docs: SC/21---Use ~ over \, as it looks better in the hypertext.

(cherry picked from commit a4edcc4)

docs/sc/021/sc21.tex

@@ -741,7 +741,7 @@ \subsection{\xlabel{obs_modes}Observing modes}
 \end{minipage}
 \begin{minipage}[t]{0.85\linewidth}
 \textsc{daisy} maps are the option for point-like or compact sources
-($<$3\,arcmin) by maximising the exposure time on the centre of the
+($<$3~arcmin) by maximising the exposure time on the centre of the
 image. The telescope moves at a constant velocity in a `spirograph'
 pattern that has the advantage of keeping the source on the array
 throughout the observation. This is shown in the top panel of
@@ -3280,7 +3280,7 @@ \subsection{\xlabel{fcf}Flux conversion factors (FCF)}
   flux density and the FWHM. The integrated flux density within a
   given aperture (30-arcsec radius default) is calculated using
   \photom\ \autophotom. Flux densities for calibrators such as Uranus,
-  Mars, CRL\,618, CRL\,2688 and HL\,Tau are already known to
+  Mars, CRL~618, CRL~2688 and HL~Tau are already known to
   \picard. To derive an FCF for other sources of known flux densities,
   the fluxes can be added to the parameter file with the source name
   (in upper case, spaces removed): \texttt{FLUX\_450.MYSRC = 0.050}
@@ -4684,4 +4684,3 @@ \section{\xlabel{acronyms}List of Acronyms}
 
 \end{document}
 
-