Tag Archives: space

Advances in antennae

An antenna is a device for sending or receiving radio signals. You’re probably most familiar with the Yagi-Uda antennae used for receiving UHF terrestrial television signals or the parabolic satellite dishes used to receive Ku-band satellite television signals.

A high-gain Yagi-Uda antennae used for terrestrial digital television.

Warships typically have a large number of antennae but this is problematic: they can be damaged easily and they increase the radar cross-section of the ship, making it easier to detect and target.

The US Navy’s Space and Naval Warfare Systems Command has come up with what they think is a good solution: an antenna made of seawater. Because seawater contains salt it is a good conductor of electricity and can be used in just the same way as metal, with the advantage being that the antenna only exists when needed and is therefore not subject to the problems already mentioned.

Further away from home, one of the most critical points in a space mission is the reentry phase when the spacecraft enters Earth’s atmosphere. The problem is that during reentry the spacecraft is surrounded by plasma, a superheated gas in which all the electrons have been stripped from their atoms. This plasma sheath absorbs and reflects any signals, making communication with the craft impossible at this critical time.

A group of US and Russian scientists have published a paper in which they suggest a solution that is similar to the water antenna above. The absorption of a signal creates a resonating layer in the plasma, and this layer can effectively become an antenna. By bouncing another signal off this layer from inside or outside the spacecraft it is possible to discern the original signal. The military are likely to be particularly interested in this solution, as it would enable communication with intercontinental ballistic missiles in flight, enabling them to be reprogrammed or disarmed.

Rods from God

The problem with bombs is getting them to their target. Dropping them from the air has always been the standard approach (Austrians used air-dropped bombs during the siege of Vienna in 1849), but this is beset by problems. Even stealth aircraft like the B-2 Spirit stealth bomber and the F-22 Raptor stealth fighter are not perfect.

The Rods from God idea did away with aircraft, and with explosives altogether. The concept is very simple: a series of satellites orbit Earth armed with “tungsten telephone poles”. Once a target has been selected and the satellite is overhead, the “pole” is released and pushed towards Earth by a small rocket motor. As the pole falls to Earth from space it requires no fuel; it is powered by gravity alone.

With such a large distance to fall the rod has plenty of time to accelerate, even when the effect of air resistance is taken into account. Hitting the ground at more than ten thousand metres per second (more than 24000 mph) the rod would be able to strike targets buried deep underground.

With a mass of more than eight and a half tonnes, a rod travelling at that speed would have an energy density of fifty million joules per kilogram, far more than TNT (4.6 million joules per kilogram) or nitroglycerin (6.4 MJ/kg). With very little warning of incoming attacks, the weapon’s speed would make it almost impossible to defend against.

Fortunately (or unfortunately, depending on your viewpoint) the Rods from God (or “kinetic bombardment”) system has yet to be deployed. The most recent mention was in a 2003 US Air Force report (PDF) that classified “hypervelocity rod bundles” as a “Post-2015” technology.

20 years ago today

4545 days after launch, on 14th February 1990, at a distance of six billion kilometres from Earth, the Voyager 1 probe turned its camera on the solar system for a “family portrait“.

One of the 60 individual photographs taken became one of the most famous space photographs of all time – the “Pale Blue Dot“. Midway down the brown stripe (caused by light reflecting inside the camera) you can just make out a bright spot – Earth.

Carl Sagan said of the image:

“Look again at that dot. That’s here, that’s home, that’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives.”

Voyager 1 is the farthest man-made object from Earth; currently it’s about 16.9 billion kilometres from Earth, 15.7 light hours away.

What’s up with the Sun?

The Sun (the big floaty fireball, not the awful “newspaper”) has been in the news lately as it’s been predicted that the Sun may interfere with the 2012 Olympics. It’s been suggested that  solar flares, ejections of material from the Sun’s surface; and the solar wind, a fast-moving stream of charged particles (normally responsible for the Northern and Southern Lights (Aurora Borealis and Aurora Australis)), could affect the satellites that are responsible for relaying television footage from the Games around the globe.

Over the last few years the Sun has been in an unusually quiet mood, but recently it seems to be “waking up”. Looking at images from the Solar and Heliospheric Observatory (SOHO) Large Angle Spectrometric Coronagraph (LASCO) you can see a clear difference between images taken now and images taken in past months.

Tuesday:

Last Month:

December:

October:

SOHO picked up its largest solar flare in two years on January 22nd:

At the time of writing the solar wind is running at somewhere between 300km and 400km per second with between 2 and 4 protons per cubic metre [source]; this is nothing to worry about. The concern is that by the time the Olympics come around we might be experiencing periods of solar weather like in January 2005 during a severe solar storm.