Microgravity Science from ESA's Microgravity Sounding Rocket Projects* (Life and Physical Sciences)

G. Seibert and W. Herfs

ESTEC, Noordwijk, The Netherlands

* This article has been published previously in ESA SP-397, Proceedings of the 13th ESA Symposium on European Rocket and Balloon Programmes and Related Research, August 1997

Introduction

With its share of 25-30%, sounding rocket activities have been a firm and solid element of ESA's Microgravity Programme since its beginning in 1982. The use of sounding rockets has unanimous support from ESA's scientific advisory groups, and of all eleven delegations of ESA's Member States participating in the EMIR (European Microgravity Research) Programme.

In mid-1996, when a continuation of the EMIR-1 was expected to be approved in form of an EMIR-2 Programme (1997-2001), this approval turned out to be extremely difficult to obtain, due to the unforeseen costs of the Ariane 5 failure and a general reduction in space budgets in most of ESA's Member States. In July 1996, approval of 154 MECU (at 1995 economic conditions) for the EMIR-2 Programme could finally be obtained - also due to subscription increases later in 1996. About 40 MECU of this EMIR-2 programme are devoted to sounding rocket activities. This means that the Maser programme can be continued until 2001 at the same flight rate as in the past, and the Texus and Maxus programmes at a lower flight rate, until a further increase in subscriptions to the EMIR-2 programme can be achieved.

A further small sounding rocket activity can be expected from the Microgravity Applications Promotion programme element of the Space Station Utilisation Preparation Programme (243 MECU) which was approved in late 1995 at the ministerial conference in Toulouse. Fostering microgravity applications projects in which non-space industry is involved as an active participant is considered to be of particular importance. In the long term, the active involvement of industry with its own researchers and engineers at no cost to ESA can be considered as one of the most important arguments for continuing with the utilisation and operation of the Space Station. As an incentive in the promotional first phase of application projects, ESA would cover the development and flight of space-rated experimental facilities for precursor experiments on sounding rockets, retrievable satellites (e.g. Foton) and Shuttle (Spacehab) missions.

Figure 1: A Minitexus sounding rocket being prepared for launch under cover of a tent at Esrange, Kiruna, (S)

Scientific Disciplines Using the Low-G Phase of Sounding Rocket Flights

Life Sciences
Although most space life sciences experiments require extended periods of time, the experiments from the areas of cell and developmental biology and plant physiology have demonstrated that in the typical periods of 7 to 13 minutes of microgravity conditions provided by sounding rockets, valid scientific results can be obtained. Typical scientific research tasks are:

• to investigate how single cells (e.g. Loxodes) are influenced by gravity regarding their spatial orientation and morphological parameters; to determine graviperception thresholds for Loxodes and Euglena, and to investigate the graviperception mechanisms;

• to examine intracellular signal transduction and gene transfer in microgravity;

• to analyse the influence of gravity on the self-organisation and development of morphological structures in microtubule solutions;

• to look into the metabolism of plant cells, polarity of statocytes which are modified by the microgravity environment.

Physical Science
The practical absence of gravity-induced convection, sedimentation and gradients of hydrostatic pressure in fluids have led materials scientists, physicists, chemists and engineers to design experiments to be carried out in the microgravity environment, i.e. experiments which involve gravity-dependent phenomena such as:

• solidification processes of metals and alloys of eutectic or monotectic composition;

• processing of composite materials with solid particles or gaseous inclusions;

• growth of single crystals of semiconductors such as Si, Ge, GaAs, etc.;

• growth of protein crystals, large and defect-free enough to perform diffraction analysis with x-rays or gamma-rays for the determination of the 3-dimensional structure of such proteins;

• fluid-dynamic experiments which relate to interfacial tension and Marangoni convection;

• diffusion experiments - in the absence of convection - to study reaction kinetics in liquid alloys and glass melts;

• critical point experiments to investigate the phase separation of binary fluids near the critical point;

• the investigation of boiling/evaporation phenomena;

• the investigation of parameters that influence the electrophoretic separation of organic solutions;

• processing of composite materials by means of dispersion electrolysis;

• investigations in the field of colloidal chemistry;

• combustion experiments which require short experiment times and which are strongly influenced by gravity;

• dust agglomeration experiments aiming at a better understanding of the initial stages of star formation.

This non-exhaustive list demonstrates the very wide spectrum of scientific experiments which can be performed during the relatively short microgravity period of a sounding rocket flight.

Figure 2: Launch of a Minitexus rocket from Esrange

General Features of Sounding Rocket Experimentation

Originally, sounding rocket experiments were conceived as low-cost precursor experiments for long-duration missions like Spacelab etc. At the same time, however, an increasing number of self-standing experiments with their own scientific justification have developed.

What makes the sounding rockets such an attractive experiment platform for scientists is above all the relatively short lead time of only one to two years between experiment approval and flight, and the availability of a large number of experiment modules for a broad spectrum of scientific investigations.

In addition, the experiment design for a sounding rocket mission is not constrained by the safety requirements which have to be satisfied on manned missions. This also results in much less cumbersome paperwork for the investigators.

A further advantage is the rather high degree of flexibility with respect to late changes in the experiment requirements during the development of sounding rocket experiment hardware. Concerning the operational aspects of sounding rocket missions, telescience has already been available since 1983! Real-time data and video downlink exists as well as a telecommand uplink for the direct control of important experiment parameters. Today it is also possible to remotely control the experiment from the user's home institute via an ISDN or satellite link.

A very important feature of sounding rocket experimentation, especially for biologists, is the possibility of late access - up to one hour before launch, and fast recovery of sensitive samples after touch down of the payload. Another significant aspect is the excellent launch site infrastructure of ESRANGE which comprises well-equipped (bio-)laboratories as well as sufficient accommodation capability for investigators and industrial teams during the launch campaigns.

During the development of a sounding rocket experiment module, close cooperation between the investigator(s) and the industrial team evolves, and often the scientists can benefit from the engineers' dedication and their experience with experimentation under the condition of weightlessness.

On the other hand, handling the experiment hardware during launch preparations and the count-down, and to experience its performance during the actual mission, gives the engineers a unique feedback and contributes significantly to the quality of their designs.

Past and Future Sounding Rocket Missions in the Frame of ESA's Microgravity Programme

In the following tables, all ESA-funded sounding rocket missions, and the experiments performed from 1995 up to now are listed in Table 1, and those presently planned for the years 1997 until 1999 in Table 2.

Table 1. ESA-funded Sounding Rocket Missions in 1995 and 1996

Table 2. ESA-funded Sounding Rocket Missions from 1997 up to 1998

Table 3 shows the number of sounding rocket experiments which have been flown up to now per ESA Member State participating in the Microgravity Programme. Table 4 presents an overview of the number of ESA-funded sounding rocket experiments per scientific disciplines.

Table 3. Geographical distribution of the flown ESA-funded Sounding Rocket exepriments

Table 4. Overview of the number of ESA-funded Sounding Rocket experiments in the various disciplines

ESA-owned Sounding Rocket Experiment Modules

Within the framework of its Microgravity Programme, ESA has developed quite a number of sounding rocket experiment modules for a broad spectrum of scientific investigations. During the first years of ESA's involvement, hardware for materials science and fluid physics experiments was developed. Then it was found that the six minutes of microgravity time offered by a sounding rocket flight are sufficient for certain cell biological investigations. Therefore also flight and ground reference modules for biological experiments were developed, followed by an electrophoresis module. In the meantime, interest in combustion experiments under weightlessness has also evolved. A first combustion module was built by DASA (D) together with SENER (E), and the hardware for two more combustion experiments is presently under development.

In the following tables 5 to 10 an overview is given of the sounding rocket experiment modules which ESA has developed. In Table 11 some new ESA modules are listed which are presently under development. In addition, not shown in this table, DASA-RI (D) has started the development of the ESA-owned experiment modules for Maxus 3, largely based on existing hardware. However, it is worth mentioning that in the TEM 06-4M for the liquid bridge experiment of Prof. Monti (I) an AGEMA 550 infrared camera will be installed as a new diagnostic tool to visualize the patterns of the Marangoni convection modes at the surface of the liquid zone.

Table 5. ESA-owned Sounding Rocket Experiment Modules

Table 6. ESA-owned Sounding Rocket Experiment Modules

Table 7. ESA-owned Sounding Rocket Experiment Modules

Table 8. ESA-owned Sounding Rocket Experiment Modules

table 9. ESA-owned Sounding Rocket Experiment Modules

Table 10. ESA-owned Sounding Rocket Experiment Modules

table 11. New Sounding Rocket Experiment Modules Developed by ESA

Figure 3: TEM 06-12, a colloid chemistry module flown on Texus 17

For the experiment of Prof. Häder (TEM 06-RO1M), a fluorescence microscope will be developed. This is a diagnostic means which has not been used so far for a European sounding rocket experiment.

Besides the Maxus 3 experiment modules, DASA-RI (D) and SENER (E) are also developing an ESA module for the combustion experiment of Prof. Joulain (F) on Minitexus 6. This module is a modification of the existing TEM SEN and will contain - as a new feature - an infrared camera (AGEMA 550) for the observation of the flame and its temperature.

In addition, DASA-RI (D) has started to develop a new module for the droplet evaporation experiment of Dr. Gökalp (F) on Minitexus 7. This module contains a pressure chamber with a heated zone inside, a droplet generation system, and a CCD camera for the observation of the droplet.

Figure 4: The Esrange site at Kiruna with launch pad/tower in the background

Conclusion

The great potential of sounding rocket experimentation and its attractiveness for the scientific users has been shown. Since 1982, ESA has flown more than five tons of scientific payloads containing 132 experiments on 36 sounding rocket missions (25 Texus, 7 Maser, 2 Maxus, 2 Minitexus). The usefulness of sounding rocket experiments, both as a preparatory step for long-term missions - be it manned or unmanned - and as independent scientific investigations, has been successfully demonstrated in the past. This has been acknowledged by ESA's scientific advisory groups and also by the delegations of the ESA Member States participating in the EMIR Programme.

The sounding rocket activities will be continued in the framework of the EMIR-2 Programme. In addition, the sounding rockets will have to take their role in preparing meaningful experiments for the International Space Station.