DeOrbitSail

Overview

Recent studies show an increasing probability of collisions between intact spacecraft and debris. The historical practice of abandoning spacecraft and upper stages at the end of mission life has resulted in 5,500 tons of space debris in low earth orbit (See, for example, Vol. 9, Issue 3 of NASA's Orbital Debris Quarterly). The uncontrolled growth of the space debris population has to be avoided in order to enable safe operations in space for the future. Space system operators need to take measures now and in the future to conserve a space debris environment with tolerable risk levels, particularly in low earth orbit (LEO) altitude regions.

As an example, the Chinese anti-satellite weapons test in 2007 destroyed the ailing Fengyun-1C weather satellite, creating over 2,300 pieces of debris. Also, in February of 2009 a collision between Russia's Cosmos 2251 and a commercial Iridium satellite created a cloud of hundreds of pieces of debris.

If a number of other explosions and/or collisions occur at altitudes which are outside the denser layers of the atmosphere, and hence not subject to rapid deorbiting by air drag, the debris sources can outnumber the sinks, and an increasing spatial density could start the onset of a cascading effect during which the particles would engage in chain reactions until they are ground to a limiting size. Altitudes with a critical particle concentration are already suspected to exist near 800, 1000 and 1500 km.

Deorbiting simply means bringing the satellite back down to Earth. After the useful life of a satellite, it poses a risk to operational satellites in the same orbit. A deorbiting system moves the satellite out of crowded orbits, either to an area of space that isn't heavily populated or back down to Earth. DeOrbitSail will return to Earth and burn up in the atmosphere.

Objectives

The European Code of Conduct for Space Debris Mitigation requires that satellites in the LEO protected region (< 2000km) are disposed of by destructive re-entry in the atmosphere within 25 years from their end of life. The DeOrbitSail project aims to demonstrate that deorbiting can be achieved with a deployable sail, and to provide a proven design for the deployment system that can be applied to systems on future spacecraft.

Top objectives

The highest-level objectives of the DeOrbitSail Project are to:

1. Provide research in the field of deorbiting
2. Provide a demonstrated and verified design for deorbiting of satellites and debris
3. Provide effective and efficient in-space propulsion technologies based on solar sails.

Secondary objectives

In addition we would like to achieve the following secondary objectives:

1. Demonstrate avoidance manoeuvre by controlling sail attitude
2. Perform sail ground imaging exercise, this will also involve a sail attitude manoeuvre.

How we will meet these objectives

The research objectives of this project will be fulfilled by the production of a satellite that can perform the following tasks:

1. Fully deploy a 4 m by 4 m sail from a 3U sized package
2. Deorbit from an altitude of 600 km in less than 180 days
3. Provide photographic, orbit trajectory and attitude data confirmation functions.

The deorbiting shall be accomplished with a design that provides the following functions:

1. Three-axis control of the s/c sufficient to maintain pointing relative to velocity vector
2. Deployable solar panels to sufficiently power all subsystems
3. Imaging capability to photograph the deployed sail
4. Space to ground communications capability.

Attitude determination and control system (ADCS)

The ADCS processing will be carried out by a software task running on the on board computer. The estimation and control loop will execute at a rate of 1 Hz. It will make use of sensor data from the following sensors:

• 3-axis resistive magnetometer
• Optical sun- and nadir sensors
• 3-axis MEMS gyroscope
• coarse sun sensing using 6 photodiodes.

Find out more about sails in space.

Advantages

DeOrbitSail will use drag to lower its orbit and demonstrate a system that can be used for solar sailing at altitudes where drag forces are very low.

The drag produced by the thin atmosphere in low earth orbit has a lot in common with the force of solar radiation pressure. Both can be captured best by maximizing the area of the spacecraft. Both produce very low levels of force. Most importantly, both are inexhaustible sources of force, requiring no propellant from the spacecraft.

Drag force can be used even when no spacecraft systems are working, and solar radiation pressure demands only an operating attitude control system. Because performance for both types of deceleration is governed by spacecraft frontal area, one design can do a good job at catching atmospheric drag at low altitudes (below about 600 km) and exploiting solar radiation pressure at high altitudes.