Nulling Interferometry

TPF-I relies on the ability to suppress starlight below the level of other sources of photon noise. Laboratory tests of interferometric nulling have now demonstrated starlight suppression at the level required for flight. The tests were conducted in an ambient lab environment (at room temperature), rather than a cryogenic vacuum, and used a 34% bandwidth centered at a wavelength of 10 microns. These tests demonstrated that the components and subsystems for starlight suppression are at TRL 4 (TRL 5 would require cryogenic testing). System-level tests, using four instead of two combined beams, have not yet been completed but are underway.

With regard to starlight suppression, almost all the work that can be done at room temperature has now been completed. The greatest gain would be had with a transition to cryogenic testing of components, subsystems, and systems, and the development of mature brassboard designs. This should be the focus of efforts in the early 2010-2020 decade.

Precision Formation Flying

The major mission risk is the reliance on a simultaneous and coordinated use of five separate spacecraft flying in formation; four telescopes each on separate spacecraft and an additional spacecraft used as a beam combiner. Guidance, navigation, and control demonstrations in the lab have shown that such control is feasible, with performance traceable to flight. However actual hardware tests in space have not yet been performed to address mission requirements.

In-space testing is necessary in the 2010-2020 decade to raise the TRL level of formation flying. This work should be done through an international collaboration and leverage both US and European expertise in separated-spacecraft rendezvous and docking.

Cryogenic Technology and Engineering

A flagship mid-infrared mission would be a cryogenically cooled observatory, and so shares many aspects of technology development with JWST, including the use of cryo-coolers, passive cooling, thermal shields, and cryogenic actuators. It also shares with Herschel the need for light-weight Silicon Carbide mirror technology. Although challenging, these technologies are expected to be mature by the time that TPF-I or Darwin launches. The major challenges are primarily those of the cryogenic engineering of a complex instrument.

In summary, technology development for TPF-I has been extremely successful. Highlights of technology development have included the following:

1. Broadband nulling has been demonstrated to the null depth required in flight, over a 34% bandwidth centered on 10 microns. (Peters et al. 2008, 2009)

2. Single-mode mid-IR fibers have been demonstrated at 10-microns using both chalcogenide glass and silver halide materials, providing the required spatial filtering performance. (Ksendzov et al. 2007, 2008)

3. Cryogenic delay lines have been demonstrated by the European Space Agency.

4. Formation flying algorithms have been demonstrated in the laboratory, using a robotic testbed, to have the performance required for flight (Scharf et al. 2008).

5. The architecture trades studies in the US and Europe converged in 2007, leading to the Emma X-Array, described previously.

6. Target catalogs and observatory performance models developed independently in Europe and the US were shown to be in close agreement.

7. Experiments within the International Space Station (using MIT SPHERES), as well as in space with rendezvous and docking (Orbital Express and ESA's ATV Jules Verne) have demonstrated GPS and video-based control of separated satellites.

8. Precursor formation flying missions are now in formulation (ESA's Proba-3) and in preparation for launch (Swedish Space Corporation's Prisma) to test RF metrology, optical metrology, and cold-gas and electrical micro-propulsion.

Researchers at JPL continued to collaborate with the Darwin mission PI, Prof. Alain Léger, and are now completing the room-temperature demonstrations with the nulling testbeds, which in 2009-2010 will focus on four-beam system-level planet detection experiments in the lab.

The formal progress of interferometry technology is documented in the whitepapers and reports listed below.

Updated: April 4, 2009