U.S. Government Efforts to Deal With Orbiting Space Junk by Michael Erbschloe - HTML preview

State of the Art of Small Spacecraft Technology:
Passive Deorbit Systems

To constrain the amount of space debris orbiting Earth, a deorbit capability is often required. If a small spacecraft is unable to be parked in a graveyard orbit or naturally reenter Earth’s atmosphere in under 25 years, a deorbit system must be integrated. In the past decade, there have only been a few advancements on passive deorbit technologies, such as drag sails and electromagnetic tethers. NanoSail-D2, CanX-7, and several TechedSat CubeSats are all CubeSat platforms that have successfully demonstrated the use of drag sails for deorbiting in LEO within the 25 year post mission requirement. Terminator Tape is another deorbit option that uses electromagnetic tethers and is currently being flown on the Aerocube-V CubeSat. Additionally, both solid rocket and electric propulsion systems have been used to increase orbit decay rates.

It has been estimated that as a result of increased space flight, there has been an accumulation of orbital debris consisting of more than 750,000 particles with a diameter 1-10 cm and over 29,000 pieces with diameters >10 cm in orbit between Geostationary (GEO) and LEO (LEO) altitudes. As a result of all the launches into space, 94% are considered to be space debris, and 64% of those are fragments with a collective mass of 7,500 metric tons.

The objective of the NASA Orbital Debris Program along with the Inter-Agency Space Debris Coordination Committee (IADC) is to limit the creation of space debris. They have mandated that all spacecraft either deorbit within a given amount of time or be placed into a graveyard orbit for safe storage. The lifetime requirement is 25 years post-mission, or 30 years after launch if unable to be stored in a graveyard orbit.

Small spacecraft are typically launched into LEO as it is a more accessible and less expensive orbit to reach. There are lots of rideshare opportunities to LEO through several commercial launch providers. The close proximity to Earth can relax spacecraft mass, power and propulsive constraints. Additionally, the radiation environment in LEO is relatively benign for altitudes below 1000 km. Small spacecraft launched at or around ISS altitude (400 km) naturally decay in well under 25 years. However at orbit altitudes beyond 600 km, it can no longer be guaranteed that a small spacecraft will naturally decay in 25 years due to uncertainties in atmospheric density, shown below. As the majority of those spacecraft are unable to be parked in a graveyard orbit because that requires additional propellant to increase their altitude, the only option for small spacecraft in lower orbits is to deorbit.

Since deorbit systems are still in their infancy, there are only a few high TRL (TRL≥7) devices guaranteed to satisfy the 25 year requirement. Deorbit techniques can be either passive or active, although the primary focus has been on the design of passive methods. Active deorbiting requires attitude control and surplus propellant post mission, such as a steered drag sail that relies on a functioning attitude control system for pointing the sail. Propulsive devices have also been examined for deorbiting techniques, however this approach is still considered risky. Even if enough excess propellant was carried for an active decay approach, and adequate attitude control capability post mission was assured, this method requires continuous operation until reentry is met, making it inconvenient and costly for a small spacecraft mission. Overall, active deorbiting methods are still considered challenging for small spacecraft, as this demand increases design complexity and uses valuable mass and volume.

In contrast, passive deorbit methods require no further active control after deployment. Therefore, this chapter will focus on passive deorbit mechanisms only. Table 12-1displays current state-of-the-art technology for passive deorbit systems.

Solar Sails: Several small spacecraft missions have been developed and launched to demonstrate passive (uncontrolled) deorbit technologies using a drag sail or boom, such as NanoSail-D2 and CanX-7. NanoSail-D2 was deployed in 2011, from the minisatellite FAStsat HSV into a 650 km altitude and 72° inclined orbit, and demonstrated the deorbit capability of a low mass, high surface area sail. The 3U spacecraft, developed at NASA Marshall Space Flight Center, reentered Earth’s atmosphere in September, 2011. CanX-7, still in orbit at an initial 800 km SSO, deployed a drag sail in May, 2017. The sail was developed and tested at University of Toronto Institute for Aerospace Studies Space Flight Laboratory (UTIAS-SFL).

Recent CubeSats have used NASA’s Exo-Brake Parachute for mission deorbiting. An Exo-Brake increases the spacecraft’s drag once the tension-based, flexible braking device that resembles a cross-parachute is deployed from the rear. The Exo-Brake development is funded by the Entry Systems Modeling project within the NASA Space Technology Mission Directorate’s Game Changing Development program. Four Technology Education Satellite (TechEdSAt) 3U CubeSat missions have used several versions of the Exo-Brake module. The latest two of the four TechEdSat spacecraft are TechEdSat-5 and TechEdSat-6; TechEdSat-5 was deployed from the ISS March, 2017, and demonstrated this deorbiting capability after 144 days in orbit

. TechEdSat-5 orbited at 400 km altitude when the Exo-Brake was enabled. TechEdSat-6 and EcMASat, 3U and 6U form factors respectively, both are also equipped with the Exo-Brake module, but have not yet been activated.

Deployables: Composite Technology Development, Inc. has developed the Roll-Out DeOrbiting device (RODEO) that consists of a lightweight film attached to a simple, ultra-lightweight, roll-out composite boom structure. It was successfully deployed on suborbital RocketSat-8 August, 2013. AAC-Clyde collaborated with the University of Glasglow to construct the Aerodynamic End-of-Life Deorbit system for CubeSats (AEOLDOS), where a lightweight, foldable “aerobrake” made from a membrane is supported by boom-springs that open the sail to generate aerodynamic drag against the upper atmosphere.

Electromagnetic Tethers: In addition to drag sails, an electromagnetic tether has also been shown to be an effective deorbit method. An electromagnetic tether uses a conductive tether to generate an electromagnetic force as the tether system moves relative to Earth’s magnetic field. Tethers Unlimited developed Terminator Tape that uses a burn-wire release mechanism to actuate the ejection of the Terminator’s cover, deploying a 30 m long conductive tape (electromagnetic tether) at the conclusion of the small spacecraft mission. There are currently two modules: one sized for 180 kg ESPA class spacecraft, and the other sized for CubeSat form factors, called nanoTerminator Tape. Reach from Tethers Unlimited show that orbit raising and lowering is most effective in low to moderate inclinations (>70deg). Terminator tape has heritage on Aerocube-V which launched in 2015, but the CubeSat is currently still in orbit and the terminator tape has not yet been activated and the terminator tape has not yet been activated.

In summary small spacecraft deorbit systems have been shown to be quite effective in meeting mandated lifetime requirements. As most small spacecraft are unable to relocate to a graveyard orbit due to propulsion limitations, deorbit system development has focused on passive devices. NanoSail-D2, CanX-7, TechEdSat-3, TechEdSat-4, and TechEdSAt-5 are all CubeSat platforms that have successfully demonstrated the use of drag sails for deorbiting in LEO within the 25 year post-mission requirement. EcAMSat and TechEdSat-6 will hopefully successfully demonstrate their deorbiting systems soon.

Williams M. Eye-opening numbers on space debris. Phys.org. https://phys.org/news/2017-03-eye-opening-space-debris.html. Published March 21, 2017. Accessed July 12, 2018.

2. European Space Agency. Space Debris. 2015.

3. National Aeronautics and Space Administration. Process for Limiting Orbital Debris.; 2012.

4. Analytical Graphics  Inc. An Evaluation of CubeSat Orbital Decay. Oltrogge D, ed. 2015.

5. Bonin G, Hiemstra J, Sears T, Zee RE. “The CanX-7 Drag Sail Demonstration Mission: Enabling Environmental Stewarship for Nano- and Microsatellites,.” In: Utah; 2015.

6. European Space Agency -. TechEdSat-5 (Technical Education Satellite-5). EO Portal. https://directory.eoportal.org/web/eoportal/satellite-missions/t/techedsat-5. Published 2017. Accessed 2018.

7. Turse D, Keller P, Taylor R, Reavis M, Tupper M, Koehler C. Flight Testing of a Low Cost De-Orbiting Device for Small Satellites. Presented at the: Proceedings of the 42nd Aerospace Mechanisms Symposium; 2014.

8. Harkness P, McRobb M, Lutzkendorf P, Milligan R, Feeney A, Clark C. Development status of AEOLDOS: A deorbit module for small satellites. 2014.

9. Hoyt RP, Barnes IM, Voronka NR, Slostad JT. The Terminator Tape: A Cost-Effective De-Orbit Module for End-of-Life Disposal of LEO Satellites. Presented at the: AIAA Space 2009 Conference; 2009.

10. Tethers Unlimited Inc. The Terminator Tape and Terminator Tether Satellite Deorbit Systems: Low-Cost, Low-Mass End-of-Mission Disposal for Space Debris Mitigation. 2014.

(NASA Official: Bruce Yost Last modified: March 12, 2019)