The Last Space Shuttle Flight: an End of an Era

Last Friday, as I write this, the space shuttle Atlantis had returned from its final mission, the final mission of the Space Shuttles. This brings to a close the Shuttle era of US spaceflight, an era which has been most disappointing. The idea of the Shuttle was a legitimate one, to try to reuse as much as possible of one’s rocket to avoid having to build one each time. However, it required so much maintenance that it was not much cheaper than traditional expendable rockets, if not more expensive. Instead of costing $50 million per flight, it cost $450 million. The Shuttles also had two failures which shut down the program for 2 1/2 years each time, and while they were flying, they only had 5 launches/year.

Automated spacecraft have repeatedly proven their worth. They can easily tolerate vacuum, ionizing radiation, and extreme heat and cold, they can be powered by sunlight or radioactive decay, they can keep going for years, and we do not have to try to bring them back. In fact, some spacecraft have been deliberately crashed into celestial objects as part of their missions, like the later Ranger spacecraft on the Moon. Spacecraft have now visited all the planets and their larger satellites, and also some asteroids and comets.

They do have some important deficiencies, however. They have hardly any onboard intelligence, and they usually have no manipulative ability. That means that they must receive very explicit instructions, and that they usually have little or no self-repair capability. For many applications, needing explicit instructions is not much a problem, but that cannot be said of planetary-surface exploration.

Real-time teleoperation is only feasible when the communication round-trip time is less than a few seconds. The Moon’s round-trip time is 2 1/2 seconds, making it borderline. Mars is much worse, with round-trip times ranging from 6 to 45 minutes, and averaging at 30 minutes. The operators of the Mars rovers plan those vehicles’ next actions and then upload their instructions to those vehicles. Instructions like move or turn or take pictures or move the arm or operate various instruments.The outer planets are even worse. Jupiter’s round-trip time is 1 1/2 hours, Saturn’s is 2 1/2 hours, Uranus’s 5 hours, Neptune’s 8 hours, and Pluto’s 11 hours — nearly half a day.

What next for NASA’s astronauts? Cadging rides on Russia’s Soyuz spacecraft until NASA has an alternative ready. An alternative much like NASA’s earlier Apollo spacecraft and the Soyuz spacecraft itself — a small spacecraft atop an expendable rocket. Back to square one. But at least NASA will not have to support the Shuttles any longer.

How to Avoid Repeating the Debacle That Was the Space Shuttle | Space Flight | DISCOVER Magazine
Driving the Mars Rovers | Linux Journal

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Dawn spacecraft now orbiting asteroid Vesta

On July 16, the Dawn spacecraft went into orbit around the asteroid Vesta, the first spacecraft ever to go into orbit around an asteroid. Dawn has returned pictures like NASA – All Eyes on Vesta. It has a typical asteroid appearance, cratered and lumpy, though it is more spherical than the smaller asteroids. It also has some odd grooves.

Dawn is powered by ion engines, which make very fast exhaust (30 km/s), and which are powered by the spacecraft’s solar panels. This enables it to carry much less fuel than what it would otherwise need. By comparison, its booster rocket, the Delta II, has much slower exhaust, at 3 km/s. By simple Newtonian mechanics, that means needing over 13 times less fuel. But the engines have VERY low thrust, accelerating the spacecraft from 0 to 60 mph in 4 days. By comparison, a fully-loaded Delta II can go 0 to 60 mph in 2 seconds.

Not surprisingly, Dawn has taken a long time to arrive; it was launched nearly 4 years ago. Even so, it flew by Mars 1 1/2 years after launch to get a gravity assist. It will stay at Vesta for a year, then depart for the asteroid Ceres, arriving there 2 1/2 years later.

In other spacecraft news, the MESSENGER spacecraft went into orbit around Mercury last March, and it has been returning lots of pictures and other data ever since. It was launched 7 years ago, and it flew by the Earth once, Venus twice, and Mercury three times to avoid consuming a lot of fuel.

NASA – NASA’s Dawn Spacecraft Enters Orbit Around Asteroid Vesta
The Prius of Space – NASA Jet Propulsion Laboratory

Happy Discovery Birthday, Neptune!

It’s the first anniversary of the discovery of Neptune. The first Neptune-year anniversary; one Neptune year is about 164.79 Earth years.

This planet was discovered as a result of some astronomers discovering that planet Uranus’s observed positions did not quite match its calculated ones. Urbain Leverrier and John Couch Adams decided that there was an additional planet pulling on Uranus, and they tried to predict its position. In 1846, some British astronomers were already searching, but without success. Leverrier tried to interest some French astronomers, also without success, but he was more successful with Johann Gottfried Galle at Berlin. On September 24th that year, Galle succeeded, finding the planet 1 degree from Leverrier’s calculated position.

After its discovery, various astronomers extrapolated Neptune’s position backwards, and discovered that some other astronomers had seen it without recognizing it, including Galileo.

When William Lassell learned of this discovery, he looked for moons of that planet, discovering Triton 17 days after Neptune itself. Neptune’s other moons are much smaller; the next moon discoveries were in 1949 and 1981.

The only spacecraft to visit Neptune has been Voyager 2 in August 1989. That spacecraft returned pictures of Neptune itself, several Neptune moons, and some Neptune rings. Neptune is bluish with white cloud streaks; it has big storms like the Great Dark Spot. Triton’s surface is icy, with nitrogen geysers.

BBC News – Neptune’s birthday and a beautiful piece of maths
Discovery of Neptune
Happy Anniversary, Neptune!
Neptune Completes First Orbit Of The Sun Since Its Discovery By Humans | SpaceRef – Your Space Reference

LHC reaches its data-production target for 2011

The Large Hadron Collider has reached its data-production target for 2011, 1 inverse femtobarn of proton-proton collisions, or 70 trillion of them. It has performed so well that it will likely make 4 more inverse femtobarns before the end of this year.

This will be enough to see the more distinctive decay signatures of various possible particles — if they exist. Particles like the Higgs particle and supersymmetric particles, which are missing pieces of the Standard-Model puzzle. These particles are either (1) very massive or else (2) have decays in which the more likely modes are difficult to distinguish from other events. For instance, the easiest-to-see decay modes of the Higgs particle are expected to be two-photon ones, but those are expected to happen only once in every 10,000 decays or so.

So the next several months could be very interesting times for particle physicists. From the LHC’s rich harvest of data, they will either get evidence of some interesting new particles, or they will rule out those particles’ existence at accessible energies.

Keith Porteus Wood at the UN today

Wood is addressing the United Nations Human Rights Council, speaking on behalf of the International Humanist and Ethical Union (IHEU) about child abuse in the Catholic Church.

RichardDawkins.net forum to close

Hello Everyone,

Just a public service announcement here. For those who haven’t heard, the RichardDawkins.net forum is closing down – in its current form at least. You can see the announcement made by forum staff here.

The current version of the forum is apparently remaining in read-only format for 30 days, so if you want to archive any of it, or download any posts you have made, or private messages in your inbox, now is the time to do it.

The Berlin Dominoes

This is such a cool way to mark the 20th anniversary of the fall of the Berlin Wall! Kids from all around the world painted giant foam dominoes, which were set up along the route of the Wall and let topple earlier today – a really imaginative way to celebrate the anniversary of an important milestone of freedom.