diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9b4a285..d89694d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -24,6 +24,7 @@ endif()
 enable_testing()
 
 add_subdirectory(src/gui)
+add_subdirectory(src/sim)
 
 #find_package(wxWidgets REQUIRED gl core base)
 #include(${wxWidgets_USE_FILE})
diff --git a/src/gui/MainWindow.cpp b/src/gui/MainWindow.cpp
index 5c659e3..fe9616e 100644
--- a/src/gui/MainWindow.cpp
+++ b/src/gui/MainWindow.cpp
@@ -41,52 +41,40 @@ MainWindowFrame::MainWindowFrame()
    // Create the layout
 
    // Create the splitter window, then we can add panels to it
-   wxSplitterWindow* windowSplitter = new wxSplitterWindow(this,
+   wxSplitterWindow* mainSplitter = new wxSplitterWindow(this,
+                                                         wxID_ANY,
+                                                         wxDefaultPosition,
+                                                         wxDefaultSize,
+                                                         wxSP_BORDER | wxSP_LIVE_UPDATE);
+   wxSplitterWindow* designSplitter = new wxSplitterWindow(mainSplitter,
                                                            wxID_ANY,
                                                            wxDefaultPosition,
                                                            wxDefaultSize,
                                                            wxSP_BORDER | wxSP_LIVE_UPDATE);
-   windowSplitter->SetMinimumPaneSize(200);
-   //wxSplitterWindow* topSplitter    = new wxSplitterWindow(this);
+   designSplitter->SetMinimumPaneSize(200);
 
 
    // NOTE, we never call delete manually on the panel since setting the parent pointer (this)
    // will put the onus on the parent to manage the resource. It'll get deleted
    // when the parent gets deleted. In this case the MainWindowFrame
-   wxPanel* rocketTreePanel = new wxPanel(windowSplitter,
+   wxPanel* rocketTreePanel = new wxPanel(designSplitter,
                                           wxID_ANY,
                                           wxDefaultPosition,
                                           wxSize(200, 100));
    rocketTreePanel->SetBackgroundColour(wxColor(100, 100, 200));
 
-   wxPanel* rocketComponentPanel = new wxPanel(windowSplitter,
+   wxPanel* rocketComponentPanel = new wxPanel(designSplitter,
                                                wxID_ANY,
                                                wxDefaultPosition,
                                                wxSize(200, 100));
    rocketComponentPanel->SetBackgroundColour(wxColor(200, 100, 100));
 
-   windowSplitter->SplitVertically(rocketTreePanel, rocketComponentPanel);
-/*
-   wxSizer* rocketDesignSizer = new wxBoxSizer(wxHORIZONTAL);
-   rocketDesignSizer->Add(rocketTreePanel, 1, wxEXPAND | wxRIGHT, 2);
-   rocketDesignSizer->Add(rocketComponentPanel, 1, wxEXPAND);
-*/
+   designSplitter->SplitVertically(rocketTreePanel, rocketComponentPanel);
 
-/*
-   wxPanel* rocketVisPanel = new wxPanel(this, wxID_ANY);
+   wxPanel* rocketVisPanel = new wxPanel(mainSplitter, wxID_ANY);
    rocketVisPanel->SetBackgroundColour(wxColor(100, 200, 100));
-*/
-
-//   wxBoxSizer* mainSizer = new wxBoxSizer(wxVERTICAL);
-//   mainSizer->Add(rocketDesignSizer, 2, wxEXPAND | wxALL, 2);
-//   mainSizer->Add(rocketVisPanel, 1, wxEXPAND | wxLEFT | wxBOTTOM | wxRIGHT, 2);
-//   this->SetSizerAndFit(mainSizer);
-   /*
-   SetSizer(mainSizer);
-   wxTextCtrl* firstNameBox = new wxTextCtrl(this, wxID_ANY);
-   mainSizer->Add(firstNameBox, 1, wxEXPAND);
-   */
 
+   mainSplitter->SplitHorizontally(designSplitter, rocketVisPanel);
 
    Bind(wxEVT_MENU, &MainWindowFrame::onAbout, this, wxID_ABOUT);
    Bind(wxEVT_MENU, &MainWindowFrame::onExit, this, wxID_EXIT);
diff --git a/src/sim/AtmosphericModel.cpp b/src/sim/AtmosphericModel.cpp
new file mode 100644
index 0000000..bc621ec
--- /dev/null
+++ b/src/sim/AtmosphericModel.cpp
@@ -0,0 +1,14 @@
+#include "AtmosphericModel.h"
+
+namespace sim
+{
+
+AtmosphericModel::AtmosphericModel()
+{
+}
+
+AtmosphericModel::~AtmosphericModel()
+{
+}
+
+} // namespace sim
\ No newline at end of file
diff --git a/src/sim/AtmosphericModel.h b/src/sim/AtmosphericModel.h
new file mode 100644
index 0000000..8d3a7a9
--- /dev/null
+++ b/src/sim/AtmosphericModel.h
@@ -0,0 +1,17 @@
+#ifndef SIM_ATMOSPHERICMODEL_H
+#define SIM_ATMOSPHERICMODEL_H
+
+namespace sim
+{
+
+class AtmosphericModel
+{
+public:
+   AtmosphericModel();
+   virtual ~AtmosphericModel();
+
+   virtual double getDensity(double altitude) = 0;
+};
+
+} // namespace sim
+#endif // SIM_ATMOSPHERICMODEL_H
\ No newline at end of file
diff --git a/src/sim/CMakeLists.txt b/src/sim/CMakeLists.txt
new file mode 100644
index 0000000..cdb8487
--- /dev/null
+++ b/src/sim/CMakeLists.txt
@@ -0,0 +1,5 @@
+add_library(sim
+   AtmosphericModel.cpp
+   GravityModel.cpp
+   WindModel.cpp)
+
diff --git a/src/sim/GravityModel.cpp b/src/sim/GravityModel.cpp
new file mode 100644
index 0000000..36d4207
--- /dev/null
+++ b/src/sim/GravityModel.cpp
@@ -0,0 +1,14 @@
+#include "GravityModel.h"
+
+namespace sim
+{
+
+GravityModel::GravityModel()
+{
+}
+
+GravityModel::~GravityModel()
+{
+}
+
+} // namespace sim
\ No newline at end of file
diff --git a/src/sim/GravityModel.h b/src/sim/GravityModel.h
new file mode 100644
index 0000000..b81a729
--- /dev/null
+++ b/src/sim/GravityModel.h
@@ -0,0 +1,19 @@
+#ifndef SIM_GRAVITYMODEL_H
+#define SIM_GRAVITYMODEL_H
+
+#include <tuple>
+
+namespace sim
+{
+
+class GravityModel
+{
+public:
+   GravityModel();
+   virtual ~GravityModel();
+
+   virtual std::tuple<double, double, double> getAccel(double x, double y, double z) = 0;
+};
+
+} // namespace sim
+#endif // SIM_GRAVITYMODEL_H
\ No newline at end of file
diff --git a/src/sim/WindModel.cpp b/src/sim/WindModel.cpp
new file mode 100644
index 0000000..6d0c065
--- /dev/null
+++ b/src/sim/WindModel.cpp
@@ -0,0 +1,19 @@
+#include "WindModel.h"
+
+namespace sim
+{
+
+WindModel::WindModel()
+{
+}
+
+WindModel::~WindModel()
+{
+}
+
+std::tuple<double, double, double> WindModel::getWindSpeed(double x, double y, double z)
+{
+   return std::make_tuple<double, double, double>(0.0, 0.0, 0.0);
+}
+
+} // namespace sim
\ No newline at end of file
diff --git a/src/sim/WindModel.h b/src/sim/WindModel.h
new file mode 100644
index 0000000..22c3462
--- /dev/null
+++ b/src/sim/WindModel.h
@@ -0,0 +1,21 @@
+#ifndef SIM_WINDMODEL_H
+#define SIM_WINDMODEL_H
+
+#include <tuple>
+
+namespace sim
+{
+
+class WindModel
+{
+public:
+   WindModel();
+   virtual ~WindModel();
+
+   virtual std::tuple<double, double, double> getWindSpeed(double x, double y, double z);
+
+};
+
+} // namespace sim
+
+#endif // SIM_WINDMODEL_H
\ No newline at end of file