Figure two shows the number of refereed HST papers versus year of publication:

From Apai 2010. See HST Overview for explanation of abbreviations.

Figure three shows the number of refereed publications versus year of publication as a function of the scientific instrument utilized with various events highlighted:

From Apai 2010. See HST Overview for explanation of abbreviations.

HST serves a large community offering observing and research opportunities to scientists worldwide.  The users interact with STScI's Space Telescope Users’ Committee.   Apai (2010) estimates HST has been used by more than 4300 registered users.  The continued evolution of HST’s instrumentation and its increased imaging and spectroscopic capabilities has stimulated this large user group.  It is important to note that the HST related papers have high citation counts.  In other words, these papers are frequently referenced in the publications of other scientists. The average number of citations per HST refereed paper is 25% greater than that for astronomical papers in general (Meylan, 2004). 

Figures 4 and 5 show the number of HST citations versus the year of publication and the HST citations from high impact papers:

Figure 4 from Apai 2010. See HST Overview for explanation of abbreviations.

Figure 5 from Apai 2010.  See HST Overview for explanation of abbreviations.

These graphs demonstrate a continuing high, if not accelerating, level of scientific productivity from HST. The last five years have probably been its most productive period. HST has consistently ranked near the top for observatory productivity with respect to the number of articles published and the number of citations these articles receive.

Conclusions – Seeing Deeper:  The Webb Space Telescope

NASA’s next orbiting observatory and successor for the Hubble Space Telescope is the James Webb Space Telescope (JWST).  JWST is a large infrared-optimized system with a 6.5 meter primary mirror (NASA, JWST 2012).  While it will be primarily an infrared telescope, it will have some capability in the visible portion of the spectrum.  The JWST and its instruments must be very cold to keep its internal infrared emission from overwhelming its instruments.  It will have a large sunshield to block light from the Sun, Moon, and the Earth.  To simplify this shielding, the JWST will be placed in orbit around the Sun at the Lagrange L2 point where the Sun, Moon, and the Earth are lined up in the same direction from the telescope.  The JWST is not designed to be serviced after launch.

The James Webb Space Telescope is an ambitious undertaking with technical challenges and cost overruns.  There has even been talk of its cancellation.  At the present time, the telescope is still a very active project with an approximate launch date of 2018.  If it performs as designed and as advertised, it will be a worthy successor to the Hubble Space Telescope. 

The fate of Hubble itself is uncertain.  The Space Shuttle Program has ended, and there is no way for further servicing of HST.  Its instruments are designed for full operation for several more years.  HST’s orbit is slowly decaying due to drag from the very tenuous atmosphere still present at its height above the Earth’s surface.  It will re-enter the Earth’s atmosphere sometime after 2019.  HST’s exact fate remains to be seen.  One possibility strongly being considered is to send a future robotic mission to it so that its de-orbiting could be fully controlled to avoid possible damage or human fatality from those portions of it surviving re-entry.  Unfortunately, HST cannot be brought back to Earth for permanent display in a place of honor, which would be a fitting tribute for its job well done. 

References

Apai D, Lagerstrom J, Neil Reid I, Levay KL, Fraser E, Nota A, Henneken E. Lessons from a high-impact observatory: The Hubble Space Telescope’s science productivity between 1998 and 2008. PSAP 2010; 122:808-826.

Freedman WL, Kennicut RC, Mould JR, Madore BF. The HST Key Project to measure the Hubble constant. Proceedings of the Space Telescope Science Institute Symposium, Baltimore, MD, USA, April 11-14, 2000; Published 2003; 14: 214-221.

Freedman WL, Madore BF, Gibson BK, Ferrarese L, Kelson DD, Sakai S, Mould JR, Kennicutt RC Jr, et al. Final results from the Hubble Space Telescope Key Project to measure the Hubble Constant. ApJ 2001; 553, #1:47-72

Gino, MC.  The Hubble Space Telescope.

HubbleSite.

HST Overview.  Space Telescope Science Institute at: HST Overview.

Livio M, Noll K, Stiavelli M. A decade of Hubble Space Telescope science. Proceedings of the Space Telescope Science Institute Symposium, Baltimore, MD, USA, April 11-14, 2000; Published 2003; 14: 260 pp.  

Meylan G, Madrid JP, Macchetto D. Hubble Space Telescope science metrics. PSAP 2004; 116: 790-796.

Riess A, Lucas M, Casertano S, Megan S, Lampeitl H, Ferguson HC, Filippenko A, Jha SW, Li W, Chornock R, Sarkar D.  A redetermination of the Hubble Constant with the Hubble Space Telescope from a distance ladder. ApJ 2009; 699, #1: 539-563. 

The NASA Astrophysics Data System (ADS).  

Publications of the Astronomical Society of the Pacific (PASP) January 2003-June 2004.

Space Telescope Science Institute: Hubble Primer.

Villard R. Hubble’s top 5 science discoveries.  Astronomy July 2010: 30-35.

The James Webb Space Telescope (2012). 

First posted 11 February 2005.

Major revision posted Wednesday 22 February 2012.

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