a reliable panel deployment mechanism could relief future CubeSat operations in providing improved power capacities to upgrade the general functionality of the system. The goal of Xatcobeo mission is to space-qualify the PDM. 12)
PDM is a payload consisting of two sets of deployable solar panels:
- Single panel deployment
- Double panel unfolding.
The first deployment mechanism is common for both sets. In the double mechanism, another mechanism is added to allow the unfolding of an extra panel. The design of the PDM is based on the following goals:
• To ensure a packed maximum envelope of 6.5 mm from the structure in stowed configuration
• To allow an easy integration in the structure of Xatcobeo. It is intended to pack with the lateral shear panel of Xatcobeo to integrate it as a single unit.
• To minimize mass of deployable parts.
The toughest requirement for the solar array deployment in the Xatcobeo mission is the necessity to fit all the systems into an envelope of 6.5 mm from the lateral plate of satellite to avoid interference with the satellite deployer. With this limitation it is possible to fit:
• One lateral aluminum shear panel, one board is fixed to the panel holding the solar cells, and one movable panel with cells in both faces over a 1.6 mm board
• One lateral aluminum shear panel, one board is fixed to the panel holding the solar cells, and two movable panels with cells on both faces over 0.8 mm boards.
Both options have been used in the Xatcobeo PDM design.
The PDM mechanism consists of two sets of deployable solar panels. In the first one, only one panel is deployed (PDM1) and the second is a double unfolding (PDM2).
Figure 5: Illustration of the sub-chassis (left) and the PDM built into the Xatcobeo CubeSat (image credit: INTA, University of Vigo)
A deployment system with a mass of 45 grams using boards of 1.6 mm thickness was completed; it is also it’s possible to obtain a double deployment with 55 grams using 0.8 mm boards (however, the mass restrictions do not permit this solution). The final design utilizes a system in a 6.5 mm envelope protruding from the satellite and allowing easy integration in the very tight space available.
A flat spring retention system has been designed to avoid in flight induced micro vibrations and act as an additional blocking system. The flat spring used should be the one that produces the greater lateral force to induce damping in the movement, but not too thick to provoke plastic deformation in the bended area. The selection of springs for PDM1 and PDM2 leads to look for springs with small stiffness: more wire turns, less wire diameter, higher spring diameter and to use only one spring.
Figure 6: Illustration of the PDM scheme (image credit: University of Vigo)
RDS (Radiation Dose Sensor):
The RDS is an INTA provided device developed in the INTA Electronics Design Laboratory. RDS is an upgrade version of the ODM (OPTOS Dose Measurement) payload developed for the OPTOS nanosatellite mission of INTA (launch planned for spring 2010). The RDS sensors are being provided by CNRS/LAAS (Laboratory for Analysis and Architecture of Systems) of Toulouse, France. The objectives of RDS are to measure TID (Total Ionizing Dose) of the incoming radiation to improve the current space environment models.
Figure 7: Functional block diagram of RDS (image credit: University of Vigo)
1) Fernando Aguado-Agelet, “Xatcobeo,” 2008 Cubesat Summer Developer’s Workshop, August 9-10, 2008, Logan, UT, USA, URL: http://mstl.atl.calpoly.edu/.../University_of_Vigo.pdf
3) Fernando Aguado, Ricardo Tubío, Javier Comesaña, Jorge Iglesias, César Martínez, Fany Sarmiento, “Xatcobeo,” 2009 CubeSat Developers' Workshop, San Luis Obispo, CA, USA, April 22-25, 2009, URL: http://mstl.atl.calpoly.edu/~bklofas/Presentations/DevelopersWorkshop2009/10_Missions_2/3_Aguado-Xatcobeo.pdf
4) “El Camino de Santiago, Xacobeo 2010 - Jacobeo 2010,” URL: http://www.caminosantiagodecompostela.com/jacobeo2010.html
5) “ESA’s new Vega launcher scores success on maiden flight,” ESA, Feb. 13, 2012, URL: http://www.esa.int/SPECIALS/Vega/SEMJ8LYXHYG_0.html
6) “Vega VV01 launch campaign,” ESA, URL: http://www.esa.int/SPECIALS/Vega/SEMY64BX9WG_mg_1.html
7) 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
8) “ESA’s CubeSats ready for flight,” ESA, Dec. 16, 2011, URL: http://www.esa.int/SPECIALS/Education/SEMG1C8XZVG_0.html
9) “ESA Cubs delivered for first Vega flight,” ESA, Nov. 14, 2011, URL: http://www.esa.int/esaMI/Education/SEM3L0WWVUG_0.html
10) “CubeSats satellite operations update,” ESA, March 28, 2012, URL: http://www.esa.int/SPECIALS/Education/SEM2KRGY50H_0.html
11) “Student CubeSats start talking to Earth,” ESA, Feb. 14, 2012, URL: http://www.esa.int/SPECIALS/Education/SEMR2ZYXHYG_0.html
12) Jose Miguel Encinas Plaza, Jose Antonio Vilán Vilán, Fernando Aguado Agelet, Javier Barandiarán, Mancheño, Miguel López Estévez, Cesar Martínez Fernández, Fany Sarmiento Ares, “Xatcobeo: Small Mechanisms for CubeSat Satellites – Antenna and Solar Array Deployment,” Proceedings of the 40th Aerospace Mechanisms Symposium, NASA Kennedy Space Center, May 12-14, 2010, URL: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100021944_2010023813.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.