Scientific Objectives and Instruments
The main novelty of the ARCHIMEDES mission is the exploration of the Mars atmosphere composition, density and gradient as well as the very weak magnetic field of Mars from an altitude of appr. 60 km down to the Mars surface. Such measurements are made possible by a balloon descending relatively slowly through the Mars atmosphere, carrying scientific instruments, then called "ballute". Another very important experiment is the COMPARE Entry Experiment with measurements of the plasma flow during entry of the ballute into the Mars atmosphere. In addition this mission profile allows obtaining images from the Mars surface during the descent from altitudes not possible before. The deceleation forces and movements of the ballute during the mission will be measured with a set of accelerometers, and the ballute trajectory will be determined through radio tracking.
These objectives are the basis for the ARCHIMEDES design and mission concept.
Never before has a balloon been used as a Mars entry vehicle. This means inflating the ballute in space before it is released for its scientific mission. The ballute will then be decelerated by crossing the thin upper Mars atmosphere, reducing the initial very high speed of the ballute until it has reached entry conditions. This is a major novelty of the ARCHIMEDES project.
This approach requires the development of new technologies for transporting the ballute to Mars, deploying and inflating it there after a 8 months travel time safely and without damaging it, and setting the ballute on a very accurate Mars entry trajectory.
All these novelties constitute inherent risks to mission success. It is therefore mandatory to obtain data on the function and health not only of the ballute itself but also of each component of the ARCHIMEDES space vehicle from the beginning of the mission up to its end, in order to confirm the selected design choices or at least to learn for future missions in case of malfunctions and eventual partial or full mission failure.
The provision of all these data requires to equip the ARCHIMEDES space vehicle and the ballute, in addition to the scientific instruments, with sufficient sensors to be able to fully evaluate all ARCHIMEDES functions throughout the mission duration. The different types of data are
- Scientific data on the Mars atmosphere, magnetic field and imaging
- Data on the dynamic behaviour of the inflated ballute while entering the Mars atmosphere
- Data on the thermal and mechanical loads during entry and descent to the ground
- Data Feedback on the function and health of the ARCHIMEDES system components throughout the mission
In order to reach these mission objectives, ARCHIMEDES carries the following instrumentation:
Scientific instruments provided by the scientific community
- the heating and flow field experiment COMPARE provided by the University of Stuttgart, measuring thermal loads and pressure during entry into the Mars atmosphere at supersonic speed
- an atmospheric sensor package provided by the Finnish Meteorological Institute measuring the atmosphere composition and pressure during descent
- a high resolution camera able to achieve a resolution of up to 20 centimetres per pixel at a distance of seven kilometres from the surface
- a magnetometer designed by the university of Braunschweig to analyse the planet’s very weak magnetic field and the interaction between the solar wind and the Martian atmosphere
- additional instruments, which may be built into the heat shield providing data on the atmospheric conditions and supporting the determination of deceleration forces
Other Instrumentation and equipment provided by the Mars Society and the institutions supporting ARCHIMEDES development
ARCHIMEDES sensoric and avionics, required to
- monitor the ARCHIMEDES health status
- monitor the ballute behaviour during its scientific mission
- reconstruct the trajectory
- transmit all relevant data to the orbiting P5-A satellite
- acceleration sensors measuring the deceleration forces on the balloon in the upper atmosphere and providing information on the density of the atmosphere and the flight path of the balloon
- temperature sensors measuring the temperatures at various locations of the ballute
- a camera measuring the deformation of the balloon during entry
- numerous sensors providing data on the function and health of instruments and avionics
- onboard computers collecting all these data and formatting them for transmission
- power generation and distribution to instruments and avionics
- transmitters for transmitting all data to the P5-A satellite
Scientific Instrument Details
Measurements of Mars’ residual crustal magnetic field were last made by the Mars Global Surveyor space craft during the aerobreaking phase of the mission, in an altitude range between 100 km and 200 km. An aerobot floating at an altitude of only a few kilometres could greatly enhance the accuracy of magnetic measurements. Profiles that chart the magnetic anomalies would give insight into the magnitude and position of magnetic minerals. The correlation of magnetic and geological structures is a prerequisite for investigating the properties of remote terrain that is hard to access. Hence, a combination of a magnetometer and a high resolution camera is an ideal set of instruments to investigate the regional geological structures.
In addition to this, a balloon based magnetometer would provide the first magnetic measurements below the ionosphere. Magnetic field measurements performed at the same time on board an orbiting spacecraft could provide insights into ionospheric properties. The magnetometer will be provided by TU Braunschweig.
"AtmosB" Atmospheric Sensor Suite
The atmospheric sensor package of the Finnish Meteorological Institute (FMI) records temperature, relative humidity and pressure. This will boost our understanding of the atmospheric dynamics and structure of the Martian atmosphere. Especially the cycles of CO2, H2O and dust are interesting parts for research and not fully understood up to now. This would also help us understand the evolution of the Martian climate.
Also be examined by these atmospheric sensors could be the characteristics of the near-surface water transport and the exchange of water between the atmosphere and possible subsurface reservoirs.
High Resolution Camera
The high-resolution planetary camera provided by the DLR Berlin will be able to achieve a resolution of up to 20 cm per pixel at a 7 km distance from the surface. The camera is a multipurpose instrument. Primarily, it provides an instrument of optical planetology. But it will also deliver oblique perspectives of the red planet, visually appealing images yet unseen from Mars that can also be presented to the public. Eventually, owing to this very perspective, it will provide the scientists searching for water (and thus life) with images of vertical patterns such as layers and gullies.
Neither landers nor orbiters are able to make these kind of images. In theory, it may even be possible that the balloon could cross-alleged ancient shorelines several times on its path. Whether this interpretation of relevant ground structures is valid, cannot be stated satisfactorily, even if more images were taken from space. These insights can only be gained using a system like the one proposed here.
A resolution of 20 cm is sufficient to identify the major layers and to determine their origin. These images may hold the clue for the answer to the question of the existence of liquid water on Mars.
Balloon Tracking & Radio Science
The characteristics of the signals transmitted by ARCHIMEDES to the orbiter along with the determination of the direction they come from as seen from the orbiter can be evaluated in order to determine the position od ARCHIMEDES and later on the ballute during its Mars atmospheric entry and descent.
"COMPARE" Entry Experiment
The entry heating and flow field experiment COMPARE is a combined pyrolytic shock-front radiation heat flux and pressure measurement system. It will contribute to our understanding of aero-thermodynamical processes associated with the entry of a low weight inflated body of considerable size into the Martian atmosphere. COMPARE is designed and built by the Institute of Space Systems of the Technical University of Stuttgart.
The low ballistic coefficient of the large and light weight balloon provides a unique opportunity to directly measure the density profile of upper atmosphere layers by detecting the balloons deceleration. The instrumentation also helps to understand the behaviour of the vehicle during its entry and subsequent descent through the sound barrier, an information crucial for the development of future heavy vehicles employing similar techniques to land heavy payloads. The Accelerometric Measurement System records six degrees of freedom and is provided by the Mars Society Germany.