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mrm101 · 5 months

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Update (augmented NASA blog release) It was later decided to replace the regulator relief valve on the Centaur stage and to allow time to do that the launch has been postponed a week to Friday 17 May at 21:16UT (06:18EDT). The oscillating behaviour of the valve during LOX tank ‘topping up’ replenishment operations, ultimately resulted in the launch team calling a launch scrub on Monday (Tuesday morning UK). After the crew had climbed out of the spacecraft and left the launch complex the valve was commanded shut and the oscillations stopped, however the oscillations then reoccurred twice during de-tanking (fuel draining) operations. After reviewing the valve’s history and examining data signatures form the launch attempt it was decided that the valve had, or would, exceed it’s certified design life of 200,000 individual operations (and also the fact the problem had reoccured in a short period of time). The Atlas V will be rolled back to the VIF tomorrow (8 May). The crew, Butch Wilmore and Suni Williams will remain at the Kennedy Space Centre crew quarters in quarantine until the next launch attempt.

It was announced, early on Monday morning (7 May) at around L-2 hours that the vehicle was not in a launch configuration and the launch attempt would be aborted and the count would enter a 65 minute hold to allow the crew to egress, assisted by the 'blue team' or the close out team in the white room at the end of the Crew Access Arm, the hatch at that point was still open.

As explained at a later briefing Tony Bruno, the ULA boss, the problem was with a spring loaded pressure relief regulator valve on the liquid oxygen(LOX) tank of the Centaur upper or second stage. This is designed to pop open if the ullage pressure got to great (the space above the LOX in the tank which is filled with helium to keep the tank pressurised and ultimately later push the propellent into the engines). On rare occasions such a valve does not seat properly and starts to oscillate or 'buzz' open and closed very rapidly, about 40htz in this case. It could be heard by the blue team and sounds like a loud buzzing.

Normally to correct this a solenoid would be operated (a electro-magnetically operated switch or lever) to force the valve closed (as is done just before launch), once released this usually stops the valve 'buzzing'. However because a crew was onboard the launch rules of ULA dictate that nothing should be done to alter the fuel state of the vehicle (outside of the launch procedure that is) and shutting this valve with the solenoid would have caused the tank pressure to increase, changing the fuel state. So they had to abort the launch attempt and get the crew off. Once the crew had got out they operated the switch and the valve stopped buzzing.

However the next worry is how much stress that valve has suffered whilst it was rapidly opening and closing and if it was slamming all the way open and closed or just partially. These valves are certified, tested for 200,000 opening and closings (they can probably last longer than that but that has not been tested) and unfortunately it is estimated that it may have been approaching that limit. There aren't any sensors attached to the valve but the launch crew can use accelerometers on the nearly engines to measure and count the vibrations caused by the buzzing valve. Then they can estimate how many times the valve opened and closed and then calculate how much structural design life it has late remaining. which is what they have been doing today (Tuesday). If the valve does not have enough life left in it to cover another launch attempt it will have to be replaced. That can be done but the rocket would have to be rolled back into the Vehicle Integration Facility (VIF), a nearby high bay. There the Centaur LOX tank would have to be supported, put under tension, and completely depressurised (it need to be pressurised, or put under tension, at all times or it would crumple) so the valve can be changed, however the Starliner spacecraft would not have to be taken off the top of Centaur during the process. This would tale several days. Currently the valve condition it is still being assessed and if it is OK, if it does not need to be changed, then another launch attempt can be made on Saturday, UK time. Pic: NASA

#Boeing CFT

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jcmarchi · 6 months

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Zero-Boil-Off Tank Experiments to Enable Long-Duration Space Exploration - Technology Org

New Post has been published on https://thedigitalinsider.com/zero-boil-off-tank-experiments-to-enable-long-duration-space-exploration-technology-org/

Zero-Boil-Off Tank Experiments to Enable Long-Duration Space Exploration - Technology Org

Do we have enough fuel to get to our destination? This is probably one of the first questions that comes to mind whenever your family gets ready to embark on a road trip.

If the trip is long, you will need to visit gas stations along your route to refuel during your travel. NASA is grappling with similar issues as it gets ready to embark on a sustainable mission back to the Moon and plans future missions to Mars.

But while your car’s fuel is gasoline, which can be safely and indefinitely stored as a liquid in the car’s gas tank, spacecraft fuels are volatile cryogenic liquid propellants that must be maintained at extremely low temperatures and guarded from environmental heat leaks into the spacecraft’s propellant tank.

And while there is already an established network of commercial gas stations to make refueling your car a cinch, there are no cryogenic refueling stations or depots at the Moon or on the way to Mars.

Furthermore, storing volatile propellant for a long time and transferring it from an in-space depot tank to a spacecraft’s fuel tank under microgravity conditions will not be easy since the underlying microgravity fluid physics affecting such operations is not well understood.

Even with today’s technology, preserving cryogenic fuels in space beyond several days is not possible and tank-to-tank fuel transfer has never been previously performed or tested in space.

Figure 1. The Gateway space station—humanity’s first space station around the Moon—will be capable of being refueled in space. Image Credit: NASA

Heat conducted through support structures or from the radiative space environment can penetrate even the formidable Multi-Layer Insulation (MLI) systems of in-space propellant tanks, leading to boil-off or vaporization and causing tank self-pressurization.

The current practice is to guard against over-pressurizing the tank and endangering its structural integrity by venting the boil-off vapor into space. Onboard propellants are also used to cool down the hot transfer lines and the walls of an empty spacecraft tank before a fuel transfer and filling operation can take place. Thus, precious fuel is continuously wasted during both storage and transfer operations, rendering long-duration expeditions—especially a human Mars mission—infeasible using current passive propellant tank pressure control methods.

Zero-Boil-Off (ZBO) or Reduced Boil-Off (RBO) technologies provide an innovative and effective means to replace the current passive tank pressure control design. This method relies on a complex combination of active, gravity-dependent mixing and energy removal processes that allow maintenance of safe tank pressure with zero or significantly reduced fuel loss.

At the heart of the ZBO pressure control system are two proposed active mixing and cooling mechanisms to counter tank self-pressurization. The first is based on intermittent, forced, subcooled jet mixing of the propellantand involves complex, dynamic, gravity-dependent interaction between the jet and the ullage (vapor volume) to control the condensation and evaporation phase change at the liquid-vapor interface. The second mechanism uses subcooled droplet injection via a spraybar in the ullage to control tank pressure and temperature. While the latter option is promising and gaining prominence, it is more complex and has never been tested in microgravity where the phase change and transport behavior of droplet populations can be very different and nonintuitive compared to those on Earth.

Figure 2. Astronaut Joseph M. Acaba installing ZBOT Hardware in the Microgravity Science Glovebox aboard the International Space Station. Image Credit: NASA

Although the dynamic ZBO approach is technologically complex, it promises an impressive advantage over the currently used passive methods. An assessment of one nuclear propulsion concept for Mars transport estimated that the passive boil-off losses for a large liquid hydrogen tank carrying 38 tons of fuel for a three-year mission to Mars would be approximately 16 tons/year. The proposed ZBO system would provide a 42% saving of propellant mass per year. These numbers also imply that with a passive system, all the fuel carried for a three-year Mars mission would be lost to boil-off, rendering such a mission infeasible without resorting to the transformative ZBO technology.

The ZBO approach provides a promising method, but before such a complex technological and operational transformation can be fully developed, implemented, and demonstrated in space, important and decisive scientific questions that impact its engineering implementation and microgravity performance must be clarified and resolved.

The Zero Boil-off Tank (ZBOT) Experiments are being undertaken to form a scientific foundation for the development of the transformative ZBO propellant preservation method. Following the recommendation of a ZBOT science review panel comprised of members from aerospace industries, academia, and NASA, it was decided to perform the proposed investigation as a series of three small-scale science experiments to be conducted onboard the International Space Station. The three experiments outlined below build upon each other to address key science questions related to ZBO cryogenic fluid management of propellants in space.

The first experiment in the series was carried out on the station in the 2017-2018 timeframe. Figure 2 shows the ZBOT-1 hardware in the Microgravity Science Glovebox (MSG) unit of the station. The main focus of this experiment was to investigate the self-pressurization and boiling that occurs in a sealed tank due to local and global heating, and the feasibility of tank pressure control via subcooled axial jet mixing. In this experiment, the complicated interaction of the jet flow with the ullage (vapor volume) in microgravity was carefully studied. Microgravity jet mixing data was also collected across a wide range of scaled flow and heat transfer parameters to characterize the time constants for tank pressure reduction, and the thresholds for geyser (liquid fountain) formation, including its stability, and penetration depth through the ullage volume. Along with very accurate pressure and local temperature sensor measurements, Particle Image Velocimetry (PIV) was performed to obtain whole-field flow velocity measurements to validate a Computational Fluid Dynamics (CFD) model.

Figure 3. Validation of ZBOT CFD Model Predictions for fluid flow and deformation of a spherical ullage in microgravity by a subcooled liquid jet mixing against ZBOT experimental results: (a) Model prediction of ullage position and deformation and flow vortex structures during subcooled jet mixing; (b) PIV image capture of flow vortex structures during jet mixing; (c) Ullage deformation captured by white light imaging; and (d) CFD model depiction of temperature contours during subcooled jet mixing. (ZBOT-1 Experiment, 2018) Image Credit: Dr. Mohammad Kassemi, Case Western Reserve University

Some of the interesting findings of the ZBOT-1experiment are as follows:

Provided the first tank self-pressurization rate data in microgravity under controlled conditions that can be used for estimating the tank insulation requirements. Results also showed that classical self-pressurization is quite fragile in microgravity and nucleate boiling can occur at hotspots on the tank wall even at moderate heat fluxes that do not induce boiling on Earth.

Proved that ZBO pressure control is feasible and effective in microgravity using subcooled jet mixing, but also demonstrated that microgravity ullage-jet interaction does not follow the expected classical regime patterns (see Figure 3).

Enabled observation of unexpected cavitation during subcooled jet mixing, leading to massive phase change at both sides of the screened Liquid Acquisition Device (LAD) (see Figure 4). If this type of phase change occurs in a propellant tank, it can lead to vapor ingestion through the LAD and disruption of liquid flow in the transfer line, potentially leading to engine failure.

Developed a state-of-the-art two-phase CFD model validated by over 30 microgravity case studies (an example of which is shown in Figure 3). ZBOT CFD models are currently used as an effective tool for propellant tank scaleup design by several aerospace companies participating in the NASA tipping point opportunity and the NASA Human Landing System (HLS) program.

Some of the interesting findings of the ZBOT-1experiment are as follows:

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444namesplus · 7 months

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human-antithesis · 11 months

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Curtain

Ab Ovo Hitherto - Obsolescence Obire Charnel Decede, Carnal Dissever Incursion Cleave Corpsurreal Avant Ullage Liaise Prestygious Decant

Redivivus Succor Oneiric Forclore Thee Obliquitious Flaw Redivivus Succor

Black Window Agape Crooken Equipoise Quaver Artifabric

Attunement Synchronous Fatum Certus

Luctus…Vade

Excedere Vita

#Portal #Experimental Death Metal #Death Metal #Australia #Bandcamp

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michaelgabrill · 11 months

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Who Let the Gas Out?: NASA Tank Venting in Microgravity Challenge

As space travel extends to greater duration and distance, missions may require a propellant refill in space. To achieve this, spacecraft may require larger tanks and efficient refueling along with tanks that have the capability of isolating propellant from ullage fluid (a gas and vapor mixture) during a vent. The goal of this Challenge is […] from NASA https://ift.tt/2EQpSKy

#NASA #space #Who Let the Gas Out?: NASA Tank Venting in Microgravity Challenge #Michael Gabrill

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readingvocabulary · 1 year

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Mervyn Peake ~~ Titus Groan

circumfusion - to pour or spread (a liquid, powder, etc) around

calid - moderately hot

catalyptic

spilth - the action of spilling; material that is spilt

umbrage - shade or shadow, especially as cast by trees

rabous

fumid - smoky, vaporous

nonagenarian - a person who is between 90 and 99 years old

peregrine - foreign

lapsury

gibbous - hunchbacked; convex, protuberant

wodge - ‘a wodge of flesh’

abactinal - situated away from or opposite to the mouth

ullage - the amount by which a container falls short of being full; loss of liquid, by evaporation or leakage

splith’d

daedal - skilful, ingenious

triturate - grind to powder

chasmic - extremely deep or large

umbrageous - shadowy

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i-love-linux-and-reject-gender · 2 months

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i hate propellant ullage

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usafphantom2 · 1 year

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👆 bringing on new fuel cooled them down. Aboard the SR-71 the fuel was used as a heat sink.

Everything about the SR-71 was complex yet incredibly engineered, so they have to find a way for the Blackbird to deal with the enormous amount of heat generated by its high-speed flight.

‘Flying at over Mach 3 is thermal problem. Everything is too hot, including any air you slow down to interact with the vehicle. You are trying to make the vehicle (and the pilots inside) survive for hours in a pizza oven, while they are getting cozy with two 500 million BTU/hour flamethrowers,’ Iain McClatchie, an aviation and turbine engine expert, says on Quora.

When you look at a graph like this, your first impression might be that the vehicle is this glowing hot thing slicing through the icy -52 C air at 80,000 feet. So naturally, you think of the air as cooling the airplane down.

I know, it seems unbelievable. Use this handy graph and see for yourself.

Basically, the shocks from the airplane heat the air around it, but the vehicle itself cools the air in contact with it down. Once the airplane passes by, all that disturbed air tumbles to a stop, leaving a path of hot air through the upper atmosphere.

‘So back to life in the pizza oven. The basic solution is (a) leave most of the airframe hot and make it out of stuff like titanium and stainless steel that are strong when hot, and (b) start with a large amount of cold fuel, and then dump heat from critical areas into the fuel before burning it. When decoupling from an aerial tanker, half the SR-71’s weight was fuel.

‘A special type of kerosene fuel, JP-7, was developed for the SR-71 to be good as a heat sink. It boils away at 285 C at 1 atmosphere pressure, which is the upper end of the kerosene range. When the plane tanked up at 30,000 feet, the kerosene might start below 0 C. At speed, it would be used to cool the avionics and cockpit, and by the time it arrived at the engine it would get up to 177 C. It was then used as hydraulic fluid for the various engine actuators, primarily the variable geometry nozzle. By the time it got to the fuel injectors it had gotten up to 316 C (but wasn’t boiling because it was at several atmospheres of pressure). At cruise, the burner cans were at 330 kPa (about 3.3x the pressure at sea level), so the fuel still didn’t boil as it left the nozzles but the droplets would have evaporated very quickly.’ McClatchie continues;

‘JP-7 is mostly a mix of hydrocarbons centered around C12H26 (dodecane). The graph above shows the vapor pressure of dodecane as a function of reciprocal absolute temperature. That makes it a bit hard to read. 0.0024, for instance, is 417 Kelvin which is 143 Celsius. Liquids start to boil when their vapor pressure is greater than the ambient pressure. I’ve labelled the boiling point of dodecane at 2900 Pa, which is the absolute pressure at 80,000 feet, and 13000 Pa, which is the minimum absolute pressure in the SR-71 fuel tanks. Note that the dodecane component of JP-7 starts to boil at 162 C at sea level… quite a bit less than the advertised 285 C which is actually when the stuff boils away completely.

‘The flash point of JP-7 is 60 C. The fuel was held in tanks whose walls were formed of the skin of the vehicle. Since fuel vapor against the top skin of the vehicle would be well over 60 C during cruise, if air was allowed in any ignition source in the tank would cause a deflagration and destruction of the vehicle. Instead, nitrogen gas from a 260-liter liquid nitrogen dewar was used to pressurize the tanks. This would have mostly been an issue during descent, when the ambient pressure rose and extra gas was needed to fill the tank ullage space.

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