Dear Colleague, We are concerned about the plan to de-orbit the Compton Gamma-Ray Observatory in early June. NASA officials at the press conference on March 24 2000 described the termination of CGRO as necessary for safety reasons because of the loss of one of three gyroscopes. Specifically, they estimated that the probability of a human casualty is 1 in 1000 if the satellite were uncontrolled when it re-entered that Earth's atmosphere some 7 to 12 years from now. However, in response to a reporter's question at the press conference they confirmed that a controlled reentry could be made with no gyroscopes; under these circumstances the probability for a casualty is 1 in 4 million, a low figure by NASA standards and examples. In light of these discrepant descriptions of the risk we are puzzled by the urgency of NASA's decision. Due to this urgency NASA may even have neglected to consider a safety risk due to uncertainties in de-orbit calculations during the current period of solar activity. We are certain that you are aware of the scientific importance of CGRO for celestial and solar observations. Until the launch of HESSI, INTEGRAL, HETE, SWIFT, and GLAST, CGRO provides the only observations of various sources of high-energy radiation. We are therefore asking for a delay in the termination of the CGRO mission until an independent review committee can ascertain the true risks and weigh them against the scientific return. For more information see http://www.reston.com/nasa/cgro/05.16.00.cgro.faq.html If you are similarly concerned with the plan to terminate the Compton Observatory, please write to any or all of the people listed below. Please act soon since re-entry begins on May 28. Although regular mail is more effective than email, because of the urgency, please use email. A suggested letter is given below. If you have special interests in CGRO, it would be good to mention that in your letter. Sincerely Yours, Michael Briggs William Paciesas James Ryan -------------------------- your Congressperson http://www.house.gov/house/MemberWWW.html or http://www.house.gov/writerep/ The Honorable Senator Kit Bond 274 Russell Office Building Washington, DC 20510 kit_bond@bond.senate.gov The Honorable Representative F. James Sensenbrenner, Jr Chairman of the House Science Committee 2332 Rayburn House Office Building Washington, D.C. 20515-4909 sensen09@mail.house.gov The Honorable Representative James T. Walsh Chair, Subcommittee on VA, HUD and Independent Agencies 2351 Rayburn House Office Building Washington, DC 20515 rep.james.walsh@mail.house.gov -------------------------------- Dear Representative I am disturbed by the recent NASA decision to de-orbit the Compton Gamma Ray Observatory (CGRO) beginning May 28 for safety reasons. Safety is clearly and correctly a very high priority in everything that NASA does. However, it is important to have a realistic safety policy that is applied uniformly to all missions. The question is: Does continuing operation of CGRO present unacceptable risk? The risk of continuing to fly CGRO was inconsistently described at the press conference on March 24, 2000. According to the NASA officials at the press conference the decision was based upon a casualty risk of 1/1000 if another gyroscope failed, yet in response to a reporter's question those same officials confirmed a risk estimate of 1 in 4 million for a controlled reentry using zero gyroscopes. The scientific case for continuation of the mission is beyond question. The NASA Senior Review made a strong case for continuing the CGRO Mission. The end of CGRO operations would affect virtually every sub-discipline of astrophysics. The study of gamma-ray bursts and high-energy emission from solar flares during the solar maximum period will be particularly hard-hit. With the damage suffered by the HESSI satellite during tests, loss of CGRO leaves the US with no capability for observing high-energy radiation from solar flares during the maximum of solar activity. The loss of CGRO will also be detrimental for many of the scientific objectives of presently operating and upcoming high-energy astrophysics missions, because it provides targets-of-opportunity, all-sky monitoring and coordinated observations over a very broad high-energy range. These missions include: ACSA, BeppoSAX, CHANDRA, INTEGRAL, HETE, RXTE, SWIFT, and XMM. There is no spacecraft planned for the next several years that can accomplish these objectives. I strongly urge you to request that an independent review committee be convened to determine the true risks of continuing the CGRO mission and to balance these with the continuing scientific return. The committee should review the options for continuing the CGRO mission and compare the risks of CGRO to the risks of other NASA science activities. The reentry should be delayed for the time necessary for the committee to make its report. Since CGRO is currently operating in a safe, long-lived orbit with a lifetime of greater than four years, the possibility of human harm during the time of such a study is minimal. It would be a national tragedy to unnecessarily destroy one of America's Great Observatories. I thank you for your past support and for your immediate attention to this issue. Sincerely yours, -------------------------- James M. Ryan Professor of Physics Space Science Center Rm. 310 Morse Hall 39 College Rd. University of New Hampshire Durham, NH 03824-3525 Phone: 603-862-3510 Fax: 603-862-4685 email: james.ryan@unh.edu