Mission description

0064-EX-CN-2016 Text Documents

Cornell University

2016-09-20ELS_182190

Cislunar  Explorers  Mission  Description   The   Cislunar   Explorers   are   competing   in   NASA’s   CubeQuest   challenge,   a   NASA   Centennial   Challenges   program,   which   offers   a   total   of   $5.5   million   to   teams   that   meet   the   challenge   objectives   of   designing,   building   and   delivering   flight-­‐qualified,   small   satellites   capable   of   advanced   operations   near   and   beyond   the   moon.   The   teams   will   compete   for   a   secondary   payload   spot   on   NASA’s   Exploration   Mission   1   (SLS/Orion).       The   Cislunar   Explorers   team   is   led   by   Professor   Mason   Peck   of   Cornell   University,   and   has   designed   their   spacecraft   to   demonstrate   a   game-­‐changing   technology:   electrolysis  propulsion.  Each  spacecraft  carries  a  tank  of  inert,  liquid  water,  which  is   then   electrolyzed   using   energy   collected   by   solar   cells,   splitting   H2O   into   hydrogen   and   oxygen   gas.   This   is   a   readily   combustible   mixture,   widely   used   in   launch   vehicles   and  spacecraft.     Hydrogen   and   oxygen   are   cryogenic   liquids   and   must   be   stored   at   very   low   temperatures   and   very   high   pressures.   For   CubeSats,   neither   are   acceptable.   CubeSat   specifications   prohibit   extreme   pressures   and   cryogenic   storage   tanks   are   too   bulky   to   be   usable   at   this   scale.   So   are   the   turbopumps   used   to   feed   LOX/LH2   rocket   engines.   Electrolysis   propulsion   achieves   very   dense   propellant   storage   of   1000   kg/m ,   several   times   denser   than   LOX/LH2   and   it   does   so   without   complex,   3 expensive,   and   heavy   additional   apparatus.   This   is   a   way   to   bring   green   propellant   into  the  CubeSat  framework,  producing  substantial  ΔV  in  a  compact,  simple  package.   The   Cislunar   Explorers   have   been   carefully   designed   around   their   use   of   water   propellant,   ensuring   passive   subsystem   symbiosis   to   reduce   the   cost   and   complexity   of   the   spacecraft.   For   example,   the   presence   of   water   acts   as   a   partial   radiation  shield  and  heat  sink  for  the  RF  Power  Amplifier.   The   most   significant   synergy   is   with   the   attitude   control   subsystem.   To   separate  the  electrolyzed  gas  from  the  liquid  water,  the  spacecraft  each  spin  about   their  major  axis,  centrifugally  forcing  the  water  away  from  the  spin  axis.  That  spin  is   facilitated  by  a  spring-­‐loaded  mechanism  that  separates  the  two  Cislunar  Explorers   from   each   other   after   deployment.   The   angular   momentum   of   the   spinning   spacecraft  keeps  it  pointed  in  the  same  direction,  like  a  gyroscope. When  a  torque  is   applied,  whether  deliberately  for  reorientation  or  as  a  side  effect  of  an  electrolysis   thruster   firing,   the   spin   axis   will   begin   to   nutate.   However,   this   nutation   will   damp   out  due  to  the  sloshing  of  water  in  the  propellant  tank  dissipating  energy,  and  the   spacecraft   will   soon   return   to   a   spinning   steady-­‐state.   Therefore,   the   Cislunar   Explorers  do  not  require  a  bulky,  power-­‐hungry  attitude  stabilization  system,  such  as   reaction   wheels.   Instead,   each   needs   only   a   single   cold   gas   thruster,   used   to   exert   torque  to  change  the  spin  axis  as  desired.

  Figure  1:  Spacecraft  Separation   the   Cislunar   Explorers   carry   several   inexpensive   onboard   cameras.   These   are   repeatedly   used   to   capture   images   of   the   Sun,   the   Earth,   and   the   Moon.   The   cameras   can   distinguish   between   the   three   bodies,   and   use   image   processing   techniques   to   compute   their   apparent   size   and   angular   separation   in   each   spacecraft’s   field   of   regard.   All   three   celestial   bodies   act   as   landmarks   in   space.   By   comparing   the   apparent   locations   of   the   celestial   bodies   with   their   ephemerides,   each  spacecraft  can  compute  its  own  and  attitude.  The  Cislunar  Explorers’  method  is   uniquely   able   to   simultaneously   determine   position   and   attitude   onboard   a   spinning   spacecraft.  This  technique  can  function  with  any  three  celestial  bodies  at  least  one  of   which  is  resolvable  as  a  discrete  disc;  these  need  not  be  the  Sun,  Earth,  and  Moon.   Brief   radio   transmissions   are   used   to   downlink   data   packets   of   computed   coordinates   to   keep   the   ground   station   appraised   of   the   spacecraft’s   position   and   attitude.   In   this   way,   the   Cislunar   Explorers   are   able   to   navigate   robustly   and   autonomously,  in  a  way  that  is  well  suited  to  lunar  orbit.     Apart  from  the  novel  technologies  to  be  demonstrated,  the  Cislunar  Explorers  make   use   of   inexpensive   and   readily   available   components   wherever   possible.   The   flight   computer   for   each   unit   is   a   Raspberry   Pi,   an   inexpensive   minicomputer   that   is   popular   with   hobbyists   and   educators.   Both   the   attitude   and   propulsion   thrusters   use   off-­‐the-­‐shelf   parts.   The   spacecraft   communicate   using   the   70   cm   UHF   radio   band,   popular   with   amateur   radio   operators   across   the   world.   The   entire   design   is   open-­‐source,   with   the   goal   of   enabling   further   innovations.   A   successful   demonstration   of   their   optical   navigation   and   electrolysis   propulsion   technologies   could   make   them   attractive   for   future   missions,   and   the   team   wants   the   space   development  community  to  be  able  to  benefit  immediately.  


Document Created: 0520-04-24 00:00:00
Document Modified: 0520-04-24 00:00:00
© 2025 FCC.report
This site is not affiliated with or endorsed by the FCC