certain level Propellant tank pressure dropped below a certain level The intermediate tank bulkhead showed signs of losing structural integrity The booster The Atlas LV-3B, Atlas D Mercury Launch Vehicle or Mercury-Atlas Launch Vehicle, was a human-rated expendable launch system used as part of the United States Project Mercury to send astronauts into low Earth orbit. Manufactured by Convair, it was derived from the SM-65D Atlas missile and was a member of the Atlas family of rockets. With the Atlas having been originally designed as a weapon system, The booster flight path deviated too far from the planned trajectory Engine thrust or hydraulic pressure dropped below a certain level Propellant tank pressure dropped below a certain level The intermediate tank bulkhead showed signs of losing structural integrity The booster electrical system ceased operating The ASIS system ceased operating The ASIS system was deemed necessary because some flight failures of Atlas vehicles (for instance, Atlas 6B) occurred so fast that it would be nearly impossible for the astronaut to react in time to manually activate the LES. Other failure modes such as a deviation from the correct flight trajectory did not necessarily pose an immediate danger to the astronaut's safety, and the flight could be aborted manually. Not all of the modifications listed below were carried on every Mercury flight and numerous changes were made along the way in the interest of improvement or as a result of flight data obtained from failed Atlas launches. Quality control and checkout procedures also improved and became more detailed over the course of the program. Aside from the modifications described below, Convair set aside a separate assembly line dedicated to Mercury-Atlas vehicles which was staffed by personnel who received special orientation and training on the importance of the crewed space program and the need for as high a degree of top-quality workmanship as possible. Components used in the Mercury-Atlas vehicles were given thorough testing to ensure proper manufacturing quality and operating condition. In addition, components and subsystems with excessive operating hours, out-of-specification performance, and questionable inspection records would be rejected. All components approved for the Mercury program were earmarked and stored separately from hardware intended for other Atlas programs and special handling procedures were taken to protect them from damage. The factory inspection of Mercury vehicles was performed by Convair personnel specially chosen for their experience, familiarity with the Atlas hardware, and who had demonstrated a favorable disposition and work ethic. Propulsion systems used for the Mercury vehicles would be limited to standard D-series Atlas models of the Rocketdyne MA-2 engines which had been tested and found to have performance parameters closely matching NASA's specifications. NASA decided that the best choice of engines would be units with roughly medium-tier performance. Engines with higher than average performance were not considered acceptable because it could not be determined exactly why a given set of engines performed the way it did, and so it was considered safest to use medium-performance ones. For the most part, NASA preferred to stay conservative with the Mercury vehicles and avoid modifying them any more than necessary. Modifications to the Atlas would largely be limited to those that improved pilot safety, and the standard D-series Atlas configuration The booster flight path deviated too far from the planned trajectory Engine thrust or hydraulic pressure dropped below a certain level Propellant tank pressure dropped below a certain level The intermediate tank bulkhead showed signs of losing structural integrity The booster electrical system ceased operating The ASIS system ceased operating The ASIS system was deemed necessary because some flight failures of Atlas vehicles (for instance, Atlas 6B) occurred so fast that it would be nearly impossible for the astronaut to react in time to manually activate the LES. Other failure modes such as a deviation from the correct flight trajectory did not necessarily pose an immediate danger to the astronaut's safety, and the flight could be aborted manually. Not all of the modifications listed below were carried on every Mercury flight and numerous changes were made along the way in the interest of improvement or as a result of flight data obtained from failed Atlas launches. Quality control and checkout procedures also improved and became more detailed over the course of the program. Nine LV-3Bs were launched, two on uncrewed suborbital test flights, three on uncrewed orbital test flights, and four with crewed Mercury spacecraft. Atlas LV-3B launches were conducted from Launch Complex 14 at Cape Canaveral Air Force Station, Florida. It first flew on 29 July 1960, conducting the suborbital Mercury-Atlas 1 test flight. The rocket suffered a structural failure shortly after launch, and as a result failed to place the spacecraft onto its intended trajectory. In addition to the maiden flight, the first orbital launch, Mercury-Atlas 3 also failed. This failure was due to a problem with the guidance system failing to execute pitch and roll commands, necessitating that the Range Safety Officer destroy the vehicle. The spacecraft separated by means of its launch escape system and was recovered 1.8 kilometres (1.1 mi) from the launch pad. A further series of Mercury launches was planned, which would have used additional LV-3Bs; however these flights were canceled after the success of the initial Mercury missions. The last LV-3B launch was conducted on 15 May 1963, for the launch of Mercury-Atlas 9. NASA originally planned to use leftover LV-3B vehicles to launch Gemini-Agena Target Vehicles, however an increase in funding during 1964 meant that the agency could afford to buy brand-new Atlas SLV-3 vehicles instead, so the idea was scrapped.

Densified liquid hydrogen/liquid oxygen is a promising propulsion fuel in the future. In order to systematically demonstrate the benefits and challenges of densified liquid hydrogen/liquid oxygen, a transient thermodynamical model considering the heat leakage, temperature rise, engine thrust, pressurization pressure of the tank, and wall thickness of tank is developed in the present paper, and the performance of densified liquid hydrogen/liquid oxygen as propulsion fuel is further evaluated in actual application. For liquid hydrogen/liquid oxygen tanks at different structural dimensions, the effects of many factors such as temperature rise during propellant ground parking, lift of engine thrust, mass reduction of the tank structure, and extension of spacecraft in-orbit time are analyzed to demonstrate the comprehensive performance of liquid hydrogen/liquid oxygen after densification. Meanwhile, the problem of subcooling combination matching of liquid hydrogen/liquid oxygen is proposed for the first time. Combining the fuel consumption and engine thrust lifting, the subcooling combination matching of liquid hydrogen/liquid oxygen at different mixing ratios and constant mixing ratios are discussed, respectively. The results show that the relative engine thrust enhances by 6.96% compared with the normal boiling point state in the condition of slush hydrogen with 50% solid content and enough liquid oxygen. The in-orbit time of spacecraft can extend about 2–6.5 days and 24–95 days

how thick to make the skin on Atlas and how much ​ pressurization was necessary to keep it structurally intact could only be solved through testing. Lesney Based on the projected weight of Centaur, JPL’s contract with Hughes for Surveyor called for a spacecraft weight of 2,500 pounds with a science payload of approximately 340 pounds. In the spring of 1962, Marshall managers informed JPL that Centaur could not lift this weight and asked for a reduction in payload weight to 2,100 pounds. This weight change had a demoralizing effect on JPL and Hughes engineers because they had to redesign the Surveyor mission to accommodate fewer scientific experiments. Whether Surveyor was even necessary for the Apollo program was called into question in 1962. In a confidential memo to Homer Newell, written in December 1961 after a visit to General Dynamics, Sloop revealed that the company considered the problem of leaks across the bulkhead so serious that the integral tank design might have to be scrapped. He reported that the company thought that it might still be feasible to fly the Surveyor and Mariner missions on Centaur because the hydrogen leaked so slowly. But because of the longer coast time of the Advent mission, liquid-hydrogen leakage might jeopardize the mission. In announcing the change to employees, a company newsletter stated, “In arriving at the Project Centaur decision, two principal factors were considered by management: the future of the company demands to a large degree on upgrading the Centaur effort to an exceptional level of efficiency, and also the company must utilize Ehricke’s unique creative talents to the fullest degree possible for originating new products, just as he originated the Centaur.” [ 12 ] Hansen’s integrity and calm leadership style earned the respect of those with whom he worked, both inside the company and within NASA. “Charlie was trying to explain its merits to a disbelieving Mrazek and from experience I knew that the only solution was to get those two gentlemen separated from the briefings so they could have at it.” [ 20 ] Bossart led Mrazek out into the factory yard, where a Centaur tank stood gleaming in the sunlight. Mrazek asked, “What’s inside it?” To which Bossart responded, “Nitrogen.” Nitrogen was used for pressurization until the rocket was filled with its liquid-hydrogen/liquid-oxygen propellants just prior to launch. Without pressurization, the thin skin of the rocket would first wrinkle, then collapse. Mrazek, familiar with the solid, reinforced walls of rockets designed by the von Braun team, was perplexed by Bossart’s insistence that nitrogen, kept at the relatively low pressure of 8 to 10 pounds per square inch, was sufficient to keep the tank rigid. He also questioned how such a thin, unbuttressed structure could be strong enough to carry a rocket aloft. To quell Mrazek’s doubts, Bossart invited him to take a sledge hammer and give the tank a whack. Failing to put even the slightest dent in the tank, he tried again, this time giving the side of the tank a glancing blow that caused the sledge hammer to fly out of his hand, knocking This was a major undertaking that Don Lesney realized would be of enormous importance to the success of Centaur. In addition to a big interstage adapter to connect Atlas with Centaur, the vehicle carried a 10-foot-diameter payload fairing. What concerned Lesney was whether the middle of the vehicle was strong enough to withstand the aerodynamic stresses caused by flying through the wind. The vehicle was double the length of the original Atlas ICBM. Questions such as how thick to make the skin on Atlas and how much  ​ pressurization was necessary to keep it structurally intact could only be solved through testing. James Womack, one of the first NASA staff at the Cape, recalled that he was familiar with more conventional propellants but had never worked with liquid hydrogen. Because the Cape operations staff knew little about liquid hydrogen, they attended the required safety lectures. They were cautioned that since hydrogen produces no visible flames during combustion, they should take a broom along every time they went near a hydrogen line. If the broom did not burst into flames, it was considered safe to proceed. I was in a meeting at Huntsville when it was admitted that even Saturn, for all of its structure, would collapse in flight without internal tank pressure. Over drinks, they admitted that it made little sense to fly all that structure. The real reason for their design was a passion for vertical check-out. [ 35 ]   ​ Lynch observed that Marshall engineers were equally conservative with respect to electrical systems. They preferred old-fashioned relays and vacuum tubes. Their junction boxes were so heavy that he thought they belonged on a battleship, not a spaceship. In contrast to the 35-percent margin of safety the von Braun team specified in its contracts, the contract between General Dynamics and the Air Force allowed a 25-percent margin. He explained, “We are inclined, I think, to be willing to take a little bit more of a design gamble to achieve a significant improvement, whereas I think they [Huntsville] build somewhat more conservatively.” [ 48 ] To designers at General Dynamics, the pressure-stabilized tank may have been a “design gamble,” but its advantages made it one worth taking. Although no longer in charge of the program, Krafft Ehricke vigorously defended the design, pointing out that the pressure-stabilized tank was also used on Atlas, a rocket deemed reliable enough to send Mercury astronaut John Glenn into orbit around Earth. In Centaur, the pressure-stabilized tank design optimized the unique characteristics of liquid hydrogen—its low density and extreme cold. The result was a dramatic savings in weight, always the driving factor behind any successful rocket design. Ehricke also strongly defended the use of liquid hydrogen fuel.

The modal response of a liquid-filled tank to external acoustic excitation can be used to infer with high resolution the mass of contained liquid, the mass flow rate of liquids into and out of the tank, and changes in tank pressure. Both contained liquid mass and internal ullage pressure affect the modal response of the tank walls through fluid mass-loading of the tank walls and pressure-induced wall stiffening, respectively. Modal Propellant Gauging refers to the technology that exploits these shifts in modal frequencies to infer the mass of propellant in a tank. MPG is a non-invasive gauging technology that has demonstrated gauging resolutions of 1% for settled propellants and 2-3% for unsettled, sloshing propellants. Extensive parabolic flight testing of the MPG system on model tanks has been conducted to validate the technology in reduced gravity. MPG testing on a qualification tank for the Orion Program's European Service Module has also been conducted and is reported here. Finite element modeling of the Orion ESM ″upper" tank is discussed and compared with measurement data. Three computational approaches to mass determination, Peak Tracking, Point Sensor, and Spectral Density methods, are described here. Use cases are defined and analyzed in the context of the Orion ESM Qualification tank data, and an implementation scheme for continuous mass gauging on the Orion ESM is discussed.