This exhibit is unmarked but matches the No. 1, WY2232 Unit Thermocouple. It looks to be a bolometer for the measurement of non-sinusoidal RF power. The side arms are probably a resonant dipole at the intended microwave frequency and a very small amount of RF will heat the bead and alter the parameters as read from the base connections via a bridge circuit.
The horizontal arms connected to the bead are 37 mm from tip to tip and this equates to a dipole tuned to around 3.3 GHz, a frequency used in centi-metric radar during WWII.
Basically the bolometer is a resistor close coupled to a thermister and sealed in a vacuum. The connections to the active region are made by very thin wires to minimise the heat loss through conduction. The device can be calibrated with a DC voltage and then be used to measure the power of an irregular waveform such as a radio RF envelope.
The active bead is at the top. The function of the lower wires is not yet known.
The mica plate holding the four wire active device.
The balloon envelope is 64 mm in diameter, and excluding the IO base pins is 135 mm tall.