Assign Administration of a Service Application with PowerShell

$serviceapp = Get-SPServiceApplication <guid>
$security = Get-SPServiceApplicationSecurity
$serviceapp -Admin $principalUser1 = New-SPClaimsPrincipal -Identity "<domain\user>" -IdentityType WindowsSamAccountName Grant-SPObjectSecurity
$security -Principal $principalUser1 -Rights "Full Control" Set-SPServiceApplicationSecurity $serviceapp -ObjectSecurity $security -Admin