Minimize NPSat-1

NPSat-1 (Naval Postgraduate School Satellite-1)

Spacecraft     Launch    Mission Status     Sensor Complement    References

NPSat-1 is a low-cost technology demonstration microsatellite developed by the students and faculty of the Naval Postgraduate School, Monterey, CA (a follow-on project to PANSAT with a launch in Oct. 1998 on Shuttle flight STS-95). The overall mission objectives of NPSat-1 are: 1) 2) 3) 4)

• To provide hands-on education in space systems for NPS students

• To demonstrate COTS technology in a spacecraft architecture as a means of decreasing development time, and increasing reliability in software development

• To provide a more capable platform for spaceflight experiments.


Figure 1: Various views of the NPSat-1 spacecraft (image credit: NPS)


The NPSat-1 configuration consists of a 12-sided cylinder with body-mounted solar cells on all cylinder sides. The structure employs an aluminum frame and side panels (there are three equipment decks). The spacecraft is three-axis stabilized. The ACS (Attitude Control Subsystem) uses a 3-axis magnetometer and a solar panel current algorithm for attitude sensing. MEMS-based rate gyroscope assembly: this COTS-based device provides rate data in three axes; accuracy range of ±5º/s; power consumption of < 80 mA at ±5 V for each gyro. The device is being used during acquisition periods. Actuation is provided by three magnetorquers. Nominally, the spacecraft is nadir-pointing. 5) 6)

The electrical power subsystem (EPS) employs triple-junction solar cells and Li-ion polymer batteries. The battery is composed of 49 Sony US18650S Li-ion cells (capacity of 225 Whr with a full charge voltage of 29.4 V). A non-volatile ferroelectric RAM (FRAM) COTS configuration memory system of 8 kByte is part of the EPS.


Figure 2: Photo of the Li-ion battery (image credit: NPS)

Demonstration of a COTS-based C&DH (Command & Data Handling) subsystem, using the PC/104-compliant ISA (Industry Standard Architecture) bus hardware and a POSIX-compliant operating system, namely Linux [distributed processing architecture, each subsystem has its own processor except RFS (Radio Frequency Subsystem)]. The C&DH features also EDAC (Error Detection And Correction)) as well as a hibernation mode to save power.

The C&DH motherboard uses a Sharp LH79520 ARM microprocessor operating at 51 MHz. The motherboard also contains a Xilinx XCV100 field programmable gate array (FPGA). Essentially nearly all of the ARM signals interface to the FPGA. This allows complete manipulation of microprocessor signals between other devices within the C&DH which can be modified via software reconfigurations during development.

The S/C size is 50 cm in diameter and 93 cm in height, the mass is 86 kg. A mission life of two years (min) is projected.


Figure 3: Block diagram of the NPSat-1 spacecraft (image credit: NPS)


Figure 4: Illustration of the NPSat-1 spacecraft (image credit: NPS)

RF communications: S-band full duplex system with asynchronous GMSK modulation; downlink at 2.207 GHz, data rate of 100 kbit/s in both directions, uplink frequency at 1.767 GHz. The NPSat-1 ground station is located at NPS for support of the TT&C function and spacecraft monitoring and control, using a single PC.


Figure 5: Expanded view of the NPSat-1 spacecraft configuration (image credit: NPS)

Development status

• March 23, 2016: Students and faculty at the Naval Postgraduate School’s (NPS) Space Systems Academic Group (SSAG) are tentatively scheduled to launch a 3-foot, 180-pound satellite dubbed NPSAT 1, as part of the next DOD Space Test Program (STP) mission onboard a SpaceX Falcon Heavy rocket from the Cape Canaveral Space Center, Sept. 15, 2016. The satellite is the product of years of student and faculty research and will carry several experiments from both NPS and the Naval Research Laboratory into orbit. 7)


Figure 6: Space Systems Academic Group Chair Dr. Rudy Panholzer, left, and Research Associate Dan Sakoda stand near one of several structural pieces to NPSAT-1 in the university’s clean room in Bullard Hall, Jan. 11. The satellite is the product of years of student and faculty research and will carry several experiments from both NPS and the Naval Research Laboratory into orbit when it launches later this year (image credit: NPS, Kenneth A. Stewart)

- The primary motivation behind the building of NPSAT-1 was education. Some 40 theses and many hours of student and faculty research contributed to the development of the satellite.

- “We are not here to build satellites, but the satellite is a nice byproduct of the educational process ... We designed it, built it and are testing it in house. We also developed the lab around it, and developed the curriculum that led to its completion,” said SSAG Chair Dr. Rudy Panholzer, a 52-year veteran of the university who has been helping guide students through the many theses that culminated in NPSAT-1 since the program’s inception.

- A key component to any mission in space is the advancement of science, and NPSAT-1 provides university students and faculty with a unique platform on which they can conduct science and engineering experiments.

• June 2019: The long wait finally came to an end for faculty and researchers in the Naval Postgraduate School’s (NPS) Space Systems Academic Group (SSAG).


Figure 7: Photo of Ronald Phelps (left) and Daniel Sakoda (lead engineer of NPSat-1) with the NPSat-1 spacecraft above their heads in the integration hall of SpaceX (image credit: SpaceX)

Launch: NPSat-1 of NPS is a secondary payload on the STP-2 rideshare mission of USAF, launched on 25 June 2019 (06:30 UTC) aboard a SpaceX Falcon Heavy launch vehicle from Launch Complex 39A at NASA’s Kennedy Space Center. The STP-2 payload includes six FormoSat-7/COSMIC-2 satellites (primary payload, each with a mass of 280 kg), developed by NOAA and Taiwan’s National Space Organization to collect GPS radio occultation data for weather forecasting. The STP-2 mission is led by the Air Force Space Command’s Space and Missile Systems Center (SMC). The total IPS (Integrated Payload Stack) has a mass of 3700 kg. 8) 9) 10) 11)

Orbit: NPSat-1 was deployed into a sun-synchronous circular orbit of 720 km with an inclination of 24º.

NPSat-1 had to sustain a very long wait to be launched. Initially, NPSat-1 was to be launched in 2007 on the STP-1 mission. Finally, NPSAT-1 was manifested on the STP-2 mission in 2017 on a Falcon-Heavy (Block 5) rocket.

The overall objective of the STP-2 mission is to demonstrate the performance of the Falcon Heavy launch vehicle. That includes the multi-burn profile for the rocket’s upper stage as well as the reuse of side boosters that first flew on the previously Falcon Heavy mission, launching the Arabsat-6A satellite in April. The goal of SpaceX is to demonstrate the capabilities of the SpaceX Falcon Heavy launch vehicle and provide critical data supporting certification for future National Security Space Launch (NSSL) missions.

The Air Force agreed to use the side boosters from the Arabsat 6A mission to familiarize military officials with SpaceX’s process of recovering and refurbishing rocket hardware. It is the first time the Air Force has used previously-flown hardware on a military satellite launch.

“STP-2 is the government’s first launch on a SpaceX Falcon Heavy vehicle, and is one of the most challenging missions the Space and Missile Systems Center has ever launched,” said Col. Robert Bongiovi, director of SMC’s launch enterprise systems directorate. “We’re putting 24 research and development satellites into three separate orbits, with a first-ever four engine start and burn of the second stage.”

“The use of the previously-flown hardware is providing critical insight into reusability and quality assurance that will allow us to provide space access to the warfighter in a more cost-effective and expedient manner, and I really appreciate the efforts of our industry partner SpaceX to make this happen,” Bongiovi said Friday in a briefing with reporters.

“The plan is to recover all three cores, two coming back to land and one out on the drone ship,” Lauderdale said Friday. “SpaceX is looking for this opportunity to demonstrate this capability (for) continued reuse. We’re excited to be part of that journey.”


Figure 8: The STP-2 mission’s multi-satellite stack before encapsulation inside the Falcon Heavy’s payload fairing (image credit: SpaceX)

The secondary payloads on this flight are:

• DSX (Demonstration and Science Experiments) mission of AFRL. The payload consists of four small technology demonstrations (600 kg) to study how spacecraft electronics respond to space radiation. DSX is to be delivered into an elliptical MEO (6-12,000 km altitude).

• GPIM (Green Propellant Infusion Mission), a demonstration minisatellite of NASA (~180 kg). 12)

• FalconSat-7, a 3U CubeSat mission developed by the Cadets of the U.S. Air Force Academy (USAFA) at Colorado Springs, CO.

• NPSat-1 (Naval Postgraduate School Satellite-1) of the Naval Postgraduate School, Monterey, CA. A microsatellite of 86 kg.

• OCULUS-ASR (OCULUS-Attitude and Shape Recognition), a microsatellite (70 kg) of MTU (Michigan Technological University), Houghton, MI, USA.

• Prox-1, a microsatellite (71 kg) of SSDL (Space Systems Design Laboratory) at Georgia Tech.

• LightSail-2 of the Planetary Society, a nanosatellite (3U CubeSat, 5 kg) will be deployed from the parent satellite Prox-1.

• ARMADILLO of UTA (University of Texas at Austin), a nanosatellite (3U CubeSat) of ~ 4 kg.

• E-TBEx (Enhanced Tandem Beacon Experiment), a tandem pair (3U CubeSats) of SRI International.

• TEPCE (Tether Electrodynamics Propulsion CubeSat Experiment), a 3U CubeSat (3 kg) of NPS (Naval Postgraduate School).

• CP-9 , a joint CP-9/StangSat experiment, which is a collaboration between PolySat at Cal Poly and the Merritt Island High School, and is sponsored by the NASA LSP (Launch Services Program). CP-9 is a 2U CubeSat while StangSat is a 1U CubeSat.

• PSat-2 (ParkinsonSat-2), a student built 1.5U CubeSat of USNA (US Naval Academy) with a mass of 2 kg.

• BRICSAT-2, a student built 1.5U CubeSat of USNA (US Naval Academy) to demonstrate a µCAT electric propulsion system and carry a ham radio payload.

• OTB-1 (Orbital Test Bed-1) a minisatellite built by SSTL (based on the SSTL-150 bus, 138 kg) and owned by General Atomics' Electromagnetic Systems Group (GA-EMS) of San Diego. One of the hosted payloads is NASA's DSAC (Deep Space Atomic Clock), a technology demonstration mission with the goal to validate a miniaturized, ultra-precise mercury-ion atomic clock that is 100 times more stable than today’s best navigation clocks.

• Ballast: Required in original mission contract to be delivered into MEO (6-12,000 km altitude); mass (< 5000 kg) and composition currently unknown.

Mission status

• NPSat-1 was deployed 1 hour and 22 minutes after launch into a circular orbit of 720 km. Ground operators at NPS (Naval Postgraduate School) in Monterey, California were able to command the spacecraft for initial telemetry downloads and were able to verify that the spacecraft was transmitting. Although, the signal could be detected, the signal strength was too week for data to be decoded. A successful packet of data was demodulated by spacecraft operators at NPS on 27 June 2019 (Ref. 11).

Sensor/payload complement: (SMS, CERTO/Langmuir Probe, CFTP, VISIM)

SMS (Solar cell Measurement System). SMS is a flight demonstration experiment of NPS. The objective is to measure the current and voltage characteristics of the solar cells under varies aspect angles to the sun to generate voltage-current (IV) curve traces twice per orbit. The test set is comprised of 22 triple-junction cells [Boeing Spectrolab product, ITJ (Improved Triple Junction) on a Ge wafer], and two commercial dual-junction control cells, positioned around the body of the spacecraft at various locations. The SMS is comprised of three subsystems: a) the analog cell measurement circuitry, b) the data converters, and c) the microcontroller. The microcontroller contains an FPGA which interfaces with the analog circuitry. The FPGA functionality includes data converters, registers for data storage and decode logic for the controller memory and interrupts. SMS is a radiation-hardened system; in addition, the data converters in the FPGA are designed to be TMR (Triple Modular Redundant) so to increase SEU (Single Event Upset) tolerance induced by radiation. The analog circuit design uses an n-channel MOSFET transistor, amplifier and tolerance resistor to create the voltage-controlled current sink. 13)

CERTO/Langmuir Probe (Coherent Electromagnetic Radio Tomography) of NRL (Naval Research Laboratory), both instruments are mounted on a deployable boom, respectively. CERTO is of ARGOS (Advanced Research and Global Observation Satellite) heritage (launch Feb. 23, 1999), a DoD research mission. The objective is to observe ionospheric densities and irregularities. The experiment consists of a three-frequency radio beacon (150, 400 and 1067 MHz) and radiating antenna mounted on the S/C. The space-based beacon system, in conjunction with a network of ground-based receivers, use differential phase techniques to derive the integrated electron density in the plane of observation. CERTO data analysis permits an impact assessment on navigational accuracy, communication systems, and remote sensing by radar. The Langmuir probe augments the CERTO data by providing on-orbit in-situ measurements. The CERTO/Langmuir Probe observation data is being used for ionospheric model updates with direct applications to such fields as communications, radar, navigation, and surveillance. 14)

CFTP (Configurable Fault-Tolerant Processor), an NPS module and fault-tolerant experiment. The objective is a demonstration of reconfigurable applications support. The configurable aspect allows in-flight upgrades to the processor configuration. The experiment consists of two Xilinx XCV600 FPGA devices. Each FPGA is capable of implementing a stand-alone processing unit, housed within the C&DH. It interfaces with the ARM processor via the 16-bit PC/104 bus for power and digital control and data. Upon reset, the CFTP automatically configures its master FPGA to implement a PC/104 controller. Indirectly, the master XCV600 device can be programmed from the ARM via the JTAG (Joint Test Action Group) interface. This JTAG manipulation allows the master device to be reprogrammed from its original configuration. The master device is capable of orchestrating reconfigurations of the second FPGA. Several application scenarios are defined (two examples): 15)

• The board is configured to act as a TMR (Triple-Modular Redundant) computer such that within FPGA, the three core processors operate in-step. Single event effects (SEE) within the processing are detected and corrected through voting logic without the need to reboot the processor. Since NPSat-1's orbit is in a relatively radiation-benign orbit, CFTP operations for the TMR configuration will focus on recording SEEs near the SAA (South Atlantic Anomaly).

• Implementation of a hardware compression engine. This implementation considers the production of JPEG imagery of the VISIM data.


Figure 9: Block diagram of the CFTP assembly (image credit: NPS)

VISIM (Visible Wavelength Imager) of NPS. A COTS-based CCD camera operated on a single-board computer; the CCD controller is a PC/104 CPU board. The CCD detector (Electrim EDC-1000E) provides 8-bit color (each) RGB Bayer pattern; the array has a size is 652 x 492 pixels with pixel sizes of 7.4 µm. A FOV of 20º x 30º is provided which translates to a ground imagery size of 200 km x 150 km at nadir (resolution of < 1 km). An initial VISIM task is to take images of the launch and deployment sequence. The snapshot imagery may be downlinked in compressed or uncompressed state.

1) D. Sakoda, J. A. Horning, S. D. Moseley, “Naval Postgraduate School NPSat-1 Small Satellite,” Small Satellite Systems and Services, Proceedings of the 4S Symposium, Chia Laguna Sardinia, Italy, Sept. 25-29, 2006, (ESA SP-625, November 2006)

2) D. Sakoda, J. A. Horning, “Overview of the NPS Spacecraft Architecture and Technology Demonstration Satellite, NPSat-1,” Proceedings of the AIAA/USU Conference on Small Satellites, Logan, UT, USA, Aug. 12-15, 2002, SSC02-I-4, URL:

3) B. S. Leonard, “NPSat1 Magnetic Attitude Control System,” Proceedings of the AIAA/USU Conference on Small Satellites, Logan, UT, USA, Aug. 12-15, 2002

4) G. Prater, D. Sakoda, A. Grant, “Overview of the Naval Postgraduate School Small Satellite, NPSat1,” 22nd AIAA International Communications Satellite Systems Conference & Exhibit, May 9-12, 2004, Monterey, CA

5) Daniel Sakoda, Ronald Phelps, Bryce Donavan, “Report of NPSAT1 battery thermal contact resistance testing, modeling and simulation,” NPS, October, 2012, URL:

6) Veronica V. Badescu, “NPSat1 MEMS 3-Axis Rate Sensor Suite Performance, Characterization, and Flight Unit Acctepance Testing,” Thesis, NPS, Sept. 2011, URL:

7) ”NPS’ Newest Satellite Prepared for Launch,” NPS, 23 March 2016, URL:

8) Stephen Clark, ”Falcon Heavy launches on military-led rideshare mission, boat catches fairing,” Spaceflight Now, 25 June 2019, URL:

9) ”NASA Technology Missions Launch on SpaceX Falcon Heavy,” NASA Release 19-049, 25 June 2019, URL:

10) ”STP-2 Mission,” SpaceX, URL:

11) ”Naval Postgraduate School NPSAT1 Spacecraft,” NPS, URL:

12) “GPIM Spacecraft to Validate Use of 'Green' Propellant,” NASA, Aug. 19, 2014, URL:

13) J. B. Salmon, R. Phelps, S. Michael, H. Loomis, “Solar Cell Measurement System for NPS Spacecraft Architecture and Technology Demonstration Satellite, NPSat1,” Proceedings of the AIAA/USU Conference on Small Satellites, Logan, UT, USA, Aug. 11-14, 2003, SSC03-X-4, URL:

14) C. L. Siefring, P. A. Bernhardt, C. Selcher, M. R. Wilkens, M. G. McHarg, L. Krause, F. Chun, L. Enloe, R. Panholzer, D. Sakoda, R. Phelps, D. Roussel-Dupre, P. Colestock, S. Close, “Integrated Multi-Point Space Plasma Measurements With Four Ionospheric Satellites,” American Geophysical Union, Fall Meeting 2006, San Francisco, CA, USA, Dec. 11-15, 2006

15) D. A. Ebert, C. A. Hulme, H. H. Loomis, A. A. Ross, “Configurable Fault-Tolerant Processor (CFTP) for Space Based Applications,” Proceedings of the AIAA/USU Conference on Small Satellites, Logan, UT, USA, Aug. 11-14, 2003, SSC03-XI-5, URL:

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 (

Spacecraft    Launch    Mission Status    Sensor Complement    Ground Segment    References    Back to top