Int J Performability Eng ›› 2013, Vol. 9 ›› Issue (6): 581-582.

• Editorial •

### Editorial

KRISHNA B. MISRA

1. Editor-in-Chief

Abstract:

Having scaled the highest peaks of mountains and explored the depths of oceans of the Earth, humans always had an intense curiosity to explore the outer space while gazing through ever powerful telescopes from Galileo's time onwards trying to learn more about the heavenly bodies and their movements. The development of several new technologies finally culminated with the launch of Sputnik 1 by the Soviet Union on October 4, 1957. This was the world's first artificial satellite weighing 83.6 kgs, orbiting the Earth in 98.1 minutes. The launch of Sputnik 1 ushered a new era of political, scientific and technological achievements that became to be known as the Space Age, which led to rapid advances in material science, rocketry, computers and many other areas largely produced by a race between U.S.A and Soviet Union, who tried to smart over each other's achievements. One of the glorious moments of 20th Century and of the space age was the landing of a man on the Moon on Apollo-11 mission, which was watched by nearly 500 million people.

Actually, the origin of space race can be traced to Germany, who beginning in the 1930s and continuing during World War II researched and built operational ballistic missiles. In fact, the Germans were able to experiment with liquid-fuelled rockets capable of reaching high altitudes and long distances. It is generally believed that developments in the USA and USSR can be attributed to this capability developed by Germany during WWII. In 1955, both the United States and the Soviet Union were building ballistic missiles that could be utilized to launch objects into space. Indeed, on 12 April 1961, the USSR launched Yuri Gagarin into orbit around the Earth on Vostok 1. Subsequently, 3 weeks later, on 5 May 1961, Alan Shepard became the first American in space, launched on a suborbital mission Mercury-Redstone 3. The space race including the Moon-race between the USA and USSR continued

Ultimately, the collapse of the USSR and the Challenger disaster in 1986 led to a slowdown of the space race resulting in a drastic cut of funds for the space program during the 1990s. When the Information Age began in the 1990s, space exploration and related technologies significantly increased. Today, several countries have space programs ranging from technological ventures to full-fledged space programs with launch facilities. Japan, India and China are the major players in this race from the Asian region and have plans to send humans into space. There are many scientific and commercial satellites in use today, with a total of thousands of satellites in orbit. Several countries like Israel, South Korea, Brazil, European Consortium, Indonesia, Malaysia, Thailand, Philippines, Iran, Bangladesh, Pakistan, and North Korea have space organizations and intend to launch their own satellites or conduct research

A spacecraft system comprises various subsystems that are determined by a mission profile. The spacecraft subsystems may include attitude determination and control (ADAC), guidance, navigation and control (GN&C), communications (Comms), command and data handling (C&DH), power (EPS), thermal control (TCS), propulsion, and structures. Typically payloads are also included.

A launch vehicle is used to transport and place a spacecraft or satellites into space. The launch vehicle propels the spacecraft from the Earth's surface, through the atmosphere, and into an orbit, the exact orbit being dependent upon the mission configuration. The launch vehicle may be expendable or reusable.

The spacecraft needs an electrical power generation and distribution subsystem for powering the various subsystems. For a mission near the Sun, solar panels are often used to generate electrical power. For spacecraft designed to operate in more distant locations, a Radioisotope Thermoelectric Generator (RTG) may be used to generate electrical power.

The spacecraft is designed to withstand launch loads imparted by the launch vehicle, and must have interfaces for all the subsystems. Depending upon the mission profile, the structural subsystems may need to withstand large loads imparted by entry into the atmosphere of another planetary body, and from landing on the surface of the planetary body.

The spacecraft is designed to withstand transit through the Earth's atmosphere and the space environment. It must, therefore, be able to operate in a vacuum with temperatures potentially below zero and ranging across hundreds of degrees Celsius as well as (if subject to re-entry) withstand the presence of plasmas. Material requirements therefore may include the use of high melting temperature, low density materials such as beryllium and reinforced carbon-carbon or (possibly due to the lower thickness requirements despite its high density) tungsten or ablative carbon/carbon composites. Depending on the mission profile, the spacecraft may also need to operate on the surface of another planetary body. The thermal control subsystem may be passive, dependent on the selection of materials with specific radiative properties. Active thermal control makes use of electrical heaters and certain actuators such as louvers to control temperature to lie within the specific ranges.

A spacecraft needs a propulsion system to perform momentum management manoeuvers. A conventional propulsion subsystem may include fuel, tankage, valves, pipes, and thrusters. The thermal control system interfaces with the propulsion subsystem by monitoring the temperature of relevant components, and by preheating tanks and thrusters in preparation for a spacecraft manoeuvre.

The payload depends upon the mission of the spacecraft. Typical payloads may include scientific instruments such as cameras, telescopes, or particle detectors, cargo, or may include a human crew.

The spacecraft may also have a module, which is basically a detachable compartment of the spacecraft. For example, a lunar excursion module (LEM) or simply a lunar module is a smaller spacecraft that carries astronauts from the command module to the surface of the Moon and back. Likewise, a space capsule is a smaller spacecraft designed to transport people and support human life in outer space. The Space Shuttle was a reusable spacecraft with wings for a controlled descent through the Earth's atmosphere.

In summary, the spacecraft and its systems must operate with very high reliability under the most unforgiving extreme conditions, from the stress and intense heat of launch and re-entry, to the near absolute zero temperature and vacuum of space including exposure to a variety of radiations and possible collision with space orbiting bodies. The spacecraft requires equipment and systems that can function in either atmospheric or non-atmospheric conditions. And importantly, the cost of a failure is always at stake in any kind of space launch. A small launch vehicle, such as the U.S. Pegasus, costs approximately $15 million, but a versatile, reusable launch vehicle, such as the U.S. Space Shuttle, costs over$1 billion. A small experimental satellite can cost a few million dollars, but an advanced spy satellite or scientific satellite may cost more than \$1 billion.

The International Space Station (ISS) is a habitable artificial satellite in low Earth orbit (LEO). It is the ninth space station following its predecessors like the Salyut, Almaz, Skylab and Mir stations The ISS has a modular structure and its first component was launched in 1998. Now it is the largest artificial station in orbit and is visible to the naked eye from the Earth. Its various components have been launched by the American Space Shuttle as well as by Russian Proton and Soyuz rockets. The ISS serves as a microgravity research laboratory with a space environment, in which crew members conduct experiments in astronomy, biology, environment, meteorology, physics, and many other areas. The ISS also serves as an international laboratory for the testing of spacecraft systems and equipment required for other missions such as to the Moon and Mars.

The greatest advantage of pursuing the rather expensive space programs has had its effect in the development of numerous spin-off technologies in many other areas, which in the long run results in significant payoffs.

The idea of space tourism is also becoming more popular in spite of the high cost. This is not without technical problems. Launch to an Earth-orbit requires accelerating to Mach 26 or a speed of about 8 kms/second, and to achieve this, a significant amount of propellant is required - about 10 tons per passenger. Rocket engines use liquid propellant and oxidizer since there is no air in space. Typically, a long-distance airliner has about half its mass as the fuel. But to get to orbit a rocket needs to be about 90% propellant. So the rest of the rocket and passengers are allocated only 10%. Such a rocket needs to have a very light structure, which should be also very strong so that it can survive the acceleration, vibration and aerodynamic stresses. In due course, reusable launch vehicles may come to be operated routinely, just like aircrafts. At present, the space programs are usually carried out by Government agencies and organizations. With private agencies coming into play, space tourism may become realizable.

The present issue of International Journal of Performability Engineering (IJPE) concerns performance related issues and case studies, as these are of importance to the readers of IJPE. Therefore it was considered appropriate to choose the theme of performance analysis of space vehicles for the special issue. Space vehicles may include satellites, unmanned space vehicles, manned space vehicles, as well as the International Space Station (ISS). Performance analyses include all types of analyses pertinent to the performance of a space vehicle. The special issue is intended to cover methods and assessments.

When I first put the idea of bringing out a special issue of this kind to Dr. William Vesely of NASA Headquarters, he agreed to work towards this possibility. And he sought some time to respond to my request, presumably for sounding his colleagues who are working on various aspects of the theme. I am delighted to see a very good response to the call for possible contributions to this issue. The result is that finally Dr. Vesely selected a set of 12 papers for this issue which I may add is also the maximum number of papers contained in any special issues brought out by the IJPE.

I owe gratefulness to Dr. Vesely for his editing and to the authors who have contributed their valuable papers to this special issue. I believe that this is a first of its kind effort that has been made by any journal. The organizations, industries, researchers and academia world over will find the information contained in this issue of interest for their work. The readers of IJPE will also find the issue of great interest.