STP-S26 (Space Test Program-S26)
STP-S26 is a USAF (United States Air Force) mission within the DoD STP (Space Test Program) managed at the Space Development and Test Wing (SDTW), Kirtland Air Force Base, NM, USA. The mission was designated “S26” to correspond to the 26th small launch vehicle mission in STP's 40+year history of flying DoD space experiments.
STP-S26 extends previous standard interface development efforts, implementing a number of capabilities aimed at enabling responsive access to space for small experimental satellites and payloads. The STP-S26 Minotaur-IV launch vehicle is configured in a Multi-Payload Adaptor configuration which includes the following features: 1) 2)
• MPA (Multi-Payload Adaptor), which was developed by Orbital Sciences Corporation for STP to launch up to four ESPA-class satellites on the Minotaur-IV.
• Provisions for the inclusion of up to four P-PODs (Poly-Picosat Orbital Deployers) to be mounted on the stage 4 avionics cylinder.
• A dual orbit capability provided by the HAPS (Hydrazine Auxiliary Propulsion System). The design provides volume and mass for four additional payloads attached to the HAPS avionics cylinder.
The mission will launch four ESPA-class satellites, manifested on the MPA, and three cubesats into LEO (Low Earth Orbit). One of the four ESPA [EELV (Evolved Expendable Launch Vehicle) Secondary Payload Adapter] satellites is STPSat-2, the primary payload of STP-S26, representing the first STP-SIV (Space Test Program-Standard Interface Vehicle) mission.
STP implemented a flexible, responsive “dual path” process for a late satellite manifest change. The goal is to delay the final manifest decision as late as possible while minimizing risk. 3)
Figure 1: Schematic view of the fully loaded ESPA stack (image credit: AFRL)
Launch: STP-S26 was launched on Nov. 20, 2010 (UTC) on a Minotaur-IV expandable launch vehicle of OSC (Orbital Sciences Corporation) with HAPS (Hydrazine Auxiliary Propulsion System) capability. The launch site was KLC (Kodiak Launch Complex) on Kodiak Island, Alaska under a contract with AAC (Alaska Aerospace Corporation). The primary payload on the STP-S26 mission was STPSat-2, the first spacecraft in the DoD STP-SIV ( Space Test Program-Standard Interface Vehicle) program managed by the Space Development and Test Wing at Kirtland Air Force Base, Albuquerque, N.M. 4) 5) 6) 7)
This launch is also the result of an NSF (National Science Foundation) program, the objective is to develop and fly CubeSat-based science missions for space weather and atmospheric research.
The STP-S26 mission demonstrated a new capability for Minotaur-IV, called MPP (Multiple Payload Platform). The MPP enables the deployment of up to 12 small satellites, consisting of four ESPA-class satellites, four smaller secondary satellites (up to 11 cubic feet each), and four P-POD carriers.
The following secondary payloads were part of the STP-S26 mission (all secondary payloads are documented in a separate file on the eoPortal):
• FalconSat-5 of USAFA (US Air Force Academy) at Colorado Springs, CO. FalconSat-5 has a mass of 161 kg.
• FASTSat-HSV (Fast, Affordable, Science and Technology Satellite-Huntsville), AL Corporation, developed by NASA/MSFC, VCSI (Von Braun Center for Science and Innovation), and Dynetics. FASTSat will be flying a total of six instruments, three of NASA and three of DoD The mass of FASTSat is 180 kg.
• O/OREOS (Organism/ORganic Exposure to Orbital Stresses), a NASA/ARC nanosatellite mission of 5.2 kg mass (triple CubeSat). 8)
• FASTRAC-1, -2, a nanosatellite pair of UTA (University of Texas, Austin) with a total mass of 54 kg.
• RAX (Radio Aurora Explorer), a triple CubeSat mission (3 kg) of NSF (National Science Foundation) - a CubeSat-based Ground-to-Space Bistatic Radar Experiment — Radio Aurora Explorer, developed by a team comprised of University of Michigan at Ann Arbor, MI and SRI International, Menlo Park, CA.
Orbit: Circular orbit, altitude = 650 km, inclination = 72º, with an orbital period of 97.7 minutes.
The STP-S26 mission delivered four ESPA-class satellites and two nanosatellites to a 650 km circular orbit at 72º inclination. The HAPS (Hydrazine Auxiliary Propulsion System) delivered two ballast masses to a secondary orbit as high as possible with a goal of 1200 km (circular), demonstrating the dual orbit capability of the Minotaur IV launch vehicle.
The ESPA-class satellites attach to the launch vehicle via the MPP (Multiple Payload Platform) and deployed using the PSC (Planetary Systems Corporation) Mark II Motorized Lightbands (MLB). The two cubesats deployed from P-PODs (Poly-Picosatellite Orbital Deployers) attached to the either side of the Stage 4 Orion-38 motor.
Figure 2: Illustration of the deployed motorized lightband (image credit: AFRL, Ref. 6)
• As the primary spacecraft on the S26 mission, STPSat-2 deploys first to minimize its risk of collision with other spacecraft.
• After one full orbit, the spacecraft must be > 800 m apart.
• The spacecraft must deploy in order of the highest to the lowest ΔV in each direction, to ensure they would continue to move away from each other throughout their orbits.
Examining the deployment sequence meeting all ground rules lead the S26 program office to select the following deployment sequence, where +V indicates the direction of launch vehicle motion (see Figure 3):
1) STPSat-2 in the +V direction
2) RAX in the –V direction
3) O/OREOS in the –V direction
4) FASTSat-HSV (including NanoSail-D2) in the -V direction
5) FalconSat-5 in the –V direction
6) FASTRAC (2 nanosatellites) in the –V direction.
This separation order is keeping approximately 0.05 m/s ΔV difference between any pair of spacecraft to ensure all spacecraft will be at least 800 m apart after one full orbit.
Legend to Figure 4: STPSat-2 (left most), FASTRAC-1/-2 (front), FalconSat-5 (right most), and FASTSat (back) are visible in this image.
Figure 5: Mission profile of STP-S26 (image credit: AFRL, Ref. 6)
The STP-S26 deployments were successful in the sense that the satellites continued to separate from one another after deployment. TLEs (Two Line Element) sets for each of the spacecraft a few days following the deployments were used to determine the relative drift rate between the satellites and from this the difference in their deployment ΔVs. However, there was a wider than expected difference in the ΔVs of consecutive deployments (Ref. 6).
STP-SIV (Space Test Program - Standard Interface Vehicle)
A fundamental goal of the DoD Space Test Program Standard Interface Vehicle (STP-SIV) is to enable more responsive and reliable access to space for small payloads. The objective of the STP-SIV concept is to utilize standardized interfaces between the spacecraft bus and payload as well as between the complete space vehicle and launch vehicle. Standardized interfaces encourage repeatable development and integration processes and enable staff to preserve and utilize lessons learned. A key aspect of this approach is a reusable spacecraft bus design which increases the return on investment in nonrecurring engineering and allows for shared ground support equipment between vehicles. A repeated spacecraft bus design also facilitates uniform quality control standards and offers leverage for bulk hardware purchase savings.
Standardization of the spacecraft-to-launch-vehicle interface is achieved by constraining interface features to allow for repeatable design and testing across missions. The STP-SIV overall mass and volume is constrained to 180 kg and an envelope of 60.9 cm x 71.1 cm x 96.5 cm to permit launches on an ESPA (EELV Secondary Payload Adapter), shown in Figure 6, and small launch vehicles including Pegasus and Minotaur class vehicles. 9)
Figure 6: Concept drawing of the ESPA secondary payload envelope (image credit: AFRL)
In 2006, BATC (Ball Aerospace Technology Company) of Boulder, CO, and Comtech AeroAstro of Ashburn, VA, were given a contract to build up to six small standard satellites for SMC/TEL (Space and Missile Systems Center / Space and Missile Test Evaluation Directorate) at Kirtland Air Force Base, Albuquerque, NM.
In this arrangement, Comtech AeroAstro is responsible for supplying the spacecraft bus as well as providing integration, launch and mission operation support. As prime contractor, BATC is responsible for the overall system including the standard payload interface design, payload integration, space vehicle environmental testing, and launch and mission support. 10) 11) 12)
STP-SIV missions are considered ideal for scientific, technology development, and risk reduction payloads. Each vehicle accommodates up to four independent payloads, is designed to operate over a wide range of LEO orbits, and is compatible with a variety of small launch vehicles. The potential to share the spacecraft and launch provides an opportunity for the cost effective access to space for a variety of payloads. 13) 14) 15)
Table 1: Overview of requirements envelope for the STP-SIV bus concept
The SDTW (Space Development & Test Wing) of SMC (Space and Missile Systems Center) is the entity that “develops, tests, and evaluates the Air Force space systems, executes advanced space development and demonstration projects, and rapidly transitions capabilities to the warfighter". SDTW is the operator of such missions as: STPSat-1, Orbital Express, TacSat-2, and NASA's CloudSat. 16) 17) 18)
In Oct. 2007, the CDR (Critical Design Review) was completed. On Jan. 7, 2009, CAA (Comtech AeroAstro Inc.) delivered the first STP-SIV spacecraft bus to BATC.
In Oct. 2009, BATC has successfully completed a comprehensive pre-shipment review for STPSat-2. 19)
Figure 7: Standard bus concept of STPSat-2 (STP-SIV), image credit: Comtec AeroAstro Inc. (Ref. 13)
Figure 8: Conceptual view of the basic STP-SIV spacecraft design (image credit: SDTW, BATC, AeroAstro)
STP-SIV defines a standard in the sense of an interface between spacecraft and payload and an interface between spacecraft and launch vehicle. The STP-SIV bus design supports the program goal of a low-risk bus by using flight-proven components, a simple structural design, and significant design and software reuse from prior missions. The design balances a low-cost and low-risk approach with significant spacecraft capability and flexibility. Table 1 highlights the threshold requirements and performance goal characteristics for the spacecraft.
The SIV (Standard Interface Vehicle) concept is considered a recurrent bus with adaptable interfaces to accommodate a range of payloads. The spacecraft will accommodate one to four payloads with a total up to 60 kg and 100 W orbit average power mounted to an external PIM (Payload Interface Module). The PIM is separable; it may be integrated in parallel with the bus to support accelerated launch schedules and reduce technical risk.
Figure 9: Schematic of STP-SIV bus and PIM to accommodate a range of payloads (image credit: SDTW, BATC)
Figure 10: Schematic view of the STP-SIV external interfaces (image credit: SDTW, BATC, AeroAstro)
Figure 11: View of the STP-SIV spacecraft bus and allowable PIM (green) envelope (image credit: SDTW, BATC)
The payloads mount to the spacecraft using a standard payload mechanical interface shown in Figure 12. The payloads mount to the PIP (Payload Interface Plate) using fasteners and holes on 2.54 cm centers. The PIM provides a total payload volume of 0.14 m3, a box of size: 66.80 cm x 49.40 cm x 44.95 cm. The allowable payload envelope in the launch configuration is shown in Figure 11.The payloads will be mounted ‘on-top’ of the bus and must fit within this volume for launch. Once the spacecraft is on orbit and deploys the solar arrays, the payloads may deploy elements as necessary to perform their missions. All deployed elements shall remain above (+ZPL) the payload interface plane (Ref. 16).
Figure 12: The PIP with the payload coordinates provides a standard mounting grid (image credit: SDTW, BATC)
The payloads are provided an unobstructed field of view of 2 steradian, oriented towards the +ZPL (nadir) axis and originating at the payload interface plane. Additionally, the payloads are provided a 2π steradian unobstructed field of view towards the +XPL (velocity direction until seasonal yaw flip), originating 55 cm from the leading edge of the PIP in the +XPL direction. This provides nearly 3π steradians of unobstructed views for the payloads.
Power interface: During normal mission operations, the S/C provides a minimum 100 W orbit average power (OAP) to the payload suite. This power is allocated between the different payloads on each mission. If the total power draw for all payloads exceeds 100 W, it may be necessary to duty cycle the payload operations to reduce the payload suite power consumption to within the capability of the S/C. Each payload is provided three switched power feeds. Each power feed provides unregulated 28±6 VDC from the S/C. The S/C provides over-current protection on each power line provided to the payload.
Data interface: The IAU (Integrated Avionics Unit) functions as the main data and command interface between the payloads. All payload command, data collection, and data storage is via the PIB (Payload Interface Board) which resides within the IAU. The PIB provides each payload one data port which consists of a 62 pin high density dHDD connector on the payload module. All payload commands and collection of high rate data, real-time data, analogs and discretes is through the single 62 pin data port. All payload data (high rate and real-time) is polled and ingested in a “round robin” scheme ensuring that no payload can monopolize the bus. Both the payload high rate and real-time data are time-stamped at the time of receipt.
The PIB ingests the payload high rate mission data, encapsulates this data in a CCSDS (Consultative Committee for Space Data Systems) compliant CADU (Channel Assess Data Unit) format and stores the formatted CADU for subsequent transmission to the ground. All high rate data is transferred via either an asynchronous UART (Universal Asynchronous Receiver/Transmitter) EIA-422 link or a synchronous EIA (Electronic Industry Alliance) compliant RS-422 link. The choice of synchronous or asynchronous data transfer method is selectable for each PL and is fixed prior to launch. The total high data rate available is 2 Mbit/s shared amongst all the payloads. The PIB provides a total mass memory storage of 8 Gbit of EDAC validated memory space. The memory is shared amongst all 4 payloads for high rate, real-time and stored state of health data (Ref. 16).
Figure 13: PIB system block diagram illustrating the standard data interface (image credit: SDTW, BATC)
Figure 14: Artist's view of the STP-SIV integrated with ESPA ring (image credit: Comtech AeroAstro)
Spacecraft to AFSCN interface: The interface between STP-SIV and ground facilities is controlled by two documents; an ICD (Interface Control Document) and the Standardized Interface Specification for the AFSCN (Air Force Satellite Control Network), SIS-000502C. SIS-000502 defines the types of service provided by the AFSCN and the design requirements for the SV radio frequency (RF) system.
The ICD describes the specific characteristics employed by the space vehicle RF system to show compliance with these requirements. This includes defining the exact operating frequency, subcarrier frequencies, modulation scheme, etc. Telecom frequencies have been selected and pre-approved by the relevant licensing organization for use on future SIVs. This eliminates risk of the sometime time-consuming approval process and enables transponder production to proceed without interruption. With predetermined frequencies, a transponder or full SIV could be produced and “on the shelf” for deployment in a responsive space application since there is no uncertainty in the mission telecom frequency and no risk of changes. 20) 21)
STPSat-2 mission operations are performed at the Research, Development, Test & Evaluation (RDT&E) Support Complex (RSC) at Kirtland AFB, NM.
Figure 15: Ground segment interface definition of the STP-SIV (image credit: SDTW)
STPSat-2 (Space Test Program Satellite-2)
STPSat-2 is the first spacecraft within the STP-SIV program and the prime payload on the STP-26 mission (Note: STPSat-2 is commonly also referred to as STP-SIV). STPSat-2 has a mass of 137 kg and accommodates two SERB (Space Experiment Review Board) experiments.
Comtech AeroAstro’s role is to design, build, and integrate the SIV bus under subcontract to prime integrator Ball Aerospace. The first SIV bus, for the STPSat-2 mission, was delivered to Ball in December 2008 (Ref.14).
Figure 16: Photo of the STPSat-2 spacecraft (image credit: BATC)
Figure 17: Photo of the deployed STPSat-2 spacecraft (image credit: BATC)
RF communications: The STP-SIV RF system is based on a single string L3 COM CXS-810C transponder. Use of the SGLS (Space Ground Link Subsystem) transponder consisting of a command/ranging receiver with embedded decryptor and power converter and a telemetry/ranging transmitter with embedded encryptor and power converter. The ground system architecture is shown in Figure 15.
Sensor complement of STPSat-2: (SPEX, ODTML)
SPEX (Space Phenomenology Experiment):
The objective is to demonstrate the suitability of sensors in the space environment.
ODTML (Ocean Data Telemetry Microsat Link):
ODTML, a next generation data collection system, is provided by ONR (Office of Naval Research). The objective is to collect data from sea-based buoys and to transmit the information back to a ground station. Current methods of obtaining data from these terminals (i.e., Service Argos and airborne platforms) are considered costly, time consuming, and/or inefficient. - ODTML is flown on TacSat-3, launched on May 19, 2009. 22) 23) 24)
ODTML is a transponder concept developed and demonstrated by Praxis Inc. of Alexandria, VA. It uses COTS (Commercial-off-the-Shelf) technologies to improve the data collection and dissemination process for remote sensors. Some capabilities of ODTML are:
• ODTML uses a two-way delay-tolerant messaging capability to provide 'Internet-like' services on global basis to support ocean platform monitoring and provide near real time situational data to web-based maps and other data analysis systems.
• ODTML uses higher bandwidths and lower power than the current Argos DCS (Data Collection System)
- > 50 kbit per node per day
- < 0.1 Joule per bit transmitted.
The ODTML network system consists of the following elements:
1) “Smart sensor nodes,” each containing an RF terminal, which collect the sensor data and communicate with the satellite payload. These smart sensor nodes are mounted on the sensor platforms, e.g., free-floating buoys or UGS (Unattended Ground Sensors).
2) Spacecraft Communications Payload (SCP), a microsatellite-mounted payload serving as a “router in the sky.”
3) Portable ground stations, acting as gateways to transfer the sensor data from the RF link to the Internet.
4) The Internet, as the communication conduit between the users and the ocean and ground-based observing platforms.
STPSat-2 mission status:
• The STPSat-2 spacecraft and the three payloads continue to operate nominally in 2012. Ball Aerospace & Technologies Corp. will provide an additional year of support for the STPSat-2 spacecraft, following completion of the initial experimental mission requirements that ended successfully on Jan. 31, 2012. 25)
The operational mission for STPSat-2, which launched on Nov. 19, 2010, has been extended for an additional year. Under contract to the SD at Kirtland Air Force Base, Ball Aerospace will continue to provide space vehicle support to the satellite through Feb. 1, 2013.
• The MMSOC-GSA (Multi-Mission Satellite Operations Center - Ground System Architecture) of SMC/SDTC is providing on-orbit operations for STPSat-2. 26)
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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.