Astronomers Learn to Work in Space

Technical Challenges Detectors Pointing and Stability Data Storage Contamination Thermal Control Background radiation

First Astronomy from Space V-2 Rocket October 10, 1946 Ultraviolet spectrum of sun 340 nm – 240 nm Bead entrance UV film

Aerobee

X-ray and Gamma Ray Detectors Geiger counters Proportional counters Solid state detectors Scintillation detectors

Explorer 11(1961)

X-ray and Gamma Ray Imagers Rotating Grating Spark Chamber Cerenkov counter Grazing Incidence telescope

Rotating Grating

Spark Chamber

Small Astronomical Satellites Three unstabilized survey satellites SAS A (Uhuru) – Rotating Grating SAS B – spark chamber SAS C tandem proportional counters

Grazing Incidence

Orbiting Solar Observatory 8 launches:

OSO 1

OSO 1 Instruments Extreme UV spectrometer nm Open photomultiplier; tungsten photo-surface Five experiments in wheel Mostly solar but included gamma ray sky survey

OSO 1 Data Handling

Optical and UV Detectors Film Photomultipliers Vidicons SEC Vidicons IPCS Digicons CCDs

Balloons

Human Assisted Missions Gemini – hand-held near UV spectrograph Apollo – Spectrometer on moon Skylab – ATM, Small UV spectrograph, various X-ray experiments Spartan Spacelab

Apollo Telescope Mount 2.1 m canister around cruciform optical bench for solar-pointed instruments Skylab controlled by control moment gyros to 3 arc min Experiments required +2.5-sec of arc stability in yaw and pitch and 5 arc min in roll Solar pointing control centered sun within ~0.3 arc sec Quartz wedge in pointing system permitted offset in 1.25 arc sec steps up to 24 min of arc

Airplanes

Orbiting Astronomical Observatory

OAO Pointing Systems 3 rate gyros + high trust jets to slow tumble at launch <0.75 o /s 3 wide-angle solar cells + gyros to orient satellite to sun-line 8 10 o solar cells to orient satellite within 0.25 o 6 star trackers (f.o.v. =1 o ) set to pick up at least 3 stars no fainter than magnitude 2 within 15 arc sec of predicted position Bore-sight star tracker to 2arcsec Fine rate gyros counteract drift Electro-magnets interact with terrestrial field to unload fine gyros with gas jets only a backup

Data Handling for OAO Magnetic core memory 100 kbits Analog data could be transmitted in real time only 40-foot dishes in Quito and Santiago 85-foot dish in Rosman, NC Commands transmitted to stations and data returned by teletype Microwave link available between control station at Goddard and Rosman Automatic safe mode if commands discrepant

Temperature Control (OAO) Problem: Space and mirror very cold, Sunlit side of satellite hot, electronics like room temperature detectors like cold temperature Gradients can distort alignment Alzac coating to maintain structure at constant temperature Experiment tube surrounded by super insulation Heat allowed to leak to structure Small heaters for electronics

Maintaining the Focus on OAO OAO B: Al + Ti shell Small mirror shunts a little light through a separate hole to two detectors, in front and behind the expected focus. At proper focus, light intensity is identical from two positions OAO C: Separation of primary and secondary depends on quartz rods, relieved during launch Focus position determined from shape of star image

OAO Mirrors OAO A: Standard quartz mirrors OAO B: Be mirror OAO C: Egg-crate quartz mirror

Infrared Observations Detectors: Bolometer Solid state Heterodyne Survey Satellite: IRAS (1983)

IRAS Focal Plane

Radio Astronomy Explorer Two V antennas each with 229m arms 37m dipole 1968: Earth orbiter 1973: Lunar orbiter