When only large companies launch satellites, the low-Earth orbit is already relatively crowded, but as the cost of entering space becomes cheaper and cheaper, more and more hardware begins to buzz overhead. Since 2019, SpaceX alone has launched nearly 1,800 satellites as part of its Starlink network, and may launch as many as 40,000 more satellites in the coming decades. They are not alone. Although their ambitions may not be so ambitious, companies such as Amazon and Samsung have announced plans to create their own satellite “giant constellations” in the near future.
At least on paper, everyone has enough space. But what to do when things go wrong? If the satellite fails and loses response, it can no longer make close contact with other objects in orbit. This is a particularly disturbing situation, because not all objects in Earth’s orbit are able to move on their own at first. If two of these uncontrollable objects find themselves in a collision, we can do nothing on the ground, we can only observe and hope for the best. The resulting hypervelocity impact can cause shrapnel and debris to fly hundreds or even thousands of kilometers in all three dimensions, creating extremely dangerous conditions for other vehicles.
One way to alleviate this problem is to design satellites so that they can quickly re-enter the Earth’s atmosphere and burn at the end of the mission. Ideally, if the vehicle does not respond or has a serious failure, the derailment procedure can even be started automatically. Of course, in order to promote the widest possible adoption, such systems must be cheap, lightweight, easy to integrate into any spacecraft design, and as reliable as possible. To be sure, this is a daunting task.
But maybe it is not impossible.Millennium Aerospace Systems, a Boeing subsidiary, recently announced Successfully deployed a promising derailment device developed by Tethers UnlimitedThe compact device called Terminator Tape is designed to quickly slow down orbiting satellites by increasing the resistance of orbiting satellites in the slender upper atmosphere.
Real space race
On November 20, 2020, the rocket laboratory electrons were launched into space, The DRAGRACER mission of the Millennium Space System Composed of two identical cube satellites, they were simultaneously released into an orbit 400 kilometers (250 miles) above the earth.The only difference between the two satellites is one of them, called alchemy, Equipped with Terminator tape equipment.Another satellite, called Divination, There is no active de-orbit capability, as a control for the experiment.
Once the two spacecraft are safely in orbit, alchemy Unfold the tightly packed 70 m (230 ft) conductive tether stored in a 180 mm x 180 mm x 18 mm terminator tape module.As the tether slowed down, it was initially estimated alchemy Will hit the dense part of the Earth’s atmosphere and burn out within 45 days.
In the end, the Terminator-equipped aircraft took about eight months to passively de-orbit.This is much longer than the pre-task estimate, but in a follow-up presentation during the SmallSat virtual meeting, Tethers Unlimited President Rob Hoyt stated that the team is still Collect data to improve their prediction of satellite deorbit rate. on the one hand, alchemy It was the first spacecraft to deploy a tether at a sufficiently low altitude, and as a result it re-entered the atmosphere, so this is basically uncharted territory. Hoyt also explained that the effectiveness of the tether depends to a large extent on current solar conditions, which makes it difficult to determine that it will slow down the vehicle before actual deployment and actual data input begins.
Nevertheless, compared to time, eight months is nothing Divination Will spend in space. Given its current speed and altitude, it is estimated that controlling the CubeSat will not re-enter the atmosphere until 2028 at the earliest. Although the team clearly needs to improve their model to estimate the de-orbit time frame, there is no doubt that Terminator tape can greatly reduce the speed of orbiting satellites.
Taking a look at your traditional satellite, it is obvious that atmospheric drag is not a big problem for designers. Despite their large solar panels, randomly placed parabolic antennas, and general asymmetry, most spacecraft experience so little resistance that the occasional propeller firing is enough to compensate. Even the International Space Station, the largest and most clumsy aircraft in human history, can only descend two to three kilometers per month. As you might expect, this effect will diminish as altitude increases, which means that some satellites, such as Pioneer 1, launched in 1958, are expected to stay in orbit for hundreds of years.
The working principle of terminator tape is at least partly by greatly increasing the surface area of the satellite. Given that the common 3U CubeSat is only 30 cm long, deploying a 70 mx 150 mm tether will increase its total surface area by approximately 150 times. Protruding from the satellite like the tail of a kite, the tether will passively reduce the orbital speed of the aircraft, as long as it is at a low enough altitude to still be subject to significant atmospheric drag.
But it’s not just that the increased surface area will help reduce the spacecraft. When the conductive tether material passes through the earth’s magnetic field, it accumulates electric charge inside it, and then induces electromagnetic resistance on the system through the Lorentz force. The tether will essentially act as a propellant-free retrograde thruster, continuously pulling the spacecraft and depriving it of power. This characteristic of the tether is especially important for high-altitude aircraft, where atmospheric drag alone may be too weak to have an effect.
Drag as a service
To add Terminator tape to an existing spacecraft, all you need is a sufficiently flat area to fix the 180 square millimeter equipment on it, and at least 808 grams of the quality budget is available. Even no matter which side of the vehicle you connect it to or which direction the aircraft is in when deployed, physics takes care of all of this.
As a spacecraft designer, the only thing you really need to care about is to provide it with an activation signal at the right time. According to the data sheet This means that 9 VDC is applied to the shape memory alloy (SMA) activator of the device for 30 seconds, during which the hot device will pull about 1.9 amps. When using a smaller version of the tether, only 300 mA @ 3 VDC is required. In either case, only free GPIO pins and MOSFETs on the vehicle computer are needed to trigger the device at the end of the normal task.
It is also wise for designers to implement auxiliary, automatic deployment signals when the vehicle fails. This can take the form of dedicated batteries, solar cells, and circuits, which can provide an activation signal after a set period of time regardless of the state of the vehicle. For tasks with a relatively short lifespan, such emergency systems may even run on long-lasting primary batteries.
In the future, such systems may not even require power to activate. As part of the aerospace industry’s evolving “design for demise” program, research is being conducted on materials and adhesives that predictably decompose based on time or external factors such as temperature and exposure to sunlight. Eventually, we may see a tether, once its cover is damaged by the space environment, it will automatically unfold; an autonomous and efficient harvester, ensuring that no satellite stays longer than it needs.