Electric (Rocket) Propulsion. EP Overview

Transcription

1 Elctric (Rockt) Propulsion EP Ovrviw Elctric Propulsion-1 Basics Rockt Propulsion Elmnts Propllant Enrgy Sourc Storag Fd Systm sam in chmical rockts Storag Convrsion Acclrator Elctric Propulsion- 1

2 Elctric Propulsion Systm Elmnts Propllant Gas (X), liquid (N H 4 ), solid (tflon) Storag Enrgy Sourc chmical, nuclar, radiation (solar) Storag Fd Systm Thrustr Thrmodynamic (nozzl), lctric, lctromagntic Convrsion to lctricity at propr V, DC/AC( frq), currnt, stady/pulsd Elctric Propulsion-3 Elctric Propulsion - Acclrators Accl. Forc Elctrothrmal Elctromagntic Elctrostatic Prssur, Lorntz, Elctrostatic, F p j B Elctrically hat Magntic and lc. Static E fild (alon) propllant and us filds acclrat acclrats chargd nozzl xpansion ionizd propllant particls (ion ngins, (rsistojts, arcjts) (MPD, pulsd colloidal and Hall(?) plasma thrustrs) thrustrs) I sp (s) 300-1,500 1,000-10,000,000-10,000+ Thrust Wight <10-3 <10-4 < Elctric Propulsion-4

3 Propulsion Tchnology Orbit Insrtion Orbit Maintnanc and Manuvring Attitud Control Typical Stady Stat Thrust [N] Advantags Isp [sc] COLD GAS Simplicity - Saf - Low Contamination CHEMICAL (a) Solid (b) Liquid Monopropllant Bipropllant Dual Mod NUCLEAR THERMAL Comparison to Chm./Nucl. Rockts NON CHEMICAL Elctro-Thrmal ( Arcjts, Rsistojt) Elctro-Magntic (Plasma) Elctro-Static Hybrid to 1x Up to 1x , to 0 - High Thrust - Hritag High Spcific Impuls Vry high spcific impuls Disadvantags - Low Spcific Impuls - Modrat prformanc - Combustion complications - Safty concrns - Unprovn - Politically unattractiv - Expnsiv - Low Thrust/wight - High systm mass - Low thrust lvl Limitd hritag ,000 Aftr Evans, Tlsat Canada intrnal cours Elctric Propulsion-5 Potntial Advantags: Idal Rockt Equation V M final u M Typical vlocity incrmnt V rquirmnts (in km/s) initial from M. Walkr Highr u Lowr propllant mass/gratr payload mass fraction idal cas (nglcts chang in gravitational potntial of propllant - gravity pnalty ) Elctric Propulsion-6 3

4 Gravity Losss Can rduc advantag of EP if propllant is carrid ovr larg chang in gravitational potntial Exampl: orbit scap V long duration spiral burn.3v impuls burn part of I sp incras ndd to mt highr V Not issu for station kping (no chang in gravitational potntial) Multipl (short) firings for larg orbital changs can also rquir narly sam V as Hohmann (impulsiv) transfr short thrust durations at sam gravitational ndpoints as Hohmann transfr Elctric Propulsion-7 Potntial Commrcial Advantags from M. Walkr * (spiral) Elctric Propulsion-8 *NSSK=N-S station kping 4

5 EP Powr Rquirmnts Jt Powr P 1 j m u 1 m u u 1 u 1 I g sp Incras in I sp (or u ) ntails incras in powr u for constant flowrat u for constant thrust For comparison, chmical rockt with thrust of just 1000 lb f (4.5 kn) and I sp = 350s, P j =7.7MW P j =66 MW for lc. rockt with I sp =3000s and sam thrust EP tnds to b powr-limitd to low thrust (and low acclration) lvls Elctric Propulsion-9 Supply Powr Rquird Supply Powr P s Ovrall convrsion fficincy has 3 main componnts T nrgy convrsion - of raw nrgy sourc to lctricity ~100% for photovoltaics dirct convrsion of photons (dos NOT includ fraction of solar radiation that can b convrtd to lctricity by typical solar array, ~18-5%) Pj T S pp total fficincy of nrgy convrsion th powr prparation and conditioning lctronics (losss in lctronics) ~9% (lctrostatic) ~98% (stady arc jts) 10-40% for nuclar thrmal, thrmodynamic cycl limits = lots of wast hat thrustr fficincy - only part of input lc. nrgy convrtd to KE 40-70% Elctric Propulsion-10 5

6 Thrust Efficincy Typical valus (vary with I sp ) Fig in Humbl, Hnry and Larson Elctric Propulsion-11 Mass Rquirmnts What limits availabl powr to EP systms? mass of powr plant and associatd systms If powr plant mass is significant fraction of propllant mass, thn som advantags of highr spcific impuls opration ar lost payload may consist mostly of powr plant/lctronics for propulsion systm Elctric Propulsion-1 6

7 Mass Rquirmnts (con t) Powr sourc mass Mass powrsourc P s s narly linar rlationship spcific mass (.g., kg/kw) Not: somtims usd for spcific mass, but also usd by othrs for spcific powr (kw/kg), i.., = 1/ s ~7-5 kg/kw lc for solar arrays (dpnds on cll dsign, substrat) s ~-4 kg/kw thrmal for nuclar ractors (dpnds on shilding) to rjct wast hat, also rquir additional mass for radiators R ~ kg/kw wast hat Elctric Propulsion-13 Mass Rquirmnts (con t) Powr prparation and conditioning Mass pp pp P pp Larg variation with typ of EP dvic (spcially if nd high voltag or powr, and short puls forming lctronics/switchs) pp ~0. kg/kw lc for typical arcjts pp ~0 kg/kw lc for PPT (pulsd plasma thrustrs) Elctric Propulsion-14 7

8 Elctric Propulsion-15 Elctrostatics - Dfinitions V potntial or voltag (somtims ) (Volts) E lctric fild (V/m, N/Coulomb) q charg (C) (q -= C) Forc F Eq Potntial Enrgy J currnt (A, Coulomb/s) j charg currnt dnsity (A/m, Coulomb/m s ) n numbr dnsity (1/m 3 ) Fdx qedx qv dv E V dx V E V j nqu x Forcs on a Chargd Particl To xamin how to us lctrical nrgy to acclrat a propllant, considr acclration of a particl with mass m and charg q Elc. Fild Mag. Fild du m qe qu B p dt Elctric Propulsion-16 q + Elctrostatic Forc E F u q Lorntz Forc + Collisional Forc (Momntum Transfr) F B m u F m B (1) 8

9 Motion of Chargd Particl in E&B Filds How dos chargd particl mov in lctric and magntic filds du q Elctric fild only E dt m lctron lightr, highr accl. + - Magntic fild only du q particl gyrats u B dt m (cntripdal accl.) radius of gyration Larmor radius frquncy of gyration cyclotron frquncy mu B qb g No work; B and F prpndicular r g qb m r g E B u Elctric Propulsion-17 Motion of Chargd Particl in E&B Filds Crossd E and B filds E fild acclrats particl upward B fild causs acclration prpndicular to u E ovrall rsult is drift vlocity normal to E and B E B u d B du m qe qu B dt B havy u d light r g m m g 1 Elctric Propulsion-18 9

10 Inducd Magntic Filds In gnral, currnt flow inducs a B fild B fild inducd by linar currnt B fild inducd by coil J B B From Spac Propulsion Analysis and Dsign, Humbl, Hnry and Larson, 1995 Elctric Propulsion-19 u Elctric Propulsion-0 Plasmas Gas composd of qual amount of ngativly and positivly chargd particls lctrically nutral ngativ particls usually - positiv particls ar positiv ions typically most of gas molculs rmain nutral Momntum quation for plasma u u u p j B t u, u u 1, 3 Currnt Dnsity (A/m ) 10

11 Elctric Propulsion-1 Inducd E Filds Hall Effct Elctron acclration lightr - acclrat mor quickly and accommodat to flow fild (most of j) collisional coupling (momntum) of lctrons and havis (ions and nutrals) is wak B p E j u B j () n n plasma rsistivity (m) m v c n collision frq. lctrons with havis Inducd E fild du Hall Effct to plasma acclrats havy motion particls in charg nutral plasma lctron prssur trm 11