Hubble Space Telescope

THE HUBBLE SPACE TELESCOPE SPACE BASED ASTRONOMY Roberto Bartali Introduction

Figure 1 Hubble Space telescope in orbit Courtesy of www.astrowww.org

For all living bodies, the Earth atmosphere contains the vital gasses for sustaining life and act as a shield for dangerous radiations, but for astronomers, it is the greatest obstacle because it is not as transparent as they wish, it reduce the quantity of light, it distort rays from the outside and it is opaque for most of the radiation wavelength. They dream to have a telescope in orbit at high altitude, where atmospheric effect are reduced, and, finally, 15 years ago, became a reality with the Hubble Space Telescope (HST) (Figure 1), the most productive scientific satellite ever made. Even when, Earth based telescope are powerful (10m diameter and advanced adaptive optics), images provided by the 2.4m HST are sharpest and the limiting magnitude reached from space are fainter.

Development of the HST In 1966, the Ramsey committee [3][4][5][6][7] recommended the construction of a 3 meter aperture telescope orbiting at high altitude, called the Large Space Telescope (LST). Organization problems and the technological restriction of those years, rise the cost of such a project and not everyone was convinced of the feasibility and scientific merit for that effort, and, soon, the LST was reduced to a 2.4 meter Space Telescope (ST), the name was changed later to the actual: Hubble Space Telescope. Its development begins between 1973 and 1974, but astronomers failed to justify the project and they get no funds. In 1975, at the Figure 2 meeting of the American Astronautical Society in HST in the construction stand at Lockeed Mísiles and Space Co. Denver [10][11], a series of papers was presented From: Sky and Telescope Feb. 1987 regarding the telescope construction, operation, instrumentation, pointing, control, data reduction and analysis, finally, in 1977 the project obtained funds and officially started. The enormous effort to make a reality the HST, was only possible by the cooperation of a great number of people and institutions not only from the USA, but Europe also [3]. This was the first big project that needed not only the best scientific knowledge, but the marketing capacity for selling the idea not only to the Government for 1

obtain the necessary budget, but also to the astronomers, most of which don’t understand, at first, the power of the HST. To do that a special institution was created: the Space Telescope Science Institute in Maryland [10][13] who’s mission is to maintain the instrument, planning observations, handling, reducing and storing observations, and making data available to the scientific community. Controlling the telescope was a duty of the Goddard Space Flight Center also in Maryland. In the decade of ´70, the general idea of the telescope was not very clear. People talk about the possibility of either man controlled or remote controlled operation, type of rocket to put it in orbit or released by the Space Shuttle. In 1986, when the construction ended (figure 2), problems arise when tested in a high vacuum chamber. After that [15][16] it would be necessary to redesign solar panels, power supply and the back up battery system, among other things. Tests of the complete systems in 1988 and 1989 failed in many ways, contaminants on the Faint Object Camera reduced the sensitivity in the UV, handshake timing problems affected the spectrograph, so, a full revision of the software was needed. Software bottlenecks reduced the overall efficiency to about 20%, and at that time there was no chance to use many instruments in parallel and no Figure 3 possibility for Solar System object observations. Space Shuttle Discovery carrying the HST on April Finally the last trouble was the way it can be 24, 1990 transported from California to Florida, the best way was From: Astronomy Jul. 1990 using the cargo bay of an Icebreaker, sailing through the Canal of Panama. First scheduled to be launched in 1983, than delayed until 1986, but due to several technical problems and, again, the needs for more funds, it have to wait until April 24,1990 (figure 3) for seeing its first light at four times the original cost. This delay carried a problem, because the Solar activity increased and scientist had to change the orbit and the altitude. Instrumentation on board of the HST The optical system of the HST is a F/24 Ritchey-Chretien, [12][13][17] with primary diameter of 2.4m and a secondary of 32 cm., the precision of the curvature must be 1/110 of wavelength for the primary and 1/65 of wavelength for the secondary (figure 4); both of Ultra Low expansion glass because in the space the telescope will be exposed to extremely changes in temperature (about 280 °F in less than 2 hours), coated with Magnesium Fluoride to achieving reflection of light from 115 nm to 1 micrometer wavelength. Finally, when mounted, the mirror was capable of concentrating light in a circle of 0.05” and its curvature error only 1/70λ. The light from the mirror reach a total of eight instruments [13][17][35], five of which are used for observations and three are used by the system for tracking purposes (figure 5). 2

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The High Speed Photometer, capable to measure a 20 magnitude star, with an accuracy of 0.1%, 100000 times per second. The instrument contains five detectors, 23 filters and is sensitive from 120 to 700 nm. The High Resolution Spectrograph for

Figure 4 HST mirror construction. From: Sky and Telescope Oct.1982

the UV, with a resolution from 2000 to 100000 and it can automatically set the exposure time. • The Faint Object Spectrograph, with broad spectrum sensitivity (from 115 to 550 nm and from 170 to 850 nm) but lower resolving power (1300 lines). • The Faint Object Camera, built by ESA, a very sensitive double imaging instrument, it can reach the magnitude 30. It has a narrow field of view and uses the full focal length capability of the optics reaching F/288. The image intensifier enhance the light 100000 times, is capable to record a single photon. • The Wide Field Planetary Camera, the most important instrument on board, it can take pictures with very high resolution and a relative wide field. The optical system reduce the F ratio to 12.9 for deep field objects and increase it to F/30 for planetary imaging. The resolution is 0.043”/pixel. It consist of eight 800x800 15 micron pixels. The instrument sensitivity is from 115 to 1100 Figure 5 nm, there are a set of 48 filters Inside the HST, the instrumentation payload From: Astronomy, January 1994 and the limiting magnitude will be 28. • The Fine Guidance Sensor is a set of three sensors placed in a semicircular path around the main instruments. Two of them lock the telescope on the guide star and the other can measure the brightness (1%) and the position of a star very precisely (0.003”). Scientific program of the HST The observing programs priority was to answer some of the fundamental cosmological questions like: how big and old is the universe? Did the Universe ever started and will it have an end? What are quasars and black holes? What is the process of star

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formation and death? Is the Sun the only star to have a planetary system? How many unsuspected things are there? Three projects was realized by the HST during the first year: • Determining the Hubble parameter with an error of 10%, this is fundamental for measuring the Universe. • Spectral analysis of 100 quasars in the UV and the determination of the matter between them and the telescope. • A medium deep survey of selected areas of the sky up to the limit magnitude, looking for galaxies or other undiscovered objects. After that, a lot of observation of all kind proposed by astronomers around the world and, also amateurs, would be allocated. Everything was observed by the HST, planets, comets, galaxies, etc. As soon as an unexpected phenomenon was detected, the HST was redirected to observe it. Upgrading the HST

Figure 6 Servicing mission to enhance features of the HST. From: Astronomy, March 1994

The worst day in the HST history, was June 27, 1990 when NASA announced that the mirror was flowed. A brief history of the maintenance and upgrading of the HST by astronaut (figure 6) on board of the Space Shuttle is: • 1993: fixed the mirror, installation of a new Wide Field and Planetary camera and a Corrective Optics system, giving to astronomers a superlative telescope; replaced two solar arrays, 3 gyroscopes, magnetometers, fuses and fixed the power supply. • 1997: installation of an IR Camera and an Advanced Spectrograph. • 1999: refurbished the guidance system and the computer. • 2002: installation of the Advanced Camera for Survey and a new cooling system for the IR the Camera.

Discoveries produced by the HST One of its primary goals was the determination of the Hubble rate of Universe expansion, [10][26] HTS observations put the value at 70 Km/s/Mpc. I will briefly describe some fields of study that take advantage from the HST: • Planetary imaging with details that only can be compared by those pictures of spacecraft orbiting closer to them. Surface details resolved on most distant and smallest object in the Solar System, like Pluto and asteroids. • Object amplified by gravitational lensing (figure 7). Many object of this type can now be studied, this make possible the verification of the Theory of Relativity. • Star forming in galaxies (figure 8). • Protoplanetary disks and protostars in molecular clouds (figure 9). 4

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Accretion disks around black holes (Figure 10). Formation of planetary nebulae. Most distant and young galaxies (Figure 11). New types of galaxies. Kuiper Beld object. Smallest stars in the Milky Way (figure 12). Quasars Supernovae In all of this fields, HST give us the proof that currents theories are right and many times offered the confirmation of what astronomer only took as a guess.

Figure 7 Gravitational lensing effect on distant galaxies Abell2218) From: ww.seds.org/hst/hst.html

Figure 8 Star forming region in NGC2366 From: www.seds.org/hst/hst.html

Figure 9 Protoplanetary disks and star borning. From: www.seds.org/hst/hst.html

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Figure 10 Accretion disk around the Black Hole in the nucleus of the Galaxy NGC4261 From: www.seds.org/hst/hst.html

Figure 11 Group of galaxies at the edge of the knowing Universe From: www.seds.org/hst/hst.htm

Figure 12 One of the smallest stars known: Gliese 623b From: www.seds.org/hst/hst.html

Conclusion The HST, by far, surpassed any expectations and astronomers have now a lot of new data to evaluate and the task may needs many years. The purpose of the HST was to give answers, and in some cases it do that very well, but, it produced a lot of questions too. Many satellites and spacecraft was sent to planets, but all of them was specifically designed for some type of investigation, and some did invaluable work and put the basis for the HST, like Hipparcos. The HST in contrast, is a “General Purpose” satellite, just like any other telescope on Earth, because it can be pointed to at any direction in the sky and observe, with all instruments onboard, at wavelength of the visible and near invisible electromagnetic spectrum and, analyze the object with one of its spectrograph. In either cases, the quality of the images are impressive, impossible to obtain from Earth, even with the best and most 6

sophisticated telescopes like Gemini, Keck or VLT. Figure 13, is a comparison of a Palomar view and the Wide Field Camera 2 of HST. I think that the main trouble with the HST was because it was planned and made well before the development of the technology needed to do that. The high cost of parts, many times was not for the construction of them, but for the technology needed to made the part itself. Public opinion and politics exert a lot of pressure and when thing are made under pressure, something always goes wrong. If astronomers accepted the delay of 5 to 10 years, proposed by the US Congress in 1974, maybe, the cost of the HST would be lesser and the performance of the instruments much better, because the technology in the fields of mechanics, Figure 13 electronics and communication grows a lot Left: : M33 star forming region (Palomar) Right: Close up of Star forming region in in the decade of the ´90. I agree that the M33 (HST) From: www.seds.org/hst/hst.html arguments they used in defense of the project was very strong, but I think that nobody was able to manage such enormous project at that time, comparable only to the Apollo project. I recognize that every people involved in the project made miracles, and thanks to them we have now a better knowledge of the Universe. Even though NASA planned the HST for 15 years and then, wished to increase its life time until 2010, in the last few weeks, US Congress freeze the funds for servicing and maintenance missions, so the telescope will be degrading itself until it die. The main reason for this, I think, is the success of the new Sptitzer observatory. As NASA say [1][2], this is the last of the 4 orbiting observatories and, results from Spitzer will be used to develop the Webb orbiting observatory, the giant successor of the HST. In the meantime, astronomers will observe in the IR band and try to get the best from the HST until it will be un-useful. References Main NASA site: [1]www.nasa.gov [2]http://www.nasa.gov/audience/forstudents/postsecondary/features/F_The_Spitzer_Space _Telescope.html NASA Archive and History: [3]http://www.google.com.mx/search?q=cache:O9eHoM_aVkIJ:www.sns.ias.edu/~jnb/Pap ers/Popular/NoTwinkle/paper.ps+%22nasa+sp-392%22&hl=es&ie=UTF-8 [4]www.hq.nasa.gov/office/pao/History/SP-4211/ch12-3.htm [5]www.hq.nasa.gov/office/pao/History/SP-4211/ch13-4.htm [6]http://history.nasa.gov/SP-4102/ch10.htm

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[7]http://history.nasa.gov/SP-4212/sources5.html [8]www.nasm.si.edu/research/dsh/sthp-p4.html Space Telescope Science Institute: [9]http://sco.stsci.edu/newsletter/PDF/2003/spring_03.pdf [10]www.stsci.org Magazines: [11]Sky and Telescope 1977: January [12]Sky and Telescope 1982: October [13]Sky and Telescope 1983: September [14]Sky and Telescope 1985: April [15]Sky and Telescope 1987: February [16]Sky and Telescope 1989: February [17]Sky and Telescope 1990: April, May, July, August, September, October [18]Sky and Telescope 1991: January, March, May, August, September, December [19]Sky and Telescope 1992: June, August, October [20]Sky and Telescope 1993: January, April, July, August, October, November [21]Sky and Telescope 1994: February, April, July, October, November [22]Sky and Telescope 1995: January, April [23]Sky and Telescope 1996: February, March, May [24]Sky and Telescope 1997: February, May, June, July, August, September, November, December [25]Sky and Telescope 1998: February [26]Sky and Telescope 2000: January, April [27]Sky and Telescope 2001: May [28]Sky and Telescope 2002: June, September [29]Sky and Telescope 2003: April, May, June, September, October [30]Sky and Telescope 2004: [31]Astronomy 1986: January [32]Astronomy 1990: July, August, September, October, November [33]Astronomy 1991: May, September, December [34]Astronomy 1993: February [35]Astronomy 1994: January, March, April, October [36]Astronomy 1995: February [37]Astronomy 1996: April, August [38]Astronomy 1997: February, June, August [39]Astronomy 1998: April, May [40]Astronomy 2000: April [41]Astronomy 2002: August, December [42]Astronomy 2003: February, December [43]Nuovo Orione, Jun.1992, Aug.1992

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[44]Cosmos, 1994: January, June [45]Tribuna de Astronomia y Universo, 2002: May [46]L’ Astronomia, 1996: July [47]National Geographic en Español, Special Edition: El Espacio, Oct.2003 Images: [48]www.seds.org/hst/hst.html [49]http://www.astrowww.org/Hubble/hubble.html

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