Imagine that you have just set up camp on Mars. Everything is up and running. You and your team have not only survived the journey from Earth, you’ve also made it through fiery re-entry and landed within a metre of your planned location. Success! So you crack open a miniature bottle of vintage whisky bottled in the year 2000 and share a sip with your companions. You want to tell the world, you want to check in with your family to say that you are “OK”.
It would be very poor if you were restricted to relaying a message though mission controllers. Simply “phoning home” for a chat wouldn’t be possible (the lag time between sentences would be at least 16 minutes). Could there be a way of sending emails? Possibly; voice messages will be fine too. But could our explorers set up a website or some “Mars blog” to document their travels? This could obviously be done remotely, with a terrestrial website, but there are strong arguments for a distributed Internet service on the Red Planet too. Can a “MarsNet” or “RedNet” be integrated with Earth’s Internet, establishing an “Interplanetary Internet”?
In the first instant, a new Mars colony probably will not need a distributed internet on the surface. One can imagine short wave radio systems or some modified “walkie-talkie” will do the job for communications between habitats and rover excursions. But over time, as the habitats turn into settlements, settlements turn into towns and eventually cities, the need for a regional/planetary Internet will grow. In fact, even in the “early years” an Internet-lite may be required for communication, data sharing and remote control of robotics.
A simple network of remote computers with radio transmitters/receivers may solve most local communication challenges, but wouldn’t it be natural for the fledgling Mars colony to want to use the existing World Wide Web on Earth? A link between Earth and Mars could be possible, but there will be many challenges facing the Interplanetary Networking Managers of the future.
Primarily, the speed of light (3×108 ms-1) puts a massive constraint on the data transfer between the planets. There will be a minimum delay between a signal being sent from Earth to be received on Mars of eight minutes (when the planets are at their closest) and a maximum delay of 18 minutes when the planets are in conjunction. This creates another issue; the line of sight (LOS) between the two planets will be blocked by the Sun in the middle. Even before and after conjunction there will be massive interference from the Sun, possibly shutting down a viable LOS link all together for weeks or months.
So how can these problems be confronted? Modifying the Deep Space Network (DSN) will be necessary; simply having a direct link between Mars and the current network of antenna here on Earth will be impractical for extended periods. Perhaps a network of satellites in Earth and Mars orbit around the Sun can be positioned in the islands of gravitational stability at the various Lagrangian Points (L) found around the orbits of the inner Solar System. The use of the Mars-Sun L1 has already been proposed as a useful position to station a solar radiation early warning system. These points can be found ahead and lagging the Earth and Mars orbits, and with a small investment in relay satellites (much like geostationary terrestrial communication satellites), it seems possible that Earth and Mars can be in constant contact.
OK, so we can solve the LOS problem through satellite technology, but the time lag problem remains. At best, should a basic internet connection be established between Earth and Mars, the result of a single mouse click will appear on the Mars computer screen after 18 minutes (the time taken for light to travel from Mars and return from Earth). This doesn’t include the time for the website to load. Unless some very advanced buffering can be done, it is unlikely that a “live” internet connection will be possible. Worst case scenario would be a webpage that takes over 40 minutes to load when the planets are furthest apart, using satellite relays to keep the connection going.
There are two solutions to this problem:
- Transmit data faster than the speed of light.
- Cache (store) as much of the terrestrial Internet as possible on Mars-based servers, regularly uploading new information depending on demand
But they have their limitations:
- Currently, there is no physical way to travel faster than the speed of light.
- There are well over 100 million (as of Feb. 2007) websites currently on the World Wide Web. In a few decades when the Mars colony is established, this number will have exponentially increased. How can such a huge number of web pages be cached on Mars-based servers? New technologies will need to be applied, as currently, this solution is not possible. If it were possible, only a very select few sites could be cached, and these would be “mission critical” sites such as NASA’s or ESA’s web pages.
Although there are practical problems with caching all websites on a huge Mars-based server, this solution is very appealing. One can imagine the Interplanetary Internet would update (or synchronize) at regular intervals, perhaps during periods of low electronic traffic. Once the mission-critical websites are uploaded, there could be a steady flow of low priority updates trickling through the network. This could be in the form of the peer-to-peer file-sharing model, like the technology behind BitTorrent, where small packets are downloaded and assembled by the client. Should the connection fail, it simply picks up where it left off as if nothing had happened. In the high-interference environment of near-Sun space, this would be essential.
New developments in file compression will also be necessary, plus images and other media associated with websites will have to be limited, or compressed to a huge degree.
This article is based on the Marspedia page “Internet”. This is a collaborative Mars wiki, growing to nearly 200 Mars-related entries. Anyone can contribute, so check out Marspedia.org to find out more.