Personal Contact

As a nurse and engineer, I found "Managing Care Through the Air" [November] too much like Big Brother. I love my independence, but if my loved ones choose to monitor my behavior remotely, then I would rather be in a nursing home or dead.

I recently spent a couple of months with my 86-year-old grandmother, who was losing cognitive ability. I cannot imagine going through that without human contact. It will always be better to be with family or even a minimum-wage caregiver than to do that alone. Remote monitoring is great for an alert person with cardiac or other problems. Reduced cognitive ability requires human contact and intervention. We must never try to replace basic human needs with technology.

Mary Tsolak

Hillsboro, Ore.

Fault Explained

"Titan Calling" [October] gives much-deserved credit to Boris Smeds's discovery of the Huygens probe's relay-link receiver's inability to compensate for a Doppler-shifted signal during its mission. But the article's description of the Huygens inquiry board's conclusion—that industry, as well as ESA and NASA reviewers, failed to notice the Doppler shift's effect on the data rate and to design the receiver accordingly—is unjustified.

From 1987 to 1992, Alenia Spazio and a U.S.-based company cooperated in developing a new spacecraft transponder. The receiver, certified to operate at data rates up to 2 kilobits per second, accommodates Doppler effects on the carrier frequency, the subcarrier, and the data rate. Derivatives of this transponder are operating successfully on various ESA near-Earth and deep-space missions.

The Huygens telemetry receiver relies on the design heritage of this transponder. But the telemetry link from the Huygens probe to the Cassini orbiter uses a much higher data rate—8 kb/s.

Alenia Spazio did, in design documentation, define the receiver to compensate for the Doppler shift's effect on the subcarrier and its higher data rate during the descent to Titan's surface. The receiver specification, however, was not explicit about the Doppler effect on the data rate, and a scaling parameter in the receiver's embedded software was not adjusted. With this parameter fixed, the ability to compensate for Doppler effects decreased as the data rate increased.

The real issue, therefore, is not any misconception in principle regarding the effect of Doppler on the data rate and the receiver design, but in the lack of a specific test, which would have caught the inconsistency between the implemented software parameter and the needs of the Huygens telemetry system. Responsibility for this shortfall in testing is shared among different reporting levels in the Huygens project. Salvaging the mission was a tremendous joint effort by many contributors from ESA, NASA/JPL, the scientific community, and industry.

Colin Jones & Luitjens Popken

Noordwijk, the Netherlands

Jones and Popken are, respectively, the Huygens system engineering manager and a member of the Huygens Recovery Task Force at the European Space Agency.

Yes to i and I

There has always been a significant distinction between the terms "internet" and "Internet" [Technically Speaking, December]. The term "internetworking" was coined in the mid-1970s for a set of interconnected private networks. Today "internet" refers to the many internets that are not part of the public Internet that most of us connect to.

Many issues and standards relate only to the Internet and have no relevance to internets. There is, for example, a distinction between the addresses in the Internet and addresses in internets. Similarly, technology issues that apply to various internets are of no concern to the Internet. The distinction between internets and the Internet is not only useful—but necessary.

John Day (M)

Foxboro, Mass.

No Protection

"Patents Lite" [Invention, November] holds that the Australian "innovation patent," with its less demanding threshold of inventiveness (only a slight difference from a prior work is needed), offers quick protection in rapidly evolving industries or for short-life-cycle products. I doubt it.

The economic value of a patent lies in its power to prevent competitors from making or using an invention. Owners of an innovation patent may stop a competitor from making an exact copy of an aspect of its design, but if the item being patented is only slightly different from a prior work, it strikes me that designing around such an "invention" would be, in many cases, relatively easy. With such a petty patent, the only competitor stopped may be the one without the imagination to make a slight change from a prior work.

Richard Wilhelm

West Linn, Ore.

Correction

In "Patent Prescription" [December], the correct Web site and patent number for the Gerbil Shirt should have been http://www.totallyabsurd.com/gerbilshirt.htm">http://www.totallyabsurd.com/gerbilshirt.htm">http://www.totallyabsurd.com/gerbilshirt.htm and U.S. Patent No. 5901666.

—Ed.