31 A Novel Approach for a Low-Cost Deployable Antenna 

Chris Amend*, Michael Nurnberger*, Paul Oppenheimer*, Steve Koss* and Bill Purdy** 

Abstract   The Naval Research Laboratory (NRL) has designed, built, and fully qualified a low cost, low Passive  Intermodulation (PIM) 12-foot (3.66-m) diameter deployable ultra high frequency (UHF) antenna for the  Tacsat-4 program. The design utilized novel approaches in reflector material and capacitive coupling techniques. This paper discusses major design trades, unique design characteristics, and lessons learned from the development of the Tacsat–4 deployable antenna. This antenna development was  sponsored by the Office of Naval Research.   Introduction   The Tacsat-4 satellite is part of a series of fast-pac ed, low-cost missions for t he Operational Responsive  Space (ORS) initiative. The spacecraft bus, funded by  the Office of the Secretary of Defense, was  designed, built and tested by a team consisting of  both NRL and Johns Hopkins University Applied  Physics Laboratory. The payload, Comm-X, is funded by  the Office of Naval Research and will provide  Communications-on-the-Move (COTM), Blue Force Tra cking (BFT), and Data Exfiltration to the user  community. The COTM capability provides UHF legacy radio support and a Mobile User Objective  System (MUOS) like channel bit (but not MUOS-like capability) for early testing. The BFT capability  collects existing UHF devices with tasking priority ex pected for underserved areas. The Data Exfiltration  capability focuses on data collection from Navy buoys, which are typically remotely located on the seas  and in littorals. The Tacsat-4 payload operates in a bent pipe fashion, working directly with legacy radios  and/or sensors and ground terminals. Tacsat-4 has several ORS system-level objectives including using a prototype bus to mature spacecraft bus standards for acquisition and to fly in a “low” highly elliptical orbit (HEO), enabling a new set of ORS missions that  require dwell, such as communications. The  deployable antenna on the CommX payload was design ed to provide UHF capability from the HEO orbit  to the ground such that no active pointin g was required by any ground assets.  

Design Requirements   The Comm-X UHF antenna is a parabolic reflector with an f/D of 0.425 and operates over a frequency range of 240 MHz to 420 MHz. The reflector surface accuracy of the antenna wa s designed such that the  root mean square (RMS) of the surface was within 6.35 mm (0.25 inch) of the ideal parabola. This RMS  requirement, very loose compared to many industry  standard reflectors, is sufficient because of the  wavelength/frequency that the payload operates at. T he antenna was designed to fit within the stowed  envelope of the Minotaur IV launch vehicle. The antenna mass allocation was 27 kg (60 lb) with a stowed first mode of >60 Hz and deployed first mode >5 Hz. The Comm-X antenna was designed as a Class D  mission, and scheduled to be completed within 12 months for <$4M.    The selected orbit of the TacSat-4 satellite is 700 km  x 12,050 km with an inclination of 63.4 degrees. The  UHF antenna is unshielded and is required to withstand 100 MRad of total ionized dose radiation in this  orbit. Additionally, the antenna will be required to withstand the thermal envir onments imposed by the  HEO orbit (-150 deg C to +150 deg C).                                                     * Naval Research Labora tory, Washington, DC  ** Purdy Engineering, Poolesville, MD 

Proceedings of the 40th Aerospace Mechanisms Symposium, NASA Kennedy Space Center, May 12-14, 2010  NASA/CP-2010-216272