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

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

Freethought Literature Translations

Some years back, I (lpetrich) tried to start a Freethought Literature Translation Project, to reach all those people who prefer languages other than English. I did not get much interest, however. But I am happy to report that some other people have been interested. Some of Ebonmuse’s fans have translated some of Ebon Musings: The Atheism Pages into various languages: French, Spanish, Portuguese, Greek, and Belarusian. So the more the better.

Daylight Atheism > New Translations on Ebon Musings

Beacon Library now at atheism.wikia.com

The Beacon Library has been at beacon.wiki-site.com but it is now gone from there. Some of its content is now at atheism.wikia.com, where it joins a lot of existing content.

Some of its content now also resides at some other wikis, Iron Chariots and RationalWiki.

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