Unfounded Optimism

Thank you for the detailed coverage of potential alternatives to the sensors on the Space Based Infrared System (SBIRS) in your July 16 and July 30 issues [“Cost, Risk Concerns Prompted USAF to Opt for 3rd SBIRS Satellite,” July 16, page A4; “USAF Hatches New Missile Warning Sensor Technology Program,” July 30, page 5].

Given the history of cost growth and schedule delays associated with developing a next-generation missile warning constellation, I was surprised to see a spokesperson for the Air Force’s Space and Missile Systems Center citing a precise estimate of what it would cost to develop and build a satellite based on new sensor technologies. The projected $2.6 billion price tag is almost certainly too low, and in any event it is way too early in the development of alternatives to be offering up such estimates. Policymakers need to keep in mind a few inconvenient truths that we have learned from past military space efforts.


, development of high-resolution focal plane arrays

always has been a protracted and painful process, from the first Midas spacecraft to the Defense Support Program (DSP) to the Space Based Infrared System (SBIRS) to the Space Tracking and Surveillance System. No one can predict with certainty how long it will take to scale up and refine the cutting-edge technologies associated with alternative sensor concepts.

Second, introduction of new hardware into the missile warning system would necessarily require the development of extensive software to tie together the space segment and allow it to communicate effectively with the ground segment. Unlike the stovepiped downlinks of the original DSP constellation, SBIRS will be collecting diverse information for diverse users with diverse requirements, so software generation needs associated with any change in the baseline architecture could be quite imposing.

Third, the notion that a wide-area staring sensor by itself could collect enough photons to satisfy all the needs of theater commanders and intelligence community users seems quite improbable. Such users

often are interested in high-priority point targets that require intensive focus to capture all available energy, but a wide-area sensor would be unlikely to glean such detail given the fact it would be monitoring vast swaths of the

Earth’s surface.

Fourth, if we could devise a sensor array capturing that degree of detail from all the coordinates in its hemispheric perspective, the resulting volume of data would overwhelm the carrying capacity of downlinks. That means sophisticated new on-orbit electronics would be required to filter, process and compress data prior to transmission.

Fifth, because SBIRS is a vital strategic warning asset with missile defense applications, it has been designed to withstand various nuclear effects such as electromagnetic pulse and scintillation. It seems unlikely that the companies designing alternative sensor technologies have even begun to think through the hardening requirements for whatever architectures they propose.

Finally, the technology-base and industrial-base demands associated with developing, fabricating and integrating alternative designs are likely to be onerous. Lead times for delivery of third-party components, development of an electronics backplane, software generation, spacecraft integration and thermal vacuum testing will all be measurable in years, with the slowest responder setting the pace for the overall effort.

The Air Force should stop offering cost, schedule and per

formance projections on any alternative to SBIRS until far more is known about the progress in developing relevant technologies. We will probably discover the alternatives are harder to develop than anticipated, and that they do not perform as well as the baseline SBIRS architecture on some critical missions. After what military space has been through over the past two decades, the last thing we need to do is base our investment choices on unfounded optimism.

Loren B. Thompson

Arlington, Va.

Rocket Motor Not To Blame for Failure

The July 2 “This Week in Space History”

[page 14], referenced the Comet Nucleus Tour (Contour) mission flight failure and erroneously cited the STAR

30 rocket motor as the cause. The STAR

30 rocket motor, successful in 100 percent

of its flights since its development in the late 1970

s, was not found to have failed.

In fact, NASA’s Mishap Investigation Board concluded that “the most probable proximate cause for loss of the Contour spacecraft was overheating of the forward-end of the spacecraft due to base heating from the [solid rocket motor]

exhaust plume.”

In essence, the rocket motor was nested too far into the spacecraft, allowing heat generated by the motor’s plume to adversely affect the structural integrity of the spacecraft bus. There was no evidence that the STAR

30 motor operated other than as designed, and extensive evidence to suggest that the spacecraft was exposed to an environment more thermally stressful than it was designed to withstand.

The key lessons learned from the Contour mission and subsequent failure investigation were a reminder of the importance of clear,

crisp communication, and the recognition that mission assurance and engineering rigor should not be sacrificed for transient cost and schedule benefits. In this case, the rocket motor was brokered from a third party, and funding constraints resulted in an arm’s length relationship with the manufacturer. Similarly, funding constraints also led the mission to conduct the motor firing “in the blind,”

without any telemetry coverage. Better communication across the spectrum of all involved stakeholders may have allowed an integrated team to identify the spacecraft and mission design deficiencies and fix them before flight.

Mike Lara

ATK Tactical Propulsion & Controls Division

Elkton, Md.