247 APM for a Constellation Intersatellite Link – EM Qualification and   Lessons Learned  

Frank Härtel* and Horst Kozilek* 

    Abstract    For a n Intersatellite Link  (ISL)  of a future constellation program , a study phase was initiated by ESA  to  design a mechanism for Radio  Frequency communication. Airbus DS  Friedrichshafen (ADSF) proposed a  design based on the Antenna Pointing Mechanism ( APM ) family with modifications that met  the stated  needs of the constellation . A qualification  program  was started beginning in September 2015 to verify the  launch and thermal loads and the equipment performance (R adio Frequency, Pointing, Microvibration and  Magnetic M oment).  Technical  challenges identified with the Engineering Model will be discussed within  this paper.  

Introduction  

The heritage of ADSF  for Antenna Pointing Mechanisms  is more than twenty years , with a series of  different pointing mechanisms.  Those mechanisms were designed to deploy and point large dish  antennas  as well as small antenna horns for the X - and Ka -Band.    Generally the requirements of such mechanisms include  the velocity  (<10 deg/sec) , the lifetime  (of more  than 5 years) , and the accuracy  (<0.2 deg) . These requirements  are not too demanding, as the Antenna  points towards  the ground station and the satellite is in a low-Earth orbit.    For the current constellation,  these requirements ar e more demanding.  As the Inters atellite Link shall  establish the RF communication between two MEO satellites , a very fast pointing velocity is needed   (> 60 deg/sec ). A higher  precision of <0.125 deg and an overall lifetime of 12 years  are also required.   These changes had a significant impact on the heritage design. The actuation chain had to be modified  with larger  motors and bearings. This led to an intensive redesign process with an increased mass. The  impacts of these modifications  have been verified within the qualification program , which will be  presented,  including results , within this paper.  

Intersatellite Link Antenna Pointing Mechanism  Background    For a constellation program, RF Inters atellite Links  between single satellites can support ranging and  communication for uploading mission data or  tele commands. These data shall be uploaded from one  single ground station to the next reachable satellite and transmitted by the Inters atellite Link  (see  Figure 1) to further  dedicated satellites. For this function each satellite has  to be equipped with two  Antenna Pointing  Mechanisms  for data transfer in the K -Band.   To establish such a constant network , the APM has to be able to point in each vector direction of the  hemisphere. Additionally the movement towards a new pointing destination has to be very quick in order to enlarge the time for the data link  communication. ADSF  has a substantial  heritage in building APMs for  communication to ground applications . ADS F follows the approach of elevation over azimuth axis pointing  systems. These systems have proven their high reliability and robustness over a mul titude of different  missions and accumulated a time in orbit of more than 35 years.  

                                                  * Airbus  Defence and Space, Friedrichshafen, Germany  

Proceedings of the 43rd Aerospace Mechanisms Symposium, NASA Ames Research Center, May 4-6, 2016