Re: Errors in Hubble report
From: Steve Willner (willner_at_cfa.harvard.edu)
Date: 12/22/04
- Next message: Rick Jones: "Re: ISS as Mars vehicle"
- Previous message: Sander Vesik: "Re: What is the radiation level at the Van Allen belts"
- In reply to: Andrew Nowicki: "Errors in Hubble report"
- Messages sorted by: [ date ] [ thread ]
Date: 22 Dec 2004 22:19:12 GMT
> "Assessment of Options for Extending the Life of
> the Hubble Space Telescope: Final Report (2005)"
>
> URL: http://www.nap.edu/books/0309095301/html/
In article <41C32A2E.DEF163F6@nospam.com>,
Andrew Nowicki <andrew@nospam.com> writes:
> Excerpt from the report, page 6:
>
> "The shuttle crew safety risks of a single mission to ISS
> and a single HST mission are similar and the relative
> risks are extremely small."
>
> This is not objective risk assessment. NASA
> Administrator Sean O'Keefe canceled a scheduled shuttle
> servicing mission in January 2004 because of the risks
> to the astronauts.
The excerpt is from the Executive Summary. Did you read the pages of
the report that justify the conclusion? Why do you think Mr. O'Keefe
is objective but the NRC panel is not?
> Excerpt from the report, page 63:
>
> "Use of the grapple system to perform the final capture
> of HST (Hubble Space Telescope) is a significant
> challenge, and this is one of the key technical aspects
> of the mission that has never been accomplished in
> the history of the space program. [...]
> If the capture takes place above North America, the
> two second delay can be greatly reduced.
How long does HST stay above North America on any one pass? More
specifically, how long does it remain within line of sight of any one
station? Has successful ground to space teleoperation ever been
demonstrated? (See again the excerpt "never been accomplished." Are
you claiming that is false?)
> The report
> does not mention any tools that can reduce the risk.
> NASA engineers are too dumb to invent such tools,
> but their Dextre project is receiving lots of free
> help from outside of NASA.
Have these tools been demonstrated? And if NASA engineers are too
dumb to invent them, what makes you think that NASA engineers can use
them effectively? Isn't this a further argument against a robotic
mission? (Mind you, I disagree with your claim about NASA engineers
-- all the ones I've worked with have been quite good at their jobs.
But if your claim were true, it would seem to lead to the opposite of
your conclusion.)
> Excerpt from the report, page 65:
>
> "The particular axial doors that the first shuttle
> servicing mission crew had difficulty with are
> not candidates for the robotic mission."
>
> Excerpt from the report, page 66:
>
> "Taking snapshot data readings of the old instrument
> upon removal can be helpful in ensuring that the new
> instrument is properly installed, but this is not
> an absolute foolproof approach unless the position
> accuracy of the integrated grapple/dexterous robotic
> system is kept within very fine tolerance constraints
> based on allowable misalignment for the respective
> instrument."
> Dextre can blindly follow its own movements with
> one millimeter accuracy. Each of its two "hands" has
> a lamp and a monochrome camera which has sufficient
> resolution to achieve accuracy of a fraction of a
> millimeter.
Have these been demonstrated in space? Can the desired location be
specified in advance? If not, how long will it take to measure the
desired location in orbit and uplink new commands to Dextre? Has
rapid command turnaround been demonstrated?
> Excerpt from the report, page 68:
>
> "In 1970 the Soviet Union space program performed
> rendezvous and capture with a non-cooperative target
> with a human operator in control and with no communication
> time delays. (A non-cooperative target is one without
> transponders or active sensors to provide other space
> vehicles with its location, identification, and/or
> relative position) In 1998, collaboration between
> ESA and NASDA produced a moderately successful
> demonstration using the Japanese Engineering Test
> Satellite (ETS) VII."
>
> Excerpt from the report, page 74:
>
> "There is some human intervention in the proposed
> robotic plan through teleoperation, and there may
> even be the potential for some reprogramming of
> robotic systems during flight as has been carried
> out with Mars landers and rovers. However, in general
> the robotic mission will of necessity be rigid in its
> design and in its ability to cope with unplanned
> anomalies such as those that have been encountered
> during each of the four previous shuttle servicing
> missions."
> The opposite is true. The shuttle missions are rigid
> because the shuttles cannot remain in orbit for a long
> time.
Time-limited is not the same as rigid.
The excerpts appear to show that the panel has considered past
experience with robotic technology. On what basis do you claim your
expertise is greater than the panel's?
> Dextre may remain in space for years and it may
> continuously upgrade the HST while small rocket launchers
> (e.g., Pegasus) provide it with new replacement parts
> and new tools.
This is not part of the baseline mission and has obvious problems of
its own. That's not to say it couldn't work, but it doesn't
contribute to the immediate objective of fixing HST.
> Sean O'Keefe was enthusiastic about the Dextre's
> mission, but he was under enormous political pressure
> to use the shuttle instead.
What is your basis for this statement? Who is applying this
political pressure, and how do you know?
-- Steve Willner Phone 617-495-7123 swillner@cfa.harvard.edu Cambridge, MA 02138 USA (Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.)
- Next message: Rick Jones: "Re: ISS as Mars vehicle"
- Previous message: Sander Vesik: "Re: What is the radiation level at the Van Allen belts"
- In reply to: Andrew Nowicki: "Errors in Hubble report"
- Messages sorted by: [ date ] [ thread ]
Relevant Pages
|
|
