Team Members. Surrey Space Centre (SSC): Study lead, payloads, ADCS (with Prof. Bong Wie), SK platform, sail technologies

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1 A Solar Kite Mission to Study the Earth's Magneto-tail Dr. Vaios Lappas C. Underwood, Luis M. Gomes, B. Wie C. McInnes, L. Tarabini, K. Wallace + 18th AIAA/USU Small Satellite Conference 18 AIAA/USU Small Satellite Conference th

2 Team Members Surrey Space Centre (SSC): Study lead, payloads, ADCS (with Prof. Bong Wie), SK platform, sail technologies Surrey Satellite Technology Ltd (SSTL): Mission analysis, RF, Power, small satellite technologies University of Glasgow: Trajectory Analysis, Mission selection, sail technologies GMV: Ground Station, Launch analysis, orbit perturbations

3 Study Goals To conceptually design a low cost, low complexity solar kite mission based on existing technologies Identify possible missions for solar kites Address specific system level challenges: attitude control, power Design the mission using existing technologies: assume a sail assembly loading of 10 gm -2 Identify preliminary requirements and suitable payloads Design a robust, affordable, low complexity solar kite mission with realistic requirements, a credible design and with a science return

4 Solar Sail Fundamentals Solar Sails (SS) : Photons, coming from the sun, hit a particular area (surface) propel this particular structure by imparting a small force F = ηpacos 2 α η: sail coefficient and has a typical value of 1.8 with film wrinkles P: SRP constant at one astronomical unit (AU) from the sun, A is the surface area of the SS α is the sun angle between the surface normal and the sun line Still can be useful to propel spacecraft, for long distances, without carrying consumables (propellant) Significant mass reduction for the spacecraft and an increase in payload mass Another key advantage is the build-up of acceleration, which can be significant, which is ideal for high V missions

5 Solar Kite (Micro-Solar Sail) For a SRP constant of P = x 10-6 N/m 2 and a thrust coefficient η = 1.8 the maximum thrust of the SK is F max = ηpa = 2.04 x 10-4 N The acceleration is then: a c = F max m ηpa = m ηp = σ = 1.2 x10 One of the enabling factors that make Solar Sail missions possible is the miniaturisation of the spacecraft bus, bringing the overall spacecraft (SK) mass down SK s vs Large Sails: Small Satellites vs Large Satellites Small Satellite Paradigm: 80% of a large mission with 20% the cost Compliment large sails (> 20 m sails) SK s: Easier to build, potentially less sail related challenges Smaller sails, less control, dynamics, manufacturing, deployment issues, more experience available, use of inflatable technologies Use MEMS, MNT, small satellite miniaturisation Short design, construction turn around 4 ms 2

6 A Solar Kite Mission to Study the Earth s Magneto-tail: GEOSAIL The geomagnetic tail around Earth poses an important scientific problem related to weather conditions on Earth Multiple studies of Nanosatellites (up to 100) for continuous multipoint measuring of the field. Geomagnetic tail missions require a spacecraft to be injected into a long elliptical orbit to explore the length of the geomagnetic tail. Orbit is inertially fixed, and the geomagnetic tail points along the Sun-Earth line, the apse line of the orbit is precisely aligned with the geomagnetic tail only once every year. Ecliptic Plane 23.5º Equatorial Plane ZIGJ Y IGJ Sun X RBF Earth X IGJ 11Re 23Re

7 GEOSAIL Mission Analysis - Compare propulsion options: - Chemical, SEP, Sail - Use 1.5 kg bus GeoSail Propulsion Options SK SEP Chemical Propulsion Options

8 SK GEOSAIL Payloads Multiple miniature payloads considered ~35 SK s are used to study the earth s magnetic tail (2-year mission): most of them can carry magnetometers and plasma detectors small number can carry space dust detectors to complement and maximise the science return from the mission

9 Solar Kite Design From SAL (10 gm -2 ) and mission V (3.5 km s -1 ), acceleration (0.11 mm s -2 ) and for a 5 x 5 m sail:

10 SK Design

11 SK Booms, Membrane There are a number of technology options for boom use on conventional solar sails. Carbon Fiber Reinforced Plastic (CFRP) booms Coilable structures These technologies are currently applied to solar sail concepts on both sides of the Atlantic. Kayser Threde and DLR booms have developed CFRP for a 20 x 20 m sail deployed on ground tests as an engineering demonstration for future solar sail missions. Able Engineering and L Garde are the main players developing coilable structures in the US with flight heritage

12 SK Booms The analysis of existing and future developments on solar sail boom technology has lead to a number of important conclusions: The mass per length ratio for the booms (specific mass) is a critical, mission enabling factor Conventional and current boom technologies can t be scaled down to a SK scale (3.535 m boom) and come heavy Analysis indicates that this technology has a use threshold for solar sails of > 20m sails Sails of < 20 m will require a 60 g/m (CFRP is 101 g/m) Coilable and hybrid booms are complex to manufacture and deploy Deployment of coilable booms is complex and has been analysed for large (> 40 m sails), making this technology difficult to implement on a SK SK will need a simple, ultra light sail with a smaller life time from large sails

13 SK Boom/Sail Deployment (II) Deployment is achieved by two miniature valves, identical to the propulsion valves used in the SK ADCS system. A 9 g gas (Helium) will inflate the structure and LHZ (15 g) be able to provide continuous pressure for a minimum 2 year lifetime of the SK. Volume for the SK boom/sail structure is the smallest possible since storage for the integrated structure is much more compact and lighter than using a traditional CFRP design

14 SK Boom/Sail Deployment SK Booms, Sail and Deployment (Nihon Concept)

15 Deployment (II) Gas Valve

16 SK ADCS Subsystem Large inertias, little mass for ADCS Large sails use cm-cp control techniques (gimballed booms etc.) Large sail control solutions won t be feasible for SK s Requirements: Moments of inertia = (1.113, 0.556, 0.556) kg-m 2, cm-cp offset = 0.01 m (0.2% of 5 meter) SRP Thrust = 0.2 mn, SRP Disturbance torque = 2 micron-m Angular momentum storage/dumping > N-m-s per hour Payload pointing accuracy = 1 Spin control scheme utilizing thrusters is selected

17 SK Control SRP Disturbance is largest disturbance: 2 micro-n-m For a 1 deg pointing requirement and a 0.2-mN solar pressure force, a spin rate of Ω = 1.2 deg/s (72 rpm) is needed Simulations conducted for the SK indicate that the required control and stabilisation requirements are feasible

18 SK Power Subsystem Simple, low cost and light Based on off-the-shelf (COTS) elements Long eclipse (up to 2.65 hours) is the limiting factor of the design Power Storage: Required for the long eclipse periods, and to support peak uses of power (downlink) The mission requires at least 4.6 A.h GaAs solar cells have been selected as the baseline

19 SK RF Subsystem Simple, low cost and light Optimised for low mass, volume, and reduced power requirement Free path loss is the limiting factor of the design S-band selected for compatibility with ground segment Uplink: Downlink S-band, 9k6, QPSK, Omni-directional coverage S-band, 38k4, QPSK, Viterbi and RS, 0.5W RF Shadowing effects of sail on antenna pattern will need to be addressed on future iteration COTS hardware is unlikely to correspond to requirements Be-spoke design likely to be required

20 SK Mass, Power Breakdown

21 Study Conclusions Complexity of Solar Sails can be reduced Small satellites (< 5 kg) an enabling factor SK can compliment large sails, conduct a large part of their missions Shorter design and manufacturing turn around Sail technology challenges can be reduced/mitigated with Solar Kites Ultra miniaturisation and MEMS technology increase sail acceleration Conventional sail technology is difficult to scale down Small size sails can use inflatable technology (ultra light) for sails < 7-10m, achieve ultra low mass SK s with a unique design prove to be an efficient, affordable and versatile solution for the niche science missions requiring high V capabilities with a significant science return

22 Thank you!!