Test masses for the G-POEM test of the weak equivalence principle

Abstract

We describe the design of the test masses that are used in the 'ground-based principle of equivalence measurement' test of the weak equivalence principle. The main features of the design are the incorporation of corner cubes and the use of mass removal and replacement to create pairs of test masses with different test substances. The corner cubes allow for the vertical separation of the test masses to be measured with picometer accuracy by SAO's unique tracking frequency laser gauge, while the mass removal and replacement operations are arranged so that the test masses incorporating different test substances have nominally identical gravitational properties.

A new class of equivalence principle test masses, with application to SR-POEM

“…Wire electric discharge machining (EDM) can be used to place the vertical faces of the TM to about 1 μm. The alternative substance, which for now is assumed to be a hard alloy of lead, can be added by the method we used for the TMs of G-POEM (Reasenberg et al 2011). Several cylindrical holes are bored into the aluminum and each is filled with a hollow cylinder (tube) of the alternative material having the same mass as the removed.…”

Design and characteristics of a WEP test in a sounding-rocket payload

“…The nominal substance pair for the first SR-POEM flight is aluminum and lead. In one TM, cylinders of aluminum are removed from the blocks and replaced by tubes of lead without changing the TM mass and having minimal effect on the moments of inertia [Reasenberg et al 2011]. About half of the TM mass will be lead.…”

“…The sounding-rocket-based principle of equivalence measurement (SR-POEM) will achieve a sensitivity σ (η) < 2 × 10 −17 in the ≈20 min portion of a single flight of a suborbital rocket in which atmospheric drag is negligible. This is a five-fold improvement over our previous design (Reasenberg et al 2011, Reasenberg and. We use subpicometer tracking frequency laser gauges (TFGs) to measure the distances from a highly stable 'TFG plate,' to two test masses (TMs), containing test substances 'A' and 'B'.…”