Search

The baseline Venera-D mission, proposed to be launched after 2026, consists of an orbiter and a landing module, which includes a lander and a small long-lived station. In this work, we present the possibility of augmenting the mission with one or two micro-spacecraft in Lagrange point orbits to significantly enhance the science return. Both L 1 and L 2 collinear points, situated at about 1 million km from Venus, are considered for scientific objectives. The paper focuses on trajectory design for the micro-spacecraft to be deployed by the Venera-D mission. The transfer scenario we propose performs the insertion of micro-spacecraft into Lagrange point orbit by making use of the main orbiter’s propulsion, while the propulsion on board micro-spacecraft is used only for trajectory correction and station-keeping manoeuvres. This scenario allows the Venera-D mission to add one or two micro-spacecraft of mass about 50 kg with only a total Δ V budget 30 m/s over 3 years on orbit.

The Spectrum–Rontgen–Gamma (SRG) space observatory was launched from Baikonur on July 13, 2019, and is currently on a flight trajectory in the vicinity of the collinear Sun–Earth libration point L2. The planned service life of the observatory is 7 years and includes an all-sky survey and in-depth studies of individual objects in the X-ray range 0.3–15 keV. We consider the technical limitations of the mission pertaining to the launch scenario, the spacecraft design and system characteristics, including the data and command transmission, orbital motion and attitude control systems, and the peculiarities of the ground segment used to accomplish these tasks. The flywheel offloading strategy for the attitude control system is analyzed within the mentioned limitations. The goal of this analysis is to determine an optimal balance between the flywheel offloading operations while controlling the attitude of the observatory, the orbital maneuvers to keep it on a given trajectory, propellant consumption, and the requirements from the scientific measurements. The proposed method allows the total propellant consumption to be minimized by coordinated control of the operation of the system of attitude control rocket engines while simultaneously using them to maintain the specified orbital parameters.

The paper focuses on a future mission to Venus, Venera-D, which is presently at the stage of defining the scientific objectives and shaping the preliminary mission architecture. The main scientific goals regarding the atmosphere, magnetosphere and internal structure of Venus are considered. The current configuration, baseline, and additional elements of the mission are described.

The article describes the trajectory scenario for the Venera-D mission. The main aspects of optimal launch dates are considered. A scenario, which enables insertion of an orbiter into a highly elliptical orbit and a lander on the surface of Venus is described. Characteristics of the choice for operational orbit and scenario ensuring scientific data transfer from the lander on the surface of Venus to the Earth are justified. In addition, possibilities of transfer of a small satellite to the vicinity of the collinear Lagrangian point of the Sun-Venus system, and also a subsatellite into the orbit of the main orbiter, are considered.

Spectrum-Roentgen-Gamma is an international X-ray astrophysical space observatory, planned to be launched in 2019. The spacecraft will operate in the vicinity of the Lagrangian point L 2 of the Sun-Earth system. The nominal lifetime of the mission is 7 years, and it includes all-sky survey and pointed observations in the 0.1–15 keV band. The paper describes technical constraints of the mission, covering launch scenario, spacecraft structure and ground data relay network, and a design of suitable operational orbits. In addition, opportunities to achieve a suitable operational orbit are discussed, including a scenario with a lunar gravity assist and a transfer with an intermediate orbit.

The Spectrum-Roentgen-Gamma (SRG) project is intended for surveying the entire sky in the X‑ray band using two telescopes mounted onboard the spacecraft of the same name (SRG). In addition, some specially chosen areas of the sky and some radiation sources are planned to be investigated after the completion of the survey. The spacecraft was planned to be launched in 2018 into the vicinity of solar-terrestrial collinear libration point L2, using the Proton-M launch vehicle with a DM-03 block upper stage. The technology for completely surveying the celestial sphere consists in scanning by rotating the parallel axes of telescopes around the spacecraft axis, which roughly followed the direction to the Sun. The measurement data, stored onboard the spacecraft, would then be transmitted to the ground receiving stations using the mean gain antenna, the axis of which coincided with the spacecraft’s axis of rotation. This imposed some constraints on the mission design. These constraints included the permissible amplitude of the trajectory of spacecraft motion relative to the libration point in the direction orthogonal to the Sun–Earth line. In addition, the consumption of the onboard propellant was allowed only for orbit correction needed for keeping the spacecraft near the libration point. In this connection, a method was developed using the upper stage in order to decrease the mentioned amplitude down to acceptable values, in the conditions of the requirements imposed on the unit. The paper presents an assessment of its effectiveness.

The European Space Agency's INTErnational Gamma-Ray Astrophysics Laboratory (ESA/INTEGRAL) was launched aboard a Proton-DM2 rocket on 17 October 2002 at 06:41 CEST, from Baikonur in Kazakhstan. Since then, INTEGRAL has been providing long, uninterrupted observations (up to about 47h, or 170ksec, per satellite orbit of 2.7 days) with a large field-of-view (FOV, fully coded: 100 deg), millisecond time resolution, keV energy resolution, polarization measurements, as well as additional wavelength coverage at optical wavelengths. This is realized by two main instruments in the 15keV to 10MeV energy range, the spectrometer SPI (spectral resolution 3keV at 1.8MeV) and the imager IBIS (angular resolution: 12arcmin FWHM), complemented by X-ray (JEM-X; 3–35keV) and optical (OMC; Johnson V-band) monitor instruments. All instruments are co-aligned to simultaneously observe the target region. A particle radiation monitor (IREM) measures charged particle fluxes near the spacecraft. The Anti-coincidence subsystems of the main instruments, built to reduce the background, are also very efficient all-sky γ-ray detectors, which provide virtually omni-directional monitoring above ∼75keV. Besides the long, scheduled observations, INTEGRAL can rapidly (within a couple of hours) re-point and conduct Target of Opportunity (ToO) observations on a large variety of sources. INTEGRAL observations and their scientific results have been building an impressive legacy: The discovery of currently more than 600 new high-energy sources; the first-ever direct detection of Ni and Co radio-active decay lines from a Type Ia supernova; spectroscopy of isotopes from galactic nucleo-synthesis sources; new insights on enigmatic positron annihilation in the Galactic bulge and disk; and pioneering gamma-ray polarization studies. INTEGRAL is also a successful actor in the new multi-messenger astronomy introduced by non-electromagnetic signals from gravitational waves and from neutrinos: INTEGRAL found the first prompt electromagnetic radiation in coincidence with a binary neutron star merger. Up to now more than 1750 scientific papers based on INTEGRAL data have been published in refereed journals. In this paper, we will give a comprehensive update of the satellite status after more than 18 years of operations in a harsh space environment, and an account of the successful Ground Segment., Kuulkers, Erik, et al., he OMC team has been funded by different Spanish grants, including Spanish State Research Agency grants PID2019–107061GB–C61 and MDM–2017-0737 (Unidad de Excelencia María de Maeztu – CAB). The INTEGRAL French teams acknowledge partial funding from the French Space Agency (CNES). The Danish JEM-X gratefully acknowledges support from the Danish PRODEX delegation through contract C90057. The INTEGRAL Italian team acknowledges support form the Italian Space Agency, ASI, along these years via different agreements, last of which is 2019–35-HH.0. LH acknowledges support from SFI under grant 19/FFP/6777 and the EU AHEAD2020 project (grant agreement 871158). MH acknowledges support from Spanish MICINN grant PID2019-108709GB-I00. TS is supported by the German Research Society (DFG-Forschungsstipendium SI 2502/1-1 & SI 2502/3-1).

The orbital observatory Spectrum-Roentgen-Gamma (SRG), equipped with the grazing-incidence X-ray telescopes Mikhail Pavlinsky ART-XC and eROSITA, was launched by Roscosmos to the Lagrange L2 point of the Sun-Earth system on July 13, 2019. The launch was carried out from the Baikonur Cosmodrome by a Proton-M rocket with a DM-03 upper stage. The German telescope eROSITA was installed on SRG under an agreement between Roskosmos and the DLR, the German Aerospace Agency. In December 2019, SRG started to perform its main scientific task: scanning the celestial sphere to obtain X-ray maps of the entire sky in several energy ranges (from 0.2 to 8 keV with eROSITA, and from 4 to 30 keV with ART-XC). By mid-June 2021, the third six-month all-sky survey had been completed. Over a period of four years, it is planned to obtain eight independent maps of the entire sky in each of the energy ranges. The sum of these maps will provide high sensitivity and reveal more than three million quasars and over one hundred thousand massive galaxy clusters and galaxy groups. The availability of eight sky maps will enable monitoring of long-term variability (every six months) of a huge number of extragalactic and Galactic X-ray sources, including hundreds of thousands of stars with hot coronae. The rotation of the satellite around the axis directed toward the Sun with a period of four hours enables tracking the faster variability of bright X-ray sources during one day every half year. The chosen strategy of scanning the sky leads to the formation of deep survey zones near both ecliptic poles. The paper presents sky maps obtained by the telescopes on board SRG during the first survey of the entire sky and a number of results of deep observations performed during the flight to the L2 point in the frame of the performance verification program.(Abriged), Comment: 30 pages, 46 figures. Astronomy & Astrophysics, 656, A132, 2021. Abstract abridged

The paper considers the problem of finding accessible areas on the Venus surface and the prospect of their increasing by extension of launch windows during the period from 2026 to 2031; taking into account the restrictions on the payload weight and the maximum overload level affecting the lander during the descent in the Venus atmosphere. The project of the Venera-D mission is used as the initial data for the work. The possibility of reaching the planet on the first and second half-turns of the heliocentric transfer orbit is analyzed. As an example, the effect of the launch window expansion for 2031 on the nature of changes in the accessible landing areas is considered. Possible payload weight expenses for launch window expansion are estimated. The launch windows are selected by solving the Lambert problem, where the transit spacecraft momentum near the Earth for the flight to Venus along the first and second half-orbit paths at the period from 2026 to 2042 is calculated. The accessible landing area is shown when increasing the launch windows initially adopted for 2031.The estimation of payload weight expenses for increasing the launch windows is performed.

The halo of the Milky Way provides a laboratory to study the properties of the shocked hot gas that is predicted by models of galaxy formation. There is observational evidence of energy injection into the halo from past activity in the nucleus of the Milky Way; however, the origin of this energy (star formation or supermassive-black-hole activity) is uncertain, and the causal connection between nuclear structures and large-scale features has not been established unequivocally. Here we report soft-X-ray-emitting bubbles that extend approximately 14 kiloparsecs above and below the Galactic centre and include a structure in the southern sky analogous to the North Polar Spur. The sharp boundaries of these bubbles trace collisionless and non-radiative shocks, and corroborate the idea that the bubbles are not a remnant of a local supernova but part of a vast Galaxy-scale structure closely related to features seen in gamma-rays. Large energy injections from the Galactic centre are the most likely cause of both the {\gamma}-ray and X-ray bubbles. The latter have an estimated energy of around 10$^{56}$ erg, which is sufficient to perturb the structure, energy content and chemical enrichment of the circumgalactic medium of the Milky Way., Comment: Author's version. 17 pages, 5 figures, Published in Nature 2020, Vol 588

System of Observation of Daytime Asteroids (SODA) is a space mission project, intended to detect and monitor hazardous asteroids approaching the Earth from the Sun direction, namely from the daytime sky. In particular, the SODA mission aims to detect small celestial objects of size about 10 m, approaching the Earth from directions inaccessible to ground-based and near-Earth space-based telescopes, and to inform beforehand whenever a risk of collision with the Earth occurs. The system uses one or two spacecraft launched into the vicinity of the Lagrangian point L1 of the Sun-Earth system, about 1.5 million km from the Earth. This paper considers main aspects of trajectory design for the SODA project at its initial stage. Selection of an orbit about L1 point, transfer from the Earth and stationkeeping in the vicinity L1 are discussed. A launch scheme making use of a lunar gravity assist is proposed to achieve a desired configuration of the two spacecraft.

Spectrum–Rontgen–Gamma (SRG) is a space observatory designed to observe astrophysical objects in the X-ray range of the electromagnetic spectrum. SRG is planned to be launched in 2019 by a Proton-M launch vehicle with a DM3 upper stage. The spacecraft will be delivered to an orbit around the Sun–Earth collinear libration point L2 located at a distance of ~1.5 million km from the Earth. Although the SRG launch scheme has already been determined at present, in this paper we consider an alternative spacecraft transfer scenario using a lunar gravity-assist maneuver. The proposed scenario allows a oneimpulse transfer from a low Earth orbit to a small-amplitude orbit around the libration point to be performed while fulfilling the technical constraints and the scientific requirements of the mission.

The opportunities to study Phobos’ internal structure provided by radio methods are considered in this paper. The necessity of these studies is related to solution of the problem of the origin of the Martian moons. Radiosounding is one of the most efficient methods of analyzing the internal structure of small space objects and, in particular, that of Phobos. The new Boomerang project planned according to the Federal Space Program of Russia for 2016—2025 within the Expedition-M program aimed at the exploration of Phobos and delivery of soil samples from its surface to the Earth, as well as the specifics of a ballistic scenario of this expedition, provide a unique opportunity to carry out radioscopy of this space object to discover the internal structure Phobos and to solve the key problem of its origin. The model of Phobos’ internal structure, radiosounding ballistic conditions, analysis of optimum frequency range of sounding, and key parameters of the device required for the experiment are considered in this paper. The significance of proposed studies and opportunities for their implementation are discussed.

At present, the capture of a suitable asteroid into an Earth satellite orbit is proposed as one of the methods for investigating asteroids within the framework of manned missions. Once the asteroid has been transferred to such an orbit, an expedition with the participation of astronauts is planned to the asteroid surface, where research is carried out and asteroid rock samples are selected and subsequently delivered to the Earth. It is in this way that the American Keck project is described at the current planning and preliminary design stage. In this paper, we solve the capture problem by a method alternative to that planned in the Keck project.

Amethod for preventing the collisions of hazardous celestial objects with the Earth by diverting them from the trajectory of their encounter with the Earth is investigated. For this purpose, we propose to use small near-Earth asteroids that are transferred to the trajectories of a gravity-assist maneuver near the Earth by imparting a comparatively small velocity impulse to them. As a result of such a maneuver, a small asteroid is thrown into the hazardous object’s interception orbit. The asteroids suitable for achieving this goal are chosen by solving Lambert’s problem. The same concept is investigated for the problem of transferring asteroids to orbits resonant with the Earth’s orbit so as to open up the possibility of regular missions to such asteroids with the goal of studying them and using their resources. The choice is made by minimizing the mentioned velocity impulse, whose admissible value is assumed to be within the limits that do not exceed 20 m s−1.

In this paper, the method of changing the trajectories of hazardous asteroids with orbits known for some years to be on a possible collision course with the Earth is considered. The method relies on the use of small asteroids (asteroid-projectiles) directed at hazardous celestial bodies by giving the projectile a sufficiently small velocity impulse ensuring the Earth gravity assist. As a result, the asteroid-projectile vector can be controllably changed over a wide range. Apophis is considered as an example of the target asteroid. The technical feasibility of this method is discussed. It is noted that despite the potential use of this elegant method, its practical implementation requires further research and development.

The atmospheric detonation of a 17 m-asteroid above Chelyabinsk, Russia on 2013 February 15 shows that even small asteroids can cause extensive damage. Earth-based telescopes have found smaller harmless objects, such as 2008 TC3, a 4 m-asteroid that was discovered 20h before it exploded over northeastern Sudan (Jenniskens, 2009). 2008 TC3 remains the only asteroid discovered before it hit Earth because it approached Earth from the night side, where it was observed by large telescopes searching for near-Earth objects (NEO’s). The larger object that exploded over Chelyabinsk approached Earth from the day side, from too close to the Sun to be detected from Earth. A sizeable telescope in an orbit about the Sun-Earth L1 (SE-L1) libration point could find objects like the “Chelyabinsk” asteroid approaching approximately from the line of sight to the Sun about a day before Earth closest approach. Such a system would have the astrometric accuracy needed to determine the time and impact zone for a NEO on a collision course. This would give at least several hours, and usually 2–4 days, to take protective measures, rather than the approximately two-minute interval between the flash and shock wave arrival that occurred in Chelyabinsk. A perhaps even more important reason for providing warning of these events, even smaller harmless ones that explode high in the atmosphere with the force of an atomic bomb, is to prevent mistaking such an event for a nuclear attack that could trigger a devastating nuclear war. A concept using a space telescope similar to that needed for an SE-L1 monitoring satellite, is already conceived by the B612 Foundation, whose planned Sentinel Space Telescope could find nearly all 140 m and larger NEO’s, including those in orbits mostly inside the Earth’s orbit that are hard to find with Earth-based telescopes, from a Venus-like orbit (Lu, 2013). Few modifications would be needed to the Sentinel Space Telescope to operate in a SE-L1 orbit, 0.01 AU from Earth towards the Sun, to find most asteroids larger than about 5 meters that approach the Earth from the solar direction. The spacecraft would scan 165 square degrees of the sky around the Earth every hour, finding asteroids when they are brightest (small phase angle) as they approach Earth. We will undertake Monte Carlo studies to see what fraction of asteroids 5 m and larger approaching from the Sun might be found by such a mission, and how much warning time might typically be expected. Also, we will check the overall coverage for all Earth-approaching NEO’s, including ground-based observations and observations by the recently-launched NEOSSat, which may best fill any gaps in coverage between that provided by an SE-L1 telescope and ground-based surveys. Many of the objects as large as 50 m, like the one that created Meteor Crater in Arizona, will not be found by current NEO surveys, while they would usually be seen by this possible mission even if they approached from the direction of the Sun. We should give better warning for future “Bolts out of the blue.”

We are undertaking a Russian-American study of orbital options to extend human exploration beyond the Moon’s orbit. For a viable program, an international collaboration (as now for the ISS) and reusable spacecraft will be needed. With reusable spacecraft, high-energy Earth orbits can be drastically modified with lunar swingbys and small maneuvers near the edge of the Earth’s gravitational sphere of influence, especially near the collinear Sun-Earth and Earth-Moon libration points, to reach desired destinations. The work will build on ideas developed by the International Academy of Astronautics’ exploration study group presented at the 2008 International Astronautical Congress in Glasgow. The first efforts could support backside lunar exploration from an Earth-Moon L2 temporary Lissajous or relatively permanent halo orbit; some quick low post-launch ΔV trajectories are presented. In a stepping stone approach, later missions could service large space telescopes near the Sun-Earth L2 libration point; explore near-Earth asteroids; and then the moons of Mars. The study will use highly-elliptical Earth orbits whose line of apsides can be rotated using lunar swingbys; then a propulsive maneuver, considerably smaller than that needed from a circular low-Earth orbit, can be applied at the right perigee to send the spacecraft on the right departure asymptote to a desired destination.

The adjustment and maintenance of spacecraft configurations by means of solar sails is considered.

The possibility of investigating the sky region near the Galactic center with instruments of the INTEGRAL orbital astrophysical gamma-ray observatory by the method of its occultation by the Earth and the Moon is considered. Existing engineering constraints on the observing conditions, such as the admissible orientation of the INTEGRAL satellite relative to the direction to the Sun and the performance of measurements only outside the Earth’s radiation belts, are taken into account. Long time intervals during which the lunar occultation center passes at angular distances of less than 2° from the Galactic center have been found. Such events occur under the adopted constraints two or three times per year without any correction of the INTEGRAL satellite orbit. The orbit can be corrected to reduce the angular distance between the Moon and the Galactic center in occultation events. The required velocity impulses do not exceed several meters per second. The possibility of the Galactic center being occulted by the Earth has been analyzed. In this case, to perform measurements, the admissible (in radiation exposure) height of the working segment of the orbit should be reduced to 25 000 km, which can be problematic. At the same time, part of the Galaxy’s equatorial region is shadowed by the Earth for a time long enough to carry out the corresponding experiments.

From 2007 the Russian Academy of Sciences and Roscosmos consider to develop a Europa surface element, in coordination with the Europa Jupiter System Mission (EJSM) international project planned to study the Jupiter system. The main scientific objectives of the Europa Lander are to search for the signatures of possible present and extinct life, in situ studies of the Europa internal structure, the surface and the environment. The mission includes the lander, and the relay orbiter, to be launched by Proton and carried to Jupiter with electric propulsion. The mass of scientific instruments on the lander is ∼50 kg, and its planned lifetime is 60 days. A dedicated international Europa Lander Workshop (ELW) was held in Moscow in February 2009. Following the ELW materials and few recent developments, the paper describes the planned mission, including the science goals, technical design of the mission elements, the ballistic scheme, and the synergy between the Europa Lander and the EJSM.

The realization of Russian–Australian scientific—educational micro-satellite “Kolibri-2000” (weight of 20.5 kg, http://www.kolibri2000.ru 20 March, 2002), delivered into an orbit by “Progress M1-7”, was the first item in the Program of Scientific—Educational Micro-Satellite (PSEMS' 2002–2007, http://iki.cosmos.ru/kollibri/mission1_e.htm ) and designate the starting point of a series at perspective scientific—educational micro-satellites (SEMS, http://www.energia.ru/english/energia/sci-education/microsat/microsat-02.html ). In the “Kolibri-2000” project, several schools equipped by School Center of Reception of the Information (SCRI), participated, including Russian schools (Obninsk http://ftschool.obninsk.org ) and two Australian schools in Sydney, Knox Grammar School ( www.knox.nsw.edu.au ) and Ravenswood School for Girls ( www.ravenswood.nsw.edu.au ). The results of the “Kolibri-2000” first measurements on the orbit near the International Space Station will be submitted in this paper which include the ionosphere reaction during the April 2002 events, and address as understanding of the coupling and feedback in the Sun–Earth interaction.

The evident tendency is the rapid growth the number of microsatellites, and it’s is fully explained by their low cost, the speed of preparation and relative simplicity of their realization. Quite often such spacecrafts are used in the educational purposes. At the same time the result of analysis shows that such satellites can also solve important fundamental scientific problems in addition to their educational purposes. But in this case it requires solving a number of additional tasks. First of all it is required to ensure comparatively high speed of the downlink telemetry for necessity of receiving of meaningful scientific results. That in turn is demanded the appropriate solutions in the on-board and ground segments of the mission. However it's necessary to save the main advantages of the microsatellites: lowcost of development, implementation and operations as well as short time of development. As an example, in the paper is considered the ground segment for Russian Academia-University microsatellite "Chibis-M" which is the first from series of the microsatellites "Chibis" used for solving different fundamental problems. The technical and methodical solutions, prospects for further development are discussed in the article.

Not in the space researches only, but mostly in all branches of the human activity the design of the projects must satisfy three main co ntradictory requirements: the project must be developed as soon as possible, it must possess extended functionality and the budget must be reduced as low as possible. So using modern solutions in design of information systems and technologies approved in the different branches may dramatically increase project efficiency. The article summarizes using of such approaches as Web 2.0, SOA, ESB in the information systems of the last Russian scientific space missions and demonstrates possible ways of the system’ evolution .

It is well known that for the most of space missions one of the strongest constraints is the rate of information transfer from the spacecraft onboard instruments to the ground station. This parameter becomes critical for the tasks, connected with planetary explorations. For example to deliver the information to be collected during planetary mapping missions with high resolution one needs to keep telemetry bit rate at the level on the limit of technical feasibility or beyond. It is true for exploration of such planets as Mars, Venus or Mercury and it is much more difficult task for big distant planets as Jupiter. In the paper the alternative method of space missions information delivery is discussed. It is p roposed to collect information in some solid memory device installed onboard spacecraft and then to send it to the Earth using very small spacecraft. This spacecraft may carry some returnable capsule to enter atmosphere or transmit collected information tr ough radio link when reaching short enough distances from the Earth.

For the practical realization of the mission to the collinear Sun-Earth libration points technical constraints play a significant role. In the paper the influence of the constraints generated by the use of piggy-back mode of the delivering spacecraft to the vicinity of libration points is studied. High elliptical parking orbit of MOLNIYA is taken as initial orbit for start to the L1, L2 libration points. The parameters of this orbit is supposed to be fixed and determined by the main payload demands.The duration of the passenger payload keeping on the mentioned 12 hours period orbit is limited for the case when launcher upper stage is used for the velocity impulse appliing to put spacecrat onto transfer orbit to the libration point. The possibilities to use one axis attitude control of the spacecraft for the executing correction maneuvers are investigated, supposing that spacecraft is spin stabilized with the spin axis directed to the Sun and maneuver impulse goes along this axis. The cost of constraits is presented in terms of characteristic velocity and time of transfer to the libration point vicinity. The goal of the paper is to understand the possibility of using regular launches of MOLNIYA communication satellites by Soyz -Fregat launch vehicle for sending low cost scientific spacecraft to SunEarth libration points.

The International Gamma-Ray Astrophysics Laboratory (INTEGRAL) is a proposed joint ESA/NASA/Russia gamma-ray astronomy mission which will provide both imaging and spectroscopy. It is currently at the final stages of an ESA phase-A study which it is hoped will lead to it being adopted during 1993 as the second 'medium-class' mission within ESA's Horizon 2000 plan. Launched in less than 10 years time it will be the successor to the current generation of gamma-ray spacecraft, NASA's Compton Observatory (GRO) and the Soviet- French Granat/Sigma mission. The baseline is to have two main instruments covering the photon energy range 50 keV to 10 MeV, one concentrating on high-resolution spectroscopy, the other emphasizing imaging. In addition there will be two monitors--an X-ray monitor which will extend the photon energy range continuously covered down to a few keV, and an Optical Transient Camera which will search for optical emission from gamma-ray bursts.

Observations of the transient X-ray source A0535+26 obtained with the Signe-2MP instrument aboard Prognoz 6 and 7 are reported. Peak fluxes for the flares of this source are plotted, and the average count for a frame is studied as a function of the rotation angle (the measurement time was 10.5 hours).