Virginia CubeSat Constellation

CubeSat Advisors: Mechanical: Dr. Robert Ash ECE: Dr. Dimitrie Popescu 435 Team Members: Kevin Scott- Team Lead Robert Kelly- Orbital modeling and power Austin Rogers- Attitude control (Physical) Joseph Kingett-Attitude control (Logic) Matthew Degroff- Prototyping and Thermal

Background -CubeSat pico satellites have been used for the past 15 years for small orbital missions. -Drag forces acting on orbiting objects depend on the shape, speed and local density of the atmosphere. -Local Low Earth Orbits (LEO) densities are controlled by solar activity. -The science data obtained from single satellite missions cannot deliver an accurate model of the LEO densities. This is due to satellites traveling much faster than the thermal speeds of the gas particles in the medium. -As a consequence, the measurements made aboard a spacecraft are similar to a series of photographic snapshots from different locations.

Mission Objectives 1. Successfully develop, integrate, test and fly a 1U CubeSat in an orbital constellation of three 1U CubeSats (with VT, HU, and UVa) 2. Obtain measurements of the orbital decay of a constellation of satellites to develop a database of atmospheric drag and atmospheric properties 3. Demonstrate a system to determine relative and absolute spacecraft position across an orbiting constellation. 4. Successfully deploy a drag brake to document orbital lifetime reduction via alteration of ballistic coefficient.

CubeSat Team Structure:

Attitude Determination and Control System (ADCS) - Physical Components Magnetorquers use the interaction between their own electrically-induced magnetic field and the magnetic field of the Earth to control satellite attitude. Digital simulations gained favor over physical ADCS testing CubeSat component selection: GOM Space P110-series solar panels with integrated magnetorquers (x and y axes) GOM Space custom PCB magnetorquer (z axis)

ADCS - Control Logic Magnetorquers follow the equation: τ=μ×B τ is the magnetic torque result μ is the magnetic moment of the solenoid B is the Earth’s magnetic field I B If current is flowing through the wire, it produces a magnetic field It will react with the ambient magnetic field producing a torque that acts about an axis that is orthogonal to the plane containing μ and B Producing rotation about the torque axis

Sun Sensors The sun sensor is essentially a photoresistor. This component has a changing resistance value dependent upon the level of light that the sensor is exposed to. The use of the sen sensor for attitude determination uses these principles to predict the position of the sun relative to the CubeSat inertial frame. Intensity changes dependent upon the incident angle. Comparing the currents measured at an incident angle and a max tabulated value The ratio of these values can be used as a cosine of the incident angle Multiplying the cos(α) term with estimated solar distance will produce the distance in the normal direction IRec= IMaxcos(α) α CubeSat

Simulated Environment Uses local magnetic field, initial angular velocity, initial orientation, and the dipole moment of the magnetorquers as initial parameters Simulates what a magnetometer would read when rotating through a constant magnetic field Estimated the torque produced by a magnetorquer when a current of 0.5 A is applied through it Parameters are editable to focus on individual parts or inputs

Power Simulations using a feature of Satellite Toolkit (STK), called the Solar Panel Tool, were completed for a period from March 1, 2018, to December 31, 2018. These used the custom model of the CubeSat with both 4 and 3 side solar panels. For the four solar panel configuration, average instantaneous power generation was 1.40 W. For three panels, 1.33 W.

Orbital Simulations Orbit simulations using STK’s High Precision Orbit Propagator (HPOP) found the following values for orbit lifetimes: Drag Brake Deployed: 57 days for Cd = 4.04 Drag Brake Undeployed: 330 days for Cd = 2.39

Orbital Simulation

Prototyping and CubeSat Development -Constrained by Nanorack deployment system (ISS Deployer) -Two piece design -Drag brake is designed into main rail housing -10cm x 10cm sides -rails are 100mm end-to-end -rails act as guides and house switches and springs for deployment

Material Selection Results Estimated Max. Deflection Estimated Max. von Mises Stress Aluminum 6061 0.04 mm 6.3E+7 Pa Windform XT 2.0 0.1 mm 4.05E+7 Pa

Material Selection Aluminum 6061 Windform XT 2.0

Gantt

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