Rockoon  Development  

Sulfur  Pulsed  Plasma  Thruster  

Development  of  a  Rockoon  Launch  Pla9orm  and  a  Sulfur  Fuel  Pulsed  Plasma  Thruster  CubeSAT  Ian  Johnson*,  Race  Roberson,  Chad  TruiC,  Jaime  Waldock,  Paige  Northway,  Michael  Pfaff,  and  Robert  Winglee  

*ikj@uw.edu,  Advanced  Propulsion  Laboratory,  University  of  Washington  SSC14-­‐P2-­‐10,  2014  Small  Satellite  Conference,  Utah  State  University  

Abstract  Using  a  balloon  to  rise  to  an  al.tude  of  30  km  before  launching  is  one  means  to  increase   the   range  of  a   rocket.   Such  a   system  will  be   capable  of  providing  an  inexpensive   and   reduced   complexity   launch   method   for   student   projects.  Addi.onally,  the  University  of  Washington  (UW)  has  recently  opened  a  CubeSAT  laboratory  to  give  students  hands-­‐on  experience  with  satellite  hardware.  Once  in  orbit,  CubeSAT  missions  are  limited,  in  part,  due  to  an  inability  of  low  power  thrusters  to  offset  atmospheric  drag.  Recent  results  show  that  a  coaxial  sulfur-­‐fuel   Pulsed   Plasma   Thruster   (PPT)   can   provide   an   impulse/energy   ra.o   of   20  mN-­‐s/kJ  from  a  10  J  discharge,  twice  as  what  a  similar  geometry  Teflon  variant  is  capable  of.  This  increase  in  performance  can  provide  CubeSATs  the  propulsion  necessary   for   sta.on-­‐keeping   in  orbit.  The  UW  plans   to   launch  a  3U  CubeSAT  from   a   rockoon   on   a   suborbital   flight   as   a   student   project   by   the   end   of   the  decade.  

Rockoon  to  LEO  Theory  

CubeSAT  Development  

Acknowledgments  The  hundreds  of  students  who  have  taken  the  ESS205  ballooning  and  ESS472  rocket   courses   for   their   countless   hours   in   furthering   our   knowledge  of   this  poten.al  launch  system.  

[1]  Rand,  James.  “Balloon  Assisted  Launch  To  Orbit  –  A  Historical  Perspec.ve”.  AIAA  33rd  Joint  Propulsion  Conference  and  Exhibit.  1997.  

[2]  Burton,  R.  L.,  and  Turchi,  P.  J.  “Pulsed  Plasma  Thruster”.  AIAA  Journal  of  Propulsion  and  Power.  Vol.  14,  No.  5.  1998  

The  PPT  is  compact,  inherently  simple,  and  inexpensive  with  a  long  and  proven  flight  history.2  

The   use   of   sulfur   over   Teflon   (C2F4)   is   ideal   for   CubeSAT   opera.on   due   to   its  increased   thrust   and   reduced   velocity   to   becer  match   spacecrad   speeds.   The  high   vapor   pressure,   low   boiling   point,   and   higher   atomic   mass   of   sulfur   are  believed  to  be  the  important  chemical  acributes  for  this  use.  

The  PPT  main  and  igniter  circuit  overview  (leW)  and  sulfur  PPT  (right).  

Stage   Ini.al  Mass  (kg)  

Fuel  Mass  (kg)  

Structure  Mass  (kg)  

Payload  Mass  (kg)  

1   1072   718   107   247  

2   247   165   25   57  

3   57   38   6   13  

4   13   9   1   3  

Inability  of  small  laboratories  to  control  the  launch  of  their  satellites  limits  the  .meline  and  orbit.      -­‐  This  nega.vely  impacts  science  capabili.es  

Tradi.onal   launch   systems   are   too   expensive,  dangerous,  and  complex  for  a  university  project.      -­‐  A  rockoon  system  reduces  all  three  factors  

Structure      •  Aluminum  6061  3U,  490g  (1/16”  thickness)      •  3D  printed  ABS  plas.c,  325g  (1/5”  thickness)              -­‐  Minimum  wall  thickness  currently  under  tes.ng  

PPU      •  27W  power  during  illumina.on,  17W  orbital  average      •  Rechargeable  Li-­‐Ion  and  deployable  solar  panels      •  6W  for  satellite  opera.on,  11W  for  PPT              -­‐  5J  PPT  discharges  at  1Hz  with  50%  electrical  efficiency  

Computer        •  ATmega-­‐1280  Arduino  board      •  Addi.onal  EMI  protec.on  due  to  proximity  of  PPT  

Telemetry      •  144MHz  ¼-­‐wave  monopole  antenna  (50cm)  for  uplink      •  430MHz  dipole  antenna  (33cm)  for  downlink        •  Deployable  with  a  Ni-­‐Chrome  wire  switch  

AZtude  Control      •  PPT  is  non-­‐rotatable  (primary  propulsion  only)      •  4  reac.on  wheels  in  tetrahedral  geometry  for  orienta.on  and  amtude  control  

Property   Value   vs.  Teflon  

Plasma  Velocity   16.8km/s   -­‐20%  

Mass  Abla.on   3.8μg/J     +92%  

Plasma  Frac.on   16%   +6%  

Specific  Thrust   18  mN-­‐s/kJ   +125%  

Power  processing  unit  (leW)  and  telemetry  (right)  schema]cs.  

Laboratory  measurements  of  iden]cal  coaxial  PPTs  with  sulfur  and  Teflon  fuel  bars.  

Principle   advantage:   Using   a   balloon   to   pass   through   the   dense   lower  atmosphere  dras.cally  reduces  drag  and  therefore  the  required  fuel  mass.1  

Four-­‐stage  rocket  design      •  ΔV=9.2km/s      •  O-­‐class  motor,  Ce=2.18km/s      •  Stage  ΔV=2.3km/s  

The   lab  has   set  a  goal  of   raising  a  CubeSAT  payload   to   suborbital   veloci.es  by  2020.  Can  be  accomplished  through  a  3-­‐stage  cluster  rocket:      •  175kg  rocket  from  25kg  rail  (14.1  m3  of  He  at  STP)      •  30kN  peak  force      •  400  m/s2  peak  accelera.on      •  2.5km/s  peak  velocity      •  400km  peak  al.tude  

Accelera]on,  velocity,  al]tude  (leW),  ver]cal  force,  and  mass  (right)  simula]ons  of  the  proposed  3-­‐stage  rockoon  rocket  for  suborbital  veloci]es.  

The   Earth   and   Space   Science   Department   at   the   UW   offers   students   the  opportunity   to   work   on   balloon   and   rocket   based   experiments.   The  development  of  the  rockoon  concept  is  a  direct  result  of  those  opportuni.es.  

The  accelera]on  (top)  and  velocity  (boCom)  profiles  of  recent  tethered  rockoon  

launches  with  single-­‐stage  single-­‐motor  rockets.  

2013  latex  balloon  launch  of  atmospheric  PPT  experiment  (leW),  2013  launch  of  single-­‐stage  rockoon  (center),  and  2014  launch  of  2-­‐stage  rockoon  (right).  

10J  PPT  firing  from  3D  printed  frame  (top)  and  Al6061  frame  (boCom)