NASA scientists, who are very concerned with the increasing hazard of impacts of orbital debris impact on spacecraft, have designed the "stuffed Whipple" shield — a lightweight, relatively inexpensive alternative to simple aluminum meteoroid/orbital-debris (M/OD) shield. The stuffed Whipple shield features an easily adaptable design that increases protection against hypervelocity impacts (HVIs), without significantly affecting previously formulated designs of spacecraft. The stuffed Whipple shield is critical to the continued human exploration of space, especially to the Space Station, inasmuch as the Station will be operating in low orbit around the Earth and will need shielding against HVIs in order to survive intact and for an appreciable amount of time and continue to safely support human habitation. Scientists project that the number of HVIs from detritus of artificial objects will increase from 2 to 5 percent per year— an increase that could produce devastating results.
The design of the stuffed Whipple shield greatly reduces the risk of loss of a spacecraft crew and/or damage to the spacecraft. It also increases crew efficiency, in that by providing more efficient shielding, it reduces the frequency of both extravehicular and intravehicular activities EVAs and IVAs to effect repairs of HVI penetrations of the outer skin of the spacecraft. It is particularly amenable to introduction in the final or nearly-completed phase of the spacecraft-design effort. The stuffed Whipple shield can be retrofitted to any extant military or commercial spacecraft.
Many previously designed space vehicles are equipped with all-aluminum shields, of a form of Whipple shield, for protection against HVIs. All-aluminum shields offer an improvement over shields of the earliest designs; however, all-aluminum shields were designed for a situation in which an HVI, while always a possibility, seemed a remote likelihood. Indeed, even the earlier Space Station designs were completed before emergence of the awareness of the artificial-debris environment and of the consequent need for greater protection, and at greater cost savings.
As the orbital-debris environment affects more commercial satellites, there will be a need to add lightweight anti-HVI shielding for protection. By virtue of its incorporation of lightweight materials and its easily adaptable design, the stuffed Whipple shield can be used on Space Station pressurized modules and on any spacecraft that typically carries a simple aluminum M/OD shield.
Better yet, the reduction in launch weight afforded by replacing the all-aluminum shield with the stuffed Whipple shield results in an estimated reduction of $345 M in the cost of launch. It is not surprising, therefore, that increased safety and decreased cost equally drive the stuffed-Whipple-shield design for the Space Station.
A stuffed Whipple shield includes front and back sheets and contains lightweight materials (the "stuffing"). The stuffing materials are selected and placed so as to break up large impinging particles, stop small impinging particles, and decelerate debris clouds before they can reach the back sheet. (In the case of the habitable Space Station modules, the back sheets are the pressure shells of the modules.)
A stuffed Whipple shield also offers a secondary support structure, which reduces system costs. This secondary structure is a mesh/Nextel (or equivalent ceramic)/Kevlar (or equivalent aromatic polyamide) blanket that can be supported in a number of ways. For example, it can be held by brackets, frames, or other supports that are modified versions of supports used in the current Space Station design to attach multilayer thermal insulation blankets. Another method of support involves mounting the blanket on a rigid graphite/epoxy or aromatic-polyamide/epoxy panel; the panel is then attached to the previously installed bumper-support structure, where its rigidity can potentially be offset by reductions in the blanket (i.e., the aromatic polyamide portion).
This work was done by Jeanne L. Crews and Eric L. Christiansen of Johnson Space Center and Joel E. Williamsen, Jennifer H. Robinson, and Angela M. Nolen of Marshall Space Flight Center. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Materials category.
This invention has been patented by NASA (U.S. Patent No. 5,610,363). Inquiries concerning nonexclusive or exclusive license for its commercial development should be addressed to
the Patent Counsel,
Johnson Space Center,
Refer to MSC-22584.