CubeSat De-Orbit Device Team
Status Report 1
MAE 435: Project Management and Design II
September 24, 2012
Overview
During the first four weeks of this project the team has been focused primarily on recovering the materials and data necessary to meet the goals of our project. We have acquired the materials that have been utilized by the previous team for the P-Pod deployment device, aerodynamic brake, and the electronics. We have now also acquired all of the experimental data and reports from the two previous teams. The team has come to the decision that the NASA Wallops Flight Facility’s RockSat-X program is the best fit for the need of our experiment versus their RockSat-C program although it is more expensive. RockSat-X was chosen because it allows the experiment to be exposed to space once the skin of the rocket is ejected. This will allow us to eject our CubeSat as opposed to RockSat-C program where the experiments remain enclosed by the skin of the sounding rocket with only atmospheric ports that would not allow us to eject our CubeSat. We signed the required “intent to fly” form and sent it to NASA for the RockSat-X program in 2013. We have successfully recruited a computer science graduate student and an electrical engineering undergraduate student to aid us in the electronic and control systems necessary for the mission of our CubeSat.
We redefined our goals for the semester based upon the feedback of our faculty advisor who was previously absent due to injury and after acquiring new data previously not available from the former team. Our goals are now to have a tested and completed P-Pod Deployment device with a quick release mechanism with the required electronics. We will have an aerodynamic brake that is tested and proven to deploy in the necessary time frame with the necessary electronics for deployment. We will also define and attain all of the necessary electronics and programming for the mission of our CubeSat. We will have a successful conceptual design review, preliminary design review, and critical design review for NASA’s RockSat-X program.
Aerodynamic Brake
Aerodynamic Brake
Once the CubeSat mission is finish, the air brake team is in charge with de-orbiting the satellite within 25 years or less. The former team came up with two options for the air brake. The first idea was to replicate the same design NASA used by inflate an aluminum Mylar balloon with benzoic acid. The second option was to use Shape Memory Alloy, Nitinol, as a frame to expand the Mylar balloon.
Benzoic Acid
If a CubeSat is ejected at a 900 km altitude from Earth the pressure reading will be around 500 Pa. In order to inflate the air brake balloon, one of the team’s options chose Benzoic Acid as it has a similar vapor pressure at the same altitude. The air brake will inflate, once the sublimation process starts.
Recovering data from the former CubeSat team showed tests were done with Benzoic Acid. The former team used a vacuum chamber to create the corresponding pressure of where the CubeSat will be orbiting. A sample Mylar party balloon with unmeasured benzoic acid was tested in the vacuum chamber for inflation. The result was inconclusive as further tests will be carrying out by our team for air brake inflation.
We have researched on Benzoic Acid and corrected the temperature needed to sublimate the acid. The Mylar balloon was not fully inflated within 300 seconds limit because they used only 60 degrees Celsius. Our collected data recommend us to use 10-15 grams of benzoic acid under 120-121 degrees Celsius to meet our restricted time limit. Results for this data are still in process as Dr. Ash still under the process of locating our Vacuum Chamber.
SMA
We are also exploring the option of shaped memory alloy for the deployment of an aerodynamic brake. The Nitinol wire that we have has a resistivity of 80 micro-ohms per centimeter. Initial designs would have the total length of the wire used for the aerodynamic to be 9.5 meters or 3.2 meters.
There are a few pressing concerns in using this shape memory alloy. Early observations noted after initial heat application the nitinol wire quickly lost its shape and began to return to its housing configuration. Also, initial calculations show a power source is needed that would prove to be outside constraints of our platform. Also, using a 3-circle design to obtain a sphere for the mylar coating would be difficult to package inside the aerodynamic brake housing.
P-Pod Deployment Device
Much of our work done since the start of the month has been spent trying to find and allocate our materials, such as the O-POD device & documentation about it and RockSat-X. According to Gregory Lemmer, the last student to work on the O-POD, we still have some work to do, but the device has been machined and is ready for further testing.
PATRAN analysis on the O-POD went through five iterations before a design was settled upon. The design models in PATRAN were analyzed for stress and vibrational analysis. The final design was created by ODU's machine shop and has been physically tested, but further testing for the ring-structure on the O-POD's open face may be necessary, as it was not accounted for in PATRAN, and may skew vibrational analysis results.We need to see what can be done to reduce twisting on the O-POD's pusher plate, as the spring makes it scrape against the rails.With more friction, the CubeSat cannot be launched as fast from the O-POD, making clearance from the rocket a worrying concern.
We have examined options for the quick-release mechanism, the most promising yet of which is a "blown resistor"- using an underrated resistor as a holding pin, until a large current from the RockSat-X power interface is applied. Another option, not explored as thoroughly, is an electronic solenoid, which would open at the required time. For lab testing, a holding pin was manually removed from the O-POD to check ejection velocity. We are weighing both quick-release mechanism options, but are still looking for alternatives. A concern is that the underrated resistor may break during the vibrations and 25g's of the rocket's launch. For any and all quick release mechanisms, however, we need something that can be triggered via command or timer from Wallops Flight Facility.
We spent several meetings trying to explain the flight profile of our sounding rocket (options are a Terrier-Orion or a Terrier-Malamute) to the rest of the team. We pointed out that the best time to deploy the O-POD and eject the CubeSat is before apogee but after the rocket passes an altitude of 95 km. Ideally we would like to eject the CubeSat when the sounding rocket has stopped rotating, but we may have to settle for a spin rate of 0.5Hz.Events during the sounding rocket's flight are tied very closely to every subgroup, as the timing and sequence of events is something that must be anticipated, in particular with microcontrollers. Since the CubeSat's time in space is very short, we need to clear it from the rocket and test the aerodynamic brake as soon as possible.
During the last meeting, we surmised that small cameras mounted on the O-POD would be advantageous for confirming the success of our deployment device. The RockSat-X deck and sounding rocket will be rotating at about 0.5Hz up until reaching apogee, so one or more cameras can have a full field of view. However, it would be best if the CubeSat had an on-board confirmation signal for inflation of the aerobrake structure, even if inflation is visually confirmed. Cameras on the O-POD would not be lacking for power, as each RockSat-X deck has 1 amp-hour.
Electronics – Langston Lewis, Jason Harris, Benjiman Crawse
So far the project calls for communication between wallops flight facility and the satellite, releasing the air brake itself, potentially a heating element to promote the reaction in a benzoic acid fueled expansion, and a way of verifying whether or not the air-brake has been successfully deployed.
Using an approach already tested by a previous CubeSat team, we are considering attaching a small ham radio to the CubeSat which will communicate with our payload. From the payload, communication systems will be provided for us, as the wallops will provide with data from the CubeSat, as well as performing the input functions for us.
The release mechanism is the next major component. We currently have two ideas proposed for releasing the brake; a small solenoid or using a small resistor which will explode when overloaded. The next component we are currently debating is the heating mechanism. We are currently between using benzoic acid with an attached heating element or running current through Nitinol wire. With benzoic acid, thermistors can be used to achieve the heat needed to begin the sublimation. Also, depending on the resistivity of the Nitinol wire, a small current can be run through the wire to achieve its desired shape.
We have agreed that cameras, similar to the ones in today’s smart phones, would be mounted on the base of the deployment device and the CubeSat itself. This way we can view the air brake as it expands from multiple perspectives, as it is imperative that the brake become fully inflated. The camera in your standard smart phone is sufficient for our project because of the low speed at which the CubeSat will move away from the payload. This low speed will provide us with enough time to view deployment if the brake is deployed shortly after ejection of satellite.