DESIGNS FOR SPACE

[Music] before the 12th century chinese could launch the first rockets in recorded history they had to plan the rocket's shape jules verne's task was easier the designs of his imagination did not have to leave the ground except in the imagination of his readers at nasa's manned spacecraft center in houston the concept and flight mechanics specialists of the advanced spacecraft technology division unlike jules verne must deal with the facts of distant flight not its fiction and unlike the ancient chinese the destination of their concepts is not within the atmosphere but is far beyond into outer space these are the tools which begin such journeys these are some of the actual historical drawings of the apollo man on the moon programs command module the sketches show how a design evolves from an original concept through conceptual stages to the design that will do the job best when used for the actual spacecraft test models of the command module are now undergoing successful tests concept designers have moved on to projects far in advance of journeys to the moon the concepts now on the design boards at the mann spacecraft center concerns such future projects as manned space stations for use as orbiting laboratories and advanced vehicles to carry man to mars and other planets all projects before reaching the hardware stage must first be thoroughly analyzed in all areas of advanced design at the mann spacecraft center this includes design of the mission mode that is the best way to accomplish a particular mission and design of the spacecraft best suited to carrying out the mission before any program of flight into space can develop mission and spacecraft designers must first chart the way through a vast complex of problems is the problem of time by what date must the mission be accomplished what is the cost of one mission mode compared to other modes solar system dynamics must be considered the relative motions of planetary bodies the environment of space is a changing environment will a particular mission mode minimize exposure to hostile elements such as solar flare radiation the size of the crew must be considered how many men are needed to do the jobs which must be done to perform the mission how many days must men survive in space or how many years to complete the mission what supplies of oxygen fuel food and equipment will be needed what is the minimum size of the spacecraft required to carry the necessary crew and supplies do launch vehicles exist with enough power for the mission mode if not can they be developed in time many other factors such as aerodynamics reliability and landing and recovery must also be considered and designed into the space flight system a good understanding of the work of advanced designers of mission mode and spacecraft can be obtained by reviewing conceptual design programs of the recent past therefore let us take the apollo moon program as an example and go back a few years to the early design stages of its mission mode and spacecraft factors such as available time and cost were established 1970 was set as the target date for landing a man on the moon and expenditures must be kept within the nation's ability to invest in scientific progress within these limitations mission designers of the flight mechanics branch of the manned spacecraft center had to recommend the best mode for accomplishing the mission a basic problem was weight the weight of the vehicle to be launched from the earth and the weight of the payload to be landed on the moon the complete liftoff weight would be immense compared to anything yet launched into space by man it would consist first of the three members of the crew required for the mission along with their pressure suits life support equipment and supplies and instruments for navigation communication and lunar exploration second liftoff weight would include a comparatively large spacecraft fully equipped capable of making the round trip and of reentering the earth's atmosphere just one item the heat shield needed to prevent the spacecraft from burning up on re-entry would weigh a great deal third starting with re-entry and working toward the total vehicle to be launched from earth lift-off weight would include the many tons of fuel and fuel tanks needed for five additional phases of the mission launching the spacecraft from the moon and into a return flight path breaking the descent to the moon's surface reducing the flight speed as the spacecraft approaches the moon mid-course maneuvers during flight and acceleration of the space vehicle after launch to the escape speed of twenty five thousand miles per hour required for a lunar trajectory finally total liftoff weight includes the launch vehicle itself and an escape tower one of the several mission modes considered when the apollo program was officially undertaken consisted of a direct flight from the earth to the moon then direct flight back to earth with vehicles as just described the direct flight mode would require a huge launch vehicle larger than any then under development to launch the total weight from the earth such a launch vehicle could not be developed within the time available a second possible mission mode was analyzed in this mode the weight to be launched into space would be divided between two launch vehicles for example one might carry the larger rocket motor required for thrust into lunar trajectory the other might carry the spacecraft and return propulsion engine the two vehicles would be separately launched with each boosting its share of the total weight into orbital flight around the earth the sections would then rendezvous and dock together the assembled space vehicle within thrust out of earth orbit into a flight path taking it to the moon's surface this mode called earth orbit rendezvous would eliminate the need for the single huge launch vehicle required for the direct flight mode but probability studies indicated a much higher risk of mission failure if two launch vehicles had to be relied upon the earth orbit rendezvous mode also added the complexities of large vehicle assembly in space most important there remained the difficulties of having to decelerate land and launch from the moon the same heavy large lunar landing vehicle of the direct flight mode further studies revealed that it was not necessary to land all three men and the entire space vehicle on the moon for example one man in the heavy re-entry module of the spacecraft and supplies and fuel for the return flight could be left in space orbiting the moon this could be done by developing a special lunar excursion module to fly from the orbiting spacecraft to the moon and back this mode is called lunar orbit rendezvous by reducing the weight of the payload to be landed on the moon total mission weight is brought down within the launch capability of a single three-stage launch vehicle already under development at the time of the decision advantages are clarified by a comparison of the vehicles required in each of the three possible modes considered briefly lunar orbit rendezvous will go like this the space vehicle will be placed in earth orbit by the three stages of the launch vehicle here it will be checked out by the astronauts and through telemetry by the mission control center in houston at a precise moment the third stage rocket engine will reignite and thrust the vehicle out of earth orbit into a trajectory that will carry it toward the moon after burnout and during the coast period the adapter carrying the lunar excursion module called the lamb will separate and the service and command modules will be repositioned so that the lamb is nose to nose with the command module which carries the three-man crew the spent third stage rocket engine will then be separated nearing the moon the service module engine will reduce flight speed so that the spacecraft will fly in an orbit around the moon about 100 miles above its surface two of the crew members will transfer from the command module to the lamb which will then be detached by firings of its own rocket descent engine and attitude thrusters the lamb will be maneuvered to a touchdown on the surface of the moon carrying the two men and only those items essential to the landing and exploration when it is time to return lift off from the moon will be accomplished by a small ascent engine leaving the descent engine and the landing structure on the moon the lamb will be thrust back into lunar orbit to rendezvous and dock with the other two modules of the spacecraft the two lunar explorers will then transfer back to the command module rejoining their comrade who remained on board the orbiting spacecraft the lamb will be disengaged and left behind in lunar orbit as the other two modules carrying the crew and return supplies are thrust back toward earth by the engine of the service module shortly before entry into the earth's atmosphere the service module will be jettisoned leaving the command module to return to earth with its passengers the lunar orbit rendezvous mode became the recommended mission mode for the apollo program its probability of success is higher its cost is lower and the saturn v launch vehicle will be available in time in addition to defining a mission profile in terms of launch vehicles and booster capacity mission designers had to consider many possible trajectories they had to consider the dynamics of the solar system particularly the motions of the moon in respect to the earth a launch window had to be selected the launch time and small area through which the spacecraft must be shot to hit the revolving moon on a predetermined date the mission had to be designed so that the returning spacecraft would enter the atmosphere at the proper angle by hitting the correct entry corridor other trajectory considerations involved efforts to avoid long exposure to the trapped electron radiation of the van allen field and consideration of the possibility of solar flare activity during the flight even before flight mechanics specialists had determined the best answers to problems of mission design other concept designers were applying their knowledge and creativity to designs for the spacecraft whichever one of the three mission modes was selected the spacecraft would require a passenger compartment or module adequate for the trip to the vicinity of the moon and back this part of the spacecraft as we have seen is the command module as an example of spacecraft design from earliest drawings to final configuration let us review some of the factors considered by concept designers of the apollo command module the prime consideration for the basic design of a spacecraft which will return to earth is entry into the earth's atmosphere because of its speed the spacecraft in orbit or on a return path from outer space has enormous kinetic energy to slow the spacecraft so that it may be landed atmospheric breaking is used this reduces the kinetic energy of the spacecraft but generates extreme heat means must be devised to dissipate this frictional heat to keep it from destroying the spacecraft in the way that most meteors are vaporized before reaching the earth research has shown that a blunt shape sets up a shock wave in front of the entering body the shock wave extends to a considerable distance away from the body in wind tunnel tests the actual wave can be photographed the heat which is produced in most of the shock wave passes harmlessly past the spacecraft at a safe distance the blunt shape also causes a very rapid slowing of the spacecraft which minimizes the time during which the craft is exposed to great heating a blunt ballistic shape was therefore chosen for the apollo command module as in the design of the mercury spacecraft although the shock wave caused by the blunt shape carries away most of the heat temperature on the vehicle entering from lunar flight will still rise as high as 5000 degrees fahrenheit designs had to provide for materials capable of withstanding or converting this heat an effective solution to the problem is the design of heat shields containing ablative materials such materials dissipate much heat by conversion into gases which steam away from the spacecraft into the atmosphere ablative material which is not changed into gas becomes char the char forms an effective layer of insulation an ablative heat shield thus leaves the basic structural material of the spacecraft intact cabin temperatures remain low enough for human survival in addition to problems of atmosphere entry hostile elements in the space environment also required consideration by the spacecraft designers to ensure protection against deadly radiation from the van allen belts and from solar flares they had to consider the shielding afforded the crew by the spacecraft and its equipment problems arose in devising protection for the space mission against meteoroids physiological needs were also considered for example for a human being to withstand the crushing g-forces of launch and re-entry research and mercury program experience had shown that astronaut restraint couches should be located so that an astronaut's back is toward the heat shield in this position adjacent couches were provided for the crew in other phases of flight the center couch should be stored to permit more freedom of movement after human factors had been integrated in the design for the command module there was the problem of equipment and supplies equipment crew accommodations and supplies also had to be integrated into the spacecraft by the time the conceptual designers consider their job complete all factors have been incorporated in the spacecraft design designs of course are modified as nasa and contractors gain new knowledge from continuing research and tests such as this parachute drop test of a boilerplate test model of the command module designs for the command module were combined with those for the other spacecraft modules the service module and the lunar excursion module enclosed in an adapter section designs for the spacecraft were then integrated with designs for other sections of the space vehicle the adapter section which houses the lam until the translunar flight is underway the escape tower the third stage propulsion vehicle and the second and first stages of the launch vehicle from the start of the apollo program spacecraft designers worked in close cooperation with concept designers for other elements of the complete apollo lunar vehicle as these same designers now move on to space stations space ferry vehicles and spacecraft for journeys to other planets their concepts will be developed in the same logical order demonstrated in the mercury gemini and apollo programs [Music] mission and spacecraft designers will continue to block out the steps for the rest of us to take toward greater knowledge of our all-encompassing environment of outer space you