The Deep Space Network, Part II

Two weeks ago I asked the question: how do we communicate with spacecraft operating around our solar system and beyond? The short answer is that we listen and talk to these probes via a network of giant (up to 230 feet in diameter!) radio telescopes.

The Green Bank radio telescope in wild, wonderful West Virginia.
Source: National Radio Astronomy Observatory.

Even knowing that we have dozens of large dish antennae able to work together to receive and transmit data, it is still amazing to me that we can communicate with, for example, Voyager 1. That little spacecraft is 17 LIGHT HOURS away from Earth! How do you receive a signal sent by a small transmitter hundreds of millions of miles away?

At this point, there are only two ways to communicate with the Voyagers. Our largest antennae, the 230 foot diameter dishes, are powerful enough to talk to the craft. Or, multiple dishes arrayed together can communicate with the Voyagers. Arraying dishes means aligning individual dishes so that they work together,  functioning as an even more powerful device, able to separate the weakest signals from background interference. You can array two dishes at the same Deep Space Network location. You can also array dishes at different locations. For example, dishes at the Very Large Array facility in New Mexico can work together with the dishes at Goldstone, receiving signals that would be too weak for one dish or one facility alone to discern.

Jodie Foster, putting the Very Large Array to good use.
Source: on-walkabout.com.

According to the Deep Space Network's operations manager, Jim Hodder, recent innovations made to the Network have further improved our ability to talk to the Voyagers. For example, we can now cool a dish antenna's receivers down to near absolute zero (-460 degrees Fahrenheit). This reduces interference with Voyager's radio signal, because any heat above absolute zero knocks electrons out of their lowest energy state orbits, just like radio waves from a spacecraft knock electrons out of their lowest energy state orbits. Less heat means less extraneous movement by electrons. Therefore, it's easier to pick out the one distant radio signal you're looking for.

Voyager 1, back when it was 17 light hours closer to Earth.
Source: Wikipedia.

When the Voyagers were launched in the late 1970s, we would likely not have been able to communicate with a spacecraft 17 light hours away. But now, it appears that the Voyagers will run out of the power needed to transmit messages before they leave the range of our radio telescopes!

A Voyager at the edge of the solar system.
Source: Space.com.

There's one other neat fact I've learned about communicating with spacecraft around the solar system. As I mentioned back in my first Deep Space Network post, there are three human-made satellites (Mars Odyssey, Mars Reconnaissance Orbiter, and Mars Express) orbiting Mars right now. As a result of this infrastructure in Mars orbit, our communications with the Curiosity rover are a bit more advanced than for the average interplanetary mission.

The base of Mount Sharp, as viewed by Curiosity.
Source: NASA.

In total, Curiosity has three methods of communicating with its human friends:

One, Curiosity can transmit signals directly to the Deep Space Network through a low-gain antenna. This antenna sends and receives data a slower rate in every direction, so that Curiosity doesn't have to point its antenna directly at Earth. Curiosity uses this antenna to transmit information, and, more often, to receive information.

Two, Curiosity also has a high-gain antenna that it can point at Earth to broadcast information directly there. This can send data at a faster rate than the low-gain antenna. Curiosity uses this antenna most often when it is receiving instructions from scientists on Earth.

Three, Curiosity usually communicates with Earth indirectly, via our Martian satellites! It can send and receive information to and from the Mars Reconnaissance Orbiter, Mars Global Surveyor, or Mars Odyssey via a UHF (short-range) antenna.

The deck of Curiosity, with the low-gain and high-gain antennae visable.
Source: JPL.

This third method of communication is particularly useful. Curiosity expends less energy to broadcast to our Martian satellites than to Earth, since the satellites are less than 300 miles away when passing overhead of the rover. But more importantly, the satellites enable communication with the rover much more often. Mars, like Earth, rotates approximately every 24 hours, and thus half the time the rover does not have a direct line of sight to Earth. So for about 12 hours out of every Martian day, Curiosity cannot use its high or low gain antennae to transmit data directly to Earth. But instead of only having access to Curiosity for only half of every day, thanks to the the three Martian satellites, JPL can contact the rover for about 16 hours out of any given day!

An avalanche on Mars, as seen from the Mars Reconnaissance Orbiter.
Source: Wikipedia.

As a result of these three methods for accessing the Deep Space Network, we can communicate with Curiosity across tens of millions of miles of outer space at up to half the speed of a typical modem in someone's house! 

Sources: io9, JPL, Wikipedia; Space Today; NASA; Popular Mechanics.

A Cold War instead of a Space War

The International Space Station has pretty much everything you could possibly need while in low Earth orbit. Including its solar panels, it is roughly the size of a (U.S.) football field. Inside, it has as much pressurized space as a Boeing 747 jet. ISS residents have access to two bathrooms, a gym, and, in case they're feeling homesick, a giant window for Earth-gazing.

Astronaut Tracy Dyson, floating in front of the cupola.
Source: Wikipedia.

The menu for the six astronauts living aboard the ISS is varied and tasty: brownies, sushi, fajitas, and cherry-blueberry cobbler. You have high-speed internet access, your own little bedroom, and once in a while, an ice cream social. 

Half of the ISS Expedition 26 crew, peeking out of their "rooms" on Christmas morning.
Source: Onorbit.

But... a 1970s Soviet military space station, the Salyut 3, has got the ISS beat in one strange way. What does Salyut 3 have that the ISS is missing? A 23 millimeter automatic cannon, mounted to the long axis of the station.

A Nudelman-Rikhter "Vulkan" gun.
Source: dailycosmicnews.blogspot.com.

Reports on the cannon, and whether it was ever fired, are a bit sketchy. Some sources identify the gun not as a Nudelmann 23 millimeter auto-cannon, but a Nudelmann NR-30 30 millimeter cannon. Despite the gun's existence being declassified after the Cold War ended, it seems that most of the information the world has on Earth's first true space weapon is hearsay and rumor.

However, the reason for the gun is clear. Salyut 3 was a military space station, meant to be crewed by air force officers and tasked with spying. The station orbited at a low altitude to aid in photographing Earth's surface (about 50 miles below there the ISS usually sits). According to Russian sources, the auto-cannon was installed "for defense against U.S. space-based inspectors/interceptors."

Salyut 3.
It is thought that the dish antenna at the bottom right is for transmitting encrypted data (i.e., spy photographs).
Source: astronautix.com.

The gun could only be pointed at a target by moving the entire space station to face the target. A periscope peering out of the station served as the gun's sight.

Salyut 3 under construction.
Source: Svengrahn.pp.se.

Its construction took into account Newton's Third Law of Motion (for every action there is an equal and opposite reaction). The station was equipped with special maneuvering engines that would automatically counteract the thrust of the gun firing with engine thrust.

Just as the cannon's operation didn't violate the laws of physics, its existence didn't violate international law either. At the time that Salyut 3 was launched, the Soviet Union had signed and ratified the 1967 U.N. treaty governing weapons in space, the Outer Space Treaty. But this Treaty only bans "weapons of mass destruction" in space. It seems unlikely that a 23 millimeter automatic weapon would qualify.

Negotiating the Outer Space Treaty.
Source: www.rocketlawyer.com.

Was Salyut 3's gun ever fired in space? Probably- though fortunately it was never aimed at any American astronauts. The commander of the only crew to actually use Salyut 3, Pavel Popovich, claims the gun was never fired while cosmonauts were on board. But, it is believed that the gun was tested at the end of Salyut 3's lifespan, while the space station was empty but before it was de-orbited.

The only crew of Salyut 3: Pilot Yuri Artyukhin and Commander Pavel Popovich.
Source: svengrahn.pp.se.

There's one other odd fact I want to share on the subject of armed space stations. While we can all be grateful that the ISS doesn't have a large automatic weapon mounted outside, there are in fact usually two pistols aboard the ISS.

Each of the ISS's two Soyuz escape pods is equipped with a pistol. Neither NASA nor the Russian Space Agency provide many details on it, but cosmonauts have said that they are the typical sidearms carried by members of the Russian military. Unlike the Salyut 3 auto-cannon, these pistols are not meant to protect against armed space invaders. Their stated purpose is to protect astronauts and cosmonauts from danger they might encounter on landing.

Space tourist Mark Shuttleworth training to shoot the Soyuz's gun.
Source: MSNBC.

Which may sound far-fetched... but history records the dangers not just of space travel, but also the dangers one may face after landing. Back in 1965 the crew of the Voskhod 2 landed 200 miles off course, deep in the Ural Mountains. They reported hearing wolves prowling around their space capsule as they waited overnight for rescue.

Voskhod 2 also featured the first ever space walk!
Here's Pilot Alexy Leonov's own painting depicting his walk in space.
Source: blog.matthen.com.

That's not the only time cosmonauts have encountered danger after landing their spacecraft. Check this out this story too!

Source: Fourmilab.ch; spaceyard.blogspot.com; astronautix; langston.com; svengrahn.pp.se; MSNBC; Wikipedia.

Carnival of Space #271!

Today I'm hosting the "Carnival of Space" for the first time! The Carnival is a weekly round-up of interesting space stories. If you've got a space-related blog, you too can join the Carnival of Space. Email carnivalofspace@gmail.com to host a weekly carnival, share a story you wrote, and get to know other space bloggers.

Welcome to the Carnival!
Source: Walt Disney, via Wikipedia.

• Discovery News shows us a shiny, metallic-looking fragment on the surface of Mars, and asks: is it a Martian reptile? Is it an alien flower? No! It's (most likely) plastic trash that fell off a Mars Rover

• At the Smithsonian blog Once and Future Moon, Lunar and Planetary Institute scientist Dr. Paul Spudis answers the questions, why is the moon gray?

• Centauri Dreams features guest blogger Stephen Ashworth this week. Mr. Ashworth explores possibilities for expanding humankind's presence in the solar system (Asteroid colonies! Commercial spaceflight to Venus!) and how exploration of the solar system may lead to exploration of interstellar space...

• Chandra X-Ray Observatory is sharing photos of four beautiful planetary nebulas imaged by NASA's Chandra X-Ray Observatory and the Hubble Space Telescope.

• This week a potentially hazardous 72 foot diameter asteroid whizzed by the Earth, coming as close as less than 20% the distance between the Earth and the Moon! Astroblogger discusses our close encounter. He even has photographs of it!

• Peter Lake hosted a Google plus Hangout this week, along with Shahrin Ahmed and Hamant Kumar. They shared photos of the Comet Hergenrother, an interview and commentary by Carl Hergenrother. Dr. Hergenrother discovered of Comet Hergenrother! And, he's the co-lead staff scientist at the University of Arizona, working on the OSIRIS-REx Target Asteroids Mission.

• Over at Next Big Future, you can read about a newly discovered comet, C/2012 S1 (ISON), which will be headed for a close encounter with Earth in 2013. On Sunday, November 28th, 2013, the comet will show up in the night sky at a magnitude of 16- brighter than the full moon! And, brighter than 1997's Hale-Bopp comet or our next major comet visitor, Comet Pan-STARRS in March 2013.

• Also at Next Big Future, there's a story about Astrobiotic's shot at the moon and the $20 million Google Lunar X prize. Astrobiotic is developing a solar-powered landing module and a small rover, as well as rover destined to explore one of the moon's poles and drill for water.

• And, you can read about SpaceX's recent mission over at Next Big Future. This past week the SpaceX Dragon capsule succeeded in resupplying the International Space Station, but failed in its secondary task of launching a satellite.

• Doc Madhattan is celebrating the anniversary of the first observation in x-ray astronomy, and commemorating an x-ray astronomy exhibition in Milano, Italy by the Astronomical Observatory of Brea with a post about the origins of x-ray astronomy.

• Doc Madhattan also shares an overview of a public talk in Milano by astronomer Martin Rees. The subject of the talk: the universe, its exploration, and the planet Earth!

• Want to learn about 11 amazing things that the Curiosity rover can do? You can learn about that over at Links Through Space!

Apparently there almost was a real, live Carnival of Space:
The Space City USA Amusement Park, planned but never constructed in Alabama.
Source: The Huntsville Times.

The Deep Space Network, Part I

Right now, there are over twenty functioning human space probes exploring our solar system (or the interstellar space just beyond it). This includes:

• Orbiting Mars: Mars Odyssey, Mars Reconnaissance Orbiter, and Mars Express. 
• Roving Mars: Curiosity and Opportunity.
• Observing the sun: Solar Terrestrial Relations Observatories A and B, the Solar and Heliospheric Observatory, Advanced Composition Explorer, and the Global Geospace Science Satellite.
• Orbiting Mercury: Mercury Messenger.
• En route to Venus: The Akatsuki probe.
• Orbiting Venus: The Venus Express.
• En route to the dwarf planet Ceres: The Dawn probe, fresh off a visit to the asteroid Vesta.
• En route to Pluto: The New Horizons probe will flyby the dwarf planet and its moons in 2015.
• En route to Jupiter: Juno will arrive in 2016.
• Orbiting Saturn: Cassini has been observing Saturn and its moons since 2004.
• En route to asteroids and comets: Chang'e 2 and Rosetta.
• Heading for interstellar space: Voyagers 1 and 2, which are leaving the solar system at speeds of over 34,000 miles per hour.

Quite an accomplishment for a species that first achieved powered flight not much more than a century ago!

One result of all this exploring is that right now, around the world, there are hundreds of human beings whose job is communicating with robots orbiting Saturn, or roaming Mars, or headed towards a close-ish encounter with the Sirius binary star system (Voyager 2 will cruise within 4.5 light years of that star in 296,000 years).

The Sirius system, as viewed by the Hubble Space Telescope.
Source: Wikipedia.

When I counted up all these active interplanetary missions, I started to wonder: how exactly do we communicate with all these spacecrafts? There are so many of them, and they're all so far away. Voyager 2, for example, is over 11.3 billion miles from Earth! 

Voyager 1.
Source: NASA.

NASA scientists communicate with interplanetary and interstellar probes via radio waves. They send and receive these waves using detectors and transmitters situated inside enormous dish-shaped antennas. Primary, NASA missions rely on dish antennas installed at three facilities around the world. Together, these three facilities comprise the Deep Space Network.

1. Goldstone Observatory in California's Mojave Desert.
It's situated 45 miles outside Barstow, California.
Source: Minglebox.

2. The Madrid Deep Space Communication Complex.
It's situated 37 miles outside Madrid, Spain.
Source: Space Today.

3. The Canberra Deep Space Communication Complex.
It's situated 25 miles outside Canberra, Australia.
Source: Wikipedia.

The Deep Space Network consists of these the three sites because Barstow, Madrid, and Canberra are positioned roughly a third of the world apart from the other. This ensures that as the Earth rotates one of them is always able to receive signals from deep space. Additionally, the three locations are fairly remote, reducing interference from Earth-based radio sources. The dish antennas at the three sites are all set in the center of bowl-shaped valleys in semi-mountainous areas, further isolating them from interference.

The Deep Space Network's 360 degree view of outer space.
Source: Wikipedia.

Each of the three Deep Space Network locations has at least four dish antennas, ranging in size from 85 feet in diameter to 230 feet in diameter. These dishes funnel radio signals towards detectors sitting below the dishes. The detectors receive high frequency radio waves from spacecraft and send back instructions via a powerful radio signals.

A dish antenna, like those that make up the Deep Space Network.
Source: exploremars.org.

The Deep Space Network serves other functions besides allowing communication between Earth-based scientists and spacecraft. Its antennas can also be used to determine a probe's distance from Earth, accurate to a distance of less than 30 feet. This tracking is necessary because the probes are too small to see with telescopes. Spacecraft tracking occurs through a process called "ranging": the dish transmits a signal to the probe, and the probe's computer knows to immediately transmit this signal right back to Earth. The time between sending the signal and receiving the reply, minus the turnaround time and divided by two, is the distance it took light to travel to the craft!

The Deep Space Network's dishes are also used by astronomers to study planets, stars and other objects in our solar system and beyond. Some of the Network's smaller (85 foot in diameter) dishes are used to communicate with Earth-orbiting satellites.

Pioneer 10.
The high-gain antenna used for transmitting to Earth is the large dish on the back of the craft.
Source: Wikipedia. 

According to JPL, NASA's interplanetary mission teams rely on a "sophisticated scheduling system" and "teams of hundreds of negotiators" to coordinate sharing of the Deep Space Network's facilities. The Network telescopes in a given location can simultaneously receive data from multiple spacecraft, so the Network is not limited to serving one craft at a time.

However, the Network's capacity is being tested... missions like Opportunity and the Voyagers are long outliving their planned lifetimes, by years and sometimes even decades. Meanwhile, new spacecraft are sent out explore. So, there is growing concern that one day soon we'll need more extraterrestrial communication abilities than the Network provides.

Mars Reconnaissance Orbiter watches Curiosity land:
We now have Martian spacecraft spying on our other Martian spacecraft!
Source: Wikipedia.

For now, the Deep Space Network is shared by each planetary mission according to a predetermined schedule. Even an extremely active mission, like Curiosity, typically only uses the Deep Space Network to send and receive data for a couple hours once or twice a day. However, this can change in an emergency. If something goes wrong with one of the spacecraft exploring the solar system, engineers will put into use the largest Deep Space Network antennas. They'll array these antennas to send and receive bigger than normal amounts of data to the craft, in the hopes of determining what has gone wrong and fixing it.

Cassini's view of Saturn. Can you see the teeny tiny dot on the left, near the second farthest out ring?
That's Earth!
Source: NASA.

There's even an instance of the Deep Space Network being used to rescue astronauts! When an oxygen tank aboard Apollo 13's service module exploded on April 13, 1970, it left the crew without enough electricity (generated by fuel cells that ran on oxygen and hydrogen) to run their spacecraft at full power.

So, in a desperate attempt to conserve the craft's limited power supply, the astronauts shut down all but a few instruments. You'll recall from the movie Apollo 13 that the Commander Lovell and the crew spent the rest of their mission floating in near darkness, in freezing temperatures.  Without the electricity to run the craft's power-hungry high-gain antennas, the astronauts relied on the craft's weaker antenna to communicate with Earth.  This antenna's signals were too weak for the Manned Space Flight Network radio dishes to receive, so the Deep Space Network stepped in. The biggest Deep Space Network antennas in existence at the time were arrayed to send and receive signals from the craft. The resulting communication was a bit patchy, but good enough to get the crew home.

Apollo 13 splashes down safely.
Source: Wikipedia.

Note: Part II of this post is available here!

Sources: io9, JPL, Supernova Condensate, Wikipedia, Space Today, Popular Mechanics.