I PAFERM, THE ULISSES PARTICLES AND FIELDS ENVIRONMENT REFERENCE MISSION I

A. Ginati I OHB-System GmbH Bremen, Germany

J.Beeck I TZN Forschungs-und Entwicklungszentrum GmbH Unterlu~, Germany I H. Kunow University of Kiel I Kiel, Germany

The paper discusses a small satellite mission that I was proposed to the (ESA) and to the German Space Agency (DARA). The idea is to support the Vlysses mission by conducting reference I measurements in the ecliptic plane. particularly during the time periods of ' polar passages. The scientific objectives, the instrumentation. and the impact on the Ulysses mission are discussed. The I mission scenario is described. the mission constraints are given, and a preliminary spacecraft I concept is shown. I 1. INTRODUCTION The proposal for PAFERM was submitted in due time to ESA. As a response ESA The Particles and Fields Environment received a total of 52 proposals. Quite I Reference Mission (PAFERM) is a result of obviously, the scientific community has a a response to a Call for Ideas that was pronounced interest in small missions. issued by the European Space Agency (ESA) This interest was conf irmed by a survey on 18 June 1990. This Call for Ideas was conducted by the Science Applications I initiated by a recommendation of the International Corporation; 91% of space Science Programme Review Team. The physicists surveyed believe that NASA recommendation was that small missions should plan more frequent smaller should be implemented into the science missions, even at the expense of large I programme. As a guideline for the missions /1/. scientific community some technical information on the characteristics of the The PAFERM mission is related to the small mission where given by the review Ulysses mission; the idea is to conduct team as follows. in-ecliptic reference measurements for I Ulysses. The period of utmost interest is total mass below 200 kg the time of the spacecraft· s passage of payload mass between 10 to 50 kg the polar regions of the Sun. Between stabilization, either spin or 3-axis June and October 1994 the heliographic I launcher: Scout II, Pegasus or Apex latitude of the spacecraft exceeds 70 orbit, low or GTO degree; this south polar pass will be operations of about 1 year duration followed by a north polar pass between development time less than three June and September 1995. Therefore, the I years planned launch for PAFERM is dated April cost to ESA, ~etween 10 to 20 MAU 1994. I I I The evaluation process within the The general interplanetary structure is European Space Agency (ESA) will continue often disturbed by non-linear processes, on for some time. Subsequently, the like e.g. shocks. Large shocks are I PAFERM proposal was submitted to the initiated if plasma is ejected from the German Space Agency (DARA) and found corona at very high velocities of about considerable interest. At the time of the 1000 k:m/s upon flares or other writing of this paper, the evaluation dramatic, often explosion-like effects in process within ESA and DARA is still the corona. The average solar wind I going on. velocity is about 400 k:m/s. The high speed plasma is pushing the normal solar 2. SCIENTIFIC BACKGROUND wind ahead and, as the velocity is above the speed of sound in the plasma, the I 2.1 Introduction ambient plasma is shocked similar to an explosion shock wave. At large distances all energy of the shock is used up to scientific aim of the Particle and Field accelerate the solar wind and the shock: I Environment Reference Mission (PAFERM) is dies out. to complement and support the scientif ic goals of the Ulysses mission, in particular of its polar passages. During I the past decade it has become evident, that. new fundamental results concerning 2.3 The Interplanetary Magnetic Field interplanetary particle and field physics as well as conclusions on solar or Solar wind and interplanetary magnetic galactic phenomena are only possible with field are intimately related due to the I sufficient accuracy if multi-spacecraft so called frozen-ion magnetic fields in measurements are used. the plasma. The general heliospheric magnetic field originates from the Sun I s surface field. While field lines are I drawn out into interplanetary space by 2.2 The Solar Wind the high electrical conductivity plasma flow of the solar wind, they also remain The solar wind originates from the very rooted within the photosphere. Therefore, I hot corona of the Sun. Some solar radii the investigation of the heliospheric away from the Sun, the solar wind is magnetic field is related to the stUdy of observed as a continous stream of hot solar magnetism, as well as to that of plasma reaching out far into the coronal structures and dynamics. Also, it I heliosphere. On average, it consists of is intimately related to the study of 95% hydrogen ions (protons), 4% helium interplanetary phenomena on all temporal ions (a-particles) and different ions of and spatial scales. other elements with an appropriate I charge-equalizing number of free While direct observations have covered a electrons. The velocity of the solar wind large range of heliocentric distances, varies widely, in general between about spacecraft orbits have been restricted to 300 k:m/s (slow solar wind streams) and the close vicinity of the ecliptic plane. I about 900 k:m/s (fast solar wind streams). Therefore, little is known with regard to the heliolatitude dependent topology of The radial expansion of the solar wind the interplanetary magnetic field. Remote determines the structure of the sensing of the solar surface field and of I interplanetary medium which is e.g. the corona indicates that it is important for propagation processes of impossible to extrapolate with sufficient energetic particles. The solar wind confidence from in-ecliptic measurements plasma flows radially away from the Sun, to the third dimension of the I carrying the solar magnetic field lines heliosphere. as frozen in fields out into space. The field lines generally, remain attached to Direct observations are therefore the solar surface. Its roots follow the necessary to provide an observational I rotation of the Sun, and consequently the basis for establishing the heliolatitude field lines in consecutive plasma volumes dependence of the heliospheric magnetic are forming an Archimedian spiral around field. These observations will be used to the Sun. investigate numerous phenomena of I Figure 1 displays the magnetic field in fundamental importance for our the plane of the solar equator and shows understanding of the heliosphere. a marked sector structure, extending into the plane of the ecliptic as well. The low-to-middle latitude regions of the I Regions with magnetic fields Sun are dominated by sunspots and active predominantly pointing towards the Sun regions. These regions are normally alter with regions of opposite direction. characterized by closed field lines in I I I the corona. Origin and characteristic The result is that there are at present features of the solar wind and the major discrepancies between theory and I magnetic fields over these regions are observations. As in the case of the solar completely unknown. The measurements of wind, we wish to study the particle Ulysses compared to PAFERM will help to behaviour at different heliographic resolve these questions. latitudes, Le. under a variety of different plasma conditions, primarily in I At high latitudes, magnetic field lines an effort to help delineate the various and solar wind flow are expected to processes involved. The changing become parallel. This will strongly configuration of the he1iospheric influence the stream-stream structure in magnetic field with latitude should give I the he1iosphere at high latitude. The rise to latitude variations in the nature investigation of their extent and of waves, shocks and other structures characteristics as a function of that affect energetic particles. he1io1atitude is very important and can I be studied by Ulysses and PAFERM together Solar energetic particles, i.e. energetic more reliable than with one spacecraft particles from the Sun are used as probes alone. to monitor the conditions and physics in the solar atmosphere. These particles I provide information on the chemical and isotopic composition of the solar 2.4 Energetic Particles atmosphere and also information on the transport and storage of particles in the I cosmic rays consist of electrons, strong magnetic fields of the corona. protons, helium nuclei, and some very Observations in the ecliptic plane are small contribution of nuclei of all other difficult to interpret since the chemical elements which propagate through particles can originate and propagate I space with very high velocities. The high through a variaty of different regions in velocities imply that the charged the corona, with the result that the particles have been accelerated in space composi tion and spectra that we observe very efficiently by electric fields. are the products of a complicated mixture I Meanwhile we know from many areas within of processes. the solar system that acceleration processes are typical for an extreme tenous plasma. A particle in a plasma of At different heliographic latitudes, the I one million degree has an energy of 86 mixture of processes involved is expected eVe 'Energetic' particles are those which to be different, and perhaps simpler. have energies well above the thermal Ulysses will enable us to make energy of the plasma, e.g. above 50 keV observations of solar particles directly and up to several GeV. over active regions, which are I predominantly found at moderate solar latitudes, or directly over the It is known since 40 years that the Sun magnetically open regions in coronal is able to accelerate particles, although holes. Again the reference measurement I the maximum energy of these solar cosmic with PAFERM is mandatory to draw rays is much smaller than the average conclusions on coronal and interplanetary energy of galactic cosmic rays. Solar propagation from the out-of-ecliptic events are relatively short intensity data. I increases following explosive chromospheric eruptions (flares). Of special interest is the acceleration process during flares. In addition 2.5 Interstellar Gas I accelerated particles can be used as 'probes' which allow conclusions on Neutral interstellar gas is swept into magnetic structures in the solar corona the heliosphere as the solar system moves and interplanetary space. relative to the local interstellar I medium. Most of the information about The solar wind and the he1iosphere are this medium is derived from indirect used as a testing ground for theories of optical measurements of the solar Lyman-a the propagation and acceleration of radiation resonantly scattered by the I energetic particles in an astrophysical neutral interstellar hydrogen penetrating plasma. There are many similarities into the heliosphere. Helium particles, between the conditions that energetic being much less affected by solar particles find in the solar wind and radiation pressure, photo-ionisation, and those that should exist in other charge exchange with the solar wind, I astrophysical plasmas. The development of provide more accurate information on the reliable theories for the propagation and state of the interstellar gas in the I acceleration have been proved difficult. vicinity of the solar system than does I I hydrogen. Ulysses will make the first rays may have an easier access to direct measurements of neutral helium in the inner solar system than near the the heliospherei these measurements will ecliptic plane, be complemented by data taken on-board I PAFERM. to advance our knowledge of the neutral component of interstellar gas by measur ing as a function of heliographic latitude the properties I 3. SCIENTIFIC OBJECTIVES and distribution of neutral gas that enters the heliosphere. The primary objectives of the Ulysses mission are to investigate for the first I time as.a function of solar latitude, the Past experience with multi-spacecraft propertl.es of the solar wind, the observations include the 2 German Helios structure of the Sun / wind interface, spaceprobes. The twin mission of Helios 1 the. heliospheric magnetic field, solar and Helios 2 during 1976 to 1979 provides I radl.o bursts and plasma waves, solar x­ valuable examples how two- or multi­ rays, solar and galactic cosmic rays and spacecraft measurements enhance the the interstellar / interplanetary neutral scientific value of single point gas and dust. The following objectives measurements. I will be achieved in connection with the reference mission PAFERM: Experience with previous missions has shown that an interdisiplinary approach to provide an accurate assessment of is essential if the complex interactions the global three-dimensional between plasma, magnetic fields, and I charged particles are to be studied on a properties of the interplanetary global scale. In the case of an magnetic field and the solar wind, exploratory mission like ulysses, this aspect is clearly of crucial importance. I to improve our knowledge of the This includes the necessity for an in­ composition of the solar atmosphere ecliptic baseline which shall be provided and the origin and acceleration of by the PAFERM mission. the solar wind by systematically I studying the composition of the Secondary objectives with much lower solar wind plasma and solar priority are magnetospheric physics energetic particles at different related to the parts of the PAFERM orbit heliographic latitudes, inside the Earth's magnetosphere. I to provide new insight into the acceleration of energetic particles in solar flares and into storage and 4. SCIENTIFIC PAYLOAD I transport of these particles in the corona by observing the particle The Particles And Fields Environment emission from solar active regions Reference Mission PAFERM is positioned to and from other magnetic act as an interplanetary, in ecliptic, I configurations which are more near Earth platform' to continously accessible for study from out of the collect data on solar, interplanetary and ecliptic, interstellar fnergetic particles, solar wind, magnetic fields, and interstellar to improve our knowledge of the neutral gas. It will provide baseline I internal dynamics of the solar wind, measurements for Ulysses. The seasonal of the waves, shocks and other dependence of the orbit and the discontinuities, and of the excentricity allow furthermore heliospheric propagation and measurements in the lobes of the I acceleration of energetic particles, magnetosphere, in the magnetosheath, and by sampling plasma conditions that in the magnetosphere as well. are expected of being different from those available for study near the The PAFERM payload consists of four I ecliptic, experiments with the following objectives: to improve our understanding of the spectra and composition of galactic COSPIN (cosmic ray and solar particle I cosmic rays in interstellar space by investigation) is a comprehensive solar, measuring the solar modulation of planetary, and interplanetary particle these particles as a function of experiment identical to the COSPIN heliographic latitude and by experiment on-board Ulysses. Its I sampling these particles over the objectives are to determine intensities, solar poles, where low-energy cosmic spectra, and chemical and isotopic I I I composition of galactic cosmic rays, The TAUS instrument will perform state of anomalous components, and solar energetic the art solar wind measurements by particles. determining 3-dimensional distribution I functions of protons and alpha particles and allowing measurements of the all The COSPIN instrumentation includes three relevant solar wind parameters with high different experiment boxes and one energy, angular and time resolution. The I electronic box. The instrumentation that hardware of TAUS that will be used for is foreseen for the PAFERM mission is the PAFERM is a flight spare model from the flight spare model from Ulysses. Soviet Phobos mission. There~ore a detailed description of the I expe~1ments can be found elsewhere /2/3/. The magnetic field experiment will The 1nstrumentation comprises five solid­ measure the interplanetary magnetic state detector telescopes and a double field. The knowledge of the Cherenkov / semiconductor telescope. The interplanetary field is very important I energy range of this particle instrument for the scientific interpretation of the is 0.3 to 600 MeV/nucleon for nuclei particle data (COSPIN) and the solar wind i.e. protons, helium and other elements; data (TAUS). The propagation of the and 1 to 300 MeV for electrons. energetic particles is mainly along the I magnetic field lines, the scattering Box 1 contains two anisotropy telescopes, centers of the particles are provided by a low energy telescope and the data­ fluctuations of the guiding magnetic processing unit. The detector consists of field. The second objective is the study I a stack of three and four solid-state of the magnetosphere. The orbit is partly detectors, respectively. The low energy inside the magnetosphere (actually for telescope is surrounded by a cylindrical the larger part of the mission), plastic scintillator as an anti­ therefore the magnetic field experiment I coincidence shield. will study the access of energetic particles to the different regions of the Box 2 houses a high-energy telescope and magnetosphere depending on the dynamic a high-flux telescope. The high-energy state of the magnetosphere. telescope is comprised of a stack of I Lithium-drifted silicon detectors s~rrounded by a plastic scintillator. The h~g~-flux telescope incorporates a single s1l1con detector. The electronics for 5. MISSION-SCENARIO I both detectors accounts for most of the volume of this box. Figure 2 is a sketch of the Earth and its magnetosphere. The Sun (not shown) is Box 3 :onsists of two separate packages. located far away on the left of this I The K1el Electron Telescope is one sketch. The magnetic field of the Earth package. This detector incorporates a is a dipole field th~t is affected by the Cherenkov detector inserted between two solar wind. At the side of the magnetosphere that points towards the surface barrier semi-conductor detectors Sun, the field is compressed causing a I and four photomultiplier tubes. Th~ bow shock; at the opposite side the field second package houses the electronics for is elongated and forms the magnetotail. this instrument. The most important point for the PAFERM The ANGAS experiment will remotely sound mission is that the Ulysses reference I the main fluid parameters of the measurements have to be conducted within interstellar gas (mainly helium) into the undisturbed solar wind. The distance which the solar system is embedded. First Earth / bow shock is approximately 10 I measurements of this kind are presently Earth radii (70,000 km). ~eing done by the GAS (or KEP-3) The implication for the PAFERM orbit is, 1nstrument on the Ulysses spacecraft. The that the maximum distance (apogee) ANGAS instrument consists of a sensor spacecraft / Earth has to exceed this 10 I incorporating the LiF-coated conversion Earth radii. Therefore the orbit foreseen surface and channel electron multiplier i~ a 400 km times 100,000 km orbit. A as detector elements. It also includes a c1rcular orbit with a distance of 100,000 tiny furnace that will be used to deposit km from the Earth has some advantage fresh layers of LiF in the case of com~ared to the chosen high eccentric I contamination during flight. orb1t, but raising the perigee from 400 km to 100,000 km takes a large amount of energy .. W~t~in the constraints given by ANGAS is based on the GAS experiment on­ the def1n1t10n of a small mission only a I board Ulysses, but is slightly modif ied ~igh eccentric orbit can be realized. An because of the different mission-profile 1ncrease of the apogee distance beyond and interface to the spacecraft. 100,000 km needs of course additional energy, but a modest increase might be I possible. I I The second mission constraint is given by total mass of about 75 kg, including the the Earth's orbit around the Sun. If adapter ring for the launcher. Other PAFERM is initially launched with the launchers, like Delta, have a better I apogee pointing towards the Sun, than six performance and could provide a higher months later the apogee is in the apogee or perigee thereby increasing the opposite direction, far down the time spent in the solar wind or magnetotail. During the polar passages of increasing the mission life-time, I Ulysses, PAFERM has to have an apogee respectively. Analyses of the propos7d within the solar wind and not down the experiments (Table 1) give the bas~c magnetotail. The time periods for the two requirements concerning volume, mass, polar passes are separated by close to a power, and data rate. An ~dditional I year, therefore a correct ini tial orbit requirement of the experiments ~s to scan ensures that the PAFERM mission can the ecliptic plane with 5 to 6 rpm with 1 deliver the Ulysses baseline measurements degree pointing accuracy and 0.1 degree/s within these two time periods. In Figure pointing stability. 2 the orbit for June (any year) and I october is given. The mechanical structure of PAFERM (Figure 4) consists of two major The launch window for PAFERM is an components, a central tube with two approximately 30 minutes time period platforms and an outer shell. The I everyday, just at a certain local time at diameter and the length of the spacecraft the launch site. The mission duration outer shell were designed to provide a should at least cover the two time mounting area for the solar cells, periods of the polar passes of Ulysses, delivering about 100 W solar power. All I this means a mission duration of at least instruments are located in the payload 16 months. compartment between the two platforms with the subsystems on the upper one. I The outer shell can easily be dismounted 6. SATELLITE CONCEPT from the central structure to ensure accessibility to all components. For thermal reasons the battery pack is The design baseline of the PAFERM mission located inside the central tube. I is the low cost approach of developing and launching a relatively complex Since the spacecraft does not have to be scientific mission within three years. This can be achieved by using existing in spin mode below al titudes less than I hardware. Most instruments to be flown on , a nadir orientation with the antenna pointing towards the PAFERM are spares from Ulysses. Earth can be easily achieved using momentum exchange between the momentum In addition to the instruments some wheel and the spacecraft. As an option, I spares of spacecraft subsystems are two smaller platforms can be used for available at ESA. Different forms of telemetry and telecommand (TM/TC) support for small missions are under components and a steerable high-gain consideration at ESA; one is that ESA antenna. This antenna will be Earth I could make appropriate spare parts left­ pointing to ensure the required data rate overs from flown projects, {e.g. Ulysses, of 10 kbps over 100,000 km apogee Giotto) available at no charge including altitude. some limited manpower for advise on I specific issues. Usage of existing In order to reduce the spacecraft costs hardware would be helpful in keeping the without reducing the reliability, the costs low and the development times spacecraft subsystem design will be within the three years frame. Further a mainly based on already existing hardware I compromise of choosing a high excentric and improved technology. The interfaces orbit but without full time coverage by between the experiments and the on-board the ground station and the limited data-handling (OBDH) system should be ability of spacecraft control will keep very similar to the Ulysses system. I costs relatively low. Therefore the OBDH interface to the instruments will be designed to be as The PAFERM spacecraft (Figure 3) can be close to the Ulysses OBCH system as launched by a Scout II and must therefore convenient. Additional tasks, like fulfill the requirements of its useable housekeeping, attitude stabilization and I volume and interfaces. Consideration of control, mass memory, pseudo sun-pulse the Scout II eliptical orbit performance for the instruments during eclipse times (launch site San Marco) determines the and the management of TM/TC can be maximum available spacecraft mass of improved using existing technology (hard­ I about 100 kg for the 400 km times 100000 and software) which are partly km high eliptical orbit. A payload mass implemented in the small satellites of 25 kg would leave for the spacecraft a BremSat and SAFIR. I I I The solar array will generate 100 W REFERENCES average power. Appropriate design of the I panel current and voltage will enable the 1/ EOS, Transactions, American use of BremSat power control electronics Geophysical Union, Volume 72, Number with a minimum of modifications. A 25, June 18, 1991, pp. 267-268. battery is used to supply power during I eclipse phases and peak power needs. To 2/ ESA bulletin, European Space Agency, demonstrate the feasibility of the PAFERM Volume 63, August 1990, 'Ulysses spacecraft with 100 kg total mass, an Launch Issue'. estimated budget breakdown for mass and I power has been done (Table 2). 3/ K.-P. Wenzel and R.G. Marsden, The International Solar Polar Mission - The attitude control and stabilization Its Scientific Investigations, ESA subsystem (Figure 5) consists of a fixed SP-1050, European Space Agency, July I momentum wheel, magnetic rods, 1983. , Sun and star sensors. Two atti tude stabilizations are designed: spin and 3-axis stabiliZation at momentum I vector perpendicular to the ecliptic. The closed loop pitch control achieves a pi tch pointing accuracy of less than 1 degree and a pointing stability of about 0.1 degree/so Additionally, any required I spacecraft spin-rate can be achieved by using momentum transfer between the momentum wheel and the spacecraft. The spin-rate will be sensed by the Sun and I star sensors. The fixed momentum wheel should be preferably run-up to the nominal rate shortly before separation, avoiding in-orbit running up using I magnetic rods. The magnetic rods are used for nutation dumping, wheel desaturation and to control the precessing of the I momentum vector. I 7. CONCLUSIONS The rationale for demanding the PAFERM mission as Ulysses baseline was explained by summarizing the scientific objectives I and giving specific examples where a reference is mandatory to achieve the objective at all. I The mission requirements, the experiments and the spacecraft foreseen for the mission were summarized (Table 3). Spare models or partially built models of the I experiments and spacecraft subsystems are on the shelf waiting to be refurbished for the PAFERM flight. A detailed spacecraft description was not given here because the spacecraft definition is not I finalized yet.

We hope that the evaluation process within ESA and DARA will result in I realistic plans to implement such a mission. Ulysses is on its way to Jupiter and towards its passages of the polar regions of the Sun. We need the go-ahead I for the PAFERM project quite soon, otherwise we will run out of time; and time is really running fast, actually, with the velocity of Ulysses, which is at I the moment the fastest operating man-made object in space. I I I I I I I I

Figure 1: Interplanetary structure in the inner heliosphere. The figure I shows the average large scale structure of the interplanetary magnetic field between Sun and Earth. I I INCOMING SOLAR·WINO DEFLECTED PARTICLES SOLAR-WIND MAGNETOTAlL ...... PARTICLES I I SOLAAWIND ~ . I I I I I EARTH'S IONOSPHERE ( 100 - 1()OO KM, I --- ~------, MAGNETOTAIL ..... \ \ , , MAGNETIC FIELD LINES I BOW SHOCK .. ,

Figure 2: The magnetosphere of the I Earth and the orbit of PAFERM. I I I ...------, "' ...... \ \ \ \ \ \ I \ \ \ \ \ \ \ \ \ I \ \ \ ~~--Tr.~.. ~ ~.. r_~-----, \ \ I \ Ufi-1lllWi1lllilC L.::=lI-"_._._".J"'~-+J _\ i I I f I I I I I I I I I I I I I I I I I I I I I ~ I L __.-....,.'-- ______p ..-"I_- ... --J 0.1 L. (n•• '_ I I I Figure 3: The PAFERM spacecraft Figure 4: Structure of PAFERM I I 1-

Pointing angle I Momentum wheel

.----+- 3- axis magnetometer I Starsensor I actuator command

Figure 5: Attitude control and I stabilization subsystem. I I I

COSPIN ANGAS TAUS MAGNET TOTAL

PI H. Kunow H. Rosenbauer H. Rosenbauer A. Balogh I

Objectives solar, neutral gas solar wind magnetic field planetary, interplanetary I particles

Data Rateslkbps 0.2 ave:r 0.05 aver 0.01 aver 0.1 aver 0.36 aver 0.2 peak 0.05 peak 0.5 peak 0.8 peak I

Mass/kg 13.02 2.2 4.2 1.8 21.22 Power/W 14.7 aver 3.0 4.5 aver 1.5 aver 23.7 aver I 17.2 peak 5.5 peak 2.0 peak 27.7 peak

Sizelm 0.20 x 0.19 x 0.23 0.2 x 0.2 x 0.2 0.22 x 0.15 x 0.18 0.25 x 0.25 x 0.25 0.29 x 0.28 1 0.19 0.13 10.13 x 0.15 0.13 x 0.13 x 0.15 I 0.25 x 0.26 1 0.11 0.17 xO.14 10.19 0.16 x 0.10 x 0.061

5 boltes 2 boxes 2 boltes 72.5 dm3 I

Experiments Analyses Matrix I I

SUBSYSTEI'l 'lASS (kg) POWER (H) orbit: highly excentric apogee / perigee: 100.000/400 km I payload 25 28 mission duration: May 94 - Oct. 95 OBOH 2 3 Batteries 8 IUectroni cs 2 2 FI'lH 3 5 ground station coverage: 6 hours/day I Torquer 3 5 downlink data rate: 10 kb/s Sun/Star Sensors 1.5 3 Structure (incl. uplink data rate: 64 b/s solar panels and adapter) 30 I TI'l/TC 10 80 spin stabilized spacecraft: Srmp Harness 3 spin axis: perp. to ecliptic Thermal Control 3 Margin 9.5 pointing accuracy: 1° pOinting stability: O.l°/s I TOTAL 100 86 spacecraft mass: 100 kg spacecraft power: 120 W I Table 2 : Budget breakdown for mass experiment mass: 22 kg and power. experiment power average: 24 W experiment power peak: 28 W I Table 3: Mission requirements I I I I