As the market for small spacecraft and cubesats has expanded since the last edition of this report, a niche has emerged for off-the-shelf assembled spacecraft buses. These buses provide integrated platforms upon which a payload can be hosted and ready to fly in a very short amount of time. As the platform may be purchased for any of a wide variety of missions, the subsystems are sized to be as diverse and capable as possible.
Two trends have emerged in the cubesat bus market: cubesat component developers with a sufficiently diverse portfolio of subsystems offering package deals, or companies traditionally offering engineering services for larger bespoke platforms miniaturizing their subsystems.
State of the Art
Table 2.1 is a list of the integrated platforms currently available for small spacecraft and Table 2.2 lists the small spacecraft platform specifications. Millenium Space Systems has been developing the Altair small spacecraft, see Figure 2.1, platform under contract from DARPA . The Altair is a smaller version of their Aquila series (up to 3000 kg) which has extensive flight heritage. So far the Altair has undergone balloon testing , thermal vacuum and vibration testing . The first launch is scheduled for 2016 on the F-15 Airborne Launch Assist Space Access (ALASA), also sponsored by DARPA.
Astro-und Feinwerktechnik Adlershof offers the TET-1 platform, which flew on a Soyuz-FG/Fregat launch in 2012 as a secondary payload, see Figure 2.2. TET-1 is larger than Altair, at 670 x 580 x 880 mm but offers the same 50 kg payload mass. The TET-1 attitude control system, reused from the BIRD (Bispectral and Infrared Remote Detection) DLR mission in 2001, provides 2 arcmin pointing and 10 arcsec knowledge .
Berlin Space Technologies produces a series of small spacecraft named the LEOS-30 TRLX, LEOS-50 TRLX, and LEOS-100. The LEOS platforms are based on designs flown for multiple TUBSAT and LAPAN missions , . Two LEOS-50 platforms will be delivered later this year as the Kent Ridge mission while a LEOS-100 will be delivered in mid-2016 , .
The LEOS-30 is a 20 kg spacecraft, allowing 5-8 kg payload capacity. UHF and S-band communications are provided, and the system is designed for a 2 year operational life. The LEOS-50 is a 50 kg spacecraft, allowing 15-25 kg payload capacity, see Figure 2.3 . UHF communications are provided for telemetry and control, while a 100 Mbps X-band link is available for data downlink. The ADCS provides 1 arcmin pointing accuracy and 10 arcsec pointing knowledge with a 10° s slew rate and less than 15 arcsec/s jitter. The vehicle is 600 x 600 x 300 mm, provides an average of 20 W payload power within a payload volume of 400 x 400 x 200 mm and is designed for an operational lifetime of 5 years .
The LEOS-100 is a larger structure reusing the LEOS-50 avionics. Due to the larger mass it provides 1 arcmin pointing accuracy and 2.5 arcsec pointing knowledge with a 5° s slew rate and less than 5 arcsec/s jitter. The vehicle is 600 x 600 x 800 mm with a mass of 65 kg, and the payload volume is 500 x 500 x 500 mm with an allowance of 30-50 kg. The larger vehicle generates more solar power and can provide 60 W average power to the payload, while the X-band communications have also been upgraded to 400 Mbps. The LEOS-100 also has options for 2 Gbps optical data downlink and cold gas or electrical propulsion .
Surrey Satellite Technology Limited (SSTL) has a long legacy of small spacecraft in orbit. There are 8 of the SSTL-100 in orbit, 10 of the SSTL-150 (see Figure 2.4), and a version modified to fit the ESPA ring called the SSTL-150 ESPA. A down-specced variant on the SSTL-150 called SSTL-X50 is in final testing for a forthcoming launch .
|Product||Manufacturer||Status||Radiation Testing (krad)|
|Altair||Millenium Space Systems||TRL 8||LEO Parts heritage|
|TET-1||Astro-und Feinwerktechnik Adlershof GmbH||TRL 9||13|
|LEOS 30/50/100||Berlin Space Technoloies GmbH||TRL 8||LEO parts heritage|
|SCOUT||Spaceflight Industries||TRL 8||15|
|SSTL-100/150/X||Surrey Satellite Technology Ltd.||TRL 9||5|
|Product||Vehicle Size (mm)||Payload Mass (kg)||Payload Power (W)||Point Control (arcmin)||Pointing Knowledge (arcsec)|
|MSS Altair||300 x 300 x 300||50||90||0.3||10|
|AF Adlershof TET-1||670 x 580 x 880||50||Unkn.||2||10|
|BST LEOS-50||600 x 600 x 300||50||20||1||10|
|BST LEOS-100||600 x 600 x 800||65||60||1||2.5|
|SSTL-150||600 x 600 x 300||50||20||1||10|
|SSTL-150 ESPA||600 x 600 x 800||65||60||1||2.5|
|SSTL-X50||600 x 600 x 800||75||60||1||2.5|
|SLI SCOUT||400 x 460 x 840||55||95||3||18|
Tyvak NanoSatellite Technology Inc. is replacing their Intrepid platform with the new Endeavour platform, available in a variety of form factors from 3U to 12U, shown in Figure 2.5 , . Two 3U Endeavour spacecraft are scheduled to fly in 2016 as NASA’s Cubesat Proximity Operations Demonstration (CPOD) , . The 3U variant weighs 5.99 kg with payload, allows 2U payload volume, and offers 15 W payload average power. The ADCS provides 0.06° pointing control and 25 arcsec pointing knowledge, 3° per second slew rate using reaction wheels and torque coils. Endeavour generates up to 70 W power, and provides S-band communications of 10 Mbps in addition to the UHF offering. Endeavour has been radiation tested for over 24 months mission lifetime (10 krad) in collaboration with Vanderbilt University , . The solar panels and radio flew on JPL’s IPEX mission in 2013, and the radio flew again on CalPoly’s Exocube mission in 2015.
The GOMX bus in Figure 2.6 from GomSpace GomSpace ApS of Denmark produces a series of cubesats under the moniker GOMX. The avionics provide 5° pointing knowledge and 10° pointing control. There are 1U, 2U and 3U variants available, directly affecting the payload volume and mass, see Table 2.3 for GOMX configurations . The variation in surface area affects available power from the solar panels. All these systems include a UHF/VHF radio link. The GOMX-1 mission flown by Aalborg University launched a 2U configuration on a Dnepr in 2013, hosting an ADSB receiver. The GOMX-2 reflight was destroyed in the CRS-3 launch. GOMX-3 has delivered a 3U configuration to the space station via a Japanese H-IIB rocket in August 2015, but has not been deployed from the station yet . A 1U variant with an integrated 3 MP optical imaging payload is available off the shelf under the name NanoEye. Two of these units have been delivered for flight but have not undergone radiation testing.
|Size||Mass before payload (kg)||Available Volume||Available Payload Power (average W)|
Blue Canyon Technologies LLC has pursued a smaller, modular form factor. The ½U XB1 module can be stacked into larger cubesat form factors . Supporting configurations up to 27U, the XB1 (Figure 2.7) centers around two XACT modules with additional power, thermal management, payload and propulsion interfaces supported with BCT flight software. The two XACT units deliver a pointing accuracy of 0.002°, a pointing stability of 1 arcsecsec-1, and a slew rate of 10°s-1 for a typical 3U cubesat. The XB1 Avionics has been through a full qualification test program and a 3U version is flying in 2016 as part of APL’s RAVAN mission. A 6U version is flying in late 2016 as part of the PlanetIQ GPSRO Constellation, and the XB1 avionics will fly on the NASA Goddard CERES mission also in 2016 .
Surrey Satellite Technology Ltd. from the UK is focusing on their larger form factors (50+ kg) , but they also offer two cubesat platforms. The Cube-X and Nano-X platforms are available in 3U, 6U, 12U and 24U, resulting in a total launch mass of 5 to 20 kg, see Figure 2.8 for the Nano-X bus.
Some manufacturers such as Pumpkin Inc. offer a package deal of components. For example, the MISC 2 Mk II provides a 3U structure allowing 100 x 100 x 165 mm payload volume, with pointing provided by the MAI-100 ADACS from Maryland Aerospace Inc. The MISC 3 also provides a 3U structure allowing 100 x 100 x 175 mm payload volume, with the option of pointing from a MAI-400 ADACS from Maryland Aerospace Inc. or a BCT XACT ADCS from Blue Canyon Technologies .
Other large-scale producers such as Clyde Space from Scotland  and ISIS from the Netherlands  offer tailored solutions, see Complete Cubesat bus from ISIS B. V. in Figure 2.9. The individual componentry they offer has flight heritage, but will be addressed individually in the subsequent chapters of this report. As they offer no standard packages they are not discussed further in this chapter. Table 2.4 lists the overall current available integrated cubesat platforms.
|Product||Manufacturer||Status||Radiation Testing (krad)|
|Endeavour||Tyvak NanoSatellite Systems Inc.||TRL 8||10|
|GOMX||GomSpace ApS||TRL 9||10|
|XB1||Blue Canyon Technologies LLC.||TRL 8||Unkn.|
|Complete Cubesat Kits||Pumpkin Inc.||N/A (no single configuration)||LEO parts heritage|
On the Horizon
As spacecraft buses are combinations of the subsystems described in later chapters, it is unlikely there will be any revolutionary changes in this chapter that are not preceded by revolutionary changes in some other chapter. As launch services become cheaper and more commonplace the market will expand, allowing universities and researchers interested in science missions to purchase an entire spacecraft platform as an alternative to developing and integrating it themselves. As subsystems mature they will be included in future platforms offered by vendors. The larger vendors will gain more flight heritage and tweak their platforms to improve performance, while smaller vendors will emerge into the market. For example, SSTL has two new offerings in development called the Next Generation Microsatellite and the FeatherCraft, both still at TRL 3 . The Next Generation Microsatellite provides a lower price point compared to the existing platforms, while the FeatherCraft features significantly increased propulsion capability with a dV of 150 m/s.
One key development likely as the industry matures is radiation tolerance and radiation hardening, especially as small spacecraft start venturing into deep space. Subsystems described later in this report include details on radiation testing, but the combination of subsystem mean time between failures (MTBF) into overall system reliability will become a key design criterion as the sample groups become large enough to be statistically significant.
In the paradigm of larger GEO buses, a number of vendors have pre-designed, fully integrated small spacecraft buses available for purchase. Due to the small market they will of course cooperate with customers to customize the platform. This paradigm is continued in the cubesat form factor, but a new design concept also emerges: due to the cubesat standard interfaces, many standardized components are available, leveraging consumer electronics standards to approach the plug and play philosophy available for terrestrial PCs and computer servers. In particular, since the previous edition of this report cubesat communications and guidance, navigation and control subsystems have matured significantly. At present software is lagging behind hardware in modularity and reusability, and represents the largest hurdle to delivering cubesat missions.