Launch System
Launcher System Drawing
| launcher_vehicle.pdf |
Overview
In order to achieve the desired constellation of Cube Satellites (cubesat) to fulfill the needs of the design, a constellation of at least 80 evenly spaced satellites on the same orbital plane is necessary. The orbital plane of the satellites is described in table 1 below. Placing multiple satellites at even intervals is a major design hurdle requiring significant effort beyond the typical cubesat launch. Typically, cubesats are launched as auxiliary payloads on existing launches, and would thus be required to have similar orbits to the primary payload, making achievement of a particular orbit difficult, and even spacing on that orbit even more difficult.
In order to achieve the desired constellation of Cube Satellites (cubesat) to fulfill the needs of the design, a constellation of at least 80 evenly spaced satellites on the same orbital plane is necessary. The orbital plane of the satellites is described in table 1 below. Placing multiple satellites at even intervals is a major design hurdle requiring significant effort beyond the typical cubesat launch. Typically, cubesats are launched as auxiliary payloads on existing launches, and would thus be required to have similar orbits to the primary payload, making achievement of a particular orbit difficult, and even spacing on that orbit even more difficult.
Due to the expected life span of cubesats, multiple launches of the constellation will be required. This is mitigated, in part, through the use of small plasma thrusters added to the cubesats, allowing for an expected life span of 6 years. In this case, only 1 launch beyond the first will be required to allow for the full targeted 10 year lifespan.
Our proposed solution to this issue is to bypass the typical piggyback solution for cubesat launches and design and launch our own mission with launcher craft that will place the cubesats in the appropriate orbit. The launcher craft will be designed in house and be launched on a SpaceX Falcon 9 rocket[1]. Each launcher craft will be capable of holding and releasing 49 cubesats each, providing overhead in case of failures. Figure 1 shows a basic premise from which the design of the launcher craft will be based.
Our proposed solution to this issue is to bypass the typical piggyback solution for cubesat launches and design and launch our own mission with launcher craft that will place the cubesats in the appropriate orbit. The launcher craft will be designed in house and be launched on a SpaceX Falcon 9 rocket[1]. Each launcher craft will be capable of holding and releasing 49 cubesats each, providing overhead in case of failures. Figure 1 shows a basic premise from which the design of the launcher craft will be based.
In order to deploy the cubesats at the required interval, the launcher craft will be launched into an elliptical orbit with a perigee altitude equal to the altitude of the cubesats and an orbital period equal to the period of the cubesats plus a separation time; this orbit is described in table 2. The maximum separation time can be calculated by dividing the cubesat orbital period by the number of satellites. Figure 2 and 3 demonstrate the orbits and process, respectively.
Falcon 9 Overview
The Falcon 9 is a two-stage rocket designed and manufactured by SpaceX as a commercial solution for transport of satellites and the company’s Dragon spacecraft into space. The first stage of the Falcon 9 transports the payload to space in a matter of minutes. The second stage then delivers the payload(s) to their desired orbits. SpaceX’s composite payload fairing allows for transport of payloads up to 13m in height and 5 meters in diameter.
Launch Calculations
The SpaceX Falcon 9 rocket has a maximum launch capacity of 8300 kg at 80 degrees inclination and 500km of altitude[2]; the desired orbit of the launch vehicle is at a lower altitude and inclination, and thus should have at least this capacity. The weight of the cubesats, launch vehicle, and other weights are calculated in table 3. This number is significantly below the maximum launch capacity of the Falcon 9; this result indicates that the launch could be shared, reducing the launch costs as projected in the budget.
The Falcon 9 is a two-stage rocket designed and manufactured by SpaceX as a commercial solution for transport of satellites and the company’s Dragon spacecraft into space. The first stage of the Falcon 9 transports the payload to space in a matter of minutes. The second stage then delivers the payload(s) to their desired orbits. SpaceX’s composite payload fairing allows for transport of payloads up to 13m in height and 5 meters in diameter.
Launch Calculations
The SpaceX Falcon 9 rocket has a maximum launch capacity of 8300 kg at 80 degrees inclination and 500km of altitude[2]; the desired orbit of the launch vehicle is at a lower altitude and inclination, and thus should have at least this capacity. The weight of the cubesats, launch vehicle, and other weights are calculated in table 3. This number is significantly below the maximum launch capacity of the Falcon 9; this result indicates that the launch could be shared, reducing the launch costs as projected in the budget.
Deployment Strategy
Deployment of the cubesats from the launcher vehicle will require a great deal of precision that will require careful design considerations. The cubesat release attachment, as seen in figure 1, will utilize some form of propellent to induce a delta-v on the cubesat tangential to both the elliptical orbit of the launcher vehicle and the desired circular orbit at perigee. An estimate of this delta-v is provided in Figure 4 below. Additionally, this deltav will be applied somewhat to the launcher vehicle, though the greater relative mass of the launcher vehicle will prevent this delta-v from being large. The launcher vehicle will require some amount of tangential thrust opposite of it’s velocity vector in order to maintain its elliptical orbit.
Deployment of the cubesats from the launcher vehicle will require a great deal of precision that will require careful design considerations. The cubesat release attachment, as seen in figure 1, will utilize some form of propellent to induce a delta-v on the cubesat tangential to both the elliptical orbit of the launcher vehicle and the desired circular orbit at perigee. An estimate of this delta-v is provided in Figure 4 below. Additionally, this deltav will be applied somewhat to the launcher vehicle, though the greater relative mass of the launcher vehicle will prevent this delta-v from being large. The launcher vehicle will require some amount of tangential thrust opposite of it’s velocity vector in order to maintain its elliptical orbit.
The variation over deployments will need to be kept at a minimum, but some variation is allowable and may be eased by utilizing more than the minimum number of required satellites.
References
[1] http://www.spacex.com/falcon9
[2]http://www.spaceflightnow.com/falcon9/001/f9guide.pdf
References
[1] http://www.spacex.com/falcon9
[2]http://www.spaceflightnow.com/falcon9/001/f9guide.pdf