FalconSat-2 is a student-built low-cost microsatellite of the USAFA (United States Air Force Academy), Colorado Springs, CO. The science objectives are to investigate F-region ionospheric plasma depletions. The educational objective is to provide hands-on experience in an exciting endeavor.
Figure 1: Illustration of the FalconSat-2 spacecraft (image credit: USAFA)
Rapid, low-cost design of FalconSat is achieved by leveraging COTS (Commercial Off-the-Shelf) hardware to the greatest extent possible. The use of COTS equipment accelerates the student involvement in satellite and mission design. In addition to the COTS hardware used, FalconSat-2 included two solar panels constructed at USAFA by cadets in addition to the two COTS solar panels. 1) 2) 3) 4) 5) 6) 7) 8)
Specifically, the spacecraft and instrument design of FalconSat-2 adopted the COTS subsystem architecture of SSTL (Surrey Satellite Technology Ltd), UK - known as SNAP (Surrey Nanosatellite Applications Program). SNAP is a satellite concept defined in terms of a flight-proven system architecture with a well-defined mechanical and electrical interface. The SNAP modules included: EPS (Electrical Power System), OBC (Onboard Computer), VHF command/data receiver (Rx), S-band data transmitter (Tx), and a SIM (System Interface Module) which provides a general-purpose digital/analog/power interface to any subsystem which does not conform to the standard SNAP power/data interface.
The structure of the FS-2 (FalconSat-2) spacecraft is a cube of 32 cm side length. The total mass is 19.5 kg, the average orbital power is 2.5 W. The primary structure consists of four identical aluminum panels as sidewalls, a baseplate and a top cover. The electronic modules are mounted around the central column walls. The battery box is mounted to the baseplate at the center of the column. The top wall houses the sensor arrays, antennas, and handling fixtures.
The subsystems include: communication consisting of the VHF uplink, S-band telemetry downlink; EPS consisting of four solar panels (single junction GaAs, 2 COTS panels, 2 built by USAFA), 7-cell battery pack (NiCAD, 4.3 Ah), a BCR (Battery Charge Regulator), and a PCM (Power Conditioning Module); C&DH (Command and Data Handling), using a CAN (Control Area Network) with microcontroller; the OBC is a StrongARM SA1100 processor, and SIM (System Integration Module).
The S/C is three-axis stabilized. The ADCS (Attitude Determination & Control Subsystem) employs a combination of Earth/sun sensors and solar panel current to determine attitude. Passive attitude control is achieved through a combination of solar-pressure spin tapes and hysteresis rods. S/C attitude is determined post-factum in ground processing.
Figure 2: Exploded view of FalconSat-2 (image credit: USAFA)
The RF communications subsystem consists of an S-band transmitter and a VHF receiver (both of SSTL). The downlink frequency is 2.22 GHz, output power of 500 mW; BPSK downlink modulation, the data rate is 38.4 kbit/s. The VHF uplink employs a monopole whip antenna. The Rx employs a CAN controller and interface; frequency of 148.015 MHz, FSK modulation, data rate of 9.6 kbit/s. USAFA operates a ground station for all data reception and transmission; also, the FS-2 monitoring and control functions are being supported at the same site.
Figure 3: FalconSat-2 is shown in the USAFA clean room (image credit: USAFA)
Launch: A launch of FS-2 took place on March 24, 2006 on a Falcon-1 vehicle of SpaceX (Space Exploration Technologies Inc., El Segundo, CA), representing the maiden flight of Falcon-1. The launch site was the “Reagan Test Site (RTS)” on Omelek Island in the Kwajalein Atoll, part of the Republic of the Marshall Islands in the Pacific Ocean - a US Military Range run by the Army (location: 9.99º N, 167.6º E).
However, the maiden flight of the Falcon-1 launch vehicle, the first privately developed and launched rocket intended to reach orbit, turned out to be a launch failure. Falcon-1 either exploded or veered off course less than one minute into its flight. Designed by SpaceX, Falcon 1 is a two stage rocket powered by liquid oxygen and purified, rocket grade kerosene. The main engine of Falcon-1, called Merlin, was the first all-new American hydrocarbon engine for an orbital booster to be flown in 40 years, and only the second new American booster engine of any kind in 25 years.
An investigation of the launch failure review board was set up by DARPA (Defense Advanced Research Projects Agency), the sponsor of the Falcon-1 inaugural flight. On July 18, 2006, the review board announced that a small aluminum nut, designed to hold the fuel pipe fitting in place, failed due to subsurface corrosion not visible to the naked eye. The resulting kerosene leak caused the main engine of Falcon-1 to catch fire shortly after the rocket cleared the launch pad, bringing the flight to a premature end. 9)
Background of FalconSat-2: FalconSat-2 was originally scheduled to launch on the Space Shuttle flight STS-114 in early 2003 - using the Hitchhiker's Palette Ejection System (PES). Unfortunately, the Columbia accident on February 1, 2003 had put the launch date on hold indefinitely. Eventually, a flight opportunity arose on the inaugural flight of the Falcon-1 launch vehicle and was taken up immediately.
Orbit: Elliptical orbit, altitude of 470 km x 650 km, inclination = 39º.
MESA (Miniature Electrostatic Analyzer)
MESA is designed and built at USAFA. The objective is to measure plasma density spectra (electron fluxes) for the study of ionospheric plasma depletions that affect GPS and other signals. A secondary goal is to qualify the MESA as a viable instrument for the measurement of thermal ionospheric electrons. A pair of MESA patch sensors and an electron RPA (Retarding Potential Analyzer) operate as a suite (in tandem) to provide in-situ sampling of ionospheric electron density and temperature along the FalconSat-2 orbit. 10) 11)
The MESA/LA (Laminated Analyzer) instrument, with a size of 5 cm x 5 cm x 0.5 cm, provides energy-resolved electron spectra in six channels ranging from 0.1 eV to 10 eV. The LA in the MESA suite of instruments is a proof-of-concept device. Its purpose is to provide flight heritage for an electrostatic analyzer configuration suitable for significant miniaturization. A key aspect of the design is that the electrostatic analyzer section is fabricated entirely of patterned conducting and insulating layers.
Figure 4: The scintillating ionosphere and measurement with MESA (image credit: USAFA)
Figure 5: Scintillations may result in significant reduction of signal to noise ratio (image credit: USAFA)
The MESA/LA instrument consists of 1,920 individual electrostatic lenses, or ESAs (Electrostatic Analyzers), in a stack of insulating and conducting sheets. The latter have been photolithographically patterned to form the electrodes of the lenses. The ESA is stacked onto a double-sided circuit board; one side of which is the current collector, while on the other side is an automatic-range-switching, dual-range linear electrometer.
MESA/LA is an energy bandpass device [(a prototype of a MEMS version); the long-term goal is the development of a true MEMS electrostatic analyzer for thermal and mildly supra-thermal charged particle]. Charged particles enter the MESA/LA device through a nominally grounded aperture, and are steered in an S-curve as they pass through an opening in a biased conducting plate. The bias on the plate determines the energy of the particles that are steered into an exit aperture in another nominally grounded plate. Offsetting the entrance and exit apertures ensure that the mapping of beam energy to plate bias is singly peaked.
The RPA, a planar gridded device, employs a known technology against which the performance of the MESA design is being compared. Each MESA/LA sensor samples the electron density over three sensor-unique energy channels (to obtain six-channel spectra) at a rate of 10 spectra/s. The RPA sweeps over a voltage range with sufficient resolution to obtain electron temperature and density at an effective rate of 1.0 measurement/s. The MESA/RPA sensors are mounted to the outside top wall of the S/C.
The primary operating mode of the MESA/RPA enables the data collection mode during the S/C eclipse phases (about 37 min/orbit). The data collection starts at 50 km (±35 km) before crossing from the dayside into the nightside orbit. The collection continues until the S/C is exposed to sunlight again. The MESA instrument collects 10 spectra/s of electron fluxes in fast mode. - The RPA measures probe current over a voltage sweep consisting of 20 steps. This results in an average data rate of 2.7 Mbit/orbit. Data compression algorithms are used to allow a nominal data downlink data of 200 kbit/orbit.
The total mass of the MESA/RPA assembly is 0.75 kg. Each MESA/RPA sensor has a a FOV of 30º.
1) C. A. Smith, “Leveraging COTS Hardware for Rapid Design and Development of Small Satellites at the USAF Academy,” 2nd Responsive Space Conference, Los Angeles, CA, April 19-22, 2004, RS2-2004-5004
2) L. Habash Krause, J. J. Sellers, C. L. Enloe, R. Humble, J. White, “A Nanosatellite Mission to Investigate Equatorial Ionospheric Plasma Depletions: The U. S. Air Force Academy's FalconSat-2,” AIAA/USU Conference on Small Satellites, Logan UT, Aug. 13-16, 2001, SSC01-VIIIa-7
3) J. Sellers, L. Sauter, C. Underwood, J. Ward, “Bounding the Problem: Microsatellite Design Using Commercial-Off-The-Self Architecture,” Proceedings of the IEEE Aerospace Conference, Big Sky, MT, March 9-16, 2002
4) J. J. Sellers, T. Lawrence, “Building a Cadre of Space Professionals:Hands-On Space Experience at the USAF Academy,” 1st Responsive Space Conference, April 1-3, 2003, Redondo Beach, CA, USA, AIAA-LA Section/SSTC 2003-1005, URL: http://www.responsivespace.com/Papers/RS1/SESSION1/SELLERS/1005P.PDF
5) M. E. B. France, T. Lawrence, W. Saylor, D. Miller, M. G. McHarg, K. Siegenthaler, J. White, “Proceedings of the 4S Symposium: `Small Satellite Systems and Services,' Chia Laguna Sardinia, Italy, Sept. 25-29, 2006, ESA SP-618
6) M. DeLorenzo, P. Van Wirt, J. J. Sellers, “Space Systems Research Center , AFOSR, Sponsored Programs Review,” Oct. 5, 2003, URL: http://usafaspace.tripod.com/other/oct03/FallReview03.pdf
7) “FalconSat Program,” USAFA, Fact Sheet, April 14, 2009, URL: http://www.usafa.af.mil/information/factsheets/factsheet.asp?id=14314
8) Cristin Anne Smith, “Leveraging COTS Hardware for Rapid Design and Development of Small Satellites at the USAF Academy,” AIAA 2nd Responsive Space Conference, April 19–22, 2004, Los Angeles, CA, USA, URL: http://www.responsivespace.com/Papers/RS2/SESSION%20PAPERS/SESSION%205/SMITH/5004P.pdf
9) B. Berger, “Board Traces Falcon 1 Failure to Broken Nut,” Space News, July 24, 2006, p. 4
10) L. Habash Krause, C. L. Enloe, R. K. Haaland, “Fast in situ Measurements of Ionospheric Plasma with the Miniature Electrostatic Analyzer (MESA): An Experiment Aboard FalconSat-2,” Proceedings of the IEEE Aerospace Conference, Big Sky, MT, March 9-16, 2002
11) L. Habash Krause, C. L. Enloe, R. K. Haaland, P. Golando, “Microsatellite missions to conduct midlatitude studies of equatorial ionospheric plasma bubbles,” Advances in Space Research, Vol. 36, Issue 12, 2005, pp. 2474-2479
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.