Forward Payload Research Articles

University small satellite program—ANUSAT

Indian Space Research Organization (ISRO) over the last 3 decades has steadily progressed towards establishment of space system for communication, Earth observation and disaster warning for national development. Also, the launchers for placing both Earth observation and communication satellites have been developed. While these efforts are being sustained on a continuous basis, ISRO initiated Small Satellite Program few years ago for demonstration of new technologies that can be adopted to operational mission as well as Small Satellite Earth Observation program to complement the existing earth observation mission. Also realizing the importance of steady flow of engineers and scientists in Space Technology, ISRO has been pursuing to promote development of micro-satellite at Indian universities that will provide hands-on experience to the university students in Space Technology and also developing new technologies for the future. Anna University at Chennai, India, has taken up the first micro-satellite program within the university environment. The micro-satellite development will be carried out at Aerospace Research Centre in Anna University with review and funding support from ISRO. The project will be implemented through involvement of students, researchers and faculty staff. The satellite is a simple spinning satellite carrying store and forward payload being the first mission and weighs less than 50 kg. The Project has commenced in January 2002. The preliminary design review of the satellite has been completed in December 2002. The micro-satellite is scheduled for launch in 2005 as an auxiliary payload in ISRO's launcher PSLV (Polar Satellite Launch Vehicle).

Electron acceleration by megahertz waves during OEDIPUS C

Observations of Electric Field Distributions in the Ionospheric Plasma ‐ A Unique Strategy (OEDIPUS C) was a tethered mother‐son experiment that was launched northward from the Poker Flat rocket range at 0638 UT on November 7, 1995, across a sequence of auroral structures. During the flight's upleg the magnetically aligned tether was deployed to a separation of ∼1.2 km and then cut at both ends. The forward payload contained a 50‐kHz to 8‐MHz stepped‐frequency transmitter. Receivers were carried on both forward and aft payloads. The transmitter swept through the frequency range every 0.5 s. During each of the 3‐ms steps the transmitter emitted only for the first 0.3 ms. The scientific complement also included multiangular electrostatic analyzers on both payloads that were sensitive to fluxes of electrons with energies from 20 eV to 20 keV. The durations of sampling and frequency steps were matched. During the flight the electron gyrofrequency was approximately twice the plasma frequency. When the transmitter swept through the local gyrofrequency, the particle detectors on both payloads detected sounder‐accelerated electrons (SAEs) independent of the energy steps being sampled. In addition, SAEs were detected at the aft payload out to separations of several hundred meters for wave emissions at harmonics of the electron gyrofrequency as well as in the upper hybrid and whistler bands. As the vehicle separation increased, significant time differences developed between the wave‐emission pulses and the onsets/durations of SAE detections. The data indicate that electrons were heated through strong wave‐particle interactions. However, a simple resonant‐interaction explanation appears inadequate. We outline requirements for any models purporting to explain OEDIPUS C measurements.

Whistler-mode radiation from a dipole

Bistatic observations of an active dipole in a space plasma were made during the suborbital tethered experiment OEDIPUS C, carried out on a sounding rocket flight in late 1995. Throughout the flight, whistlermode waves were transmitted at 25 kHz from a 19-m dipole on the forward payload to a 13-m dipole on the aft payload. This frequency was very much less than the plasma frequency f p , which in turn lay well below the gyrofrequency f c for most of the flight. The change of f p with time caused the receiver position to be swept through the 25-kHz group resonance cone during a segment of the flight. Signal strengths were found to be enhanced along the group cone, as predicted by theory. Observed radiated levels are about a hundred times greater than theoretical predictions based on independent estimates of the driving-point current. The modulation of the received signal caused by the spin of the receiving dipole was consistent with the theoretical expectation that the quasielectrostatic electric field is polarized predominantly along the wave-vector direction.

An analysis of whistler mode radiation from a 100 mA electron beam

Observations of whistler mode radiation generated by 2‐, 4‐, and 8‐keV electron beams with a current of 100 mA, are analyzed. The electron accelerator was carried to ionospheric heights by a Nike Black Brant V rocket (National Research Council of Canada NVB‐06). The instability causing the whistler mode radiation is investigated. Spectral measurements (0.1–13.0 MHz), from a sweeping receiver located on the ejected forward payload, are used to determine the nature of the instability. The sweeping receiver was connected alternatively to an electric or a magnetic dipole antenna. Most of the whistler mode radiation detected was consistent with Cerenkov radiation. The radiation fields observed were too large (cB ∼ 0.1 µV/m Hz1/2) to be explained by incoherent processes. If electrostatic bunching in the beam at the plasma frequency is responsible for the whistler radiation, there would be a correlation between the plasma frequency radiation, and the whistler mode radiation for electron beams that are fired toward the detector. The observed correlation is minimal. Hence no evidence was found to support the hypothesis that electrostatic bunching at the plasma frequency was responsible for the enhancement of the whistler mode radiation produced by the NVB‐06 electron beam.

VLF emissions from a modulated electron beam in the auroral ionosphere

A discrete VLF frequency of 3 kHz was successfully radiated by a modulated electron beam on a rocket launched into an active aurora. Instrumentation on this flight included a programable electron accelerator on the aft section with various particle and field detectors on the aft section as well as the ejected forward payload. The accelerator programmer included a current modulation period at fixed electron energy for 0.45‐s duration approximately every 11 s throughout the flight. In each of these program steps, 4‐kV electrons are current modulated at a 3‐kHz rate between Imin=0 or 10 mA and Imax ≅80 mA. The forward payload, which was ejected at about 10 m/s, included a pair of spherical double probes separated by 2.75 m and connected to a VLF receiver operating between 30 Hz and 18 kHz. Both this broadband receiver output as well as various narrow band channel outputs were directly telemetered to ground. Post flight spectrum analysis of the broadband VLF data clearly indicates that signals during the 3‐kHz accelerator modulation periods were propagated to the forward payload. A detailed analysis of these modulated pulses detected by the VLF receiver is presented. A time‐delay analysis between the start of the modulation and detection at the forward payload indicates time delays up to 0.2 s. The electron beam is believed to have produced a beam‐plasma discharge making a radiation efficiency calculation difficult. However, absolute received signal strength was about 1 mV/m at 1.4‐km separation.