Category The Universe, Exploring the Universe, Solar System, The Moon, Space, Space Travel

NASA’s deep space 1 probe launched in 1998, was the first craft to use ion technology in space. It flew close to the near-Earth asteroid Braille (also known as 1992 KD), guided by an automated navigation system. Afterwards, it investigated the comet Borrelly, completing its mission in late 2001. Deep Space 1 is an experimental craft that is also testing several other new technologies, including more efficient solar panels, and an autonomous operations system, which allows the craft to think and act on its own. Its success has made scientists optimistic about the use of ion technology.

Deep Space 1 is the first interplanetary spacecraft to use an ion propulsion system for the primary delta-v maneuvers. The purpose of the mission is to validate a number of technologies, including ion propulsion and a high degree of spacecraft autonomy, on a flyby of an asteroid and two comets. The ion propulsion system has operated for a total of 3500 hours at engine power levels ranging from 0.48 to 1.94 kW and has completed the encounter with the asteroid 1992KD and the first set of deterministic burns required for a 2001 encounter with comet Wilson-Harrington. The system has worked extremely well after an initial grid short was cleared after launch. Operation during this primary mission phase has demonstrated all ion propulsion system and autonomous navigation functions. All propulsion system operating parameters are very close to the expected values with the exception of the thrust at higher power levels, which is about 2 percent lower than that calculated from the electrical parameters. This paper provides an overview of the system and presents the first flight validation data on an ion propulsion system in interplanetary space

Originally designed to test a dozen new technologies including the use of an ion engine for spacecraft propulsion, Deep Space 1 far outstripped its primary mission goals by also successfully flying by the asteroid 9969 Braille and comet Borrelly. The flybys produced what are still considered some of the best images and data ever collected from an up-close encounter with an asteroid or comet.

The success of Deep Space 1 set the stage for future ion-propelled spacecraft missions, especially those making the technically difficult journey to asteroids or comets, such as NASA’s Dawn mission.

July 29, 1999: Having completed its technology testing within the first couple months after launch, Deep Space 1 makes a bonus flyby of the asteroid 9969 Braille, flying within about 17 miles (27 kilometers) of the object.

November 1999: While embarking on a new journey to comet Borrelly, the spacecraft’s star tracker used for determining its orientation in the zero gravity of space fails, nearly ending Deep Space 1’s extended mission.

June 2000: Engineers develop a new way to operate the Deep Space 1 spacecraft after the potentially mission-ending failure of its star tracker. Software is radioed to the probe using the camera on board to serve as a replacement navigational tool. The operation marks one of the most successful robotic space rescues in the history of space exploration.

September 2001: Deep Space 1 approaches comet Borrelly, using all of its advanced science instruments to collect important data on the comet’s environment and its icy, rocky nucleus. Despite the challenges faced by the spacecraft, it’s able to snap the best up-close pictures of a comet to-date.

While the particles expelled from an ion drive travel much faster than the gases from a conventional rocket, they are not massive enough to provide sufficient thrust. Rockets such as the Space Shuttle can produce millions of pounds of thrust at lift-off, whereas, to begin with, an ion drive can only produce around 20-thousandths of a pound of thrust. This is not enough force to escape Earth’s gravitational pull. Crafts with ion drives have to be carried into space by a conventional rocket, but once they have left Earth’s orbit, their velocity continues to increase, until they reach much faster speeds than rockets. Ion drives are also much more efficient, using only 80kg (1761bs) of xenon in a two-year mission.

Chemical rockets were the powerhouses of the space age. But after 90 years of development, further engine refinements aren’t expected to lead to major improvements in terms of thrust (these rockets are fundamentally limited by the energy held in chemical bonds).

Litchfield argues that research in chemical rocketry should still constitute the major effort of NASA research, especially towards generating fuel at the destination planet, rather than carrying it all on board. For example, those on Mars might split ice from the polar caps into hydrogen and oxygen to use as rocket fuel. These engines use electrical energy to create super-heated plasma and fire it through a supersonic nozzle to generate thrust.

These kinds of engines have been used in Russian satellites since the 1970s and by Lockheed Martin A2100 satellites, using hydrazine as fuel. These engines are efficient, but the thrust they generate is extremely low, meaning their only likely use will be to orient satellites in orbit.

Now we’re getting to the futuristic stuff. The ion drive engine is a thruster where molecules of an unreactive fuel, such as xenon, are given a positive or negative charge (“ionised”) and accelerated by an electric field to be shot out the back.

The thrust is incredibly low, equivalent to the pressure exerted by a sheet of paper on the palm of your hand, so an ion engine is very slow to pick up speed. But over a long-range mission, it can deliver 10 times as much thrust per kilogram of fuel as a chemical rocket.

The Dawn space probe, currently in orbit around dwarf planet Ceres (and responsible for the first striking photos of mysterious bright spots), used its ion drive to become the first spacecraft to enter and leave the orbits of multiple celestial bodies.

The payload bay is where the Shuttle’s cargo is kept during flight. It measures 18.3m by 4.6m (60ft by 15ft), which is large enough to hold two small buses end to end. The two large bay doors can be opened when the Shuttle reaches low-Earth orbit, allowing the cargo to he lifted into space.

Payload is the carrying capacity of an aircraft or launch vehicle, usually measured in terms of weight. Depending on the nature of the flight or mission, the payload of a vehicle may include cargo, passengers, flight crew, munitions, scientific instruments or experiments, or other equipment. Extra fuel, when optionally carried, is also considered part of the payload. In a commercial context (i.e., an airline or airfreight carrier), payload may refer only to revenue-generating cargo or paying passengers.

For a rocket, the payload can be a satellite, space probe, or spacecraft carrying humans, animals, or cargo. For a ballistic missile, the payload is one or more warheads and related systems; their total weight is referred to as the throw-weight.

The fraction of payload to the total liftoff weight of the air or spacecraft is known as the “payload fraction”. When the weight of the payload and fuel are considered together, it is known as the “useful load fraction”. In spacecraft, “mass fraction” is normally used, which is the ratio of payload to everything else, including the rocket structure.

There is a natural trade-off between the payload and the range of an aircraft. A payload range diagram (also known as the “elbow chart”) illustrates the trade-off. The top horizontal line represents the maximum payload. It is limited structurally by maximum zero-fuel weight (MZFW) of the aircraft. Maximum payload is the difference between maximum zero-fuel weight and operational empty weight (OEW). Moving left-to-right along the line shows the constant maximum payload as the range increases. More fuel needs to be added for more range.

The vertical line represents the range at which the combined weight of the aircraft, maximum payload and needed fuel reaches the maximum take-off weight (MTOW) of the aircraft. If the range is increased beyond that point, payload has to be sacrificed for fuel.

The maximum take-off weight is limited by a combination of the maximum net power of the engines and the lift/drag ratio of the wings. The diagonal line after the range-at-maximum-payload point shows how reducing the payload allows increasing the fuel (and range) when taking off with the maximum take-off weight.

The second kink in the curve represents the point at which the maximum fuel capacity is reached. Flying further than that point means that the payload has to be reduced further, for an even lesser increase in range. The absolute range is thus the range at which an aircraft can fly with maximum possible fuel without carrying any payload.

Picture Credit : Google

Earth’s atmosphere is made up of minuscule particles of rock and gas. When an orbiter re-enters the atmosphere, it impacts with these particles, heating up because of friction. Parts of the Shuttle can reach up to 1500°C (2732°F), which is hot enough to cause them to melt. Because of this, the nose tip and wing edges are protected by heat-absorbing tiles that prevent the orbiter from getting too hot.

Spacecraft re-entry is tricky business for several reasons. When an object enters the Earth’s atmosphere, it experiences a few forces, including gravity and drag. Gravity will naturally pull an object back to earth. But gravity alone would cause the object to fall dangerously fast. Luckily, the Earth’s atmosphere contains particles of air. As the object falls, it hits and runs against these particles, creating friction. This friction causes the object to experience drag, or air resistance, which slows the object down to a safer entry speed. 

This friction is a mixed blessing, however. Although it causes drag, it also causes intense heat. Specifically, shuttles face intense temperatures of about 3000 degrees Fahrenheit (about 1649 degrees Celsius). Blunt-body design helps alleviate the heat problem. When an object — with blunt-shaped surface facing down — comes back to Earth, the blunt shape creates a shock wave in front of the vehicle. That shock wave keeps the heat at a distance from the object. At the same time, the blunt shape also slows the object’s fall. The Apollo program, which moved several manned ships back and forth from space during the 1960s and 1970s, coated the command module with special ablative material that burned up upon re-entry, absorbing heat.

Unlike the Apollo vehicles, which were built for one-time use, space shuttles are reusable launch vehicles (RLVs). So instead of merely using ablative material, they must incorporate durable insulation. On the next page, we’ll delve more deeply into the modern re-entry process for shuttles.

Picture Credit : Google

The Space Shuttle was a partially reusable low Earth orbital spacecraft system operated by the U.S. National Aeronautics and Space Administration (NASA). Its official program name was Space Transportation System (STS), taken from a 1969 plan for a system of reusable spacecraft of which it was the only item funded for development. Operational missions launched numerous satellites, conducted science experiments in orbit, and participated in construction and servicing of the International Space Station (ISS). The first of four orbital test flights occurred in 1981, leading to operational flights beginning in 1982.

Unfortunately there are many risks relating to space travel. With the tremendous forces involved, accidents inevitably occur. In 1986, the Challenger orbiter exploded when a joint between two segments of one of the boosters came loose. Tragically, everybody on board died.

From 1981 to 2011 a total of 135 missions were flown, all launched from Kennedy Space Center (KSC) in Florida. During that time period the fleet logged 1,322 days, 19 hours, 21 minutes and 23 seconds of flight time. The longest orbital flight of the Shuttle was STS-80 at 17 days 15 hours, while the shortest flight was STS-51-L at one minute 13 seconds when the Space Shuttle Challenger broke apart during launch. The shuttles docked with Russian space station Mir nine times and visited the ISS thirty-seven times. The highest altitude (apogee) achieved by the shuttle was 350 miles (560 km) when servicing the Hubble Space Telescope. The program flew a total of 355 people representing 16 countries. The Kennedy Space Center served as the landing site for 78 missions, while 54 missions landed at Edwards Air Force Base in California and one mission landed at White Sands, New Mexico.

The first orbiter built, Enterprise, was used for atmospheric Flight but future plans to upgrade it to orbital capability were ultimately canceled. Four fully operational orbiters were initially built: Columbia, Challenger, Discovery, and Atlantis. Challenger and Columbia were destroyed in mission accidents in 1986 and 2003 respectively, killing a total of fourteen astronauts. A fifth operational orbiter, Endeavour, was built in 1991 to replace Challenger. The Space Shuttle was retired from service upon the conclusion of STS-135 by Atlantis on 21 July 2011.

Picture Credit : Google

After extensive preparation, the STS lift off from the launch tower. After eight seconds, the rocket is travelling at 160km/h (100mph), but it only takes one minute to reach 1600km/h (1000mph). At a height of 45km (28 miles), the solid rocket boosters are jettisoned. They fall back to Earth, using parachutes. When the fuel in the external tank is used up, it too is jettisoned, burning up in Earth’s atmosphere. Once the orbiter reaches a low-Earth orbit, it stays there for up to two weeks before beginning the dangerous return trip.

The space shuttle was developed by the National Aeronautics and Space Administration, more commonly known as NASA. The vehicle consists of a winged orbiter, two solid-rocket boosters, and an external fuel tank. As with previous spacecraft, the shuttle is launched from a vertical position. Liftoff thrust is derived from the orbiter’s three main liquid-propellant engines and the boosters. After two minutes, the boosters use up their fuel, Separate from the Spacecraft, and after deployment of parachutes are recovered following splashdown. During this time, the speed of the shuttle is about 1400 meters per second.

After about eight minutes of flight, the orbiter’s main engines shut down; the external tank is then jettisoned and burns up as it reenters the atmosphere. The orbiter meanwhile enters orbit after a short burn of its two small Orbiting Maneuvering System (OMS) engines. At this time, its top speed is an amazing 8,000 meters per second! To return to earth, the orbiter turns around, fires its OMS engines to reduce speed, and, after descending through the atmosphere lands like a glider.

After four orbital test flights (1981-1982) of the space shuttle Columbia, operational flights began in November of 1982. On January 28, 1986, a shuttle exploded shortly after takeoff, killing all seven astronauts. Shuttle flights were suspended until September 1988, while design problems were corrected, and then resumed on a more conservative schedule; NASA was forced to reemphasize expendable rockets to reduce the cost of placing payloads in space. By the end of 2000, 102 missions had been completed and five different orbiters had been seen in service.

Picture Credit : Google