The fluxgate magnetometers to be supplied by UCLA for the ST5 mission rely on a long heritage in building research-grade instrumentation. UCLA fluxgate magnetometers have been employed in state-of-the-art investigations of magnetospheric and solar system magnetic fields for over 35 years. During this time the accuracy and precision of the magnetometer has grown even as its mass, size and power decreased.

The Early Years: ATS, OGO 5, Apollo and PVO

The UCLA magnetometry group was established in the mid 1960s by P. J. Coleman when it furnished fluxgate magnetometers for ATS 1 and 6 and OGO 5. In 1971 and 1972 the Apollo 15 and 16 subsatellites carried UCLA fluxgate magnetometers of a very simple design in a low field environment. In 1972 and 1973 UCLA was selected to build both the ISEE 1 and 2 fluxgate magnetometers as well as the Pioneer Venus orbiter magnetometer. Both presented challenging design issues but quite different ones. The ISEE magnetometer required a very precise measurement of a magnetic field whose strength varied from 5 nT to over 8000 nT. UCLA built a highly linear magnetometer with two gain states. Oversampling and averaging provided 14-bit accuracy and 16-bit resolution. The Pioneer Venus spacecraft was a spinning spacecraft whose data rate at times was insufficient to return even one vector-per-spin period. We therefore developed a Walsh-Transform-based despinner to provide accurate vector information under all telemetry rates. The ISEE 1 and 2 spacecraft lasted 10 years and the Pioneer Venus mission 14. All three magnetometers were still operating upon entry into the atmosphere.

Galileo

The innovation of the UCLA magnetometer group continued with development of the Galileo fluxgate magnetometer. This magnetometer again provided 16-bit resolution data through oversampling and averaging. In addition it stored and returned despun average data between telemetry sessions so there could be total orbital coverage. This instrument launched in 1989 is still functioning normally after 11 years in space, much of which was in a very harsh radiation environment.

Polar

The Polar magnetometer launched in February 1996 is a highly accurate magnetometer with further advances in low noise and linearity. Polar has a 16-bit A/D converter and can amplify the signal by another factor of 8 so the basic magnetometer was designed to 19-bit precisio. The magnetometer was accurate to within 0.01%. The Polar magnetometer included both an inboard and outboard magnetometer, each with two gain states to allow for measurements at perigee (2 Earth radii geocentric distance) and apogee (9 Earth radii). Two other magnetometers, that on FAST launched in August 1996, and that on FedSat now awaiting launch, are simplified derivatives of the Polar design.

FAST

The FAST magnetometer is a simplified version of the Polar magnetometer.The FAST magnetometer, with a 64,000 nT range and 2 nT resolution,

FedSat engineering unit showing electronics board and chassis.

was designed to operate at low altitudes (< 4000 km altitude) with ambient fields ranging from 10,000 to 50,000 nT in magnitude. The FAST instrument could acquire data at a variety of rates, up to 512 Hz.

FedSat

The FedSat magnetometer also uses the highly successful Polar design with techniques to reduce mass and power developed on the FAST program and UCLA's ground-based effort. The magnetometer has a 60,000 nT range and is sampled at either 10 or 100 Hz. The analog board weighs 200g.

Table: Modern components and continued improvements have lowered the mass of the UCLA basic circuitry.

Mission Name	Ranges [nT]	Cadence [nT]	Mass [g]	Area [in2]
ISEE	8000, 556	4, 16	500	100
Galileo	16,000, 512, 32	0.05, 3, 32	500	100
Polar	47,000, 5700, 700	8.3, 100	400	70
FAST	64,000	Up to 512	350	60
FedSat	60,000	10,100	200	35

Table: UCLA Heritage as it relates to the ST5 Performance Specifications.

ST5 Performance Specification	UCLA Heritage
Dynamic Range: +/- 64,000 nT	FAST
Resolution: 1 to 2 nT in 64,000 nT 0.1 to 0.2 in 1000 nT	FAST, Polar, Ground-Based Polar, FAST, FedSat
Absolute Accuracy: < +/- 0.25%	Polar (< 0.01%)
Intrinsic Noise: < 0.1 nT rms	Breadboard Test
Zero stability: <+/- 0.5 nT	Polar, Pioneer Venus
Axes Orthogonality: < 2°	Polar, FAST
Orthogonality Knowledge: < 0.1°	Polar, FAST (< 0.01°)
Axes Alignment: < 2°	Polar, FAST
Alignment Knowledge: < 0.1°	Polar, FAST (< 0.1°)

For more information, contact Robert J. Strangeway, strangeway@igpp.ucla.edu.

Last updated June 11, 2001