Archimedes (space probe)

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Archimedes entering the Martian atmosphere (artist's impression)

Archimedes is a balloon probe designed and developed by the Mars Society Germany for exploring the Martian atmosphere . Archimedes is to be transported to Mars as a secondary payload on another mission.

concept

The probe is named after the ancient Greek scientist Archimedes of Syracuse, who among other things discovered the swimming principle and recognized the laws of hydro - and aerostatics . At the same time, the name stands for a summary description of the mission and its instruments are: A erial R obot, C arrying H igh resolution I maging, a M agnetometer E xperiment and D irect E nvironment S sensor.

Archimedes' concept is that the balloon is already inflated in space and acts as a hypersonic braking device when it enters the Martian atmosphere , and then leaves the atmosphere in a lower orbit. After several such atmospheric flights, it should remain in the atmosphere and slowly sink to the ground. During the entire descent, measurement data should be recorded in the hypersonic and subsonic areas. In addition, the residual magnetic field of Mars is to be measured and its surface recorded with high-resolution images during the descent from different heights. Such measurements are not possible when a conventional lander enters the atmosphere.

Based on their own investigations, those involved in the project are of the opinion that this concept is feasible.

development

In addition to the Mars Society Deutschland eV (MSD) and institutes from various universities, the University of the Federal Armed Forces in Munich is particularly involved with its institutes for space technology, lightweight construction and thermodynamics. Other university institutes have made contributions.

The mobile rocket base of the German Aerospace Center (DLR-MoRaBa) provides the rockets and launch options for the MIRIAM simulation and testing program, which is intended to provide evidence of the feasibility of the ARCHIMEDES Mars mission.

The project receives basic support from the company IABG in Ottobrunn, which makes its space test center available free of charge for experiments as part of Archimedes. Numerous other companies contribute donations in kind and services. For example, the Lohmann Tapes Neuwied company developed a high-temperature-resistant adhesive tape specifically for the production of the balloon, and the apprentice workshop at the Lüneburg Scharnebeck ship lift built a device for welding the balloon segments.

Since 2016, the development of Archimedes has also been funded by the ESA Technology Support Program.

As a project of the Mars Society Deutschland eV, the Archimedes project is designed for the broadest possible participation of those interested in space travel. All balloons and many electronic components are made by members of the MSD and other volunteers on a voluntary basis and in their free time.

Archimedes' launch was originally planned for 2018 on board AMSAT Germany's P5A spacecraft , but this project has been discontinued. Archimedes can also fly with other Mars probes after a corresponding technical adjustment. The basic mission concept remains unchanged.

background

Research balloons have been used on Earth in a wide variety of scientific fields for a long time. But their use also appears sensible and possible on other planets. Since a balloon can travel through all areas of the atmosphere for a longer period of time, it enables direct measurements of pressure, density and atmospheric flows from the ionosphere to the ground, as well as images from perspectives that are not possible from orbit or from a landed probe . By following the path that the balloon takes, controlled only by the wind and the temperature conditions, additional conclusions and scientific findings are possible.

While French balloons were successfully used on Venus as early as 1985 as part of the Soviet VEGA missions, all concepts for a Mars balloon have so far failed due to the much thinner atmosphere of the planet, which offers the balloon body only very little lift. This atmosphere requires a relatively large balloon with the lowest possible weight in order to be able to carry a suitable payload. With such a construction, the balloon material and its folding and packaging, as well as the unfolding and the inflation process, which later have to take place under space conditions and without any human intervention, are technical challenges due to the thin balloon skin with a large area. Various investigations and experiments in the early phase of the project had clearly shown that inflating the balloon both during the approach through the atmosphere and from a landing module on the surface of Mars is hardly feasible with the available means and furthermore does not offer the possibility of measuring data record at greater heights.

A new approach was therefore chosen for Archimedes: the balloon is already inflated in space and itself serves as a body of resistance when it enters the atmosphere. Since the atmospheric pressure on Mars is only around 10 mbar, the balloon only needs to be inflated to around 20 mbar in order to remain plump in the Martian atmosphere. A balloon with a very thin outer skin can withstand this internal pressure, which enables a lightweight construction. Parachutes or brake rockets are not necessary and no more critical maneuvers have to be carried out during the flight. This means that both the structure of the spacecraft and the mission profile can be significantly simplified. The large area and the low weight of the balloon ensure high deceleration even in layers of the atmosphere with a very low density. Furthermore, the resulting heat is distributed over a comparatively large surface.

construction

The instruments are housed in an instrument holder at the “south pole” of the balloon and are covered with a “nose cap” in such a way that the spherical shape of the balloon is retained. This cladding not only serves as a heat shield , but also houses special instruments for examining the high atmosphere and the flow field during fast atmospheric airflows and at the same time protects the instruments for deeper atmospheric layers from heating up during the hypersonic phase. Shortly before the speed drops below the speed of sound , it is thrown off and releases the other sensors.

Instruments

The instruments are developed by different institutes. The Archimedes instrument tray contains:

These weather instruments are used as soon as the nose cap, which protects the instrument carrier when entering the atmosphere and at hypersonic speeds, is blown off, while the magnetometer and the camera can record data right from the start.

So that additional experiments can be carried out in space and during entry, the nose cap itself is also equipped with instruments:

  • AMS, Accelerometric Measurement System: Accelerometers for precise measurement of deceleration in the high atmosphere from the Mars Society Germany.
  • COMPARE experiment to measure the dynamic pressure and the heating of the hypersonic compression shock, from the Institute for Space Systems at the University of Stuttgart .

Mission history

After the primary satellite arrives on Mars and has reached its final orbit around the planet, Archimedes will be disconnected and decelerated to a lower orbit along with its own propulsion unit, which also contains the helium tanks and all the devices for inflating the balloon. The carrier satellite remains on its higher orbit and serves as a relay station for data transmission to earth if necessary.

As soon as the suitable conditions are given - good weather, secure radio link to earth, entry on the day side of the planet - Archimedes is slowed down even further, so that the lowest point of the orbit lies just within the high atmosphere. Before this point is reached, the balloon is inflated and separated from the drive unit. Its orbit then touches the Martian atmosphere, which after being immersed several times slows it down so much that it remains in the atmosphere and sinks to the surface. From the inflation process onwards, scientific measurements are carried out and the data transmitted throughout the mission. It is expected that the balloon will fall below the speed of sound at a height of around 50 to 60 km, so that even the weather sensors can be used over a longer period of time and a complete atmosphere profile can be recorded over the entry path. After about 60 minutes the bottom is reached and the mission is over.

MIRIAM-1 balloon in space

Due to its complexity, the ARCHIMEDES Mars mission is being prepared in an extensive development and simulation program on Earth.

Status of the development and simulation program

MIRIAM-2 balloon during the inflation test in the IABG

The following flight attempts have been carried out or are planned:

  • On a parabolic flight campaign of the ESA , a scale model of an early version of the ejection mechanism was in 2005 weightlessness successfully tested
  • During the REGINA flight test ( RE sidual G as IN flation test for A rchimedes), a model of the deployment system on the REXUS-3 sounding rocket was brought from the Esrange in Kiruna , Sweden, to an altitude of 90 km and tested under space conditions.
  • In October 2008, the flight test MIRIAM-1 was also in Kiruna ( M ain I nflated R eentry I nto the A tmosphere M ission Test), in which the entire operating cycle of the system by inflating the balloon until it enters the atmosphere, including data transmission should be tested. For this purpose, a DLR-MoRaBa REXUS-4 rocket brought a balloon with a 4 m diameter to a height of 140 km. The mission was only a partial success. Due to a malfunction in the separating mechanism of MIRIAM-1, the balloon inflation unit was detached too late and the inflation process started while the balloon was still packed until the overpressure finally separated the inflation tube from the system. When the flight system finally detached itself from the rocket, the balloon was released immediately and unfolded in an uncontrolled manner and with only approx. 10% of the intended amount of gas. On-board electronics, software and data transmission worked as intended. Although the balloon did not fully unfold and then entered the atmosphere as planned, the data received proved the basic functionality of the design.
  • On November 3, 2015, balloon ejection tests for MIRIAM-2 were carried out during a parabolic flight. The balloon package only moved a few centimeters out of the container. It turned out, among other things, that the spring force of the ejection mechanism was designed too weak.
MIRIAM-2 balloon package during the ejection test during a parabolic flight
  • An overall improved version of the balloon ejection mechanism was finally tested with full success as part of another parabolic flight campaign on December 15, 2017.
  • The next flight test is currently planned for autumn 2021. MIRIAM-2 will then be launched again with a rocket from DLR-MoRaBa, but this time it will reach a height of over 200 km. This extends the mission time compared to MIRIAM-1, so that more time is available for separating the balloon carrier from the rocket and for the inflation process, which significantly improves the mission's chances of success. Compared to MIRIAM-1, MIRIAM-2 will also fly with a much more developed balloon, which largely corresponds to the Martian balloon in terms of material, manufacturing method and function. The balloon segments were no longer connected with adhesive tape, but welded together. Numerous other improvements compared to MIRIAM-1 are intended to ensure the success of the MIRIAM-2 mission.

MIRIAM-1 and MIRIAM-2 are complex space vehicles, as the balloon must first be transported into space in a tightly packed state. There, the balloon has to be unfolded fully automatically, inflated in stages and then released for its actual mission, to enter the earth's atmosphere. The measurement data obtained during this mission phase should provide information about the behavior of the balloon and thus prove the feasibility of the Mars mission. Of course, testing the systems for transporting and releasing the balloon is also an essential objective of the mission.

MIRIAM-2 construction drawing

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