Standards Development

Scope

This standard specifies two total leak testing methods for spacecraft, including helium mass Spectrometer vacuum leak testing method and helium mass Spectrometer accumulation leak testing method. The standard specifies the general requirements, application objects, system composition, leak testing processes, and document’s requirements. The standard applies to the leak testing of spacecraft component, subsystem and system level products.

The detection of a test gas using mass spectrometers is far and away the most sensitive leak detection method and the one most widely used in industry. The mass spectrometer leak detector(MSLD) developed for this purpose make possible quantitative measurement of leak rates in a range extending across many powers of ten whereby the lower limit 10-13 Pa·m3/s, thus making it possible to demonstrate the inherent gas permeability of solids where helium is used as the test gas. It is actually possible in principle to detect all gases using mass spectrometry. Of all the available options, the use of helium as a tracer gas has proved to be especially practical. The detection of helium using the mass spectrometer is absolutely unequivocal. Helium is chemically inert, non-explosive, non-toxic, is present in normal air in a concentration of only 5 ppm and is quite economical.

A mass spectrometer will operate only in a vacuum. Due to the minimum vacuum level of 1×10-2 Pa, a high vacuum will be required. Turbomolecular pumps and suitable roughing pumps are used in modern leak detectors. Associated with the individual component groups are the required electrical- and electronic supply systems and software which, via a microprocessor, allow for the greatest possible degree of automation in the operating sequence, including all adjustment and calibration routines and measured value display.

Purpose

1.1 Purpose

The purpose of this standard is to provide all Space Agencies two total leak detection methods for spacecraft, including the general requirements, application objects, system composition, leak detection processes, and document’s requirements. The standard applies to the leak testing of spacecraft component, subsystem and system level products, using the helium mass spectrometry vacuum leak detection method and helium mass spectrometry accumulation leak detection method. This standard defines a standard set of flight hardware leak test requirements that provide the necessary verification of pressure integrity for spacecraft, subsystems and their components, and payloads (both pressurized and sealed). Compliance of qualification and acceptance test programs and procedures with this standard will provide consistency across the Agencies and its contractors, facilitating the sharing of hardware between centers and programs. This standard has been developed for spacecraft, subsystems and their components, and payloads that will operate in space environment (Earth’s orbit and beyond) but may be tailored to include other operating environments. The leak test methods included are generally regarded as the most critical and the ones having the highest cost and schedule impact.

1.2 Applicability

This standard defines baseline leak test methodologies that are applicable to all spacecraft, subsystems and their components.

Small instruments may be treated as components. This standard is developed for the typical flight hardware or payload wherein one qualification unit or article is built and serves to qualify the design, while other units undergo acceptance testing for workmanship screening purposes and are subsequently used for flight. If a protoflight approach is used, the qualification unit or article is also used for flight. Consistent and effective leak testing is a critical aspect of functional verification for all of these types of hardware and payload items. The major objective of leak testing is to verify proper assembly and workmanship during qualification and acceptance testing. The principal goal of the leak test method is to reliably verify the maximum allowable leakage rate (MALR) requirement set for the spacecraft, subsystems and their components, and payloads in the applicable drawings and/or specifications. Tailoring the leak test method, with supplemental analysis, is appropriate in some cases.