Tag Archives: space travel

Apollo guidance computer, 1969

I watched a 1969 film on YouTube about the inner workings of the Apollo Guidance Computer that helped put a man on the moon. The navigation details are fascinating. I had no idea that the astronauts used a sextant to shoot bearings to stars!

Integrated circuits vintage

7400The film shows logic gates that are packaged in TO cases. (TO cases are small diameter metal cans used to house transistors.) By 1967 these would have been obsolete. In 1967 we were already developing products with readily-available quad NAND gates (using TTL — transistor-transistor logic). These 7400-series parts were packaged in 14-pin plastic DIPs (Dual In-line Packages). The higher spec’d 5400 series were packaged in ceramic DIPs. I’d guess that the Apollo Guidance Computer (AGC) in the film was designed well before that — maybe 1964 or even earlier.

I’m a little confused. The Wikipedia description of the AGC states that it exclusively used Fairchild resistor-transistor logic (RTL) dual NOR gates in a flat-pack. Hmmmm. That’s not what the film shows.

In any case, both the single logic gate in a can and the dual RTL NOR gates in a flat pack would have been obsolete by 1969. I would have thought that NASA projects would have used the latest technologies, not 5 year old technologies. I guess that subsystems within large projects such as Apollo acquire momentum, and once they’ve been proven, the “If it ain’t broke, don’t fix it” motto applies.

It’s an interesting film, regardless.

SpaceX rocket takes off and returns to launch pad

This is an amazing video.

Elon Musk’s SpaceX has been working on a system that will return the launch missile intact to its launch pad, ready for the next launch. This video clip was taken two days ago at their Texas launch facility. They moved the rocket horizontally 100 meters, hovered, and tilted it 30 degrees from vertical.

This is a step toward the goal of using Grasshopper to boost succeeding stages to a high altitude before it returns to its launch pad.

SpaceX CEO Elon Musk’s reasoning: This booster, while “cheap”, costs 50 to 60 million dollars. The fuel costs about two hundred thousand dollars. If we can re-use the booster a thousand times and amortize its capital cost over a thousand launches, the cost per launch will be low.

This is a triumph of servo system design and high-pressure high-flow rate fluid control. The trick is to make the rocket’s engine respond quickly while keeping the servo loop stable. I imagine that the signals from many sensors of all types are monitored by the guidance computer. The resultant control of thrust is impressive.

Flash Gordon

Last week I watched Flash Gordon on Youtube. It’s a gorgeous black and white print of all 13 episodes of the 1936 space opera set in the twenty-second century starring Buster Crabbe. The sets and costumes are ridiculous, and so is the plot, but it was great fun. I liked the snapping, crackling electrical gadgets in the laboratory of Ming (The Merciless), emperor of the planet Mongo.

Ming and the boys watch his big-screen Spaceograph
Ming and the boys watch his wide-screen Spaceograph

This movie is part of a tradition harking back to Wagner’s Siegfried, Sir Gawain, and Beowulf. Scenes from the radium furnace room are low-rent versions of Fritz Lang’s 1926 Metropolis, and the adventures of a hero and a princess from another planet were told again in 1977’s Star Wars. George Lucas borrowed the same imaginative wipes between scenes.

Even the comments are entertaining:

  • Funny how Ming dresses all his men in hotpants and tights!
  • Considering Mongo is such a technically advanced planet it’s surprising nobody thought to invent trousers.
  • Dale Arden must have some heavy pheromones . . . first Ming wants her as his bride, and now King Vulcan . . . it must be the blonde hair.
  • The controls on my car’s a/c are more complicated than those on Dr. Z’s lab equipment

As I said, it’s great fun. I give it two thumbs up.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Tim Wu hosts a new podcast

Slate is hosting a new podcast by Tim Wu, author of The Master Switch: The Rise and Fall of Information Empires. (He coined the phrase “net neutrality”. His thesis is that information industries naturally move from open to closed models as they mature — at the expense of the consumer.) His podcast is called Stranger Than Fiction and is available on Slate. I found it on tunein:rps201305u22_193841

Law professor and author Tim Wu talks to leading science fiction writers about whether we're already living in the future.

Recent guests:

  • Alastair Reynolds
  • Margaret Atwood
  • Cory Doctorow
  • Neal Stephenson

Since age 14, I’ve had little interest in science fiction, but these interviews reveal fascinating ideas about SETI, communication across vast distances (how about using neutrinos rather than electromagnetic waves?), privacy, and intellectual property issues today.

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Extending the Internet off-Earth

Tracy Caldwell Dyson in Cupola ISS

Self portrait of Tracy Caldwell Dyson in the Cupola module of the International Space Station observing the Earth below during Expedition 24.
photo: NASA/Dyson
Providing Worldwide Web access to the International Space Station is one thing.

Providing the ability to browse the web from Mars and beyond will be quite another.

Today, the crew aboard the International Space Station (ISS) can browse the web about as easily as you or I can. It’s relatively easy to provide web access, because the ISS orbits at an altitude of less than 300 miles, so packets traverse the radio link quickly and then they travel on terrestrial fiber. [Description of NASA’s Disruption Tolerant Networking for Space Operations (DTN)]

In the future, browsing the web across millions of miles will be tough, because of network latency, which is the transit time required for a packet to travel from sender to receiver, and good old multi-path RF (radio frequency) signal problems familiar to mobile radio users. Doppler shift may also cause trouble.

When we earthlings browse the web, our computer converses with at least two servers: our DNS (domain name system) server, and the desired web server. These conversations take place at nearly the speed of light — 186,000 miles per second. Typical latency across a few hundreds or thousands of miles is so small that we’re barely aware of these conversations.

Once we leave the realm of Earth, though, long distance radio links will cause long network latencies. The distance to Mars varies, but if we assume a minimum of 40 million miles, network latency will approach 4 minutes. (Our mechanical hero, Explorer 1, is 11 billion miles away. Radio signals from it require 14 hours to reach us.) Because of relative movement between transmitter and receiver, there’s bound to be transmission errors, and if just one garbled packet must be resent, it will require 8 minutes.

Some form of FEC (forward error correction) will help, but impose its own overhead. I suppose that frequency diversity may help the multi-path problem, but it will impose a complexity and power-consumption cost. I’ve never tried to use a web browser on such a sluggish network, but I’m sure that it’s frustrating, if not impossible. To some extent, the users could be helped by installing local DNS and caching proxy servers on Mars, but this would work only for frequently visited static pages.

RF signal latency will either halt exploration or force colonization

The Landing of Columbus at San Salvador, October 12, 1492.

Space explorers will eventually need to create their own little colonies far removed from Earth — sort of what the colonists did in the new world. Not only will their new colonies include their own local networks, but quite likely their own dialects, and eventually their own languages. As mankind explores the solar system and beyond, it’s likely that the explorers and colonists will develop their own amenities and technologies. Will their bodies evolve to adapt to their new environments? If so, at what point does it make sense to define them as something other than Homo Sapiens?

The next question is, Are we descendants of colonists from a distant planet?

Visit my website: http://russbellew.com
© Russ Bellew · Fort Lauderdale, Florida, USA · phone 954 873-4695

Voyager 1 is, like, far out.

Voyager 1 Schematic
schematic: NASA
Voyager 1 is leaving the solar system. That’s 11 billion miles from Earth!


NASA announced that Voyager 1, which weighs about 1500 pounds and was launched in 1977, is apparently at the edge of the solar system and is now entering interstellar space. It’s not likely to collide with any stars: the nearest star is about 4.5 light-years away, and at Voyager’s current velocity (about a million miles a day), it would require 40,000 years to travel that far. (Outer space is huge beyond my imagination.) In any case, it’s not headed in that direction.

It’s impossible to learn about Voyager 1 and its sister, Voyager 2, without being amazed. It was originally projected to have a lifetime of perhaps 12 years. It’s been almost 35 years since its launch, and it’s still transmitting data back to Earth, 24×7. Its transmitter output power is a puny 20 Watts!

Meanwhile, back on planet Earth, for about 8 hours every day, the huge 70 meter diameter dishes of the Deep Space Network (DSN) listen to the incoming data from Voyager 1 at the slow speed of 160 bps (bits per second). (The old Telex system operated at 110 bps and the first modem that I had operated at 300 bps, c 1978.) These bits now require about 14 hours to travel the 11 billion miles from Voyager 1 to Earth.

Very rarely, commands are transmitted from Earth to Voyager 1.

If any of this captures your interest, you’ll find much more detail in Wikipedia:

Everyone who was or is associated with this project should be proud of this amazing achievement. And just in case either Voyager is ever found in a scrapheap in Alpha Centauri, it can serve as a jukebox to play, among other selections, music by Chuck Berry and Mozart. (What, no Bach?!)