2 High Performance Single Unit CubeSat Design Approaches
2.1 CubeSat Market Observations
2.1.2 Commercially-Procured Spacecraft
Unlike Planet Labs’s Dove satellites, Spire Global’s triple unit Lemur-2 Cube-Sats (cf. page 2) are no completely independent development of the company, but relying on the power system and solar cells commercially-procured from Clyde Space, as stated by Ostrove in [31].
Sky and Space launched theThree Diamondsdemonstrator mission (cf. page 2, [8]). The satellites are based on the advanced triple unit CubeSat platform of Danish supplier GomSpace [32]. The satellites of the Kepler Communications constellation are based on the Clyde Space triple unit CubeSat bus [33].
And Aerial & Maritime is procuring the first four satellites of its planned constellation from Danish CubeSat company GomSpace. The satellite bus is based on the advanced GomSpace platform with heritage from the GOMX-3 mission, which is presented by Gerhardt, Bisgaard, and Alminde in [34].
But not only NewSpace companies procure CubeSat buses on the market. The spacecraft of NASA’s RAVAN mission as presented by Swartz et al. in [35]
is based on Blue Canyon Technologies’s XB3 integrated triple unit CubeSat platform [36]. RAVAN is a technology demonstration mission for radiometry instruments used for analyzing the earth energy imbalance, which is a measure for climate change (cf. Swartz et al. in [37]).
This enumeration of CubeSat missions based on commercially-procured space-craft buses does not claim to completeness. Most CubeSat suppliers like Pumpkin, ISIS, SSTL, Clyde Space, or GomSpace are offering integrated plat-form solutions. To get a better understanding of those platplat-forms’ capabilities, their characteristics have been collected in tables 2.1 to 2.3. The tables show, that the majority of integrated platforms aims at triple unit CubeSats, with only three platforms aiming for single or double unit application. Besides the stated target CubeSat size, integrated platforms would be capable of supporting larger or smaller CubeSat form factors, with implications foremost on attitude control, due to the differing moment of inertia, and on payload power, due to solar cell area and therefore available power.
2.1.2.1 Payload Volume
Single unit platforms allow for a maximum payload volume ratio of 25 %. In comparison to the larger platforms, which are in a range between 50–66.7 % of payload volume, this appears to be very small. The observed behavior is explained by the fact, that single and triple unit platforms of the same vendor rely on a similar set of CubeSat subsystems. For compatibility reasons with other suppliers, those subsystems are implemented on individual printed circuit boards (PCBs) and conform to the PC/104 form factor, which is the de-facto standard used for board-to-board connectors in the CubeSat industry [38].
2.1.2.2 Payload Mass
While the CubeSat design specification [25] intends for a total of 1.33 kg mass per unit, spacecraft like Planet Labs’s Dove [6] or NASA’s RAVAN [46]
weigh more than the 4 kg allowed for a triple unit CubeSat. Other vendors of CubeSat deployers, however, have establisehd a 2 kg per unit maximum mass limitation. The same limit has been adopted by integrated platform vendors (cf.
table 2.1). Hence, overall satellite volume translates to a total maximum mass Table 2.1:Integrated CubeSat platforms: mechanical and electrical characteristics
Brand Name Satellite Payload Source
Volume Volume Mass Power
U U kg W
Clyde Space 1 0.2 2 [33]
GomSpace Basic 1 0.25 0.17 1.3 [32, 39]
Space Inventor 2 1.25 0.3 20 [40, 41]
BCT XB3 3 2 4.5 60 [42]
Clyde Space 3 1.6 12 [33]
GomSpace Advanced 3 2 3.5 [32]
ISIS Basic 3 2 4 2 [43]
ISIS Advanced 3 1.5 3 3.5 [43]
SSTL Cube-X 3 2 2 6 [44]
Tyvak Endeavour 3 2 65 [45]
of 2 kg, 4 kg and 6 kg for single, double, and triple unit CubeSats, respectively.
Based on available payload masses and the above maximum masses, single and double unit CubeSats achieve a rather homogeneous payload mass ratio of about 8 %. The very small payload mass ratio of the two-unit platform, in contrast to its 62.5 % payload volume ratio, is explained by the aluminum housings used for all subsystem to increase radiation tolerance [40], making them significantly heavier than the subsystems of most other companies.
Triple unit payload mass ratios show a wide spread, spanning from 33.3 % for the Cube-X [44] to 75 % for the XB3 platform. Due to poor documentation in the original sources, no clear trend for payload mass ratio is distinguishable.
However, available payload mass of 3 kg for a triple unit platform is realistic, as three out of four entries show 3 kg and above available payload mass.
2.1.2.3 Payload Power
In their 2010 survey [47], Bouwmeester and Guo state, that for CubeSats with body-mounted solar cells the available specific power increases for smaller satellite masses. They explain this with the fact, that satellite mass is related to the outer satellite dimensions with the third power, while available solar cell area is related only with the second power to the outer dimensions. For satellites with a mass between 1–2 kg, Bouwmeester and Guo document a maximum specific power of 2 W/kg. It drops to about 1 W/kg for satellites in the range of 4–6 kg.
Table 2.1 lists a maximum payload power of 2 W/U for the single unit plat-forms, equal to a specific payload power in the range of 1–2 W/kg, which agrees well with the specific powers presented by Bouwmeester and Guo in [47]. The situation for double and triple unit spacecraft appears to be very inhomogeneous, with available payload powers between less than 1 W/U and 21.7 W/U. Expressed as specific power, this would be in a range of up to about 16 W/kg.
Observed available payload power of single unit spacecraft is well explained by the fact, that the small satellites usually do not feature deployable solar panels.
Values of 4 W/U and above seen for the double and triple unit variants are
also well explained with the application of deployable solar panels. Smaller values of less than 4 W/U were observed for several platforms. A closer look at the original data sources shows, that except for the ISIS basic bus, the given average payload powers are the absolute minimum values, and may easily surpass 24 W, as stated e.g. in [43].
2.1.2.4 Attitude Determination
According to the survey of Bouwmeester and Guo [47], sun sensors and magnetometers are the most commonly used sensor type within all pico- and nanosatellites between 1957 and 2009. Nearly 30 % of all missions in their database were equipped with either one or both of these sensor types. Funke et al. in their 2016 analysis on the characteristics and development of small satellites [48] state, that coarse sun sensors, magnetic field sensors, and angular rate gyroscopes have become the state of the art for small satellite attitude determination. To achieve precision attitude knowledge, however, additional star cameras are necessary.
The column for attitude knowledge data gathered in table 2.2 shows the biggest gaps. Only three triple unit platform manufacturers explicitly state the attitude knowledge. Tyvak’s is ranked top among the others with few arcsec attitude knowledge, while Clyde Space’s and GomSpace’s platforms support attitude knowledge in the range of few arcmin.
2.1.2.5 Attitude Control
In table 2.2, a clear distinction can be seen between low-precision systems with 5° and above pointing accuracy, and high-precision systems that feature a pointing accuracy of better than 1°. A similar distinction is made for agility, represented by the slew rate of maneuvers. While GomSpace’s single unit CubeSat platform has only a slew rate of 0.17 °/s, all triple unit platforms feature 3 °/s and above. The larger slew rates of the triple unit platforms are achieved using sets of at least three reaction wheels.
With a pointing accuracy of 7.2 arcsec and a slew rate of 10 °/s, Blue Canyon Technologies’s integrated triple unit CubeSat platform stands out from all other platforms. This performance is achieved using reaction wheels and a sensor bank that comprises, among other, two star cameras.
2.1.2.6 Communications
According to Funke et al. in [48], the most commonly used band for com-munication on CubeSats is UHF. All basic configurations in table 2.3 host UHF communications equipment, and achieve up to 19.2 kbps data rate. The majority of advanced configurations feature at least S-band communication, which starts at a data rate of 3.40 Mbps. The high-end variants offer additional X-band communication, with data rates up to 800 Mbps in the case of the Clyde Space platform.
2.1.2.7 Harness and Connectors
Bouwmeester, Langer, and Gill in [38] state, that the PC/104 connector
"has become the de-facto standard wiring harness in CubeSats, as most commercial developers provide their subsystems with this interface". Their survey showed, that a growing number of CubeSats to be launched will implement the PC/104 connector, which they justify with the increasing availability of commercial subsystems that feature the 104-pin stackable connector. They further conclude, that a small majority of participants in their survey states that the PC/104 connector is too big, while otherwise no major problems are seen with the standard.
Bouwmeester, Langer, and Gill in [38] recommend that a future standard interface connector for CubeSat subsystems should be smaller than the PC/104 connector. They further conclude that this standard interface should have a fixed pin allocation to achieve general compatibility between subsystems.
Table 2.2:Integrated CubeSat platforms: attitude determination and control system characteristics
Brand Satellite ADCS Source
Volume Knowledge Accuracy Slew
U arcmin ° °/s
Clyde Space 1 5 [33]
GomSpace 1 0.17 [32, 39]
Space Inventor 2
BCT 3 0.002 10 [42]
Clyde Space 3 3.5 5 [33]
GomSpace 3 6 0.1 [32]
ISIS 3 10 4 [43]
ISIS 3 1 3 [43]
SSTL 3
Tyvak 3 0.043 0.057 3 [45]
Table 2.3: Integrated CubeSat platforms: communication system characteristics
Brand Satellite Communication Source
Volume Band Rate
U kbps
Clyde Space 1 VHF, UHF 9.6 [33]
GomSpace 1 UHF [32, 39]
Space Inventor 2 UHF 19.2 [40]
BCT 3 UHF, S, X 15 000 [42]
Clyde Space 3 VHF, UHF, S, X 800 000 [33]
GomSpace 3 UHF, S 7 500 [32]
ISIS 3 VHF, UHF 9.6 [43]
ISIS 3 VHF, UHF, S 3 400 [43]
SSTL 3
Tyvak 3