Category Science

Which spacecraft achieved first lift-off from the moon?

The race to the moon in the first decades of the second half of the 20th Century is littered with many firsts. While some of these are extremely popular and known to almost everyone, there are others that are not as famous, but equally important in the grand scheme of things. Among the latter is the Surveyor 6 spacecraft, achieved the first lift-off from a celestial body.

The Surveyor series of spacecraft were robotic landers, managed by NASA, whose objectives included making soft landings on the surface of the moon, studying the lunar surface and in general, aiding the planned human landings in the future. While lunar orbiters had provided orbital imagery, those were to be combined with ground-level data gathered by the Surveyor spacecraft at potential Apollo landing sites, thereby making ourselves mission-ready for the grand challenge ahead.

An elusive target

Surveyor 6 was the sixth in a series of seven crew-less spacecraft that proved to be highly successful. The intended target for this spacecraft was nearly in the centre of the moon’s Earth-facing hemisphere, a small lunar mare (any flat, dark plain of lower elevation on the moon) that went by the name Sinus Medii (Latin for “Bay of the Centre”)

Apollo mission planners were looking for a close-up of this area as it appeared rougher than other proposed sites for landing. NASA’s two previous attempts to land here using Surveyor spacecraft hadn’t been successful.

While Surveyor 2, launched on September 20, 1966, went out of control following a mid-course correction, Surveyor 4, launched on July 14, 1967, crashed and failed during the final descent to the lunar surface after an otherwise faultless mission. With only two approved Surveyor flights, including Surveyor 6, remaining, the onus was on the planners to succeed this time.

Basaltic surface

The Surveyor 6 was launched from Cape Canaveral, which contains NASA’s launch pads, on an Atlas-Centaur rocket on November 7, 1967. Landing was scheduled to occur 65 hours after lift-off and Surveyor 6 managed a safe landing on Sinus Medii on November 10, 1967. After routine post-landing checks and routine and reconfiguration for surface operations, it started sending images of the site where it had landed on the moon.

The images showed scientists that it had landed on a relatively level surface and also allowed them to determine the landing site based on orbital imagery. The site was found to be very similar to the previous three Surveyor mare landing sites and that it would support human landing.

The crucial experiments to measure the surface chemistry with an alpha scattering detector showed that landing area was basaltic. This showed that the surface measurements where Surveyor 6 landed were remarkably similar to Surveyor 5’s measurements obtained two months earlier over 700 km away. In effect, it further validated that the terrestrial area of the moon was made of basalt, an important detail for the Apollo mission planners.

First to land twice

On November 17, 1967, Surveyor 6 performed another important experiment. The NASA engineers commanded the Surveyor 6 engine to fire its three main liquid propellant thrusters briefly. As a result, Surveyor 6 not only became the first spacecraft to lift-off from the moon, but also the first to be launched from any celestial body. Not to mention, it was the first to land twice on the surface of the moon.

Even though the Surveyor rejected the first shut-down command, the second command from the ground controllers turned off the engines. All this happened inside 7 seconds, during which time the Surveyor 6 reached an estimated peak altitude of about 10 feet, before landing about eight feet west of its original landing point.

The engineering test successfully demonstrated that rockets could be restarted on the moon, providing another tick in a huge list prepared with a human mission in mind. Following this small lunar hop, Surveyor 6 employed its cameras to study its original landing footprints and determine the soil’s mechanical properties.

Before the onset of the lunar night on November 24, 1967, Surveyor 6 had returned close to 30,000 images of the lunar surface. Even though controllers were able to regain contact on December 14, 1967 and the spacecraft had survived the two week lunar night, no significant data was returned, primary landing operations ceased and the mission ended. By then, however, Surveyor 6 had completed the data acquisition needed for the Apollo missions, freeing up Surveyor 7 to be sent to a site of greater scientific interest and getting us closer to making one small step on the moon.

 

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Which is the second artificial nuclear reactor?

 

We have a thing for firsts. Be it the first human being to climb the Mt. Everest, the first to set foot on the moon, or any such feat, they leave an indelible mark in our collective consciousness. The ones who come second, even though achieving an equally significant accomplishment, often fade from our memory. One such second is the X-10 Graphite Reactor, the second artificial nuclear reactor after the Chicago Pile-1 (CP-1).

Before we take a look at X-10, we have to understand the circumstances in which it came about. The authorisation of the Manhattan Project by the U.S. President Franklin D. Roosevelt during World War II meant that scientists began their research and development to produce the first nuclear weapons. In December 1942, CP-1 became the world’s first artificial nuclear reactor as the experiment led by American-Italian physicist Enrico Fermi achieved the first human-made self-sustaining nuclear chain reaction. 

Need for plutonium

While CP-1 was a success as a scientific experiment and showed that nuclear chain reactions could be controlled, it was built on a small scale, which meant that recovering significant amounts of plutonium wasn’t feasible. As plutonium, a transuranium element that had been recently discovered, was seen as a potential ingredient for atomic weapons, producing it for research was a priority. 

The X-10 Graphite Reactor was thus born as an experimental air-cooled production pile that would help in designing the full-scale helium-cooled reactors that were also being planned. Whereas the X-10 Pile or Clinton Pile was to be built at the Oak Ridge site, the latter was planned to be constructed at Hanford. DuPont company was roped in to work with the University of Chicago to design and build both these reactors. 

Less than a year

Even though the design wasn’t completely ready, DuPont went ahead with the construction of the reactor in early 1943. The X-10 was to be a massive graphite block (24-ft cube), protected by concrete and having 1,248 horizontal channels that were to be filled with uranium slugs surrounded by cooling air. The face of the pile was to be used to push new slugs into the channels, while irradiated ones fell into an underwater bucket at the rear. 

These buckets of irradiated slugs were left to undergo radioactive decay before being moved to a separation facility , where remote-controlled equipment were used to extract the plutonium. Racing against time, the construction of the reactor was completed in less than a year. 

On November 4, 1943, the X-10 went critical for the first time. This meant that the number of neutrons being produced were equal to the number of neutrons being absorbed, which in turn produced the same number of neutrons. A reactor thus operates in a steady-state when it becomes critical. By the end of November, X-10 started producing small but significant samples of plutonium, which were experimentally valuable. 

Important learning

Even though it was decided that water should be used as a coolant for the Hanford reactors while X-10 was still under construction, X-10 provided important results and learning. The X-10 suppled the Los Alamos National Laboratory with the first significant amounts of plutonium, fission studies in which influenced the bomb design. The engineers, technicians, safety officers and reactor operators who worked on X-10 gained great experience, which they were able to apply once they moved to Hanford. 

Once the war was over, the reactor was put to use for peacetime efforts, producing radioisotopes, utilised in industry, medicine and research. It remained in operation until 1963, when X-10 was shut down permanently. By 1965, the X-10 Graphite Reactor was designated a National Historic Landmark by the U.S. government and added to the National Register of Historic Places in 1966. Recognised by the American Chemical Society as a National Historic Chemical Landmark in 2008, the control room and reactor face are still accessible to the public through tours provided by the Oak Ridge National Laboratory. 

 

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HOW DOES FOG FORM?

          Fog is cloud that forms close to the ground. It appears when the wind is light, the air is damp and the sky is relatively clear. It often forms when moisture in the air close to the ground condenses and spreads upwards — this is called radiation fog. It is most common at the beginning or end of the day, when the ground cools down quickly.

          Fog is a natural weather conditions that can cause visibility to become zero. It can cause accidents on normally safe roads and is such a serious weather condition that schools delay the start of the day until the sun burns it off. So how does fog form? First it is important to understand that fog is basically a cloud on the ground. This means like clouds it is a collection of tiny water droplets formed when evaporated water is cooled. The way it is cooled determines how fog is formed.

          The first way that fog is formed is by infrared cooling. Infrared cooling happens due to the change of seasons from summer to fall and winter. During the summer the ground absorbs solar radiation. As air passes over it is made warm and moist. When the seasons change this mass of warm moist air collides with the cooler that is now prevalent. This cause is the water vapor in the air mass to condense quickly and fog is formed. This fog is often called radiation fog due to the way it forms. This kind is the most common type of fog. It also happens when an unseasonable day of warm weather combined with high humidity is followed by dropping temperatures.

          The next way that fog forms is through advection. Advection is wind driven fog formation. In this case warm air is pushed by winds across a cool surface where it condenses into fog. There are also other kinds of fog like hail fog or freezing fog. Each of these conditions is where condensed water droplets are cooled to the point of freezing. There is also fog formed over bodies of water. One type is sea smoke. This is a type of fog that forms when cool air passes over a warm body of water or moist land.

          In general we see that fog is formed whenever there is a temperature difference between the ground and the air. When the humidity is high enough and there is enough water vapor or moisture fog is sure to form. However the kind of fog and how long is last and its effects will depends on the different conditions mentioned. One interesting kind of fog actually helps to make snow melt faster.

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WHAT IS A HAIR HYGROMETER?

          One of the simplest ways to measure humidity is to use a hair hygrometer. This uses a piece of human hair, which stretches or contracts according to the amount of water in the air. In a weather house — a type of hair hygrometer — a hair attached to a turntable stretches and contracts, making the man appear in humid conditions and the woman appear when it is drier.

          These devices use a human or animal hair under some tension. The hair is hygroscopic (tending toward retaining moisture); its length changes with humidity, and the length change may be magnified by a mechanism and indicated on a dial or scale. In the late 17th century, such devices were called by some scientists hygroscopes; that word is no longer in current use, but hygroscopic and hygroscopy, which derive from it, still are. The traditional folk art device known as a weather house works on this principle. Whale bone and other materials may be used in place of hair.

          In 1783, Swiss physicist and geologist Horace Bénédict de Saussure built the first hair-tension hygrometer using human hair.

          It consists of a human hair eight to ten inches long, b c, fastened at one extremity to a screw, a, and at the other passing over a pulley, c, being strained tight by a silk thread and weight, d.

          The pulley is connected to an index which moves over a graduated scale (e). The instrument can be made more sensitive by removing oils from the hair, such as by first soaking the hair in diethyl ether.

 

 

 

 

 

 

 

 

 

 

 

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WHAT IS RELATIVE HUMIDITY?

          To Measure humidity accurately, meteorologists look at relative humidity. This is the amount of water in the air, relative to the maximum amount of water that it can hold at that temperature. To measure relative humidity, a wet and a dry thermometer are used. The wet bulb is covered with wet muslin. The water in the muslin evaporates, making the temperature around the wet bulb cooler than that around the dry bulb. The amount of water that evaporates increases along with the dryness of the air — the greater the difference in temperature, the lower the humidity. A smaller difference means higher humidity. The thermometers are housed in a Stevenson screen, to shade them from the Sun.

           Relative humidity (RH) is the ratio of the partial pressure of water vapor to the equilibrium vapor pressure of water at a given temperature. Relative humidity depends on temperature and the pressure of the system of interest. The same amount of water vapor results in higher relative humidity in cool air than warm air. A related parameter is the dew point.

              Climate control refers to the control of temperature and relative humidity in buildings, vehicles and other enclosed spaces for the purpose of providing for human comfort, health and safety, and of meeting environmental requirements of machines, sensitive materials (for example, historic) and technical processes.

              A hygrometer is a device used for measuring the humidity of air.

             The humidity of an air and water vapor mixture is determined through the use of psychrometric charts if both the dry bulb temperature (T) and the wet bulb temperature (Tw) of the mixture are known. These quantities are readily estimated by using a sling psychrometer.

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WHICH PARTS OF THE WORLD HAVE LOW HUMIDITY?

           Desert regions have very low levels of humidity — often less than 10%. The low levels of water vapour in the air and, indeed, the general scarcity of water makes conditions for life very difficult. Agriculture is practically impossible in such areas and is only really successful in places where levels of humidity tend to be moderate.

           Deserts cover 20 percent of the earth’s surface yet are the driest regions in the world. Their lack of humidity is particularly striking because hot areas can hold so much moisture. Rainforests, for instance, combine warm air and high precipitation to produce some of the highest areas of humidity in the world. Deserts, on the other hand, are very dry, so they’re antithetical to most life.

          Deserts are prone to having long periods of little to no rain before receiving short bursts of precipitation, but the amount of humidity that does enter the air is rare. The desert air is so dry that the rate of evaporation regularly exceeds the rainfall rate, and the rainfall may even evaporate before it hits the ground.

          Desert conditions are also exacerbated by the fact that desert organisms respond to the low humidity by preserving as much water as they can without losing it to evaporation. Many desert plants have evolved a waxy structure called a cuticle that can keep water inside. Small leaves and white hairs that reflect heat may also be strategies for dealing with desert conditions.

         Humidity also affects human health conditions in general (some more and some less of course). For example, high humidity levels in the hot temperatures will make the feeling of heat much worse, since the sweat which regulates our body temperature cannot evaporate as quickly. The best relative humidity, that feels the most comfortable is somewhere around 45%. But nor extremely high neither extremely low humidity is good for human health, even though both high and low humidity climate conditions have pros and cons. 

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