Paul wrote:
"The rocket body is a 12 inch diameter aluminum tube."

The tube could be slotted lengthwise and the gap insulated to make a
slot antenna. Low profile can minimize atmospheric drag.

Look at page 320 of Kraus` 3rd edition of "Antennas". On page 321 Kraus
writes:
"Typical slotted cylinder dimensions for resonance are D= 0.125 WL,
L=0.75 WL, and the slot width about 0.02 WL."

12 inches, the rocket tube diameter, is 30.48 cm. If this is 1/8 WL, the
WL= 2.438 m and F=123 MHz.

The length of the slot is 0.75x2.438=1.83 meters. Slot width is
0.02x2.438m=4.9 cm.

The length od the slotted cylinder is greater than 1/2-wavelength as
needed for resonance because the cylinder circumference is not an
infinite sheet.

Polarization is the same direction as the voltage across the slot,
horizontal when the cylinder is erect. It has been used as an
omnidirectional VHF broadcast antenna. The slotted cylinder can be
scaled for any frequency.

Best regards, Richard Harrison, KB5WZI