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StriX-α : A minisatellite class SAR (Synthetic Aperture Radar) satellite mission

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StriX-α is a X-SAR minisatellite (~150 kg class) collaborative demonstration mission under development of the Japanese institutions: JAXA/ISAS, the University of Tokyo, TItech (Tokyo Institute of Technology), Keio University, Japan Space Systems, and the private company Synspective Inc. of Tokyo.

Naming of the mission: Strix is the mythological basis for the scientific name of the owl family. An owl is a bird known for its ability to see things clearly at night, and has long been a symbol of knowledge and wisdom in many human cultures. Synspective’s small SAR satellite shares these aspects of the owl, resembling it in its orbit around the Earth. 1) 2) 3)

The overall objective is to provide a viable solution for a smallsat SAR mission with a size of about 0.7 x 0.8 x 0.9 m in launch configuration and with a deployed antenna of 4.9 m x 0.7 m (Figure 2), providing an expected stripmap resolution of 3 m from an orbit of ~600 km. The main specification of SAR observation is shown in Table 1.

Parameter

SAR mode

Strip Map

Sliding Spotlight

Altitude

500 km

500 km

Resolution

3 m

1 m

Center frequency

9.65 GHz (X-band)

Swath width

30 km

10 km

Chirp bandwidth

75 MHz

300 MHz

Polarization

VV

Antenna size

4.9 m x 0.7 m

Antenna efficiency

50%

Tx peak power

100 W

Tx duty cycle

25%

System loss

0.6 dB

System noise figure

2.6 dB

Off nadir angle

15~45º

PRF (Pulse Repetition Frequency)

3000~7000 (TBD) Hz

NESZ (beam center) Noise-Equivalent Sigma Zero

-20 dB

-16 dB

Ambiguity (beam center)

>15 dB

Table 1: SAR observation specification

A waveguide is embedded at the center of the rear surface in order to feed RF to the antenna panel through coupling slots. The antenna panel consists of a dielectric honeycomb core and metal skins, which work as a parallel plate guide for RF. The front surface with two dimensional arrays of radiation slots works as an antenna radiator for vertical polarization in SAR mode. In order to achieve 1 m ground resolution, the antenna bandwidth should be about 300 MHz.

On-board SAR instruments

The RF peak power is selected to 1000 W that is realized by GaN solid state amplifiers, instead of vacuum tube TWTAs. A chirped transmitting signal is amplified in six GaN HEMT 200 W amplifier modules to be combined in a wave-guide resonator. The on - duty ratio is 25% to in crease the average power.

A SAR-Electronics Unit (S-ELU) handles transmitting signal generation, receiving signal processing (frequency conversion and analog-to-digital conversion) for SAR sensor. The S-ELU for small satellites is developed based on an airborne SAR instrument. The chirp bandwidth is 300MHz for 1m ground resolution. The received signal is converted to digital signal of 8 bit x 720 M sample/s. The data compression rate is about 50%. The receiving duty cycle is about 50% to acquire reasonable signal-to-noise ratio. After time stretching process, the average data rate is 1.5 Gbit/s. In the SAR observation mode, this 1.5 Gbit/s SAR data is transferred to MDR (Mission Data Recorder) through a serial RapidIO (sRIO) interface.

The MDR consists of commercial 16 NAND flash memory devices and the total memory capacity is 768 GB. Total dose tolerance of NAND devices is confirmed by Co60 irradiation test. Single event upset errors are corrected by standard error correction code for commercial NAND devices. A commercial FPGA (Field Programmable Gate Array) device is utilized for high speed data flow and standard powerful error correction code. Special cares are paid to thermal heat path and thermal stress of BGA (Ball Brid Array) packaging. In down link communication mode, stored data are transferred to high data rate X-band transmitter (XTX). XTX has dual polarization (RHCP/LHCP) channels to increase its down link capability. Stored data are switched to the 2 channels and they are transferred to XTX through Xilinx Aurora data interface. The data rate between MDR and XTX is 2 Gbit/s per one channel and the total data rate is 4 Gbit/s.

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Figure 1: Left: 1kW X-band power amplifier installed on satellite body. Center: SAR Electronics Unit converted from air plane application. Right : 768GB, 2Gbit/s Mission Data Recorder with NAND memory (image credit: Synspective)


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Figure 2: Upper view: StriX with the deployed X-SAR antenna. Lower Left: Non-contact waveguide feeding with choke flange. Lower Right: Honeycomb antenna panel with slot array and embedded waveguide (image credit: StriX Team)

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Figure 3: Artist's rendition of the StriX-α microsatellite in orbit (image credit: Synspective)


Development status

• November 24, 2020: The dedicated mission for Synspective is scheduled for lift-off during a 14-day launch window opening on 12 December UTC and will launch from Rocket Lab Launch Complex 1 on New Zealand’s Māhia Peninsula to a targeted 500 km circular low Earth orbit. 4)

- For this mission, Rocket Lab will utilize a custom expanded fairing to encompass Synspective’s wide-body satellite – the first use of the expanded fairing options that Rocket Lab recently introduced alongside a suite of vehicle performance improvements, including advances in battery technology which enable an improved payload lift capacity up to 300 kg. Rocket Lab will also perform an advanced mid-mission maneuver with its Kick Stage space tug that will shield the StriX-α satellite from the sun to reduce radiation exposure ahead of payload deployment.

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Figure 4: Synspective’s StriX-α satellite is encapsulated inside Rocket Lab’s payload fairing before launch (image credit: Rocket Lab)

• October 10, 2019: Norwegian Ground Network specialist and provider of EO services KSAT, and Japanese Space Industry Start-up, Synspective are announcing their global alliance. 5)

- Tokyo based Synspective Inc., will develop a constellation of small Synthetic Aperture Radar (SAR) satellites over the next few years aimed at providing solutions and data for the global market, using high resolution data. The first satellite is planned to launch in 2020.

- The partnership between the two companies will secure Synspective's cost effective ground support for their constellation, during LEOP and the operational phase. KSAT will be able to include SAR data and applications from the future constellation in their already extensive SAR portfolio.

- "We are delighted to work with KSAT. We recognize the value of their vast global network as well as their leadership in the space industry and believe that by working together we can get one step closer to achieving mission and worldwide coverage. I believe that in order to expand the SAR market in New Space, synergetic collaborations are essential. I can see that synergy with our alliance with KSAT and look forward to working together" said Motoyuki Arai, CEO of Synspective Inc.

- With their integrated network of ground stations uniquely located for minimal data latency, and agreements with all available SAR missions, KSAT has become a global "power house" for commercial SAR.

- "We are very happy about this agreement marking the beginning of what we hope to be a long and fruitful relationship with our friends at Synspective. Closely following the new and exciting companies coming up in the Japanese NewSpace market, we are dedicated to supporting the Japanese space industry and looking forward to collaborating on data and land-based SAR applications from Synspective in the future" says Rolf Skatteboe, President and CEO of KSAT.

- The constellation will be supported on the KSAT Lite network where KSAT provides ground station as-a-service (GaaS) to the operators through their global integrated network of ground stations.

- KSAT Lite is optimized for small satellites and large constellations. This easy-to-use, ever expanding network, both in number of locations, bands, customers and capabilities, grows as the constellations grow, the economy of scale benefiting each individual operator.

• September 9, 2020: Synspective Inc., a Japanese company providing satellite data and derived solutions, using small-sized SAR (Synthetic Aperture Radar) satellites, launches its first “Land Displacement Monitoring” service which enable ground movement monitoring in millimeters, obtained through image analysis of SAR (Synthetic Aperture Radar) satellites data. 6)

About LDM (Land Displacement Monitoring) Service

- The “Synspective Land Displacement Monitoring” service originates from InSAR (Interferometric SAR) analysis that is capable of detecting timely vertical land displacement, in millimeters, over a wide area. This Service enables periodical observation and understanding of land subsidence and deformation.

- It takes a lot of time and labor to understand the risk of land subsidence and landslides over a wide area. By leveraging Synspective’s new service, cost and time is reduced, when compared to the traditional observation and control techniques associated with these ground change risks. This new service’s expected use is multifaceted and can be applied in many land risk management projects such as construction projects, airport maintenance projects, and subway development projects, among others. In addition, remote area/site surveying can be extremely relevant in disaster struck areas where human access is restricted or dangerous, or where social movement is restricted due to the recent COVID-19 virus impact.

- Synspective offers this solution on a subscription basis through a SaaS(solution as a service) format. You can access the platform without installing the software and are able to check the analysis results on the web. User-friendly UI/UX enables users to intuitively understand the analysis results without any prior knowledge of satellite data.

- Capability and functionality of this service were tested through preliminary utilization projects with several companies and organizations, including through participation in a PoC project by Singapore Land Authority, a statutory board under the Ministry of Law of Singapore. Through the insights and lessons learned from this PoC project, further utilization models were developed. This project also provided Synspective with feedback for improvements to the service, which has been incorporated in the current release.

Figure 5: Land displacement service (video credit: Synspective)

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Figure 6: Demonstration image of the LDM service (image credit: Synspective)

• April 14, 2020: Japanese synthetic aperture radar (SAR) company Synspective announced April 14 it will launch its first satellite with Rocket Lab after initially selecting Arianespace for that mission. 7)

- Rocket Lab said it signed a contract with Synspective to launch the StriX- α SAR satellite on an Electron rocket from New Zealand in late 2020. Terms of the launch contract were not disclosed.

- One year earlier, though, Synspective announced a launch contract with Arianespace for the StriX-α spacecraft. At the time, the spacecraft was slated to fly as a rideshare payload on a Vega launch in 2020. That schedule looked to be in doubt, though, because of delays caused by a Vega launch failure in July 2019. The Vega was scheduled to return to flight in March, but that mission has been delayed indefinitely after the closure of the spaceport in French Guiana by the French government due to the coronavirus pandemic.

- The 150 kg StriX-α will be the only payload on the smaller Electron rocket, giving Synspective greater control over the launch schedule and orbit for the satellite, something the companies hinted at in the Rocket Lab statement.

- “We are very pleased to work with Rocket Lab, a pioneer in rocket ventures. We are also grateful for their flexibility in accepting our requests on the satellite’s orbit and launch period,” said Motoyuki Arai, founder and chief executive of Synspective.

- “We understand just how important it is to have control over your orbit and your launch schedule when building out a constellation, so we’re proud to be delivering that capability to Synspective on Electron,” Peter Beck, chief executive of Rocket Lab, said. Small launch vehicle developers like Rocket Lab have long emphasized such benefits of dedicated launches versus flying smallsats as rideshares on larger launch vehicles.

- A Synspective spokesperson said in an April 14 email that the company had a good relationship with Arianespace, but decided to move -α to Rocket Lab “as a result of adjusting the launch timing and the orbit of the satellite.” The company expects to use the Arianespace contract for the launch of a future satellite instead.

- StriX-α will be the first in a constellation of about 25 SAR satellites that Synspective plans to launch over the next several years to provide geospatial data products. The company said in July 2019 it has raised $100 million since the company’s formation 17 months earlier.




Spacecraft

Named after “Strix uralensis”, the scientific name of the owl, the SAR minisatellite can gather data 24 hours a day, 7 days a week, regardless of weather conditions. The owl is known for its keen eyesight, and like its animal namesake, the StriX satellite constellation can target data with a ground resolution of 1-3 m, single polarized (VV), and a swath width of more than 10-30 km. The StriX observation modes are Stripmap and Sliding Spotlight mode and each satellite has an SAR antenna that is 5 m in length and stowed during launch. The simple design of the satellites allows for affordable development of the constellation.

The development of the SAR originally began as part of the Japanese government’s program called ImPACT (Impulsing Paradigm Change through Disruptive Technologies Program). As a result, the development team consists of experienced members and reviewers from space and consumer product industries with universities and space agencies.

SAR data downlink system and its demonstration: The observed data is transmitted to the ground station through a high-speed X- band link. We have already demonstrated high speed downlink of 64 APSK, 100 Msample/s with the Hodoyoshi-4 satellite in 2014 [ 8) 9)]. Based on this technology, we are developing a dual polarization channel X-band link with a total 2-3 Gbit/s capability.

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Figure 7: Photos of the communication system. Left : High speed X-band transmitter. Center : Medium Gain Antenna (MGA), Right : 10 m ground station antenna (image credit: Synspective)

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Figure 8: Artist's rendition of the deployed StriX minisatellite with a mass of ~150 kg (image credit: Synspective)

Synspective is preparing for and developing two demonstration satellites, StriX-α and StriX-β, which are scheduled for launch in 2020 and 2021.


Launch: The StriX-α minisatellite of Synspective was launched on December 15, 2020 (10:09 UTC, corresponding to 23:09 NZT) on an Electron vehicle of Rocket Lab from Launch Complex 1 on Mahia Peninsula, New Zealand. 10) 11)

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Figure 9: A Rocket Lab Electron launcher takes off from Launch Complex 1 on Mahia Peninsula, New Zealand on 15 December 2020 (image credit: Rocket Lab)

Orbit: Sun-synchronous orbit, altitude of ~500 km, inclination = 97.3º.

Rocket Lab named the mission: 'The Owl's Night Begins' in a nod to Synspective’s StriX family of synthetic aperture radar (SAR) spacecraft developed to be able to image millimeter-level changes to the Earth’s surface from space, independent of weather conditions on Earth and at any time of the day or night. Strix is also the genus of owls.

The StriX- α satellite onboard this mission will be the first of a series of spacecraft deployments for Synspective’s planned constellation of more than 30 SAR minisatellites to collate data of metropolitan centers across Asia on a daily basis that can be used for urban development planning, construction and infrastructure monitoring, and disaster response.

Synspective is one of several companies planning to build out constellations of radar satellites for Earth-imaging. ICEYE of Finland and California-based Capella Space have already launched multiple small satellites with sophisticated radar payloads.

The StriX constellation will have a ground resolution of 1 to 3 meters according to Synspective.

“Congratulations to the team at Synspective for the successful deployment of their first satellite,” said Peter Beck, Rocket Lab’s founder and CEO. “We’re proud to be able to continue to provide dedicated launch opportunities for small satellite customers like Synspective. Electron provides truly tailored access to space, enabling our customers to choose exactly when they launch and under their specific mission parameters.”

“Thanks to the efforts and hard work of both the Rocket Lab and Synspective teams, we were able to achieve a successful launch as scheduled, despite the difficult environment of COVID-19,” said Motoyuki Arai, founder and CEO of Synspective. “With the launch of StriX-α, Synspective will be able to demonstrate its satellite capabilities and data processing technology.

Rocket Lab did not attempt to recover the Electron’s first stage on this flight, following the company’s first successful retrieval of an Electron booster on a previous launch last month. Rocket Lab aims to eventually catch boosters falling under parachutes with a helicopter for refurbishment and reuse.

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Figure 10: Timeline of launch events for Rocket Lab's 17th mission (image credit: Rocket Lab)




Mission status

• December 15, 2020: Synspective Inc., a SAR satellite data and related solutions provider, announced today that “StriX-a”, its first SAR satellite, has successfully been put into its target orbit. 12)

- At 19:09 on December 15th (JST), the small SAR satellite “StriX-α” was launched by Rocket Lab’s Electron, from New Zealand’s Mahia Peninsula launch site, and put into target orbit: a Sun Synchronous Orbit (SSO), with an altitude of 500 km.

- Functions including both observation and data acquisition, will be verified over the next several months. Details will be updated on Synspective’s website.



1) ”Synspective,” URL: https://synspective.com/satellite/

2) Hirobumi Saito, Budhaditya Pyne, Kouji Tanaka, Makoto Mita, Tomoki Kaneko, Jiro Hirokawa, Takashi Tomura, Hiromi Watanabe, Prilando Rizki Akbar, Koichi Ijichi, ”Proto-Flight Model of SAR for 100kg class Small Satellite,” Proceedings of the 33rd Annual AIAA/USU Conference on Small Satellites, August 3-8, 2019, Logan, UT, USA, paper: SSC19-IV-01, URL: https://digitalcommons.usu.edu
/cgi/viewcontent.cgi?article=4375&context=smallsat

3) Hirobumi Saito, Akbar, Prilando Rizki, Ravindra Vinay,Hiromi Watanabe, Atsushi Tomiki, Jiro Hirokawa, Miao Zhang, Seiko Shirasaka, ”Compact X-band Synthetic Aperture Radar with deployable plane antenna -project of a 100 kg class SAR satellite,” Proceedings of the 4S Symposium: `Small Satellite Systems and Services,' Valletta, Malta, 30 May – 3 June 2016, URL: http://www.isas.jaxa.jp/home/saito_hirobumi_lab/_src/sc1242/SAR.pdf

4) ”Rocket Lab to Launch Dedicated Mission for Japanese Earth Imaging Company Synspective,” Rocket Lab, 24 November 2020, URL: https://www.rocketlabusa.com/about-us/updates/
rocket-lab-to-launch-dedicated-mission-for-japanese-earth-imaging-company-synspective/

5) ”A new alliance begins between KSAT and Japanese SAR satellite startup Synspective,” Space Daily, 10 October 2019, URL: http://www.spacedaily.com/reports/
A_new_alliance_begins_between_KSAT_and_Japanese_SAR_satellite_startup_Synspective_999.html

6) ”Synspective Announces the Release of its first SAR-based Land Displacement Monitoring Service,” Synspective Press Release, 9 September 2020, URL: https://synspective.com
/news-press/land-displacement-monitoring/

7) Jeff Foust, ”Synspective shifts launch of first satellite to Rocket Lab,” SpaceNews, 14 April 2020, URL: https://spacenews.com/synspective-shifts-launch-of-first-satellite-to-rocket-lab/

8) H. Saito, T. Fukami, H. Watanabe, T. Mizuno, A. Tomiki, and N. Iwakiri, “World Fastest Communication from a 50 kg Class Satellite - Microsatellite Hodoyoshi-4 Succeeds in 348 Mbit/s,” IEICE Communications Society GLOBAL NEWSLETTER Vol. 39, No.2, 2015

9) H. Saito, T. Fukami, H. Watanabe, T. Mizuno, A. Tomiki, and N. Iwakiri, “High bit-rate communication in X- band for small earth observation satellites - Result of 505 Mbit/s demonstration and plan for 2 Gbit/s link,” AIAA/Utah State University Small Satellite Conference, SSC16-VII-5, Logan, Utah, USA, Aug. 2016

10) Stephen Clark, ”Rocket Lab closes out year with launch of Synspective’s first radar satellite,” Spaceflight Now, 15 December 2020, URL: https://spaceflightnow.com/2020/12
/15/rocket-lab-closes-out-year-with-launch-of-synspectives-first-radar-satellite/

11) ”Rocket Lab Successfully Launches 17th Electron Mission, Deploys SAR Satellite for Synspective,” Rocket Lab, 15 December, 2020, URL: https://www.rocketlabusa.com/about-us/updates/
rocket-lab-successfully-launches-17th-electron-mission-deploys-sar-satellite-for-synspective/

12) ”Synspective's First Satellite "Strix-α" Successfully Reached Its Target Orbit,” Synspective Press Release, 15 December 2020, URL: https://synspective.com
/news-press/successfully-reached-its-target-orbit/



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 (herb.kramer@gmx.net).

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