Cubesat Midterm Report
Design and Development of a CubeSat De-Orbit Device
Students:
An Kim
CianBanco
David Warner
Edwin Billips
Langston Lewis
Thomas Work
Mackenzie Webb
Benjamin Crawse
Jason Harris
Faculty Advisor:
Dr. Robert Ash
Abstract
CubeSats, shown in Figure A, are a common satellite used by universities and institutions for research in space. At 1000 cm3 the CubeSat can be integrated into many different rocket payloads. A CubeSat satellite will orbit at 900 km altitude from the earth for 1,000 years without any type of brake or modifications for it to de-orbit in less time. It is the objective of our team to design and test a prototype of an aerodynamic brake that can be placed on a CubeSat and effectively reduce its time in low earth orbit to within 1000 years. It is also our objective to design and test a prototype of a deployment device that can be mounted and eject our CubeSat form a sounding rocket payload. It is our goal to define the telemetry necessary for the mission of our CubeSat from the launching of the sounding rocket, to the timing and ejection of our CubeSat and deployment of the aerodynamic brake. Telemetry will also be needed for the verification of deployment of the brake and adequate drag.
Figure A 1U CubeSat
Table of Contents
Abstract...... 2
Table of Contents...... 3
1.List of Figures...... 4
2. Introduction...... 5
3. Sounding Rocket Test Flight...... 7
4. Deployment Device...... 10
4.1 Introduction………………………………………………………………………..10
4.2 Previous Research……………………………………………………………….11
4.3 Conclusion………………………………………………………………………...12
5. De-orbit Device...... 13
5.1 Introduction………………………………………………………………………..13
5.2 Previous Research………………………………………………………………..13
5.3 Conclusion…………………………………………………………………………17
6. Electrical Circuitry: Micro-Controllers and Various, Necessary Components...... 18
6.1 Introduction………………………………………………………………………..18
6.2 Analysis……………………………………………………………………………18
6.3 Conclusion/Future Work………………………………………………………….19
7. References...... 21
8. Updated Gantt Chart...... 22
9. Conclusion…………………………………………………………………………………..23
1. List of Figures
i)Figure A 1U CubeSat
ii)Figure 3.1 RockSat-X deck plate
iii)Figure 3.2 Sounding Rocket Payload Stack
iv)Fig 5.1a Orbiting height as a function of time without a de-orbiting device
v)Fig1.1b Orbiting height as a function of time with a de-orbiting device
2. Introduction
Since the beginning of the Space Age, thousands of defunct satellites, components, and associated debris have accumulated in Earth’s immediate orbital neighborhood. Orbiting at high altitudes, their lifetimes can span a thousand years or more, and during that time will remain a hazard to all satellites with similar orbits. The hazard of space debris was made apparent when the windshield of the Space Shuttle was damaged significantly in a collision with a tiny flake of paint that had a relative velocity of 2 km/s to 8 km/s.[1]Collectively, this group of orbital refuse is known as space debris, or “space junk”.
Though no treaty exists for the mitigation of space debris, the United Nations has formed an eleven-nation study to address the issue, and the United Nations Office for Outer Space Affairs has set up a group of mandates meant to stop the growing space debris problem. The Inter-Agency Debris Coordination Committee (IDAC) has pressed NASA, ESA, and private groups to deorbit satellites orbiting below 2000km within 25 years of mission completion. Most picosatellites (CubeSats) fall into this area, as a typical orbit is only at a 900 km altitude.CubeSats are often launched as hosted payload aboard a bigger rocket, and serve as “bricks” to meet payload weight requirements. At a 900 km altitude, a CubeSat can remain in orbit for well up to 1,000 years, and may prove to be a hazard to other satellites, present and future.
Our goal is to develop an aerodynamic brake which will diminish a satellite’s orbital time from 1,000 years to the mandated 25 years. An aerodynamic brake will take advantage of the conditions of near-Earth space, which is not a perfect vacuum; enough monatomic oxygen is present to provide a noticeable effect of drag on a structure with a large surface area. It is this same effect that deorbited Skylab earlier than expected (before it re-entered, a rendezvous with the then-new Shuttle was planned), and which now requires that the International Space Station be periodically boosted into higher orbit. Echo 1, a passive communications satellite launched into Earth orbit, experienced a measurable drag effect, largely in part to its 40m diameter balloon, which provided a large surface area for drag in orbit.
We propose to develop an aerodynamic brake component small enough to be installed on commercial CubeSats, using only a minimum of available volume and mass constrained by the CubeSat design, and with off-the-shelf constituent parts. Using a single-unit (1U) CubeSat (10cm x 10cm x 10cm) as our mission template, we will pursue two main options to reducing a satellite’s lifetime. One option is to use sublimating benzoic acid to inflate a 1.22m diameter balloon; benzoic acid goes from solid to gas at low pressures and mild temperatures, making it attractive for application in a space environment. The inflated balloon would present a large surface area for drag to take effect. The alternative option is to use Shape Memory Alloy (SMA) to deploy a similar balloon-shaped structure. Nitinol, a commercially availableSMA, expands and contracts under heat, making it able to flex or draw out complex structures. By evenly heating a Nitinol wire assembly, the aerodynamic brake can deploy in full. The option of using benzoic acid along with Nitinol wire to reinforce the shape of the aerodynamic brake will also be explored.
We plan to test both deployment options until one is clearly superior. In addition, we will examine our material options for the balloon structure; we are looking at Kapton, Mylar (PET film), and aluminized versions of said materials for the balloon structure. We plan to test the balloons in a vacuum chamber, and validate the aerodynamic brake’s functionality with a suborbital flight. The ultimate objective of the project is to design and test a de-orbit system for CubeSats that can reduce its time in low earth orbit to within 25 years. The de-orbit device must prove to be a robust and viable system having commercial viability at a minimum cost. Three current options for performing the experimental tests necessary to accomplish these objectives are through a high altitude balloon, orbital demonstrator, and suborbital sounding rocket. A suborbital sounding rocket flight is the current option being pursued by the team.
3. Sounding Rocket Test Flight
The current platform for the necessary experimental test of our CubeSat with an installed de-orbit device currently being pursued by the team is through a sounding rocket test flight. Sounding rockets provide a relatively simple and inexpensive way for students and researchers to perform research in a low earth orbit environment. Sounding rockets are divided into two parts: the payload and a rocket motor.[3] When the sounding rocket is launched it takes a parabolic trajectory. As the rocket motor uses its fuel it separates and falls back to earth while the experiments placed on the payload are conducted in the low earth orbit environment. Once the payload re-enters its gently brought down to earth by a parachute.
The program the team is currently pursuing for a sounding rocket test flight is NASA’s RockSat-X program at Wallops Flight Facility. The RockSat-X program utilizes the Terrier-Improved Malamute Suborbital sounding rocket that will reach apogee at approximately 160 km altitude from earth.[2] The sounding rocket’s skin and nose cone will eject after second stage burn-out of the Malamute launcher. RockSat-X utilizes decks shown in Figure 3.1 for customers to mount their payloads as opposed to the canisters used in its predecessor RockSat-C. The RockSat-X decks are in a stacked configuration interconnected by longerons spanning the entire length of the RockSat-X payload as shown in Figure 3.2. The decks are designed to provide customers direct access to the environment of space and allow payloads to deploy booms and other mechanical devices once the skin is ejected.
Figure 3.1 RockSat-X deck plate
Payload Stack ↑
Figure 3.2 Sounding Rocket Payload Stack
Wallops Flight Facility still provides sounding rocket flights through the predecessor of RockSat-X; the aforementioned RockSat-C program. The team considered both options. due particularly to the difference in cost to participate in the program. The RockSat-C is the cheapest option at $12,000 for a canister compared to $24,000 for a RockSat-X deck plate. The access that RockSat-X provides to the low earth orbital space environment that will allow for the ejection of a CubeSat, along with the superior power and telemetry provided compared to RockSat-C are the primary reasons that it is determined by the team to be the best sounding rocket option for our experiment. The team intends to submit an “Intent to Fly” form with the necessary $2000 deposit to Wallops for the RockSat-X sounding rocket launch in 2014.
4. Deployment Device
4.1 Introduction
The team has designed the “ODU Picosatellite Orbital Deployer”. This design is based on California Polytechnic State University’s “Poly Picosatellite Orbital Deployer”, or P-POD for short. This design has become the standard for many successful orbital flights. Our team’s design, the “O-POD”, plays a critical part in getting the cubesat away from the sounding rocket. The O-POD houses a spring inside its length, which is compressed while the cubesat is stored within. A quick release mechanism holds the spring and cubesat back, until a timer event from the RockSat-X power interface signals its release. With the deployer freed, the spring pushes the cubesat out at a modest lateral velocity, 1.6 m/s. This imparted motion gives the cubesat clearance to operate the De-Orbit Device, away from the rocket.
Although the cubesat is constrained severely by mass, size, and power requirements, the O-POD rests on a deck which has room for 30 lb mass, and 1 amp-hour of provided electrical charge. This deck rotates with the sounding rocket at 0.5 Hz for the majority of the microgravity window, and is directly exposed to the vacuum conditions of space. Unlike the cubesat, the O-POD remains in the sounding rocket, and can be considered a recoverable, provided thermal insulation for wires. The team has considered sharing pins for the deck’s power interface with possible flight partners, in the interest of reducing cost. As only one timer event is required for the O-POD, this opens up options.
4.2 Previous Research
The previous team assessed the following design criteria when making the O-POD:
- Must withstand 25g loads
- Minimal weight & material
- Eject cubesat at ~1.6 m/s
- Must withstand vibration tests
The dimensions of the O-POD, in Figure 4.1 are 12.7cm W x 12.7cm H x 19.62cm L, the same dimensions as the span on the RockSat-X deck plate. The structure is made of bolted Al-7075-T651 plates, a material which is high strength and can easily be machined. When joined, the plates form a rectangular box with internal rails, which provide a guideline for a pusher-plate and the spring. The plates are 7mm thick, and the entire assembly is 1.477kg.
Extensive PATRAN analysis has been performed on the O-POD, through five iterations of design. Each step refined the model’s mesh and geometry, providing increasingly accurate results with the improvements.
The previous team worked on “pinned” measurements of ejection velocity, using distance markers, manual release, and a cardboard mockup of the CubeSat. This mockup’s coefficient of friction varied with humidity, as it was constructed of cardboard. Tests were performed without deciding on a quick release mechanism option, as choosing was deemed premature. However, linear solenoids were considered.
4.3 Conclusion/Future Work
The present team is working on continuing the PATRAN analysis started by the previous team, with the intent being to account for a mounting plate between the O-POD and the RockSat-X deck. Velocity measurements with a newer mockup, of Aluminum construction, will provide more accurate results than a cardboard one. The current team plans to choose a quick release mechanism option as soon as possible, with consideration going toward Vectran Line Cutters or Linear Solenoids, as suggested by the previous team for its budget-conscious and simple design advantages.
5. De-Orbit Device
5.1 Introduction
The objective of the de-orbit device is to successfully deploy a spherical balloon from a 1U CubeSat 9x9x1 cm storage space. When the spherical balloon is fully inflated, the corresponding drag will act like an aerodynamic brake that will greatly reduce the 1U CubeSat de-orbiting time. The main concerns of the de-orbiting device after deployment are the ability to withstand ultraviolet radiation, atomic oxygen, changes in temperature, and micro meteor impact.
Weight and volume are critical constraints of the de-orbiting system due to the restrictions of the CubeSat. Sending payloads into orbit is based on cost per unit mass, and varies by space programs. Therefore, CubeSat must be small in volume and mass but must have sufficient space to fit the de-orbit mechanism. Since the CubeSat provides low budget access to space, the de-orbit device must also be economical. Overall, if the CubeSat de-orbit mechanism is intended to be used commercially; it must be small, affordable, and able to withstand the conditions of space over vast periods of time.
5.2 Previous Research
The starting point of the CubeSat project was to research and design a suitable membrane for the de-orbiting mechanism. The study focused on the membrane portion of the de-orbiting mechanism through the lifetime of a 1U CubeSat. A prototype may be modeled for the de-orbit mechanism based on the study.
A proper polymer for constructing the membrane must withstand ultraviolet radiation and atomic oxygen; and the best available material is Upilex® brand polyimide film produced by UBE industries. Upilex® is commonly used to protect against ultraviolet radiation and can also protect against atomic oxygen with the addition of a silicon oxide coating.
Another key aspect of the aerodynamic brake mechanism is the shape and size of the membrane. When selecting shapes of the membrane, the shape must meet a certain cross-sectional area to produce a desired drag. Based upon assumption, the membrane cross section will always be facing perpendicular to the direction of travel. However, this assumption is not entirely accurate. The CubeSat will rotate, turn, and tumble. The position of the membrane may change based on the orientation of the CubeSat and may not yield its maximum cross-section projected into the direction of travel. To combat this potential problem, we will construct the membrane in the shape of a sphere.
Previous groups also conducted research using ODU’s virtual lab Satellite Tool Kit (STK) simulation and concluded it would take the 1U CubeSat at least 480 years to return back into Earth from an altitude of 800 km under unassisted conditions (Figure 1.1a). The National Space Treaty requires all satellites that accomplish their missions to descend back to Earth in under 25 years. Through the STK simulation, it was determined that the 1U CubeSat satellite would return to Earth within 126 months with a minimum cross-section area of 0.5625 square meters (Figure 1.1b). This would allow the U1CubeSat to descend without violating the National Space Treaty.
Fig 5.1aOrbiting height as a function of time without a de-orbiting device
Fig1.1bOrbiting height as a function of time with a de-orbiting device
Another great source of background information for the aerodynamic brake is the NASA’s Echo I Satellite project. In 1960, NASA deployed a 100-foot diameter inflatable satellite using a mix of sublimating compounds. NASA used benzoic acid and anthraquinone to reduce the need of compressed gas, thus reducing the need of regulators and storage device. The benzoic acid was evenly distributed within the membrane of the satellite. When mixed with anthraquinone, the benzoic acid turned from a fine solid powder into a paste, allowing the compound to inflate the satellite. The sublimation process of benzoic acid required minimum solar heat to inflate, but problems arise as the satellite passes through the shadow of Earth (Clemmons).
Through the successful launch of NASA’s Echo 1 Satellite, ODU’s former team tried to apply the same deployment method towards the CubeSat de-orbit mechanism. Though NASA used benzoic acid and anthraquinone, the team was restricted from using anthraquinone due to financial limit. Even without anthraquinone, benzoic acid alone at 900 km altitude with solar heat will produce a vapor pressure of between 3 to 5 torr (400~650 Pa). This estimation of pressure will be used to inflate the de-orbit mechanism as the exterior pressure at 900km altitude is minimal.
Another process the ODU former team carried out was tests of benzoic acid’s inflation with the use of store bought Mylar balloons. The sizes of the Mylar balloons were 18 inches in diameter; one balloon was filled with 10 grams and the other with 15 grams or acid. Air was removed from the balloons and sealed with space grade epoxy to ensure sealant in a space-like environment. The balloons were then folded tightly and tested within a vacuum chamber under ambient room temperature. The test inflations were successful; however no record of Mylar balloon fully inflated within the 300 second limits.
5.3 Conclusion/Future Work
Based upon the successful inflation tests made by the previous ODU CubeSat team, benzoic acid is currently the best choice of inflating the U1 CubeSat de-orbiting system. The next objective of the inflation tests is to determine the temperature at which the benzoic acid will inflate the aerodynamic brake within the restricted time. According to Emerald Performance Material sheet, benzoic acid will sublimate at roughly 12.5*C at 160 km altitude. In order to achieve full inflation of benzoic acid in less than 300 seconds, a thermistor will be added to the test system to increase the system’s temperature.
The second goal of the inflation tests is to verify the amount of benzoic acid to inflate the 18 inches balloons. The mass of benzoic acid must be calculated and evenly distributed within the Mylar balloon. The even distribution of benzoic acid will assist in the unraveling of the tightly folded balloon.