ISS Utilization: NREP (NanoRacks External Platform) - A commercial hosted Payload Service
The NanoRacks EPP (External Platform Program) provides a commercial gateway to the extreme environment of space. It is an ideal location for Earth and deep space observation, sensor development and testing for advanced electronics and materials. 1) 2) 3)
The NREP delivers research results concerning biological testing, sensor target testing, satellite communications components testing, power systems testing, and materials testing. Delivered results will include, but are not limited to, data and payload return. The facility is equipped with its own power supply to distribute power to experimental containers. An internal computer system monitors and controls the flow of power to the containers, receives commands from on-ground users, and communicates research data to those users. NREP provides a unique opportunity for automated experiments that require vacuum exposure.
Airbus Defence and Space (former Astrium North America Inc.) of Houston, TX, is the designer and manufacturer of the Platform. The NREP (NanoRacks External Platform) will host payloads in the open space environment while attached to the JEM-EF (JEM External Facility). 4) There are a number of applications that the External Payload Platform provides, including: sensor target testing, biological testing, access to station power and data, flight qualification, materials testing, and more. The NREP will allow for high data rates, payload return, risk mitigation, and predictable and frequent service. 5)
EPP (External Platform Program) system: The size of the external payload platform and payload items is limited by constraints on handling the assembly on-board the ISS and on transferring it through the JEM airlock. The EPP dimensions almost fully use the allowable item envelope specified for the JEM airlock. The EPP flight unit external configuration is shown in Figure 1. A significant portion of the airlock allowed envelope is used by the grapple fixture interface required during the RMS operation and by the PIU (Payload Interface Unit) standard interface to the JEM-EF which is not shown in the figure. Therefore, the standard experiment payload size is 10 x 10 x 40 cm or 4U in the CubeSat standard. Also 1U, 2U, 3U, and multiples of the 4U shape are feasible. 6) 7) 8)
Figure 1: Photo of the NREP (EPP) flight unit including the JEM-RMS interface (image credit: Airbus DS, NanoRacks)
The NREP allows for various configurations with different standard sizes of payloads. An example is shown in Figure 2. Standard payloads have a width and a height of 10 cm and a length from 1U (10 cm) up to 4 U (40 cm). NREP is able to accommodate up to 9 4U CubeSat-size payloads outside of station with a standard mission duration of 15 weeks. The Platform continues to allow for NanoRacks' end-to-end mission services that are offered across all of The Company's space station opportunities. Also 1U, 2U, 3U, and multiples of the 4U shape are feasible. The payloads will interface to a standard sized interface plate suitable for up to nine standard 4U CubeSat sized payload containers (Figure 2).
Figure 2: Example of EPP multi-payload configuration showing the baseplate with combined 1U, 2U, 3U, and 4U payload items (view from bottom), image credit: Airbus DS, NanoRacks
Alternatively, EPP can be operated in the unique payload configuration for one single payload using the entire available volume as specified in Figure 3. In this case the single payload needs to be designed for the base plate mechanical interface on EPP. There is no mass restriction for standard payloads, but high density payload design can result in payloads with a mass up to 4 kg. The unique payload is limited to a mass of 35 kg.
Figure 3: EPP unique payload configuration (image credit: Airbus DS, NanoRacks)
Power Supply and Data Handling: The power supplied to each payload is limited by the heat rejection capability of the payload and restricted by the heat radiation allowed to be radiated to the inside of the EPP. The primary thermal interface between the payload and the EPP is through the base of the payload volume. There, a special silicone thermal gel pad covers the interface area between the payload container and the EPP base plate. This pad is attached to the payload on ground and covered by a removable paper to protect the gel pad prior to the payload on-orbit installation.
Payload data is transferred to the ISS infrastructure using a USB 2.0 standard power and data interface. The data stream is transmitted through WiFi/Ethernet based communication protocols to the NanoRacks subracks in the EXPRESS (Expedite the Processing of Experiments to Space Station) Rack 4 in the JEM-PM (Pressurized Module) via FTP (File Transfer Protocol). For this purpose a WiFi communication system is embedded on the EPP. This system utilizes an Ubiquiti/SR71 wireless radio which communicates with the EPP DHS ( Data Handling System) and generates the wireless signal to the ISS Wireless Access Point. The MIL-STD-1553B interface available on the JEM-EF is only used for the commanding and monitoring of the EPP.
Each active payload and the overall EPP status can be monitored online by the H&S (Health & Status) stream which is sent every second. Some bits of the H&S stream can be customized to the payload operator's requirements. The EPP payloads can be commanded after the commands have been processed by the NASA/MSFC (Marshall Space Flight Center). The commands are uploaded using the MIL-STD-1553B standard. Payload data can be downlinked with the MRDL (Medium Rate Data Link) with currently 3 Mbit/s. This data rate is expected to be improved in the near future. The overall payload communication setup is summarized in Figure 4, standard payload resources in Table 1.
Figure 4: EPP payload communication and data flow implementation (image credit: Airbus DS, NanoRacks)
Table 1: Standard EPP payload resources
Platform Environment: The mechanical environment during launch and return is very much mitigated, especially regarding the shock loads to be expected, due to the transportation of payload canisters inside standardized CTBs (Cargo Transfer Bags). A very important aspect unique to the ISS operations is the vibrational environment originating from the ISS crew and ISS mechanical system operations. The station experiences a constant high frequency jitter vibration which superposes the rather low frequency drift. The jitter acts as disturbance of the microgravity conditions and needs to be taken in to account in the payload mission design.
Outside the ISS, the EPP is exposed to direct solar light, reflected solar light from Earth's atmosphere, infrared radiation from the Earth, and cosmic microwave background. Taking into account these thermal fluxes as well as reflections from the ISS structure and a solar beta angle variation of -75º to +75º a worst cold and worst hot case have been identified in the thermal analysis conducted as part of the EPP design activities. The worst cold case is a combination of all payloads being inactive with the thermal conditions of the worst case orbit, while the hot case is a combination of all payloads being active and radiating the maximum power of 30 W. Within these extreme cases, the payload wall temperatures vary between 222 and 339 K.
The ISS provides an exceptionally clean environment to external payloads. The external contamination control requirements limit contaminant deposition to 130 Å/year on external payloads and ISS sensitive surfaces. Measurements of contaminant deposition on ISS returned hardware have demonstrated that these requirements are indeed met at ISS payload sites. Contamination fluxes emanating from the ISS are assessed in several areas of the station, including the JEM-EF. The flux of molecules is limited by design such that at 300 K the mass deposition rate on the sampling surfaces is limited to 1 x 10-14 g cm-2s-1 on a daily average and will not exceed 1 x 10-6 g cm-2yr-1.
Viewing Conditions: The basic mission of the EPP Service is to use the ISS as payload-supporting platform comparable to a common satellite platform but benefiting from the extraordinary infrastructure of the station. The ISS is an ideal platform for various kinds of missions in LEO (Low Earth Orbit), but especially in the field of observation. The presence of the space station in LEO provides the opportunity for collecting Earth and space science data and to test space-related technologies in the relevant environment. From an average orbit altitude of about 400 km, details in observed features can be layered with data originating from orbiting satellites, to compile the most comprehensive information available. In its 51.6º inclination orbit, the ISS passes over roughly 85% of the Earth's surface and 95% of the world's populated landmass every 1 to 3 days.
A viewing assessment with the EPP installed at JEM-EF site No 4 shows very good visibility conditions10. Figure 5 shows the accommodation site of EPP on JEM- EF, while Figure 6 provides a fisheye representation of the view to the ISS port side with viewing obstructions, caused by ISS structures. The pathway of the solar arrays is indicated as light red circle. The starboard side view being symmetrical with respect to the available viewing cone, the analysis demonstrates that EPP is able to provide an optical access in a cone of 40 opening angle from forward to rear direction with respect to the nominal ISS attitude.
Figure 5: JEM-EF configuration analyzed with MCE payload installed on JEM-EF site No 8 and EPP on JEM-EF on site No 4 (Image credit: NanoRacks)
Micro-vibrational Environment: The microgravity environment on the JEM-EF is confirmed by JAXA to have very good condition and to reach approximately 10-6 g. However, this condition may be disturbed by atmospheric drag, exhaust gas from pressurized modules, crew activity, and ISS attitude maneuvers. There are 3 MME (Microgravity Measurement Equipment) sensor assemblies installed in the JEM-EF. The data measured shows accelerations from 200 µg to 0.01 g since the commissioning of the equipment in 2009. The results are shown and compared with the ISS microgravity environment specification in Figure 7. EPP is an ideal platform thanks to its excellent viewing conditions and low structural response to ISS jitter vibrations. Structural-dynamic simulations with the EPP performed with various kinds of payload configurations demonstrate the usability of the platform for remote sensing missions. The rotational response at the different EPP standard payload positions has been analyzed based on the acceleration environment measured on the JEM-EF ( Japanese Experiment Module Exposed Facility) by JAXA. Taking into account various EPP mission complements and payload eigen frequencies it is demonstrated by analysis that the rotational response around Nadir and other axes stay well below 0.01 arcsec (Figure 8). Due to the shape of the first structural eigen modes, EPP slot P4 is optimal with respect to rotations around the X-axis which is most relevant for line of sight vibrations in Nadir viewing.
Figure 7: Acceleration environment measured on the JEM-EF1 (image credit: JAXA, NanoRacks)
Figure 8: Frequency response in the rotational degree of freedom for the fully occupied EPP installed on the JEM-EF (image credit: JAXA, NanoRacks)
Payload Mission Opportunities and Use Cases: Table 2 gives an overview of the use cases envisioned for the EPP including an assessment of the suitability of the system for various payload missions. Due to its nadir viewing capability EPP is an ideal platform for any Earth-related remote sensing. Applications requiring zenith viewing, however, can be made possible with slight system modifications.
Table 2: Overview of external platform use cases
Table 3 compares the common utilization scenario with the commercial approach. One major change is the significant acceleration of mission preparations which is enabled by two factors. The commercial scheme rules out lengthy negotiations with the International Partners, because no payload sponsorship is necessary any more. The second and equally important factor is the simplification of the payload qualification. Since payload functionality is entirely the customer's responsibility, the testing and qualification philosophy remains unaffected by any third party interference. The reviews commonly held are reduced to one review only which is the safety review. Accordingly, the EPP Service only requires minimal information on the payload itself.
Table 3: Comparison of common and commercial ISS utilization
The further utilization of the ISS outside its classic role as low gravity and human spaceflight research platform is among the primary objectives of this new commercial service. A comparison with the dedicated spacecraft solution commonly pursued by small payload missions shows that this conventional solution does not necessarily result in an optimal compliance with the requirements in terms of orbit selection and space segment design. Furthermore, the dedicated spacecraft solution often has significant overall mission cost affiliated and the mission time line is very often affected by launch delays which is increasingly unacceptable for commercial service missions building upon revenues generated by the payload in orbit. Therefore, EPP and the utilization of ISS can be a good opportunity for conducting space missions in LEO on a low cost and fast track basis.
Launch: NREP was part of the payload launched on the Japanese HTV-5 (H-II Transfer Vehicle) on August 19, 2015 from TNSC (Tanegashima Space Center) in Japan. NREP is expected to be operational starting early spring 2016. 9)
Also on board of HTV-5 were 16 CubeSats, which include 14 Planet Labs Doves Flock- 2B, the University of Aalborg's AAU-SatX-5 and Gomspace's GOMX-3.
Launch: The launch of NREP was originally manifested on the Cygnus CRS Orb-3 mission, which was launched on Oct. 28, 2014 and experienced a launch failure; however, a delay of the NREP system saved the day for NanoRacks. The NREP is now manifested on SpaceX CRS-7, set to launch in June 2015.
Note: NREP was slipped to Orb4, and has since been re-manifested to fly on SpaceX CRS-7 since the Cygnus Orb-4 launch date is still in flux. The current launch date for SpaceX CRS-7 is June 13, 2015. It is launching with 2 payloads that are sharing a 4U payload enclosure. These payloads were contracted through CASIS, and are showcasing an electronics experiment investigating the effects of radiation, and a solar cells experiment testing different types of cell chemistry in the space environment. There are several other payloads currently being developed for a launch in the fall of 2015. Experiments currently in development range from Earth observation to testing of a corrosion inhibitor in the space environment. 10)
According to NanoRacks, NREP, or simply the EPP (External Payload Platform), will start operations in the spring of 2016 on slot 4 of the JEM-EF. The platform is operated under the NanoRacks' Space Act Agreement with NASA and embedded into payload end-to-end services provided by Airbus Defence and Space (Airbus DS) and NanoRacks to commercial and institutional customers worldwide (Ref.6).
The small size EPP is an approach of a new kind to foster the utilization of infrastructure available on the ISS. With the end of the ISS assembly phase the exploitation of on-orbit resources for the contributing nations' scientific and economic benefit is extensively performed. However, further capacities in the station's infrastructure do exist which can contribute to the utilization if used efficiently. Therefore, it remains the driving objective for the partners and their affiliated industrial contractors to foster further opportunities to access the ISS and to promote the extensive use of the station as in-orbit laboratory for the benefit of the space community world wide.
The EPP is part of a commercial service covering the project development, mission preparation and management, payload integration into the ISS operations, and payload operations. This service is realized in a cooperation between the companies NanoRacks and Airbus Defense and Space -Space Systems in the United States with development and engineering services as well as payload business development provided by Airbus Defence and Space in Germany. The EPP Service represents a new approach to provide low-cost research infrastructure in the space environment. It transforms the station into a commercially available laboratory in space with the capability to support missions in various fields.
Platform Concept of Operations:
The launch of payloads to the ISS is a resource that is very well available for small size payloads transported in a pressurized environment among other resupply items required by the station operations. With the aim of providing a reliable and easy to prepare way of transportation to ISS, payloads are launched pressurized to the station and are installed into EPP within the JEM-PM (JEM Pressurized Module). A unique feature of the JEM-PM is its airlock which is used to transfer from the pressurized part directly to the JEM-EF supported by the RMS (Robotic Manipulation System) which is very efficient in terms of required crew resources.
Due to the high frequency of flights and the flexibility of the vehicle manifests the risk of a delay in the payload readiness can be mitigated by delaying to the next flight opportunity which on average is available not more than two months later. The launch within the system of ISS resupply flights introduces an unparalleled reliability of the access to low Earth orbit for small size payloads. The size of the payload items is limited by handling constraints on-board the ISS. Therefore, the standard experiment payload size is a multiple of a 4U CubeSat, which demands miniaturized hardware solutions. However, every payload can extensively use all ISS resources required: mass is not limited, power only limited by the payload heat radiation capability, the datalink is a USB 2.0 standard bus enabling a real-time and private data link connecting the ground operator directly at his desk.
The airlock is nominally operated once a week with a maximum frequency of two operations per day. EPP payloads will be exchanged on a periodic basis in consistency with the ISS operational planning. At a prescheduled time the crew removes the payload items from their CTB (Cargo Transportation Bag) and installs them on the EPP inside the Japanese module. When all payload items are installed, the crew places the EPP on the JEM airlock slide table to move it inside the airlock. - Upon inner hatch closure the airlock is depressurized in a time frame of approximately six hours. At completed depressurization and remote opening of the outer hatch the crew uses the slide table to further move the EPP outside the airlock and the JEM-RMS to take EPP from the slide table and to install it on JEM-EF. Alternatively, the JEM-RMS is able to point the fully equipped EPP into predefined directions while supplying power under the same conditions as on the JEM-EF. The small size EPP is manifested for the JEM-EF site No. 4 until the year 2020 (Figure 9). At this position, the platform has an excellent view into the nadir direction, power supply, data connection via the standard PIU (Payload Interface Unit) and video surveillance if required. The EPP Service is a full end-to-end service covering the entire mission (Table 4).
Table 4: EPP Service and Payload Mission Elements
Programmatic Approach and Mission Schedule:
The EPP standard mission scenario is designed to provide fast-track and reliable access to the ISS. In the nominal mission scenario payload items are installed not later than one year after the contractual agreement, stay in operation for 15 weeks, and are returned to the customer as an optional service. The nominal mission schedule in terms of time to launch (L) is defined in Table 5 together with the activities performed and deliverables to be produced by the parties involved. Compared to the current lead times to be expected in the standard ways to access ISS which are in the order of 27 months, the EPP mission scenario is more than twice as fast. Furthermore, the items required and processes involved as summarized in Table 5 show the paradigm change in ISS payload missions initiated by the EPP Service. The service provider only requires hardware qualification with respect to safety certification in the ISS Program and the verification of interfaces to the EPP system. As a fully commercial approach the EPP Service neither requires the payload developer to demonstrate functionality nor to justify mission performance. With this philosophy, the EPP Service reduces efforts required for review processes significantly and to increase the efficiency mission budgets are spent.
Table 5: Nominal mission schedule, tasks and items required from the involved parties
1) "External Platform," NanoRacks, URL: http://nanoracks.com/products/external-platform/
2) "NanoRacks External Platform (NREP) Standard Interface Definition Document," Astrium North America, Doc. No.: ANA–EPP–IDD–0001, Issue 7, March 20, 2014, URL: http://nanoracks.com/wp-content/uploads/NanoRacks_Interface_Document_for_External_Platform_Customers.pdf
3) "NanoRacks' Space Station External Payload Platform Completes Manufacture," NanoRacks, June 19, 2014, URL: http://nanoracks.com/external-payload-platform-completes-manufacture/
4) "NanoRacks' Space Station External Payload Platform Completes Manufacture," NanoRacks Press Release, June 19, 2014, URL: http://nanoracks.com/external-payload-platform-completes-manufacture/
5) Per Christian Steimle, Uwe Pape, Carl Kuehnel, Michael Jonhson, "External Payload Platform Service - A new fast track and low cost access to the outside of the International Space Station," Proceedings of the 65th International Astronautical Congress (IAC 2014), Toronto, Canada, Sept. 29-Oct. 3, 2014, paper: IAC-14.B3.3.8
6) Per Christian Steimle, Carl Kuehnel, Michael Johnson, "The International Space Station As Low-cost Hosting Plat-form for LEO Missions Using the NanoRacks External Platform," Proceedings of the 66th International Astronautical Congress (IAC 2015), Jerusalem, Israel, Oct.12-16, 2015, paper: IAC-15.B4.5.8
7) "NanoRacks External Platform (NREP) Standard Interface Definition Document," NREP Team, Airbus DS, Issue 7, March 24, 2015, URL: http://nanoracks.com/wp-content/uploads/Current-edition-of-Interface-Document-for-NanoRacks-External-Platform-NREP.pdf
8) "Hosted Payload and SmallSat Summit," Washington D.C., USA, Oct. 15, 2014, URL: http://www.ormanagerconference.com/wp-content/uploads/2014/12/NanoRacks_ShortenPayloadPath.pdf
9) "NanoRacks External Platform, CubeSats, Launched to ISS on Japanese HTV-5," NanoRacks, Aug. 19, 2015, URL: http://nanoracks.com/external-platform-cubesats-launched-on-htv-5/
10) Information provided by Conor Brown of NanoRacks, Houston, TX, USA.
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 (email@example.com).