documentclass[12pt,letterpaper,oneside,chapterprefix=on]{scrbook}

%Margins
usepackage[letterpaper,left=1.5in,top=1in,right=1in,bottom=1in]{geometry}

%Type
usepackage{fontspec}
setmainfont{Times New Roman}
usepackage{unicode-math}
setmathfont{xits-math.otf}
usepackage[doublespacing]{setspace}
setlengthparindent{0.5in}

usepackage{microtype}
usepackage{lipsum}

%Remove vertical space above/below chapter headings:
%http://tex.stackexchange.com/questions/43087/remove-space-before-chapter-title-with-koma-      script-scrbook
renewcommand*{chapterheadstartvskip}{vspace*{-baselineskip}}
renewcommand*{chapterheadendvskip}{vspace*{0in}}

setkomafont{disposition}{normalcolorrmfamily}
setkomafont{chapter}{centeringMakeUppercase}

begin{document}

frontmatter

chapter*{Abstract Title Page}
chapter*{Abstract}
chapter*{Copright Page}
chapter*{Title Page}

tableofcontents
listoffigures

mainmatter

chapter{Introduction}
lipsum[1-2]
appendix
backmatter

end{document}

documentclass[12pt,letterpaper,oneside,chapterprefix=on]{scrbook}

%Margins
usepackage[letterpaper,left=1.5in,top=1in,right=1in,bottom=1in]{geometry}

%Type
usepackage{fontspec}
%setmainfont{Times New Roman}
usepackage{unicode-math}
setmathfont{xits-math.otf}
usepackage[doublespacing]{setspace}
setlengthparindent{0.5in}

usepackage{microtype}
usepackage{lipsum}

%Remove vertical space above/below chapter headings:
%http://tex.stackexchange.com/questions/43087/remove-space-before-chapter-title-with-koma-      script-scrbook
renewcommand*{chapterheadstartvskip}{vspace*{-baselineskip}}
renewcommand*{chapterheadendvskip}{vspace*{0in}}
renewcommand*{chapterformat}{chapappifchapterprefix{nobreakspace}thechapter}

setkomafont{disposition}{normalcolorrmfamily}
setkomafont{chapter}{centeringMakeUppercase}

makeatletter
renewcommand*{@@makechapterhead}[1]{chapterheadstartvskip
  {%
    setlength{parindent}{z@}setlength{parfillskip}{fill}%
    normalfontsectfontnobreaksize@chapter{}%
    if@chapterprefix
      let@temparaggedsection
    else
      let@tempa@hangfrom
    fi
    @tempa{ifnum c@secnumdepth >m@ne%
        if@mainmatter
          if@chapterprefix
            expandaftersize@chapterprefix
          else
            expandaftersize@chapter
          fi
          {chapterformat}%
          if@chapterprefix
            size@chapterprefix{}endgrafnobreak%vskipbaselineskip
          fi
        fi
      fi
    }%
    {raggedsection interlinepenalty@Msize@chapter{#1}par}}%
  nobreakchapterheadendvskip
}
makeatother

begin{document}

frontmatter

chapter*{Abstract Title Page}
chapter*{Abstract}
chapter*{Copright Page}
chapter*{Title Page}

tableofcontents
listoffigures

mainmatter

chapter{Introduction}
lipsum[1-2]
appendix
backmatter

end{document}

documentclass[12pt,letterpaper,oneside,chapterprefix=on]{scrbook}

%Margins
usepackage[letterpaper,left=1.5in,top=1in,right=1in,bottom=1in]{geometry}

%Type
usepackage{fontspec}
%setmainfont{Times New Roman}
usepackage{unicode-math}
setmathfont{xits-math.otf}
usepackage[doublespacing]{setspace}
setlengthparindent{0.5in}

usepackage{microtype}
usepackage{etoolbox}
usepackage{lipsum}

%Remove vertical space above/below chapter headings:
%http://tex.stackexchange.com/questions/43087/remove-space-before-chapter-title-with-koma-      script-scrbook
renewcommand*{chapterheadstartvskip}{vspace*{-baselineskip}}
renewcommand*{chapterheadendvskip}{vspace*{0in}}
renewcommand*{chapterformat}{chapappifchapterprefix{nobreakspace}thechapter}

setkomafont{disposition}{normalcolorrmfamily}
setkomafont{chapter}{centeringMakeUppercase}

makeatletter
patchcmd{@@makechapterhead}{vskip.5baselineskip}{}{}{}
makeatother

begin{document}

frontmatter

chapter*{Abstract Title Page}
chapter*{Abstract}
chapter*{Copright Page}
chapter*{Title Page}

tableofcontents
listoffigures

mainmatter

chapter{Introduction}
lipsum[1-2]
appendix
backmatter

end{document}

renewcommand*{chapterformat}{chapappifchapterprefix{nobreakspace}thechapter}

documentclass[12pt,letterpaper,oneside,chapterprefix=on]{scrbook}[2015/04/23]

%Margins
usepackage[letterpaper,left=1.5in,top=1in,right=1in,bottom=1in]{geometry}

%Type
usepackage{fontspec}
setmainfont{Times New Roman}
usepackage{unicode-math}
setmathfont{xits-math.otf}
usepackage[doublespacing]{setspace}
setlengthparindent{0.5in}

usepackage{microtype}
usepackage{lipsum}

RedeclareSectionCommand[beforeskip=0pt,afterskip=0pt,innerskip=0pt]{chapter}

setkomafont{disposition}{normalcolorrmfamily}
setkomafont{chapter}{MakeUppercase}
renewcommand*raggedchapter{centering}

begin{document}

frontmatter

chapter*{Abstract Title Page}
chapter*{Abstract}
chapter*{Copright Page}
chapter*{Title Page}

tableofcontents
listoffigures

mainmatter

chapter{Introduction}
lipsum[1-2]

chapter{Chapter 2}
lipsum[1-2]
appendix
backmatter

end{document}