In the last post I discussed traversing the asteroid belt – a minefield of danger for our spaceship right at the start of our star mission. But there are other bodies flying around in space that we have to avoid and there is often confusion as to their true nature.

I’m referring to asteroids, meteoroids, meteors, meteorites and comets and over the next couple of posts I will define these objects and try to explain their origins and composition.

Let us start with some simple definitions …

  • Comet – a relatively small solar system body comprising ice and debris that orbits the Sun. When close enough to the Sun they display a visible coma (a fuzzy outline or atmosphere due to solar radiation) and sometimes a tail.
  • Asteroid – a solar system body that orbits the Sun. Made of rock and metal, they can also contain organic compounds. Asteroids vary in size from 500-1000 km across to millions which are less than 50 km. They are concentrated in the asteroid belt between Mars and Jupiter.
  • Meteoroid – a small rock or particle of debris in our solar system. They range in size from dust to around 10 metres in diameter .
  • Meteor – a meteoroid that burns up as it passes through the Earth’s atmosphere is known as a meteor. If you’ve ever looked up at the sky at night and seen a streak of light or ‘shooting star’ what you are actually seeing is a meteor.
  • Meteorite – a meteoroid that survives falling through the Earth’s atmosphere and then collides with the Earth’s surface is known as a meteorite.

You can see that asteroids, meteoroids, meteors and meteorites have certain similarities and links and I will leave their detailed description to the next post.

Comets are different and I will focus the rest of this post on them.  

A comet is an icy small solar system body which when close to the sun displays a coma – a fuzzy, temporary atmosphere and sometimes a tail. Both effects are due to solar radiation and solar wind on the nucleus of the comet. They range in size from hundreds of metres to tens of kilometres and are made up of aggregations of ice, dust and rocky particles. Their most interesting characteristic is they keep turning up at regular intervals and have been observed for thousands of years.


The most famous comet is Halley’s Comet which is visible from Earth approximately every 75 years – so some of you will see it twice! It last appeared in 1986 and will reappear in 2061. Astronomer Edmond Halley determined the periodicity of this comet in 1705 and it was named after him.

In 1986 Halley’s comet became the first object of its kind to be observed by a close approach of a spacecraft. This confirmed the ‘dirty snowball’ definition of a mixture of volatile ices – water, carbon dioxide and ammonia – mixed with rocky substances. The comet proved to be a more solid, rocky structure than previously predicted.

The origin of comets is still uncertain. They were once thought to have originated outside the solar system, but more recent theories suggest they were formed during the formation of the solar system and are permanent members of it.


Comets are only seen from Earth about once per year but there are more than 4000 known comets and  it is estimated that there are a trillion comet-like bodies in the outer solar system.

That’s a huge number of potentially dangerous objects to steer our spaceship through on our mission to the star Seren.

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 Between the orbits of the planets Mars and Jupiter lies the asteroid belt; a huge region of asteroids and minor planets presenting its own dangers to our star mission.

So not only do we have to set a collision course for Jupiter [previous post] but we have to navigate the equivalent of a solar minefield of objects ranging in size from 400 – 900 km diameter down to billions of dust sized objects. The largest object is Ceres, a dwarf planet at 950 km diameter, followed by Vesta, Pallas and Hygiea which are all in excess of 400 km.

But avoiding these is relatively simple due to their large size. It is the millions of smaller objects that pose the highest danger to our spacecraft. There are estimated to be around 1 million asteroids in the belt of diameter greater than 1 km. There are billions of smaller objects.


Furthermore the asteroid belt is the ‘birthplace’ of the many rogue asteroids which get flung out onto collision courses with other planets in the solar system including Earth.

Some we know about – eg the asteroid that passed between Earth and Moon [last post] and others take us completely by surprise as in Russia recently [last post]. The latter could be disastrous to a spacecraft travelling at 100,000 km/hour so we will have to develop very advanced detection systems by the end of this century to get us safely out of the solar system.

However, the asteroid belt is so thinly distributed that collisions would be highly unlikely. In fact many unmanned spacecraft have passed through it without incident. But it is a very different matter for a manned mission – we would have to be 100% certain of avoiding a collision as we travel 100 million km through the minefield. Further, collisions between asteroids occur frequently within the belt seeding rogue asteroids which could suddenly be on a course to damage our starship and terminate our mission before it leaves the solar system. Or worse, deflect our ship and crew directly into the gas giant Jupiter.

Even when we exit the asteroid belt there are further areas of asteroids called the Greeks, Trojans and Hildas to navigate but these are a much lesser threat to our mission.

So space is a dangerous place to travel through and we haven’t even left our solar system. To get beyond Jupiter is about 1 billion km and our star is 10 light years away – each light year is 10 trillion km so we have to travel 100 trillion km! We’ve barely covered 0.001% of the distance to our star. What else could go wrong?                                         

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Let us assume that our artificial intelligence [AI] computer has completed building our starship in Mars orbit in 2150. It is capable of half-light speed and housing a crew of seven astronauts in cryo-hibernation for at least 20 years.

Its journey to a star 10 light years away will be full of dangers but most will occur whilst it is traversing our solar system at relatively low speeds. Space is not as empty as it seems. We have already filled the upper atmosphere of Earth with tens of thousands of pieces of space junk and any one of these could cause disaster to Earth based missions.

Our solar system is crammed with objects, many of which we know about but even we can be taken completely by surprise – witness the events in Russia recently when a small meteor exploded above ground. In February an asteroid the size of an Olympic swimming pool passed between Earth and the Moon’s orbit and even inside the thousands of communications satellites in space. But we knew this was coming and that it posed no danger.

So we have to be prepared for every eventuality when we finally leave Mars orbit. But our biggest threat is about to happen. We have to set a collision course for Jupiter! – the largest planet in our solar system.


Jupiter is the fifth planet from the sun and is a gas giant with a mass two and half times the mass of all the other planets in the solar system combined. It is nearly 320 times the mass of Earth and that is why our starship is hurtling towards it a velocity of 100,000 km/hour [estimate of future capability].

But Jupiter’s orbital velocity is about 50,000 km/hour and it is charging directly towards our starship – the combined relative velocity is 150,000 km/hour. But this is deliberate as we are about to perform a common manoeuvre in space called the slingshot. We’ve been doing this since the early 70’s eg the Voyager missions and it is done to accelerate and redirect our craft onto its desired trajectory in space.

In essence we use the huge gravitational force of Jupiter to capture our spaceship and send it around the planet and sling it in the opposite direction of travel. In so doing its velocity increases significantly according to a simple equation [Wikipedia]. Our starship would double its velocity to 200,000 km/hour but we are going to fire advanced rockets at a critical point as we pass around Jupiter and this will accelerate us to 1 million km/hour.

It sounds simple but there are huge dangers if we miscalculate our speed and trajectory as we approach Jupiter – get it fractionally out and we will bounce off the gravitational field of the planet onto the wrong course or worse we will be dragged inexorably towards the surface of Jupiter. Further the timing of the firing of the rockets is equally critical to achieving the optimum boost to the slingshot. Finally we must remember that our starship will weigh about 200,000 tonnes. That’s an awful lot of momentum if we get anything wrong.

And, of course, a crew of astronauts who will be totally reliant on the AI computer systems getting everything perfectly right as we swing around Jupiter in the first critical stage of accelerating towards half-light speed. But this slingshot is only the first of the dangers – more in the next post.

Meanwhile perhaps you would like to join the crew of Lifeseeker-1 as she is flung around Jupiter in 2150 at the start of a 20 year journey to the star Seren.                                                


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In previous posts I have talked about the absolute requirement of a computer system that can be totally relied upon to control a star mission. I have postulated that we need to advance from our current highly technical – but sometimes unreliable – systems to a level of reliability and logic that can only be realised by true artificial intelligence [AI].

We are probably at least 50 years from this level of AI and certainly 100 years before our AI network designs and constructs a Mars base. This would be the nerve centre to build a starship in Mars orbit for a voyage to the stars in the middle of the 22nd century. 

But how far can we advance computer capability in the next 100 years and can we ever realise the ultimate design – a true molecular computer! 

Current capability manufactures integrated circuits [microchips] on up to 450 mm diameter wafers of silicon at wire dimensions of 20-40 nanometres. Typically 1416 microchips each 10 mm square are fabricated on each wafer simultaneously to tolerances that are astoundingly minute. There are billions of transistors and other electronic components on each chip which is the size of a fingernail. A fabrication plant costs $5 billion and is built to resist earthquakes as NO vibration can be tolerated throughout the process.


All this process sophistication is aimed at cramming incredible numbers of micro-transistors into smaller and smaller spaces producing 5 terabyte hard drives and 8 gigabytes RAM memory chips. Basically each byte is a single memory slot which is a switch [in simple terms] that can either be ‘off’ for 0 or ‘on’ for 1. This is the basis of the digital age where all information can be expressed in binary code in 0’s or 1’s, stored and processed in our computers and wirelessly transmitted around the world via Internet and telephonic communications.  For example the number 3245 is represented in binary code as 110010101101 which would occupy 12 bytes of memory set to on-on off-off-on-off-on-off-on-on-off-on. All our data can be stored and processed in this form but we need an awful lot of memory slots to do this.

Future computer development will pack increasingly more bytes into our chips but we will reach a physical constraint – there is a practical limit to how small we can make the circuits on the silicon wafers. The printing and etching processes will have reached their capability. 

So where next for the computers of the mid and late 21st century?

Scientists at IBM have created an alternative to silicon for the logic gates on microchips that will ensure the continuing shrinkage of the basic digital switching mechanism for at least 10 more years. The IBM breakthrough, first reported in Nature Nanotechnology and by the New York Times, uses carbon nanotubes, a type of molecule that is an alternative to silicon,  for the creation of miniature logic gates in microprocessors. You can read more in this link

Now watch what IBM can do with individual carbon monoxide molecules – a video at the molecular level! 

Further, a group of future-minded researchers are expressing optimism about the potential of tiny nanoelectronic components, organic molecules, carbon nanotubes and individual electrons that could serve as the underlying technology for new generations of microprocessors emerging around 2015.

This is the direction of the ultimate molecular computer but we are a long way from this yet. However we will certainly need this technology to develop AI computers to build and control our star missions of the future.

But what do you think?                                                    


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