ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
αLOCKING LI NKAGE TL OUTBOARD BRACKETBC A P T TSLOCKING LINKAGE TL OUTBOA RD BRACKETCB A α P TTS 

Figure 3a. S chematic configura tion o f brac ket           Figure 3b. Schematic configur ation of bra cket                           & Locking li nkage- East reflector                                  & Locking linkage-West reflector  

Results of the  analysi s for both the refle ctors  In the case of the Ea st reflector a s the ap plied  torque i n the reverse  direction increases t he p oint of  conta ct at ‘A’ shifts toward s ‘B’. The plot of torque vs. angul ar move ment of the out-boa rd bracket is give n  in Figu re 4. It is seen th at as th e point of co ntact shifts towa rds ‘B’ the a ssembly tend s to become selflocking a nd the lockin g linkage does not get lifted up fo r any mag nitude of the external torque.  In the case   of the We st reflector th e point of conta ct at ‘A’ shifts  towards ‘B’ wi th increa se in  applied to rque. Once th e  point of conta ct is at ‘B’ the  mecha nism become s unstable and the  lockin g linka ge has a ten dency to get  lifted even fo r lower valu es of appli ed torque  as shown in Figure 4. If the  application of the torque  is  contin ued, th e locking lin kage gets lifted an d rides over the sector allowing for rotation  of th e refle ctor in  the stowi ng di rectio n. 

-1001020304050607080 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 theta (de grees)Torque ( N-m)WESTEAST  

Figure 4.  Estimated torque vs. Angular mo vement of Ou tboa rd bracke t for reverse moment 

Similar plots f or a di sturbi ng torqu e in the forward di rection fo r both the refle ctors is as shown in Figure 5.  As the to rque incre ases t he me chanism be come s self-lo cking and do es not allow fo r further rotation  of  the reflec tor.   90
01020304050607080 0 0.005 0.01 0.015 theta (degrees)Torque ( N-m)EASTWEST 

Figure 5.  Estimated torque vs. Angular mo vement of Ou t-board bracke t for forward moment 

From the a bove analysi s it is se en that:  • For the E ast reflecto r, the locking li nkag e and out-bo ard bracket g eometry i s such that the  assembly  once locke d become s self-lockin g for to rques in both the forwa rd and reve rse direction.  • For the  West reflecto r, the l ocking li nkag e and  out-b oard bracket g eometry i s such that th e assembly   once locke d become s self-lockin g for t orque in the forwa rd direction, whe reas for a reverse torqu e  excee ding 10 Nm the l ocking lin k gets lifted up  and allo ws th e outb oard b racket to  rotate in the   reverse di rection.  

Tests condu cted on Ea st and Wes t reflector mech anism 

Tests were condu cted in d ifferent pha ses for the follo wing:    - Single hing e cha racterization to verify the analysi s.  - System level tests on spacecraft to characteri ze the l atching phenom enon and capability to  ensure the specified p ointing accura cy under exte rnal disturban ces.  -   Single hing e cha racteristics   The a bove a nalysi s was v erified experi mentally at suba ssembly l evel by apply ing a reverse  torqu e on a  hinge assem bly. A single hinge assem bly of East a nd West reflector was characterized for To rque vs.   angul ar mov ement of Ou tboard b racket. The test se tup i s as shown in th e Figure 6a.  A gradually  increa sing load (P ) was applied at on e end of the out-bo ard bracket a nd th e corre sponding rotational  movement of  the bra cket was compute d from the di al indicator reading s as shown in th e test setu p. The  rotational  movement of the  Outboa rd bracket vs. a pplied torque i n the reverse direction i s shown in Figu re  6b.   91
Figure 6a.  Test se t-up fo r hinge asse mbly .        Figure 6b.  Charac teris tics for rev erse torque    D3 240 m m OUTBOARD BRA CKET INBOARD BRACKET120 mm D2 D1 P ANGLE (DEG)TORQU E (N-m) EAST WEST16 14 12 10 8 6 4 2 0 00.050.10.15 0.20.250.30.35 0.4 0.450.5

It is seen f rom the above measured ch aracteristics f or a single hinge a ssembl y that the locking lin kage  starts riding over the  out-b oard bracket for an applie d reverse to rque of 6 Nm which works out to 12 Nm  for the reflect or assembly. The comp uted numb er of 10 Nm (Ref F igure. 4 ) with the incl usion of mea sured  friction to rque of 2 Nm a lso works o ut to 12 Nm thus vali datin g the a nalysi s. The difference in th e  measured an d com puted angle s can b e attributed t o the presence of cle arances at the sp herical be aring  joint and du e to measu rement limitations as the co rrespondi ng num bers involved  are very sm all.     

Tests on East  and We st ref lectors   Tests on th e refle ctor a ssembly  under Ze ro ‘g’ were cond ucted in order  to study the latchin g  characteristics for both the r eflectors. The Reflector assembly was  supported on a surface plate through  an ai r-bea ring pad as shown in Figure 7a. A cceleromete rs mo unted on th e refle ctors provided th e  respon se of the sy stem. T he reflecto r was stowed back by 3 d egree (approx.) with res pect to the latc hed  positio n and allowed to latch. The re sponse plots for the East and west refle ctors are shown in Figure 7 b  and 7 c. The plots show that the West reflector ha s rebound ed th ree times before the final lat ch (as can be  seen from the rigi d body mode s), whereas the Ea st reflector shows pure vibratory mo de, which indicates  proper lat ching, and no di sturb ance to the locking li nkage assembly due to the reverse shock. This te st  also d emonstrates th e pre sence of po sitive torque m argins at an gles very cl ose to the final position. Thi s  is all  the more im porta nt for the  West  refle ctor a s a po sitive lat ch-up demonstrate s the presen ce of  potential ene rgy in the spri ng system to  initiate moti on as the mo mentum in th e system red uces to ze ro  each time the motion initiates in the forward di rection.        92
REFLECTOR   AIR BE ARING  PAD  SURF ACE  TABLE 

Figure 7a. T est se t-up fo r reflec tor de ployment under zer o’g’ 

Figure 7b. Response plot for East reflector                      Figure 7c. Resp onse plot for West refle ctor      Another te st conducted was to m easure the respon se of the refle ctor in the lat ched position  for di sturbing   torque s that is experi enced by the reflector du ring the thruste r firing ope ration s for the purpo se of statio n  keeping of th e S/C. This test on the West refle ctor was required  in orde r to verify at syste m level the  torque required for unlat ching of the reflector. Th e root moment at the hinge axi s due to thruster firing wa s  comp uted to be 0.35 Nm. An actual mo ment of 4 Nm wa s applie d and rel eased su ddenly on the We st  reflecto r in th e depl oyed condition under zero’ g’. The  response of the West reflector is as shown Figure 8.   93
It is seen th at the mech anism a ssembl y is stable without any rigi d body motio ns thu s demonstrating a  margi n of > 1 0 with re spect to the adequ acy of locking  mecha nism for 4 Nm di sturbing to rque. 

 0-0.08 500100015002000 2500300035004000-0.10-0.06-0.04-0.02 0.00 0.02 0.04 0.06 0.08 0.10 TIME (msec)LINE AR (g ) Figure 8.  Re spons e plot for West r eflector. 

Design modi fication in West re flector brack et to c orrect the a nomaly . 

A modificatio n in the geometry of th e slot a s shown in  Figu re 9a with  all other detail s remaining  identical  was analy zed for the b ehavior of the l ocking lin kage for reverse  and forwa rd torque. T he mech anism  characteristic is ide ntical t o the ea rlier config uration for a forwa rd torque while for a reverse torqu e the  mech anism become s self-locking a s in the case of East refle ctor. The pl ot of torque  vs. angular  movement of the out-bo ard bracket for b oth forw ard and reve rse torque i s given in the Figure 9b. 

 LOCKING LINKAGEEXISTING MODI FIED TL 10.5° 0.03 0.01 0204060 THETA (DEG)  0.02 80 REVERSE   FORWARDTORQUE (N-m)  0 0.04

Figure 9a. M odified con figuration o f bracke t       Figure 9b. Plot of torq ue vs.angula r movement      & Locking linkage- West reflector                           of the Out-board bracket 

From the above analysi s it is cl ear th at a mino r modification in the  slot geo metry of the outboard bracke t  with all oth er element s rem aining i denti cal as before will elimin ate the reboun d anomaly see n in the We st  reflecto r mechani sm.   94
Design r equirements for satis factory perform ance  

All the an alysis a nd te sts concl uded that the West reflector me chanism d esign limitations have resulte d in  the reb ound a cou ple of times o n depl oyment. Ho weve r, on ce th e final latch up occu rs the mechani sm  was stabl e for all on-o rbit loads. A modified desig n for the We st reflector was worke d out in whi ch the   above limitati ons were ov ercome. However, b efore impleme ntation of th e same minim um requireme nts  for the satisfa ctory pe rform ance of the d eployment m echanism for the We st reflector were cri tically looked  into and worked out as foll ows:   • Positive latch -up in spite  of rebound s to be en sured. i.e. as the reflector move s backward s and  forwa rd after each latch, it is to be ensured that sufficient torq ue margi n exists even just before   the final latch . This is extremely impo rtant as only the potential energy in itiates the motio n since  the kineti c energy at the st art of motion is ab sent.   • The configu ration of the l atched reflect or has to be stable even unde r the on-orbit distu rbances  caused during the S/C m aneuve rs. The maximum t orque that th e refle ctor experie nces during  thruste r firings are to be analy zed and a dequate margin demonst rated t o ensure th at the   deploye d reflector i s stable.  The extensiv e analysi s and tests have conclusively demon strated  that:   • Positive latch -up ha s been ensu red by design, as a torque m argin of >2 exist s which has been   demon strated  by tests also.    ♦ Positive margin >10 exi sts with respect to 0. 35 Nm (max) torque that will be experienced by the  antenn a duri ng thrust er firin gs and the sa me wa s dem onstrated by tests.  As all  the above re quirements were met, the de sign was cl eared in th e present form, i.e.,  witho ut any  modificatio ns with a full understandi ng of the r ebound  phenom enon, which would happe n on-orbit duri ng  latching. 

On-or bit per formance 

INSAT-2E was l aunched on April  2, 199 9 and both the reflectors were  deploye d successfully. A s  predi cted fo r West refle ctor, sub sequent to the fi rst lo cking, re bounds as seen o n ground were observe d  on-orbit also.  The dwelled  plots of the pitch rate of the S/C i n Figure 10 indicate three  rebo unds before  the final latch -up. Th e micro-switch status in dication as seen in Fi gure 10 also has to ggled from ‘lo cked ’  to ‘unlocke d’ showing th ree re bounds as expe cted. The station  keepi ng ma neuvers which have be en  carrie d out til l date do es not indi cate any distu rbances to the deploye d reflector, which validates th e  analysi s and tests. 

 2 0 4 6 8 10 12 14 16 18 20 22 24 26 28 300.0 -0.50.51.01.5 TIME ( SEC)WEST ANTENNA HING E      MICR OSWITCH TIME  FROM : 11-APR-1999. 07:49:00 TO 11-A PR-1999 07:49:30PROC PITCH RATE (DEG/S) TIME ( SEC) TIME  FROM : 11-APR-1999. 07:49:00 TO 11-A PR-1999 07:49:3004 8 12 16 20 28 24-0.4-0.2 0.0 0.2 0.4 

Figure 10.  Micro-s witch status and Pitch rate o f S/C during  West refle ctor deplo yment.  95
Lesso ns lear ned 

A couple of le sson s learne d from the ab ove experie nce can be summari zed a s follows:   1. Design chan ges, which may loo k minor, shoul d not be igno red and must be  thoroug hly looked i nto  before im plementing. The  desig ns were verified for the dynamic l oads assumi ng the asse mbly to be   equivalent to a stru cture after latch -up. As the de grees of fre edom we re con straine d during the abov e  study the anomaly was missed during the a nalysi s. Hencefort h, the de signs are to be verified for  adeq uacy of withsta nding the dynamic load a s a mechanism al so. The geome try of the mecha nism  after locking i s to be su ch that in either d irectio n the m echanism mu st become self-locking.   2. Any new de sign, even with mino r geometri cal chang es should be tested  for integrat ed mode  encompa ssing all possibl e loads. Thi s provide s sufficient lea d-time for und erstandin g and correctin g  non-nomi nal behavio rs if any. Otherwi se surprises if any will be revealed only at later stage wh erein  even mino r modificatio ns may be difficult to be implem ented.   

Conclu sion     Analytical stu dies and in strume nted te sts we re carried out in vie w of the a nomaly notice d in the West  reflecto r. The analytical re sults match well with the tests ca rried out and cle arly explain the phen omen on  notice d during the de ployment test s. The Ea st reflector was also a nalyzed  and results explain the   observed behavior. A mo dification in t he geo metry of the outboa rd bracket of  West refle ctor ha s been  worke d out to overcome t he above anomaly. Ho wever, as it wa s evident tha t the existing  desig n was  adeq uate to meet the on-orbit requi rements i n spite of the non-nomi nal beh avior the same was flo wn  without any correctio ns. Th e on-o rbit ob servation s match well with the gro und te sts and p redictions.       Ackn owledgements 

Than ks are due to Sri. A.Shanka ra, Sri H.N.Suresha kumar and Sri S.Nare ndra fo r their particip ation  durin g the course of the  above work. Authors al so than k Sri.V.Sridharamu rthy DPD (Mechanisms)- INSAT-2E for his g uidance. Authors wish to tha nk Sri. M.Nage swara Rao, Group Di rector-Spa cecraft  Mech anisms Grou p for his critical eval uation an d constant guid ance during the course of the above work.  The a uthors also than k Sri.A.Bhaskaranarayana, Project Director, INSAT-2 E, Shri.V.R.Katti, Geosat   Programme  Director, Sri. H. Narayana mu rthy, Deputy D irector, Mec hanical Sys tems Area and  Dr.P.S.Goel , Dire ctor, ISAC for their continuou s revi ew du ring the  above wo rk and supp ort. 

Referen ces 

1. Spacecraf t Mech anism Gro up, ISAC, “INSAT -2E Mechani sm Detail ed De sign Revi ew Do cument“  Septembe r 1997.  2. Spacecraft  Mechani sm Grou p, ISAC, “A note  on analysi s and tests carried out for lat ch-up anomaly of  West refle ctor deploym ent- INSAT-2E”, Novemb er 1998.  3. Spacecraft  Mechani sm Grou p, ISAC, “INSAT- 2E On o rbit performa nce of d eployment m echanisms”,   July 199 9. 

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The sp ecific desi gn re quirements fo r the laun ch latch are a s follo ws.  Stiffness:  ~5 0% increa se in gimbal natu ral freq uency over unlo cked config uratio n.  Interface Parallelism:  ±.04 6° between mounting I/F plate and paylo ad I/F plate  Life:  1 on-orbit unlatch + 50 latch/u nlatch cycles during pre -flight testing  Relia bility:  Si ngle fault tole rant ele ctrical operatio n  Status Indicat ion:  Position sen sing must  provi de feed back for lat ched/un-l atched mecha nism status.  Environme nt:  1200g sho ck, 30g si ne vibration, 26 grms ra ndom vi bration  Operation s:  Mech anism must be re-se ttable with a quantifiably controlle d preload 

Figure 1.  Gimbal Sho wing Launc h Latch Assembly

Launch L atch Design 

The Anten na Pointing Me chani sm (APM ) two -axis gi mbal is a tilt-table gim bal o perable in two deg rees of  freedo m. It consi sts of an o utput platform  mounted on a cente r pivot, tilted in two axes by ortho gonal line ar  actuato rs articulate d between the o utput platform and a simil arly shape d ba se plate th at mounts th e  assembly to t he spa cecraft. The center pivot is a two degree -of-freedom asse mbly of elasti c flex pivots  config ured as a Cardan  joint. Angula r range  of the  elastic flex pi vots is suffici ent to support the gimb al  motion. The  gimbal i s designed to  mini mize required envelope, which results in a derived requireme nt for  compac t design of the latch mec hanism to fit in t he available sp ace betwe en the cente r pivot assem bly  and th e two l inear a ctuato rs. The requirement for pre-launch access to reset the me chanism re sults in  challengin g ergonomic and for packagi ng the con straints. 

The lau nch la tch me chanism is de signed to rigidi ze and strength en the cente r pivot of the tilt table gim bal.  Its function i s to tie the gimbal o utput platform directly to fixed stru cture th rough fou r spring beam  membe rs arrayed in a circula r pattern  surrou nding  the center pivot. The stiffness of the  launch lat ch  membe rs protects the cen ter pivot, and the combin ation of the center pivot su spension and  the launch   latch is suffici ently stiff to p revent dam aging load s from being tra nsferre d to the linear a ctuato rs. 

The o peratio nal range  of the gim bal is from 3  to 5 d eg of tilt on ea ch axi s. The refore, di splacement of th e  gimbal outpu t plate i s relatively small near the pivot. The la unch latch  mechanism i s located n ear th e  pivot, so that the motion of the rest rainin g membe rs upon rel ease can be small, while a ccommodating the   operational e nvelope of th e gimbal outp ut plate.  

The potential for ove rstressing of th e elastic suspension me mbers of the cente r pivot exists. Avoiding thi s  potential p roblem is a key issue a ddressed in th e design of the l aunch lat ch. Fo ur pins on th e undersid e of  the gimb al top platform a re engaged by spring beam memb ers when the launch latch i s enga ged. T he  98
spring be am membe rs move radially ou tward to e ngage the pin s, generating a  symmetri cal set of radi al  force s that h ave no net resulta nt force  on the cente r pivot asse mbly. Rotation of the ring prod uces two   orthog onal sets of equal op posing force s, and no net lateral rea ction on the ce nter pivot. 

Engage ment of the rotatin g ring me mber with the pi ns an d beam s is a ma nual function. Ro tation of the  ring m oves it s roll ers into conta ct with t he ra mp fa ces of the spri ng beam s, mo ving the bea ms out ward by  cam actio n. The o uter fa ces of the  spring  beams conta ct the l ocking pins, and the  sprin g bea ms are  captu red and com pressed betwe en the rollers and th e lockin g pin s. Wh en all  parts are fully enga ged, th e  ring i s secu red by a latch mechani sm, which holds it in position. The gimbal  then stays i n the l atched  config uratio n until the ring is relea sed by an Un latch comman d. The Unlatch comma nd extends the  plung er of a h ot wax actuat or, rele asing the ring lat ch and freei ng th e gimbal. 

Base  HED Spring BeamRoller  Lockin g Ring  Lockin g PinOuter Gim bal Ring 

Figure 2.  Exploded Vie w of Gimbal an d Launch L atch 

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Latched Pos ition 

The ring, t he memb er de signed  for ma nual rotation  to the lat ched position, i s equi pped with four roller  assembli es. Each roller assembly is positione d to en gage an adjacent spring m ember and locking pi n. As  the ring  is m anually rotate d, the rolle r assembli es simultaneo usly conta ct the spring beams and d eflect  them outwa rd toward the locking pin s. Once co ntact is made bet ween the sp ring beam a nd the locking   pin, an integral spri ng esta blishes the desired preloa d in the joint. The ri ng conti nues to rotate until its arm   enga ges a lo cking pa wl, which lat ches it in the launch  latched p osition. 

Spring Beam  Roller Lockin g  Pawl  Ring Lockin g Ring  Arm  Wax Actuato r Lockin g Pin  Figure 3 100
Preload Latc hing Point 

The d eflectio n of the p reload spri ng fea ture is limited  to preve nt oscillation of t he spri ng under vib ration.   The p reload spring botto ms o n a stop, with its fu rther defle ction du e to hi gher loa ds (highe r tha n the  prelo ad) prev ented. The stop is form ed by an adju stable set screw in one arm of the spri ng me mber. 

The lat ched positio n and the preloa ds on the  lockin g pins are establish ed when the  arm o n the rotating   ring engages the lo cking  pawl. T he lo cking p awl rotat es on a fixed  pivot. Its en gageme nt with  the a rm on  the locking ring is so confi gured that the line of actio n of the cont act force pa sses through t he pa wl pivot,  and no component of that force te nds to unlatch th e pawl. The m echani sm is self-lockin g until relea sed by  the Unlat ch comman d.    

Latched Position Ring Lockin g Pin RollerSpring Beam Unlatche d Setscrew Roller Spring Beam Lockin g Pin  Figure 4Pin  Engagement 101
Unlatched P osition 

Unlat ching occurs when t he hot wax motor o utput is extend ed on comma nd. The force e xerted on th e  pawl by the actuato r rotat es the p awl out of the latche d po sition . The torqu e exerted is adequ ate to  overcome the  conta ct friction between the pawl a nd the locking ri ng arm an d relea ses the pawl from th e  ring. T he to rque comp onent of the roller-to-sp ring beam preloa d force s causes the ring to  rotate out of the   latche d position, and the ri ng then rotat es back to its origin al unlat ched position . 

The laun ch la tch assem bly is acce ssible from one si de of the gimbal (Fig.1). The arm on the lo cking rin g is  oriente d for access f rom th e side, a nd is configured with a thread ed recepta cle. Resetting i s accompli shed  by installing a  resetting tool  in the rece ptacle  and rotat ing the ring to  the latched p osition. 

RingLockin g Pin Roller Spring Beam  Spring Beam Roller Lockin g Pawl   Ring Lockin g Ring Arm Wax Actuato r Lockin g Pin  Figure 5  102
Trigger Mec hanism 

The trig ger mechanism consists of th e wax a ctuato r, the lo cking pawl, an d the l atch a rm (integral  with th e  rotating ring). A manual in put force is exerted on th e latch to rotate the rin g, allowin g the lo cking p awl to   enga ge the l atch an d prevent rotation of the rin g. The locking arm pawl engagement is m aintained by the   prelo ad appli ed at  the contact p oint betwee n the  locking  pawl and th e ring. This preload is du e to th e  lateral  components of th e forces at th e spring  beam-to-roller conta cts, and the resultin g torque on the ring.  A torsion al spring is u sed to return the p awl to its la tched po sition, regardless of the orientatio n of the ring.  Release of the latch is initiated by applying power to  the wax actu ator. The act uator outp ut rod extends,   conta cting th e locking pa wl as sho wn in the figure below, and in ducing a torq ue on the locking pa wl to  relea se it fro m the latch arm. With the locking pa wl rotated a way from the latch arm, the ri ng is free to  rotate and relieve the prelo ad on the lo cking pi ns. 

Latched Pos ition 

Unlatched P osition  Figure 6Lockin g PawlLockin g Ring Arm Wax Actuato rLockin g PawlLockin g Ring  Arm  Wax Actuato r

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Develo pment  and Te sting 

Develo pment  test ha rdware wa s constructed to prove out the la unch latch design. The te st hardware was  designed to simulate th e main gim bal pivot and the  laun ch lat ch mech anism. On on e gim bal axis, a  previou sly built linear a ctuator was used to simulate  the ma ss and CG lo catio n of the  flight  actu ator, fo r  accurate syst em dynamic simulation and also for the capability of tilt ing the platform on that axis in   subsequent testing. An  articulate d dummy link, a gain simulating t he ma ss an d CG l ocation  of the flight  actuato r, was use d in the orthogo nal lo cation of t he seco nd actuator. The l aunch lock m echanism m oving  parts were free of any we t lubricant, to prevent contamination of the payload, and sliding surfaces we re  coate d with T iolube  1175 dry lub ricant. Dicronite  dry lubricant was used i n the rollers fo r the launch latch  to red uce sli ding fri ction in  the me chanism during engagem ent. T he paylo ad mass a nd center of g ravity  locatio n were simulate d by tooling as shown in th e figure to pro vide a valid config uratio n for dynami c  testing (i.e., shock, ran dom vibration, an d sine vibration). 

Dummy Y-axi s  actuato r used  for  ETU tes ting Linea r Actuat or Sub-reflecto r  dummy mass 

Figure 7  Figure 8.  De velopmental Test Unit (S ubrefle ctor plate is remov ed for clarity )     

104