Would they have allowed their satellite to be launched on an untested platform?

That's the idea of putting a 'worthless' payload up first.

A tungsten or brass (LAGEOS) sphere covered in optical and radar retroreflectors is cheap and inert. The major cost for that type of mission is the launch.

Given 3-6 months, $<1M all-in, and a team of engineers and scientists, it would be quite possible to get something ready to rock. Such an instrument would allow an ever-improving test of solar-system dynamics for many millenia.

If Elon is reading and plans to do something similar again, get in touch (cah49@uw.edu). We'll make science happen.

Or, just launch a dense one of these: http://www.landfallnavigation.com/davis-emergency-radar-refl...

Agreed. I'm not a Musk fanboy, but most rockets are initially tested with inert dummy payloads. The choice wasn't between a Tesla and a science satellite, but between a Tesla and sand.