OrbitalHub

After six years of tremendous effort and more than $100 million USD spent, SpaceX made a successful launch of Falcon 1. Falcon 1 is the first booster built by a private company to ever reach the Earth’s orbit. This is the fourth Falcon 1 mission.

Credits: SpaceX

The booster lifted off yesterday from the testing site on Omelek Island in the Kwajalein Atoll located in the central Pacific some 2,500 miles southwest of Hawaii.

The previous three missions were not successful, but SpaceX managed to remove all the stumbling blocks out of the way. In less than two months from the previous attempt, on August 2nd 2008, SpaceX had another booster ready for launch.

The payload carried by the Flight 4 mission is a mass simulator that weighs around 165 kg. The payload did not separate but remained attached to the second stage as it orbits the Earth.

Falcon 1 is a two-stage booster. It uses liquid oxygen and rocket grade kerosene as fuel. The booster is 21.3 meters long and 1.7 meters in diameter. It weighs 27, 670 kg when ready to launch. The first stage of the booster is powered by a Merlin 1C engine and the upper stage is powered by a Kestrel engine.

The Merlin 1C engine is a turbo pump fed engine, while the smaller Kestrel engine uses tank pressure to inject the fuel into its combustion chamber. In order to simplify the design, the Merlin engine uses the high-pressure kerosene to cool the combustion chamber and the nozzle. In addition, the engine uses the high-pressure kerosene for the hydraulic actuators, thereby eliminating the need for a separate hydraulic power system.

Credits: SpaceX

Falcon 1 is the first in a family of launch vehicles that SpaceX will build and operate. NASA awarded Commercial Orbital Transportation Services (COTS) funding to SpaceX to demonstrate delivery and return of cargo and potentially a human crew to the International Space Station (ISS). In order to achieve these goals, SpaceX is developing a bigger booster, Falcon 9, and a cargo and crew capsule, Dragon.

SpaceX holds a unique position in the launch vehicle market, being able to take over the delivery of supplies and human crews to the ISS, after the Space Shuttle’s retirement in 2010. For more information about SpaceX and its fleet of launch vehicles, check out their website.

In a previous post we presented the most common solution for power generation onboard unmanned spacecrafts (solar cells and secondary batteries) and mentioned some of the manned spacecrafts that employ this solution.

Credits: NASA

However, solar cells, in combination with secondary batteries, are not usable for missions beyond the asteroid belt, because there the sun’s energy becomes too diffuse. As deep space missions were designed, a new power source was required. The radioisotope thermoelectric generators, also known as RTGs, met the requirements for this kind of mission. RTGs are proven, compact, and reliable power sources that can produce up to several kilowatts of power and operate under severe conditions for many years.

RTGs convert the heat generated by a decay of radioactive fuel into electricity. There are two major components that RTGs consist of: the heat source that contains the radioactive material and a set of solid-state thermocouples that convert the heat energy to electricity. The principle that RTGs rely on is not a new discovery. In 1821, Thomas Johann Seebeck discovered the effect that bears his name and that allows us to convert heat directly into electricity using a simple and robust device. An electrical current is generated when two dissimilar electrically conductive materials are connected in a closed circuit and their junctions are kept at different temperatures. The heat generated by the radioactive decay is used to heat the hot junction of the thermocouple, and exposure to the cold outer space is used to maintain the temperature of the cold junction.

Credits: NASA

Over the years, RTGs have been used safely and reliably on many missions. Among these missions: some of the Apollo flights to the moon, the Pioneer spacecrafts, the Viking landers, the Voyager missions, the Galileo mission, the Ulysses mission, and the Cassini-Huygens mission. The present conversion efficiency achieved by the thermocouples is around 10%, and research continues in order to improve it. Because of the internal resistance and other losses, the overall RTG efficiency is typically 6-7%, which means that the amount of waste heat for every unit of electrical energy produced is quite large.

Even if the radioisotopes used present a loss in energy with time, the half-life of the radioisotopes is not a major life-limiting factor of current RTGs. Major life-limiting factors include the degradation of the thermoelectric elements and the breakdown of insulators because of temperature and radiation.

The radiation emissions from RTGs can damage the electronics onboard spacecrafts. This is why it is necessary to mount the units on booms at some distance from the body of the spacecraft or, at least, provide shielding of some sort in the on orbit configuration. One important thing to mention is that in the launch configuration, when the RTG boom cannot be deployed, the radiation exposure cannot exceed the inherent radiation tolerance of the onboard electronics.

There are two more solutions spacecraft engineers employ to generate power onboard spacecrafts and we will present them in our next post. Please come back later to read our conclusion to the series.

The conversations between the astronauts onboard the International Space Station and the flight controllers at the Mission Control are now being broadcast live on NASA’s website. The communications are available to the public 24 hours a day, seven days a week.

Credits: NASA

In order to open the audio stream, go to the NASA web page, click on the NASA TV(live) tab at the center of the page, and then click on the Shuttle and Station Audio link.

You will have to be patient because most of the time the broadcast is silent. I managed to catch 15 minutes of conversation this morning! The conversation was between NASA’s astronaut Gregory Chamitoff and the Mission Control in Houston.

Just to remind you, Gregory is also getting ready for the chess matches organized by NASA and the U.S. Chess Federation beginning on Monday, September 29th.

Carnival of Space #72 is hosted by Jennifer Ouellette at Twisted Physics. Check out the great articles from around the space blogosphere this week!

NASA’s return to the Moon requires careful preparation. Finding safe landing sites, locating potential resources, and taking measurements of the radiation environment are some of the tasks the Lunar Reconnaissance Orbiter (LRO) spacecraft will perform while in lunar orbit. LRO is an unmanned mission that will create a comprehensive atlas of the moon’s surface and resources.

The data gathered by LRO will be crucial in designing and building a permanent lunar outpost. The data will also be used to reduce the risk and increase the productivity of the future manned missions to the Moon.

The launch of LRO is scheduled for February 2009. An Atlas V rocket launched from the Kennedy Space Center will place the LRO on a transfer trajectory. After 4 days, the spacecraft will reach the Moon and after performing additional orbital maneuvers, it will move into its final orbit. The LRO’s final orbit will be a circular polar orbit 50 kilometers above the lunar surface.

Credits: NASA

The mission is designed to last for one year, with a possible extension. The total mass of the spacecraft is around 1,000 kilograms, of which 500 to 700 kilograms will be the fuel. The power is supplied by articulated solar arrays, and for the peak and eclipse periods a Li-Ion battery is used. The bandwidth of the communication link will be approximately 100-300 Mbps.

The LRO payload is comprised of six scientific instruments and one technology demonstration.

The Cosmic Ray Telescope for the Effects of Radiation (CRaTER) was built and developed by Boston University and the Massachusetts Institute of Technology in Boston. CRaTER will help explore the lunar radiation environment. The data gathered by measurements will help in the development of protective technologies that will keep future lunar crews safe.

The Diviner Lunar Radiometer Experiment (DLRE) was built and developed by the University of California, Los Angeles and the Jet Propulsion Laboratory in Pasadena, California. DLRE is capable of measuring surface and subsurface temperatures from orbit.

The Lyman-Alpha Mapping Project (LAMP) was built and developed at the Southwest Research Institute in San Antonio. LAMP will be used to map the entire lunar surface in the far ultraviolet spectrum.

Credits: NASA

The Lunar Exploration Neutron Detector (LEND) was developed at the Institute for Space Research in Moscow. This detector will create high-resolution maps of the hydrogen distribution and gather data about the neutron component of the lunar radiation.

The Lunar Orbiter Laser Altimeter (LOLA) was conceived and built at NASA’s Goddard Space Flight Center. LOLA will generate high-resolution three-dimensional maps of the moon’s surface.

The Lunar Reconnaissance Orbiter Camera (LROC), developed at Arizona State University at Tempe, will image the lunar surface in color and ultraviolet. LROC will be able to capture 1 m resolution images of the lunar poles.

The technology demonstration is called Mini-RF Technology Demonstration. The primary goal of this demonstration is to locate subsurface water ice deposits. The advanced single aperture radar (SAR) that will be used is capable of taking high-resolution imagery of the permanently shadowed regions on the lunar surface.

The data gathered by LRO will help us develop a better understanding of the lunar environment. This understanding is essential for a safe human return to the Moon and for the future exploration of our solar system.

After a short introduction to the power systems requirements and design factors, we will continue by covering the first solutions adopted by spacecraft designers: the batteries and the solar arrays (aka solar cells).

Credits: NASA

Batteries were used as a primary source of power onboard early spacecrafts. The obvious limitation is that batteries have limited energy storage capabilities and could not keep spacecrafts operational for more then a few days. Most space missions require a reliable power source running for a longer period of time.

Batteries remain the primary means of energy storage onboard spacecrafts. Batteries are divided into two major categories: primary batteries and secondary batteries.

Primary batteries offer higher energy and power densities but are not rechargeable. They are useful for one-time events such as expendable launch vehicle stages. Secondary batteries are rechargeable batteries.

Solar arrays are very well suited for long missions in space. The life expectancy of a solar cell power system is limited only by the degradation of its components. Spacecrafts operating for extended periods of time become feasible with the development of solar arrays. However, if only solar cells are used for generating power, spacecrafts that enter eclipse periods cannot employ only solar cells for power generation.

Credits: NASA

The first low-powered spacecraft designs were using the spacecraft skin for the solar cell deployment. In the case of drum-shaped spacecrafts, only about 40% of the arrays were illuminated by the Sun at any time. Because most of the time the available area on the fixed spacecraft structure is not enough from the standpoint of power requirements, deployable solar arrays are now used. The solar arrays of this type are deployed from the main structure after the spacecraft is injected into orbit.

The deployable panels are designed as extremely lightweight structures due to the fact that they are firmly locked to the spacecraft during the launch. In order to optimize the generation of power, these panels are designed to allow sun tracking.

Credits: NASA

Considering the limitations of the solar arrays, a reliable solution can be reached by employing solar cells and batteries at the same time. Solar arrays can generate power when direct sunlight is available in orbit, while rechargeable batteries can handle peak loads and provide power during eclipse periods. Solar panels and batteries in combination are a common solution used for the unmanned spacecrafts launched to date. The most notable exception is the deep space mission probes using radioisotope thermoelectric generators (we will cover them in a future post).

The early manned spacecrafts, including Mercury, some of the Gemini, and the Russian Vostok /Voshkod vehicles, used batteries. The Russian Soyuz employs solar cells and batteries similar to a typical unmanned spacecraft. The space stations built so far, Salyut, Skylab, Mir, and the International Space Station, have all used solar cells as the primary power source, having secondary batteries for load leveling and eclipse periods.

In the following posts we will see what solutions are available for missions that cannot rely on solar power as a primary source of energy.