Attitude determination and control (ADCS)

Also known as ADCS, AOCS, GNC, Attitude control

Measures the orientation of the spacecraft and turns it where the mission needs it. From magnetometers and magnetorquers to star trackers and reaction wheels, small-satellite ADCS covers pointing from tens of degrees to arcseconds.

Document
SQ-SS-003
Updated
20 Oct 2026
Reading time
7 min
In this tab

Definition#

An attitude determination and control system () measures where the body axes of a spacecraft point and drives them to the target the mission needs. The determination side turns sensor readings into an attitude estimate; the control side computes the torque that closes the gap between estimate and target and commands the actuators[1]. Pointing a camera or an antenna, turning arrays to the Sun and firing a thruster along the right axis all depend on this loop.

Classes of missions#

The pointing requirement spans several orders of magnitude:

  • Passive or only. Most amateur-radio and educational missions only need to slow the spin. Passive magnetic stabilization with a permanent magnet and belongs here.
  • Coarse pointing (a few degrees). Magnetometer, cosine Sun sensors and point arrays at the Sun or an antenna at nadir.
  • Fine pointing (below a degree). Reaction wheels, fine Sun sensors and star trackers serve Earth observation, optical communication and astronomy.

Integrated ADCS units in the NASA report declare pointing between 0.002° and 5°; a unit of this class flew on the 6U MarCO and ASTERIA missions[2].

The control loop#

flowchart TB
  S["Sensors"] --> K["Attitude estimation"]
  K --> C["Control law"]
  C --> A["Actuators"]
  A --> D["Spacecraft dynamics"]
  B["Disturbance torques"] --> D
  D -->|"measurement"| S

After separation a spacecraft usually spins at a few to a few tens of degrees per second. The first job is to remove that spin (detumbling). The magnetic law reduces the rate with nothing more than a magnetometer and magnetorquers, without an attitude estimate[3].

Approaches flown on PocketQubes#

ADCS is where the size, weight and power limits of PocketQubes bite hardest, and where off-the-shelf parts and published design data are scarcest[4]:

ApproachTypical hardwareCapability and limitsExamples
Passive magnetic (PMAC)Permanent magnet, soft-magnetic hysteresis rodsNo power; aligns one axis with the field; slow damping; sensitive to magnet–rod coupling and residual dipolesGrizu-263A, many 1P and 1.5P missions
Gravity gradient and damperElongated body, viscous damperNo power; points the long axis at the Earth; needs inertia asymmetry, hence multi-unit formatsSTECCO (6P)
Active magneticMagnetorquers (wound or PCB-integrated), magnetometer or IMUDetumbling and coarse pointing; momentum dumping; torque limited by field strength and geometryDelfi-PQ, POQUITO
Three-axis with wheelsWheels, Sun sensors, magnetometer, magnetorquersInertial pointing (about 5° worst case on Unicorn-2); enables imaging; highest power and volumeUnicorn-2

References

  1. [1]Markley, F. L., & Crassidis, J. L. (2014). Fundamentals of Spacecraft Attitude Determination and Control. Space Technology Library, vol. 33. Springer.doi:10.1007/978-1-4939-0802-8
  2. [2]NASA Small Spacecraft Systems Virtual Institute. (2026). Guidance, Navigation, and Control. State-of-the-Art of Small Spacecraft Technology (2026 edition), Chapter 5. NASA Ames Research Center.nasa.gov(accessed 20 October 2026)
  3. [3]Avanzini, G., & Giulietti, F. (2012). Magnetic detumbling of a rigid spacecraft. Journal of Guidance, Control, and Dynamics, 35, 1326–1334.doi:10.2514/1.53074
  4. [4]nadir lab. (2026). PocketQube picosatellites: A review of standards, mission trends and miniaturization constraints, with lessons learned from Grizu-263A, Türkiye’s first PocketQube [Preprint]. nadir lab.Read on nadir lab.
  5. [5]Bouwmeester, J., Radu, S., Uludag, M. S., Chronas, N., Speretta, S., Menicucci, A., & Gill, E. K. A. (2020). Utility and constraints of PocketQubes. CEAS Space Journal, 12(4), 573–586.doi:10.1007/s12567-020-00300-0
  6. [6]Franzese, V., Kanavouras, K., Bruce Rosete, C., Gouvalas, S., Sajjad, N., Alandihallaj, M., Herasimenka, A., & Hein, A. (2025). System design of the POQUITO PocketQube mission. CEAS Space Journal.doi:10.1007/s12567-025-00624-9
  7. [7]nadir lab. (2026). Materials engineering for PocketQube picosatellites: A scaling-based review and design guide [Preprint]. nadir lab.Read on nadir lab.
  8. [8]The CubeSat Program, Cal Poly SLO. (2022). CubeSat Design Specification, Rev. 14.1 (CP-CDS-R14.1). California Polytechnic State University.nasa.gov

Cite this SatWiki entry

@misc{nadirlab2026adcs,
  author       = {{nadir lab.}},
  title        = {{Attitude determination and control (ADCS)}},
  year         = {2026},
  month        = oct,
  howpublished = {nadir lab. SatWiki SQ-SS-003 (Rev. 3)},
  url          = {https://nadirlab.space/en/wiki/adcs/}
}