November, 2003

Specialised industries, such as the military or space industries, are increasingly using solutions based on commercial « off-the-shelf » (COTS) products. It is a way to reduce costs and deployment time of new systems.

NASA has called on New Mexico State University to investigate the feasibility of a "proximity wireless networks", a simple and robust system to enable communication between the elements of robotic exploration missions (rovers, probes, in-space vehicles, etc). A typical scenario is when a rover, having explored an area, moves to an elevated point from where it will have the possibility to connect to a relay station that will resend data to Earth. The key points for this kind of equipments are:

Miniaturisation

- Low energy consumption

- Use of simple protocols

- Costs

The technical characteristics that are targeted are the following: 1 Mbps over 10 meters, 10 kbps over 100 m, 2.4 GHz frequency, a 1 month to 1 year lifespan, a low power (1 to 100 mW) and $5 to $50 cost hardware items.

Principles of W-LAN over Mars (© NASA)

However the constraints specific to the harsh environment and security requirements of space missions involve that existing technologies must be adapted. The evaluation of the necessary modifications is at the heart of current research efforts. Studies are planned in three stages:

1. Simulate the propagation condition over planetary surface

2. Understand limitations of COTS wireless technology in this specific environment

3. Propose modifications to enable the use of such systems

For the first stage NMSU has selected ATDI to assist them in its task. In order to analyse the utilisation conditions, studies will first be based on simulations realised with radio coverage calculation software. The results of this analysis will be validated by measurement campaigns conducted in the desert.

To simulate scenarios of exploration missions, it was necessary to obtain precise terrain data of the Red Planet. This was done by the Mars Orbiter Laser Altimeter (MOLA). MOLA is on board the Mars Global Surveyor satellite. It acquires the raw terrain data by measuring the travel time of a laser pulse. A Digital Terrain Model at 10m resolution is then built and loaded into HerTZ Mapper, ATDI's simulation software, to calculate the coverage from various locations. A specific Radio Waves Propagation Model has been implemented and adapted to account for specific climate, atmospheric and terrain characteristics of Mars. Various configurations have been analysed, placing the rovers in various spots of the planetary surface and calculating the generated radio coverage.

In the middle of the flat and rocky desert of New Mexico, a great approximation of the Mars terrain, the propagation model has been validated. Researchers have set up a small transmitter similar to the ones used in rovers. By measuring the received signal around this spot and by comparing it to simulation, they could confirm that calculation matches reality.

Coverage near a crater

The wireless network will not be installed on Mars before some years since substantial work remains to be completed. However, it is interesting to see that, in order to analyse the feasibility of adapting commercial equipments to space exploration, researchers rely on tools that have already proven their use in classical applications. The high versatility of ATDI software made it the ideal tool for such a purpose. Indeed, it is thanks to intensive cooperation with a large array of customers, spanning telecom operators, local authorities, equipment manufacturers, civil security or engineering companies, that ATDI was able to collect a broad expertise in wireless network planning.

ATDI is proud of the trust invested in them by leading research institutes into innovative technologies.

References:

- Bhasin, Kul "Proximity Wireless Networks" 18 July 2003.
http://scp.grc.nasa.gov/porfolio/pn/index.html (29 Sept. 2003).

- De Leon, Phillip. (2003, Sept. 29). [Interview]. New Mexico State University

- Smith, David "Mars Orbiter Laser Altimeter (MOLA) Science Investigation" 26 June 2003.
http://ltpwww.gsfc.nasa.gov/tharsis/mola.html (29 Sept. 2003).