The reliance on recall is discussed in chapter 4, part 3 g ^

Overview

The spacecraft module simulates the major subsystems of the actual vehicle. The module contains the following models:

ADACS CCDM Payload

Power and Pyrotechnics Propulsion

Structures Thermal

In addition to the above subsystems the spacecraft module estimates the V required for orbital insertion and de-orbit. The module calculates the individual subsystem masses as well as the total mass, and estimates spacecraft volume for the launch module.

Inputs

The spacecraft module uses the design vector and the orbital information from the satellite database to complete its calculations. The inputs to the spacecraft module are:

Total Delta-V (200-1000 : 100) Power (Solar or Fuel Cells)

Communications (TDRSS or AFSCN) Antenna type (High or Low-gain) Propulsion Type (Electric or Chemical) Orbit apogee and perigee.

Outputs

The spacecraft module outputs:

Bus mass Payload mass Dry mass Propellant mass Total mass

Estimated bus cost Estimated payload cost Estimated TFU cost Estimated software cost Total volume

Diameter Length

Lifetime without deorbit Lifetime with deorbit

Lifetime with insertion and deorbit Maximum average power required Maximum peak power required Latency

Assumptions

The dimensions of the spacecraft are approximated assuming the dimensions of a 2:1:1 cylinder.

For lifetime and V calculations, the spacecraft model estimates the ballistic coefficient of drag assuming a Cd of 1.7. This coefficient of drag value is actually lower than the value used in the preliminary ICE design. Three lifetime values are estimated for analysis purposes – one assumes insertion and de-orbit is performed by the spacecraft propulsion system; another assumes that insertion is performed by the IUS and only de-orbit must be performed by the spacecraft; and the final lifetime provides the “ideal” mission life by assuming that insertion and de-orbit both take place without using spacecraft fuel.

Fidelity Assessment

The fidelity on the model is low for a detailed design but adequate for our purposes.

Verification

The spacecraft model was tested and verified using a wrapper script which passed controlled variables into the module for known outputs.

5.4.3 Launch Module

Overview

This module selects the minimum cost launch vehicle for the particular satellite architecture based on a branch and bound algorithm optimized for minimizing cost. The launch vehicle selected is a function of the satellite mass, the stowed dimensions of the satellite, the orbital (perigee) altitude, orbital inclination, and launch site. Each satellite will have a dedicated launch vehicle. Once the launch vehicle has been selected, the total cost of initial deployment is

determined based on current cost estimates. In order to minimize computation time in the algorithm, pre-processing was done to determine the injected mass range for the design vector inclinations and perigee altitudes for each launch vehicle. The file containing the post-processed data for selecting the minimum cost launch vehicle is contained in the MATLAB launch.m file.

The source code for the branch and bound algorithm can be found in the appendix of this document.

Inputs

The launch module post-processed file (launch.m), takes inputs from the satellite database. The inputs from the satellite database are as follows:

Inclination (radians)

Perigee Altitude (kilometers) Satellite Mass (kilograms) Satellite Diameter (meters) Satellite Length (meters)

A complete description of the launch vehicles including dimension (fairing diameter and fairing length), as well as cost, is included in a launch vehicle database. The launch vehicles considered are: Pegasus XL (Orbital Sciences Corp.), Minotaur (Orbital Sciences Corp.), Taurus (Orbital Sciences Corp.), Athena II (Lockheed Martin), Delta II (Boeing), and Atlas II (Lockheed

Martin). The launch sites considered are Cape Canaveral (Florida), Vandenberg AFB (California), and Kodiak Island (Alaska).

Outputs

The outputs from the launch module are both final code outputs and are used by other modules.

The outputs are as follows:

Launch vehicle Launch site

Launch cost (nominal)

An error is returned if the input architecture cannot be launched from a U.S. launch site (i.e. too large for a U.S. vehicle or an unreachable inclination).

Constraints

Since this mission is to be conducted by the Department of Defense (DoD), Air Force Research Laboratory (AFRL), only launch vehicles manufactured in the United States as well as launch sites in the United States were considered. Nearly half of the launch vehicles in the database were not considered because of this constraint.

Key Assumptions Fundamental Equations

This model makes use of the satellite mass, orbital inclination, and perigee altitude to determine the appropriate launch vehicle selection. Satellite mass is the largest driver in launch vehicle selection, sizing, and cost considerations. The pre-processing of the algorithm assumed a rubber spacecraft to determine the maximum injected mass capability. The maximum injected mass capability is 25% greater than the spacecraft mass to account for the deployment cradle. A linear degradation model was available based on an optimal performance inclination for a particular launch vehicle, but was not used in this simulation.

Rationale for simplifications

This model makes use of an approximate satellite mass, orbital altitude, and inclination to

determine the launch vehicle selection criteria. Because of the nature of this mission, the number of available launch vehicles was much less than if it were to be a civil launch. Therefore, the small launch vehicles available have a fairly high probability of success; which is why the branch and bound algorithm used the assumption of minimizing only with respect to cost. If the minimization was to be only with respect to risk, the launch vehicles selected may not be

available for a particular orbital inclination or would be far more powerful than necessary. It was not practical to use the linear degradation model due to the extremes of our orbital inclinations, 0⁰ and 90⁰, which are far from the respective performance inclinations.

Evolution of calculations

The pre-processing branch and bound algorithm for minimizing cost, risk, or a weighted combination of cost and risk has remained similar to the B-TOS code. The module used in the simulation (launch.m) is much different from the one used in B-TOS. This new module incorporates injected mass capability ranges for each launch vehicle and selects out those

satellites that do not fit in the payload fairing. This module also selects the launch site based on the orbital inclination.

Fidelity Assessment

The costing model contains the same launch vehicle data as B-TOS. The launch vehicle data is the most accurate that could be found and has not changed since the previous version. Because the selection of the launch vehicle is based on minimizing cost, the failure rate of the launch vehicles is not considered. Launch site is considered because of the design inclinations and is incorporated into the module. The branch and bound algorithm does permit launch vehicle selection based on minimizing cost, minimizing risk (or failure rate), or a combination of minimizing cost and risk based on a weighting factor for each minimizing parameter which is determined by the user. If risk were to be a minimizing parameter, it would be computed over a small number of launch vehicles which are very successful or have very few launches which affects the fidelity of the reliability estimate for each launch vehicle.

Verification

The pre-processing of the branch and bound algorithm was done under numerous spacecraft masses, orbital inclinations, and perigee altitudes to determine the range of spacecraft masses that could be launched. The code incorporated the payload fairing dimensions to ensure that the input dimensions of a particular architecture would fit on the selected launch vehicle. Launch vehicles, launch sites, and costs were calculated for various orbital altitudes and inclinations. The post-processed data was cross-referenced with the launch vehicle performance data to ensure that the launch module incorporated the appropriate injected mass ranges for the given orbital altitude and inclination.