Gyro-Control of a Solar Sailing Satellite
by
Hendrik W. Jordaan
Willem H. Steyn
Electronic Systems Laboratory
Department of Electrical & Electronic Engineering
Stellenbosch University
January 20, 2017
International Solar Sailing Symposium
Background
Attitude ControlSolar sailing
Gyro-Control
Conclusion
Situated about 30 minutes
away from Cape-Town,
South-Africa
Stellenbosch
International Solar Sailing Symposium
Background
Attitude ControlSolar sailing
Gyro-Control
Conclusion
History with microsatellites,
SunSat, SunSpace,
SumbandilaSat
Current main focus is on ADCS
research
Develop ADCS CubeSat
components which is sold
under CubeSpace brand
Also involved in a number of
interesting international projects
Stellenbosch University
International Solar Sailing Symposium
Background
Attitude ControlSolar sailing
Gyro-Control
Conclusion
• Current solar sailing missions main payload is the solar sail
• Future missions will have other science payloads e.g.
image payloads
• Main specification driver for attitude control is mission
payload
• Attitude control requirements for solar sailing is low, only
slow manoeuvres and rough attitude stability relative to a
sun angle.
• High sampling and long exposure payloads very stringent
attitude requirements
Attitude Requirements
International Solar Sailing Symposium
Background
Attitude ControlSolar sailing
Gyro-Control
Conclusion
• Largest difference between a solar sail and standard
spacecraft is the large MoI, which is obtained when
deploying a large space structure.
• When comparing the MoI of a 80m2 and 100m2 square sail
there is a 43.9% increase in the MoI with less than a meter
increase in boom length.
• The attitude control actuator specifications should increase
• This is dependent on the sail/spacecraft MoI ratio
• Ratio of the sail MoI relative to the entire spacecraft MoI
Standard Satellite vs Solar Sail Satellite
Parameter 80m2 Sail 100m2 Sail
Boom length 6.325m 7.071m
MoI Ixx=Izz 10.149kg.m2 14.607kg.m2
MoI Iyy 20.299kg.m2 29.213kg.m2
International Solar Sailing Symposium
Background
Attitude ControlSolar sailing
Gyro-Control
Conclusion
• The sail/spacecraft MoI ratio is determined simply by λ =max(𝚲) with 𝚲 = 𝑰𝑆/𝑰 where 𝑰𝑆 the MoI of the sail and 𝑰 is
MoI of the entire spacecraft.
• Small λ indicates rotational dynamics of spacecraft is
dominant
• Larger λ indicates that the dynamics are greatly influenced
by the sail
• MoI will greatly influence the attitude performance either
increase in sail size or vibration of non-rigid elements
• Some control attitude control methods will greatly influence
this ratio and thus less suitable to scale to larger solar sails.
• Manoeuvres are limited by actuator specifications and the
non-rigid dynamics of the sail
Standard Satellite vs Solar Sail Satellite
International Solar Sailing Symposium
Background
Attitude ControlSolar sailing
Gyro-Control
Conclusion
• Current attitude control methods can be separated into two
categories:
• Active methods
• Thrusters (gas and electric)
• Standard magnetorquer rods
• Reaction and momentum wheels
• Solar thrust methods
• Changing CoM
• Translation stage
• Control boom
• Mass-balasts
• Changing CoP
• Reflective changes
• Control vanes
• Sail shape changes
• Review by Fu et al. 2016
Current attitude control methods
International Solar Sailing Symposium
Background
Attitude ControlSolar sailing
Gyro-Control
Conclusion
• Spinning sail has a number of advantages above stabilised
sail
• Unsymmetrical solar thrust averaged to spin vector
• Centrifugal force produce internal force
• Major drawbacks are
• Satellite bus is rotating, limits mission payload
• Angular momentum bias resists angular manoeuvres
Spinning Solar Sail
Standard Spinning Solar Sail Slow Spinning Solar Sail
International Solar Sailing Symposium
Background
Attitude ControlSolar sailing
Gyro-Control
Conclusion
• The tri-spin solar sail consists of three sections rotating
relative to each other.
• The nett angular momentum of the spacecraft is zero
• Similar to connecting two dual-spin satellite to each other
• The gyro tri-spin solar sail is created by placing these
rotating structures on two-axes gimbals.
Tri-Spin Solar Sail
Tri-Spin Solar Sail Gyro Tri-Spin Solar Sail
International Solar Sailing Symposium
Background
Attitude ControlSolar sailing
Gyro-Control
Conclusion
• This configuration creates a dual CMG configuration
• Torque multiplication achieved with small changes in gimbal
angles
• Steering laws of gimbal angles, assuming scissoring, can
be used to determine required gimbals angels and control
inputs for certain torque requirements
Gyro Control
International Solar Sailing Symposium
Background
Attitude ControlSolar sailing
Gyro-Control
Conclusion
Gyro Control (cont)
International Solar Sailing Symposium
• Creates a scalable attitude actuator – angular momentum of
the sail is used to determine the actuator performance
• Larger angular momentum requires smaller gimbal angles
to obtain reference torque
Background
Attitude ControlSolar sailing
Gyro-Control
Conclusion
Gyro Control (cont)
International Solar Sailing Symposium
• Investigated the effects of some control inconsistencies
• Angular momentum bias, gimbal angle errors and MoI
uncertainties are investigated
Background
Attitude ControlSolar sailing
Gyro-Control
Conclusion
• High performance attitude control must be achieved on
solar sail satellites to make it appropriate for science
missions.
• Some control methods scale much better to larger sails than
others.
• Gyro tri-spin solar sail produce an attitude control actuator
that scales with the MoI of the sail
• Comes at a cost e.g. large mechanical complexities
• Starting to exist the realm of ignoring sail vibrations
Conclusion
International Solar Sailing Symposium
Background
Attitude ControlSolar sailing
Gyro-Control
Conclusion
• The current trend is for more deployables on smaller
spacecrafts, not only true for solar sails.
• Smaller spacecrafts are more susceptible to non-rigid
influence.
• Future ADCS needs to be able to handle active damping of
vibrations to be able to operate mission payloads.
Final Remarks
International Solar Sailing Symposium
Background
Attitude ControlSolar sailing
Gyro-Control
Conclusion