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By tchall, September 13, 2009 6:09 AM

Communication modules

Radiation-Hardened, High-Data-Rate Ka-Band Modulator and Transmitter

Technology Details
NASA requires that all future “near-Earth” missions (near-Earth defined as any spacecraft within one million kilometers of Earth) requiring more than 10 MHz of downlink data bandwidth operate in the 25.5 to 27.0 GHz band. Developed for NASA’s Solar Dynamics Observatory mission and adapted for the Lunar Reconnaissance Orbiter mission, this spaceflight
transmitter meets and/or exceeds all of NASA’s performance requirements and is the first to be designed for Ka-band.
How it works
This design consists of a phase-locked oscillator; a high-bandwidth, QPSK vector modulator; a medium-power, Ka-band solid-state power amplifier, a highly efficient DC-DC converter; and radiation-hardened, high-rate driver circuitry that receives I and Q channel data. The radiation-hardened design enables the Ka-band communications downlink system to transmit
130 Mbps of data (300 Msps after data encoding) to the ground system. The low error vector magnitude of the modulator reduces the implementation loss of the transmitter in which it is used, thereby increasing the overall communication system link margin.
Why it is better
Prior high-rate transmitters exist for X-band (~8 GHz) and Ku-band (~15 GHz), but those can’t take advantage of the Ka-band frequencies. This new Ka-band transmitter and modulator offer several unique design features that improve upon the current state of the art and enable the use of this high-frequency radio band. One design element that sets this technology apart is its unique packaging scheme and mechanical design that creates a compact, back-to-back cavity enclosure that utilizes die attach, substrate attach, wire bonding, and conventional surface mount technologies.

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By tchall, September 13, 2009 6:09 AM

Robotics
Rover
Etc

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By tchall, September 7, 2009 10:12 AM

Escape Velocity and Escape Speed

Escape Velocity and Escape Speed are two similar yet different terms.
This surface escape velocity is the speed required for an object to leave a planet if the object is simply projected from the surface of a planet and then left without any more kinetic energy input.
In practice the vehicle’s propulsion system will continue to provide energy after it has left the surface.

A planet has mass M (Earth 6.0×10²⁴ kilograms), and a planet has gravity and the object is located a distance from the center of the planet or planets radius r (Earth’s radius is 6.4×10⁶ meters) and the object you are trying to project has a mass m.

Thus

v_{e = EQUATION GOES HERE}

Escape Velocity

Newtons example of escape velocity of a projectile

This more or less refers to projectiles, and the initial speed required of them to escape the gravitational forces of a planet.
Take for example a rile and if you were to fire it upwards, what would be the required initial velocity required of the bullet to escape the earths gravity.
i.e. so that gravity will never manage to pull it back.

This would depend on the mass of the planet and the distance from the center point.

On the surface of the Earth, the escape velocity is about 11.2 kilometers per second, which is approximately 34 times the speed of sound (mach 34) and at least 10 times the speed of a rifle bullet. However, at 9,000 km altitude in “space”, it is slightly less than 7.1 km/s.

If an object moves fast enough it can escape a massive object’s gravity and not be drawn back toward the massive object.

More specifically, this is the initial speed something needs to escape the object’s gravity and assumes that there is no other force acting on the object besides gravity after the initial boost.

This is not the case with rockets.  Their intial speed is 0 km/s, and then this is gradually accelerated as they continue to thrust upwards.

Rockets leaving the Earth do not have the escape velocity at the beginning but the engines provide thrust for an extended period of time, so the rockets can eventually escape. The concept of escape velocity applies to anything gravitationally attracted to anything else (gas particles in planet atmospheres, comets orbiting the Sun, light trying to escape from black holes, galaxies orbiting each other, etc.).

How do you do that?

Find the escape velocity from the surface of the Earth. Using the acceleration of gravity, you can find that the Earth has a mass of 6.0×1024 kilograms. The Earth’s radius is 6.4×10 6 meters. Since the mass and distance from the center are in the standard units, you just need to plug their values into the escape velocity relation.
The Earth’s surface escape velocity is Sqrt[2× (6.7×10-11) × (6.0×10 24)/ (6.4×10 6)] = Sqrt[1.256×10 8] = 1.1×104 meters/second (= 11 km/s).

Here are some other surface escape velocities: Moon = 2.4 km/s, Jupiter = 59.6 km/s, Sun = 618 km/s.

Formula
Mass of central object = [(orbital speed)2 × distance)/G.
Mass of central object (Kepler's 3rd law) = (4p2)/G × [(distance)3/(orbital period)2].
Orbital speed = Sqrt[G × Mass / distance].
Escape velocity = Sqrt[2G × Mass / distance].

Escape velocity relative to Equator and Spin of the Earth

The escape velocity relative to the surface of a rotating body depends on direction in which the escaping body travels. For example, as the Earth’s rotational velocity is 465 m/s at the equator, a rocket launched tangentially from the Earth’s equator to the east requires an initial velocity of about 10.735 km/s relative to Earth to escape whereas a rocket launched tangentially from the Earth’s equator to the west requires an initial velocity of about 11.665 km/s relative to Earth. The surface velocity decreases with the cosine of the geographic latitude, so space launch facilities are often located as close to the equator as feasible, e.g. the American Cape Canaveral (latitude 28°28′ N) and the French Guiana Space Centre (latitude 5°14′ N).

Gravitational Space Wells

Comments (1)

By tchall, September 7, 2009 10:11 AM

Distance to moon

The average distance to the Moon is 382,500 km.
The distance varies because the Moon travels around Earth in an elliptical orbit.

At perigee, the point at which the Moon is closest to Earth, the distance is approximately 360,000 km.

At apogee, the point at which the Moon is farthest from Earth, the distance is approximately 405,000 km.

Diameter of the Moon and Earth

The Earth’s diameter as 12,756 km and the Moon’s diameter as 3,476 km.

Therefore, the Moon’s diameter is 27.25% of Earth’s diameter.
An official basketball has a diameter of 24 cm. This can serve as a model for Earth.

A tennis ball has a diameter of 6.9 cm which is close to 27.25% of the basketball.
(The tennis ball is actually 28.8% the size of the basketball.)

These values are very close to the size relationship between Earth and the Moon.
The tennis ball, therefore, can be used as a model of the Moon.

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By tchall, September 7, 2009 10:08 AM

Maria (dark areas) and Terrae (light areas)

Full Moon from Northern Hemisphere

You will notice when looking at the moon’s surface dark and light areas.
The dark areas are called maria. There are several prominent maria.

• Mare Tranquilitatis (Sea of Tranquility): where the first astronauts landed
• Mare Imbrium (Sea of Showers): the largest mare (700 miles or 1100 kilometers in diameter)
• Mare Serenitatis (Sea of Serenity)
• Mare Nubium (Sea of Clouds)
• Mare Nectaris (Sea of Nectar)
• Oceanus Procellarum (Ocean of Storms)

The remainder of the lunar surface consists of the bright hilly areas called terrae.
These highlands are rough, mountainous, cratered regions.

The Apollo astronauts observed that the highlands are generally about 4 to 5 km (2.5 to 3 miles) above the average lunar surface elevation, while the maria are low-lying plains about 2 to 3 km (1.2 to 1.8 miles) below average elevation.

The Moon makes a complete orbit around the Earth every 27.3 days (the orbital period), and the periodic variations in the geometry of the Earth–Moon–Sun system are responsible for the phases of the moon, which repeat every 29.5 days (the synodic period).

Sides of the Moon

Locked Lunar Phase with earth

The Moon is in synchronous rotation, which means it rotates about its axis in about the same time it takes to orbit the Earth. This results in it keeping nearly the same face turned towards the Earth at all times. The Moon used to rotate at a faster rate, but early in its history, its rotation slowed and became locked in this orientation as a result of frictional effects associated with tidal deformations caused by the Earth.

The side of the Moon that faces Earth is called the near side, and the opposite side the far side. The far side is often inaccurately called the “dark side,” but in fact, it is illuminated exactly as often as the near side: once per lunar day, during the new moon phase we observe on Earth when the near side is dark. The far side of the Moon was first photographed by the Soviet probe Luna 3 in 1959. One distinguishing feature of the far side is its almost complete lack of maria.

Gravity of the Moon and Mass Concentration

Mass concentration or mascon is a region of a planet or moon’s crust that contains a large positive gravitational anomaly.
In general, the word “mascon” can be used as a noun to describe an excess distribution of mass on or beneath the surface of a planet (with respect to some suitable average), such as Hawaii. However, this term is most often used as an adjective to describe a geologic structure that has a positive gravitational anomaly, such as the “mascon basins” on the Moon.

Type examples of mascon basins on the Moon are the Imbrium, Serenitatis, Crisium and Orientale impact basins, all of which possess prominent topographic lows and positive gravitational anomalies. Examples of mascon basins on Mars include the Argyre, Isidis, and Utopia basins. Theoretical considerations imply that a topographic low in isostatic equilibrium would exhibit a slight negative gravitational anomaly. Thus, the positive gravitational anomalies associated with these impact basins indicate that some form of positive density anomaly must exist within the crust or upper mantle that is currently supported by the lithosphere. One possibility is that these anomalies are due to dense mare basaltic lavas, which might reach up to 6 kilometers in thickness for the Moon. However, while these lavas certainly contribute to the observed gravitational anomaly, uplift of the crust-mantle interface is also required to account for its magnitude. Indeed, some mascon basins on the Moon do not appear to be associated with any signs of volcanic activity, suggesting that the mantle uplift might even be super-isostatic (that is, uplifted above its isostatic position). It should be noted that the huge expanse of mare basaltic volcanism associated with Oceanus Procellarum does not possess a positive gravitational anomaly.

The lunar mascons alter the local gravity in certain regions sufficiently that low and uncorrected satellite orbits around the Moon are unstable on a timescale of months or years. This acts to distort successive orbits, causing the satellite to ultimately impact the surface. The lunar mascons were discovered by Paul M Muller and William Sjogren of the NASA Jet Propulsion Laboratory (JPL) in 1968^[1] from analysis of the highly precise navigation data from the unmanned pre-Apollo Lunar Orbiter spacecraft. At that time, one of NASA’s highest priority “tiger team” projects was to explain why the Lunar Orbiter spacecraft being used to test the accuracy of Project Apollo navigation were experiencing errors in predicted position of ten times the mission specification (2 kilometers instead of 200 meters). This meant that the predicted landing areas were 100 times as large as those being carefully defined for reasons of safety. Lunar orbital effects resulting from strong gravitational perturbations were ultimately revealed as the cause. William Wollenhaupt and Emil Schiesser of the NASA Manned Spacecraft Center in Houston then worked out the “fix” that was first applied to Apollo 12 and permitted its landing within 300 meters of the target, the previously-landed Surveyor 3 spacecraft.

Specifications
Diameter    3476 km, (0.27 x Earth’s)
Average Distance from Earth    384400 km
Temperature    Day:123°C Night: -233°C
Atmosphere    minimal – none
Magnetism weak (probably no significant iron core)
Time to orbit Earth    27.322 days
Time to spin once    27.322 days
Gravity    1/6 (0.16) of Earth’s