PRE2016 3 Groep19
Group members
- Jeanpierre Balster - 0864027
- Mike Beckers - 0943224
- Elise Levert - 0883583
- Joël Peeters - 0939193
- Kady Schotman - 0958295
- Elise Verhees - 0950109
Planning
A rough planning of the whole project containing the milestones in the process:
Week 1: Decide on the subject by brainstorming.
Week 2: Do some basic research about the chosen subject and make a presentation about it (including objectives and approach).
Week 3: Create a planning (inclusive a presentation about it), finalize definition deliverables, define milestones. Start working on specific tasks of the literature research.
Week 4: State-of-the-art literature research. Decide solution on Thursday.
Week 5: Do further more detailed literature. Begin Netlogo simulation.
Week 6: Refine solution based on literature. Continue on Netlogo simulation.
Week 7: Finalize NetLogo deliverable.
A Gantt chart of the planning is given below. LR is literature research. SR is solution research, so combining the knowledge from the literature research to find the best solutions. For more detailed explanation on the different tasks, see section 'Approach'.
Case study
Group 19 will work on researching a space cleaning robot. This is currently a relevant problem; millions of pieces of space debris are orbiting the Earth. These pose a threat to satellites and spacecrafts which can collide with the debris (forming even more debris). Even if from now on nothing would be shot into space anymore, the amount of space debris would still increase, since pieces of debris can collide with each forming new pieces of debris. The problem needs to be solved using an Artificial Intelligent autonomously functioning device, since it is not possible to control the device from Earth, due to the time it would take to receive and send information from and to space (the debris would already be out of reach before the information is send back to Earth). The robot should be able to autonomously complete the following tasks: locate the debris, either collect and store the debris or push it in the right direction, return to Earth. Furthermore, research should be done on how to get rid of the debris. Will the robot burn the debris upon reentering of the Earth's atmosphere or will it bring he debris back to Earth (for the use of recycling).
Objectives
The objectives are answering the following research questions through literature research:
Furthermore, a NetLogo simulation will be made.
Approach
The approach is to realize the following deliverables:
1. A literature research on:
- The current impact of the space debris on society
- The current impact of the space debris on enterprises
- The current ways of finding space debris
- The current ways approaching the debris (to catch it)
- The current ways of retrieving debris from space (catching and storing or pushing in the right direction)
- The current ways if getting rid of the debris (burn up/bring back to Earth)
- The current ways of returning the device to earth
2. A concept for the best solution / improving existing solutions
- The impact of the solution on society
- The impact on enterprises of the solution
- The best way to find debris
- The best way to approach it
- The best way to retrieve the debris from space
- The best way to get rid of it
- The best way to return to earth
3. A Netlogo simulation
- Which will simulate the search path
- Which will simulate transporting the debris
USE aspects
The relevant USE aspects in our project.
Retrieving Mechanisms
Electrodynamic tethers can be used to remove space debris. In this option, the tether attaches itself to a piece of debris and current is induced along the tether. A Lorentz force is created between the tether and Earth’s magnetic field, causing the space debris to accelerate. This can significantly decrease the time needed for the object to de-orbit, particularly for debris close to earth (Barbee).
A momentum exchange tether could also be used to change the path of debris. Here, the tether, moving at high speeds, will attach to a slower moving piece of debris. If the debris is released at its highest retrograde velocity, then it will come closer to the atmosphere (lower perigee) (Barbee).
Lasers for vaporization are rather unfeasible as they require high precision and power. The debris moves quickly and somewhat unpredictably, so the precision is a huge issue. Also, the power requirement is beyond our current capabilities. The object could also potentially explode if it contains some unspent propellent. A laser in space could even infringe upon UN regulations (Barbee).
Surface material could be sent into space and affect the travel path of all objects which hit it. The object would be at risk of breaking and creating more space debris (Barbee).
Reflective Solar Sails are another alternative. They could attach onto debris, and as solar photons strike the sail, the object will in turn accelerate. The issue with solar sails is that it may not significantly alter the acceleration of the orbiting bodies unless it is acting on the body for months. At low altitudes this technology couldn’t be used due to corrosion (Barbee).
Another general concept is to produce streams of air from within the atmosphere that will be directed towards debris to change its travel path. Methods of producing these air streams vary from balloons to high altitude planes. This approach could affect multiple pieces of space debris in one attempt and is at no risk of creating more space debris if it fails (David).
The use of ion beams is also considered to help move debris; one such example is the Ion Beam Shepherd. The concept is to create an ion beam which will produce a force that can propel the debris forward. This also forces the mission to move in the opposite direction with the same force; thus, two beams are necessary in order to move the debris forward and keep the mission in the same position relative to the debris (Zuiani).
A net mechanism could be used. This would consist of four mass which will be shot out with a spring. The masses will pull the net out and surround the debris. The net size can be rather easily adjusted. This net is attached to a tether which is controllable using a reel and a motor. The net, once encompassing the debris, will close behind the target and tighten slightly. The object, now captured, will be slowed down and sent on a new travel path (Bischof).
Considerations for our project
For our purposes, the vaporization lasers, surface material, and streams of air are almost immediately out of consideration. We plan to create a software that will create a travel path to the debris, so these capture mechanisms would not be of use to us. A solar sail can also be put aside as the concerns for this mechanism seem to be too technical for us to investigate. The amount of drag produced by solar photons may be near impossible for us to learn and estimate in the time needed. This leaves the tethers, ion beams, and nets. The tether seems to be the most popular mechanism used in space debris missions. The electrodynamic tether may be much more efficient than the momentum exchange tether, as the momentum exchange tether requires more control. The net seems a bit difficult to execute, as the encompassing and closing of the object requires even more control than the tether. The ion beam may require less control, and it seems to be the simplest solution. Still, the other options have not been ruled out and a discussion with the group may help produce a more informed decision.
Getting rid of space debris
Burning in atmosphere
Often space junk gets attracted by the Earth and starts to fall down, but most of it burns up in the atmosphere and will never reach the surface (Redd). This could also be used as a method to actively get rid of the space debris through burning the debris in the Earth’s atmosphere on purpose. However, how will this affect the Earth’s atmosphere and to which dimensions of space debris would this physically be possible.
When pieces of debris fall down, nearly all thrash bigger than 10 cm will not entirely burn up, but instead be fragmented into smaller pieces. These pieces will fall into water most of the time since about 70% of the Earth’s surface is water (Redd), but when deliberately sending debris into the Earth’s atmosphere one wants to make sure that no large chunks start raining down and damage property. There are two important factors that influence the extent to which a piece of space debris will burn up. First of all, the size; obviously smaller pieces are more likely to burn up entirely then larger ones. Secondly, the speed with which the atmosphere is entered. The Earth’s atmosphere is full of matter, which means that a lot of friction is created when space junk speeds through it with high velocity. Friction creates heat. Heat, when reaching the boiling point of the debris, vaporizes the space debris layer by layer. ("How big does a meteor have to be to make it to the ground?") But even more important, due to the high kinetic energy, the air in front of the debris will get compressed and compressing air means its temperature will increase. However, it is a bit more complicated, since size plays yet another role: smaller pieces slow down more quickly since the friction is very large compared to their mass. Eventually they might just start drifting down. This means that sometimes, very small dust grains will not burn up whereas a bigger piece of debris would’ve melted away. (“Why burn up on entering Earth's atmosphere”)
It is therefore not possible to define one maximum size for a piece of space debris to get burned up in the atmosphere. By controlling the entrance speed of Earth’s atmosphere, it is possible to ‘change’ this maximum size. However, this will only work up to a certain size, so the very large chunks of space debris will never be able to entirely burn up in Earth’s atmosphere.
But what is exactly the (chemical) impact on Earth’s atmosphere of burning up all this space debris in it. In 1994 a study team commissioned by the Environmental Management Division of the Space and Missile Systems Center looked into the impact of burning space debris in the atmosphere on stratospheric ozone. Their findings were that ozone was affected. When space debris travels through the Earth’s atmosphere with high speed, a shock wave is created. This shock wave produces nitric oxide, causing a decrease in stratospheric ozone (known as ozone depletion). However, the impact is not significant on global level. (David)
Still, more research needs to be done on the density of particles, types of particles, and how long they are suspended in the atmosphere to determine the long term effect of actively pushing large amounts of space debris into the Earth’s atmosphere. (David)
Big space junk – burning or pushing away
The section above mainly focused on the smaller debris that is already orbiting the Earth for some time. But what is done with ‘new’ space debris, meaning for example old space stations and satellites that are nearing their end and have not yet been broken down into smaller pieces. These objects will likely be too large to entirely burn up in the Earth’s atmosphere.
At the moment there are two ways of getting rid of these satellites. Which way to go depends on how high the satellite is orbiting Earth.
Satellites closer to Earth will use their last bit of fuel to slow down. They will then fall out of orbit, and burn up in the Earth’s atmosphere. The smaller satellites might burn up to such an extent that they can do no harm anymore. However the bigger ones, like space stations and larger spacecraft in low orbit, will not entirely burn up before reaching the surface. To make sure such a space station does not crash down in for example a big city, space operators plan for their old satellites to crash down in the so-called spacecraft cemetery. This spacecraft cemetery is situated in the Pacific Ocean, as far away from any human civilization as possible.
Satellites that are further away from Earth, would need more fuel to slow down than those closer to Earth. Most of these high orbiting satellites need less fuel to get farther away from Earth then to get back. Therefore, these satellites will be send even farther away from Earth instead of sending them back to Earth. Similarly to the spacecraft cemetery, these satellites will be send into a graveyard orbit. This orbit is almost 200 miles higher than where the farthest away active satellites are orbiting. Here they will continue orbiting, some of them for a very long time. For now, they will not be able to bump into the intact satellites and therefore will not cause any more debris to form. But may be some time in the future, humans need to send some kind of space cleaning device to get rid of these satellites. ("Where do old satellites go when they die?")
Recycling of space debris
Destroying space debris is one way of getting rid of it. Another option could be collecting reusable junk and recycling it. There is over a $300 billion worth of dead satellites drifting through space (Vijayaraghavan). The United States Department of Defense (DAPRA) is already working on a program called The Phoenix program that aims at recycling space debris (old satellites that stopped working). They are looking into recycling parts of broken satellites that can still be used to incorporate into new space systems. According to DAPRA director Regina Dugan "If this program is successful, space debris becomes space resource". The program wants to use a robot to reclaim still-working antennas from dead satellites which orbit the Earth in the graveyard orbit (see section about big space junk) and attach these antennas to new smaller satellites (satlets) launched from Earth. This would save a lot of launch costs, since antennas are big and bulky and they therefore need a lot of fuel to be send to space. Launching the satlets without antennas is thus much cheaper. (SPACE.com staff)
However, recycling space debris is not as simple as recycling plastic bottles. According to DARPA program manager David Bernhart: “Satellites in orbit are not designed to be disassembled or repaired, so it’s not a matter of simply removing some nuts and bolts. This requires new remote imaging and robotics technology and special tools to grip, cut and modify complex systems.” (Pultarova)
The robot that DAPRA is working on will have grasping arms and remote vision systems. The Phoenix program can make use of some existing ‘Earth technology’ to start with. These technologies include surgery systems that make it possible for doctors to do the surgery from thousands of miles away and remote imaging systems used by oil drillers to view as far as the ocean floor thousands of feet underwater. However, these systems need to be adapted to work in outer space where there will be no gravity, vacuum, and harsh-radiation. (SPACE.com staff)
References
Barbee, B. W., Alfano, S., Gold, K., Gaylor, D., Pinon, E., "Design of Spacecraft Missions to Remove Multiple Orbital Debris Objects," Advances in the Astronautical Sciences, Vol. 144, Univelt, Inc., San Diego, CA, 2012, pp. 93-110, also AAS/AIAA Paper AAS 12-017, 35th Annual AAS Guidance and Control Conference, Breckenridge, CO, February 3-8, 2012
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"RemoveDebris: Experiments." Surrey Space Center. University of Surrey, n.d. Web. 21 Feb. 2017. http://www.surrey.ac.uk/ssc/research/space_vehicle_control/removedebris/experiments/
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Zuiani F., Vasile M. Preliminary Design of Debris Removal Missions by Means of Simplified Models for Low-Thrust, Many-Revolution Transfers. International Journal of Aerospace Engineering, Volume 2012 (2012), Article ID 836250