 point.

There is no spoon tipping point: YouTube
Your question really just asks about how long an approximation or simplification is valid, and that's purely up to you and how much error you can tolerate by using your approximation. 

Also:
While you would like to imagine that there can be two satellites in the same orbit but one behind the other, the problem is that the Earth's gravitational field is not uniform, so it will not follow in the same path. Orbits are not perfectly closed or repeatable because of this. 
It's a hard task to get out of the idea that there are really such things as fixed orbits, it's a jump of intuition, but that's the reality; there isn't. All you have is a gravity field with it's lumpy deviations, plus drag, solar pressure, and the Sun's and Moon's gravity (plus more), and a sophisticated numerical propagator that calculates step-by-step how a body might move in this complex and ever-changing field of accelerations.
Welcome to the edge of space!

A:

I'm going to add to the pre-existing answer, from the perspective of classical mechanics and astronomy:  
Any two masses that you can take, with any initial conditions in position and velocity, will pose a so-called two-body problem. This 'problem' is a, for all times, exactly solvable mathematical description and solution of the setup you've been asking about. 
Now what you propose, to increase the mass of the satellite to the point where it becomes'relevant' would simply be a binary system (of stars, planets, blackholes, whatever). Both bodies then orbit the common barycenter, which is a constant of motion.
This is still true for the special case when one mass is much smaller than the other, but then the barycenter happens to coincide with the center of the more massive body, so it looks as if there is an orbit around the more massive body.
In real-life things are more complicated than just a two-body problem. Then all masses tug on all the others, and binary barycenters (for example the barycenter for the Sun-Jupiter system) move as well and are not a constant of motion anymore. For earthly satellites in geostationary orbit, perturbations from the other solar system bodies play a role already, and/or station-keeping in L2 requires firing of thrusters from time to time.

point. 

 There is no spoon tipping point: YouTube 
 Your question in truth barely asks about how long an approximation or reduction is valid, and that's purely up to you and how much error you can tolerate by practice your approximation. 

 Also: 
 While you would wish to think that there can be two satellites in the same eye socket but one behind the other, the problem is that the Earth's gravitational playing field is not uniform, so it will not adopt in the same path. orbit are not perfectly closed or repeatable because of this. 
 It's a hard job to get out of the idea that there are really such thing as fixed orbits, it's a jump of intuition, but that's the reality; there isn't. All you own is a gravity field with it's lumpy deviations, plus drag, solar atmospheric pressure, and the Sun's and Moon's gravity (plus more), and a sophisticated numerical propagator that calculates step - by - step how a body might move in this complex and ever - changing battlefield of accelerations. 
 Welcome to the edge of quad! 

 A: 

 I'm going to add to the pre - existing answer, from the position of classical automobile mechanic and astronomy:  
 Any two masses that you can take, with any initial condition in position and velocity, will pose a so - called two - body trouble. This' problem' is a, for all times, exactly solvable mathematical description and solution of the setup you've been asking about. 
 Now what you project, to increase the mass of the satellite to the point where it becomes'relevant' would simply be a binary system (of stars, planet, blackholes, whatever). Both bodies then orbit the common barycenter, which is a constant of apparent motion. 
 This is still true for the special case when one multitude is much smaller than the early, but then the barycenter happens to coincide with the center of the more massive body, so it look as if there is an eye socket around the more massive body. 
 In real - life sentence things are more complicated than merely a two - body trouble. Then all masses tug on all the others, and binary barycenters (for example the barycenter for the Sun - Jupiter organization) travel as well and are not a constant of motion anymore. For earthly satellite in geostationary orbit, perturbations from the other solar system bodies play a function already, and/or station - keeping in L2 requires firing of thrusters from time to time.
 polnt.

There is no spoon tipking point: YouTubg
Yiur quxstion deally jjst asks about how long an a'prozimatuon or simplification ks valid, wnd that'w pucely up to you ais how mmeh erdlr ymn can tolerate ny using yogr approximatimn. 

Apso:
While you would like to imagine ehat thrrf can be two swtelkytes pn the same orbit but one behins the ouher, the problem ix that the Earth's gravitatlonap field is not univorm, so it qill bot follow iv the same path. Orbits are not perfectly closed or reoeatayle because od tjhs. 
It's a hacd tash to get out of the hdea thst there are rcally suxh things as fixed oruits, it's a jump of igtuition, tuc that's the reality; tyeee ist't. Anl yuy hxve ix z gravlty field witg it's lumpy deviations, plus drsg, wolar pressurs, and ehq Sun's and Moon's gravity (plus more), and d skphisticated numerical propagator that calcupates ste[-by-step how a body might move in this complex and ever-rhxngnkn fidod of accelerations.
Welcome to the edge of space!

W:

J'm gping to add to the pre-exixtlnb answer, from jhe perspedtive of classical mechanycs abd astronjmy:  
Any two masses that you cab take, with cny initial conditiond in positiun amd vekocity, will pose a so-cauled two-body prlblem. Thia 'problem' is a, fof akl times, exactly solvable maehematicao dexcriptiun amd solttion of tje sebgp you've been askijg ablud. 
Now what you propose, to increase the mass of the sateklhte to the 'oint ehere it becoies'relevant' woold simplv be a binary syatem (of stars, planqts, blackholev, whatever). Bovh bodies theb orvit the zommon barycenyer, which is a consrant of motion.
This is atill true for cke special case wnen onq laxs hs much smalner ghav the uther, but tmen the barycenter happens do ckincide with the crnber of thg more mafsive body, so it looks as if thtre is an orbiy atound the more massive body.
In rsal-life tjinns are more cjmpllcatgd than jusc a two-body problem. Then all masses tug in all the others, qnd binary barycentgrs (for examplx the farycentes for the Sun-Jupiter system) move as wtll and are not a constznt of motiln anymore. For earthly satellites in geostationary orbit, perturbations frim the other solar sysyem bmdnes play w ropx already, and/or snation-keeping in L2 requires firiig of thruvtzrs from time to time.

point. There is no spoon tipping point: question just asks how long an and purely up to and how much you can tolerate by using your Also: While you would like to imagine that there can be two satellites the same orbit but one behind the other, the problem is that the gravitational is uniform, it will not follow in the same path. Orbits are not perfectly closed or repeatable because this. It's a hard task to get out the idea that there really such things as fixed it's jump of but the there isn't. All have is a gravity field with it's lumpy deviations, plus drag, solar pressure, and the Sun's and gravity (plus a sophisticated propagator calculates how a body in this complex and ever-changing field to the edge of space! A: I'm going add to pre-existing answer, from the perspective of mechanics and astronomy: Any two masses that you take, with any initial conditions in position and velocity, will pose a so-called two-body problem. is a, for all exactly solvable mathematical and of setup been asking Now what you propose, to increase the mass of the satellite the point where it becomes'relevant' would simply be a binary stars, blackholes, whatever). Both then orbit the common which a constant of motion. still for when mass much smaller than the but then the barycenter happens coincide with the center so it looks as if there is an around the more massive body. In real-life are more complicated than just a two-body problem. Then all masses tug all the binary barycenters (for example the barycenter for the system) move as well are not a constant of motion anymore. For earthly in orbit, perturbations the other solar bodies play a already, and/or station-keeping requires firing thrusters time
 point.

There is no spoon tippinG point: YouTUbe
YoUr qUesTiOn reAlly Just asks about hOW lonG an approximation or simpLificAtIOn is VAlId, and That's puRElY UP to YoU aNd hOw MUcH erroR yoU can tolErate by usiNg yOuR approximatiON. 

ALso:
While yoU woUld like to imaGinE that tHeRe cAN be twO saTelliTes in tHE same oRbit but onE bEHind thE Other, thE PRoBlem Is that the Earth's grAViTAtional field is Not uniFoRM, sO IT wiLl nOt follow in ThE same PAth. OrbiTS aRE NOt pERfectly closed Or repeatablE BecAuse of ThIs. 
IT'S a hard Task tO gET ouT of the idea tHat tHere are reAlly suCH things AS fixed oRbits, iT's a JumP of iNTuItIon, BuT ThaT'S tHe rEAliTy; there iSn'T. ALl you Have IS A GRaviTy fIeld With iT's lumpy deviatIonS, pluS DraG, solaR presSure, AnD the SUn's and moon's GrAvity (plus more), anD a soPhisticatEd nUmEriCaL propAGator tHat CalCulates Step-by-sTEp hOw A BODy Might move in this comPlEX AnD ever-chaNging fIElD oF AcceleraTiOns.
welcOME to thE edgE Of Space!

A:

I'm Going tO AdD tO the pre-ExIsting AnSweR, frOm the PErspEctive Of classiCal meCHanics and astroNOmy:  
Any two massES tHAT yOU can TakE, with any iniTial COndiTionS In PosITion aNd velOcITy, WIll pose a so-called two-BoDy probLem. ThIs 'problem' is a, fOr all times, EXACtly solvAble MAtHEmatical descriPtion And solutioN Of the setUp you'Ve been asKing about. 
nOW what you ProPosE, to IncREAsE the mass of the SATellItE to the pOinT where iT beComEs'rEleVaNt' would siMply be a bInArY sYsTem (Of staRS, planets, BlAckHoLes, WhateVEr). Both BodieS theN oRbIT thE common BArYCEnteR, wHiCh is A coNsTant oF motIOn.
THis is stIll true foR thE SpecIaL cAse when One mass is much SmAller than tHe OthEr, but tHEN the baryCenter happens to coincide WIth the cEntEr of tHe moRe massive BodY, so it lOokS As if thEre is aN orbiT aRouND The moRE MaSsiVe Body.
In real-LIFe tHings ArE morE compliCated than just a two-bODy pRoblem. Then all MasSes tUG On All THe OTheRs, ANd bINAry barycenters (fOr example tHe BArYcenter for THe SUn-jupiter System) mOve as WEll and aRe not a conStant of moTiOn anYMOre. for earthly SatellitEs in geostATionaRY oRbit, pErtUrbatiOnS frOm the Other sOLar SysteM bodieS pLay a roLe alrEaDy, and/or sTation-keeping in L2 requireS firinG of thRusTers from tIme TO tiMe.

 point.

There is no spoon  tipping p oint:  Yo uTu be 
You r qu estion reallyj ustasks about how long an  appr ox i mati o nor si mplific a ti o n  is  v al id,  a n dthat' s p urely u p to you a ndho w much error yo u can tole rat e by using y our  appro xi mat i on. 
Al so:
W hile y o u woul d like to  i m aginet hat the r e  c an b e two satellitesi nt he same orbitbut on eb eh i n d t heother, the  p roble m  is tha t  t h e Ear t h's gravitati onal fieldi s n ot uni fo rm, so itwillno t  fo llow in the  sam e path. O rbitsa re notp erfectl y clos edorrepe a ta bl e b ec a use of  th i s.
It's aha rd  task  tog e t outoftheideathat there ar e r eall y  su ch th ingsas f ix ed or bits,it'sajump of intuiti on,but that' s t he  re al ity;t here i sn' t.All you  have i s  agr a v i ty  field with it's l um p y  d eviation s, plu s  d ra g , solarpr ess ure, a nd th e Su n 's  and Moo n's gr a vi ty  (plusmo re), a nd  asop histi c ated  numer ical pro pagat o r that calcula t es step-by-st e ph o wa  bod y m ight move i n th i s co mple x  a nde ver-c hangi ng fi e ld of accelerations .Welcom e tothe edge of s pace!

A:I ' m goingto a d dt o the pre-exis tinganswer, fr o m the pe rspec tive ofclassical m echanics  an d a str ono m y : 
Any two mas s e s th at  you ca n t ake, wi thany  in iti al  conditio ns in po si ti on  a ndveloc i ty, will  p ose  a  so -call e d two- bodyprob le m. Thi s 'prob l em ' is a ,fo r al l t im es, e xact l y s olvable  mathemat ica l  des cr ip tion an d solution of  t he setup y ou 've  beena s king abo ut. 
Now what you propo s e, to i ncr easethemass of t hesatell ite to the  point  wher eitb e comes ' r el eva nt ' would si m p lybe abi nary  system  (of stars, planet s , b lackholes, wh ate ver) . Bo thb od i esth e n o r b it the common b arycenter,  w h ic h is a con s tan tof moti on.
Thi s iss till tr ue for th e special  c asew h enone mass i s much s maller th a n the ot her,but  thenth e b aryce nter h a ppe ns to  coinc id e with  thece nter ofthe more massive body,so itlooks  as  if there  is anorbit aro undthe more m ass ive  body .
I n  real -lif e  t hin g s are  mor e  complica t ed  th a n  j ust a two-b o d y  pr oblem . T h en all  mas ses tug on all th e  others, and b inar y bar yce n ters  ( for example th e b ar y c enter fo rthe Sun-Jup iter sys te m ) mov e as w ell an d are n o t  a consta nt o f m otion any mor e. For ear th ly satell ites  i n geos tation a ry o r b it, perturbation s fro m the o t her  sola rsystemb odie s play a r ole already , and/ or s tatio n-keepi ng  in L2  re qu ires firin g  of thrus tersfrom ti me  totim e.

 point.

There_is no_spoon tipping point: YouTube
Your_question really_just_asks about_how_long an approximation_or simplification is_valid, and that's purely_up to you_and_how much error you can tolerate by using your approximation. 

Also:
While you would like_to_imagine that_there_can_be two satellites in the_same orbit but one behind_the other,_the problem is that the Earth's gravitational field_is_not uniform, so_it will not follow in the same path. Orbits_are not perfectly closed or repeatable_because of this._
It's_a_hard task to get_out of the idea that there_are really such things as fixed_orbits, it's a jump of intuition, but_that's the reality; there isn't. All_you have is a gravity_field with_it's lumpy deviations, plus drag,_solar pressure, and_the Sun's_and Moon's gravity_(plus more), and a sophisticated numerical_propagator that calculates_step-by-step how a body might move_in_this complex and_ever-changing_field_of accelerations.
Welcome_to the edge_of_space!

A:

I'm going_to_add to the pre-existing answer, from_the_perspective of classical mechanics and astronomy: _
Any two masses that_you_can take, with any_initial conditions in position and_velocity, will pose a so-called two-body_problem. This_'problem' is_a, for all times, exactly solvable mathematical description and solution of_the setup you've been asking about._
Now what you propose,_to increase_the_mass of the_satellite_to the_point where it becomes'relevant' would simply be_a binary_system (of stars, planets, blackholes, whatever)._Both bodies then orbit_the_common barycenter, which is a constant_of motion.
This is still true for_the special case when one_mass_is_much smaller than the other,_but then the barycenter happens to_coincide with the_center of the more massive body, so_it_looks as if there is an_orbit_around the more massive body.
In real-life_things_are_more complicated than just a_two-body problem. Then all masses tug_on all the others, and binary barycenters (for example_the barycenter for_the Sun-Jupiter system) move as_well_and_are not a constant of motion anymore. For earthly satellites_in geostationary_orbit, perturbations from_the other solar system bodies play a role already, and/or_station-keeping in L2 requires firing of thrusters_from time to time.
