The backbone network must provide a high data rate transmission over a very long distance. Currently, data are transmitted using X-band frequency. This allows for a relatively low rate of data transmission compared with Ka-band. In the future, Ka band frequency RF equipments are to be employed. This band is used because it can increase the radiated power of the transmitter. In addition, it can handle a higher rate of bit-stream. We will hence discuss some of the technology that is needed for employing Ka-band frequency.

Figure 1 - TWT Technology

In order to operate at Ka-band, the amplification of power must be considered to a great extent. High efficiency Ka-band 30W and 100W Travelling Wave Tube Amplifiers (TWTA) are employed. A TWTA works by modulating the velocity of electrons near the source of the electron beam by an input signal. This goes through a wire helix where the electron beam is transferred into electromagnetic waves. This electromagnetic wave will then carry the information of the modulating signal.

Ultra low noise cooled receivers are also used in Ka-band technology. This must be employed because of the extreme low temperature. Low Noise Amplifiers (LNA) use high electron mobility transistors (HEMT) to work in cold weather. For future rovers, Jet Propulsion Laboratory (JPL) and NASA is trying to develop metamorphic HEMT power MMIC technology for a Ka-band solid-state amplifier.

Furthermore, to support a strong backbone network, apart from the TWTA and Ka-band MHEMT MMIC solid state amplifier, other technologies include high rate modem circuit, efficient optical power sources and microradian acquisition and tracking technology.
Currently, there is a 32GHz TWTA 20W amplifier on the Cassini Spacecraft. However, to allow for a better space backbone network, NASA is trying to develop space-qualified amplifiers to produce greater than 200W of RF power. In order to achieve this, a different sort of circuit is required. A point worth noting is that previously, to produce an amplifier with the desired specifications, many trials must be made. Nevertheless, with recent improvement in computer modelling capability, it was able to design and make the required amplifier with much fewer iterations. Furthermore, with recent developments in Heterostructure materials , MHEMT MMIC amplifiers of size 0.1 micron can have an efficiency of 50%.

Since the backbone network transmits data in such a long distance, a lot of interference might occur during the transmission. Therefore, a system where a high Signal to Noise Ratio (SNR) must be employed. A laser telescope which utilises optical technology is used to 'promise large gains in signal to noise ratio'.

In order to send data back to Earth, it is essential to have a good and well-defined protocol for communication. The backbone network currently supports a variety of protocols, such as the Internet-based protocols (for applications), as we have discussed before. In addition, using IP can support internet capabilities to the space backbone. These services include temporary storage, network switching, firewall protection, e-mail, ftp, XML etc. Other types of protocol which are suggested include Near Earth Space Protocol (SCPS-TP) and deep-space protocols such as Consultative Committee for Space Data Systems (CCSDS) File Delivery Protocol (CFDP). CFDP is advantageous because it transmit data as a file instead of bit-stream. Furthermore, there is no need for an end-to-end communication. This means that not all the data is required to be collected at the end before the entire information to be recovered. This protocol can accommodate some lost in data which is very possible as data are passed through such a long distance.

In conclusion, the current development in materials and computer modelling allow for a quick development in the amplification stage of the signal from Mars back to Earth, giving a great start to the building of the Space Backbone network. However, with the increase in interest of Mars Exploration, data transmission must start looking at multi-Mbps rates instead of kbps rate which can be achieved by optical links. Further, NASA talked about a possible use of 200W TWTAs instead of the 20W currently used. Finally, it is essential to look at the size of antennas with a push towards larger and lightweight antenna structures. With the use of various protocols in the backbone network, data can be transferred safely from Mars back to Earth.