Attitude Determination and Control System (ADCS)

Andrew TudorSWARM 2

29 November 2010

Approximation of Space Craft Geometry

Ares V payload bay dimensions and resulting individual spacecraft approximation, m=300 kg

Attitude Determination

• Control the craft WRT some reference frameSensor Typical Performance Weight Range (kg) Power (W)

Inertial Measurement (Accelerometers and Gyros)

Gyro drift rate = 0.003 – 1 deg/hourLinearity = 1-5 e-6 g/g2 over 20-60 g

1 – 15 10-200

Sun Sensors Accuracy = 0.005 to 3 degrees

0.1 – 2 0 – 3

Star Sensors (Scanners and Mappers)

Attitude Accuracy = 0.0003 – 3 degrees

2 – 5 5 – 20

Horizon Sensors1) Scanner / Pipper2) Fixed Static Head

Attitude Accuracy = 1) 0.1 – 1 degree (LEO)2) <0.1 - .25 degree

1) 1 – 42) 0.5 to 3.5

1) 5 – 102) 0.3 – 5

Magnetometer Attitude Accuracy = 0.5 – 3 degrees

0.3 – 1.2 < 1

Attitude Determination

• High TRL and simplicity is preferred• Combination of sensors for initialization and

redundancy– GPS to initialize star sensors– Star sensors are very common and have a high TRL– 2 attitude determination sensors

• Information is shared among other systems

Attitude Control

• Quantify disturbance environment

• Size actuators– Reaction Wheels– Thrusters

Disturbance Type Disturbance Quantification (Nm)Gravity Gradient 0Solar Radiation 6.41e-5Magnetic Field 4.05e-5Aerodynamic 4.78e-5

Total Disturbance (Td) 1.524e-4

Guidance, Navigation and Control System (GN&C)

Andrew TudorSWARM 2

29 November 2010

Guidance

• Guidance = Orbit Control• Autonomous on-station control– Constellation maintenance– Fast control in debris field– Maneuvers while out of contact

• Ground based “special case maneuvers”– Debris deorbiting– Orbital transfers– End of life maneuvers

• Semi-Autonomous Control System

Navigation

• Navigation = Orbit Determination

• Global Positioning System– Position and velocity

information– Real time data– Possible inertial

navigation outside LEO• Orbits can be propagated

using E.O.M.