ASTRID-2 is Sweden's second scientific microsatellite developed by the Swedish Space Corporation's Space Systems Division in Solna, Sweden. Astrid-2 was launched piggyback on a Kosmos 3M rocket from Plesetsk at 1157:07 UT on 10 December 1998. It entered an orbit at 968-1014 km altitude, 83° inclination.Data reception and satellite control was conducted from SSC's facility Solna near Stockholm. On July 24, 1999 the contact with the satellite was lost during a passage. Several attempts to re-establish the contact have been made without any results. During the 7.5 months in orbit, Astrid-2 delivered a large quantity of data to the scientists. The scientific mission was h igh resolution E-field and B-field measurements in the auroral region, e lectron density measurements, h igh resolution measurements of the electron and ion distribution functions, and u ltraviolet auroral imaging and atmospheric UV-absorption measurements. The satellite was s pin-stabilized with the spin axis pointing at the sun. Its total mass was about 30 kg and it carried scientific instrumets weighing about 9 kg. The size of the spacecraft with deployed solar panels is 1700 x 1100 x 300 mm. The d ownlink data rate was 128 kbit/s
Astrid-2:s markstation i Solna.
EMMA (Electrical and Magnetic field Monitoring of the Aurora) is a comprehensive scientific experiment measuring both electrical and magnetic fields. EMMA is logically divided into three parts, EMMA system unit, EMMA E-field unit and EMMA B-field unit. The EMMA system unit controls the experiment units, buffers scientific and housekeeping data and communicates with the satellite system unit. Data can be buffered during several orbits and dumped to ground whenever the satellite has an ground connection. EMMA system unit do also control LINDA (Langmuir INterferometer and Density experiment for Astrid-2). EMMA was developed at the Space Plasma Physics Group at the Royal Institute of Technology in Stockholm.
LINDA (Langmuir INterferometer and Density experiment for Astrid-2) consists of two 10mm diameter spherical probes mounted on two light weight booms. The booms are 0.61m long and mounted on the outer tips of the solar panels giving a probe to probe separation distance of 2.9 meters. The scientific goal is to measure the fine structure of the plasma density irregularities down to 1 m scales and, by using two probes, distinguish between temporal and spatial effects. This will be achieved by using a high sampling rate (32 ksampl/s) and by using snapshot technique. The measured quantities are the plasma density derived from the probe current and the relative density variations derived from the variations in the probe current. LINDA was developed by the Institute of Space Physics in Uppsala, Sweden.
MEDUSA (Miniaturized Electrostatic DUal-tophat Spherical
Analyzer)
is a combined electron and ion spectrometer. The instrument is
provided jointly by the
Southwest Research Institute, San
Antonio, Texas, and
the Swedish Institute of Space Physics, Kiruna Division. Electrons and ions with
energies up to 18 keV/q will be measured simultanoesly, with a resolution of 16
energy sweeps per second for electrons, and 8 seconds for ions. Particles are
measured in 16 sectors in the plane of acceptance, which is almost parallel to
the satellite spin plane. MEDUSA includes a CPU for instrument control and data
compression. It weighs 1.5 kg, consumes 5.3 W (includes the PIA
photometers) and transmits 32 kb/s of data
(includes the PIA photometers).
PIA (Photometers for Imaging the Aurora)
consists of two spin-scanning photometers (PIA-1/2) for auroral imaging and one
sunward looking photometer (PIA-3) for atmospheric absorption measurements. PIA
is provided jointly by the Max-Planck-Institut für
Aeronomie, Lindau, Germany, and the Swedish
Institute of Space Physics, Kiruna Division. PIA-1 and PIA-2 have four pixels
each, and a focal width of 250 mm. PIA-3 is located under the sunward facing
platform, and views the Sun in Lyman-alpha (121 nm) via a diffuse reflector.
The photometers are sampled at 256 samples per second and they
weigh 0.6kg.
The
ASTRID-2 System Unit (ASU-2), houses electronic functions of the satellite
platform such as telemetry (TM), telecommand (TC), power etc.
The unit consists of five printed circuit boards, with the
following content:
The downlink operated at 22008.1629 MHz transmitting convolutionally encoded BPSK at 128 kbit/s. The transmitter was made by AeroAstro, USA. The antenna was a patch antenna measuring 60x50mm and made FFV Aerotech AB, Sweden. The uplink operated on 2033.35 MHz Up link using 10 kbit/s FSK. The onboard receiver was made by AeroAstro, USA. The antenna was a patch antenna measuring 65x50mm and made by FFV Aerotech AB, Sweden.
The solar panels
were
manufactured by the
Satellite Power
Corporation, USA and used s
ilicon BSF/R
cells with conductive
cover glass. The cell size was
20.6 x 52.7 mm. The
satellite used six panels
with each
83 cells. The panels measured
288 x
388 mm of 10 mm aluminium honeycomb. The t
otal nominal
power was 90 W, 40 V @ 28ºC.
The battery was made up of
22
NiCd / VRE
1,6 CE (1,6 Ah) cells from SAFT in France.
The satellite will be spin-stabilized, but when it separates from the main satellite it is tumbling slowly. A sun-presence detector will trigger the spin-up rocket motor when the sun is illuminating the solar panels. If no such signal is obtained the spin-up rocket fires after a predetermined time. After spin-up the solar panels are deployed and magnetic torque coils are used to steer the spin axis close to the sun. This steering can be done either by commands generated on the ground or by an on-board algorithm that uses sun-sensor and magnetometer data. This algorithm, which we call SUNSEEKER, is proprietary to SSC. The normal operating mode in orbit is to use this algorithm to control the spin axis orientation automatically. The spin rate is adjusted periodically by autonomous on-board commands or by ground command.
The star imager was made by the Technical University of Denmark (DTU) based on the Ørsted star sensor.
The solar aspect angle sensor was supplied by ACR, Sweden. It had an accuracy of ± 0.15o in the solar angle range 4-30o measured from the spin axis.
The magnetometer was made by Göran bergman at SSC. It consisted of two units of a two-axis design, thus providing three-axes measurments. The two unitswere fluxgate magnetometers with a r esolution of ± 1o.
The spin-up rocket motor was supplied by the National Defence Research Establishment, Sweden. It used s olid propellant, HTPB + ammonium perchlorate. It had a total i mpulse of 10Ns and burn time of 0.25s. The motor's t otal mass was 150 g.
The magnetic torquers were m anufactured by SSC using c opper wire air coils in aluminium frames. There were one spin coil and one precession coil. The spin coil physical area was 0.066 m2, its magnetic dipole moment13 Am2 and the current through the winding 0.35A. The corresponding data for the p recession coil was 0.178 m2, 17 Am2, 0.28 A.
The nutation damper was made by SSC based on the t ube-with-endpot fluid damper principle. It had a t ime constant of 14 minutes at 10 r.p.m.
We control the
temperature of the satellite by covering the top and bottom platforms with
15-layer multi-layer insulation (MLI) and by covering the side faces of the
satellite with black single-sheet foil. The battery cells are mounted in a
milled aluminium block to provide a uniform cell temperature. Batteries, radio
system and thermal compensation heater are mounted on the System Unit and that
provides a stable temperature for the whole S/C.
Separation system
The separation system is developed by SSC and is the same system used in ASTRID-1 and by a future TUBSAT.