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Th4...E.Z.2422543Z MAY 63 CITE 1022 

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SAF-SS 

SAF-SS9 

DORIAN 

FOR R. J. FORD FROM L. S. NORMAN 

SUBJECT: MOL ORBIT ALTITUDES 

1. FOLLOWING INFORMATION IS FURNISHED REGARDING- YOUR QUERY ON MOL 

ORBIT FLEXIBILITY, PARTICULARLY OPERATIONS AT LOW PERIGEE ALTITUDES. 

ALSO, WE ASSUME THAT YOU ARE COMPLETELY FAMILIAR WITH THE OPERATIONAL LIMITS EXPRESSED IN FIGURE 3-1 OF THE SEPTEMBER 1966 SP/OR 

(VOL). REFERENCE SHOULD ALSO BE MADE TO W. SAMRSON'S BRIEFING 0 16 

NOV 1967 OH FILE IN YOUR OFFICE COVERING BASELINE AND NOMINAL ORBIT 

SELECTION, RANGE OF ORBIT CHANCES AT 1-8 DAYS, AND ORBIT SUSTENANCE 

CONCEPTS. 

2. OPERATIONS AT LOW PERIGEE, BUT WITHIN SP/OR LIMITS, FOR MANNED 

AND UNMANNED FLI GHTS, ARE CONSTRAINED ONLY BY THE MOUNT OF VELOCITY 

FOR ORBIT SUSTENANCE WHICH IS AVAILABLE USING THE ATTITUDE CONTROL 

AND TRANSLATION SYSTEM. PRESENT PROPELLANT BUDGET PROVIDES A TOTAL 

INCREMENT OF VELOCITY INCREASE OF 420 FPS WHICH PERMITS MAINTENANCE 

OF THE BASELINE 80-187 ORBIT AND A NUMBER OF OTHER ORBITS OF INTEREST 

WITH A MOOERATE AMOUNT OF PERIGEE DRIFT. A CONSTRAINT IS THAT OF THE 

PAGE 2 

NEED FOR TRAMINS THE VEHICLE AND UPDATING THE EPHEMERIS AFTER AN 

ORBIT ADJUST IS MADE SO THAT THERM:IUD IN-,TRACK NAVIGATIONAL 

ACCURACY C BE ACHIEVED. OPERATIONS PLANS ALLOW FOR THREE TRACKING 

STATION CETTACTS !N ORBIT ADJUST AND PAYLOAD OPERATIONS. 

THIS INTER': CAN BE REDUCED SY USE OF THE CREW TO REFINE POINTING 

ACCURACIES RHR,OuGH USE OF THE ATM, AND BY TELEMETRY, HOKZVER, THE 

PREFERRED C6NCEPT IS TO ADJUST THE ORBIT !0 MORE THAN ONCE PER DAY, 

AT SUOCYCLE 12 OR 13. THE CURRENT FLIGHT Y1CLE TIME LINZ IS BASED 

oN AN ORBIT ADJUST EVERY 3 DAYS, FOI CO PURPOSES 71. :AYE RUN 

A PROFILE OF ORBIT SUSTENANCE PER '.AY VE'i PERIGEE ALTITUDE AS 

FOLLOWS: BONU - 15 FPS/DAY, 75E - 19.2 FiEIDAY, 70NM 27.4 FPS/DAY, 

65NU . 46.5 FPS/DAY, 60 NM 113.8 FPS/DAY. THIS PROFILE ASSUMES A 

2..BURN ORBIT ADJUST TO RESTORE THE ORIGINAL ORBIT, INCLUDING PERIGEE 

LOCATION, ON A SELECTED REV EACH DAY. IT IS ALSO BASED UPON CALCU0 

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C. 

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J4R0 APPROVED FOR 

REEASE 1 JULY 2015 

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LATED DRAG. CHARACTERISTICS ANDA PARTICULAR ATMOSPHERE/SOLAR 

ACTIVITY MODEL, THUS ARE TYPICAL RATHER THAN ABSOLUTE VALUES. IN DEVELOPING THESE FIGURES WE ASSUMED THAT AVERAGE Q WOULD BE HELD AT 

16-2/15 FOR TARGET COVERAGE PURPOSES HENCE THE INITIAL APOGEE WAS INCREASED FOR EACH CASE AS PERIGEE DECREASED. IT SHOULD BE NOTED THAT 

PERIGEE ALTITUDES BELOW TOW ARE OUTSIDE OF SP/OR LIMITS. 

PAGE 3 - 

3. FOR PLANNING PURPOSES ONE CAN USE THE RELATIONSHIP THAT AN ORBIT 

ADJUST OF ONE FPS AT APOGEE CHANGES PERIGEE ALTITUDE BY 0456 MILES 

AND VICE VERSA, THUS, IF THE OPERATIONAL SITUATION PERMITS RELAXATION 

OF THE ORBIT NAVIGATION REQUIREMENT, IT IS QUITE FEASIBLE TO REDUCE 

THE PERIGEE ALTITUDE FOR A FE w ORBITS ANO THEN RESTORE IT TO THE 

NORMAL ALTITUDE. FOR SOME CASES THIS METHOD SAVES FUEL. 

4. THE SP/DR LIMIT ON MAXIMUM ALTITUDE OF APOGEE IS BASED ON THE 

ABILITY OF THE GEMINI 8 TO REENTER FROM ANY PLACE ON THE ORBIT. IF 

REENTRY IN DAYLIGHT ONLY RATHER THAN AT ANY TIME IS ASSUMED, THEN 

REENTRY WILL BE INITIATED NEAR PERIGEE, UNDER CONDITIONS ACCEPTABLE 

TO THE GEMINI 8, FOR ALL PLANNED OR CONTINGENCY CASES. PRELIMINARY 

STUDIES INDICATE THAT, IN SUCH A CASE,. THE APOGEE LIMIT CAN 

RAISED TO MO MILES OR EVEN HIGHER* 

5. AS FAR AS PERIGEE ALTITUDES (LOW THE'SP/DR LIMIT OF rnmAs CONCERNED, CURRENT DATA INDICATES THAT CONTINUED OPERATION SIGNIFIf 

CANTLY BELOW SUCH LIMITS IN THE ORBITAL CONFIGURATION IS NOT ACHIEVABLE WITHOUT minim DEGRADATION. FOR SONE CASES MISSION TERMINATION 

IS REQUIRED AND FOR OTHERS THERE IS:LOSS OF RECOVERY CAPABILITY, 

IN ORDER TO DETERMINE THE ACTUAL OPERATIONAL CAPABILITIES OF THE 

SYSTEM, STUDIES OF SPECIFIC SITUATIONS AND RECOVERY STRATEGIES OF 

PAGE 4 100I-E--C-R-4E-4--. 

INTEREST SHOULD BE RERFORMED TO DEVELOP THE CONSTRAINTS IN DETAIL. 

EXAMRLES OF THE TYEES CF QUESTIONS WHICH WE SHOULD EXPLORE ARE: 

(A) How MANY LOV MS WOULD BE FLOWN? (8) IS PAYLOAD OPERATION REQUIRED DURING OR AFIER SUCH LOW' ORBITS? (C) IS MISSION TERMINATION 

DURING THE MISSION REV OR AT THE NEXT OPPORTUNITY AN ACCEPTABLE ASSUWTION? (D) CAN THE PERIGEE BE RAISED FOR SEVERAL REVS BEFORE DEORBIT TO ALLOW EQUIPMENT CoOLDowN? 

6. AERODYNAMIC HEATING DATA CURRENTLY AVAILABLE ISSED ON MC DONNELL STUDIES OF GEMINI IN A MINNUM LIFETIME (11 REV) ORBIT, THIS• 

INITIAL ORBIT WAS 80 BY 85 NM, AND THE 11TH REV PENETRATED 400,030 

t J.; 

g. .e 1; 
RBLE 1 JULY 2015 

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FT. IN THIS CASE, THE HEATING WAS SUFFICIENT AFTER 11 REVS To PERvANENTLY DAMAGE THE GEMINI DROGUE AND PILOT CHUTES AND RAISE CABIN AIR 

AND WEROUS PYROS TO TEMPERATURE LIMITS WHICH MACE INITIATING A 

REENTRY UNSAFE. AFTER COOL DOM, HOWEVER, REENTRY COULD SE ACD0vPUSHED BUT LESS RELIABLY—DUE TO LOSS OF OROGUE AND PILOT CHUTES. 

THE VEHICLE IS FULLY CONTROLLABLE IN ATTITUDE FLYING EITHER GEMINI 

FoRwARD OR GEMINI AFT AT LO1 APOGEES. HOWEVER, THE GEMINI AFT CONFIGURATION IS AERODYNAMICALLY UNSTABLE MO IOULD PROBABLY REQUIRE MORE 

FREQUENT ATTITUDE CORRECTION THAN THE ORE STABLE GEMINI FORWARD CONDI/10N, IF ATTITUDE CORRECTION WERE NECESSARY DURING A PHOTO SEQUENCE, 

PAGE 5 PrS7~..""rirLr" 

ST.T PHOTO DECRADATIO.1 MIGHT ()am. MTH EITHER THE GEMINI AFT OR 

GEMINI FCTWRO, TEE LABORATORY HADIATGR LLD SUFFER AERODYNAMIC 

HEATiNG, ?JD EELON 73 MILES LOSS OF LA00:ZATORY THERMAL CONTROL IS 

LIKELY. VITH GEMINI AFT, THE GEMINI HEATING PROBLEM 19CULD NOT BE 

PRESENT, BUT THE END CAP OVER THE PRIMARY MIRROR WOULD EXPERIENCE 

A CONSIDERAILE TEEPERATURE RISE, THE EFFECTS OF THtS CONDITION HAVE 

NOT SEEN ANALYZED. 

7. THE FOLLOBING IS AN EXAMPLE OF AN OPERATIONS SEQUENCE WHICH COULD 

BE CONSIDERED. AN INITIAL ORBIT WITH AN BO MILE PERIGEE AND APOGEE 

IN THE 170 TO 275 NILE RANGE IS ESTPLISHEC. PERIGEE IS LO ERED ON 

COMMANDTO AN AGREED-UPON MINIMUM:VALUE FOR 2 REVS, FLYING GEMINI 

FORWARD, THEN IS RAISED BACK TO MUT 80 MILES FOR MORE THAN ONE REV. 

THE CREW TRANSFERS ALL PRODUCTS INTO THE GEV/NI B AND REENTERS AT THE 

NEXT PLANNED RECOVERY AREA. IF THE mu/rum PERIGEE IS BELCV 70 

MILES, AND DEPENDING ON THE ACTUAL PERIGEE ALTITUDE„-IT MIGHT SE NECESSARY TO TRANSFER THE CREW TO THE GEM, CURING THE LOW ORBITS AND 

DEPRESSURIZE THE LABORATORY, DUE TO LA3ORATORY HEATING, IT SHOULD 

BE NOTED THAT, SHOULD PRODUCT BE PRESEVT IN THE GEMINI B DURING THE 

LOO ORBITS DEGRADATION WOULD RESULT CUE TO GEMINI HEATING. 

8, IN CASE OF THE UNMANNED VEHICLE, Tom` E?/CR LIMIT IS 7014 AND THE 

PACE 6 1022 

ACTS FUEL CU GET PERMITS A MISSION OF, OVER 3 DAYS AT THAT ALTITUDE. 

lLE MIT PER BELOW 70NMAPPEAR FEASIBLE, PAYLOAD OPERATIONS .„,., 

CO BE EXPECTED TO BE DEGRADED BY NAVIGATIONAL UNCERTAINTIES, PAR4'... 

TICULV.LY AS RELATED TO THE SMALL FIELD OF VIEW, AND THE LACK OF A 

C''?.n? T.0 REFINE POINTING ACCURACIES. • . 

. 

9, THE NUMBER OF ALTERNATE SEQUENCES IS GREAT, AND EACH HAS AN !VFW 

UPON OPERATION. PLEASE ADVISE IF YOU REQUIRE FURTHER INFORMATION. 

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