KOMA-Scipt scrbook: How to change V-space between chapter prefix and title

KOMA-Scipt scrbook: How to change V-space between chapter prefix and title

My university has style requirements for my dissertation that seem to be
tailored to users of MS Word and the like. In particular, the formatting
of section headers differs only by use of caps/bold/italics from the rest
of the text. What I need is to replicate chapter headings that in MS Word
would result from the following input sequence:
[entire document double-spaced]
Chapter 1 [return]
Chapter Title [return]
This is the text of the chapter....
The only thing I haven't figured out is how to force the vertical space
between the prefix and title to be a simple double-space just like
everywhere else in the document. What am I missing?
\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}
\setlength\parindent{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}{\normalcolor\rmfamily}
\setkomafont{chapter}{\centering\MakeUppercase}
\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}