孤
=
孑
+
瓜
:
Gitta Giraffe (gu) is currently the space station's lone (孤) inhabitant. To feel less lonely (孤), she drew a mosquito's (孑) face on a melon (瓜) to have somebody to talk to in front of the space station (Ø1).
独
=
犭
+
虫
:
Everyone has left the space station, only the animals are left: Doggy Dog (du), the dachshund (犭) and the mosquito (虫). They have noone who throws them a stick or exposes their bare body parts to bite. All alone (独), they wait in the space station's entrance (Ø2).
于
=
亅
+
二
:
Mnemonic symbol: prepositions are what glue the sentence together. Honey is as sticky as glue, so I'll represent 于 by a honey jar.
Yu the Great was assigned to repair the electrics of the space station's entrance, but instead she was snacking some honey from a honey jar. Now her capacitor got stuck in the honey and she has to use a crowbar to lever it out.
(of time or place) in; at; on / (indicating any indirect relation) to; toward; vis-à-vis; with regard to; for / (indicating a source) from; out of / (used in comparison) than / (used in the passive voice) by
Sherlock Holmes (sh) is cleaning a flower pot (廿) under the shower of the space station's bathroom (Ø4) with a loofah (L) because he didn't quite understand a poster next to the shower from the WHO (世) explaining dangers arising from different germs.