CUBESATS Deep-space CubeSats: thinking inside the box Roger Walker and colleagues CubeSats: small but perfectly formed consider the potential for sending Downloaded from https://academic.oup.com/astrogeo/article-abstract/59/5/5.24/5099069 by guest on 22 September 2018 nanospacecraft into deep space. CubeSats are modular spacecraft, using multiple standard-sized units of 10 x 10 x 10 cm ince the introduction of the CubeSat (figure 1); the size of the resulting spacecraft standard in the early 2000s, there has is measured by the number of units, e.g. 3U Sbeen a proliferation of nano-/small or 6U. The capabilities of these satellites have microsatellites in low Earth orbit, with increased significantly in recent years, notably 100–300 or more launched annually and at in pointing, propulsion and communications a growing rate (according to reports from as well as the availability of compact optical/ SpaceWorks and Euroconsult). CubeSats radio frequency/environment payloads. have reduced entry-level costs for space CubeSats are launched inside a standard missions in low Earth orbit (LEO) by container which simplifies launcher more than an order of magnitude (see box accommodation while ensuring safety for “CubeSats: small but perfectly formed”). the primary passenger, thus facilitating 1 Example of a 1U CubeSat shell. There is a This has brought new players into the widespread low-cost piggyback launch weight standard too – the finished launch unit space sector and launch opportunities for opportunities on many different launch must not exceed 1.33 kg. (ESA/G Porter) CubeSats have increased significantly in vehicles worldwide. At the same time, the the last decade to address the associated extensive use of miniaturized electronics, entry-level costs mean that the true power of demand. With more piggy back oppor- sensors/actuators and a stacked integration CubeSat-based nano- or small microsatellites tunities, platform capabilities and small approach has cut spacecraft production and lies in their operation as distributed systems, payloads have rapidly advanced to a level integration costs. The dramatically lower such as constellations or swarm formations. that are suitable for real operational mis- sions. Niche commercial applications are emerging based on operating multiple within the frame of the ESA General Stud- escape or Earth escape trajectories. For the CubeSats together in distributed systems, ies Programme on lunar and interplanetary time being, piggyback flight opportunities e.g. constellations and swarms. CubeSat mission concepts. must be found, either on a launcher upper How far can this new paradigm be These studies have involved either stage carrying a primary spacecraft, or on extended from the safety of LEO out to mother–daughter system architectures, the primary spacecraft itself as part of its cis-lunar and deep space, and what unique where the CubeSats are carried to a target mission. However, these opportunities are new missions can be performed? Piggy- destination such as lunar rare, and the constraints on back opportunities for CubeSats to lunar orbit or to a near-Earth object “The first inter planetary nanospacecraft deployment orbit and interplanetary space are already (NEO) on a larger spacecraft nanospacecraft can significantly influence becoming available, and innovative minia- and deployed at the target in mission was launched the Dv (velocity impulse) and turized technologies are being developed order to fulfil their mission, in May, to Mars” transfer window needed to overcome the severe technical challenges or a completely stand-alone to reach the final mission des- of deep-space missions. Performance system executing its own mission. The tination – and hence the feasibility of such a has reached a level where the first inter- mother–daughter architecture alleviates mission. Table 1 shows our assessment of a planetary nanospacecraft mission (NASA’s the technical challenges of propulsion, range of missions that could be performed Mars Cube One – MarCO) was launched long-range communication and deep-space beyond Earth orbit for a given set of piggy- in May 2018 as part of the InSight mission environment survivability, because the host back flight opportunities. (Klesh & Krajewski 2018). And, as was the spacecraft provides resources and accom- case for LEO, it is expected that there will modation during the cruise, as well as Asteroid Impact Mission be an order of magnitude reduction in the communications to Earth ground stations, Within the ESA General Studies Pro- entry-level cost of interplanetary mis- in conjunction with local inter-satellite gramme, the third edition of the Sysnova sions, thus paving the way to new mission links with the deployed CubeSats. For a technical challenge focused on Cubesat applications and architectures based on stand-alone deep-space CubeSat (i.e. where Opportunity Payload of Intersatellite distributed systems of deep-space nano- there is no mothercraft), these challenges Networking Sensors (COPINS). The overall spacecraft. This article addresses some of have to be tackled and suitable technology objective of the challenge was to investigate the missions that may be performed with solutions identified and/or developed. new mission concepts involving a number such distributed systems, their system There are presently no dedicated small of CubeSats operating together in inter- architectures and enabling technologies, launchers that can cost-effectively inject planetary space in support of the objec- based on a number of studies completely nanospacecraft onto specific near-Earth tives of the proposed ESA Asteroid Impact 5.24 A&G • October 2018 • Vol. 59 • aandg.org CUBESATS 1 Mission scenarios with respect to different piggyback flight opportunities piggyback launcher primary CubeSat CubeSat final propulsion feasibility (≤12U) on spacecraft deployment destination type spacecraft PSLV/Ariane 6 Lunar Pathfinder highly eccentric low lunar orbit/ chemical mono- yes lunar orbit Earth–Moon L2 propellant spacecraft Soyuz/Ariane 6 HERA Didymos binary NEO Didymos binary NEO cold gas yes launcher Ariane 5 JUICE Venus-bound Venus high-altitude chemical mono- yes (4 × 3U CubeSat trajectory atmosphere swing-by propellant entry probes with microcarrier) launcher Soyuz/Ariane 6/ various telecom geostationary lunar orbit/ electric no (excessive Δv, time Falcon 9/Atlas V transfer orbit NEO rendezvous and radiation dose) Downloaded from https://academic.oup.com/astrogeo/article-abstract/59/5/5.24/5099069 by guest on 22 September 2018 launcher Ariane 6 various transfer to NEO rendezvous/ electric yes (use of L2 halo orbit astronomy Sun–Earth L2 Sun–Earth L5/ for waiting until transfer heliocentric (<1 au) to target) launcher Space Launch System Orion lunar transfer lunar orbit/ electric yes trajectory NEO rendezvous launcher Space Launch System Orion lunar transfer lunar orbit/ chemical no (excessive Δv) trajectory NEO rendezvous launcher Proton/Atlas V ExoMars/ Mars transfer Mars orbit electric yes (but excessive Mars 2020 trajectory duration for spiral down) launcher Proton/Atlas V ExoMars/ Mars transfer Mars orbit chemical no (excessive Δv) Mars 2020 trajectory 2 Illustration of the AIM spacecraft and deployed CubeSats at asteroid Didymos during the DART hypervelocity impact. (ESA) Mission (AIM). AIM had three different the smaller component of the Didymos the main spacecraft would then retreat to objectives relating to technology flight binary asteroid (nicknamed Didymoon) at a distance of 100 km, ready for the impact demonstration in interplanetary space, very high velocity; AIM was envisaged as a up to a month later. The CubeSats would investigation of NEO mitigation techniques means to rendezvous with the target aster- perform their mission up until two months and acquiring new scientific knowledge for oid in advance, in April 2022, and charac- after the impact date, i.e. for three months understanding solar system evolution. The terize the binary system before, during and in total, using a 1 Mbps S-band inter- proposed COPINS payload consisted of two after the impact event. The launch of the satellite link (ISL) with the main space- or more CubeSats carried on the main AIM AIM spacecraft was proposed for 2020 on craft’s communications system (and each spacecraft in their deployment systems (two the Soyuz/Fregat launcher from Kourou other) for telecommand, housekeeping and 3U deployers), and released in the vicinity into a direct escape trajectory, with arrival payload telemetry transfer. Five different of the target asteroid Didymos, where the at the asteroid after about 22 months. Dur- CubeSat concepts were selected by ESA main AIM spacecraft acted as a commu- ing the rendezvous phase, the distance to for parallel studies via an open competi- nications data relay between the CubeSats the Sun and Earth is close to 1 au and from tive announcement of opportunity (AO) and Earth ground stations (figure 2). 0.5 to 0.1 au respectively. process, as described in table 2. The ESA AIM mission (ESA AIM Team After an initial measurement phase, the The AIM mission did not receive the 2015) was proposed as part of the AIDA AIM spacecraft would be manoeuvred to required funding for implementation, but international cooperation, together with a within 10 km of the binary asteroid. Before the objectives and concept remain valid. US spacecraft, Double Asteroid Redirection DART’s impact, the COPINS CubeSats Therefore a new mission proposal called Test (DART). DART is planned to impact (Walker et al. 2016) would be released and HERA has since been formulated based A&G • October 2018 • Vol. 59 • aandg.org 5.25 CUBESATS 2 Overview of the five AIM COPINS CubeSat mission concepts name organization system mission payload ASPECT: VTT, single 3U CubeSat with spectral imaging of Didymoon before/ imaging spectrometer in VIS/ Asteroid Spectral Uni. Helsinki, <1° pointing, cold gas after impact from 4 km orbit NIR: 1–2 m GSD; Imaging Aalto Uni. propulsion 1 m s–1 Δv SWIR spectrometer DustCube Uni. Vigo, single 3U CubeSat with characterize ejected dust plume after in situ nephelometer, Uni. Bologna, cold gas propulsion impact from 3–5 km orbit, transfer to remote nephelometer MICOS 2 m s–1 Δv, optical IR rel.