ESA’s gravity mission GOCE

ESA’s Gravity field and steady-state Ocean Circulation Explorer (GOCE) has been developed to bring about a whole new level of understanding of one of the Earth’s most fundamental forces of nature – the gravity field.

Dubbed the ‘Formula 1′ of spacecrafts, this sleek high-tech gravity satellite embodies many firsts in terms of its design and use of new technology in space to map Earth’s gravity field in unprecedented detail. As the most advanced gravity space mission to date, GOCE will realise a broad range of fascinating new possibilities for the fields of oceanography, solid Earth physics, geodesy and sea-level research, and significantly contribute to furthering our understanding of climate change.

Although invisible, gravity is a complex force of nature that has an immeasurable impact on our everyday lives. It is often assumed that the force of gravity on the surface of the Earth has a constant value, but in fact the value of ‘g’ varies subtly from place to place. These variations are due to a number of factors such as the rotation of the Earth, the position of mountains and ocean trenches and variations in density of the Earth’s interior.

	GOCE to map gravity as never before

Over its lifetime of about 20 months, GOCE will map these global variations in the gravity field with extreme detail and accuracy. This will result in a unique model of the geoid, which is the surface of equal gravitational potential defined by the gravity field – crucial for deriving accurate measurements of ocean circulation and sea-level change, both of which are affected by climate change. GOCE-derived data is also much needed to understand more about processes occurring inside the Earth and for use in practical applications such as surveying and levelling.

GOCE takes six simultaneous measurements of the gravity field

Since the gravitational signal is stronger closer to Earth, the ‘arrow-like’, five-metre long GOCE satellite has been designed to cut through of what remains of the Earth’s atmosphere at just 250 km above the surface of the planet. This low-orbiting spacecraft is the first mission to employ the concept of gradiometry - the measurement of acceleration differences over short distances between an ensemble of proof masses inside the satellite.

GOCE is equipped with three pairs of ultra-sensitive accelerometers arranged in three dimensions that respond to tiny variations in the ‘gravitational tug’ of the Earth as it travels along its orbital path. Because of their different position in the gravitational field they all experience the gravitational acceleration of the Earth slightly differently. The three axes of the gradiometer allow the simultaneous measurement of six independent but complementary components of the gravity field.

Although the gradiometer forms the heart of the satellite, to measure gravity there can be no interference from moving parts so the entire spacecraft is actually one extremely sensitive measuring device.

GOCE is dedicated to measuring Earth’s gravity field and modelling the geoid with unprecedented accuracy and spatial resolution. Data from this advanced gravity mission will improve our knowledge of ocean circulation, which plays a crucial role in energy exchanges around the globe, sea-level change and Earth-interior processes. GOCE will also help to make significant advances in geodesy and surveying.

GOCE satellite

The sleek, elegant aerodynamic design of GOCE immediately sets it apart from most other satellites. Since it is vital to ensure that the measurements taken are of true gravity and not influenced by any movement of the satellite, this unique five-metre long arrow-shaped satellite has none of the moving parts often seen in other spacecraft. Therefore, the satellite together with its instrumentation actually forms a single composite gravity-measuring device.

The orbit of the satellite must be as low as possible to observe the strongest possible gravity-field signal – hence GOCE has been designed to skim above the Earth at a height of just 250 km. Its slim elongated form enables it to cut through the wisps of atmosphere that are still present at this height.

The need to fly low and be ultra-stable has lead to a novel satellite design that minimises air drag and torque and excludes mechanical disturbances. The result is a slim 5 metre-long satellite with a cross sectional area of about 1m2 and weighs in at about 1050 kg. The satellite is symmetrical about its horizontal plane and has two winglets that provide additional aerodynamic stability. Once in orbit, the same side of the satellite remains facing the Sun. The satellite is equipped with four body-mounted and two wing-mounted solar panels, which use triple junction Gallium Arsenide solar cells. Due to the orbit and satellite configuration, the solar panels will experience extreme temperature variations. The design has therefore had to include materials that will tolerate temperatures as high as 160°C and as low as -170°C.

One S-band communication antenna is mounted on each wing. One faces upwards and one downwards so that full spherical coverage is achieved. The wing that points towards space carries two GPS antennas.

Inside GOCE

Inside the satellite

The satellite consists of a central octagonal tube with seven internal floors that support the equipment and electronic units. Two of the floors support the gradiometer, which is mounted at the heart of the satellite close to its centre of mass. The spacecraft structure is built largely of carbon-fibre reinforced plastic sandwich panels to guarantee stable conditions under varying temperatures and at the same time to limit mass.

The satellite has to cope with large temperature variations - during nominal measurement modes eclipses last up to 10 minutes and during survival modes eclipses last up to 30 minutes. Temperature control is achieved mainly by passive means such as coatings and blankets and active control by heaters where necessary. The internal equipment is protected against the hot temperatures of the solar panels by multi-layer insulation blankets, which are positioned between the solar panels and the main body of the satellite.

The cold side, which faces away from the Sun, is used in part as a radiator to dissipate heat into space. All the external coatings, in particular those situated in the direction of flight, are protected against high atomic oxygen flux, which would otherwise erode unprotected materials very quickly at this low orbit. Due to its stringent temperature stability requirements (for the gradiometer sensor heads, in the range of milli-Kelvin) the gradiometer is thermally decoupled from the satellite and has its own dedicated thermal-control system.

Technical details

Mission details
Launch: 2009
Duration: about 20 months, including a 3-month commissioning and calibration phase, followed by science measurement phases adapted to a long-eclipse hibernation period.

Mission objectives
- to determine gravity-field anomalies with an accuracy of 1 mGal (where 1mGal = 10^–5 ms^–2).
- to determine the geoid with an accuracy of 1-2 cm.
- to achieve the above at a spatial resolution better than 100 km.

Mission orbit
Orbit: Sun-synchronous, near-circular, dusk-dawn, low-Earth.
Inclination: 96.7°
Measurement altitude: about 250 km
Hibernation altitude: above 270 km

Configuration
GOCE is a slim, octagonal spacecraft approximately 5 m long and 1 m in diameter. It is a rigid structure with no moving parts weighing about 1050 kg.

Payload
- gradiometer; 3 pairs of 3-axis, servo-controlled, capacitive accelerometers (each pair separated by a distance of about 0.5 m).
- 12-channel dual-frequency GPS receiver with geodetic quality.
- laser retroreflector enables tracking by ground-based lasers.

Launch vehicle
Rockot (converted SS-19), from Plesetsk, Russia.

Flight operations
Monitored and controlled by ESA-ESOC via the Kiruna ground station in Sweden and secondary ground station in Svalbard, Norway.

Data processing
- level-1b products generated by the Payload Data Ground Segment (PDGS) at ESA-ESRIN.
- level-2 products (including gravity-field models and precise GOCE orbits) generated by the High-level Processing Facility (HPF) - a European consortium of ten scientific institutes.

The Industrial Core Team comprises:
Thales Alenia Space (Italy) - satellite prime contractor
EADS Astrium GmbH (Germany) - platform contractor
Thales Alenia Space (France) - gradiometer
ONERA (France) accelerometer & system support

The Core Team leads a consortium of 41 companies distributed over 13 European countries.

Windows 7, codename Blackcomb is the next big Operating System in works at the Microsoft labs. Though a completely new product, it runs on the architechture of the earlier Windows Vista. So, Vista in essence is a stepping stone to something bigger, that is, Windows 7.

Windows 7 is a much needed upgrade for Windows Vista than a new OS.

In fact, what started out as Blackcomb in 2003, resulted in the release of its little brother Longhorn A. K. A. Windows Vista because of a delay in the original plans of Windows 7. But, Windows Vista laid a solid groundwork for Windows 7 to improve on. Windows Vista repaired many security holes found in Windows XP, but wasn’t the most comfortable OS to work with. Microsoft plans to address all the issues in their next OS.

Screenshot

So whats new in Windows 7?

Windows 7 includes a number of new features, such as advances in touch, speech, and handwriting recognition, support for virtual hard disks, improved performance on multi-core processors, improved boot performance, and kernel improvements.

Windows 7 adds support for systems using multiple heterogeneous graphics cards from different vendors, a new version of Windows Media Center, Gadgets being integrated into Windows Explorer, a Gadget for Windows Media Center, the ability to visually pin and unpin items from the Start Menu and Taskbar, improved media features, the XPS Essentials Pack being integrated, Windows PowerShell Integrated Scripting Environment (ISE), and a redesigned Calculator with multiline capabilities including Programmer and Statistics modes along with unit conversion.

Many new items have been added to the Control Panel including: ClearType Text Tuner, Display Color Calibration Wizard, Gadgets, Recovery, Troubleshooting, Workspaces Center, Location and Other Sensors, Credential Manager, Biometric Devices, System Icons, Action Center, and Display. Windows Security Center has been renamed the Windows Action Center (Windows Health Center and Windows Solution Center in earlier builds) which encompasses both security and maintenance of the computer.

The taskbar has seen the biggest visual changes, where the Quick Launch toolbar has been merged with the task buttons to create an enhanced taskbar or what Microsoft internally refers to as the “Superbar”. This enhanced taskbar also enables the Jump Lists feature to allow easy access to common tasks. The revamped taskbar also allows the reordering of taskbar buttons.

Screenshots have appeared demonstrating a new feature called ‘Peek’. Peek is a quick way of making all visible windows transparent for a quick look at the desktop. A Microsoft spokesman said that “this will be useful for users who want a quick look at the news” in reference to RSS gadgets on the desktop.

Unlike Windows Vista, window borders do not turn dark when maximized when Windows Aero is applied. Instead, it remains in Aero Transparency even when maximized in Windows 7.

For developers, Windows 7 includes a new networking API with support for building SOAP based web services in native code (as opposed to .NET based WCF web services), New features to shorten application install times, reduced UAC prompts, simplified development of installation packages, and improved globalization support through a new Extended Linguistic Services API.

At WinHEC 2008 Microsoft announced that color depths of 30-bit and 48-bit would be supported in Windows 7 along with the wide color gamut scRGB (which for HDMI 1.3 can be converted and output as xvYCC). The video modes supported in Windows 7 are 16-bit sRGB, 24-bit sRGB, 30-bit sRGB, 30-bit with extended color gamut sRGB, and 48-bit scRGB.

Also the beta version is out!

Download

Ever imagined a speed of 250 kmph or 0-100 kmph in 4 seconds without burning fuel? This car, could be a reality, according to two 18 year old boys from Hardward-Westlake High School in California, USA. This car utilizes solar panels, airflow recovery and other modern technologies to create this revolutionary eco-friendly supercar, christened the Formula AE.

The two creators, Maxx Bricklin and Rory Handel, have in fact started a company called RORMaxx, that is developing the prototype of this student built wind-assisted vehicle.

The vehicle utilizes lightweight aluminium and super strong steel in a Formula 1 style shell. The bodywork sports paper thin solar panels that could fully recharge itself in 1 and a half hours. The creators claim that with the help of a new prototype battery this time could be reduced to 6 minutes. A full battery can power this vehicle for 320 km.

The car initially starts with the help of the solar power and as it moves, it will take the help of the air flow around it to power it. The wind around it will rotate the four strategically placed turbines, which will be pleasing to the eye and will provide the thrust once in speed. A generator will convert the energy from the turbines and thus power the vehicle.

Providing rapid acceleration is often tough in electric cars, but with the help of modern ultra capacitors, the electricity will be stored and can be recalled in rapid succession with the help of the ultra capacitors which are capable of charging and discharging very quickly.

Although still in prototype stage and no plans of commercial release as yet, this green car is aimed at auto enthusiasts looking for a greener road. It is estimated to be priced around $80,000 to $1,50,000.