Monthly Discussion



The Hubble Space Telescope


After a decade of operations, observations, and publications, the scientific effectiveness of the Hubble Space Telescope (HST) is being questioned. The telescope痴 days had always been numbered. NASA has long planned to end Hubble's spectacular run and bring it down in 2010 to make way in the budget for the James Webb Space Telescope (JWST), scheduled to be launched in 2011.

Still, some astronomers are urging that Hubble's life be extended. They argue that the telescope has grown even more productive in its years in orbit, thanks to periodic service calls by astronauts. These astronomers say that killing Hubble in its prime makes little sense, either scientifically or from the standpoint of public relations. "Hubble is by far the best news NASA has now," a senior astronomer said.

Steven Beckwith, director of the Space Telescope Science Institute, has gathered lots of statistics around the telescope痴 successes in an effort to extend its life.* I have retained only a couple of graphs from his reports and tried to see whether the telescope痴 planned end makes sense from the point of view of a natural process that approaches completion.

Exhibit 3 shows the evolution of the cumulative number of referred papers based on HST data. (迭eferred papers are publications that have undergone a critical review and selection by a group of scientists). On the same graph I also show the S-curve that fits the process and the delimitations of the various growth phases, 都easons, as describe in Conquering Uncertainty.

We see that presently the telescope is just coming out of 都ummer its most productive season.


Exhibit 3. The growth of scientific publications based on data provided by the HST.


The rate of growth of the purple curve gives us the life cycle of the process and is shown in Exhibit 4. It depicts rather eloquently that the HST is at turning point of its productivity curve.


Exhibit 4. The life cycle of the HST as measured by the number of annual scientific publications.


There is independent corroboration of the fact that the HST is presently at its turning point. Exhibit 5 shows the natural-growth life cycle describing the evolution of the percentage of publications based on HST in the 5 major astronomical journals (The Astrophysical Journal, The Astronomical Journal, Astronomy and Astrophysics, Monthly Notices of the Royal Astronomical Society, and Publications of the Astronomical Society of the Pacific). This metric is different from the one in Exhibit 4 because it directly takes into account the competition with other sources of astronomical data.



Exhibit 5. The life cycle of the HST as measured by the evolution of its share in the 5 major astronomy journals.


The fact that the data point for year 2002 is above the trend in both Exhibits 4 and 5 is not very significant. Such a fluctuation could be due to the numerous recent discussions generated around the HST in efforts to extend its life. The conclusion that the HST is entering its fall season seems sound.

If this is indeed the case, the provisional date of 2010 for brining the HST down appears rather timely. By 2010 the HST will have completed 97% of its growth potential (see Exhibit 3) and the launching of the JWST in 2011 can be seen as just-in-time replacement.

Drawing on the seasons metaphor we can say that during the next five years幽ST痴 fall擁ts reason for existence, besides continuing to collect data, should be to 鍍each, i.e. provide knowledge essential for the success of the follow-up JWST. Granted the winter-like replacement season toward the end of the decade will be trying for data-hungry astronomers. But this is the nature of transitional periods. The argument to extend HST痴 life to cover that period does not conform to the natural aspect of competitive growth.


* http://sco.stsci.edu/newsletter/PDF/2003/spring_03.pdf